Download Sources, transport, reservoirs and fate of dioxins

A better knowledge of sources, transport, reservoirs and fate of
persistent organic pollutants (POPs) in the Baltic Sea environment is
crucial for the identification of effective actions against these compounds.
In this report the present situation regarding sources and current
fluxes of persistent pollutants in the Baltic Sea ecosystem is presented.
The compounds selected for the study were: polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). These
classes of compounds represent a broad range of physical-chemical
Based on current knowledge and some new field measurements
in air, sea water and sediments, mass balances for the selected POPs
were calculated. These mass balances indicate that the atmosphere
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spectrum of most chemicals listed in the Stockholm Convention.
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Report 5912
Naturvårdsverket 106 48 Stockholm. Besöksadress: Stockholm – Valhallavägen 195, Östersund – Forskarens väg 5 hus Ub, Kiruna – Kaserngatan 14.
Tel: +46 8-698 10 00, fax: +46 8-20 29 25, e-post: [email protected] Internet: www.naturvardsverket.se Beställningar Ordertel: +46 8-505 933 40,
orderfax: +46 8-505 933 99, e-post: [email protected] Postadress: CM Gruppen AB, Box 110 93, 161 11 Bromma. Internet: www.naturvardsverket.se/bokhandeln
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properties, and hence their environmental behaviour encompasses the
Sources, transport,
reservoirs and fate of
dioxins, PCBs and HCB in
the Baltic Sea environment
Cair (fg TEQ m-3)
issn 0282-7298
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NATURVÅRDSVERKET
isbn 978-91-620-5912-5
Cair (pg m-3) Csediment (pg TEQ g-1 OC)
REport 5912
Sources, transport, reservoirs and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Sources, transport,
reservoirs and fate of
dioxins, PCBs and HCB
in the Baltic Sea
environment
2002
2003
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2005
Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB
in the Baltic Sea environment
Main authors:
Karin Wiberg,
Department of Chemistry, Umeå University,
Michael McLachlan,
Department of Applied Environmental Science, Stockholm University,
Per Jonsson,
Department of Applied Environmental Science, Stockholm University,
Niklas Johansson,
Swedish Environmental Protection Agency
Contributing authors:
Sarah Josefsson, Eva Knekta, Ylva Persson and Kristina Sundqvist,
Department of Chemistry, Umeå University;
James Armitage, Dag Broman, Gerard Cornelissen,
Anna-Lena Egebäck and Ulla Sellström,
Department of Applied Environmental Science, Stockholm University
and Ingemar Cato, Geological Survey of Sweden
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Orders
Phone: + 46 (0)8-505 933 40
Fax: + 46 (0)8-505 933 99
E-mail: [email protected]
Address: CM Gruppen AB, Box 110 93, SE-161 11 Bromma, Sweden
Internet: www.naturvardsverket.se/bokhandeln
The Swedish Environmental Protection Agency
Phone: + 46 (0)8-698 10 00, Fax: + 46 (0)8-20 29 25
E-mail: [email protected]
Address: Naturvårdsverket, SE-106 48 Stockholm, Sweden
Internet: www.naturvardsverket.se
ISBN 978-91-620-5912-5
ISSN 0282-7298
© Naturvårdsverket 2009
Print: CM Gruppen AB, Bromma, 2009
Cover photo: Titus Kyrklund, Naturvårdsverket
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Preface
The importance of the persistence of a compound released to the environ­ment
became apparent in 1966 when PCBs were demonstrated to be abun­dant in
biota. This was the first time a non-intentionally spread chemical was found
to accumulate and cause effects in the environment. Unfortu­nately, since then,
many other compounds with similar properties have been detected in the
environ­ment.
During the last decades, the environmental pollution of PCBs, dioxins
and other persistent organic pollutants (POPs) has been extensively studied
in numerous media in many countries all over the world. In Sweden, there
has been much focus on the situation in the Baltic Sea and its surroundings.
Since around the 1970s, the levels of dioxins and PCBs have shown de­creasing
environmental trends. For some POPs, these trends have levelled off in many
areas since the mid-1980s and have remained more or less stable since then.
In 1972, the use of PCBs in open systems was banned and thereafter many
other actions have been taken in order to reduce emissions of dioxins and
other POPs. These measures obviously had a great impact on the situation.
The lack of profound improvement during the last fifteen years is, however,
troublesome and suggests the presence of hitherto unknown sources and/or
that the importance of some known (primary and secondary) sources has been
misjudged.
The aim of the current work was to identify the sources that contribute to
the present pollutant situation including current fluxes of POPs to, from and
within the Baltic Sea. Some well-known POPs were selected (PCBs, dioxins
and HCB) as representatives for a broad range of physical-chemical proper­
ties. These compounds are also known to have different (primary) sources and
they represent both intentionally and unintentionally formed pollutants. Based
on current knowledge and new measurements, the current pollution scenario
of the Baltic Sea ecosystem was modelled in order to get an over­view of the
relative impact of various sources. Future scenarios were also predicted including varying pollution source strengths.
The results from this study are intended to be used together with other
rele­vant information to form an up-to-date basis for a new Swedish strategy
on POPs with special emphasis on POPs formed unintentionally.
Swedish EPA, January, 2009
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Abbreviations
AOC
amorphous organic carbon
BC
black carbon; also referred to as soot carbon
b.w.
body weight
DF
dibenzofuran
DD
dibenzo-p-dioxin
DL-PCBs
dioxin-like PCBs
DOM
dissolved organic matter
d.w.
dry weight
EC
European Commission
EMEPEuropean Monitoring and Evaluation Program
(Co-operative programme for monitoring and evaluation of the long-range transmission of air pollutants in
Europe)
EOCl
extractable organic chlorine
fg
femtogram (1 fg = 0.001 pg)
H
Henry’s law constant
HCB
hexachlorobenzene
HELCOM
Helsinki convention
HxCDD
hexachlorinated dibenzo-p-dioxin
HxCDF
hexachlorinated dibenzofuran
HpCDD
heptachlorinated dibenzo-p-dioxin
HpCDF
heptachlorinated dibenzofuran
IMO International Maritime Organization
I-TEFtoxic equivalency factors according to NATO/CCMS
1988
I-TEQ
toxic equivalents according to I-TEFs
KAW air – water partition coefficient
KOA
octanol – air partition coefficient
KOW octanol – water partition coefficient
l.w.
lipid weight
mg
milligram (1 mg = 0.001 g)
NDL-PCBs
non-dioxin-like PCBs
NERI National Environmental Research Institute
of Denmark
ng
nanogram (1 ng = 0.001 μg)
NODC National Oceanographic Data Centre of Germany
OC
organic carbon
OCDD
octachlorinated dibenzo-p-dioxin
OCDF
octachlorinated dibenzofuran
OM
organic matter
PAHs
polycyclic aromatic hydrocarbons
PCB(s)
polychlorinated biphenyl(s)
PCDD(s)
polychlorinated dibenzo-p-dioxin(s)
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
PCDD/F(s)polychlorinated dibenzo-p-dioxin(s) and polychlori­
nated dibenzofuran(s); commonly known as dioxins
PCDF(s)
polychlorinated dibenzofurans(s)
PCP
pentachlorophenol
PeCDD
pentachlorinated dibenzo-p-dioxin
PeCDF
pentachlorinated dibenzofuran
pg
picogram (1 pg = 0.001 ng)
POC
particulate organic carbon
POM
polyoxymethylene (material used for passive sampling)
POP(s)
persistent organic pollutant(s)
PUF
polyurethane foam
PVC
polyvinyl chloride
SPM
settling (or suspended) particulate matter
STP
sewage treatment plant
TCDD
tetrachlorinated dibenzo-p-dioxin
TCDF
tetrachlorinated dibenzofuran
TDI
tolerable daily intake (for humans)
TEFtoxic equivalency factor; factor indicating the esti­mated
toxic potency of an individual DD, DF or dioxin-like
compound as compared to 2,3,7,8-TCDD. Note that
many different sets of TEFs have been pro­posed since
the 1980s.
TEQtoxic equivalent; concept developed to express the
overall toxicity of a mixture of dioxins and dioxinlike compounds as a single value. The TEQ value is
obtained by adding the product of the concentration or
amount and the TEF for each toxic compound.
TOC
total organic carbon
TWI
tolerable weekly intake (for humans)
WHO
World Health Organization
WHO-TEF toxic equivalency factor according to WHO; two sets
issued, in 1998 and 2006
WHO-TEQtoxic equivalents according to one of the WHO-TEF
sets
w.w.
wet weight
μg
micrograms (1 μg = 0.001 mg)
ΣPCB7sum of the PCB congeners 28, 52, 101, 118, 138, 153
and 180
2,3,7,8-chlorinated the 17 congeners with chlorines at position 2,3,7 and
dioxins8 (2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, 1,2,3,4,7,8HxCDD, 1,2,3,6,7,8-HxCDD, 1,2,3,7,8,9-HxCDD,
1,2,3,4,6,7,8-HpCDD, OCDD, 2,3,7,8-TCDF,
1,2,3,7,8-PeCDF, 2,3,4,7,8- PeCDF, 1,2,3,4,7,8HxCDF, 1,2,3,6,7,8-HxCDF, 1,2,3,7,8,9-HxCDF,
2,3,4,6,7,8-HxCDF, 1,2,3,4,6,7,8-HpCDF,
1,2,3,4,7,8,9-HpCDF, OCDF)
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Innehåll
1 Sammanfattning
1.1 Trender och den nuvarande situationen i Östersjöns miljö, samt för den
svenska befolkningen
1.2 Utsläpp från industrin
1.3 Nya mätningar i fält 1.4 Massbalansmodellering 1.4.1 Bassängerna som helhet:
1.4.2 Områden med förhöjda halter (till exempel nära industrier, städer och
förorenad mark)
1.5 Rekommendationer för framtida forskning
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2 Summary
2.1 Trends and the current situation in the Baltic Sea e­ nvironment including the
Swedish population 2.2 Industrial emissions
2.3 New field measurements
2.4 Mass balance modelling
2.4.1 The basins as a whole:
2.4.2 Non-pristine areas (e.g. near industries, cities and contaminated land)
2.5 Recommendations for future research
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3 Introduction
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4 The Baltic Sea environment 4.1 Physical environment of the Baltic Sea
4.2 Sediment dynamics in the Baltic Sea 4.2.1 Erosion bottoms
4.2.2 Transportation bottoms
4.2.3 Areas of accumulation
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5 The selected POPs and their trends in Baltic Sea biota
5.1 PCDD/Fs
5.2 PCBs
5.3 HCB
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6 POPs in the Baltic Sea environment
6.1 Distribution between environmental compartments
6.2 Industrial emissions
6.2.1 Previous and current PCDD/F emissions in Europe
6.2.2 Atmospheric emissions of PCDD/Fs in the Baltic Sea area
6.2.3 Emissions of PCDD/Fs in Sweden
6.2.4 Emissions of PCBs and HCB in Sweden
6.2.5 PCDD/F, PCB and HCB emissions from various branches
6.2.6 Emissions of PCDD/Fs and HCB in Denmark and Finland
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
6.3 POPs in the atmosphere
6.3.1 PCDD/Fs in air – previous measurements
6.3.2 PCDD/Fs in air – new measurements
6.3.3 PCBs and HCB
6.4 POPs in soils
6.5 POPs in the water body
6.5.1 Advective water in- and outflow of POPs to the Baltic Sea
6.5.2 Surface water – previous measurements
6.5.3 Surface and deep water – new measurements
6.6 POPs in sediments 6.6.1 Sediment-water exchange – new measurements
6.6.2 Levels of POPs in Baltic sediments – new measure­ments
6.6.3 Levels and trends of POPs in Baltic sediments
6.6.4 Relation between total organic carbon, black carbon and POP levels 6.6.5 Sediment burial of POPs in the Baltic Sea
6.6.6 The impact of bioturbation on POP fluxes in the sedi­ment
6.7 Influence of temperature
6.8 Degradation
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7 Methodology employed to model POP behaviour in the Baltic Sea85
7.1 Introduction to chemical fate modelling
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7.2 The POPCYCLING-Baltic model
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7.3 Model parameterization
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7.4 PCDD/Fs
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7.4.1 Physical-chemical properties
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7.4.2 Enhanced sorption to organic carbon
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7.4.3 Initial concentrations
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7.4.4 Concentrations in air
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7.5 PCBs
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7.5.1 Physical-chemical properties
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7.5.2 Enhanced sorption to organic carbon
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7.5.3 Initial concentrations
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7.5.4 Concentrations in air
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7.6 HCB
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7.6.1 Physical-chemical properties
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7.6.2 Initial concentrations
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7.6.3 Concentrations in air
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8 Current inventories, sources, and fate of POPs: A modeland statistics-based synthesis
8.1 PCDD/F s
8.1.1 PCDD/F inventories 8.1.2 PCDD/F flows 8.1.3 Evaluation of model predictive power for PCDD/F 8.1.4 Congener pattern analysis of the PCDD/Fs 8
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
8.2 PCBs
8.2.5 PCB inventories
8.2.6 PCB flows
8.2.7 Evaluation of model predictive power for PCBs
8.3 HCB
8.3.1 HCB inventories
8.3.2 HCB flows 8.3.3 Evaluation of model predictive power for the HCB
8.4 Summary and comparison of the behaviour of the POPs
8.5 Linking POP levels in water and sediment to levels in Baltic Sea fish
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9 Evaluation of the future ­­devel­opment of the contamina­tion
of the Baltic Sea
9.1 PCDD/Fs
9.2 PCBs
9.3 HCB
9.4 Uncertainties in the assessment
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10 Conclusions and future research
10.1 New field measurements
10.1.1 Air and atmospheric deposition measurements
10.1.2 Surface sediments: 10.1.3 Surface, deep sea and sediment pore-water: 10.1.4 Sediment-water exchange: 126
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11 Reference List
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
1 Sammanfattning
Den här rapporten behandlar persistenta organiska föroreningar (POP) i
Östersjöns miljö – deras källor, förekomst och omsättning. Den är resultatet
av ett uppdrag som Naturvårdsverket fick från Miljödepartementet. Projekt­
gruppen bestod av medlemmar från Umeå universitet, Stockholms univer­si­tet,
Naturvårdsverket och Sveriges geologiska undersökning (SGU).
Uppdraget var att bedöma källor, beskriva den rådande situationen och
under­söka nuvarande flöden av POP i Östersjöns ekosystem. Ämnena som
valdes ut för studien var polyklorerade bifenyler (PCB), hexaklorbensen
(HCB), polyklorerade dibenso­furaner (PCDF) och polyklorerade dibenso-p-­
dioxiner (PCDD); de två senare allmänt kända som dioxiner (PCDD/F).
Substanserna som ingår i dessa ämnes­grupper täcker ett brett spektrum
av fysikalisk-kemiska egenskaper, och deras beteenden i miljön är därmed
repre­sentativa för de flesta ämnen som tas upp i Stockholms­­konventionen.
Ämnena har olika källor. PCDD/F bildas oavsiktligt i många olika pro­cess­er,
till exempel vid förbränning och som biprodukter i kemikalie­industrin. HCB
bildas också vid förbränning, men har dessutom tillverkats och använts som
fungicid. PCB är industri­kemikalier med ett flertal användnings­områden, till
exempel som isolerolja. Ytterligare ett skäl för att välja att undersöka PCDD/F
och PCB är att halterna av dessa ämnen i fisk överskrider EU:s gränsvärden.
Halterna av PCDD/F i miljön har inte minskat i samma utsträckning som halterna av till exempel PCB och HCB, vilket har setts som en indikation på att
det finns pågående, ännu inte identifierade, utsläpp av PCDD/F.
Tillvägagångssättet som projektgruppen valde var att göra massbalanser
för de ut­valda föroreningarna genom att använda en modifierad version av
en existerande massbalansmodell (POPCYCLING-Baltic). I ett första skede
­utfördes en osäkerhets­analys för att identifiera de viktigaste kunskaps­brist­­
erna. Sedan gjordes mätningar i fält av luft, havsvatten och sediment för att
minska dessa osäkerheter.
1.1 Trender och den nuvarande situationen
i Östersjöns miljö, samt för den svenska
befolkningen
Östersjöns biota: Sedan miljöövervakningen startade på 1970-talet har
­minsk­ande halter av PCB och HCB observerats i biota från Östersjön (sill­
grissle­ägg från Egentliga Östersjön och strömming från Bottenhavet). För
PCDD/F sågs en trend av avtagande TEQ-nivåer på 1970-talet, men minsk­
ningen planade ut i mitten av 1980-talet och nivåerna har sedan dess varit
tämligen stabila. Ny forskning har visat att från 1990 och 15 år framåt har
halterna av vissa dioxin (PCDD)-kongener (till exempel 2,3,7,8-TCDD och
OCDD) minskat signifikant i sillgrissleägg från Östersjön, medan stabila eller
till och med ökande trender observerats för de flesta andra toxiska PCDD/Fkongener.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Sveriges befolkning: I början av 2000-talet hade över 10 % av den svenska
befolkningen ett dagligt intag av PCDD/F och dioxin-lika PCB som över­skred
gränsen för tolerabelt dagligt intag rekommenderad av den Europeiska kommissionen. Forskning har visat att de allmänna nivåerna av PCB och PCDD/F
i svensk mat har minskat sedan 1970-talet. I överensstämmelse med dessa
observationer har koncentrationerna av PCB, PCDD/F och HCB i bröstmjölk
uppvisat en avtagande trend sedan 1970-talet. Tydligt avtagande koncentrationer av PCB och HCB har också uppmätts i blodserum från svenska män
under perioden 1991 till 2001. Däremot har TEQ-nivåerna i samma befolkning inte minskat signifikant mellan 1987 och 2001. Detta tillskrivs stabila
eller ökande nivåer av flera furan (PCDF)-kongener.
Ytsediment: Längs Östersjöns kust finns flera tungt industrialiserade områ­den,
och det har framkommit att den svenska kusten har ett flertal så kallade hot
spots för PCDD/F förknippade med industriell aktivitet.
Vad gäller PCDD/F-trenderna i utsjösediment finns det begränsat med
information. Medan nivåerna tydligt avtar i utsjöområden i Finska viken
på grund av omfattande utsläppsminskningar, är situationen i Bottenhavet
och Egentliga Östersjön oklar. Det finns få mätningar, men dessa indikerar
att det har skett en minskning sedan 1970-talet. Minskningen har emellertid
planat ut i Egentliga Östersjön, och i Bottenhavet verkar halterna av dioxin
(PCDD)-kongener minska, medan furan (PCDF)-kongenerna inte visar någon
avtagande trend.
För PCB finns det mer data tillgängligt. Under de senaste 10–20 åren
har en tydlig minskning av PCB-koncentrationerna observerats i sediment
i Botten­havet och Egentliga Östersjön. I Bottenhavet minskade koncentrationerna i medeltal med en faktor 5.6 och i Egentliga Östersjön med 4.5.
Att PCB-koncentrationerna minskar i utsjösediment ligger i linje med de
minskande halterna i strömming från Bottenhavet samt i sill/strömming
och sillgrissle­ägg från Egenliga Östersjön. Det finns även indikationer på
­minskande HCB­-koncentrationer i Östersjösediment.
Det har tidigare föreslagits att den avsevärt lägre PCB-koncentrationen i
sedi­ment i dag kan vara en följd av ökad sedimentackumulation, orsakad av
en ökad frekvens av kraftiga stormar på 1990-talet. Under 2000-talet har man
emellertid fortsatt att observera lägre koncentrationer, trots lugnare väderförhållanden, vilket motsäger denna hypotes. Den uppmätta minsk­ning­en av
PCB-koncentrationer är således mest troligt ett resultat av ett minskat inflöde
av PCB till Östersjön.
1.2 Utsläpp från industrin
Europa och Östersjöregionen: Den så kallade ”Europeiska dioxinemissions­
inventering­en”, som organiserades av den Europeiska kommissionen,
om­fattade en storskalig inventering av europeiska PCDD/F-utsläpp från
1985 till 2005. I allmänhet har avsevärda reduktioner uppnåtts för industri­
ella utsläpp under den studerade tids­perioden, och inom en nära framtid
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
kommer de icke-industriella utsläppen troligtvis att överskrida utsläppen från
­industrin. I dag anses sintring av järnmalm vara den viktigaste utsläpps­källan,
följt av den källa som tidigare var viktigast, förbränning av kommun­alt avfall.
Målet för EU:s femte aktionsprogram var att minska utsläppen av PCDD/F
med 90 % från 1985 till 2005, och slutsatsen blev att detta mål endast kan
uppnås för några av källtyperna. Bland länderna runt Östersjön ­rapporterade
Tyskland, Ryssland och Polen de högsta utsläppen av PCDD/F till luft i
Östersjö­regionen; sammantaget stod de för mer än 95 % av de totala utsläppen. Aktuell information om utsläppen i Östersjöregionen är emellertid osäker
på grund av brist på data.
PCDD/F-utsläpp i Sverige: I en kartläggning av PCDD/F-källor i Sverige
beräknades de totala utsläppen från alla industrisektorer i Sverige vara
­160–480 g WHO-TEQ år-1 till avfall/deponi, 16–84 g WHO-TEQ år-1 till luft
och 1,9–2,4 g WHO-TEQ år-1 till vatten och sediment. Merparten av utsläppen till luft tros fortfarande härröra från förbränning. Bland förbränningskällorna tros storskalig biobränsleförbränning, mer eller mindre småskalig
icke-industriell förbränning (så kallad ”backyard burning”) och ­förbränning
av fossila bränslen vara de dominerande källorna, medan utsläpp från förbränning av kommunalt avfall nu anses vara obetydliga. Å andra sidan
kan avfall (främst aska) från förbränning av kommunalt avfall innehålla
­betydande mängder PCDD/F. Avfallet deponeras och kan ge upphov till
utsläpp till land och vatten.
Naturvårdsverket genomförde nyligen en kartläggning av halterna av
diox­in­er och andra POP i närheten av flera pappers- och massafabriker, nedlagda eller i bruk. Den fokuserade på POP-halterna i olika miljömatriser (fisk,
vatten och sedimenterande partiklar) i närheten och på avstånd från dessa
anläggningar. Slutsatsen blev att även om inte alla mätningar visade på för­
höjda halter fanns det klara indikationer på lokal miljöpåverkan från några av
anläggningarna, och uppföljningsstudier krävdes vid vissa av platserna för att
ytterligare klargöra situationen. Nyligen genomförde även Skogs­industrierna
en dioxinkartläggning som omfattade mätningar vid nio an­läggningar.
Avloppsvatten, rökgaser, luft och slam analyserades. Några pågående
PCDD/ F-utsläpp upptäcktes. Undersökningen fastslog att bidrag av PCDD/F
från punktkällorna tillsammans med bidrag från inflöden till recepienterna på
ett ungefär kunde förklara skillnaderna i PCDD/F-halter mellan fiskar fångade
nära industrierna och på referensplatser.
PCB- och HCB-utsläpp i Sverige: Tidigare har de huvudsakliga utsläppen av
PCB till miljön uppkommit under produktion och genom läckage och för­
luster från produkter och system som innehåller PCB. I dag är förmod­lig­en
sekundära källor, som avdunstning från mark, ansvariga för en stor del av
­halterna i luft. PCB-utsläppen i Sverige har beräknats uppgå till 10–31 kg år‑1
till avfall/deponi, 0,4–1,1 kg år-1 till luft och 0,1 kg år-1 till vatten och sediment. De största utsläppen bedömdes komma från förbränning och från
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
­ emikalieindustrin. HCB-utsläppen beräknades till 13–32 kg år-1 till luft,
k
3–26 kg år-1 till avfall/deponi och 0,01 kg år-1 till vatten och sediment. För­
bränning och kemikalieindustrin rapporterades vara ansvariga för den största
delen av utsläppen.
1.3 Nya mätningar i fält
Mätningar i Östersjön av luft, våt- och torrdeposition, ytsediment, sediment­
porvatten samt yt- och djupvatten genomfördes i denna studie. Dessa mät­
ning­ar var nöd­vändiga för att minska osäkerheten i de massbalans­beräkning­ar
som skulle utföras.
Luft och atmosfärisk deposition: Under vintern 2006/2007 togs luft- och
bulk­depositions­prover i Aspvreten (södra Sverige) och Pallas (norra Fin­land)
för att identifiera de regioner som var de största källorna till atmosfär­iskt
inflöde av PCDD/F till Östersjön. Då koncentrationerna av PCDD/F i atmo­
sfären är högre under vintern än under sommaren, inträffar den största delen
av den årliga depositionen under vinterhalvåret. Korta provtag­nings­tider
användes och endast prover där luftmassans ursprung säkert kunde spåras
valdes ut för analys av 2,3,7,8-substituerade PCDD/F-kongener. Flera prover
samlades också in under sommar­halvåret.
Regionen som luftmassorna kunde härröra från delades in i sju sektorer.
De högsta koncentrationerna uppmättes i luft som hade passerat över den
euro­peiska kontinent­en. I luft som hade passerat över de brittiska öarna och i
luft från norr var koncentrationerna låga. PCDF-koncentrationerna var högre
än PCDD-koncentration­erna i luft som kom från söder och öster, medan det
motsatta förhållandet rådde i luft från väst-nordväst. Variationen i koncent­
rationerna var mycket lägre inom en sektor än mellan sektorer.
Var PCDD/F som våtdeponerades i Östersjön under de sex månader
som studien ägde rum (d v s under vintern) härrörde från beräknades också.
Resultaten visade att ~40 % av våtdepositionen av PCDD/F hade sitt ur­sprung
i den sydvästra sektorn, medan ~20 % kom från luft från den södra sektorn.
Den partikelbundna torrdeposi­tion­en av PCDD/F förväntas vara liten jämfört
med våtdepositionen under de för­hållanden som råder i Europa.
Våt- och torrdepositionen av PCDD/F som uppmättes under samma
tid uppgick till ~200 pg WHO-TEQ m–2 eller 1,1 pg WHO-TEQ m–2 dag–1.
Beräkning­ar av ursprung­et till den gasformiga depositionen till Östersjön
­indikerar att bidragen från de olika regionsektorerna var jämförbara.
Detta delprojekt visar tydligt att halterna av PCDD/F över Östersjön
och den atmosfär­iska depositionen av PCDD/F till Östersjön ­huvudsakligen
bestäms av luftströmmar­nas rörelsemönster. Dessa kan variera betydligt
från år till år, och därmed också depositionen. För att kunna göra en bättre
extra­polering av resultaten i tid och rum undersöktes korrelationen mellan
PCDD/ F-koncentrationer och atmosfärsparametrar som är enklare/mer rutinartade att bestämma. En stark korrelation mellan koncentra­tion­en av partikelbundna PCDD/F och koncentrationen av sotkol (så kallade soot carbon eller
black carbon, BC) upptäcktes, med en korrelationskoefficient (r2) på 0,80.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Ytsediment: Kustnära och utsjösediment från Egentliga Östersjön och Botten­
havet samlades in under 2007 och dess innehåll av PCDD/F, PCB och HCB
analyserades. För att få ett stort dataset inkluderades även data från andra
studier i utvärderingen.
I allmänhet var sedimentens koncentrationer av PCDD/F, normaliserade
till sedi­ment­torrvikt, ungefär en faktor 2-3 högre i Egentliga Östersjön än
i Bottenhavet. Om de däremot normaliserades till organiskt kol (OC), med
hänsyn till att sediment i Egentliga Östersjön har en avsevärt högre halt totalt
organiskt kol, fanns det inga skillnader mellan de två bassängerna. I likhet
med detta var koncentrationerna av ΣPCB7, normaliserade till torrvikt, i
medel 4–5 gånger lägre i Bottenhavet än i Egentliga Östersjön. Denna skillnad blev mindre tydlig om data normaliserades till OC. Koncentration­erna av
HCB verkade inte skilja sig nämnvärt åt mellan sediment från Botten­­havet och
Egentliga Östersjön.
Variationen i halterna av PCDD/F och PCB i utsjösediment visade sig till
stor del kunna förklaras med variationer i halten organiskt kol. Innehållet
av OC förklarade 80–90 % av variationen i PCDD/F och PCB, medan
innehåll­et av sotkol (black carbon) bara svarade för 50–70 % av variationen.
En låg korrelation mellan OC-innehåll och HCB-koncentration observerades
(r2=0,28).
Ytvatten, djupvatten och sedimentporvatten: Koncentrationen av så kallade
fritt lösta (freely dissolved) POP i yt- och djupvatten mättes genom användning av passiva provtagare (av typen POM). Provtagarna utplacerades på
olika platser i Egentliga Östersjön och Bottenhavet under våren och sommaren 2007, och hämtades in efter tre månader. Medelkoncentrationen av dioxin
i kustnära och utsjövatten var 1,1 respektive 2,5 pg WHO-TEQ m–3. De mot­
svarande ΣPCB7-koncentrationerna var 5,8 och 24 ng m–3. Det fanns inga
signifikanta skillnader i koncentrationer mellan yt- och djupvatten i varken
Egentliga Östersjön eller Bottenhavet.
Koncentrationerna i sedimentporvatten från samma platser i Östersjön
som vatten­proverna togs på bestämdes genom användning av passiva provtagare (av typen POM) i skaktest. Koncentrationerna av POP i porvatten
samvari­erade i allmänhet med koncentrationerna i sediment.
Utbyte mellan sediment och vatten: För de kustnära stationerna var medel­
värdet av kvoten mellan koncentrationerna i porvatten och överliggande vatten
3,6 ± 1,6 för PCDD/F och 1,0 ± 0,6 för PCB. Detta indikerar att de kustnära
sedimenten fungerar som en PCDD/F-källa för överliggande vatten, medan det
inte finns någon koncentra­tions­gradient för PCB och de kustnära sedimenten
inte utgör vare sig betydande sänkor för eller källor till PCB. För PCDD/F i
djupvatten var kvoten 1,1 ± 0,5, vilket tyder på att det inte finns en koncentrationsgradient och att sedimenten i utsjöområden varken utgör betydande
sänkor eller källor för ett diffusivt utbyte av lösta PCDD/F. För PCB var denna
kvot 0,7 ± 0,3, vilket antyder att koncentra­tions­­gradienten för PCB är liten.
Gradientens riktning indikerar att sedi­menten kan vara en sänka för PCB.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Mätningarna i sediment och vatten möjliggjorde beräkningar av fördelnings­
koefficienter mellan totalt organiskt kol och vatten (KOC) för dessa Öster­sjö­­
sediment. Totalt organiskt kol innefattar amorft organiskt kol (amorphous
organic carbon, AOC) och sotkol (black carbon, BC). Den observerade bind­
ningen till AOC+BC i Östersjösediment var starkare än vad bindningen till
enbart AOC beräknades vara utifrån standardmetoder för riskbedömning.
Detta indikerar att de ekotoxikologiska riskerna från PCB och PCDD/F i
Östersjösediment är 10–30 gånger lägre än vad uppskattningen skulle bli om
riskbedömingen baserades på enbart bindning till AOC.
1.4 Massbalansmodellering
För modelleringen användes de nya data som presenterades i föregående
avsnitt samt data från en omfattande litteraturstudie. Beräkningarna genom­
fördes för hela Öster­sjön, men den detaljerade utvärderingen av resultaten
fokuserade på de två största bassängerna, Bottenhavet och Egentliga Öster­
sjön. Arbetet utfördes i flera steg:
1) Den nuvarande förekomsten av och uppehållstiden för de utvalda
föro­rening­arna i Östersjöns miljö beräknades.
2) Den nuvarande storleken på sänkor, källor och flöden av
förorening­ar i och mellan bassängerna i Östersjön uppskattades.
3) Modellens tillförlitlighet utvärderades.
4) Modellen användes för att utvärdera de framtida föroreningsnivåerna i Östersjöns miljö. Avsikten med dessa simuleringar var att
under­söka den möjliga effekten av minskade koncentrationer i
atmosfären på den framtida koncentrationen av dessa föroreningar i
Östersjön.
Nedanstående tabell sammanfattar de huvudsakliga resultaten av mass­balans­
modellering­en.
HCB
PCB
PCDD/F
Nuvarande situation i Östersjön
Mängd (vatten + ytsediment*)
540 kg
2800 kg (ΣPCB7)
10 kg TEQ
% av mängd i vatten
40
9
4
Uppehållstid (år)
0,34
1,8
11
Största källa
Atmosfär
Atmosfär
Atmosfär
Största sänka
Atmosfär
Atmosfär
Begravning i
sediment
Botten­havet
Oförändrat
Oförändrat
År 2025:
~40 % lägre än
nuvarande nivå
Egentliga Östersjön
Oförändrat
Oförändrat
År 2025:
~15 % lägre än
nuvarande nivå
Botten­havet
År 2025:
~90 % lägre än
nuvarande nivå
År 2025:
~90 % lägre än
nuvarande nivå
År 2025:
~65 % lägre än
nuvarande nivå
Egentliga Östersjön
År 2025:
~90 % lägre än
nuvarande nivå
År 2025:
~90 % lägre än
nuvarande nivå
År 2025:
~85 % lägre än
nuvarande nivå
**
Framtida utveckling i Östersjöns ytvatten
Scenario 1***
Scenario 2****
*Översta 2 cm; **Bottenhavet; *** Oförändrade koncentrationer i atmosfären; ****Koncentrationerna i
atmosfären minskade linjärt till 10 % av initialvärdet under en tioårsperiod.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
De huvudsakliga slutsatserna som kan dras från massbalansmodelleringen,
osäkerhetsanalyserna, mönsteranalyserna och jämförelser med andra studier
och mätdata finns summerade nedan.
1.4.1 Bassängerna som helhet:
• Atmosfären är den dominerande yttre källan till HCB och PCB i
Östersjön, och koncentrationerna av HCB och PCB i vattenmassan
kommer att reagera snabbt när koncentrationerna i atmosfären
ändras. Dessa slutsatser ansågs vara högst säkra för HCB och
myck­et säkra för PCB. Den atmosfäriska depositionen av dessa
ämnen är mycket större än det beräknade inflödet från floder och
kända direkta inflöden. Bra överensstämmelse mellan modellerade
och uppmätta koncentrationer i vatten och sediment över en tidsserie
stöder denna slutsats. Inflödet till vattenmassan från atmosfären är
tydligt större än inflödet från sedimenten, även när hänsyn tas till
osäkerheter i modellen. Följ­aktligen fungerar inte sedimenten som en
buffert för vattenmassan mot yttre påverkan från luft. Dessutom
visar miljö­övervak­ningsdata att koncentration­erna av PCB i ytsediment har minskat parallellt med koncentrationerna i luft.
• Atmosfären är den största källan till PCDD/F i Bottenhavet och
Egentliga Östersjön. Denna slutsats anses vara ganska säker.
Modellerings­resultaten tyder på att inflödena från atmosfären är
större än inflödena från andra kända källor. De indikerar också att
inflödena från atmosfären är tillräckligt stora för att förklara dagens
halter av PCDD/F i vattenmassan. Dessutom indikerar analysen av
kongenermönstret att PCDD/F i utsjösediment i Bottenhavet och
Egentliga Östersjön huvudsakligen har atmosfäriskt ursprung.
• Koncentrationerna av fritt lösta PCDD/F i Bottenhavet och
Egentliga Östersjön minskar om koncentrationerna av PCDD/F
i atmosfären förblir på dagens nivåer. Denna slutsats anses vara
ganska säker. Processen som kontroll­erar tidsfördröjningen mellan
minskningen av koncentrationerna i luft och minskningen i vatten är
transporten av PCDD/F från sediment till vatten. Koncentrationerna
i ytsediment har en responstid på flera årtionden på för­ändringar i
inflödet av föroreningar till Östersjön. Detta beror på den långa
uppehållstiden PCDD/F har i Östersjöns system. Därför reagerar
också flödet från sediment till vattenmassa långsamt på förändringar.
Eftersom den atmo­sfär­iska depositionen av PCDD/F har minskat
under de sista år­tiondena kommer det troligen att ske en successiv
minskning av de fritt lösta koncentrationerna under de kommande
årtiondena. Detta är inte helt säkert eftersom det kan finnas andra,
ännu inte identifierade, stora källor till PCDD/F som inte har minskat de senaste åren. En annan osäkerhet är kopplad till storleken på
den förutsagda minsk­ningen. Detta kommer att bero på i) storleken
på minskningen i in­flödet från atmosfären under de senaste årtiondena
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
ii) uppehålls­tiden för PCDD/F i bassängerna. Scenariot för minskning av PCDD/F-koncentrationerna i luft under de senaste 20 åren
baseras på empi­riska observationer och bedöms vara ganska tillförlitligt.
• En minskning av PCDD/F-koncentrationerna i luft kommer att
skynda på minskningen av koncentrationerna av fritt lösta PCDD/F
i Bottenhavet och Egentliga Östersjön. Denna slutsats anses vara
ganska säker. Detta är en konsekvens av att den atmosfäriska
de­positionen är den dominerande källan till PCDD/F i dessa
­bassänger. Den kvarvarande osäkerheten beror på möjligheten att
det finns andra stora, oidentifierade, källor.
• Hastigheten med vilken koncentrationerna av fritt löst PCDD/F
minskar kommer att vara som modellen förutsagt. Denna slutsats
anses vara ganska osäker. Hastigheten på minskningen i Östersjöns
ytvatten misstänks vara överskattad på grund av den enkla modell­
strukturen i POPCYCLING-Baltic. Minskningshastigheten i de
övriga vattenmassorna är tätt kopplad till uppehållstiden för
PCDD/F, vilken i sin tur är kopplad till modellens antagande
an­gående ytarea och det sedimentdjup som står i kontakt med
vatten­massan, liksom hastigheten med vilken föroreningarna begravs
i sedimentet. Även om dessa antaganden har en empirisk grund är de
osäkra, och det har ännu inte varit möjligt att utvärdera deras
till­förlitlighet, till exempel genom att mäta elimineringshastigheten
för mycket hydrofoba ämnen i dessa vattenmassor. Dessutom kan
uppehålls­tiden påverkas av störningar i miljön, som kraftiga stormar,
vilka kan resuspendera ackumulerat sediment och sålunda göra att
begravda PCDD/F åter kommer i omlopp
• Hastigheten på minskningen av koncentrationerna i fisk kommer att
vara parallell med hastigheten på minskningen av de fritt lösta
koncentrationerna i vattenmassorna. Denna slutsats anses vara
myck­et osäker. Mätningarna på sill/strömming under de senaste
15 åren har visat att så inte behöver vara fallet. Minskningen i
tillväxt­hastighet för sill/strömming tros ha orsakat en större
bioackumuler­ing av PCDD/F, med konsekvensen att koncentrationerna av PCDD/F i sill/strömming inte minskade under denna
period, trots att de fritt lösta koncentrationerna (förmodligen)
minskade. Det är således möjligt att ekossystemförändringar kan
sakta ner eller öka den förväntade responsen hos fisk på en minskning av de fritt lösta koncentrationerna.
1.4.2 Områden med förhöjda halter (till exempel nära industrier, städer
och förorenad mark)
• Analyser av ytsediment längs den svenska kusten har visat att mönst­
ret av PCDD/F i sediment från områden nära urbaniserade eller
industrialiserade zoner ofta skiljer sig signifikant från mönstret i
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
atmosfären. Receptor­modellering har visat sig vara ett effektivt
redskap för att spåra och kvanti­fiera PCB- och PCDD/F-källor, så
kallad källfördelning (source apportioning). En receptormodelleringstudie av PCDD/F-källor i Öster­sjön pågår för närvarande.
Preliminära resultat stöder de observationer som gjorts i denna
undersökning, nämligen att det atmosfäriska inflödet är större för
utsjöområden medan kustnära områden ofta har ett mer komplext
bidrag från olika källor, och att icke-atmosfäriska källor kan vara
betydande lokalt/regionalt.
1.5 Rekommendationer för framtida forskning
Föroreningssituationen i Östersjön fortsätter att vara ett problem, speciellt
vad gäller PCDD/F och dioxinlika PCB. Halterna av dessa ämnen i fisk gör att
det finns restriktioner för försäljningen av fisk från Östersjön.
Även om detta projekt har bidragit till en större förståelse av förorenings­
situationen i Östersjön, finns det ett flertal områden där kunskap saknas eller
är osäker. Det är främst för PCDD/F som det finns stora osäkerheter. De
största kunskapsbristerna inkluderar:
• Nuvarande utsläpp av PCDD/F till luft. Denna undersökning har
tyd­ligt visat att problemen med PCDD/F i Östersjön på det hela taget
orsakas av långväga lufttransport, där källor i kontinentala Europa
är viktiga. Följ­aktligen är det viktigt att fastställa huruvida dagens
bild av PCDD/F-utsläpp stämmer med det atmosfäriska inflödet av
PCDD/F till Östersjön.
• Nuvarande utsläpp till Östersjöns vatten. Dessa inkluderar inflöden
med sötvatten, industriutsläpp och läckage från förorenad mark. Det
finns stora osäkerheter i alla dessa kategorier. Det är troligt att de
främst påverkar föroreningssituationen i kustnära områden.
• Det tycks som om dioxinerna (PCDD) minskar mer än furanerna
(PCDF) i flera matriser, inklusive biota från Östersjön, blodserum
från svenska män, och möjligen också i Östersjösediment. Börjar
utsläppen domineras av PCDF istället för PCDD, eller beror detta
skifte på andra faktorer?
• Tidstrender för PCDD/F-koncentrationer i Östersjösediment och
‑luft. Dessa behövs för att utvärdera resultaten av modelleringar.
• Halter och föroreningar av PCDD/F och dioxinlika PCB i Östersjöns
ytsediment. Stora områden av Östersjön har aldrig undersökts.
Analys av föroreningsmönstret i ytsediment kan användas för att
spåra källor. För närvarande finns det bara data för källfördelning i
begränsade områden av Östersjön (Sveriges kust).
• En större förståelse av ytsedimentens ackumulering och ombland­
ning. Detta är nödvändigt för att få fram mer tillförlitliga uppskatt­
ningar av hur lång tid det tar för Östersjön att svara på förändringar
i inflöden av PCDD/F.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
• En större förståelse av föroreningsdynamiken mellan sediment,
vatten och biota. Varför ser vi en variation i tid och rum hos
förorenings­nivåerna i fisk i Östersjön? Beror det på biologiska
faktorer (till exempel tillväxthastighet och födomönster)? Hur
viktiga är föroreningsnivåerna i sediment för nivåerna i biota?
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
2 Summary
This report deals with sources, transport, reservoirs and fate of selected
persistent organic pollutants (POPs) in the Baltic Sea environment. It is the
result of a commission that the Swedish Environmental Protection Agency
was given by the Swedish Ministry of Environment. The project group
in­cluded m
­ embers from Umeå University, Stockholm University, the Swedish
Environmental Protection Agency and the Geological Survey of Sweden.
The commission was to estimate sources, describe the present situation,
and investigate the current fluxes of persistent pollutants (POPs) in the Baltic
Sea ecosystem. The compounds that were chosen for the study were poly­
chlorinated biphenyls (PCBs), hexachlorobenzene (HCB), polychlorinated
dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs).
These classes of compounds represent a broad range of physical-chemical properties, and hence their environmental behaviour encompasses the spectrum of
most chemicals listed in the Stockholm Convention. The sources of the compounds differ. PCDD/Fs are formed unintentionally in a number of different
processes, e.g. during combustion and as by-products in the chemical industry.
HCB is also formed during combustion, but in addi­tion it was produced and
used as a fungicide. PCBs are industrial chemicals with a wide range of uses,
e.g. as insulating fluids. A further reason for se­lecting PCDD/Fs and PCBs is
that currently, the levels of these compounds in fish exceed the limit for marketing of fish within the EU. The environ­mental levels of PCDD/Fs have not
decreased to the same extent as e.g. PCBs and HCB, which has been interpreted as an indication that there are ongoing, not yet identified, PCDD/F emissions.
The approach chosen by the project group was to calculate mass balances
for the selected POPs by using a modified version of an existing mass balance
model (POPCYCLING-Baltic). In a first stage, an uncertainty analysis was
conducted to identify the most important knowledge deficits. Thereafter field
measurements in air, sea water and sediments were under­taken to reduce these
uncertainties.
2.1 Trends and the current situation in
the Baltic Sea ­environment including
the Swedish population
Baltic biota: Decreasing trends of HCB and PCB concentrations have been
observed in Baltic biota (guillemot egg from the Baltic Proper and herring from the Bothnian Sea) since the monitoring started in the 1970s. For
the PCDD/Fs, a decreasing trend of the TEQ levels was seen in the 1970s,
but the decrease has levelled out since the mid-1980s and TEQ levels have
re­mained rather stable since then. Recent research has shown that from 1990
and 15 years onward, some dioxin (PCDD) congener levels have decreased
­significantly in Baltic guillemot egg (e.g. 2,3,7,8-TCDD and OCDD), while
stable or even increasing trends were observed for most other toxic PCDD/F
congeners.
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Swedish population: In the early 2000s, >10% of the Swedish population had
a daily intake of dioxin and dioxin-like PCBs above the tolerable daily intake
(TDI) limit recommended by the European Commission. It has been shown
that the general levels of PCBs and PCDD/Fs in Swedish food have decreased
since the 1970s. In accordance with these observations, the con­centrations
of PCBs, PCDD/Fs and HCB in human milk have shown de­creasing trends
since the 1970s. Distinct decreasing concentrations of PCBs and HCB have
also been observed in blood serum from Swedish men during the period
1991– 2001. In contrast, the TEQ levels in the same population did not
decrease significantly between 1987 and 2001. This is mostly attrib­uted to
stable or increasing trends of several of the furan (PCDF) congeners.
Surface sediments: The coast of the Baltic Sea includes several heavily industrialized zones, and it has been shown that the Swedish coast includes a number
of PCDD/F hot spots associated with industrial activity.
There is limited information on PCDD/F trends in Baltic offshore sedi­
ments. While levels are clearly declining in offshore areas of the Gulf of
Finland due to extensive reduction of emissions, the situations in the ­Both­nian
Sea and the Baltic Proper are unclear. Measurements are few, but these indicate that there has been a decrease since the 1970s. However, in the Baltic
Proper, the decrease seems to have levelled off, and in the Bothnian Sea, the
concentrations of dioxin (PCDD) congeners appear to be declining, while the
furan (PCDF) congeners do not show a declining trend.
For the PCBs, more data are available. During the last 10–20 years, a
­dis­tinct decrease of PCB concentrations has been observed in sediments in
the Bothnian Sea and the Baltic Proper. In the Bothnian Sea, the decrease was
on average a factor of 5.6 while in the Baltic Proper it was a factor of 4.5.
These decreasing PCB concentrations in offshore sediments are in line with
the decreasing trends in herring from the Bothnian Sea and herring and guillemot egg from the Baltic Proper. There are also indications of decreas­ing HCB
­concentrations in Baltic sediments.
It has previously been suggested that the distinctly lower PCB concentra­
tions in sediments today could be caused by an increased bulk sediment accumulation rate as a result of an increased frequency of severe storms in the
1990s. However, the lower concentrations have continued to be observ­ed
through the 2000s despite calmer conditions, refuting this hypothesis. Hence,
the registered decrease in PCB concentration is most likely the result of
decreased input to the Baltic Sea.
2.2 Industrial emissions
Europe and the Baltic area: The so called “European Dioxin Emission
Inventory”, organised by the European Commission, included a large scale
inventory of European PCDD/F emissions from 1985 to 2005. In general,
considerable emission reduction has been achieved for the industrial ­sources
over the studied period, and in the near future the non-industrial emission
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sources will probably exceed those from industrial installations. Today, iron
ore ­sintering is believed to be the most important emission source type followed by the former “No. 1”, municipal waste incineration. The goal of
the 5th Action Programme was to reduce PCDD/F emissions by 90% from
1985 to 2005, and it was concluded that this goal can only be achieved for
some source types. Among the Baltic countries, the highest air emissions
of PCDD/ Fs to the Baltic Sea area were reported by Germany, Russia and
Poland, which together contributed more than 95% of the total emissions.
However, current data on emissions in the Baltic Sea region are uncertain due
to missing information.
PCDD/F emissions in Sweden: In a survey of PCDD/F sources in Sweden, the
total annual emission from all industrial sectors in Sweden was esti­mated to
be 160–480 g WHO-TEQ yr-1 to waste/landfills, 16–84 g WHO-TEQ yr-1 to
air and 1.9–2.4 g WHO-TEQ yr-1 to water and sediments. Most emissions of
PCDD/Fs to air are still believed to originate from combustion. Among the
combustion sources, it is believed that large scale bio-fuel incin­eration, back­
yard burning and combustion of fossil fuels are the dominant sources, while
emissions from municipal waste incineration are today con­sidered insignificant. On the other hand, waste from municipal waste incin­eration (mainly
ash) contains significant amounts of PCDD/Fs. The waste is deposited at landfills and may cause emissions to soil and water.
The Swedish EPA recently conducted a survey of the levels of dioxins and
other POPs in the vicinity of a number of operating and closed pulp and paper
plants. It focused on POP levels in various environmental compart­ments (fish,
water and settling particulate matter) at sites near and distant from these sites.
It was concluded that, although not all measurements showed elevations,
there are clear indications of local environmental im­pacts from some of the
mills, and follow-up studies are needed at selected sites to further elucidate the
situation. The Swedish Forest Industries Fed­eration also recently conducted a
dioxin survey including measurements at 9 mills. Waste water, flue gases, air
and sludge were analysed. Some current PCDD/F emissions were detected. It
was stated that the contributions of PCDD/F from the point sources together
with tributary inflows to the re­ceiving recipients could roughly explain the
­differences in PCDD/F levels in fish caught near the industries compared to
reference locations.
PCB and HCB emissions in Sweden: Previously, the primary emissions of
PCBs to the environment occurred during production and through leakage
and losses from PCB-containing products and systems. Today, secondary
sources, such as re-volatilisation from soils, probably contribute a large part
of the levels in air. Emissions of PCBs in Sweden have been estimated to be
10–31 kg yr-1 to waste/landfills, 0.4–1.1 kg yr-1 to air and 0.01 kg yr-1 to water
and sediments. The largest emissions were estimated to originate from combustion and from the chemical industry. The emissions of HCB were estima-
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ted to be 13–32 kg yr-1 to air, 3–26 kg yr-1 to waste/landfills and 0.01 kg yr-1
to water and sediment. Combustion sources and the chemical indus­try were
reported to be responsible for the largest emissions.
2.3 New field measurements
Field measurements of Baltic air, bulk deposition, surface sediment, sedi­ment
pore-water and surface and deep sea water were undertaken within this study.
These measurements were needed for reduction of the uncertainties in the
mass balance calculations that were to be done.
Air and atmospheric deposition: During the winter of 2006/2007, air and bulk
deposition samples were collected in Aspvreten (southern Sweden) and Pallas
(northern Finland) in order to identify the major source regions for atmospheric input of PCDD/Fs to the Baltic Sea. Note that atmospheric con­centrations
of PCDD/Fs are much higher during winter than during summer, so that most
of the annual deposition occurs during the winter half-year. Short sampling
times were employed and only samples with stable air mass back-trajectories
were selected for the analysis of the 2,3,7,8-substituted PCDD/F congeners.
Several samples were also collected during the summer half-year.
The region for air mass origin was divided into 7 compass sectors. The
highest concentrations were found in air that had passed over the European
continent. In air that had passed over the British Isles and air from northerly
directions, the concentrations were low. The PCDF concentrations were
higher than the PCDD concentrations in air from the south and east, while the
opposite was true in air from the west-northwest. The variability in the concentrations was much lower within a sector than it was between the sec­tors.
The origin of the wet deposition of PCDD/Fs to the Baltic Sea was esti­
mated for the 6‑month study period (winter). The results indicate that ~40%
of the wet deposition of PCDD/F derived from air that originated from the
southwest sector, while ~20% derived from air from the south sector. The dry
particle-bound deposition of PCDD/Fs is expected to be small compared to
wet deposition under European conditions.
The PCDD/F bulk deposition measured during the same period amounted
to ~200 pg WHO-TEQ m–3 or 1.1 pg WHO-TEQ m–2d–1. Estimates of the ori­
gin of the gaseous deposition to the Baltic Sea indicate that the contributions
from the various compass sectors were quite comparable.
This subproject clearly indicates that the levels of PCDD/Fs over the Baltic
Sea and the atmospheric deposition of PCDD/Fs to the Baltic Sea are pri­
marily determined by the air flow pattern. The air flow pattern can vary con­
siderably from year to year, and hence so may the deposition. In order to be
able to better extrapolate these results in space and time, correlations be­tween
the PCDD/F concentrations and the concentrations of more easily/ routinely
determined atmospheric parameters were explored. A strong cor­relation between the concentration of particle-bound PCDD/F and the soot carbon concentration was found, with a correlation coefficient (r2) of 0.80.
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Surface sediments: Offshore and coastal Baltic Proper and Bothnian Sea sediments were sampled during 2007 and analysed for PCDD/Fs, PCBs and HCB.
To obtain an extensive data set, data from other studies were also in­cluded in
the evaluation.
In general, the PCDD/F concentrations in sediment, when normalised to
dry weight (d.w.), were approximately a factor 2–3 times higher in the Baltic
Proper than in the Bothnian Sea. However, if normalised to organic carbon
(OC), taking into account the substantially higher TOC content in the Baltic
Proper sediments, there were no differences between the two basins. Simi­larly,
the dry weight normalised ΣPCB7 concentrations were on average 4–5 times
lower in the Bothnian Sea than in the Baltic Proper. This difference was less
pronounced if the data were normalised to OC. The HCB concen­trations
seemed to be quite similar in Bothnian Sea and Baltic Proper sedi­ments.
It was shown that the variability in PCDD/F and PCB levels in offshore
sediments could largely be explained by variation in organic carbon (OC)
levels, while a low correlation was observed between OC content and HCB
concentration.
Surface, deep sea and sediment pore-water: The freely dissolved concen­
trations of POPs in deep water and surface water were measured by using
passive sampler strips (POM). The samplers were deployed at different sites
in the Baltic Proper and Bothnian Sea during the spring-summer of 2007 and
harvested after three months. The average dioxin concentrations were 1.1 and
2.5 pg WHO-TEQ m–3 in coastal and offshore waters, respectively. The corre­
sponding ΣPCB7 concentrations were 5.8 and 24 ng m–3. There were no significant concentration differences between surface and deep sea water in either
the Baltic Proper or the Bothnian Sea.
Pore-water concentrations in Baltic sediments from the same sampling
sites as the water samples were determined by employing passive samplers
(POM) in a batch shaking test. The POP concentrations in the pore-waters
generally co-varied with the sediment concentrations.
Sediment-water exchange: For the coastal stations, the average ratio of the
pore-water/overlying water concentration was 3.6 ± 1.6 for the PCDD/Fs
and 1.0 ± 0.6 for the PCBs. This indicates that the coastal sediments act as a
source of PCDD/Fs to the overlying water, whereas for the PCBs there is no
concentration gradient and the sediments in the coastal areas neither consti­
tute strong sinks nor strong sources of PCBs. For PCDD/Fs in deep water, the
ratio was 1.1 ± 0.5, which suggests that there is no concentration gradi­ent
and that the sediments in the offshore areas constitute neither strong sinks
nor strong sources for the diffusive exchange of dissolved PCDD/Fs. For PCBs
this ratio was 0.7 ± 0.3, suggesting that there is only a slight con­centration
­gradient for PCBs. The direction of the gradient indicates that the sediments
could be a PCB sink.
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The sediment and water measurements allowed calculation of the total organic carbon–water partition coefficients (KOC) for these Baltic Sea sedi­ments,
where total organic carbon refers to amorphous organic carbon (AOC) and
soot (black) carbon (BC). The observed binding to AOC+BC in Baltic Sea
sediments was stronger than the binding to AOC alone predicted using standard risk assessment methodologies. This indicates that the ecotoxicological
risk from PCBs and PCDD/F in the Baltic Sea sediments is 10–30 times lower
than would be predicted if the risk assessment would be based on sorption to
AOC alone.
2.4 Mass balance modelling
For the modelling, the new data presented in the previous section and data
from an extensive literature search were used. The calculations were con­
ducted for the whole Baltic Sea, but the detailed assessment of the results
focused on the two largest basins, the Bothnian Sea and the Baltic Proper. The
work was conducted in several steps:
1) The current inventory and residence time of the selected contami­
nants in the Baltic Sea environment was estimated.
2) The current magnitude of the sources, sinks, and flows of contami­
nants in and between the basins of the Baltic Sea was assessed.
3) The reliability of the model was evaluated.
4) The model was applied to evaluate the future development of the
contaminant levels in the Baltic Sea environment. The purpose of
these simulations was to investigate the potential impact of re­duced
atmospheric concentrations on the future concentrations of these
contaminants in the Baltic Sea environment.
The table below summarises the principal outcome of the mass balance
modelling.
HCB
PCBs
PCDD/Fs
Inventory (water + surface sediment*)
540 kg
2 800 kg (ΣPCB7)
10 kg TEQ
% of inventory in water
40
9
4
11
Current situation in the Baltic Sea
Residence time (yr)**
0.34
1.8
Major source
Atmosphere
Atmosphere
Atmosphere
Major sink
Atmosphere
Atmosphere
Sediment burial
Bothnian Sea
Unchanged
Unchanged
At year 2025:
~40% below
current level
Baltic Proper
Unchanged
Unchanged
At year 2025:
~15% below
current level
Bothnian Sea
At year 2025:
~90% below
current level
At year 2025:
~90% below
current level
At year 2025:
~65% below
current level
Baltic Proper
At year 2025:
~90% below
current level
At year 2025:
~90% below
current level
At year 2025:
~85% below
current level
Future development in Baltic surface water
Scenario 1***
Scenario 2****
*Upper 2 cm; **Bothnian Sea; *** Unchanged atmospheric concentrations; ****Atmospheric concentrations were linearly reduced to 10% of the initial values over a 10-year period
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The main conclusions that can be drawn from the mass balance modelling, the
uncertainty analyses, the pattern analyses and comparisons with other studies
and measurement data are summarised below.
2.4.1 The basins as a whole:
• The atmosphere is the dominant external source of HCB and PCBs
to the Baltic Sea, and the concentrations of HCB and PCBs in the
water column will react quickly to changes in the concentrations in
the atmosphere. These conclusions were considered to be highly
certain for HCB and very certain for PCBs. The atmospheric deposition of these chemicals is much larger than the estimated riverine
inputs and known direct inputs. Good agreement between predicted
and measured concentrations in water and sediment including time
trends supports this. The input to the water column is clearly larger
from the atmosphere than from the sedi­ments, even given the uncertainties in the model. Consequently, the sediment reservoir does not
significantly buffer the water column against changes in the external
forcing from air. Furthermore, the monitoring data show that the
PCB concentrations in surface sediments have de­creased in parallel
to the air concentrations.
• The atmosphere is the major source of PCDD/Fs to the Bothnian
Sea and the Baltic Proper. This conclusion is considered to be quite
certain. The modelling results indicate that the inputs from the
atmosphere are larger than the inputs from other known sources.
They also indicate that the atmospheric inputs are sufficiently large
to explain the current levels of PCDD/Fs in the water column.
Furthermore, the congener pattern analy­sis indicates that the
PCDD/ Fs in offshore surface sediments of the Both­nian Sea and the
Baltic Proper are largely of atmospheric origin.
• The freely dissolved PCDD/F concentrations in the Bothnian Sea
and the Baltic Proper decrease if the PCDD/F concentrations in the
atmosphere remain at current levels. This conclusion is considered to
be quite certain. The process determining the lag between the
decrease in the concentra­tions in air and in water is the transfer of
PCDD/Fs from surface sedi­ment to water. The concentrations in the
surface sediment respond over a period of several decades to changes
in the rate of input due to the long residence time of the PCDD/Fs in
the Baltic Sea system. Thus the flow of PCDD/Fs from the sediment
into the water column also responds over a time period of decades to
changes in the rate of input. Since the atmo­spheric deposition of
PCDD/Fs has decreased over the last decades, there is likely to be an
ongoing decrease of the freely dissolved concentrations in the next
decades. The major uncertainty associated with this conclu­sion is
that there could be other unidentified large sources of PCDD/Fs that
have not decreased over recent years. There is further uncertainty
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associated with the magnitude of the predicted decrease. This will
depend on i) the magnitude of the decrease in the atmospheric input
over the last decades; ii) the residence time of the PCDD/Fs in the
basins. The sce­nario for the decrease in PCDD/F concentrations in
air over the last 20 years is based on empirical observations and is
judged to be quite reli­able.
• Reducing the PCDD/F concentrations in the atmosphere will accelerate the reduction in the freely dissolved PCDD/F concentrations in
the Both­nian Sea and the Baltic Proper. This conclusion is considered
to be quite certain. This is a consequence of atmospheric deposition
being the domi­nant source of PCDD/Fs to these basins. The residual
uncertainty lies in the possibility that there are other major unidentified sources.
• The rate of decrease of the freely dissolved PCDD/F concentrations
will be as predicted. This conclusion is considered to be quite uncertain. The rate of decrease in the surface water of the Baltic Sea is
suspected to be overestimated due to the simple structure of the
POPCYCLING-Baltic model. The rate of decrease in the other water
bodies is closely linked to the PCDD/F residence time, which is in
turn linked to the assumptions in the model regarding the surface
area and mixed depth of the surface sediments as well as the sediment burial rates. Although these assump­tions have an empirical
basis, they are uncertain, and it has not yet been possible to evaluate
their correctness, e.g. by measuring the elimination rate of very
hydrophobic chemicals from these water bodies. In addition, the
residence time may be modified by environmental disturbances such
as intense storms which resuspend accumulation sediments and thus
bring buried PCDD/Fs back into circulation.
• The rate of decrease in the concentrations in fish will parallel the rate
of decrease in the freely dissolved concentrations in the water bodies.
This conclusion is considered to be very uncertain. The observations
of levels in herring over the last 15 years have shown that this need
not be the case. The decrease in the rate of growth of the herring is
believed to have resulted in stronger bioaccumulation of the PCDD/
Fs, with the con­sequence that the PCDD/F concentrations in herring
did not decrease during this period, although the freely dissolved
concentrations (pre­sumably) did. Hence it is possible that changes in
the ecosystem may slow down or accelerate the expected response of
the fish to a decrease in the freely dissolved concentrations.
2.4.2 Non-pristine areas (e.g. near industries, cities and contaminated land)
• Analyses of surface sediments along the Swedish coast has shown
that the PCDD/F patterns in sediments sampled near urbanised and
industri­alised areas often differ significantly from atmospheric
patterns. For source apportioning, receptor modelling has been
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shown to be an effect­ive tool for tracing and quantifying PCB and
PCDD/F sources. A recep­tor modelling study for PCDD/Fs sources
in the Baltic Sea area is under way. Preliminary results support the
findings in this study, namely that the atmospheric inputs are large
for offshore sites, while in coastal zones, the contribution from
various sources is often much more complex and non-atmospheric
sources can be significant on a local/regional scale.
2.5 Recommendations for future research
The POP pollution situation in the Baltic Sea continues to be a problem, especially for PCDD/Fs and dioxin-like PCBs, which contaminate the fish so that
marketing of Baltic fish in the EU is restricted.
Although the current project has contributed to a better understanding of
the contamination situation in the Baltic Sea, several areas for which knowledge is uncertain or lacking have also been identified. It is primarily for
the PCDD/Fs that the uncertainties are high. The major knowledge deficits
in­clude:
• Current emissions of PCDD/Fs to air. This work has clearly demon­
strated that the PCDD/F problem in the Baltic as a whole is caused
by long range atmospheric transport, whereby sources in continental
Europe play a major role. Consequently, it is important to establish
whether current understanding of PCDD/F emissions is consistent
with the atmospheric input of PCDD/Fs to the Baltic.
• Current emissions to Baltic Sea water. These include fresh water
in­flow, industrial effluents and leakage from contaminated land.
There are large uncertainties in all these categories. It is likely that
they pri­marily affect the contamination situation in coastal zones.
• It appears that the PCDDs are declining more than the PCDFs in a
number of matrices including Baltic biota, blood serum of Swedish
men, and possibly also in Baltic sediments. Is there a shift towards
emissions rich in PCDFs rather than PCDDs, or can this be attributed
to other factors?
• Time trends of PCDD/F concentrations in Baltic sediments and Baltic
air. These are needed for the evaluation of retrospective/perspective
predictions.
• Levels and contamination of PCDD/Fs and dioxin-like PCBs in Baltic
surface sediments. Large areas of the Baltic Sea have never been
in­vestigated. Contaminant pattern analysis of surface sediments can
be used for tracing sources. Currently, the data available only allow
for source apportionment in limited parts of the Baltic Sea (along the
Swedish coast).
• A better understanding of surface sediment accumulation and
­mixing. This is needed to produce more reliable estimates of the
response time of the Baltic Sea to changes in PCDD/F inputs.
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• A better understanding of sediment-water-biota contaminant dynam­ics.
Why do we see spatial and temporal variation in contaminant levels
in fish in the Baltic Sea? Is it due to biological factors (e.g. growth
rate and feeding habits)? How important are the contaminant levels
in sediment for the levels in biota?
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3 Introduction
By direction of the Swedish Ministry of Environment, the Swedish Envi­
ronmental Protection Agency was given a commission to estimate sources,
describe the present situation and investigate the current fluxes of persistent
pollutants in the Baltic Sea ecosystem.
The project was performed during 2007 by a group including Karin
Wiberg (project coordinator), Sarah Josefsson, Eva Knekta, Ylva Persson and
Kris­tina Sundqvist (Umeå University); James Armitage, Dag Broman, Gerard
Cornelissen, Anna-Lena Egebäck, Per Jonsson, Michael McLachlan and Ulla
Sellström (Stockholm University); Niklas Johansson (Swedish Envi­ronmental
Protection Agency) and Ingemar Cato (Geological Survey of Sweden).
Two groups of contaminants and one individual compound were chosen
as representatives for POPs, including both intentionally and unintentionally
produced pollutants. The compounds that were chosen to act as model sub­
stances were: polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB),
polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-pdioxins (PCDDs). PCDFs and PCDDs are commonly designated as dioxins.
The selected compounds are all priority substances and are globally distrib­
uted organic contaminants. These three classes of compounds represent a
broad range of physical-chemical properties, and hence their environmental
behaviour encompasses the spectrum of most chemicals listed in the Stock­
holm Convention. The sources of the compounds differ. Dioxins are formed
un­intentionally in a number of different processes, e.g. during combustion and
as by-products in the chemical industry. HCB is also formed during combustion, but in addition it was produced and used as a fungicide. PCBs are industrial chemicals with a wide range of uses, e.g. as insulating fluids.
Dioxins and PCBs are present in high concentrations in fish from the Baltic
Sea, and a large portion of the catch exceeds the limits for dioxins and dioxinlike compounds in food set by the European Commission (The Commission
of the European Communities 2006). This has resulted in marketing restrictions for the fish industry in the EU countries surrounding the Baltic Sea. The
environmental levels of dioxins have not decreased to the same extent as e.g.
PCBs, which have been interpreted as an indication that there are ongoing,
not yet identified, emissions.
The approach chosen by the project group was to calculate mass balances for the selected POPs by using an existing mass balance model, the
POPCYCLING-Baltic (Wania et al. 2001). In a first stage, an uncertainty
analysis was conduct to identify the most important knowledge deficits.
Thereafter field measurements in air, sea water and sediments were under­
taken to reduce these uncertainties. For the modelling, these new data and
data from an extensive data search were used. The calculations focused on the
Bothnian Sea and the Baltic Proper.
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4 The Baltic Sea environment
The Baltic Sea is classified as a particularly sensitive sea area by the United
Nations’ International Maritime Organization (IMO) due to criteria such as
vulnerability and the uniqueness of the ecosystem. The following chapter aims
to give an introduction to the physical environment of the Baltic Sea.
4.1 Physical environment of the Baltic Sea
The drainage area of the Baltic Sea is 1 729 000 km2, and its surface area
including the Danish sounds (Belt Sea) is 370 000 km2 (Stigebrandt 2001).
It is a shallow sea with an average depth of approximately 60 m. The Baltic
Sea can be divided into different basins: the Bothnian Bay, Bothnian Sea, Gulf
of Finland, Baltic Proper, Gulf of Riga and Belt Sea. The two northern­most
basins, the Bothnian Bay and the Bothnian Sea, constitute the Gulf of Bothnia.
Often the Kattegat Sea is included as part of the Baltic Sea (Figure 1). The
Baltic Sea is semi-enclosed with limited exchange of water through the shallow Belt Sea between the Baltic Proper and the Kattegat (Stige­brandt 2001). It
has a positive freshwater balance; i.e. the inflow of fresh­water from rivers and
precipitation is higher than the inflow of saline water from the Kattegat. This
has created a brackish sea. The turnover time for the entire water mass has
been estimated to be 25–35 years (Sjöberg 1992).
Figure 1. The drainage area and the seven basins of the Baltic Sea (HELCOM 2002).
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The density difference between salt water and fresh water creates a perma­nent
stratification of water in the Baltic Proper. Dense saline water is over­laid by
less saline surface water. The two layers are separated by a halo­cline, a sharp
gradient in salinity and density that inhibits mixing of the water bodies. The
halocline is found in the Baltic Proper at a depth of 60–70 m (Stigebrandt
2001). The presence of the less saline surface water and the shallowness of
the Belt Sea contribute to a limited inflow of saline seawater into the Baltic
Proper. Since seawater inflow is the major engine of water exchange in the
deep water layer, periods of limited inflow result in large areas of the seabed
under the deep water becoming anoxic.
The major basins are interconnected by straits through which the
exchange of water takes place. Each basin has a positive fresh water balance,
which creates a gradient of decreasing salinity towards the Gulf of Bothnia.
The halocline diminishes towards the Gulf of Bothnia due to vertical mixing
of saline and fresh waters that decreases the salinity differences between the
water masses.
The climate in the Baltic is mainly influenced by winds from the west or
southwest. In the winter, the air flow from the south-west is strong, in contrast to the weaker and more westerly air flow in the summer. The annual
precipitation in the area is usually between 400 to 600 mm yr-1, with areas of
high precipitation, e.g. 1 500 to 2 000 mm yr-1, in the Scandinavian highlands
(Bergström et al. 2001). Parts of the Baltic Sea are normally cov­ered with ice
in the winter. During mild winters the ice coverage is limited to the Bothnian
Bay, while during severe winters the ice covers most of the sea except parts of
the Baltic Proper.
Nine countries border on the Baltic Sea, and the drainage area encompasses fourteen countries. The drainage area covers both highly populated and
industrialized regions as well as remote areas. Examining land use from a
national perspective, the contribution of urban areas to the Baltic drainage
basin varies from 14% for Denmark to 2% for Finland. Forests account
for 16% of the Danish part of the drainage basin and 70% of the Swedish
(Sweitzer et al. 1996). The German part of the drainage basin consists of
72% farmland, while only 6% of the Swedish portion is farmland. The Baltic
Sea drainage basin has about 85 million inhabitants, of which 45% live in
Poland. The long water turnover time (25–35 years) in combination with a
dense population and heavy industry has resulted in rather severe pollution of
the Baltic Sea with a number of hazardous substances as well as high nutrient
loads.
4.2 Sediment dynamics in the Baltic Sea
The sediments in the Baltic Sea are the final sink for the emitted POPs. Thus,
it would be preferable if the POPs associated with the sediments were permanently buried. The following chapter will discuss some im­portant aspects of
this burial and some processes that may remobilize POPs from sediment.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
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There are several different systems to classify bottom types based on their
physical and chemical properties. The following sediment classi­fication system
(Håkanson and Jansson 1983) has been used:
- Accumulation areas dominate where fine materials with grain sizes
less than 0.006 mm are continuously deposited.
- Transportation areas are characterised by a discontinuous depo­si­tion
of fine particles/aggregates, i.e. periods of accumula­tion are interrupted by periods of resuspension and transporta­tion.
- Erosion areas prevail where there is no deposition of fine matter.
Obviously any classification is a simplification of reality, and there is a
con­tinuum of sediments ranging over all three sediment types. This chapter
addresses the importance of sediment dynamics when interpreting temporal
trend data on contaminants in sediments.
4.2.1 Erosion bottoms
In the Baltic Sea, erosion is a significant process not only in coastal areas but
also in shallow offshore areas. In total, erosion bottoms are estimated to constitute approximately 30% of the bottom area. The occurrence of erosion
bottoms is strongly associated with water depth. In shallow waters near the
coasts, Christiansen et al. (1997) found that resuspension occurred during
15–35% of the year, whereas in deeper areas, the bottoms were resuspended
during less than 3% of the year.
Suspended matter derived from wave-induced resuspension has been
shown to be of significant importance for the sedimentation process (e.g.
Christian­sen et al. 1997). It was found that the resuspended portion commonly ex­ceed­ed 50% of the total sedimented matter in a coastal area of the
Baltic Sea (Brydsten 1993, Axelsson and Norrman 1977, Brydsten 1990,
Jonsson et al. 1990). Eckhéll et al. (2000) found that between 1969−1993 erosion/resus­pension accounted for on average 70% of the deposited matter in
the open NW Baltic Proper. During individual windy years, the eroded/resuspended portion may increase to 85%.
4.2.2 Transportation bottoms
Approximately 40% of the bottom area of the Baltic Sea is classified as transportation bottoms. The transportation bottoms may be characterised as the
transition zone in which eroded sediments are transported to the final accumulation areas in the deep offshore bottoms of the Baltic. Due to the large
share of erosion and transportation bottoms (2/3 in the Baltic Proper), one
has to keep in mind that the delay time for contaminant changes to be manifested in the deep accumulation areas may be substantial (Jonsson 2000).
A contaminant-carrying particle may have passed through a number of
re­suspension events before being trapped in the anoxic sediments years to
decades after it first enters the water column. Particle-associated contami­nants
may be retained in long-term transportation bottoms until strong energy input
from waves, currents or sub-marine slides resuspends the sediments years to
­decades after the first deposition.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
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4.2.3 Areas of accumulation
Large areas of the Baltic Sea are classified as accumulation areas for fine material. Although it may vary in different parts of the Baltic Sea, in off­shore areas
an average of 30% of the bottom area is considered to constitute this type of
bottom. In general, accumulation bottoms are found at depths greater than
75–80 m, although in more shallow areas accumulation can occur in topographic depressions as shallow as 50 m in wind-exposed areas. The yearly
accumulation rate in the surface sediment is generally between 1 mm and
4 mm. Some characteristics of the Baltic Sea accumulation sedi­ments are summarised in Table 1. The accumulation areas may be divided into: 1) bioturbated sediments and 2) azooic laminated sediments. In the bioturbated sediments
animals are causing a more or less effective mixing of the upper sediment.
This process is discussed further in Chapter 6.6.6.
Table 1. Brief characteristics of the Baltic Sea accumulation sediments.
Mainly <60 μm
Grain size
Mud content
>90%
TOC content
2−10%
Redox conditions
Upper cm temporarily oxic, temporarily anoxic
Dynamics
Sedimentation rate offshore: mean 1–3 (range 0.5–20) mm yr–1
Sedimentation rate archipelago: mean 17 (range 1–70) mm yr–1
Laminated sediments
In areas where poor oxygen conditions (< 2 mg O2 L–1) cause elimination of
the benthic fauna, laminated sediments are often created. The seasonal changes in the composition of sedimenting matter are preserved in the sedi­ments as
more or less distinct annual varves or lamina (Figure 2).
In the deepest parts of the major basins of the open Baltic Proper, laminated sediments have been deposited on anoxic bottoms for more than a
hundred years, indicating natural oxygen deficiency in these areas (Jonsson
et al. 1990). The area of laminated sediments has expanded since the 1940s,
and in the late 1980s approximately one third of the Baltic Proper at depths
ex­ceeding 75–80 m had laminated surface sediments. Due to the lack of benthic macrofauna and subsequently low bioturbation, laminated sediments can
be used to study changes in the contaminant levels with a high temporal resolution.
However, it is important to bear in mind that the lamination is not a static
phenomenon. In 1993 a major inflow of saline water occurred through the
Danish Sounds into the Baltic Sea. The oxygenation of the sea floor allowed
benthic fauna to recolonise, causing bioturbation down to a couple of centi­
metres below the sediment surface. The oxic episode after 1993 may be seen
in the sediment column as a 1–2 cm thick bioturbated layer, over-layered by
laminated sediments.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
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Figure 2. Typical laminated sediment from the open N Baltic Proper. In situ image taken with a
sediment profile imaging camera at 125 m depth. The total length of the image is approximately
10 cm.
Storm-induced erosion causes changed sediment accumulation rates
From long-term registration of waves along the German Baltic coast it has
been shown that the annual frequency of storm waves increased from 1831 to
1990 (Baerens and Hupfer 1994). A strong relationship was shown be­tween
dry matter deposition and the frequency of wind speeds in excess of ≥14
m s–1 expressed as annual means. Figure 3 shows the strong relationship between the gale frequency and the deposition of dry matter. Changes in storm
frequency may be used to indicate whether extra care should be taken when
interpreting temporal trend monitoring.
Resuspension of old clays affects sediment carbon content
In numerous investigations it has been shown that the sediment carbon con­
tent is of great importance for the sediment burial of hydrophobic organic
contaminants. There­fore, processes/mechanisms that may alter the organic
carbon content have to be taken into consideration in trend monitoring.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
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Dry matter deposition 3 yr running average
Gale frequency annual
Gale frequency 3 yr running average
500
12%
10%
400
8%
300
6%
200
4%
100
2%
0
1960
1965
1970
1975
1980
1985
1990
Gale frequency ( 14 m s-1)
-2
-1
Dry matter deposition (g m yr )
600
0%
1995
Figure 3. Dry matter deposition (3-year running average, each year the mean of measurements
from 3 cores) and the frequency of wind velocities ≥ 14 m s–1 (gale force; individual years and
3-year running mean) for the period 1969–1993 (from Eckhéll et al. 2000).
800
10
700
9
8
600
7
500
6
400
5
4
300
3
200
100
0
1965
2
Mean deposition (3 yr running average)
TOC (% dw) (3 yr running average)
1970
1975
1980
1985
TOC
OC(%
(%d.w.)
d.w.)
-2 yr-1)
Dry matter
deposition
(g m(g/(m
2 year))
Dry matter
deposition
In Figure 4, it is demonstrated that the dry matter accumulation rate de­creased
by approximately 50% in the 1980s. This was accompanied by an increase
in total organic carbon (TOC) content from 3–4% to 7–8% during the same
period of time. The interpretation of this is that the erosion/ resus­pension of
mainly minerogenic matter from glacial and postglacial clays increases during
windy years, whereas the carbon input from primary production is more constant and thus makes a stronger contribution to the dry matter flux during
calm years with low dry matter sedimentation rates.
1
1990
0
1995
Figure 4. Dry matter deposition and TOC content in sediment from the NW Baltic Proper versus
time. A 3-year running average of the means of the 3 cores is shown (from Eckhéll et al. 2000 and
Jonsson, unpublished data).
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
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5 The selected POPs and their
trends in Baltic Sea biota
The substances included in this study (PCDD/Fs, PCBs and HCB) were emitted mainly prior to the 1980s. However, despite the considerable emission
reductions during the 1980s, these substances are still present and affecting
the Baltic Sea environment. This is due to a number of reasons, e.g. the Baltic
Sea being a rather closed ecosystem as described in the previ­ous chapter
(Bergström et al. 2001, Stigebrandt 2001). The hydrophobic properties result
in the compounds accumulating in the fatty tissues of orga­nisms. Humans are
consequently exposed by intake of food. This chapter describes the pollutants,
their origin, the human exposure/risk and the con­centration trends in Baltic
Sea biota.
5.1 PCDD/Fs
Polychlorinated s (PCDDs) are a group of 75 compounds with the same chemical backbone (congeners), and the similarly structured polychlorinated
dibenzofurans (PCDFs) are a group of 135 congeners. The various PCDD/F
congeners differ in chlorination degree (from 0 up to 8 chlorines per congener)
and chlorination pattern. Among these 210 con­geners, 17 congeners are considered biologically active and toxic.
Commonly, when dioxins are analysed, only the toxic congeners, i.e. the
17 PCDD/Fs that have a 2,3,7,8-chlorine substitution pattern, are quantified
and reported. Of the 17, the 2,3,7,8-tetra-chlorinated (TCDD), exhibits the
highest toxicity. To compare the risk of different con­geners, toxic equivalency
factors (TEFs) were introduced. These factors relate the toxicity of each toxic
congener to 2,3,7,8-TCDD. The 2,3,7,8-TCDD toxic equivalence (TEQ) of
a mixture of compounds is calculated by adding the products of the concentration and the TEF for each toxic con­gener. The TEF values have evolved
over time. The values most commonly referred to in the literature are the
WHO-TEFs, the current standard which was adopted by the World Health
Organization in 1998 and revised in 2006 (van den Berg et al. 1998, 2006),
and the international TEFs (I-TEFs), which were adopted by NATO/CCMS
and employed through much of the 1990s (NATO/CCMS 1988). The three
TEF schemes are listed in Table 2.
In the WHO-TEF concept, dioxin-like (DL) PCBs are also included, and
reported values may refer to PCDD/F-TEQs, DL-PCB-TEQs or total (PCDD/F
and DL-PCB) TEQs.
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SWEDISH ENVIRONMENTAL PROTECTION AGENCY
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Table 2. TEF schemes according to I-TEF, WHO-TEF (2006) and WHO-TEF (1998).
Congener
I-TEF
WHO-TEF
WHO-TEF
NATO/CCMS 1988
van den Berg 2006
van den Berg 1998
2378-TCDD
1
1
1
12378-PeCDD
0.5
1
1
123478-HxCDD
0.1
0.1
0.1
123678- HxCDD
0.1
0.1
0.1
123789- HxCDD
0.1
0.1
0.1
1234678-HpCDD
OCDD
2378-TCDF
0.01
0.01
0.01
0.001
0.0003
0.0001
0.1
0.1
0.1
12378-PeCDF
0.05
0.03
0.05
23478-PeCDF
0.5
0.3
0.5
123478-HxCDF
0.1
0.1
0.1
123678-HxCDF
0.1
0.1
0.1
123789-HxCDF
0.1
0.1
0.1
234678-HxCDF
1234678-HpCDF
1236789-HpCDF
OCDF
0.1
0.1
0.1
0.01
0.01
0.01
0.01
0.01
0.01
0.001
0.0003
0.0001
Dioxins are unintentionally formed in various processes, often in high tem­
perature processes and in the presence of chlorine. The most important known
sources are:
• Chemical manufacturing, especially the production of chlorine gas in
the chlor-alkali industry, as well as the production of chlorophenols
and PCBs.
• Industrial processes such as chlorine bleaching in the pulp and paper
industry.
• Combustion processes such as municipal waste incineration and
metallurgic processes.
• Secondary sources, such as sediment leakage to water and volatilisa­
tion from soil and vegetation surfaces.
In the Baltic Sea region, the pulp and paper industry, metallurgic industry and
combustion processes are believed to have been the major dioxin emission
sources during the last decades. However, in the Gulf of Finland, the production of chlorophenols has been a major regional source. The contaminated
sediments of River Kymijoki still act as important secondary sources of dioxins to the Gulf of Finland (Isosaari et al. 2002).
The historically high emissions of POPs have resulted in high loads of
con­taminants to the Baltic Sea ecosystem. In 1991, the Swedish National
Food Administration introduced food recommendations for the consumption of Baltic Sea fish to reduce the intake of dioxin-like compounds. In
1998–1999, the average daily intake for the Swedish population was 1.1 pg
39
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
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WHO- TEQ kg–1 body weight (b.w.) for women and 1.0 pg WHO-TEQ kg–1
b.w. for men (Lind et al. 2002). Fish from the Baltic Sea contributed 15–18%
of the daily intake, while fish in total contributed 50–55% of the daily intake.
In an attempt to lower the general exposure of dioxins and dioxin-like
compounds to the European Union populations, the European Commission
introduced maximum allowed limits for food and feed. Currently, a large
portion of the fish caught in the Baltic Sea exceeds the limit for marketing
of fish within the EU. The EU Scientific Committee for Food has set a tolerable weekly intake (TWI) of dioxins and dioxin-like compounds of 14 pg
WHO- TEQ kg–1 b.w. week-1 (The Commission of the European Commu­
nities 2006). This limit is commonly referred to as a tolerable daily intake
(TDI) of 2 pg WHO-TEQ kg–1 b.w. d–1. In Sweden 12% of the population has
a daily intake above the European Commission TDI (Lind et al. 2002).
In a risk exposure study by the National Food Administration of Sweden
(2007), it was concluded that the levels of dioxins in food have decreased
since the 1970s. In accordance with these observations, the concentrations
in human milk have decreased since 1996 (National Food Administration
2007). In contrast to the decreasing dioxin levels in food and human milk,
the TEQ concentration in blood serum from Swedish men (n=26) did not
show any significant decreasing trend between 1987 and 2001 (Hagmar et al.
2004; Rylander et al. 2008). On the other hand, the concentration of several dioxin (PCDD) congeners decreased significantly (five out of seven of the
2,3,7,8-substituted PCDDs). Among the PCDFs, it was only the 2,3,7,8-TCDF
that decreased significantly, while OCDF showed significant increase. Among
the 26 men, nine were classified as high consumers of fatty fish from the Baltic
Sea. The serum levels of this group did not deviate from the average time
trend levels of TEQ.
The major part of the daily intake of dioxins originates from animal
foods, and in particular fish. In contrast to the general food levels, the levels
of dioxin in herring from the Baltic Sea have not decreased since the 1990s
(Figure 5) and it has been shown that fishermen’s families from the east
coast have higher concentration of dioxins and PCBs in blood as compared
to fishermen’s families from the west coast (National Food Administration
2007).
Figure 5 and Figure 6 show the trends of TEQ-levels in Baltic herring
muscle and guille­mot egg (Bignert et al. 2007a, Olsson et al. manuscript A).
As seen in Figure 6, there were decreasing trends from the 1970s in guille­
mot egg from the Baltic Proper and herring from the Bothnian Sea, but these
decreasing trends have levelled out since the 1980s. The TEQ trends in herring
from other Baltic locations (Bothnian Bay and Baltic Proper) have only been
re­corded since the end of the 1980s, and these show increasing (Bothnian Bay
on lipid weight (l.w.) basis) or stable (Bothnian Bay on wet weight (w.w.) basis
and Baltic Proper on w.w and l.w. basis) trends (Figure 5). The 2,3,4,7,8PeCDF is the major contributor to the TEQ value in Baltic biota. Since the
level of this congener has been relatively stable from around 1980 in Baltic
40
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
guillemot egg, this is the reason why also the TEQ levels have been stable for
the last decades (Olsson et al. manuscript B). Recent re­search has shown that
from 1990 and 15 years onward, some PCDD con­gener levels have decreased
significantly in Baltic guillemot egg (e.g. 2,3,7,8-TCDD and OCDD), while
stable or even increasing trends (although not statistically significant) have
been observed for most other toxic PCDD/F congeners (Olsson et al. manuscript B).
-1
pg TEQ g w.w.
TCDD-equivalents,
pg/g fresh wt, herring muscle
Harufjarden
Utlangan
Fladen
2.0
2.0
2.0
1.5
1.5
1.5
1.0
1.0
1.0
.5
.5
.5
.0
90
95
00
05
.0
90
95
00
05
.0
90
95
00
05
pia - 08.04.19 16:08, tcddecwo
Figure 5. Concentrations (geometric mean) and 95% confidence interval of dioxin concentrations in herring muscle (pg TEQ g–1 w.w.; n=10) from fish caught in Haru­fjärden (Bothnian Bay),
Utlängan (Baltic Proper) and Fladen (Kattegat) from 1989 to 2005 (Bignert et al. 2007a and
Olsson et al. manu­script A). The dotted line represents the geometric mean of the annual means.
3.5
TCDD
equivalents,
ng/g fat, Guillemot egg, early
TCDD
equivalents,
Guillemot
eggng/g f at, guillemot egg, earlyöla
Guillemot
egg
PCDD/F-TEQ ng g-1 l.w.
PCDD/F-TEQ, ng/g l.w.
7
w.w.
6
3.0
5
2.5
4
2.0
ng/g l.w.
1.5
3
1.0
2
.5
1
.0
Herring
muscle
Herring
muscle
PCDD/F-TEQ
pg g-1
PCDD/F-TEQ,
pg/g w.w.
70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 06
0
80
85
90
95
00
05
Figure 6. Time trends of dioxin concentrations in guillemot eggs from Stora Karlsö (ng TEQ g–1
l.w.; n=10; Baltic Proper; Bignert et al. 2007a) and herring from Ängskärsklubb (pg TEQ g–1 w.w.;
n=12–20; Bothnian Sea; Olsson et al. manuscript A). Geometric means and 95% confidence intervals are given.
41
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
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It is interesting to note that there is a concentration difference between herring
from Harufjärden (Bothnian Bay) and Utlängan (Baltic Proper) compared to
herring from Fladen (Kattegat), with significantly higher dioxin concentrations in fish from the north-eastern sites. Spatial differences have also been
observed in the congener composition of the dioxins and dioxin-like PCBs in
herring going from the North Sea to the Baltic Proper (Karl and Ruoff 2007).
The contribution of dioxin-TEQ to the total TEQ increases in an easterly
direction, going from the North Sea to the Skagerrak and Kattegat and further
into the Baltic Proper (Karl and Ruoff 2007). As pointed out in section 6.5.2,
the concentrations of dissolved PCBs decrease moving from the Kattegat into
the Baltic Proper, which may explain the west-to-east trend in the contribution
of the dioxin-TEQ in herring. A com­parison with herring levels reported by
Bignert et al. (2007b) confirms this trend and verifies the high levels in Baltic
fish (Figure 7). Bignert et al. (2007b) discussed the geographical distribution
of dioxins in the Gulf of Bothnia and showed that fish from the southern part
of the Bothnian Sea exhibit 30% higher concentrations as compared to fish
from the northern part of the Baltic Proper, the central and northern parts of
the Bothnian Sea, and the Bothnian Bay (Figure 7).
dioxin-like PCBs
y
Ba
a
an
Se
th
ni
Se
ia
n
Bo
th
n
n
or
lB
N
tra
th
ot
hn
ia
ia
n
th
n
Bo
h
C
en
Bo
a
Se
op
Pr
c
l ti
Ba
a
Dioxins
ut
So
Sk
or
N
12
10
8
6
4
2
0
er
pg/g w.w.
dioxin-like PCBs
Dioxins
Se
a
ag
er
C
oa
ra
k
st
Ka
of
t te
M
g
ec
at
t
kl
en
b
ur
R
So
üg
g
en
ut
h
a
of
re
Bo
a
Ea
rn
st
h
of
o
B o lm
C
r
n
oa
ho
st
lm
of
Po
C
oa
la
nd
s
S o t of
La
ut
h
tv
of
ia
G
ot
la
nd
12
10
8
6
4
2
0
B)
th
pg/g w.w.
A)
Figure 7. Dioxin and dioxin-like PCB TEQ (pg TEQ g–1 w.w.) in herring from the North Sea, the
Skagerrak Sea and various basins of the Baltic Sea. The figures are based on data from A) Karl and
Ruoff (2007) and B) Bignert et al. (2007b).
5.2 PCBs
Polychlorinated biphenyls (PCBs) are a group of compounds consisting of
209 congeners with one to ten chlorine atoms. Among these, there are twelve
congeners with a structure and toxic mechanism similar to the diox­ins (PCBs
77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189). These are
often referred to as dioxin-like PCBs (DL-PCBs) or co-planar PCBs, and they
have been assigned TCDD toxic equivalence factors (Table 3). The TEFs for
DL-PCB are generally lower than those for the toxic PCDD/Fs, but since the
prevalence of PCBs generally is higher, the contri­bution of DL-PCBs to the
42
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
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total TEQ is significant in most environmental compartments (e.g. in Baltic
herring; Figure 7). To date, the non-dioxin-like PCBs (NDL-PCBs) have not
been assigned TEFs, but ongoing discussions within the EC indicate that NDL
may be included in the TEF scheme in the near future.
Table 3. TEF schemes for DL-PCBs according to WHO-TEF (2006) and WHO-TEF (1998).
Congener
WHO-TEF
WHO-TEF
van den Berg 2006
van den Berg 1998
non-ortho substituted
PCB 77
0.0001
0.0001
PCB 81
0.0003
0.0001
PCB 126
0.1
0.1
PCB 169
0.03
0.03
mono-ortho substituted
PCB 105
0.00003
0.0001
PCB 114
0.00003
0.0005
PCB 118
0.00003
0.0001
PCB 123
0.00003
0.0001
PCB 156
0.00003
0.0005
PCB 157
0.00003
0.0005
PCB 167
0.00003
0.00001
PCB 189
0.00003
0.0001
In environmental monitoring and scientific research, seven PCB congeners are
typically analysed, the so-called indicator PCBs (ΣPCB7). The industrial production of PCBs started in the 1920s; it increased up to the 1970s and was
ceased out in the 1990s (Breivik et al. 2002). Major fields of applica­tions were
as heat resistant oils and lubricants in electrical equipment and hydraulic systems, and in carbon paper. Previously, the primary emissions of PCBs to the
environment occurred mainly during production and through leakage and
losses from PCB containing products and systems. Today, sec­ondary sources,
such as re-volatilisation from soils, probably contribute to a large part of the
levels in air.
As for the dioxins, the major human PCB exposure pathway is through
in­take of animal food in general and fish in particular (National Food
Admini­stration 2007). The levels of PCBs in food have decreased since the
1970s. In contrast to dioxins, the PCBs displayed distinct decreasing blood
con­centrations from 1991 to 2001 (Hagmar et al. 2004); however, there
was considerable variation between individuals included in the study. The
con­centration of PCB #153 in human milk has also been decreasing since
the 1970s (National Food Administration 2007). Interesting to note is that
there are indications of higher levels of some PCBs (118, 153, 156 and 180)
in human milk from women living on the east coast of Sweden compared
to women living on the west coast (Lignell et al. 2006). These women had
­declared a higher intake of Baltic fish compared to women on the west coast
during their childhood. Studies conducted by Karl and Ruoff (2007) and
43
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Bignert et al. (2007b) have shown that the DL-PCBs have a lower variation in
herring concentrations between basins as compared to dioxins (Figure 7). Fish
from the southern parts of the Baltic Proper (samples taken outside Born­holm
Island, Poland and Latvia) showed the highest concentrations of DL-PCBs.
Figure 8 shows the time trend of ΣPCB7 in herring muscle from fish caught
at four locations in the Baltic Sea (Bignert et al. 2007a) and Figure 9 shows
the trend in guillemot eggs from Stora Karlsö (Baltic Proper). In both herring
muscle and guillemot egg, the ΣPCB7 levels have decreased since the start of
the monitoring in 1978.
μg ΣPCB7 g-1 l.w.
sPCB, µg/g lipid w., herring muscle
Angskarsklubb
Harufjärden
,p
4.0
Utlängan
Landsort
,p
4.0
,p
4.0
3.5
3.5
3.5
3.5
3.0
3.0
3.0
3.0
2.5
2.5
2.5
2.5
2.0
2.0
2.0
2.0
1.5
1.5
1.5
1.5
1.0
1.0
1.0
1.0
.5
.5
.5
.5
.0
.0
78
83
88
93
98
03
.0
78
83
88
93
98
03
,
4.0
.0
78
83
88
93
98
03
78
83
88
93
98
03
Figure 8. Concentrations (geometric mean) and 95% confidence interval of PCB con­centrations in
herring muscle (µg ΣPCB7 g–1 l.w.; n=12–20). The fish were caught in Harufjärden (Bothnian Bay),
Ängskärsklubb (Bothnian Sea), Landsort (Baltic Proper) and Utlängan (Baltic Proper) between
1978 and 2005 (Bignert et al. 2007a). The dotted line represents the geometric mean of the annual means.
μg ΣPCB7 g-1 l.w.
sPCB, µg/g lipid w., guillemot eggs, early laid. St Karlso
,p
400
300
200
100
0
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
00
02
04
06
Figure 9. Concentrations (geometric mean) and 95% confidence interval of PCB concentrations
(µg ΣPCB7 g–1 l.w.; n=10) in early laid guillemot eggs sampled between 1968 and 2006 at Stora
Karlsö (Baltic Proper) (Bignert et al. 2007a). The dotted line represents the geometric mean of the
annual means.
44
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
5.3 HCB
Hexachlorobenzene (HCB) has been used intentionally as a fungicide, a lubri­
cant, a wood preservative, and in the production of printing ink (USEPA
2000). It is also unintentionally formed during combustion and in processes in the chemical industry. In Sweden, the use of HCB was banned in 1980
(Swedish Chemical Agency 2007). HCB is moderately toxic to humans and
wild life at low doses, but is not included in the TEF scheme.
HCB has been monitored since 1979 in guillemot egg and since 1987 in
herring muscle. As with PCBs, the levels have decreased over time (Figure 10
and Figure 11) (Bignert et al. 2007a). In human blood the HCB levels showed
a clear decreasing trend between 1991 and 2001 (Hagmar et al. 2004).
Regardless of the fish consumption (low, medium or high fish con­sumption),
the HCB concentrations in blood from Swedish men decreased by more than
50% during this period (Hagmar et al. 2004).
-1
HCB,
l.w. lipid
μg
HCB gµg/g
Harufjärden
(
.12
)
,
w., herring muscle
Angskarsklubb
,
(
.12
)
,
Landsort
,
(
.12
)
,p
,
Utlängan
.10
.10
.10
.10
.08
.08
.08
.08
.06
.06
.06
.06
.04
.04
.04
.04
.02
.02
.02
.02
.00
.00
87
92
97
02
.00
87
92
97
02
(
.12
)
,
,
.00
87
92
97
02
87
92
97
02
Figure 10. Concentrations (geometric mean) and 95% confidence interval of HCB concentrations (µg g–1 l.w.) in herring muscle (n=10). The fish were caught in Haru­fjärden (Bothnian Bay),
Ängskärsklubb (Bothnian Sea), Landsort (Baltic Proper) and Utlängan (Baltic Proper) between
1987 and 2005 (Bignert et al. 2007a). The dotted line represents the overall geometric mean.
l.w.
μgHCB,
HCB g-1µg/g
lipid w., guillemot egg, early laid. St Karlso
5
4
3
2
1
0
79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06
Figure 11. Concentrations (geometric mean) and 95% confidence interval of HCB levels (µg g–1
l.w.; n=10) in early laid guillemot egg from Stora Karlsö (Baltic Proper) sampled between 1979 and
2006 (Bignert et al. 2007a). The dotted line represents the geometric mean of the annual means.
45
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
6 POPs in the Baltic Sea environment
This chapter gives an overview of the fate and fluxes of environmental pollutants. It also summarises the present situation regarding emissions and levels
of dioxins, PCBs and HCB in the Baltic Sea environment.
6.1 Distribution between environmental
compartments
The environmental fate of chemicals is governed by the chemical’s ­proper­ties
and the properties of the receiving media. This results in differences in
environ­mental distribution between compound classes and between con­geners
within compound classes. The most important chemical properties affecting
the distribution of persistent environmental pollutants are the partition coefficients (Mackay 2001). These describe the distribution of a compound in a
two phase system at equilibrium, i.e. air-water, lipid-water, sediment-water,
etc. A selection of physical-chemical properties of dioxins, PCBs and HCB is
shown in Table 4, and an overview of important fluxes and partition coefficients is shown in Figure 12.
Table 4. Range of physical–chemical properties for selected POPs
(Swedish Environmental Protection Agency 2007*)
Molecular weight
Substance
Log KOW
(g mol-1)
H
(m3 Pa mol-1)
Chlorinated dioxins
(mono-octa CDDs)
4.8 – 8.2
219 – 460
0.68 – 49
Chlorinated furans
(mono-octa CDFs)
4.4 – 8.6
203 – 444
0.19 – 34
Chlorinated PCBs
(mono-deca CBs)
4.5 – 9.1
189 – 499
0.91 – 952
5.7
285
172
HCB
KOW = octanol-water partition coefficient; H = Henry’s law constant
*The data are from the database PhysProp and the calculation program The Estimation program
Interface (EPI) SuiteTM, v.3.12 (US-EPA).
The pollutants can be dissolved in water, sorbed to particles or present in the
gaseous phase. The gains and losses (inflows and outflow) can be classified as
i) diffusive fluxes, ii) advective fluxes and iii) fluxes due to degradation of the
pollutant. Diffusive fluxes include dry gaseous deposition, evapora­tion, sorption and dis­solution. The magnitude of the diffusive fluxes be­tween compartments depends on differences in chemical potential (or fuga­city) between
compartments. These differences, in turn, depend on the de­gree of pollution,
inherent properties of the chemical and characteristics of the various compartments. Advective fluxes refer to transport of pollutants with a moving media.
Examples of advective fluxes are: wet and dry atmo­spheric deposition, inflow
via air masses and fresh water, sedimentation, resuspension and erosion.
46
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Temperature
Atmosphere
Emissions
Kow
Kaw
Inflow
Koa
Outflow
Degradation
Diffusion
Run off
Koa
Advection
Kaw
Water Body
Inflow
Inflow/outflow
Outflow
Kow
Kaw
Kow
Emissions
Disolved
Emissions
Koa
Kow
Sediment
Terrestrial System
Sorbed to
particles
Gaseous
Figure 12. Schematic picture of partition coefficients (KAW, KOW, KOA) and impor­tant fluxes in a
multimedia environmental system.
Hydrophobic compounds like dioxins, PCBs and HCB tend to accumulate
in organic carbon rich compartments (e.g. soils and sediments) or lipid rich
organisms (e.g. animals and humans). The accumulation can be enhanced if
the soils and sediments have a high content of black carbon (soot). For fish
and other aquatic biota, the important uptake routes are diffusion across the
gills and ingestion of feed. The main POP elimination routes of aquatic organisms are through diffusion across the gills, excretion and biotransform­ation.
POPs have differing susceptibility to bio­transformation. The net result of
uptake and elimination of POPs is called bio­accumulation. Bioaccumula­tion
often results in increased concentration of POPs with increasing age of the
organism. For highly persistent POPs such as dioxins, PCBs and HCB, biomagnification is also seen. Biomagnification is an increase in lipid normalised
concentration from lower to higher trophic levels in the food web.
The relative abundance of congeners within a compound class (e.g.
PCDD/ Fs and PCBs) in an environmental compartment is described as the
congener pattern. In this report, the congener pattern of dioxins relates to
abundance of individual 2,3,7,8-substituted PCDD/F congeners in relation
to the sum of all seventeen 2,3,7,8-substituted PCDD/Fs. Correspondingly,
the congener pattern of PCBs describes the abundance of the individual
PCB7- congeners in relation to the sum of all PCB7-congeners (ΣPCB7).
The congener pattern present in emissions is often modified during transport and fate. Figure 13 illustrates the dioxin congener pattern in several
environ­mental compartments. For example, the aerosol compartment was
domi­nated by OCDD and 1,2,3,4,6,7,8-HpCDD, while the gaseous phase
con­tained a larger contribution from 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF and
2,3,4,7,8-PeCDF (results from this study). Figure 14 shows the correspond­ing
mean ΣPCB7 composition of the different compartments.
47
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Soilsoil
Soil
0.6
0.6
0.5
0.4
0.3
0.2
0.2
0.0
0.0
aerosol
Aerosol
Aerosol
Fraction of sum
Baltic Sea
Sea herring
herring
herring
Baltic
0.8
0.4
0.20
0.3
0.15
0.2
0.10
0.1
0.05
0.0
air gaseous
Atmospheric gas phase (PUF adsorbtion)
0.00
fresh water dissolved
+particulate
Dissolved
water
Dissolved and
and particulate
particulate phase
phase in
in fresh
fresh
water
marine
water dissolved
Dissolved phase in marine water
(passive
sampling)
0.4
0.6
0.3
0.4
0.2
0.2
0.1
0.0
0.0
Bothnian
Sea
sediment
sediment
Bothnian
Sea
Bothnian
Sea
sediment
0.4
Proper
sediment
BalticBaltic
Proper
sediment
Baltic
Proper
sediment
0.4
0.3
0.2
0.1
0.1
0.0
0.0
2378-D
12378-D
123478-D
123678-D
123789-D
1234678-D
OCDD
2378-F
12378-F
23478-F
123478-F
123678-F
234678-F
123789-F
1234678-F
1234789-F
OCDF
0.2
2378-D
12378-D
123478-D
123678-D
123789-D
1234678-D
OCDD
2378-F
12378-F
23478-F
123478-F
123678-F
234678-F
123789-F
1234678-F
1234789-F
OCDF
0.3
Figure 13. Congener patterns of 2,3,7,8-chlorinated dibenzo-p-dioxins (DDs) and dibenzofurans
(DFs) plotted as fraction of the sum of the 2,3,7,8-substituted DDs and DFs in background soil in
Denmark, Sweden, Norway and Estonia (Vikelsoe 2004, Matscheko et al. 2002, Hassanin et al.
2005, Roots et al. 2004), herring from the Gulf of Bothnia (Sundqvist et al. 2007, Bignert unpublished data), offshore sedi­ment from the Bothnian Sea and the Baltic Proper (Sundqvist et al.
manuscript, and results from this study), the atmospheric gas phase and aerosols (results from this
study; average over a six‑month period, the average was weighted to correct for variation in composition due to air mass origin), dissolved phase in offshore water of the Bothnian Bay and Baltic
Proper (results from this study using passive sampling) and the particulate and dissolved phases
in fresh water from seven Swedish rivers (Wiklund, personal communication; Andersson, personal
commu­nication). Error bars indicate one standard deviation.
48
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Soil
soil
Baltic Sea herring
Herring
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
P
C
B
_2
8
P
C
B
_5
2
P
C B
_1
01
P
C
B
_1
1
8
P
C
B
_1
3
8
P
C
B _ 1
5
3
P
C
B _ 1
8
0
0
P
C
B
_ 2
8
P
Aerosol
air+aerosol
Fraction of sum
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
P
C B
_ 2
8
P
C
B
_5
2
P
C
B
_ 1
01
P
C
B
_1
1
8
P
C
B
_ 1
3
8
P
C
C
B
_1
5
3
P
P
C
C B
B
_ 1
8
0
marineinparticulate
(>0.7um)
Particulate phase
marinewater
water
(>0.7µm)
0.4
C
B
_ 5
2
P
C
B
_ 1
0 1
P
C
B
_ 1
1
8
P
C
B
_ 1
3
8
P
C
B
_1
5
3
P
C
B
_1
8
0
precipitation
Atmospheric gas phase (PUF adsorption)
Aerosol
0.0
P
C B
_2
8
P
C
B
_5
2
P
C B
_1
0 1
P
P
C
C
B
B
__ 11
11
88
P
P
C
C B
B
__ 11
33
88
P
P
C
C B
B
__ 11
55
33
P
P C
C
B
B __ 11
88
00
marine dissolved
water (<0.7um)
Dissolved phase in marine
marine
water
water(passive
(passive
sampling)
sampling)
1.0
0.8
0.3
0.6
0.2
0.4
0.1
0.2
_2
8
P
C B
_5
2
P
C B
_1
01
P
C B
_1
1
8
P
C
B
_1
3
8
P
C
B
_ 1
5
3
P
C B
_1
8
0.0
0
P
C B
_ 2
8
P
C B
_5
2
P
C B
_1
0 1
P
Gulf ofSea
Bothnia
sediment
Bothnian
sediment
0.2
0.1
0.1
B
_ 5
2
P
C
B
_ 1
01
P
C
B
_1
1
8
P
C
B
_1
3
8
P
C
B
_1
5
3
P
C
B
_1
8
0.0
0
PCB 180
C
PCB 153
P
PCB 138
8
PCB 118
_2
PCB 101
B
PCB 52
C
PCB 28
P
P
C
B
_ 2
8
P
C B
_5
2
P
C
B
_1
01
PCB 101
0.2
PCB 52
0.3
PCB 28
0.3
0.0
C
B
_1
1
8
P
C B
_1
3
8
P
C B
_1
5
3
P
C B
_1
8
0
Baltic Proper
Baltic Proper
sediment
sediment
P
C
B
_ 1
1
8
P
C B
_1
3
8
P
C B
_1
5
3
P
C
B
_1
8
0
PCB 180
B
PCB 153
C
PCB 138
P
PCB 118
0.0
Figure 14. The calculated mean congener pattern of ΣPCB7 plotted as frac­tion of ΣPCB7 in herring
from the Gulf of Bothnia (Bignert unpublished data, Bignert et al. 2007b), soil from Sweden and
Norway (Meijer et al. 2003, Armitage et al. 2006), sediment from the Bothnian Bay and Baltic
Proper (results from this study; Sund­qvist et al. manuscript; Cato and Kjellin 2005; Cato, personal communication) dissolved phase in water from the Baltic Proper and Bothnian Bay (results
from this study) and the particulate (>0.7µm) fraction in marine water from the Baltic Proper
(McLachlan et al. 2003, Schulz-Bull et al. 2003, Schulz-Bull et al. 2004, Smith and McLachlan
2006, Wodarg et al. 2004, Sobek et al. 2004), in air from Sweden and Finland and in precipitation from Sweden and Germany (EMEP 2007). Error bars indicate one standard deviation.
49
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
6.2 Industrial emissions
6.2.1 Previous and current PCDD/F emissions in Europe
The so called “European Dioxin Emission Inventory”, organised by the
European Commission, include a large scale inventory of European PCDD/F
emissions from 1985 to 2005. In general, considerable emission reduction has
been achieved for the industrial sources over the studied period, in contrast to
the non-industrial sources (Quaß et al. 2004). In a near future, the emissions
from non-industrial sources will probably exceed those from industrial installations. Today, iron ore sintering is believed to be the most important emission
source type followed by the former “No. 1”, municipal waste incineration
The goal of the 5th Action Programme was to reduce PCDD/F emissions by
90% from 1985 to 2005, and it was concluded that this goal can only be
achieved for some source types, and particularly not for the non-industrial
ones. Measurements from a large number of in­stallations are missing, especially from metal industries in Spain and Italy.
6.2.2 Atmospheric emissions of PCDD/Fs in the Baltic Sea area
The total emissions of dioxins to air by Baltic Sea countries were recently estimated to be 4.6 kg WHO-TEQ yr-1 (HELCOM 2006). The annual emis­sion
of dioxins decreased between 1990 and 2004. The decrease varied be­tween
9% in Poland and up to 39% in Sweden (HELCOM 2006). On the contrary,
some countries reported on an increase in emissions in 2004 as compared to
1990, e.g. Lithuania and Germany. The reason for the reported increase in
Germany is connected to the fact that emissions for some sectors (e.g. petroleum refining) were estimated and submitted for the period 2000-2005, but
not for 1990-1999. The highest emissions of dioxins to the Baltic Sea area
were reported by Germany, Russia and Poland, which together contributed
more than 95% of the emissions (HELCOM 2006). Estonia, Lithuania and
Latvia reported low yearly dioxin emissions (HELCOM 2006). Current data
on the emission of POPs in the Baltic Sea region are uncertain. Some countries
have not reported data at all, and emission data from some industrial sectors
were rough estimates rather than based on measurements, or they were based
on old measure­ment data.
According to a recent HELCOM report, understanding of the concerns
re­lated to POPs is still low in some Baltic countries (e.g. Latvia, Lithuania,
Poland and Russia; HELCOM 2007). These countries often lack informa­tion
on releases of hazardous compounds from industrial sources. In Poland, a
substantial part of the dioxin emissions stem from the use of coal in the residential sector (HELCOM 2007). In a recommended action plan, it was stated
that the Polish emissions to air could be reduced by more than 40% by ceasing backyard burning, by using dry hardwood instead of coal, and by optimizing the stove conditions in residential homes (HELCOM 2007). Furthermore,
the emissions could be substantially reduced by pre­venting landfill fires and by
installing the best available technology for flue gas cleaning (HELCOM 2007).
50
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
6.2.3 Emissions of PCDD/Fs in Sweden
In a survey of PCDD/F sources in Sweden, the total yearly emissions from all
industrial sectors in Sweden were estimated to be 160 to 480 g WHO- TEQ
yr-1 to waste/landfills, 16 to 84 g WHO-TEQ yr-1 to air and 1.9 to 2.4 g
WHO-TEQ yr-1 to water and sediments (Swedish Environmental Protection
Agency 2005). The main emissions of PCDD/Fs to air are still believed to originate from combustion. Among the combustion sources, it is believed that
large scale bio-fuel incineration, backyard burning and combustion of fossil
fuels are the dominant sources (Umeå University 2005). The emis­sions from
municipal waste incineration are today considered as insignifi­cant. On the
other hand, waste from municipal waste incineration (mainly ashes) contain
significant amounts of PCDD/Fs. The waste is deposited at landfills and may
cause emissions to soil and water.
6.2.4 Emissions of PCBs and HCB in Sweden
Emissions of PCBs in Sweden were estimated to be 10 000–31 000 g yr-1 to
waste/landfills, 370–1 100 g yr-1 to air and 13 g yr-1 to water and sediments
(Swedish Environmental Protection Agency 2005). The largest emissions
were estimated to origin from combustion and from the chemical industry.
The emissions of HCB were estimated to be 13 400–32 400 g yr-1 to air,
2 600–26 000 g yr-1 in waste/landfill and 14 g yr-1 to water and sediment
(Swedish Environmental Protection Agency 2005). Combustion sources and
the chemical industry were reported to be responsible for the largest emis­
sions.
6.2.5 PCDD/F, PCB and HCB emissions from various branches
The forest industry, and in particular the pulp and paper industry, has histo­
rically been responsible for high emissions of dioxins to water. Some PCB
emission has also been observed, probably due to the use of recycled paper in
the production. Despite strong reductions of emissions, primarily by changing
the bleaching process, high levels of dioxins are still found in surface sediments sampled near pulp and paper mills (Sundqvist et al. 2006). The highest
levels in herring and sediment are found in the southern Bothnian Sea, an area
with a high concentration of pulp and paper industry (Sundqvist et al. 2006,
Bignert et al. 2007b).
The Swedish Environmental Protection Agency has, from 2005 to 2008,
conducted a survey of the levels of dioxins and other POPs in the vicinity of a
number or existing and closed pulp and paper industries. The survey focused
on POP levels in various environmental compartments, mainly fish (perch and
viviparous blenny), water and settling particulate matter (SPM). Fish samples
were taken near industrial effluents (“near-sites”) and 5–20 km away from
the industrial discharges (“distant-sites”). The authors chose to divide the
mills into the following three categories: i) ECF: chlorine dioxide (ClO2) used
in the bleaching process, ii) TCF: chlorine free bleaching proc­ess and in this
study also production of non-bleached pulp, iii) TMP: thermo-mechanic pro-
51
SWEDISH ENVIRONMENTAL PROTECTION AGENCY
Report 5912 • Sources, transport, reservoirs
and fate of dioxins, PCBs and HCB in the Baltic Sea environment
duction of pulp and in this study also board produc­tion. In addition, samples
were taken at sites where chlorine gas (Cl2) was formerly used in the bleaching
process. In a draft version of a report about contamination levels in the vicinity of pulp and paper industries (Swedish Environmental Protection Agency
unpublished) and in Olsson et al. (2005), it is shown that the concentrations
of HCB, PCB and WHO-TEQ in perch (but not viviparous blenny) sampled
near some of the ECF and TMP sites were elevated in relation to the samples
representing more distant locations. An elevation of the dioxin levels, expressed as TEQs, at “near-site” vs. “distant-site”, of >30% was seen at 7 out of
13 sites (range –50% to +225%). In the TCF category, none of the 4 sites
showed clear elevation (range –30% to +17%) and at mills that formerly used
chlorine gas in the bleaching process (n=4) the range was –18% to +33%.
There were no statistically significant differences in the near/distant perch
level ratios between cate­gories. The PCDD/F levels in water and SPM ­samples
showed deceasing trends in transects taken from sites connecting to pulp
& paper and board industry (inner, intermediate and outer measurements).
Elevations (inner/ outer) were seen at 4 out of 5 sites, and for these 4 sites the
elevations ranged from 20% to 770% for SPM and from 19% to 120% for
dissolved water concentrations. The authors of the draft report conclude that,
although not all measurements showed elevations, there are clear indications
of a local environmental impact from some of the mills, and follow-up studies
are needed at selected sites to further elucidate the situation.
The Swedish Forest Industries Federation also recently conducted a
dioxin survey including measurements at 9 mills. Waste water, flue gases, air
and sludge were sampled (ÅF 2008). Some current PCDD/F emissions were
detected. In a draft report (IVL 2008a), it is stated that the contri­butions of
PCDD/F from the point sources together with tributary inflows to the re­ceiv­
ing recipients could roughly explain the differences in PCDD/F levels in fish
caught near the industries compared to reference conditions. Tentative mass
balances were made for two recipients and the mill effluents accounted for 2%
and 25%, respectively, of the total PCDD/F loads (in­cluding e.g. inflowing sea
water and atmospheric deposition).
In Sweden, the emissions of dioxins to water and air from the chemical
industry have mainly been from the chlor-alkali industry (Swedish Envi­ron­
mental Protection Agency 2005). The chemical industry has also con­tributed
to dioxin emissions by production of hydrochloric acid and poly­vinyl chloride
(PVC). The production of PVC is also associated with emissions of PCBs and
HCB (Swedish Environmental Protection Agency 2005). HCB can also be
formed in chlor-alkali processes. Emissions from the chemical industry mainly
occur through disposal of contaminated sludge and release of polluted water
and air.
The metallurgic industry has emitted large quantities of dioxins to air.
In a recent report from Jernkontoret (2006), it was stated that the air emission from the Swedish steel producers is 3–5 g WHO-TEQ yr-1, including the
DL-PCBs, which contribute with 10–20% to the total TEQ-value.
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6.2.6 Emissions of PCDD/Fs and HCB in Denmark and Finland
The atmospheric PCDD/F emissions in Denmark were estimated to 11–163 g
I-TEQ yr-1 in 2002 (Hansen and Libak Hansen 2003). The major sources were
from waste treatment (mainly municipal waste incineration), fires and energy
production (mainly biomass combustion) (Hansen and Libak Hansen 2003).
In Finland, the PCDD/F and HCB air emissions were recently esti­mated to be
26.2 g I-TEQ yr-1 and 35.7 kg yr-1, respectively (SYKE 2007). For PCDD/Fs,
the major sources were from the energy sector (71%), par­ticularly from public
energy and heat production, and for HCB, 94% of the emissions were from
the industrial section, mainly the chemical industry.
6.3 POPs in the atmosphere
In the atmosphere, POPs are present in the vapour phase, attached to aerosol
particles or dissolved in precipitation. As air-borne pollutants they can originate from sources within the catchment area as well as from sources located
outside the catchment.
The degree of adsorption of POPs to aerosols in the atmosphere depends
on the octanol-air partition coefficient (KOA), the temperature and the available surface of aerosols. Most of the selected POPs will preferably partition
into organic phases in aerosols rather than occur as vapours. However, the
limit­ed amount of particles in the atmosphere results in significant amounts
of POPs in the vapour phase (Axelman et al. 2001; Swedish Environmental
Protection Agency 2007).
The transfer of POPs from the atmosphere to the Baltic Sea catchment
area occurs by dry and wet deposition. Wet deposition includes deposition by
rain or snow, where the pollutant is either dissolved in droplets or attached
to particles captured by precipitation. Dry deposition occurs either with the
pollutant attached to particles or as gaseous diffusion. The dry gaseous deposition is a diffusion process driven by the chemical disequilibrium be­tween
the atmosphere and the surface medium. If there is a net diffusive transport
to the surface one speaks of absorption, while a net diffusive transport to the
atmosphere is referred to as volatilisation.
6.3.1 PCDD/Fs in air – previous measurements
A recent study of dioxins in the atmosphere in Sweden reported a decrease
of dioxin concentrations by a factor of three compared to the 1980s (IVL
2006). The monitor­ing took place in 2004 and 2005 at Råö at the Swedish
west coast and the atmo­spheric concentrations ranged between 0.5 and 10 fg
WHO-TEQ m–3 for bulk air (particle-bound and gaseous). The correspond­ing
average concentration at a Danish air monitoring site within the Co-operative
Programme for Monitoring and Evaluation of the Long-range Transmission
of Air pollutants in Europe (EMEP) was 27 fg WHO-TEQ m–3 (Hovmand
et al. 2007). The average dioxin deposition at Råö was reported to be 1.3 and
0.5 pg WHO-TEQ m–2d–1 in winter and summer respectively (IVL 2006). The
Danish deposition data varied between 2.2 and 3.5 pg WHO-TEQ m–2yr–1
(Hovmand et al. 2007).
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6.3.2 PCDD/Fs in air – new measurements
During the winter of 2006/2007, air samples were collected in Aspvreten
(southern Sweden) and Pallas (northern Finland) in order to identify the
major source regions for atmospheric input of PCDD/Fs to the Baltic Sea.
Short sampling times (24 h) were employed and only samples with stable air
mass back-trajectories were selected for the analysis of the 2,3,7,8-substituted
PCDD/F congeners. Several samples were also collected during the summer
half-year.
In Figure 15 and Figure 16, the PCDD and PCDF concentrations (TEQs)
in air samples from Aspvreten (particle-bound and gaseous, respectively) are
shown grouped according to the compass sector from which the air mass
primarily originated. The highest concentrations were found in air that had
passed over the European continent (southwest, south and east: sectors A2,
B1 and B2). In air that had passed over the British Isles and air from north­
erly directions, the concentrations were low. The PCDF TEQ-concentrations
were higher than the PCDD concentrations in air from southwest, south, east
and northeast (sectors A2, B1, B2 and C), while the opposite was true in air
from west-northwest (sectors A1, D2 and D1) (Figure 15). The variabil­ity in
the concentrations was much lower within a sector than it was be­tween the
sectors.
PCDD
D1
PCDF
(fg TEQ/m )
3
C
20
15
10
D2
5
0
#
A1
#
*
*
A2
B2
B1
Figure 15. Particle-bound PCDD and PCDF concentrations (fg WHO-TEQ m–3) in air samples from
Aspvreten collected during October 2006–April 2007. The samples were grouped according to the
compass sectors of the origin of the air sampled. The boundaries of the compass sectors employed
are illustrated by the dotted lines. Samples marked with * are from May 2005 (i.e. the summer
season), and samples marked with # are from the winter season of 2005–2006.
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PCDD
D1
PCDF
(fg TEQ/m )
3
3
C
2.5
2
1.5
1
D2
0.5
#
0
*
#
A1
*
B2
A2
B1
Figure 16. Gaseous PCDD and PCDF concentrations (fg WHO-TEQ m–3) in air samples from
Aspvreten collected during October 2006–April 2007. The samples were grouped according to the
compass sectors of the origin of the air sampled. The boundaries of the compass sectors employed
are illus­trated by the dotted lines. Samples marked with * are from May 2005 (i.e. the summer
season), and samples marked with # are from the winter season of 2005-2006.
The origin of the wet deposition of PCDD/Fs to the Baltic Sea was esti­mated
for the 6‑month study period. Note that atmospheric concentrations of
PCDD/Fs are much higher during winter than during summer, so that most
of the annual deposition occurs during the winter half-year. For each day, the
compass sector of air mass origin was determined and the average particlebound PCDD/F concentration for this compass sector was multi­plied by the
amount of precipitation on that day and a constant scavenging ratio. The
total deposition for the 6‑month period was estimated and then the fractional contribution of air from each compass sector to this total deposi­tion was
determined. The results are plotted in Figure 17. They indicate that ~40%
of the wet deposition of PCDD/F derived from air that originated from the
southwest sector (A2), while ~20 % derived from air from the south sector
(B1). Bulk deposition samples were also collected (on a monthly basis) during
the air sampling campaign. The total PCDD/F bulk deposition for this period
was ~200 pg WHO-TEQ m–2 or 1.1 pg WHO-TEQ m–2d–1. Good agreement
between the measured bulk deposition and the wet deposition estimated from
the air concentrations was obtained when a scav­enging ratio of 154 000 was
used, which is similar to scavenging ratios re­ported in the literature (Mackay
et al. 1986).
Gaseous deposition is also a major pathway of PCDD/Fs into the Baltic
Sea (Chapter 8.1.2.). The origin of the gaseous deposition to the Baltic Sea
was roughly estimated for the 6‑month study period by multiplying the average gaseous PCDD/F concentration in air from each compass sector by the
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fre­quency with which the air over the Baltic Proper originated from that
sector. The results indicate that the contributions from each sector to gaseous
depo­sition were quite comparable (Figure 18). There is, however, considerable
uncertainty in the contribution from the west, northwest, and north sectors
due to the small number of data points for these sectors.
PCDD
D1
PCDF
50
C
%
40
30
20
10
D2
0
A1
B2
A2
B1
Figure 17. Relative contribution (in percent) of different sectors of air mass origin to the wet deposition of PCDDs and PCDFs (WHO-TEQs) to the southern Baltic Sea.
PCDD
D1
PCDF
30
C
25
%
20
15
10
5
D2
0
A1
B2
A2
B1
Figure 18. Relative contribution (in percent) of different sectors of air mass origin to the gaseous
PCDD and PCDF concentrations (WHO-TEQ) in air over the southern Baltic Sea.
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Note that dry particle-bound deposition of PCDD/Fs is expected to be small
compared to wet deposition under European conditions, even at landlocked
sites more affected by local emissions of large particles with short atmo­spheric
residence times (Kaupp and McLachlan 1999).
This work clearly indicates that the levels of PCDD/Fs over the Baltic Sea and
the atmospheric deposition of PCDD/Fs to the Baltic Sea are primarily determined by the air flow pattern. The air flow pattern can vary considera­bly from
year to year, and hence so may the deposition. In order to be able to better
extrapolate these results in space and time, correlations between the PCDD/F
concentrations and the concentrations of more easily/routinely determined
atmospheric parameters were explored. A strong correlation between the concentration of particle-bound PCDD/F and the soot carbon concentration was
found, with a correlation coefficient (r2) of 0.80 (Figure 19). In Aspvreten, the
soot concentration is measured continuously, and so it should be possible to
estimate PCDD/F concentrations in air from the soot data.
log PCDD/F-TEQ
3
(fg/m)
1.5
-1.5
1.0
r2 = 0.80
0.5
-1.0
0
-0.5
log soot (µg/m3 )
0.5
-0.5
Figure 19. Correlation of the concentration of particle-bound PCDD/Fs with the concentration of
soot in air.
6.3.3 PCBs and HCB
ΣPCB7 is routinely monitored in air and precipitation in European countries
by EMEP. The mean concentrations of ΣPCB7 for the years 2000–2007 was
calculated within this study based on monthly EMEP-data covering Sweden,
Germany and Finland. In precipitation, the mean concentration was 2.8 ng L–1
(standard deviation 5.0 ng L–1; n=314) and in bulk air it was 11 pg m–3 (standard deviation 9.9 pg m–3; n=257). The corresponding concentrations for the
years 1990–1999 were 1.3 ng L–1 (standard deviation 1.5 ng L–1; n=262) in
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precipitation and 15 pg m–3 (standard deviation 16 pg m–3; n=183) in bulk air.
The atmospheric wet and dry deposition of ΣPCB7 in Sweden was reported to
be 1.5 and 1.3 ng m–2d–1 in winter and summer respectively (IVL 2006).
Similar to ΣPCB7, HCB is routinely monitored in European air and
precipi­tation by EMEP. The calculated mean concentration of HCB in precipitation sampled at two German EMEP stations was 0.58 ng L–1 (standard
deviation 0.60 ng L–1, n=94). The corresponding concentration for the years
1990-1999 was 0.15 ng L–1 (standard deviation 0.42 ng L–1, n=93). The HCB
con­centration in bulk air was monitored at a EMEP station in Finland, and
the calculated average was 38 pg m–3 (standard deviation 13 pg m–3, n=11).
6.4 POPs in soils
Chlorinated dioxins, furans and biphenyls and HCB are hydrophobic chemi­
cals with octanol-water partition coefficients (KOW) ranging from 4.4 up to 9.1
(Table 4). This means that they tend to partition into organic matter (OM) of
soil and sediments. In soil, OM will reduce the mobility of POPs by acting as
a sink. With increasing hydrophobicity of the POPs, the strength of the association with OM increases. OM of different origin and level of decay differs
in hydrophobicity and POPs will have a correspond­ingly different tendency
to associate with them. Black carbon, a soot frac­tion of OM formed from
anthropogenic and natural combustion sources, has been shown to ­possess a
strong sorption capacity for POPs (Cornelissen et al. 2005). Planar POPs, e.g.
PCDD/Fs and polycyclic aromatic hydro­carbons (PAHs), have a particularly
strong affinity for black carbon.
Although most POPs have low mobility in soil due to their high affinity
for OM, POPs may still move through soils via migration of colloids (small
OM particles) and dissolved organic matter (DOM; Persson 2007, Isosaari
et al. 2000). For highly hydrophobic compounds, such as PCDD/Fs, PCBs and
HCB, this co-transport is important for the mobility (Persson 2007). Eleva­
tion of particulate and dissolved organic matter has been shown to occur in
streams during snowmelt and other hydrological events (Laudon et al. 2004).
Thus, an elevation of POP fluxes during such events is likely to occur. For
instance, a study of PAHs and PCBs after severe floods in the Czech Republic
in 1997 showed a relocation of the POPs (Hilscherova et al. 2007). Sedimentassociated contaminants were mobilized and deposited on the flooded areas.
In addition, washout of contaminants from the flooded soils was observed.
The mobility of POPs from soils to surrounding waters is poorly investigated
in contrast to other substances that also associate with OM, e.g. radionuclides
and metals.
Measurements of background levels of POPs in soil are scarce. Average
soil concentrations of PCDD/Fs were calculated based on results from studies conducted in Norway, Denmark, Sweden and Estonia (Hassanin et al.
2005, Vikelsoe 2004, Matscheko et al. 2002, Roots et al. 2004), and it was
found to be 53 pg WHO-TEQ g‑1 d.w. (standard deviation 50 pg WHO-TEQ
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g–1 d.w.; n=20). The average ΣPCB7 concentration in soils from Norway and
Sweden was 3.1 ng g–1 d.w. (standard deviation 6.2 ng g–1 d.w.; n=50; Meijer
et al. 2003; Armitage et al. 2006), and for HCB, the mean concen­tration in
Norwegian background soil was 1.0 ng g–1 d.w. (standard devia­tion 0.9 ng g–1
d.w.; n=46; Meijer et al. 2003).
6.5 POPs in the water body
As shown in Figure 12, POPs reach the Baltic Sea water by many routes:
• direct emissions from industries (see also 6.2)
• air-water gas exchange (see also 6.3)
• atmospheric wet and dry deposition (see also 6.3)
• sediment-water gas exchange (see also 6.6.1)
• sediment resuspension and particle-water gas exchange (see also 6.6)
• advective fresh water inflow via rivers, precipitation and ground­
water.
• advective inflow from connecting seas and from deep water (if
exist­ing)
In the water phase, the POPs can be present either in the freely dissolved
form or adsorbed to surfaces (primarily particulate organic matter). Hydro­
phobic compounds associate only to a small extent with mineral matter
(Schwarzenbach and Westall 1981).
6.5.1 Advective water in- and outflow of POPs to the Baltic Sea
The major inflow of water to the Baltic Sea occurs via precipitation, inflow
from rivers and water intrusions from the North Sea. The latter plays an
im­portant role for the ecosystem, but due to the relatively low flow of water,
it does not contribute significantly to the input of POPs to the Baltic Sea
(Assmuth and Jalonen 2005).
Secondary sources include leakage from contaminated soils, sediments
and landfills through the groundwater to a water course. Contaminated soil
in­cludes e.g. dioxin-contaminated sawmill soils, where chlorophenols have
been used as preservatives. Dioxins and HCB are also present at former chloralkali sites. The contribution from contaminated soils is difficult to estimate.
However, rough estimates have been made for some sites. At the former
sawmill site in Marieberg (Kramfors municipality), representing one of the
major chlorophenol contaminated sites in Sweden, the dioxin leakage from
the site was estimated to be 15 to 40 mg WHO-TEQ yr-1 to the con­necting
bay (Kramfors municipality 2007). A similar estimate was made at the former
chlor-alkali site in Bengtsfors (Bengtsfors municipality), and the outflow of
dioxins was calculated to be 1.7 to 8.3 mg I-TEQ yr-1 (Sundberg et al. 2003).
There are few studies that have reported POP concentrations in river
water. Dioxin concentrations for some Swedish rivers (Dalälven, Husån,
Delånger­ån, Hamrångsån, Emån, Ljusnan and Göta älv) were reported to be
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in the range 7 to 120 pg WHO-TEQ m–3 (Andersson, personal communication; Wiklund, personal communication). These are bulk concentrations
(dissolv­ed and particulate fractions).
There is an outflow of brackish water from the Baltic Sea through the
Danish Belt and Kattegat. The estimated outflow is 15 500 km3 yr-1 (Sjöberg
1992). This surface water carries POPs and discharges POPs from the Baltic
Sea.
6.5.2 Surface water – previous measurements
In a study by Broman et al. (1991), the concentration range of dioxins in
marine water from the Bothnian Bay, Bothnian Sea and Baltic Proper was
found to be 0.3-3.6 pg WHO-TEQ m–3 in the dissolved fraction (<0.7 µm)
and 0.6-2.9 pg WHO-TEQ m–3 in the particulate fraction (>0.7 µm). The
sampling technique was active water sampling, i.e. pumping water through
filter and adsorbent (polyurethane foam; PUF). The fraction adsorbed on the
PUF was defined as the dissolved fraction.
The mean concentration of ΣPCB7 and HCB in marine water from the
Baltic Proper was calculated within this study. The ΣPCB7 is based on data
from a number of studies (NODC 2007, McLachlan et al. 2003, Schulz-Bull
et al. 2003, Schulz-Bull et al. 2004, Smith and McLachlan 2006, Wodarg et
al. 2004, Sobek et al. 2004). The average dissolved water concentration was
11 ng m–3 (standard deviation 8 ng m–3; n= 170; <0.7 µm), while the parti­
culate fraction (>0.7 µm) contained 4.3 ng m–3 water (standard deviation
5.0 ng m–3; n=144). Monitoring cruises conducted in four consecutive years
each showed decreasing concentrations of PCBs moving eastward from the
Mecklenburg Bight to the Baltic Proper (McLachlan et al. 2003, Schulz-Bull
et al. 2003, Schulz-Bull et al. 2004, Wodarg et al. 2004).
A mean HCB concentration in dissolved marine water was calculated
based on results from environmental monitoring in the Baltic Proper (Wodarg
et al. 2004, Schulz-Bull et al. 2003, Schulz-Bull et al. 2004, McLachlan et al.
2003). The calculated mean was 7.5 ng m–3 (standard deviation 0.8 ng m–3;
n=83; <0.7 µm). The particulate fraction (>0.7 µm) contained 0.6 ng m–3
water (standard deviation 0.8 ng m–3 water, n=83).
6.5.3 Surface and deep water – new measurements
Within this project, the freely dissolved concentrations of POPs in Baltic
deep and surface water were analysed by using passive sampler strips. Con­
taminants distribute between the water and the passive sampler by diffusion, and the quantification of the water concentrations relies on empirically
de­termined equilibrium partition coefficients.
The passive sampler strips were made of polyoxymethylene (POM). They
were placed at three coastal and three offshore sites (Figure 25; Table 5) in
the spring- summer of 2007. For the coastal sites, it was assumed that the
water mass was well-mixed and that the contaminants were homogenously
distributed. Therefore, the samplers were placed at one level (a couple of
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meters above the sea bottom). In deeper areas, the water may be less mixed,
or even distinctly stratified, as is the case in the Baltic Proper. The offshore
samplers were therefore placed at two levels: 25 m and 60–120 m below the
surface, where the latter depth corresponds to a couple of meters above sea
bottom. The construction of an offshore rig is shown in Figure 20. A buoy
placed at approximately 25–30 m below the surface was used to keep the rig
in an upright position. Stainless frames (Figure 21) were deployed 3 m below
the buoy and 1 m above the sediment surface. A 150–200 m long line was
attached to the main anchor and a small anchor was deployed at the end of
the line. This line was dragged up with a small anchor from the ship when the
rig was taken in. The samplers were exposed for at least 3 months, which is
the time required for reaching equilibrium between the sampler and the water.
After harvesting, the POM strips were immediately cut into pieces and put in
glass flasks which were stored deep-frozen until extraction and analysis.
The dissolved water concentration of ΣPCB7 (including all stations, both
coastal and offshore) ranged from 3 to 44 ng m–3. The corresponding value
for dioxins ranged from 0.8 to 3.2 pg WHO-TEQ m–3. The concentration of
dioxins may be slightly overestimated due to a possible chromatographic coelution between a non-2,3,7,8-substituted PeCDF-congener and the 2,3,4,7,8PeCDF congener. The overestimation was judged to be maximum 25%.
The average dioxin concentrations at the different sites were:
Coastal: 1.0 pg WHO-TEQ m–3 (n=6; range 0.79-1.5 pg WHO-TEQ m–3)
Offshore: 2.4 pg WHO-TEQ m–3 (n=12; range 1.7–3.2 pg WHO-TEQ m–3).
The average ΣPCB7 concentrations at the different sites were:
Costal: 5.7 ng m–3 (n=6; range 3.0-10 ng m–3)
Offshore: 20 ng m–3 (n=12; range 5.5-44 ng m–3).
The concentrations of HCB could not be determined as a measured ­passive
sampler/water equilibrium partition coefficient was not available.
25-30 m
Stainless frame with POM
Stainless frame with POM
1m
Figure 20. The construction of the POM rig. In deep waters, sampling was conduct­ed at two depths
(as shown) and in coastal waters at one depth.
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Figure 21. A stainless steel frame with POM strip.
As can be seen in Table 5, there were no distinct concentration ­differences
between surface and deep sea water, neither in the Baltic Proper nor in
the Bothnian Sea. An interesting result, however, is that the dioxin levels
are somewhat higher in the Baltic Proper than in the Bothnian Sea, while
the opposite is true for PCBs. The reason for this geographical pattern is
un­known, and more measurements are needed before definite conclusions can
be drawn.
Table 5. Concentration ranges for dissolved PCDD/Fs and ΣPCB7 at differ­ent depths in
the Bothnian Sea and the Baltic Proper.
Sampling
Bothnian Sea
Baltic Proper
Bothnian Sea
Baltic Proper
depth
PCDD/Fs
PCDD/Fs
ΣPCB7
ΣPCB7
(pg WHO-TEQ m-3)
(pg WHO-TEQ m-3)
(ng m-3)
(ng m-3)
25 m
1.8–2.2
2.6–3.2
25–37
5.5–8.1
60–120 m
1.7–2.1
2.5–3.2
20–44
8.2–9.1
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6.6 POPs in sediments
As in soil, hydrophobic pollutants will primarily partition into the ­organic
matter of sediments and suspended material. Particles suspended in the water
body will be deposited when they reach calm water or through aggre­gation.
This formation of sediments will eventually result in permanent burial.
However, sediments deposited in shallow water may be subject to resuspension. Thus, the sediment-associated POPs may be brought back into solution.
Furthermore, the bioturbation of sediments by organisms can bring POPs
back into suspension. The extents of bioturbation, wave- and current-induced
resuspension, mineralisation, deposition of particles, diffusion and degradation of the chemical determine whether the sediments act as a sink or as a
source of the pollutant.
The coast of the Baltic Sea includes several heavily industrialized zones.
Along the Gulf of Bothnia there are a number of pulp and paper mills and
steel mills. Several chemical factories are situated both on the coast of the Gulf
of Finland and the Baltic Proper. These industries have been known to emit
dioxins and other POPs. Sediments sampled near industrialized and urban
areas often show higher concentrations as compared to sediments from background sites. This is shown by the distribution of dioxins in sur­face sediment
samples along the Swedish coast in Figure 22 (Sundqvist et al. 2006). The
Swedish coast includes a number of dioxin hot spots associ­ated with industrial
activity (Sundqvist et al. manuscript).
x4
Bothnian Sea
Figure 22. Sediment sampling locations in the Baltic Sea and Σ tetra through octa-chlorinated
DD/F concentrations (each bar unit equals 5 ng g–1 d.w.). The highest value was decreased 4 times
for clarity (TISS, Thematic Images and Spatial Statistics) (Sundqvist et al. 2006).
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6.6.1 Sediment-water exchange – new measurements
POPs in sediments equilibrate between sediment particles, pore-water and
overlying water. The POPs present in the pore-water constitute a potentially
mobile and bioavailable fraction. The relation between freely dissolved con­
centration in the overlying water and pore-water gives an indication of the net
flow of dissolved POPs between the two compartments. If pore-water concentration > overlying water concentration, one can expect a net diffu­sive transport of dissolved POPs from the sediment to the water column. Note that the
overall mass transfer of POPs between sediment and water is also influenced
by particle deposition and resuspension.
Within the scope of this study, the pore-water concentrations in 14 sedi­
ments were determined. The sediments were sampled during 2007 from the
same sampling sites as the water samples described earlier (Figure 25). The
pore-water concentrations were determined by using passive samplers (POM),
where the POMs were allowed to equilibrate by shaking a sediment-water
slurry for 30 days at room temperature.
As expected, the POP concentrations in the pore-waters generally covaried with sediment concentrations. The average pore-water concentration
was 3.5 pg WHO-TEQ m–3 (n=14; range 1.6–7.4 pg WHO-TEQ m–3). These
values may be slightly overestimated due to a possible chromatographic coelution between a non-2,3,7,8-substituted PeCDF-congener and the 2,3,4,7,8PeCDF congener. The overestimation was judged to be maximum 25%.
For the coastal stations, the average ratio of the pore-water/overlying
water dioxin concentration was 3.6 ± 1.6 (average for all congeners; 3 sites;
tripli­cates). For the PCBs the average ratio was 1.0 ± 0.6. This indicates that
the coastal sediments act as a source for PCDD/Fs to the overlying water,
­whereas for the PCBs there is no concentration gradient and the sediments in
the coastal areas neither constitute strong sinks nor strong sources for PCBs.
For PCDD/Fs in deep water, the ratio was 1.1 ± 0.5, which suggests that
there is no concentration gradients and that the sediments in the offshore
areas constitute neither strong sinks nor strong sources for the diffusive
ex­change of dissolved PCDD/Fs. For PCBs this ratio was 0.7 ± 0.3, suggesting that there is only a slight concentration gradient for PCBs, but that the
di­rection of the gradient indicates that the sediments could be a PCB sink.
The sediment and water measurements allowed calculation of total organic carbon–water partition coefficients (KOC) for these Baltic Sea sediments,
where total organic carbon refers to amorphous organic carbon (AOC) and
soot (black) carbon (BC). Previously, the partition coefficient KOC was used
to describe the partitioning between AOC and water. Here, we use the KOC
to describe the partitioning between BC+AOC and water and KAOC is used
to describe partitioning between AOC and water. In Figure 23, the log KOC
of various dioxin congeners are plotted vs. their log KOW (Sacan et al. 2005)
and in Figure 24, the log KOC of various PCB congeners are plotted vs. their
log KOW (Schenker et al. 2005). In addition, the figures show the equi­lib­rium
partition coefficient between amorphous organic carbon and water (KAOC)
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as predicted by the regression of Seth et al. (1999). It was observed that the
binding to BC+AOC in Baltic Sea sediments is stronger than for AOC alone.
These high KOC values (a factor of 10–30 times higher than KAOC) indicate that
the ecotoxicological risk for PCDD/F and PCBs in the Baltic Sea sediments is
10–30 times lower than would be predicted if the risk assessment would be
based on KAOC.
11
log KOC (L/kg)
10
9
8
7
6
5
6
7
log KOW
LFER-KAOC
8
9
OC Baltic sediments, PCDD/Fs
Figure 23. Log KOC vs. log KOW for various PCDD/F congeners (average for all sediments; n=14). The
line shows a regression for predicting KAOC, i.e. the parti­tioning between amorphous organic carbon
(without BC) and water according to the regression suggested by Seth et al. (1999). Log KOW values
are from Sacan et al. (2005).
log KOC (L/kg)
9
8
7
6
5
5
6
log KOW
LFER-KAOC
7
8
OC Baltic sediments, PCBs
Figure 24. Log KOC vs. log KOW for various PCB congeners (average for all sedi­ments; n=14). The
line shows a regression for predicting KAOC, i.e. the partition­ing between amorphous organic carbon
(without BC) and water according to the re­gression suggested by Seth et al. (1999). Log KOW values
are from Schenker et al. (2005).
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6.6.2 Levels of POPs in Baltic sediments – new measure­ments
Within this study, offshore and coastal sediments were sampled and ana­
lysed for PCDD/Fs, PCBs and HCB. The offshore sampling was performed
at seven accumulation bottom stations in the Bothnian Sea and at five sta­
tions in the Baltic Proper in June–July 2007 (Figure 25). Two of the stations
in the Bothnian Sea were later classified as transport bottoms due to low
carbon content and were therefore rejected in the evaluation. In the Baltic
Proper, coastal sediments were sampled from transport bottoms in three areas
(Figure 25). Differential GPS (DGPS) was used for the positioning, with an
accuracy of ±10 m or better.
Figure 25. Sediment and water sampling locations used in this study. POM (polyoxymethylene) was
used as a passive water sampler.
Before sampling, a measuring grid of approximately 500×500 m was run by
means of echosounding at each sampling site to describe the topographical
conditions in the area before the exact position for sediment sampling was
chosen. Surface sediment samples (0–2 cm) were taken with a modified Ponar
sampler (Håkanson and Jansson 1983; Figure 26), which allows free water
passage through the sampler during descent and sediment penetration. Great
care was taken to ensure that the sediment surface was intact, e.g. that a bacterial film of Beggiatoa and clear supernatant water were present.
At each offshore station sediment cores were taken with a Gemini double
corer (Figure 27). The core was only accepted if the sediment surface was
intact. These cores were used for description of the sediment type, down-core
stratification, lamination, bioturbation structures etc. The samples and intact
cores were stored cold until analysis. The results from this study are presented
in the next chapter (6.6.3).
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Figure 26. Sediment sampling by the Ponar sampler.
Figure 27. The Gemini corer ready for operation.
6.6.3 Levels and trends of POPs in Baltic sediments
The levels of POPs in Baltic sediments including their spatial distribution
and time trends were investigated. To obtain an extensive data set, data from
one offshore station in the Bothnian Sea and five stations in the Baltic Proper
were included from Sundqvist et al. (manuscript and unpublished data).
Furthermore, for PCBs, eight offshore stations in the Baltic Proper and two in
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the Bothnian Sea from the national Swedish sediment monitoring programme
(Cato and Kjellin 2005) were included in the evaluation of the large-scale distribution patterns and time trends.
PCDD/Fs
Spatial distribution
In Table 6 and Table 7, average concentrations and ranges of selected
PCDD/ Fs in surface sediments obtained in this study and by Sundqvist et al.
(manuscript) are compiled together with previous measurement data for offshore sediments from the Bothnian Sea (Verta et al. 2007, Rappe et al. 1989)
and the Baltic Proper (Koistinen et al. 1997, Rappe et al. 1989, Kjeller and
Rappe 1995). The concentrations of HpCDF and OCDF from Rappe et al.
(1989) were left out of the compilation due to uncertain data quality (no
internal standard in combination with unstable GC-column).
Different analytical methods were used to determine the PCDD/Fs. In
some of the studies, a co-elution occurred between a 2,3,7,8-substituted congener and a non-2,3,7,8-substituted congener. These data were not included
in the calculation of mean concentrations. As seen in Table 6 and Table 7, the
con­centrations found in this study and by Sundqvist et al. agree well with data
from other studies of recent samples (from the 2000s).
Table 6. Concentrations (pg g–1 d.w.; average and range) of selected PCDD/Fs in surface sediments
sampled at offshore sites in the Bothnian Sea. The data are from this study and Sundqvist et al.
(manuscript) together with data from Verta et al. (2007) and Rappe et al. (1989).
Bothnian Sea (offshore)
Reference
and site
Sampling period
2378-TCDD
12378-PeCDD
OCDD
2378-TCDF
23478-PeCDF
This study and
Sundqvist et al.
(manuscript)
Verta
et al.
Verta
et al.
(2007)
(2007)
Rappe
et al.
(1989)
US5B
SR5
SR5
Rappe
et al. (1989)
Iggesund
30 km
n=10
n=1
n=1
n=1
n=1
2005–2007
2000s
2000s
1986
1986
0.55 (0.24–0.68)a
0.40
0.47
1.0
1.9
1.3 (0.6–1.9)
1.5
1.8
3.5
3.6
53 (24–76)
63
73
89
96
8.4 (3.0–12)
4.7
6.0
8.3
11
6.2 (4.8–7.0)b
5.5
6.6
7.7
5.7
1234678-HpCDF
33 (15–54)
80
38
-
-
OCDF
44 (17–74)
115
59
-
-
a Data from this study only, n=5
b Data from Sundqvist et al. (manuscript) only, n=5
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Table 7. Concentrations (pg g–1 d.w.; average and range) of selected PCDD/Fs in surface and subsurface (2–4 cm) sediments sampled at off­shore sites in the Baltic Proper. The data are from this
study and Sundqvist et al. (manuscript) together with data from Koistinen et al. (1997), Rappe et
al. (1989), Kjeller and Rappe (1995).
Baltic Proper (offshore)
Rappe
et al. (1989)
Kjeller and
Rappe (1995)
Kjeller and
Rappe (1995)
BY15
40
P18
P18
n=1
n=1
n=1
n=1
1993
1986
1988 (core)
0–2 cm
(corresponds
to an average
sampling year
of 1985)
1988 (core)
2–4 cm
(corresponds
to an average
sampling year
of 1978)
0.93 (0.37–1.6)a
<2
1.4
1.0
0.55
12378-PeCDD
3.4 (1.3–7.3)
5.0
6.5
3.5
5.2
OCDD
273
Reference
and site
Sampling period
2378-TCDD
This study
and Sundqvist
et al.
(manuscript)
Koistinen
et al. (1997)
n=10
2005–2007
204 (74–355)
265
250
273
2378-TCDF
18 (5.8–44)
42
14
13
16
23478-PeCDF
15 (7.6–28)b
19
15
16
20
1234678HpCDF
83 (32–154)
118
-
87
141
OCDF
95 (37–167)
58
-
73
190
a Data from this study only, n=5
b Data from Sundqvist et al. (manuscript) only, n=5
In general, PCDD/F sediment concentrations normalised to dry weight are
approximately a factor 2–3 times higher in the Baltic Proper as compared to
the Bothnian Sea (Table 6 and Table 7). If normalised to carbon, however,
taking into account the substantially higher TOC content in the Baltic Proper
(Table 8), there are no differences between the two basins.
Table 8. Average TOC content (% d.w.) of Baltic Sea sediments
sampled during 1989–1993 and 2003–2007.
Sampling period
n
Average TOC content (% d.w.)
Bothnian Sea
1989–1993
5
3.1
2003–2007
8
2.9
Baltic Proper
1989–1993
13
6.1
2003–2007
19
7.8
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Time trends
Decreasing trends of PCDD/F concentrations have been registered towards the
sediment surface in cores from Gulf of Finland (sites K15, LL3a and JML1b:
Isosaari et al. 2002; site AKL: Verta et al. 2007) and in offshore cores from
the Bothnian Sea and the Baltic Proper (site SR5: Verta et al. 2007; site P18:
Kjeller and Rappe 1995). Verta et al. (2007) concluded that this indicates a
general and clear decrease in input of dioxins to the Baltic Sea. The data from
this study and Sundqvist et al. (manuscript) confirm the decreasing trend in
the Bothnian Sea (Table 6) for the PCDDs, but suggest that the PCDF levels
have been relatively stable. The data from the Baltic Proper, however, do not
indicate any substantial decrease when the few available historical data (n=3)
are compared to the recent data (Table 7). Considering the few measurement
data available and considering also that the core from the Baltic Proper was
sampled in the 1980s (Kjeller and Rappe 1995), it is difficult to draw any
conclusions about the recent time trend for PCDD/Fs in Baltic Proper surface
sediments.
PCBs
Spatial distribution
Since the sum of PCBs is often based on different congeners and different
numbers of congeners, comparisons between data sets are difficult. How­ever,
for some studies the large-scale spatial distribution of PCB concentra­tions
in Baltic Sea could be assessed. Based on a limited number of surface sediment samples (n=11), Gustavson and Jonsson (1999) showed slightly increasing concentrations of PCBs from north to south in a data set from 1989.
However, Axelman et al. (2001) sampled a larger number of surface sediments
(n=44) and suggested a uniform distribution of PCBs in the Baltic Sea when
the concentrations were normalised to organic carbon. Also, the atmospheric
input of total PCB indicated a uniform deposition of PCBs to the Baltic Sea
(Agrell 1999). On the other hand, Jonsson (2000) found a small but relatively clear gradient with almost two times higher sPCB concentrations (sum
of congeners 52, 101, 105, 118, 138, 153 and 180) in the S Baltic Proper
(lat 540000–560000; mean 382 ng g–1 OC) compared to the Gulf of Bothnia
(lat 602000–650000; mean 213 ng g–1 OC).
Time trends
In contrast to the decreasing trends of PCBs in Baltic biota, increasing sediment concentrations of PCBs were registered in the 1970–80s (Niemistö and
Voipio 1981, Perttilä and Haahti 1986, Nylund et al. 1992, Blanz et al. 1999),
coinciding in time with a large-scale expansion of laminated sedi­ments in the
Baltic Proper (Jonsson 1992). In the 1980s, decreasing concen­trations were
registered as shown by several studies of sediments from the NW Baltic Proper
(Kjeller and Rappe 1995, Axelman et al. 1995, Broman et al. 1994; also displayed in Figure 28, from Jonsson et al. 2000).
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Figure 28. Concentration plots of sPCBs obtained from former investigations of dated sediment
cores in different parts of the Baltic Proper and the Gulf of Finland (from Jonsson et al. 2000).
Figures refer to the following cores and papers: 1 = P18 in Kjeller and Rappe (1995), 2 = Axelman
et al. (1995), 3 = TEILI in Perttilä and Haahti (1986), 4 = XV-1 in Perttilä and Haahti (1986),
5 = Nylund et al. (1992), 6 = 18021 in Blanz et al. (1999).
Jonsson (2000) demonstrated that the general down-core concentration trend
on dry weight basis for sPCBs in the Baltic Proper was an increase from the
early 1970s and up to around 1990 (Figure 29), which is in contrast to the
decreasing concentrations trends for PCBs in pelagic biota from the Baltic
Proper (Chapter 5). There was no trend between 1970 and 1990 if PCB data
were normalised to organic carbon (Figure 29).
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400
sPCB (ng g-1 OC)
sPCB*10 (ng g-1 dw)
sPCB
300
200
1990
1985
1980
1975
1970
1965
1960
1955
1950
1945
1940
1935
0
1930
100
Figure 29. Mean sPCB concentrations (ng g–1) in time intervals in eight cores from the Baltic
Proper and Gulf of Finland normalised to dry weight (d.w.) and organic carbon (OC). (From Jonsson
2000).
If bioturbated and laminated cores were treated separately, slight increases
were found in bioturbated cores, whereas laminated cores showed decreases
of 20–50% from 1979-1981 to the early 1990s (Figure 30).
Jonsson (2000) argued that the degradation of PCBs is probably insignifi­
cant in the laminated sediments. This was demonstrated by the absence of
major changes in the congener composition with increasing sediment depth in
the cores (Figure 31).
In chapter 4.2, the importance of considering the sediment dynamics was
emphasised when down-core trends are interpreted. Changes of the overall
sediment accumula­tion rate in the depositional areas most likely affect the
carbon content, which sub­sequently affects the burial of hydrophobic con­
taminants. By assuming a constant sediment accumulation rate during the
last decades, which has been the common way of presenting deposition data
by several authors, Jonsson (2000) found that the sPCB deposition increased
gradually in the 1940–60s, thereafter levelling out at 15–20 g sPCB (km)–2 yr–1
(Figure 32). These deposition trends were re-evaluated after publication of
the results of Eckhéll et al. (2000). They demonstrated a significant varia­tion
in the bulk sedimentation rate from the 1960s and onwards that was highly
correlated with the annual frequency of wind speeds ≥ 14 m s–1. Following
this re-evaluation, the PCB deposition gradually increased in the 1940–1960s,
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reaching peak values in the 1970s, and thereafter substantially decreasing
during the late 1970s and 1980s (Figure 32). Around 1990, the PCB deposition increased again, coinciding in time with the increasingly windy conditions and increased dry matter deposition in the early 1990s. The trend in
PCB deposition, assuming inter-annually variable deposition rates, clearly
­resembles PCB concentration trends in Baltic biota (Bignert et al. 1998).
600
sPCB (ng g-1 OC)
500
400
Laminated cores
171, E. Gotland Deep
178, W. Gotland Deep
180, N. Baltic proper
182, C. Gulf of Finland
187, NE Gulf of Finland
300
200
100
0
1965
600
sPCB (ng g-1 OC)
500
1970
1975
1980
1985
1990
1995
Bioturbated cores
169, Gdansk Bay
170, Off Lithuania
167, Bornholm
400
300
200
100
0
1965
1970
1975
1980
1985
1990
1995
Figure 30. Concentration of sPCB (ng g–1 OC) in dated laminated and bioturb­ated sediment cores
from the Baltic Sea. (From Jonsson 2000).
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1990-1993
(%)
100
80
60
40
20
0
PCB#101
PCB#118
PCB#105
PCB#138
PCB#153
PCB#180
PCB#118
PCB#105
PCB#138
PCB#153
PCB#180
PCB#118
PCB#105
PCB#138
PCB#153
PCB#180
PCB#118
PCB#105
PCB#138
PCB#153
PCB#180
PCB#118
PCB#105
PCB#138
PCB#153
PCB#180
1980-1989
(%)
100
80
60
40
20
0
PCB#52
PCB#101
1970-1979
(%)
100
80
60
40
20
0
PCB#52
PCB#101
1940-1969
(%)
100
80
60
40
20
0
PCB#52
PCB#52
PCB#101
1900-1939
100
(%)
50
0
PCB#52
PCB#101
Figure 31. Mean PCB congener composition in time intervals from eight dated sediment cores from
the Baltic Proper and the Gulf of Finland (From Jonsson 2000). The data are presented as the
fraction (%) in relation to PCB 153.
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sPCB - Constant sed. rate
sPCB - Variable sed. rate
sPCB deposition ng km yr
ΣPCB7 deposition
(g km-2 yr-1)-2 -1
25
20
15
10
5
2000
1995
1990
1985
1980
1975
1970
1965
1960
1955
1950
1945
1940
0
Figure 32. Deposition rates of sPCB in sediment cores. Mean values from the Baltic Proper and the
Gulf of Finland assuming a constant sedimentation rate (yellow bars) and a variable sedimentation
rate accounting for the inter-annual variability reported by Eckhéll et al. 2000 (blue bars) (from
Jonsson 2000).
In Table 9, PCB concentration data for surface sediments from 1989-1993
(Gustavson and Jonsson 1999, Jonsson 2000) and 2003-2007 (this study,
Sundqvist unpublished, Cato and Kjellin 2005) are compiled. The dry weight
normalised ΣPCB7 concentrations are on average 4–5 times lower in the
Bothnian Sea as compared to the Baltic Proper, and this was also the case
some decades ago.
Table 9. Mean concentrations (ng g–1 d.w.) of PCBs in Baltic Sea surface sedi­ments sampled in 1989–1993
(Gustavson and Jonsson 1999, Jonsson 2000) and 2003–2007 (this study, Sundqvist unpublished, Cato and
Kjellin 2005).
(ng g-1 d.w.)
PCB 28
PCB 52
PCB 101
PCB 118
PCB 138
PCB 153
PCB 180
ΣPCB7
2.1
91
31
1.4
55
21
6.7
86
100
Mean
SD %
% ΣPCB7
0.32
50
4.8
0.78
117
11.6
Bothnian Sea 1989–1993 (n=5)
0.61
0.39
1.7
59
92
104
9.1
5.8
25
Mean
SD %
% ΣPCB7
0.09
66
7.6
0.08
64
6.7
Bothnian Sea 2003–2007 (n=7)
0.16
0.19
0.29
45
37
41
13
16
24
0.29
41
24
0.17
48
14
1.2
47
100
Mean
SD %
% ΣPCB7
1.1
79
4.6
3.4
89
14
Baltic Proper 1989–1993 (n=9)
3.2
1.9
5.6
70
98
50
13
8.1
24
6.4
62
27
3.4
37
15
24
47
100
Mean
SD %
% ΣPCB7
0.35
109
6.6
0.47
104
8.9
Baltic Proper 2003–2007 (n=13)
0.91
0.74
1.3
96
64
74
17
14
24
1.1
81
21
0.59
80
11
5.3
81
100
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A distinct decrease in sediment concentrations has occurred in both basins
during the last 10-20 years. In the Bothnian Sea, the decrease was on aver­age
a factor of 5.6 while in the Baltic Proper it was a factor of 4.5. These decreasing PCB concentra­tions in offshore sediments are in line with the decreases
in herring from the Bothnian Sea (3.5 times) and the Baltic Proper (2-4 times).
Also the PCB concentra­tions in guillemot eggs from the Baltic Proper (Stora
Karlsö) have decreased by a factor 3 during the same time period.
As was discussed earlier (Chapter 4.2), a change in the bulk sedimentation
rate might affect the sediment concentrations of hydrophobic substances, and
furthermore, there is a highly linear relationship between annual bulk accumulation rate and annual frequency of wind speeds ≥ 14 m s-1. In Figure 33,
the gale (≥14 m s–1) frequency at Gotska Sandön in the North Baltic Proper
is plotted vs. time. The 1950–70s were characterised by a high fre­quency of
gales. These windy decades were followed by a very calm decade (the 1980s).
In the early 1990s, the frequency of gale force winds increased substantially
with a peak value in 1993. The decade from the mid 1990s until the present
has been the calmest period recorded since 1950.
Figure 33. Gale frequency (≥14 m s–1) at Gotska Sandön (N Baltic Proper). Red line = 3-year
­average. (Data from SMHI 2007).
The two data sets compared in Table 5 are 1989–1993 and 2003–2007, i.e.
one data set that can be considered to represent a windy period and one that
repre­sents a much less windy period. Theoretically, the carbon content in the
sediments would be higher in the 2000s due to a smaller portion of eroded
minerogenic matter in the sediments. Taking into account that POPs show an
affinity for organic matter, a higher carbon content would lead one to expect
higher POP concentrations in the early 2000s. However, the opposite was
observed for PCBs in both the Bothnian Sea and the Baltic Proper. A compari-
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son between the average TOC contents during the two periods showed no difference in the Bothnian Sea. In the Baltic Proper, on the other hand, the TOC
content increased by 28 % from 1989–1993 to 2003–2007. This increase has
to be considered with due reservation because of the pos­sible problems with
the TOC analyses in the 2003–2007 data (Cato and Kjellin 2005). In any
case, the calm conditions during the 2000s refutes the hypothesis that the distinctively lower PCB concentrations found in recent surface sediments could
be caused by an increased bulk sediment accumu­lation rate . Thus, the registered decrease in ΣPCB7 concentration is con­firmed and most likely depends on
a decreased input to the Baltic Sea.
HCB
The HCB concentrations found in this study were quite similar in Bothnian
Sea and the Baltic Proper with mean values of 356 and 404 pg g–1 d.w.,
re­spectively. Former investigations of HCB in sediments sampled between the
1990s and early 2000s indicate quite variable sediment concentrations. These
data were compiled together with the data from this study and are presented
in Table 10.
Table 10. HCB concentrations (pg g–1 d.w.; range) in surface sediments from different areas of
the Baltic Sea.
Area
Sampling
n
HCB
Reference
year
(pg g–1 d.w.)
Baltic Proper and
Gulf of Finland
2001–2002
7
2–360
Pikkarainen 2007
SE Baltic Proper
1996–2005
3
670–1330
SW Baltic Proper
1993
19
10–750*
Dannenberger 1996
Gulf of Bothnia
1990s
2
790/840
Strandberg et al. 1998
Sapota 2006
Bothnian Sea
2007
5
169–514
This work
Baltic Proper
2007
5
264–790
This work
* Mainly sandy sediment
Due to the scatter of the data in space and time, limited information on spa­tial
and temporal trends could be obtained. However, most of the data indi­cate
a general level of a few hundred pg HCB g–1 d.w. From the results in the SE
Baltic Proper, there are indications of decreasing concentrations in recent years
(Sapota 2006). Similarly, de­creasing trends are indicated if data from the Gulf
of Bothnia collected in the 1990s (Strandberg et al. 1998) are compared with
the Bothnian Sea data from this study.
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6.6.4 Relation between total organic carbon, black carbon and POP levels
Relation between PCBs and OC
In several local/regional investigations of Baltic Sea surface sediments, the
concentrations of organic contaminants normalised to dry weight were highly
correlated with the organic carbon content. However, in the Baltic Sea sediment baseline study (Jonsson 2000), which covered the entire Baltic Sea, the
concentrations of ΣPCB7 and individual PCB congeners showed rather poor
relationships with TOC in surface sediments (r2=0.41–0.59) and sediment
cores (r2=0.25–0.33). The regression for surface sediments did not explain
more than approximately half of the variation, which suggests that other factors are of importance for the burial of PCBs in the sediments.
The data from this study (n=25) including data from Sundqvist (unpub­
lished data) (n=6) and data from the national Swedish sediment monitoring (Cato and Kjellin 2005) (n=10) showed no relationship between TOC
(% d.w.) and ΣPCB7 (ng g–1 d.w.) at all (r2=0.05; Figure 34). A thorough data
check showed that the poor correlation was caused by the data set from Cato
and Kjellin (2005), belonging to the Baltic Proper. The mean ΣPCB7 con­
centration in these data was approximately a factor 2 lower than the mean of
the rest of the data set. If these data were excluded, the relationship im­proved
substantially (r2=0.49, Figure 35). The PCB concentrations reported in the
study by Cato and Kjellin (2005) agree with the other data if normal­ised on a
dry weight basis. Due to the possible problems with the TOC de­terminations
we have chosen to present the PCB data on a dry weight basis when describing the distribution in space and time.
20
18
r2=0.05
16
(n=25)
ΣPCB7 (ng g-1 d.w.)
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
18
OC (% d.w.)
Figure 34. Relationship between OC (% d.w.) and ΣPCB7 (ng g–1 d.w.) in surface sediments from
the Bothnian Sea and the Baltic Proper. The data included are from this study, Sundqvist (unpublished), and Cato and Kjellin (2005).
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20
18
16
r2 =0.49
(n=15)
ΣPCB7 (ng g-1 d.w.)
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
OC (% d.w.)
Figure 35. Relationship between OC (% d.w.) and ΣPCB7 (ng g–1 d.w.) in surface sediments from
the Bothnian Sea and the Baltic Proper. The data included are from this study and Sundqvist (unpublished). Data from Cato and Kjellin (2005) are excluded.
Correlations between PCDD/Fs, PCBs, HCB, OC and BC
In many contexts, it has been argued that the content of black carbon (BC)
can better explain the variation of organic pollutant concentrations in sedi­
ments than total organic carbon (OC), which is the sum of amorphous OC
and BC. In this investigation, both OC and BC were analysed in the surface
sediment samples from the Baltic Proper (n=7) and the Bothnian Sea (n=5). In
Table 11, data for six 2,3,7,8-substituted PCDD/F congeners, ΣPCB7, HCB,
TOC and BC are compiled. It should be noted that this correlation study is
based on data from this study only (n=12), and correlation values therefore
differ from the statistical analyses discussed above. High correla­tion values
(r2) were obtained between OC and the PCDD/F congeners (r2=0.81–0.94) as
well as between OC and ΣPCB7 (r2=0.92). Low correlation was shown between OC and HCB (r2=0.28). In general, substantially lower r2 values were
obtained between the different compounds and BC. However, this lower correlation was primarily attributed to one sample. By excluding this outlier, the
correlation values increased to similar values as for OC.
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Table 11. Correlation matrix (r2) for selected PCDD/Fs, ΣPCB7, HCB, TOC and BC from 12 stations in the Baltic
Proper (n=7) and the Bothnian Sea (n=5) (data from this study only).
2378- 123782378- 23478TCDD
PeCDD
OCDD
TCDF
PeCDF
OCDF
∑PCB7 HCB
OC
BC
2378-TCDD
12378-PeCDD
OCDD
2378-TCDF
23478-PeCDF
OCDF
PCB7
HCB
OC
BC
BC excl. outlier
1
0.93
0.86
0.98
0.93
0.86
1
0.97
0.96
0.99
0.94
1
0.91
0.98
0.94
1
0.96
0.88
1
0.94
1
0.87
0.58
0.81
0.51
0.68
0.96
0.43
0.93
0.65
0.93
0.97
0.32
0.94
0.68
0.93
0.93
0.57
0.88
0.53
0.78
0.98
0.43
0.94
0.63
0.92
0.88
0.26
0.92
0.56
0.95
1
0.41
0.92
0.56
0.94
1
0.28
0.02
0.01
1
0.73
1
1
6.6.5 Sediment burial of POPs in the Baltic Sea
Based on bulk sediment accumulation data from Jonsson et al. (1990), Borg
and Jonsson (1996), Perttilä et al. (2003), Jonsson (Ed. 2003) and Algesten
et al. (2005), the sediment accumulation rates in the different basins of the
Baltic Sea were calculated and compiled (Table 12). These basin-related accumulation rates were used to calculate the annual sediment burial of ΣPCB7
and sum of the 2,3,7,8-substituted PCDD/Fs (Table 13).
Table 12. Estimated average TOC content (% d.w.) and dry matter and carbon deposition
(ton yr-1) in the basins of the Baltic Sea.
Dry matter deposition
n
(ton yr-1)
Bay of Bothnia
16
6,720,0001
Bothnian Sea
68
Baltic Proper
Organic carbon
deposition (ton yr-1)
Average TOC
content (% d.w.)
252,0001
3.81
37,900,000
1
1,430,000
3.81
17
37,200,0002
2,830,0002
7.62
Gulf of Finland
6
10,500,000
3
618,000
5.93
Gulf of Riga
4
3,200,0004
189,0004
5.94
95,520,000
5,319,000
Total Baltic Sea
1
3
1 Compiled from analyses in Jonsson et al. 1990, Borg and Jonsson 1996, Algesten et al. 2005, Jonsson
unpublished material; and assuming the same deposition rate and TOC content in the Archipelago Sea as
in 17 bays from Stockholm archipelago (Jonsson, Ed., 2003).
2 Compiled from analyses of dated cores in Jonsson et al. 1990 and Perttilä et al. 2003.
3 Data from Perttilä et al. 2003.
4 From Borg and Jonsson 1996 assuming the same TOC content as in the Gulf of Finland.
PCDD/Fs
So far, to our knowledge, no reliable calculation of the total sediment burial of
PCDD/Fs in the Baltic Sea has been presented. The number of data has been
too small to allow such a calculation. Although our set of data on PCDD/Fs
still is limited, the number of data points was considered to be sufficient to
roughly estimate the total PCDD/F burial. Considering the rea­sonably small
variation in PCDD/F concentrations in the Bothnian Sea and the Baltic Proper,
2 and 4 times respectively, and the good correlation with OC (Table 11), the
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estimate is probably fairly good. Offshore data from the Gulf of Finland were
also included (Verta et al. 2007). The PCDD/F burial in the Gulf of Finland
(Table 13) constitutes 33% of the total burial in the Baltic Sea. In contrast
to the ΣPCB7 concentrations of Gulf of Finland, the PCDD/F concentrations
are new data from around 2000. The calculation implies that the relative
importance of the Gulf of Finland as a sink for PCDD/Fs is significant. The
down-core trends, however, indicates a more rapid decrease in this area compared to e.g. the Bothnian Sea.
Table 13. Estimated annual sediment burial of ΣPCB7 (kg yr–1) and sum of the 2,3,7,8-substituted
PCDD/Fs (kg yr–1) in the basins of the Baltic Sea.
Annual
No. of
Annual
No. of
Area
Dry matter
Mean
Mean
sediment
samples
sediment
sampdeposition
conc.
conc.
burial of
for
burial of
les for
(ton yr-1)
ΣPCB7
ΣPCDD/Fs
ΣPCB7
ΣPCDD/Fs
ΣPCDD/Fs
ΣPCB
(pg g–1
(ng g–1
(kg yr–1)
d.w.)
n
d.w.)
n
(kg yr–1)
Bay of Bothnia
6720000
Bothnian Sea
37900000
7
1.2
10
195
45
7
Baltic Proper
37200000
13
5.3
10
574
197
21
Gulf of Finland
10500000
6
102
2
17533
105
18
3200000
3
1.8
17534
6
6
361
54
Gulf of Riga
Total Baltic Sea
1
2
3
4
1.21
1951
2
95520000
8
1
Assuming the same concentration as in the Bothnian Sea
Assuming the same concentration as in 1993. From Perttilä et al. 2003.
LL3a and JML1b. From Verta et al. 2007.
Assuming the same concentration as in the Gulf of Finland
PCBs
Based on analyses of PCBs in surface (0–2 cm) sediments and estimates of dry
matter accumulation rates in different parts of the Baltic Sea, Jonsson (2000)
estimated the annual sediment burial of ΣPCB7 for the period 1990-1993 to
923 kg yr-1, and the total sediment inventory of ΣPCB7 in Baltic Sea sediments
was calculated to be 75 tons. Axelman et al. (1997) calcula­ted the inventory
of ΣPCB7 in the water mass to 570 kg. Based on these calcu­lations, Jonsson
(2000) estimated the average retention time for ΣPCB7 in the water mass to be
<1 year, and suggested that this indicates that the Baltic Sea is an efficient trap
of PCBs, and that the Baltic Proper laminated sediments more efficiently trap
PCBs than bioturbated sediments.
The sediment burial calculated from recent data (Table 13) is approximately 2.5 times lower than the rate calculated by Jonsson (2000), which is in
rea­sonable agreement with the general decreasing concentration trend from
around 1990 to the early 2000s. According to the calculations, the Baltic
Proper constitutes the main sink, accounting for 55% of the total burial. The
other basins contribute less, except the Gulf of Finland, where the sediment
burial was calculated to be 29% of the total burial in the Baltic Sea although
it constitutes only 8% of the total area. The data from the Gulf of Finland and
Gulf of Riga were derived from the Baltic Sea sediment baseline study in 1993
and probably overestimate the situation in the 2000s. If we assume a decrease
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similar to that observed in the Bothnian Sea and the Baltic Proper between
1990 and the early 2000s, the burial in the Gulf of Finland and the Gulf of
Riga concerning the early 2000s may be recalculated to 21 and 1.2 kg yr-1
respectively. Subsequently, the total sediment burial of ΣPCB7 in the Baltic Sea
is then reduced to 272 kg yr-1.
6.6.6 The impact of bioturbation on POP fluxes in the sedi­ment
The movement of POPs across the sediment-water interface is of great
im­portance for their fate. By permanent burial in the sediments the pollutants
are removed from the aquatic ecosystems, while mechanisms which facili­tate
the transport of pollutant from the sediment into the water will increase the
load in the water.
One activity influencing the transport across the sediment-water interface
is bioturb­ation. Bioturbation can be defined as the mixing of particles and
pore-water in sedi­ment by macrofauna (Thibodeaux 2005). It is more in­tense
in the surface layers of the sediment, but the depth to which the bio­turbated
layer extends is highly species-specific. The Baltic Sea has rela­tively low species diversity, with a few species dominating the benthic community. During
the last twenty years the invading poly­chaete Maren­zelleria spp. has spread in
the entire Baltic Sea and become a domi­nant species in many areas. It can dig
deeper in the sediment than previously present species, down to around 35 cm
(Zettler et al. 1995). It thus has the potential to affect deeper layers of contaminated sediment.
Research on bioturbation and its effect on contaminant fate point at an
in­creased outflow of contaminants from sediment as a result of bioturbation. In a study by Gunnarsson et al. (1999), the release rate of a tetrachloro­
biphenyl added to the sediment surface was 220% higher in bioturbated
systems compared to non-bioturbated. Karickhoff and Morris (1985) noticed
an increased flux of chlorinated hydrocarbons, including HCB, from the sediment to the surface in the presence of bioturbating tubificid worms. In systems
without worms the flux out of the sediments was controlled by diffusion, and
subsequently very low.
There are different types of bioturbation. Some species rework particles,
while others bioirrigate, i.e. pump water, for instance to oxygenate their burrows. Generally, it can be assumed that POPs which partition strongly to
particles will be more affected by particle reworking than by bioirrigation.
Ciarelli et al. (1999) found that the increased release of PAH was mostly due
to an increase of the suspended particles and the particle-bound con­taminant
in the aqueous phase, not an increase of the freely dissolved con­centration of
the contaminants.
In addition to a direct influence on POP movement, bioturbation can also
affect the fate of POPs by its influence on microfauna and nutrient cycling
in the sediment. The importance of bioturbation on the transformation of
organic matter can be a result of increased oxygenation of the sediment (e.g.
Kristensen 2000). Since POPs preferentially sorb to organic matter, a change
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in the organic matter quality will also affect the sorption of POPs. The quantitative effects of bioturbation on the fate of POPs in the Baltic Sea, either as
a result of direct resuspension/solubilisation or as a result of a change in the
organic matter quality, remain to be investigated.
Another activity that has the potential to affect the sediment-water interface is trawling. It stirs up the top centimetres of sediment and disturbs the
benthic macrofaunal community. Investigations in the Gulf of Maine, USA,
showed that during periods of intense trawling the amounts of ­resuspended
sediment and benthic worms collected in sediment traps 25 m above the
bottom increased greatly (Pilskaln et al. 1998). How large impact trawling has
on the fate of POPs in the Baltic Sea has not been determined.
6.7 Influence of temperature
Temperature is an important environmental factor affecting the distribution
and fate of POPs. The ambient temperature affects several important prop­
erties such as vapour pressure, water solubility, degradation processes and the
Henry’s law constant. The average air temperature above the Baltic Sea ranges
from 0.3°C in the Bothnian Bay to 7.2°C in the Baltic Proper (HELCOM
2002). The determination of physico-chemical properties is normally carried
out at +20–25°C, and they must be corrected to the ambient temperatures
(Beyer et al. 2002). Temperature also affects environmental processes, e.g. rate
of evaporation, production of biomass, vertical water movements, ice cover
and currents.
6.8 Degradation
POPs are persistent and will thus be present in the environment for a long
time. Persistence is evaluated using half-lives (h), defined as the time it takes
to reduce a concentration to half of the initial concentration. In model­ling, the
degradation rate constant (h–1) is used, which is calculated from the half-life
assuming first order degradation kinetics. Degradation will be sub­stantial if
the half-life of the substance in the compartment is short and that compartment has high capacity to store the substance.
The overall degradation rate constants in a certain media include all
impor­tant degradation processes. They are compartment- and temperaturespecific, and often also site-specific (Mackay 2001, Sinkkonen and Paasi­virta
2000). Therefore, degradation rates measured at one location are not always
applicable at other locations. Furthermore, degradation rates de­termined
in the laboratory are not easily extrapolated to environmental con­ditions
(Sinkkonen and Paasivirta 2000, Wania et al. 2001). Low tempera­tures,
lower OH radical concentrations and partitioning to particles generally cause
longer atmospheric lifetimes of POPs compared to lifetimes calcu­lated from
laboratory-derived reaction rate constants. Thus, degradation rates are not
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only an essential property but difficult to determine accurately. Sinkkonen and
Paasivirta (2000) showed that data on degradation rates for PCBs and dioxins
are generally very scarce, especially for biodegradation at low temperatures.
Aronson et al. (2006) also stressed the lack of biodegra­dation data for organic
chemicals.
Photodegradation includes direct photolysis and reactions with OH radicals, ozone, nitrogen oxides and other radicals and can occur in air, water
and soils. Since photodegradation in soils solely occurs close to the surface
and the photodegradation rate in natural water is low (due to low OH radical concentration), the atmosphere is the most important compartment for
photo­degradation of POPs (Sinkkonen and Paasivirta 2000). The degrada­tion
in the atmosphere is faster for POPs in the gas phase than for POPs ad­sorbed
to particles. Atmospheric degradation half-lives for various PCBs in the Baltic
Proper environ­ment have been estimated to be 3 days–1.4 years and for dioxins 1 week–1 year.
Biodegradation can occur in water, soil and sediments. The rate of bio­
degradation depends on several characteristics of the surrounding environ­
ment such as tempera­ture, moisture content, diversity and activity of the
microorganism community, and concentration of oxygen. Biodegradation of
PCBs and PCDD/Fs in soils and sedi­ments in the Baltic Sea environment is
very slow (Sinkkonen and Paasivirta 2000, Kjeller and Rappe 1995). Sink­
ko­nen and Paasivirta (2000) estimated the degradation half-lives in soil and
sediments to be 3–38 years for PCBs and 17–274 years for dioxins. They also
suggested degradation half-lives for PCBs and PCDD/Fs in water to be ten
times longer than in air. Table 14 summarises half-lives for PCBs, diox­in and
HCB in air, water, soil and sediment.
Table 14. Range of suggested degradation half-lives (h) for PCBs, HCB and PCDD/Fs in air,
­ ater, soil and sediment for Baltic Proper environment (Sinkkonen and Paasivirta 2000,
w
Mackay et al. 2006).
PCBs
HCB
PCDD/Fs
Air (h)
72 – 12 000
3 753 – 37 530
200 – 9600
Water (h)
1 450 – 240 000
23 256 – 50 136
4000 – 192 000
Soil (h)
26 000 – 330 000
23 256 – 50 136
150 000 – 2 400 000
Sediment (h)
26 000 – 330 000
150 000 – 2 400 000
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7 Methodology employed to model
POP behaviour in the Baltic Sea
7.1 Introduction to chemical fate modelling
Multimedia fate and transport models are mathematical tools for prediction
of transport, distribution and fate of compounds that have been introduced
into the environment (Mackay 2001). Physico-chemical properties of the
compound, environmental characteristics and emission data are used for the
calculations. The environment is divided into a number of different com­
partments, e.g. air, water, soil and sediment, which are considered to be wellmixed and homogeneous with respect to both environmental charac­teristics
and chemical contaminants. The model simulates emissions of the chemical
to the different compartments and degradation of the chemical therein. The
compartments are linked by the relevant inter-compartmental chemical transport processes (Figure 36).
Air
Aerosols
Transport in and out of the
unit world
Degradation
Biota
Transport between
compartments
Soil
Water
Suspended sediments
Sediments
Figure 36. Schematic picture of a multimedia model. The environment is divided into a number of compartments (e.g. air, aerosols, soil, biota, water, suspended sediments and sediments).
Degradation and different transport processes can be included.
Multimedia fate and transport models are used to integrate the information
on chemical emissions, levels, reservoirs, and mass flows described in the previous chapters. Through such models the multitude of information and the
complexity of chemical behaviour in the environment can be synthesized to
give an overall picture of the chemical fate, to identify key factors con­trolling
the levels in the environment, and to evaluate the impact of different management scenarios on chemical levels in the future.
In the next three chapters, a multimedia fate and transport model for
POPs in the Baltic Sea called POPCYCLING-Baltic is used to assess the
major sources of three different chemical groups: PCDD/Fs, PCBs, and
HCB. The assessment was conducted for the whole of the Baltic Sea, but the
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presentation of the results focuses on the two largest basins, the Bothnian
Sea and the Baltic Proper. This work addresses basin scale contamination; it
does not deal with hot spots that may have a local influence but that do not
contribute significantly to contamination at the basin scale. In this chapter
the POPCYCLING-Baltic model is presented and the model input parameters for each chemical group are summarized. Chapter 8 contains the model
assessment of the current contamination situation, focusing on the quantity
and location of the chemicals in the Baltic Sea (the inventory), the major pathways by which the chemicals are entering and leaving the Baltic Sea (the
mass flows), and evaluating the predictive ability of the model by comparing
model predictions with empirical observations. Finally, in Chapter 9 the future
contamination of the Baltic Sea is assessed using different model scenarios that
simulate the effects of reductions in emissions.
7.2 The POPCYCLING-Baltic model
The model employed to simulate the environmental fate of PCDD/Fs,
PCBs and HCB in the Baltic Sea environment was a modified version of
POPCYCLING-Baltic (Wania et al. 2000). POPCYCLING-Baltic is a nonsteady state multi-compartment mass balance model that includes the entire
drainage basin of the Baltic Sea as its model domain. The terrestrial environment (10 zones) includes freshwater and associated sediments, vegetation
(forest canopy) and soil (forest, agricultural) while the aquatic environment (16
zones) includes water and sediments. The aquatic environment is divided into
coastal (10) and open water (6) zones in order to represent shallow areas (<
20 m) and deeper areas of the Baltic Sea separately. The terrestrial and aquatic environments are overlaid by atmospheric compartments (4 zones), which
represent the troposphere covering the drainage basin. Full details of the rationale determining the model domain and internal subdivisions are presented in
Wania et al. (2000) and a map of the model domain is presented in Figure 37.
Figure 37. Maps showing the compartmentalisation of the terrestrial (A), marine (B) and atmospheric (C) environments of the Baltic Sea drainage basin in the POPCYCLING-Baltic model. Each of
the ten terrestrial units is represented by five compartments (agricultural soil, forest soil, forest
canopy, fresh water, fresh water sediment), each of the marine units by a water and a sediment
compartment (from Wania et al. 2000).
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The model code of POPCYCLING-Baltic as described in Wania et al. (2000)
and downloadable from http://www.utsc.utoronto.ca/~wania/ downloads.html
was modified to incorporate the following features:
• Initial concentrations in all compartments can be defined by the user.
• Atmospheric concentrations can be ‘decoupled’ from the rest of the
model domain (i.e. atmospheric concentrations become boundary
conditions that are specified as model input).
• Scenarios can be defined for atmospheric concentrations whereby the
initial concentrations can be reduced (or increased) over a certain
period of time to a fraction of the initial values over the course of the
model simulation (e.g. reduced to 10% of initial concentration over
a period of 10 years).
• A term to represent enhanced sorption to organic carbon was intro­
duced to account for situations where contaminants exhibit greater
sorption to sediments and suspended solids than would be predicted
by the default algorithm used in the model code (i.e. the generic
lin­ear free-energy relationship between the octanol-water (KOW) and
organic carbon-water (KOC) partition coefficients proposed by
Karickhoff (1981)).
7.3 Model parameterization
A complete description of the model parameterization process and a compi­
lation of the default values for environmental characteristics of the Baltic
Sea environment are presented in Wania et al. (2000). The default parameter
values can also be accessed through the user interface of the POPCYCLINGBaltic model itself, which is available to the public upon request. One of the
more important considerations affecting the fate and distribution of ­organic
chemicals in the marine environment is the cycling of particulate organic
carbon (POC). The production (i.e. primary productivity) and subsequent processing of POC (e.g. sedimentation, mineralization, re­suspension, and burial)
have a strong influence on the behaviour of hydro­phobic contaminants due
to the high proportion of the total mass typically associated with particulate
carbon. In light of more recent information about POC dynamics in the Baltic
(e.g. the OC burial rates given in Table 12, the thickness of the bioturbated
layer in the sediment discussed in Chapter 8), the model input parameters
describing the mass balance of POC were ad­justed to more accurately represent these processes. Apart from these ad­justments, default values were used
for the environmental parameters.
In addition to environmental characteristics, the model requires as inputs
physical-chemical properties of the chemical of interest, the direct emissions of
the chemical to water, the initial concentration of the chemical in the dif­ferent
media (for each of the compartments), and the concentration of the chemical
in air during the whole time period of the simulation.
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The physical-chemical properties required by the model are described in detail
by Wania et al. (2000). They include phase partition coefficients (two of the
following: air/water partition coefficient (KAW), the octanol/water partition
coefficient (KOW), octanol/air partition coefficient (KOA)), the corresponding
heats of phase transfer, and rate constants for chemical de­gradation in different environmental media.
Reliable estimates of the direct emissions of the chemicals of interest were
not available. Consequently they were set to zero and the potential relevance
of direct emissions was assessed by comparing available estimates of direct
emissions with the model predictions of other mass flows of the chemical into
the Baltic Sea (Chapter 8).
Two different sets of initial concentrations were used: one for retrospective
model simulations, for which early measurements of the substances in sam­
ples collected in the late 1980s and 1990s were used, and one for ­prospec­tive
model simulations, for which data from recent sampling campaigns were
employed. Available data were carefully screened for quality and representativeness. For each set of data, summary statistics were calculated and then used
to initialize concentrations in each environ­mental medium. Initial concentrations in geographical areas where no recent monitor­ing data were available
were assumed to be equal to concentrations in the closest neighbouring area.
The initial concentrations in the forest canopy and water were not important
for the simulations, as these concentrations responded quickly to the controlling influence of the concentrations in air and sedi­ments. The initial concentrations in sediments were based on measured concentrations normalised to the
organic carbon content.
Seasonal variability in atmospheric concentrations was included. The initial concentrations in all zones were varied around the median value using a
sinusoidal function.
The selection of the physical-chemical properties, initial concentrations,
and air concentrations is summarized for each of the chemical groups in the
fol­lowing three sections.
7.4 PCDD/Fs
7.4.1 Physical-chemical properties
Simulations were conducted separately for the seven 2,3,7,8-substituted
dibenzo-p-dioxins and the ten 2,3,7,8-substituted dibenzofurans. The results
(e.g. predicted concentrations, mass flows) were summed after adjusting the
predicted values by the appropriate toxic equivalency factor (WHO-TEF;
Van den Berg et al. 2006) to give 2,3,7,8-TCDD toxicity equivalents (TEQs).
The physical-chemical properties (e.g. partition coefficients, their temperature dependencies, degradation rates) for the 17 congeners were taken from
literature sources (Govers and Krop 1998, Beyer et al. 2002, Sinkkonen and
Paasivirta 2000).
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7.4.2 Enhanced sorption to organic carbon
Enhanced sorption to black carbon (BC) has previously been suggested for
PCDD/Fs in marine environments (Persson 2003). In the model simulations
it was initially assumed that there was no enhanced sorption to black carbon,
and a sensitivity analysis of the influence of this parameter on the model outcomes was conducted.
7.4.3 Initial concentrations
Since there were very few data available for PCDD/F concentrations in accumulation sediments prior to 2000, the modelling approach employed for the
PCDD/F was different than for the other chemical groups. Reversed modelling
was employed, whereby an initial concentration in sediment for the year 1986
was selected such that the model simulation gave a good pre­diction of the current concentration in sediment. The thus obtained initial concentrations in
sediments were compared with measurements of samples collected in 1985
and 1986 (Rappe et al. 1989, Kjeller and Rappe 1995). The current concentrations in sediment were taken from data collected be­tween 2005 and 2007
(this study, Sundqvist et al. manuscript). Initial con­centrations in soils were
based on EU reference background concentrations (Gawlik et al. 2007) due to
a lack of reliable background data for the Baltic Sea watershed. No distinction
was made between agricultural and forest soils.
7.4.4 Concentrations in air
The current PCDD/F concentrations in air were derived from the recent data
summarised in 6.3.2. The measurements allowed an estimate of the ­average
atmospheric concentrations during the winter half-year of 2006/2007 at
Aspvreten and Pallas. The average concentration for the whole year was estimated assuming that the average concentration during the summer half-year
was a factor of 4 lower than during the winter half-year. The seasonal­ity in
the concentrations was assumed to be a factor of 9 with maximum values
in January. The concentration scenario for Aspvreten was applied to the
atmospheric compartments A2, A3, and A4, while the average of the scenarios
for Aspvreten and Pallas was applied to compartment A1 (Figure 37).
For the retrospective simulations, the atmospheric concentrations were
assumed to have decreased in a linear manner between 1986 and 2006 by
a factor of 4. This assumption was based on estimates of the time trends of
PCDD/F emissions during this period (Quaß et al. 2004) and on time trends
of PCDD/F concentrations in tree foliage from Germany (Rappolder et al.
2007). Note that most of the PCDD/F in the air over the Baltic Sea is from air
that originates from the European continent (Chapter 6.3).
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7.5 PCBs
7.5.1 Physical-chemical properties
Simulations were conducted separately for 7 PCB congeners (IUPAC #28, 52,
101, 118, 138, 153 and 180) and then the results were summed. The physical­chemical properties for these seven PCBs were included in the database
accompanying the original POPCYCLING-Baltic model. This database can be
accessed through the user interface of the model. All default values presented
in the model database were adopted with the exception of the degradation
half-lives, which were based on Sinkkonen and Paasivirta (2000) instead. In
general, the degradation half-lives proposed by Sinkkonen and Paasivirta were
longer than the default values accompanying the model.
7.5.2 Enhanced sorption to organic carbon
Enhanced sorption to black carbon may also be an important factor for some
PCBs, particularly for co-planar PCBs such as PCB 28 and PCB 118, which
were included in these simulations. However, measurements of the distribu­
tion of PCBs between suspended particulate matter and the water column in
the Baltic Proper (Wodarg et al. 2004, Smith and McLachlan 2006) did not
indicate any significant degree of enhanced sorption to organic carbon for any
measured PCB congener. Based on this empirical evidence, no en­hanced sorption to organic carbon was introduced.
7.5.3 Initial concentrations
For the retrospective calculations, initial concentrations of PCBs in sedi­ments
were based on data from Gustavson and Jonsson (1999) and Jonsson (2000).
For the prospective simulations, initial concentrations of PCBs in sediments
were based on reported measurements from NODC (2007), NERI (2007)
and published reports by Cato (2006) and Verta et al. (2007). Repre­sentative
background measurements for this period were available from locations corresponding to the Bothnian Sea, Baltic Proper, Danish Straits, Kattegat and
Skagerrak zones of the model domain (Figure 37).
Representative background concentrations in freshwater sediment ­covered
only a limited geographical area (multiple sites in Sweden, two sites in
Poland). However, since the reported measurements in freshwater sediments in
Sweden (Sundin et al. 2000) and the few in Poland (Kowalewska et al. 2003;
Falandysz et al. 2006) were generally within the interquartile range (IQR) of
the marine sediments, it was assumed that the PCB concentrations in fresh­
water sediments were equal to those in marine sediments in the clos­est geographical region.
Initial concentrations in soil were based on representative background
con­centrations taken from Meijer et al. (2003) and Armitage et al. (2006).
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The monitoring sites were limited to locations in Sweden and Norway and
were assumed to be broadly representative of conditions across the model
domain. Furthermore, no distinction was made between agricultural and
forest soils. The model endpoints evaluated were not sensitive to the mag­
nitude of the initial soil concentration.
7.5.4 Concentrations in air
PCB concentrations in the atmosphere were based on data from stations in
Sweden (Rörvik, Råö, and Aspvreten) and Finland (Pallas). Atmospheric
concentrations in compartments A2 – A4 were extracted from the data from
the three southerly stations only, while the concentrations in compartment
A1 (Figure 37) were estimated as the average of the median values for the
three southerly stations and the data from the northerly station (Pallas). The
­seasonal variability in the simulated concentrations reflected the seasonality
in the observations, with peak concentrations in August and a difference between the concentrations in August and February of a factor of 3-8, depending
on the congener.
For the retrospective simulations the concentrations were assumed to have
decreased by a factor of 3 between 1989 and 1999 and remained constant
after that.
7.6 HCB
7.6.1 Physical-chemical properties
Physical-chemical properties (e.g. partition coefficients, temperature dependencies, degradation rates) for HCB were included in the database accompanying the original POPCYCLING-Baltic model. No changes were made to
these default values.
7.6.2 Initial concentrations
There were insufficient data of documented quality on HCB levels in recent
accumulation sediments from the Bothnian Sea and the Baltic Proper. Con­
centrations measured in sediments from nearby waters (Kattegat, Skagerrak,
Nordic freshwater systems) were used as a guideline to initialize the model,
but the initial concentrations in sediment were an unimportant parameter for
simulating HCB behaviour as the HCB concentrations in sediment respon­ded
within several years to the concentrations in the atmosphere (Chapter 6.3).
Since the concentrations in the atmosphere have been rela­tively con­stant over
the last decade, the predicted current concentrations in water were nearly
independent of the initial concentration assumed in sedi­ment.
Due to the lack of reliable background data for the Baltic watershed, HCB
concentrations in background soil from Norway (Meijer et al. 2003) were
used to initialize all geographical regions of the Baltic.
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7.6.3 Concentrations in air
Due to the absence of evidence of strong time trends in HCB levels in the
Baltic Sea region in the last two decades and the large quantity of high quality data from the current decade, the historical simulations for HCB were
re­stricted to the period 2000-2005. The HCB concentrations in air collected
at the EMEP monitoring stations in Lista and Birkenes, Norway, and at Pallas
were used. The average annual concentration was 55 pg m–3 in the atmo­
spheric compartments A2, A3, and A4, while it was 46 pg m–3 in A1. The
average concentration was overlain by a sinusoidal seasonal varia­bility with
a maximum in October and a max:min range of a factor of 2.
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8 Current inventories, sources,
and fate of POPs: A modeland statistics-based synthesis
In this chapter different aspects of the past and current behaviour of the
three groups of POPs are assessed with the help of the available data and the
POPCYCLING-Baltic model.
First, the current inventory of contaminants in the Baltic Sea environment was estimated. The inventories were calculated using the best estimates
of current concentrations of the PCDD/Fs, PCBs, and HCB in seawater and
surface sediments, together with the volumes of these compartments. The
surface sediments were assumed to be 2 cm deep based on field observa­tions
showing this to be a typical thickness of the bioturbated layer of sedi­ments in
the Baltic Sea (Per Jonsson, personal communication). There is a much larger
inventory of the chemicals stored in sediments below this depth. Under some
conditions, this deeper reservoir may also be returned to the active circulation
in the Baltic Sea (e.g. via unusual resuspension events, sediment slumping,
deeper bioturbation), so the numbers given here may be underestimates. The
results are presented for the whole of the Baltic Sea. They provide insight into
the magnitude of the contaminant reservoirs in the Baltic Sea and the relative
importance of seawater and sediment for con­taminant storage.
Second, the current magnitude of the sources, sinks, and flows of contami­
nants in and between the basins of the Baltic Sea was assessed. The flows and
the inventories were calculated from the historical simulations con­ducted to
evaluate the model (see below). The results from the final year of the simulation were used to calculate the annual flows. This approach was justified
because of the good agreement between simulated and measured current concentrations of the chemicals. The results are presented below for two basins:
the Bothnian Sea and the Baltic Proper. Note that the simula­tions were not
conducted assuming steady-state (i.e. dM/dt = 0), and hence the sum of the
inflows/sources to a given compartment may not balance the outputs/losses.
The contaminant flows provide insight into the main proces­ses and sources
controlling the long-term fate of contaminants in the Baltic Sea.
Third, the reliability of the model was assessed. This was done by initialis­
ing the model with measured or estimated earlier contaminant concentra­tions
in sediment (from the 1980s for PCDD/Fs and PCBs, from 2000 for HCB),
and running the models using the best estimates of air concentrations from
this time point until 2007 as a boundary condition (Chapter 9). The ­predicted
concentrations of the contaminants in water and surface sediments over this
time period were then compared with contaminant concentrations that have
been measured. In addition, available measurements of contami­nant flows
were compared with model predictions. This assessment gives insight into the
model’s capability to predict the contaminant fate, and hence into the relia-
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bility of the evaluation of the current sources, sinks and flows of contaminants (above) as well as the predictions of their concentrations in the future
(Chapter 9).
Finally, for the PCDD/Fs a statistical analysis of the congener patterns that
have been measured in different matrices was undertaken. The congener patterns found in the major PCDD/F reservoir in the Baltic Sea (the sedi­ments)
were compared with the patterns present in a range of potential sources.
Since the PCDD/Fs are very persistent in the environment, many features of
the PCDD/F congener patterns in the emissions should be con­served in the
environ­ment. Consequently, this comparison is another tool to identify the
major source(s) of PCDD/Fs to the Baltic Sea.
8.1 PCDD/Fs
8.1.1 PCDD/F inventories
The total PCDD/F inventory in Baltic Sea surface sediments was 10 kg TEQ,
while the water column contained 4% of this quantity (0.4 kg TEQ). Note
again that the inventory in sub-surface sediments is much greater than the
inventory in the surface sediments. However, only the surface sediments are
included here, as only they are considered to be available for recircula­tion
back into the water column.
The large size of the inventory in surface sediments compared with water
indicates that the surface sediments are a potential major source of PCDD/Fs
to the water column. Indeed, they could potentially buffer the concentrations
in the water column. In evaluating the potential impact of PCDD/F sources on
the contamination of the pelagic environment of the Baltic, one should compare the magnitude of the sources with this inventory in the surface sediments
(i.e. 10 kg TEQ). Sources that do not markedly in­crease the inventory in the
surface sediments will not markedly increase the contamination of the pelagic
environment of the Baltic Sea as a whole.
For instance, it has been estimated that the sediments of the Kymijoki
River in Finland contain 17.3 kg TEQ (Verta et al. 2006). If a significant
portion of this sediment was to be mobilized and transported to the Gulf of
Finland in the next years, then it would have a sizeable impact on the PCDD/F
in­ventory in the surface sediments there. On the other hand, a former sawmill
site with contaminated soil containing 0.24 kg TEQ of PCDD/Fs (Kramfors
municipality 2007) would not have a measurable impact on the PCDD/F
levels in the Baltic Sea as a whole, even in the extremely unlikely event that
all of this contamination is transferred to the Baltic in a short period of time.
Indeed, the total inventory in surface sediments of 10 kg can be compared
with the 5–50 kg TEQ estimated to be present in soil from pressure treat­
ment and dipping at sawmills in Sweden (Swedish Environmental Protec­tion
Agency 2005). Since only a very small fraction of this soil can be ex­pected to
be transported to the Baltic Sea over a period of several decades (i.e. within a
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period similar to the residence time of PCDD/Fs in the Baltic Sea system, see
below), this source of PCDD/Fs is highly unlikely to con­tribute significantly
to the contamination of the Baltic Sea as a whole. This does not preclude that
a local contamination of Baltic Sea sediments of lim­ited geographical extent
may occur in some cases.
8.1.2 PCDD/F flows
The current magnitude of the flows of PCDD/F TEQs between the various
compartments in the Baltic Proper and the Bothnian Sea (Figure 37) are presented in Figure 38 and Figure 39, respectively.
(a)
(b)
23.0
82.6
Total Atmospheric Deposition
Riverine Input
21.0
Total Atmospheric Deposition
Coastal/Open Exchange
(a)
9.5
Interbasin Exchange
19.2
63.6
Volatilization
2.0
8.1
20.9
Degradation
2.6
19.2
Degradation
120.5
143.4
(b)
Volatilization
Surface-Deep Exchange
Water-Sediment
8.7
152.1
Sediment-Water
9.8
Deep-SurfaceExchange
Degradation
504.9
Water-Sediment
1.2
Burial
0.6
Degradation
378.8
345.0
Sediment-Water
Burial
14.9
Degradation
Figure 38. Model estimates of current mass flows of PCDD/F in the coastal (a) and open water (b)
compartments of the Baltic Proper (in g TEQ yr-1).
(a)
(b)
7.0
20.3
Total Atmospheric Deposition
Riverine Input
11.1
Total Atmospheric Deposition
Coastal/Open Exchange
(a)
5.1
Volatilization
1.0
Degradation
Interbasin Exchange
8.1
29.6
15.8
14.1
Degradation
113.2
8.2
6.9
78.2
110.0
Water-Sediment
Water-Sediment
Sediment-Water
(b)
Volatilization
70.8
Burial
62.6
Sediment-Water
5.0
Degradation
0.9
Burial
0.3
Degradation
Figure 39. Model estimates of current mass flows of PCDD/F in the coastal (a) and open water (b)
compartments of the Bothnian Sea (in g TEQ yr-1).
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Considering the marine environment as a whole (i.e. the water and the sediment compartments), the major external source of PCDD/Fs to all the model
regions is atmospheric deposition. This conclusion is not surprising, since
it was not possible to obtain reliable estimates of the direct emissions of
PCDD/ Fs to the Baltic Sea, and these were not included in the simula­tions.
However, the potential relevance of other sources can be explored by comparing those estimates that are available with the total atmospheric deposition
to the Bothnian Sea and the Baltic Proper, which is estimated to be 133 g
TEQ yr-1 (Figure 38 and Figure 39). It has been estimated that the highly contaminated Kymijoki River in Finland emitted 44 g I-TEQ yr-1 to the Gulf of
Finland in 2001 (Verta et al. 2006). This is greater than the atmospheric deposition to the Gulf of Finland and indicates that this river continues to be an
important source of PCDD/Fs to this basin. On the other hand, the emissions
of PCDD/Fs from the Marieberg sawmill site, one of the major chlorophenol
contaminated sites in Sweden, which were estimated to be 0.013 g TEQ yr-1
(Kramfors municipality 2007), are negligible com­pared to the atmospheric
deposition to the Bothnian Sea.
The major sink for PCDD/Fs in the marine environment is sediment
burial. Volatilisation back to the atmosphere is smaller than deposition as a
con­sequence of the strong tendency of PCDD/Fs to associate with particles
in the atmosphere and the water column. Gaseous deposition is nevertheless
an important deposition mechanism, contributing the majority of the atmo­
spheric deposition of the lower chlorinated congeners. The degradation of
PCDD/Fs is also small compared to sediment burial. Since sediment burial
occurs on a time scale of decades, this means that once PCDD/Fs enter the
Baltic Sea they will remain available in the marine environment for a long
time. The PCDD/F residence time in the basins (both water and sediments
together) was estimated by dividing the current inventory in the basin by the
current loss rates, yielding values of 11 years for both the Bothnian Sea and
the Baltic Proper. This indicates that PCDD/F levels in the Baltic Sea envi­
ronment as a whole will react slowly to changes in PCDD/F inputs. More
insight into the expected response of the different phases (sediment, surface
water, deep water) is given in Chapter 9.
The potential for inter-basin migration of PCDD/Fs can be assessed in a
similar manner. Comparing the rate of export from the deep water basins in
Figure 38 and Figure 39 with the inventories in the respective basins indi­cates
that 0.06% and 0.7% of the inventory in the Baltic Proper and the Bothnian
Sea, respectively, is transported to adjacent basins annually. This indicates that
PCDD/F contamination will move only very slowly between the major basins
of the Baltic Sea.
It is also instructive to examine the sources and sinks to the water column
alone, since the concentrations in the water column determine the PCDD/F
levels in most fish species including herring. The sediments are the most
important sources to the water column, followed by the atmosphere.
The relative importance of sediment to water transfer is greatest in the
coastal areas. This is a consequence of the more intensive cycling of POC
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between the water column and the sediment in the shallower water. Since
there are few accumulation sediments in the shallow coastal areas, the coastal
surface sediments do not contain a large PCDD/F reservoir that can serve as
a long term source of PCDD/F to the water column. The sediment to water
transfer is largely the result of resuspension of recently deposited sediments
on transportation bottoms. Export to the open water is the major net loss
mechanism for the water column in the coastal compartment. Simplified,
the mass balance indicates that the sum of the riverine/direct inputs and the
net atmospheric deposition is exported to the open water compartment. The
PCDD/F concentrations in the coastal water are governed by the intensity
of the mixing with the open water. The assumptions con­cerning this mixing
made in the model represent a large scale average; they are not applicable to
specific riverine or point sources. These kinds of sources will typically be characterised by strong concentration gradients close to the point of discharge,
with the steepness of the gradient governed by the local hydrology.
For the open water of the Bothnian Sea, the sediment is the most
important source of PCDD/Fs. Atmospheric deposition is about 3 times less.
Sedi­mentation is the dominant removal process. Degradation is of secondary
importance, and inter-basin exchange plays no significant role. This indi­cates
that the concentrations in water (and hence herring) are governed by both the
PCDD/F concentrations in the atmosphere and the PCDD/F reser­voirs in the
sediments. The relative importance of these sources will be ex­plored in more
detail in Chapter 9.
The open water of the Baltic Proper shows a different behaviour due to
the presence of the halocline. The halocline acts as a barrier to the upward
transport of POC from the deep water to the surface water. As a conse­
quence, atmospheric deposition is the dominant source to the surface water,
and POC sedimentation to the deep water is the dominant sink. Hence the
concentrations in the surface water are closely linked to the concentrations
in the atmosphere, while the level of contamination in the sediments plays
almost no role. In the deep water, on the other hand, the PCDD/F input from
sediments is three times larger than the indirect atmo­spheric input from the
surface water, so it can be expected that both the PCDD/F concentrations in
the atmosphere and the PCDD/F inventory in the sediments will affect the
PCDD/F concentrations in the deep water. Note that the model exaggerates
this aspect of PCDD/F behaviour by assuming that the deep water compart­
ment has the same surface area as the surface water compartment.
In summary, atmospheric deposition is the major known external source
of PCDD/Fs to the Baltic Sea, while the PCDD/F inventory in the surface sediments also has a major influence on the PCDD/F levels in the water column.
The Kymijoki River has been and continues to be a major source to the Gulf
of Finland, and it cannot be ruled out that there are other important riverine
or direct sources in the less well studied regions of the Baltic Sea. The section
on congener pattern analysis (Chapter 8.1.4) gives more insight into this issue.
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8.1.3 Evaluation of model predictive power for PCDD/F
Several PCDD/F datasets were available that allowed the evaluation of a
number of key features of the model. These features included the model’s ability to predict the atmospheric deposition, the dissolved water concentra­tions,
and the time trend in sediment concentrations. In addition, a bio­accumulation
model was used to predict the concentrations in herring from the output from
the POPCYCLING-Baltic model, and these concentrations were compared
with measured values.
Recently, bulk atmospheric deposition was measured at Aspvreten,
a moni­toring station located on the Swedish Baltic coast to the south of
Stockholm, for 5 months between November 2006 and April 2007 (Chapter
6.3.2). The bulk deposition measurements captured the PCDD/Fs ­associated
with wet deposition and dry sedimentation of aerosols. The deposition
fluxes ranged between 0.37 and 4.3 pg TEQ m–2d–1 with a mean of 1.1 pg
TEQ m–2d–1. This compares favourably with the predictions of the model,
which gave an aver­age of 0.7 pg TEQ m–2d–1 for wet deposition and dry deposition of aerosols for this period. This indicates that the model does a satis­
factory job predict­ing the atmospheric deposition from the air concentrations;
however, it would appear to somewhat underpredict this source of PCDD/Fs
to the Baltic Sea.
The ability of the model to predict time trends was assessed by initializing
it in 1986 with a PCDD/F concentration in surface sediments and running it
using a scenario for the PCDD/F concentrations in air from 1986 until 2006
(Figure 40, top panel). During this period the concentrations in air were assumed to decrease linearly by a factor of 4 to current levels based on time trend
information from the European Dioxin Emissions Inventory (Quaß et al.
2004) and time trends of PCDD/Fs in bioindicators of atmospheric ­depo­sition
(spruce and pine needles) in Germany (Rappolder et al. 2007). The initial
(1986) concentrations in sediment were selected such that the model gave
good predictions of the current (2005-2007) concentrations in sedi­ment.
The model predicts the water concentrations based on the external forcing from the PCDD/F concentrations in the atmosphere and the internal forcing from the PCDD/F concentrations in the sediments. During 2006–2007,
measured data for PCDD/F concentrations in the water of the Baltic Sea were
gathered (Chapter 6.5.3). The samples were collected using a passive ­sampler
that sampled only the dissolved phase of the water column. The measured
concentrations averaged 2.0, 2.7, and 2.6 pg TEQ m–3 in the Bothnian Sea,
Baltic Proper surface water, and Baltic Proper deep water, respectively. The
dissolved concentrations predicted by the model for 2006–2007 were ~2.5 pg
TEQ m–3 for all 3 water bodies (Figure 40, middle panel). The good agreement
indicates that the model does an acceptable job at predicting the PCDD/F concentrations in the dissolved phase. This is a key output of the model, since the
concentration in the dissolved phase gov­erns the bioaccumulation of PCDD/Fs
through the food chain.
One of the uncertainties in modelling PCDD/F fate is the degree of
en­hanced sorption of these chemicals to organic carbon (Chapter 7.4.2). A
sensitivity analysis was conducted to assess the impact that enhanced sorp­
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tion would have on the long term fate of PCDD/Fs in the water column.
The results showed that enhanced sorption to the sediments had very little
in­fluence on either the PCDD/F concentrations in the water column or in the
sediments (although it did strongly influence the freely dissolved concentra­
tion in sediment pore-water and hence the availability of PCDD/Fs to benthic
organisms). This can be explained by the fact that the diffusion of PCDD/Fs
between the sediment and the overlying water, the process that is influenced
by enhanced sorption, plays an insignificant role in the fate of PCDD/Fs in the
Baltic Sea. Instead, sediment-water exchange of these chemicals is dominated
by deposition and resuspension of particulate matter.
On the other hand, enhanced sorption of PCDD/Fs to the organic material in the water column had a strong influence on chemical fate. Although
the total concentration of PCDD/Fs in the water column was not influenced,
enhanc­ing the sorption reduced the magnitude of the key model endpoint,
the freely dissolved concentration, which in turn reduced both volatilisation
and de­grada­tion of the PCDD/Fs. Without enhanced sorption in the water
column, the model over-predicted the measured freely dissolved concentra­
tions of PCDD/Fs in the Bothnian Sea and in the deep water of the Baltic
Proper. Enhancing the sorption in these two water bodies by a factor of 2 gave
the good prediction of the freely dissolved concentrations shown in Figure 40.
For the surface water of the Baltic Proper, however, an excellent prediction
was obtained with no enhanced sorption. This could be inter­preted as an
indication that the aging of the organic material in the water column results
in an increase in its sorption capacity for PCDD/Fs, i.e. the fresher organic
material from recent primary production in the surface water of the Baltic
Proper has a lower sorption capacity than the more aged organic material in
the deep water or in the Bothnian Sea, where the lack of stratification results
in mixing of fresh organic material with resuspended, aged material. Given
the pioneering nature of the measurements of the PCDD/F concentrations in
the water, this interpretation should be regarded as preliminary. Note that the
enhanced sorption in the water column was of no consequence for the major
­conclusions drawn from this study (see below).
Returning to the PCDD/Fs in surface sediments, the simulations suggested
that the concentrations decreased by a factor of ~3 between 1986 and 2006.
Measurements of PCDD/Fs in surface sediments collected between 1986 and
1988 indicate that the concentrations at that time were similar to the concentrations today (Table 6 and Table 7), but the limited number of sam­ples (2 for
each basin), the considerable natural variability in surface sedi­ment concentrations, the fact that the analyses were made two decades ago, and the fact
that the organic carbon content was not measured but estimated mean that
these data give an uncertain estimate of average PCDD/F levels. As noted in
Chapter 6.6.30, one recently analysed sediment core from the Bothnian Sea
indicates that the PCDD/F levels in surface sediments have decreased during
the last 2 decades (Verta et al. 2007). We conclude that the model predictions
are not inconsistent with the empirical observations when the uncertainties in
the latter are taken into account.
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Air
Cair (fg TEQ m-3)
30
25
20
15
10
5
0
1985
1990
1995
Csediment (pg TEQ g-1 OC)
Cdisolved (pg TEQ m-3)
Water
16
14
12
10
8
6
4
2
0
1985
1990
2000
2005
2010
Bothnian Sea
Bothnian Sea
Baltic Proper Surface
Baltic Proper Surface
Baltic Proper Deep
Baltic Proper Deep
1995
Sediment
2000
2005
2010
Bothnian Sea Model
Bothnian Sea Data
Baltic Proper Model
Baltic Proper Data
1000
800
600
400
200
0
1985
1990
1995
2000
2005
2010
Year
Figure 40. Comparison of the model prediction of the PCDD/F concentrations in the Baltic Sea
compared with measurements. The upper panel shows the PCDD/F concentrations in air that was
used as input to the model for compartments A2 – A4. The middle panel shows the freely dissolved PCDD/F concentration in the water of the Bothnian Sea and the Baltic Proper predicted by the
model (lines) compared to the concentrations measured in this study (symbols showing mean ±1
standard deviation). The lower panel shows the PCDD/F concentrations in surface sediment of the
Bothnian Sea and the Baltic Proper predicted by the model (lines) compared with monitoring data
(symbols showing mean ±1 standard deviation, data from Rappe et al. 1989, Kjeller and Rappe
1995, Sundqvist et al. manu­script; this work). All concentrations are expressed on a TEQ basis.
Note that the simula­tions presented here included enhancing sorption by a factor of 2 to organic
matter in the water column of the Bothnian Sea and the deep water of the Baltic Proper.
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The uncertainty in the model predictions of time trends of PCDD/F concen­
trations in sediment was assessed by rerunning the model simulations using
the new estimates of sediment burial of organic carbon that were made for
this report (see Chapter 6.6.4, Table 12). These estimates were higher by a
factor of 2 for the Baltic Proper and a factor of 5 for the Bothnian Sea than
the values used for the initial simulations that were based on Jonsson (2000).
The time trends in PCDD/F concentrations in surface sediments predicted
by the two different simulations are compared in Figure 41. The influence
of the higher burial rates was relatively small in the Baltic Proper, but in the
Bothnian Sea the PCDD/F concentrations in surface sediments were predicted to be 10 times higher during the late 1980s than for the de­fault scenario.
Over the past 20 years the concentrations were postulated to have decreased
by a factor of 30. This is clearly inconsistent with the empirical observations.
A similar comparison for the PCBs also revealed results inconsistent with
empirical observations, which were otherwise pre­dicted well by the model (see
Chapter 8.2.3). Hence it was concluded that the high burial scenario was not
realistic.
This comparison highlights the importance of sediment burial for the fate
of PCDD/Fs in the Baltic, particularly in the Bothnian Sea. The time constant
for burial of PCDD/F is equal to the rate of accrual of new sediment mate­rial
divided by the depth of the surface sediment layer. The depth of the mixed
surface sediment layer was assumed to be 2 cm based on observa­tions of the
thickness of the bioturbated surface layer in sediment cores from the Baltic
Proper sampled several months after transition from anoxic to oxic conditions (Per Jonsson, personal communication). The diversity of accumulation
sediments in the Baltic Sea is large. In the anoxic stratified sediments of the
Gotland Deep in the Baltic Proper, the mixed layer depth will be <2 cm, while
in the oxic sediments in the shallower Bothnian Sea there is evidence that the
mixed layer depth is considerably greater. Two thirds of the cores taken in
accumulation sediments from the Bothnian Sea fail to show a distinct Cs-137
peak as a result of the fallout from the Cherno­byl accident in 1986 (Per
Jonsson, personal communication). This indicates that there is intense vertical
mixing of these sediments. Deeper mixing will lengthen the residence time of
contaminants in the surface sediment. A better understanding of surface sediment accumulation and mixing is needed to produce more reliable estimates
of the response time of the Baltic Sea to changes in PCDD/F inputs.
In summary, the evaluation indicates that the model gives reasonable pre­
dictions of the atmospheric deposition and the freely dissolved concentra­tions
of PCDD/Fs in water. There is some uncertainty regarding the model predictions of time trends in sediments. It is possible that the recovery time of the
Baltic Sea sediments following reduction of PCDD/F inputs may be different
than predicted by the model.
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Bothnian Sea high burial
Bothnian Sea default
Bothnian Sea Data
Baltic Proper high burial
Baltic Proper default
Baltic Proper Data
7000
6000
5000
4000
3000
2000
1000
0
1985
1990
1995
2000
2005
2010
Year
Figure 41. Comparison of the model prediction of recent PCDD/F concentra­tions in the surface
sediments of the Baltic Sea using different assumptions for the burial rate of sediment organic
carbon. The default scenario and the measured data are the same as in Figure 40 and are based
on the sediment organic carbon burial rates of Jonsson (2000). The high burial scenario is based
on the sediment organic carbon burial rates from Table 12.
8.1.4 Congener pattern analysis of the PCDD/Fs
In addition to the mass balance modelling, a second method was used to
gain insight into the sources of PCDD/F contamination in the Baltic Sea. The
congener pattern of the PCDD/Fs in the Baltic Sea was compared with the
congener pattern present in different potential sources of the PCDD/F contamination. PCDD/Fs lend themselves to a congener pattern analysis because:
- 17 different congeners of PCDD/Fs are commonly analysed;
- the congener patterns of emitted PCDD/Fs vary widely from source
to source and are often unique to a source type;
- PCDD/F congeners are very persistent in the physical environment,
and therefore the source pattern tends to be conserved in the physical environment.
There is, however, one major caveat to the above. Although the PCDD/F
pattern of congeners with similar physical chemical properties (i.e. within a
homologue group) tends to be conserved, changes can occur between con­
geners with widely different physical chemical properties. This is because differences in partitioning behaviour can lead to fractionation of the PCDD/F
mixture during its passage through the environment. This was taken into
account in the data normalization.
The assessment of the PCDD/F inventory in the Baltic Sea indicated that
the surface sediments contain >99 % of the PCDD/F in the Baltic marine
envi­ronment. Therefore the congener pattern in the surface accumulation
sedi­ments best represents the pattern of the PCDD/F contamination in the
Baltic Sea. The data from both the older surface accumulation sediments
(1985/1986) and the more recent surface accumulation sediments (2005–
2007) were included in the analysis.
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The congener patterns in these sediment samples were compared with the patterns from 14 source and effluent samples. The majority of the ­effluent samples were collected in Sweden as part of the Swedish Dioxin Survey (Cynthia
de Wit, personal communication). These samples included ­effluent from the
pulp & paper and other industries. A contaminated soil from a plant that
used the chlor-alkali process, a sediment heavily polluted with Ky-5 (technical
chlorophenol-product dominated by 2,3,4,6-tetra-chloro­phenol; Koistinen et
al. 1995; site KRSE2) and four different pentachloro­phenol (PCP) technical
products were also used.
Given the finding in the modelling work indicating that the atmosphere
was the major external source of PCDD/Fs to the Baltic Sea, ambient air
(com­bined gas-phase and particle-bound) and bulk deposition samples were
also included in the comparison. The 24 h ambient air samples collected in the
framework of this project at Aspvreten during 2006 and 2007 were em­ployed
together with 30-day bulk deposition samples from the same period and location.
In order to minimize the effect of pattern changes caused by physical
­chemical fractionation of the PCDD/F (see above), the data were normalised
as follows:
• the tetra- and penta-chlorinated DD/F congeners were normalised to
the sum of the 5 tetra- and penta-chlorinated DD/F congeners
• the hexa-chlorinated DD/F congeners were normalised to the sum of
the 7 hexa-chlorinated DD/F congeners
• the hepta- and octa-chlorinated DD/F congeners were normalised to
the sum of the 5 hepta- and octa-chlorinated DD/F congeners
The normalised data were then subject to principle component analysis using
the software package SIMCA-P Version 10 (Umetrics AB). The data were
scaled to unit variance and mean centred.
Figure 42 shows plots of the first two principle components. They yielded
cumulative r2 and q2 values of 0.53 and 0.20, respectively. The object plot
(Figure 42, bottom plot) shows a tight cluster at the intersection of the axis
that contains the current surface sediment samples. The tightness indicates
that the congener pattern in these samples is very uniform. One of the sur­face
sediment samples from 1985/86 also lies in this cluster, but the other three are
spread out above and to the right. This may indicate more hetero­geneity in the
PCDD/F pattern in the surface sediments at that time. The two samples to the
right are both from the Bothnian Sea (SR5 and Iggesund 30 km, Rappe et al.
1989, see also Table 6), and both contain comparatively higher levels of the
more chlorinated DDs.
The object plot further shows that the air samples form a half circle above
and to the left of the current sediments. The comparatively large spread in the
air samples indicates that there is considerable variation in the PCDD/F pattern. This likely reflects variation in the PCDD/F emissions sources to the air.
Each of the air samples had a stable air mass origin during the short ­sampling
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period. Since the sampling strategy minimized the mixing of different air
masses, it is likely to have maximized the differentiation in the PCDD/F patterns in the air. The bulk deposition samples, which were inte­grated over a
longer period of time, are grouped closer together. They lie within the space
covered by the air samples, a short distance above the sediment cluster.
All of the other potential sources included lie very distant from the sediment cluster. These include three of the technical PCP mixtures, two pulp and
paper plant effluents, effluents from two bleached sulphate mills, effluent from
a paper recycling plant, scrubber water from the rubber industry and PVC
burning, the soil contaminated by the chlor-alkali process and the sediment
polluted by Ky-5 (the last two points lie to the lower left in the object plot).
There are two exceptions. One is a PCP technical product with an unusual
pattern (Witophen P, see Hagenmaier and Brunner 1987), which lies to the
right of the sediment cluster. The second is effluent from the Rönnskärsverken,
which groups with the atmospheric samples above the cluster. Since this
source is located in the north of the Baltic, it is unlikely that it is the dominant
source of the PCDD/F contamination of the sediments of the Baltic Proper.
The loading plot (Figure 42, top plot) provides insight into the differences between the samples. The PCDDs all lie to the right in the plot, together
with most of the sources, while the PCDFs lie to the left, together with the
sediment and atmospheric samples and the chlor-alkali and Ky-5 sediment
sources. The vertical downward differentiation is most strongly influenced
by 2,3,7,8-TCDF, 1,2,3,7,8,9-HxCDF, 1,2,3,4,7,8,9-HpCDF and OCDF,
while vertical upward differentiation is most strongly influenced by 2,3,4,7,8PeCDF 1,2,3,6,7,8-HxCDF, 2,3,4,6,7,8-HxCDF, and 1,2,3,4,6,7,8-HpCDD.
High contributions of the latter congeners would tend to place ob­jects higher
in the plot, while high contribution from the other group, would tend to
place objects lower in the plot. Indeed, the sediment samples had consistently
higher contributions of OCDF than the atmospheric samples did, which may
partly explain the vertical separation of the sediment sam­ples from many of
the atmospheric samples in the object plot. The four air samples that lie at or
below the x-axis also all had high OCDF contributions. The concentrations
of 1,2,3,4,7,8,9-HpCDF and 1,2,3,7,8,9-HxCDF were low in all samples, and
below the limit of quantification in many of the air samples, which may also
have contributed to the vertical separation.
It is possible that some of the differences arise from analytical artefacts
re­lated to the congeners discussed above. The atmospheric samples were analysed in one laboratory, while the sediment samples were analysed in a second
laboratory.
The similarity between the PCDD/F congener patterns in accumulation
sediments and in ambient air/atmospheric deposition provides further evi­
dence that atmospheric deposition has been the major source of the current
basin scale PCDD/F contamination of surface sediments in the Baltic Proper
and the Bothnian Sea. This hypothesis is strengthened by the fact that the patterns in the two industrial sources that are believed to have been most signifi-
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cant, namely pulp and paper mill effluent and use of chlorophenol for wood
treatment, are clearly different from the patterns in remote surface sediments.
Note that the contribution from various sources to surface sediments in coastal areas affected by human activities is often more complex than at offshore
sites.
Figure 42. Loading plot (top) and object plot (bottom) showing the first and second components
from the PCA analysis of PCDD/F patterns in surface accumulation sediments from 2005/07
(05– 07 Sed; this study and Sundqvist et al. manuscript) and 1985/86 (85 Sed; Rappe et al.
1989, Kjeller and Rappe 1995), in atmospheric deposition samples (AD; this study), in air samples (ITM Air; this study) and in samples representative of sources (Sources).
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8.2 PCBs
8.2.5 PCB inventories
The total inventory of PCBs (ΣPCB7, kg) in Baltic Sea surface sediments (top
2 cm) was 2500 kg, while the water column contained ~10% of this quantity
(285 kg). Like the PCDD/Fs, the surface sediments contain a large inventory
of PCBs compared with the water column. Thus the surface sedi­ments must
be considered to be a potential major source and buffer of the PCB contamination in the water column.
8.2.6 PCB flows
The magnitude of the mass flows of PCBs (ΣPCB7, kg yr-1) between the various
compartments in the Baltic Proper and Bothnian Sea are presented in Figure
43 and Figure 44, respectively.
Considering the marine environment as a whole, the major external source
is atmospheric deposition, which exceeds the estimated riverine inputs by
2 orders of magnitude. There was insufficient information available to esti­
mate direct emissions of PCBs to the Baltic Sea for the model simulations.
However, available information on emissions from specific sources or source
classes can be compared with the atmospheric deposition. For in­stance, it
was estimated that the total quantity of ΣPCB7 in sewage sludge produced in
Stockholm County in 2003 was 2.2 kg (Swedish Environmental Protection
Agency 2005). It can be assumed that <1% of this quantity was released via
the sewage treatment plant (STP) effluent to water, i.e. <0.02 kg. Compared
to the annual atmospheric deposition of ΣPCB7 to the Baltic Proper of 500 kg,
this quantity is negligible. In another example, total annual emissions of PCBs
from the Swedish chemical industry to water were estimated to be 1.1–16 g
TEQ for the period 2001–2004 (Swedish Environmental Protection Agency
2005). Assuming a conversion factor for TEQ to ΣPCB7 of 100, this would
amount to 0.11–1.6 kg ΣPCB7 yr-1. This is also very small compared to the
atmospheric deposition to the Baltic Proper of 500 kg ΣPCB7 yr-1. Based on
available information, the input of PCB from point sources is much less than
the atmospheric deposition. Note that this does not mean that emissions of
PCBs are trivial. To the contrary, the dominance of atmospheric deposition
is a consequence of the persistence and mobility of PCBs in the environment.
New emissions of PCBs contrib­ute to the pool of PCBs circulating in the
environ­ment.
The major sink for the PCBs in the marine system is volatilisation.
Sediment burial is also significant, but about 3.5 times less than volatilisation. De­gra­dation amounts to about one third of the burial, while inter-basin
ex­change is negligible. The large volatilisation of the PCBs stands in contrast
to the behaviour of the PCDD/Fs. It can be attributed to the weaker tendency
of the PCBs to associate with POC in the water column and to their higher
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air/water partition coefficients. The presence of volatilisation as a major
sink means that PCBs are dispersed from the Baltic Sea marine envi­ronment
more quickly than the PCDD/Fs. Using the current inventories and current
loss rates, the PCB residence time was estimated to be 2.4 years for the Baltic
Proper and 1.8 years for the Bothnian Sea.
(a)
(b)
106.2
401.2
Total Atmospheric Deposition
Riverine Input
3.0
Total Atmospheric Deposition
Coastal/Open Exchange
(a)
96.5
Interbasin Exchange
338.1
37.9
Volatilization
0.7
7.4
25.2
Degradation
5.4
10.4
Degradation
89.7
61.5
(b)
Volatilization
Surface-Deep Exchange
Water-Sediment
13.2
60.0
Sediment-Water
4.1
Deep-SurfaceExchange
Degradation
205.0
Water-Sediment
0.5
Burial
1.1
Degradation
138.4
127.9
Sediment-Water
Burial
24.1
Degradation
Figure 43. Model estimates of current mass flows of ΣPCB7 in the coastal (a) and open water (b)
compartments of the Baltic Proper (in kg yr-1).
(a)
(b)
28.3
87.7
Total Atmospheric Deposition
Riverine Input
2.7
Total Atmospheric Deposition
Coastal/Open Exchange
(a)
28.6
8.6
0.2
6.1
Volatilization
Degradation
Interbasin Exchange
83.3
4.3
Degradation
23.3
3.5
3.6
20.1
23.5
Water-Sediment
Water-Sediment
Sediment-Water
(b)
Volatilization
11.9
Burial
15.5
Sediment-Water
3.4
Degradation
0.2
Burial
0.3
Degradation
Figure 44. Model estimates of current mass flows of ΣPCB7 in the coastal (a) and open water (b)
compartments of the Bothnian Sea (in kg yr-1).
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Examining the sources and sinks to the water column alone, atmospheric
deposition (largely gaseous deposition) is the most important source and volatilisation is the most important sink in all basins. In most cases the atmospheric deposition and the volatilisation are very similar. This is an indication that
the PCBs in the atmosphere and the Baltic Sea are close to a partitioning equilibrium. This implies that there is an intimate link between the concentrations
of PCBs in the atmosphere and in the water column of the Baltic Sea.
Despite this common feature, there are important qualitative ­differences
in the water column mass balances between the coastal and open water
compartments and between the Bothnian Sea and the Baltic Proper. The relative importance of sediment-to-water transfer is greatest in the coastal areas.
As discussed previously, this is a consequence of the more intensive cycling
of POC between the water column and the sediment due to the shallower
water. Since there is little accumulation sediment in the shallow coastal areas,
the sediments do not contain a large PCB reservoir that can serve as a long
term source of PCBs to the water column. Instead, over a time scale of years
the inputs are governed by atmospheric deposition and, to a lesser extent,
by riverine/direct inputs and inflow from the open water. Volatilisation is the
major loss mechanism, while advection to the open water is also considerable.
Simplified, the mass balance indicates that the concentrations in the coastal
water are largely governed by equilibration with the atmosphere, although
there is a net transfer of riverine inputs and excess atmospheric deposition to
the open water.
For the open water of the Bothnian Sea, the input from sediment is negligi­
ble compared to atmospheric deposition, and volatilisation is large com­pared
to transfer to the sediment. This indicates that the PCB concentrations in the
water are almost completely controlled by atmospheric exchange.
The open water of the Baltic Proper shows once again a different behaviour due to the presence of the halocline. Atmospheric deposition is practically the only source in the surface water due to the very low transport
upwards through the halocline. Volatilisation is the dominant sink, as for the
Bothnian Sea. However, in contrast to the Bothnian Sea the volatilisation in
the Baltic Proper is considerably lower than the atmospheric deposition. This
can be attributed to the sedimentation of some of the PCBs out of the surface
water into the deep water, where it is no longer available for ex­change with
the atmosphere. This can be viewed as a “stripping” process that lowers the
PCB concentrations in the surface water and hence reduces volatilisation. In
the deep water, on the other hand, the input from sediments is of comparable
magnitude to the indirect atmospheric input from the sur­face water, so it can
be expected that both the PCB concentrations in the atmosphere and the PCB
inventory in the sediments will affect the PCB concentrations in the deep water.
In summary, atmospheric deposition is the major external source of PCBs
to the Baltic Sea. Atmospheric concentrations control the concentrations in
the water column. The large PCB reservoir in sediments has little influence on
the water concentrations, with the possible exception of the deep water of the
Baltic Proper.
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8.2.7 Evaluation of model predictive power for PCBs
The different environmental behaviour of the PCBs compared to the PCDD/Fs
means that a somewhat different approach must be taken to evaluating model
performance for this set of chemicals. Because the atmo­spheric deposition to
the Baltic Sea occurs largely via gaseous diffusion, wet and dry particle-bound
deposition is of little relevance for the mass bal­ance. However, the ability of
the model to predict the water concentrations is of central importance.
The model was employed to predict the PCB concentrations in the dissolved phase of the Baltic Proper by conducting a simulation from 1989 to 2007
as described in Chapter 7. The approximation of the ΣPCB7 concentration
in air that was used as model input is shown in the upper panel of Figure 45
together with the monitoring data that were used to derive this approxima­
tion. The middle panel shows the dissolved concentration in the surface water
of the Baltic Proper predicted by the model and compares it with the monitoring data (the ΣPCB6 plotted as the monitoring data do not include PCB 28).
Only in recent years has the quality of the sampling and analytical methods
been sufficient to reliably measure PCBs in seawater. The agree­ment is very
good, demonstrating that the model predicts the PCB concen­trations in water
well.
The ability of the model to predict time trends was evaluated using the
PCB concentrations in sediment, as measured data were available from the
late 1980s. The lower panel of Figure 45 shows the results for the Bothnian
Sea and Baltic Proper open water compartments. Both the model predictions
and the measurements indicate a decrease in the PCB concentrations in surface
sediment by a factor of ~5 during this period. The good agreement indicates
that the model predicts the time trends of PCB levels in the Baltic Sea well.
In summary, the model evaluation indicates that the model gives good
pre­dictions of the PCB concentrations in water. These predictions, when com­
bined with a bioaccumulation model, give good estimates of the PCB levels in
herring. In addition, the time trend of PCB levels in the surface sedi­ments, the
major reservoir of available PCBs in the Baltic, is predicted well by the model.
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Air
60
Cair (pg m-3)
50
40
30
20
10
0
1/1/1988
12/31/1992
12/31/1997
12/31/2002
12/31/2007
18
16
14
12
10
8
6
4
2
0
1988
1993
1998
2003
2008
Csediment (ng g-1 OC)
Cdissolved (pg L-1)
Water
700
Sediment
Bothnian Sea Model
600
Bothnian Sea Data
500
Baltic Proper Model
400
Baltic Proper Data
300
200
100
0
1988
1993
1998
2003
2008
Year
Figure 45. Comparison of the model prediction of the ΣPCB7 concentra­tions in the Baltic Sea with
measurements. The upper panel shows the ΣPCB7 concentrations in air measured in southern
Sweden and Norway (symbols, data from EMEP 2007) and the concentration that was used as input
to the model for compartments A2 – A4 (line). The middle panel shows the freely dissolved ΣPCB6
concentration in the surface water of the Baltic Proper predicted by the model (line) compared to the
concentrations measured in the German monitoring program and a Swedish research pro­ject (symbols
showing mean ±1 standard deviation, data from McLachlan et al. 2003, Wodarg et al. 2004, Sobek
et al. 2004, Schulz-Bull et al. 2004, Schulz-Bull et al. 2005; PCB 28 was not quantified and hence
the sum of just 6 PCB congeners is plotted). The lower panel shows the ΣPCB7 con­centrations in
surface sediment of the Bothnian Sea and the Baltic Proper predicted by the model (lines) compared
with monitoring data (symbols showing mean ±1 standard deviation) (Gustavson and Jonsson 1999,
Jonsson 2000, Cato and Kjellin 2005, Sundqvist unpublished, this work).
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8.3 HCB
8.3.1 HCB inventories
The total inventory of HCB in the Baltic Sea was estimated for the water
column and surface sediments based on the most current (2000–2006) con­
centrations in each geographical area and the volume of each compartment.
The resulting HCB inventory in Baltic Sea surface sediments (top 2 cm) was
320 kg, while the water column contained 220 kg. The ratio of the quantity
in the water column and the quantity in surface sediments is much higher for
HCB than for PCDD/Fs and PCBs.
8.3.2 HCB flows
The magnitude of the mass flows of HCB (kg yr-1) between the various
compartments in the Baltic Proper and Bothnian Sea are presented in Figure
46 and Figure 47, respectively.
Considering the marine environment as a whole, the major source of HCB
is atmospheric deposition, which exceeds the estimated riverine inputs by
al­most three orders of magnitude. There was insufficient information avail­
able to estimate direct emissions of HCB to the Baltic Sea for the model simulations. However, available information on emissions from specific sources or
source classes can be compared with the atmospheric deposition. For instance,
total annual emissions of HCB from the Swedish chemical industry to water
were recently estimated to be 50–70 g (Swedish Environ­mental Protection
Agency, 2005). This is very little compared to the annual atmospheric deposition of 890 kg to the Baltic Proper. Based on available information, the input
of HCB from point sources is much smaller than the atmospheric deposition.
Note that this does not mean that emissions of HCB are trivial. As with the
PCBs, the dominance of atmospheric deposition is a consequence of the persis(a)
(b)
201.3
763.0
Total Atmospheric Deposition
Riverine Input
2.6
Total Atmospheric Deposition
Coastal/Open Exchange
(a)
200.9
Volatilization
0.1
Degradation
3.7
Water-Sediment
3.6
Sediment-Water
Interbasin Exchange
762.4
18.9
(b)
Volatilization
1.3
18.0
6.5
Degradation
10.4
9.4
Surface-Deep Exchange
12.3
2.6
Deep-SurfaceExchange
Degradation
16.3
Water-Sediment
0.02
Burial
0.1
Degradation
2.6
Burial
14.7
Sediment-Water
2.0
Degradation
Figure 46. Model estimates of current mass flows of HCB in the coastal (a) and open water (b)
compartments of the Baltic Proper (in kg yr-1).
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(a)
(b)
72.1
228.2
Total Atmospheric Deposition
Riverine Input
1.7
Total Atmospheric Deposition
Coastal/Open Exchange
(a)
73.6
Volatilization
0.03
Degradation
Interbasin Exchange
228.0
4.8
(b)
Volatilization
1.0
4.7
Degradation
2.7
2.4
2.6
1.5
Water-Sediment
Water-Sediment
1.5
Sediment-Water
0.4
Burial
3.2
Sediment-Water
0.3
Degradation
0.01
Burial
0.04
Degradation
Figure 47. Model estimates of current mass flows of HCB in the coastal (a) and open water (b)
compartments of the Bothnian Sea (in kg yr-1).
tence and mobility of HCB in the environment. New emissions of HCB contribute to the pool of HCB circulating in the environment.
The major sink for HCB in the marine system is volatilisation. Sediment
burial is insignificant, which is a reflection of the low affinity of HCB for suspended particulate material in the water column. Degradation and inter-basin
exchange are also negligible compared to volatilisation. The presence of volatilisation as a major sink and the fact that there is no large sediment reservoir
means that HCB levels in the Baltic Sea marine environment can drop even
more quickly than PCB levels. Using the current inventories and current loss
rates, the HCB residence time was estimated to be 0.24 years for the Baltic
Proper and 0.34 years for the Bothnian Sea.
Examining the sources and sinks to the water column alone, atmospheric
deposition (gaseous deposition) is by far the most important source and volatilisation by far the most important sink in all cases. No other processes play
a significant role in HCB fate in the Baltic Sea. In most cases the atmo­spheric
deposition and the volatilisation are very similar. This is an indica­tion that the
HCB in the atmosphere and the Baltic Sea are close to a parti­tioning equilibrium. This implies that there is an intimate link between the concentrations
of PCBs in the atmosphere and in the water column of the Baltic Sea. It is only
in the deep water of the Baltic Sea where this link be­comes weaker, since the
transport of HCB across the halocline is slow.
In summary, atmospheric deposition is the major external source of HCB
to the Baltic Sea, and atmospheric concentrations control the concentrations
in the water column. The HCB reservoir in sediments is insignificant and has
almost no influence on the water concentrations.
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8.3.3 Evaluation of model predictive power for the HCB
As shown above, the behaviour of HCB in the Baltic Sea is governed by
­gaseous exchange with the atmosphere; sediments play a negligible role.
Hence, the key aspect of model performance is its ability to predict the HCB
concentrations in water from the concentrations in the atmosphere.
The model was employed to predict the HCB concentrations in the dis­
solved phase of the Baltic Proper by conducting a simulation from 2000 to
2005, initializing the HCB concentrations in sediment with measured data
from the Kattegat, and using a scenario for the HCB concentrations in air
based on weekly measurements from the EMEP monitoring stations ­(Chap­ter
7.6 and Figure 48). The modelled HCB concentrations in water were compared
with measured values (Figure 48). Since 2000, a large number of measure­ments
have been made of HCB concentrations in the water of the Baltic Proper. The
modelled and measured concentrations in water show good agreement. This
demonstrates that the model predicts the HCB con­centrations in water well.
Cair (pg m-3)
Air
160
140
120
100
80
60
40
20
0
2000
2001
2002
2003
2004
2002
2003
2004
2005
Water
Cdissolved (pg L-1)
12
10
8
6
4
2
0
2000
2001
2005
Figure 48. Comparison of the model prediction of the HCB concentrations in the Baltic Sea compared with measurements. The upper panel shows the HCB concen­trations in air measured at the
EMEP stations in Lista and Birk­enes, Norway (symbols, data from EMEP 2007) and the concentration that was used as input to the model for compartments A2 – A4 (line). The lower panel shows
the freely dis­solved HCB concentration in the surface water of the Baltic Proper predicted by the
model (line) compared to the concentra­tions measured in the German monitor­ing program (symbols showing mean ±1 standard deviation) (data from McLachlan et al. 2003, Wodarg et al. 2004,
Schulz-Bull et al. 2004, Schulz-Bull et al. 2005).
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8.4 Summary and comparison of the behaviour
of the POPs
Table 15 summarises some key characteristics of the environmental behav­iour
of the three classes of POPs in the Baltic Sea identified in this chapter.
Table 15. Summary of key characteristics of POP behaviour in the Bothnian Sea and
the Baltic Proper.
HCB
PCB
PCDD/F
Inventory (water + surface
sediment)
% of inventory in water
540 kg
2 800 kg (ΣPCB7)
10 kg TEQ
40
9
4
0.34
1.8
11
Major source
Atmosphere
Atmosphere
Atmosphere
Major sink
Atmosphere
Atmosphere
Sediment burial
Residence time (yr)*
* Bothnian Sea
One common feature of all three POP classes is that they enter the Baltic
Proper and the Bothnian Sea primarily via the atmosphere. For HCB the
atmospheric input is so large that it is implausible that other sources make a
major contribution. The atmospheric input of PCBs is also much larger than
other known sources. For PCDD/Fs, the situation is less clear. There is a possibility that there are other, as yet unidentified major riverine or direct sources
of PCDD/Fs. However, analyses of congener patterns in offshore sediments
and atmospheric samples indicate that atmospheric deposition of PCDD/Fs is
a major source. It should be noted that sediments sampled near industrialised
and urbanised areas have shown PCDD/F patterns that are distinctly different
from the atmospheric pattern.
The residence time of the chemicals in the basins also influences the poten­
tial role of non-atmospheric sources. The residence time is much shorter for
HCB and PCBs than it is for PCDD/Fs. This means that the levels of these chemicals in the Baltic Sea will respond rapidly (within several years) to changes
in the inputs. This coupled with the intensive air – water exchange of gaseous
HCB and PCBs means that the concentrations of these chemicals in the water
column are essentially regulated by the concentrations in the atmosphere.
Even if there would be major riverine or direct sources, their impact on the
Baltic Sea would be reduced by volatilisation.
For the PCDD/Fs, on the other hand, a long residence time is coupled with
a low potential for volatilisation. Once PCDD/Fs enter the Baltic Sea, sedi­
ment burial is the major loss mechanism. They accumulate in sediments, and
the large chemical inventory in the sediment can become a major source to the
water column, particularly when levels in the atmosphere decrease. This can
be amplified if deeper bioturbation or increased gale frequency lengthens the
PCDD/F residence time by increasing the active layer of the surface sediments.
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8.5 Linking POP levels in water and sediment to
levels in Baltic Sea fish
Current understanding of POP bioaccumulation in pelagic fish indicates that
the concentrations in the fish are linearly proportional to the freely dissolved
concentrations in the water column. Hence, for a given food chain a de­crease
in the dissolved concentrations of the POPs would result in a pro­portional
decrease in the concentrations in the fish.
Several mechanistically based mathematical models of bioaccumulation
in aquatic ecosystems have been assembled. One, the ACC-HUMAN model
(Czub and McLachlan 2004), has been employed to model the bioaccumu­
lation of PCBs in herring in the Baltic Proper. A historical scenario for the
freely dissolved PCB concentrations in the Baltic Proper was constructed
based on the recent measurements discussed above as well as time trend information. This was used as input for the ACC-HUMAN model, which then
predicted the lipid-normalised concentrations in herring. In Figure 49, the
predicted concentrations of the individual congeners in 4-year old herring
and cod are compared with the concentration of PCB 153 measured in the
Swedish Environmental Monitoring Program (IVL 2008b). The agreement is
good, which indicates that the understanding of POP bio­accumulation in the
Baltic and its link to the freely dissolved concentration is sound.
Peltonen et al. (2007) applied a different bioaccumulation model to
predict the concentrations of PCDD/Fs in herring from the Bothnian Sea.
Although this model had no direct link to the concentrations in the physical
environ­ment (the model input was the concentration in the fish’s prey), this
work illustrates the importance of fish growth rates and feeding habits on the
PCDD/F concentrations in herring. It shows how changes in these variables
can result in time trends in PCDD/F concentrations in herring that differ from
the time trends of the PCDD/F concentrations in the physical environ­ment.
Hence, a decrease in the freely dissolved concentrations of the PCDD/Fs may
not result in a proportional decrease in the concentrations in herring if the
structure of the ecosystem changes; the decrease may be larger or smaller, or
the concentrations could even increase.
At this point it is instructive to return to the spatial trends in PCDD/F
levels in herring that were discussed in Chapter 5.1 and to explore whether
they are related to gradients in contamination of the physical environment
or in the structure of the ecosystem. One observation was an increase in
the lipid-normalized concentrations moving from the Baltic Proper into the
Bothnian Sea. Peltonen et al. (2007) show that this may be explained by the
slower growth rates of the northern herring populations, i.e. that this spatial trend is related to differences in the structure of the ecosystem. Another
demonstra­tion that gradients in concentration in biota need not be related
to gradients in contamination of the physical environment is provided in
Figure 7a. PCB concentrations in herring are seen to increase moving from the
Kattegat to the open Baltic Proper. However, as discussed in Chapter 6.5.2,
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a decreas­ing (i.e., opposite) gradient in PCB concentration in water between
the Mecklenburg Bight and the Baltic Proper has been consistently observed.
Hence, the even stronger west to east gradient in PCDD/F concentrations in
herring compared to PCBs (Figure 7a) could be explained by there being no
gradient in the PCDD/F contamination of the water column. Alternatively, it
may be a consequence of the fact that PCDD/F concentrations in herring are
more strongly influenced by differences in growth dilution than PCBs due to
their greater hydrophobicity.
Figure 49. Concentrations of PCB 153 in 4-year old herring and cod from the Baltic Proper over
time as predicted by the ACC-HUMAN model and as measured in the Swedish environmental monitoring program (IVL 2008b). See Czub and McLachlan (2004) for details on the model and the
scenario employed.
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9 Evaluation of the future ­­
devel­opment of the contamina­tion
of the Baltic Sea
The modified POPCYCLING-Baltic model was applied to evaluate the future
development of the contaminant levels in the Baltic Sea environment. Two different scenarios were chosen based on the finding that atmospheric deposition
is the major source of all 3 chemical groups. In Scenario 1, no changes to contaminant levels in the atmosphere were made, while in Scenario 2 atmospheric
concentrations of the contaminants of interest were linearly reduced to 10%
of the initial values over a 10-year period. The pur­pose of these simulations
was to investigate the potential impact of reduced atmospheric concentrations
on the long-term dynamics of these contami­nants in the Baltic Sea environment. The results for each scenario are pre­sented in the following sections.
9.1 PCDD/Fs
For scenario 1 (unchanged atmospheric concentrations) the predicted future
PCDD/F concentrations in the water column (pg TEQ L–1) and in surface sediments (pg TEQ g–1 dry weight) of the Baltic Proper (surface water and deep
water) and Bothnian Sea are shown in the left panels of Figure 50. The concentrations in the surface sediments continue to decrease gradually, largely as
a result of burial by less contaminated new sediment. The con­centrations in
water also decrease slowly to a level ~60% below current levels. The concentrations in the Baltic Proper surface water stabilize most rapidly – by about
2015 – while the decrease in the Baltic Proper deep water and in the Bothnian
Sea is more gradual, continuing over at least 40 years.
For scenario 2 (reduced atmospheric concentrations), the reduction in
PCDD/F concentrations in the atmosphere is followed by a decrease in the
water column (the right panels of Figure 50). This decrease is most immedi­
ate for the Baltic Proper surface water, and by 2025 (when the concentration
in the atmosphere has again stabilized) the concentration in water has al­ready
dropped to ~20% of its value in 2015. The decrease in the Bothnian Sea water
is more gradual as a result of the buffering effect of the surface sediments;
after 10 years the concentration has only dropped ~45%, and it takes 25 years
for it to approach 20%. The response in the deep water of the Baltic Proper is
also slow, but somewhat more rapid than in the Bothnian Sea. The PCDD/F
concentrations in the surface sediments also decrease, but more gradually.
This is in accordance with the long residence times of PCDD/F in the Baltic
marine environment.
The simulations suggest that the freely dissolved PCDD/F ­concentrations
in the water of the Baltic Proper and the Bothnian Sea will continue to
de­crease over the next 20 years to about a factor of two below current
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levels as a result of the slow response of the Baltic system to the decreases in
­atmo­spheric inputs that have already occurred over the last decades. Since
the dissolved concentrations in water determine the concentrations in fish, a
parallel decrease in the concentrations in the fish stocks would be expected,
barring changes in the food web structure and energetics. Eventually the concentrations in most fish would lie below the current EU guidelines for marketing as food.
No Change
7
4
3
2
1
0
2005
2015
2025
3.5
Baltic Proper Deep
1.5
1
0.5
2015
2025
300
2035
2
1
0
2005
2045
Bothnian Sea
250
Csediment (pg TEQ g-1 OC)
3
2015
2025
3.5
2
Baltic Proper
2035
2045
Bothnian Sea
3
Baltic Proper Surface
2.5
Baltic Proper Deep
2
1.5
1
0.5
0
2005
2015
2025
300
2035
2045
Bothnian Sea
250
Baltic Proper
200
200
150
150
100
100
50
0
2005
4
2045
Baltic Proper Surface
2.5
0
2005
5
Bothnian Sea
3
Cdissolved (pg TEQ m-3)
2035
Reduced Air Concentrations
6
Cair (fg TEQ m-3)
5
Cdissolved (pg TEQ m-3)
Cair (fg TEQ m-3)
6
Csediment (pg TEQ g-1 OC)
7
2015
2025
Year
2035
2045
50
0
2005
2015
2025
2035
2045
Year
Figure 50. Simulations of future PCDD/F concentrations in the Baltic Sea assum­ing that the
PCDD/F concentrations in air remain at current levels (left hand panels) or that the PCDD/F concentrations in air decrease from their current levels beginning in 2015 to 10% thereof in 2025
(right hand panels). The upper panels show the concentrations in air for compartments A2 – A4
(model input). The middle panels show the dissolved concentra­tions in the water of the Baltic
Proper and the Bothnian Sea. The lower panels show the concentrations in the corre­sponding surface sediment. All concentrations are for PCDD/F TEQs.
The simulations also show that this gradual reduction in PCDD/F concen­
trations could be markedly accelerated by reducing the concentra­tions in the
atmosphere, and that the final steady state concentrations would also be reduced. Indeed, the absence of other known major current sources of PCDD/Fs to
the Baltic Proper and the Bothnian Sea suggests that this is the only option for
positively influencing the PCDD/F concentrations in the water.
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Regarding the possibilities for reducing atmospheric deposition to the Baltic
Sea, there is evidence that regional emissions of PCDD/Fs to air have an
impact on the PCDD/F concentrations in air over the Baltic Sea. The PCDD/F
concentrations in air are much higher in air masses that have passed over the
industrialized areas to the south, southeast, and southwest of the Baltic Sea
than in air that has come from the north, northeast, or north­west (Chapter
6.3.2). This suggests that the PCDD/F emissions in central, eastern, and western Europe significantly impact the concentrations in air over the Baltic Sea.
It was estimated that air from these southerly, south-easterly, and southwesterly directions accounted for ~80% of the wet depo­sition and ~50% of
the gaseous deposition of PCDD/F to the Baltic Sea during the study period
(October 2006 to April 2007). Thus it is likely that reducing PCDD/F emissions to air in industrialized Europe would result in a reduction of PCDD/F
levels in the Baltic Sea. Further insight into the most important source areas
could be provided by atmospheric dispersion model­ling, but that was beyond
the scope of this study.
Moreover, it may also be possible to reduce the PCDD/F concentrations in the fish stocks by fisheries management techniques. This approach
builds on reducing the water-to-fish bioaccumulation of the PCDD/Fs, which
could mean lower concentrations in fish, even if the PCDD/F concentrations
in water were not to change. This could be achieved by e.g. increasing the
growth rate of the fish (Peltonen et al. 2007).
9.2 PCBs
The model predictions for ΣPCB7 for scenario 1 (unchanged ΣPCB7 con­
centrations in the atmosphere) are shown in the left panels of Figure 51.
The ΣPCB7 concentrations in the Bothnian Sea and the surface water of the
Baltic Proper remain at their current levels. The concentrations in the sur­
face sediments continue to decrease somewhat, particularly in the Baltic
Proper, as does the concentration in the deep water of the Baltic Proper,
but the decrease is small compared to that observed and modelled for the
last years (Figure 45). This suggests that the PCB distribution in the Baltic
Sea/ atmosphere system has approached a steady state.
The predictions for scenario 2 (a 90% decrease in ΣPCB7 concentrations
in the air beginning in 2015) are shown in the right panels of Figure 51. The
ΣPCB7 concentrations in the water of the Bothnian Sea and in the surface
water of the Baltic Proper react quickly to the change in the concentrations
in the atmosphere; they also decrease to ~10% of the original level with little
time delay with respect to the concentrations in air. The ΣPCB7 con­centrations
in the deep water also decrease, albeit more slowly, while the sediments show
an even slower decrease that extends over several decades. Eventually the concentrations in all compartments approach a new steady state where the concentrations are 10% of the current levels.
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Cair (pg m-3)
Reduced Air Concentrations
2025
Cdissolved (pg L-1)
12
2045
Baltic Proper Surface
8
Baltic Proper Deep
6
4
2
90
80
70
60
50
40
30
20
10
0
2005
2015
2025
2035
Baltic Proper
2025
2035
2015
2025
2045
2035
2045
Bothnian Sea
10
Baltic Proper Surface
8
Baltic Proper Deep
6
4
2
0
2005
2045
Bothnian Sea
2015
20
18
16
14
12
10
8
6
4
2
0
2005
12
Bothnian Sea
10
0
2005
Csediment (ng g-1 OC)
2035
Cdissolved (pg L-1)
2015
Csediment (ng g-1 OC)
Cair (pg m-3)
No Change
20
18
16
14
12
10
8
6
4
2
0
2005
90
80
70
60
50
40
30
20
10
0
2005
2015
2025
2035
2045
Bothnian Sea
Baltic Proper
2015
2025
2035
2045
Year
Year
Figure 51. Simulations of future PCB concentrations in the Baltic Sea assum­ing that the PCB concentrations in air remain at current levels (left hand panels) or that the PCB concentrations in air decrease
from their cur­rent levels beginning in 2015 to 10% thereof in 2025 (right hand panels). The upper panels show the concentra­tions in air for compartments A2 – A4 (model input). The middle panels show
the dissolved concentrations in the water of the Baltic Proper and the Bothnian Sea. The lower panels
show the concentrations in the corresponding surface sedi­ment. All concentrations are for ΣPCB7.
The simulations clearly demonstrate that reducing the PCB concentrations in
air is an effective way to reduce the PCB levels in the Baltic Sea. The concentrations in the water column are more closely coupled to the concen­trations in the
atmosphere than is the case for the PCDD/Fs, which causes the concentrations in
water to respond more quickly to changes in the con­centrations in air. For PCBs
it is even clearer that there are no effective alternatives to reduce the water concentrations; they will stay close to their present levels if the inputs do not change,
and atmospheric deposition is the only PCB source that has a significant impact
on the PCB mass balance, at least for the Bothnian Sea and the Baltic Proper.
Reducing the atmospheric concentrations of PCBs requires not just
regional, but hemispheric efforts. PCBs have a longer residence time in the
atmo­sphere than PCDD/Fs, and hence they are more subject to long range
atmospheric transport. Hence, a substantial portion of the PCBs in the
atmosphere over the Baltic Sea may not originate from the Baltic drainage
basin. In addition, PCBs are subject to secondary emissions from reservoirs
in the environment such as soils. It is possible that a considerable portion of
the PCBs entering the atmosphere over the European continent originate from
these sources and not from primary emissions.
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9.3 HCB
The model predictions for HCB for scenario 1 (unchanged HCB concentra­
tions in the atmosphere) are shown in the left panels of Figure 52. The HCB
concentrations in the water column remain at their current levels.
The predictions for scenario 2 (a 90% decrease in HCB concentrations
in the air beginning in 2015) are shown in the right panels of Figure 52. The
HCB concentrations in the water of the Bothnian Sea and in the surface water
of the Baltic Proper react in step with the change in the concentrations in the
atmosphere; they also decrease to ~10% of the original level with virtually no
time delay with respect to the levels in air.
The HCB contamination of the Baltic Sea is closely tied to the levels in the
atmosphere. However, the opportunities to reduce HCB levels in the atmo­
sphere by local or regional actions are limited. HCB is an organic contami­
nant with an extremely high long range transport potential. It also partitions
readily from the air into other media such as soil and water which buffer its
concentrations in the atmosphere. Consequently, HCB is truly a global con­
tamination problem; similar concentrations are measured in air around the
Northern Hemisphere (Barber et al. 2005). The only realistic possibility for
reducing its levels in air are successful action to reduce emissions interna­
tionally (e.g. through the implementation of the Stockholm Convention), and
time. Following elimination of HCB sources on a global scale, the HCB inventory currently circulating in the environment will slowly decrease as the HCB
is removed to more permanent sinks like deep sea sediments. However, this
process is slower than for other POPs, as suggested by the comparatively small
fraction of HCB in Baltic Sea sediment in relation to the water column when
compared with PCBs and PCDD/Fs (Chapter 8.4).
Reduced Air Concentrations
80
80
70
70
60
60
Cair (pg m-3)
Cair (pg m-3)
No Change
50
40
30
50
40
30
20
20
10
10
0
0
2015
2025
2035
2005
2045
8
8
7
7
Cdissolved (pg L-1)
Cdissolved (pg L-1)
2005
6
5
4
3
2
Bothnian Sea
1
Baltic Proper Surface
2025
2035
2045
Bothnian Sea
Baltic Proper Surface
6
5
4
3
2
1
0
2005
2015
0
2015
2025
2035
2045
2005
2015
2025
2035
2045
Figure 52. Simulations of future HCB concentrations in the Baltic Sea assuming that the HCB concentrations in air remain at current levels (left hand panels) or that the HCB concentrations in air
decrease from their current levels beginning in 2015 to 10% thereof in 2025 (right hand panels).
The upper panels show the concentra­tions in air for compartments A2–A4 (model input). The lower
panels show the dissolved concentrations in the water of the Baltic Proper and the Bothnian Sea.
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9.4 Uncertainties in the assessment
In the following the uncertainty of the modelling results is explored. The discussion is structured around the major conclusions of Chapters 8 and 9 using
a 6-level qualitative scale (highly certain, very certain, quite certain, quite
uncertain, very uncertain, and highly uncertain):
a) Air is the dominant external source of HCB and PCBs to the Baltic
Sea. This conclusion is considered to be highly certain for HCB and
very certain for PCBs. The atmospheric deposition of these chemi­cals
is much larger than the estimated riverine inputs and known direct
inputs. There is a lack of information on PCB and HCB inputs along
the south-eastern coast between the Neva and the Oder rivers, so it
cannot be ruled out with certainty that there are significant sources.
However, the good agreement between predicted and meas­ured
concentrations in water and sediment including time trends supports
this conclusion. Note that the highest PCB concentrations in water
have not been measured in the south-eastern parts of the Baltic
Proper, but rather in the south-western parts (e.g. Wodarg et al.
2004).
b) The concentrations of HCB and PCBs in the water column will react
quickly to changes in the concentrations in the atmosphere. This
conclusion is considered to be highly certain for HCB and very
cer­tain for PCBs. The input to the water column is clearly larger
from the atmosphere than from the sediments, even given the uncertainties in the model. Consequently, the sediment reservoir does not
signifi­cantly buffer the water column against changes in the external
forcing from air. Furthermore, the monitoring data show that the
PCB concentrations in surface sediments have decreased in parallel
to the air concentrations. A residual uncertainty for the PCBs is the
possibility of major riverine/direct inputs along the south-eastern
coast (which is considered unlikely, see a) above), inputs that must
also have decreased in parallel with the air concentrations during the
last 20 years.
c) The atmosphere is the major source of PCDD/Fs to the Bothnian Sea
and the Baltic Proper. This conclusion is considered to be quite
certain. The modelling results indicate that the inputs from the
atmo­sphere are larger than the inputs from other known sources.
They also indicate that the atmospheric inputs are sufficiently large
to ex­plain the current levels of PCDD/Fs in the water column.
Further­more, the congener pattern analysis indicates that the
PCDD/ Fs in offshore surface sediments of the Bothnian Sea and the
Baltic Proper are largely of atmospheric origin. It should be noted
that other sources can be dominant on a local scale. Analyses of
surface sedi­ments along the Swedish coast has shown that the
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PCDD/F patterns in sediments sampled near urbanised and industrialised areas often differ significantly from atmospheric patterns.
While there is compelling evidence for the importance of atmo­
spheric deposition, there is a major riverine source in the Gulf of
Finland, and it is conceiv­able that there are also major nonatmospheric sources in less well studied parts of the Bothnian Sea or
the Baltic Proper. The pattern analysis suggests that any such major
source(s) would have a pattern similar to the atmospheric pattern or
dominated by selected toxic congeners. A river could for instance be
a recipient for combustion residues with high PCDD/F levels.
Information on the PCDD/F discharge of the major rivers entering
the Baltic is needed to assess this possibility.
For source apportioning, so called receptor modelling has been
shown to be an effective tool for tracing and quantifying PCB and
PCDD/F sources (Masunaga et al. 2003, Du and Rodenburg 2007,
Sundqvist et al. 2008). This technique utilizes comprehensive con­
gener patterns and multivariate statistical tools (e.g. positive matrix
factorization) to reconstruct source patterns in a region, which then
can be linked to specific sources. A receptor modelling study for
PCDD/Fs sources in the Baltic Sea area is under way (Sundqvist
un­published). Sediment from >140 sites along the Swedish coast was
analysed for all tetra- through octa-CDD/F congeners and these data
constitute the basis for the study. For each sampling location, the
contribution from various sources are being quantified and appor­
tioned. Preliminary results support the findings in this study, namely
that the atmospheric inputs are large for offshore sites. In coastal
zones, the contribution from various sources is often much more
complex.
It should also be noted that the congener pattern analysis has its
shortcomings. By focusing on the similarity of the pattern of all
­seventeen 2,3,7,8-substituted congeners (as was done in the current
study), this approach can miss meaningful contributions of specific
sources to one or several congeners if these sources did not signifi­
cantly distort the overall pattern. For instance, it is conceivable that
the chlor-alkali source pattern, which is dominated by the lower
chlorinated furans, could significantly contribute to the levels of
2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, and 2,3,4,7,8-PeCDF in Baltic Sea
sediments without markedly affecting the (atmospheric) pattern of
the remaining 14 congeners. Different techniques are required that
focus on key “signature” components of the sources in question and
on the key congeners from a risk perspective (i.e. 2,3,7,8-TCDD,
1,2,3,7,8-PeCDD, 2,3,7,8-TeCDF, and 2,3,4,7,8-PeCDF). Finally, it
could be better to use environmental samples (e.g. sediments, soils)
in highly impacted source areas to characterize the source signatures,
rather than product or effluent samples.
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d) The freely dissolved PCDD/F concentrations in the Bothnian Sea
and the Baltic Proper will decrease if the PCDD/F concentrations in
the atmosphere remain at current levels. This conclusion is
­consid­ered to be quite certain. The process determining the lag
between the decrease in the concentrations in air and in water is the
transfer of PCDD/Fs from surface sediment to water. The concentrations in the surface sediment respond over a period of several
­decades to changes in the rate of input due to the long residence time
of the PCDD/Fs in the Baltic Sea system (Table 15). Thus the flow of
PCDD/Fs from the sediment into the water column also responds
over a time period of decades to changes in the rate of input. The
un­certainties in the degree of sorption of the PCDD/F to the surface
sediments do not alter this fact. Since the atmospheric deposition of
PCDD/Fs has decreased over the last decades, there is likely to be an
ongoing decrease of the freely dissolved concentrations in the next
decades.
The major uncertainty associated with this conclusion is the same as
that discussed under c) above, namely that there could be other
un­identified major sources of PCDD/Fs that have not decreased over
recent years. There is further uncertainty associated with the magni­
tude of the predicted decrease. This will depend on i) the magnitude
of the decrease in the atmospheric input over the last decades; ii) the
residence time of the PCDD/Fs in the basins. The scenario for the
decrease in PCDD/F concentrations in air over the last 20 years is
based on empirical observations and is judged to be quite reliable.
The uncertainty in the residence time of the PCDD/Fs is discussed in
f) below.
e) Reducing the PCDD/F concentrations in the atmosphere will acceler­
ate the reduction in the freely dissolved PCDD/F concentra­tions in
the Bothnian Sea and the Baltic Proper. This conclusion is considered to be quite certain. This is a consequence of atmospheric deposition being the dominant source of PCDD/Fs to these basins. The
residual uncertainty lies in the possibility that there are other major
unidentified sources (see c) above).
f) The rate of decrease of the freely dissolved PCDD/F concentrations
will be as illustrated in Figure 50. This conclusion is considered to be
quite uncertain. The rate of decrease in the surface water of the
Baltic Sea is suspected to be overestimated due to the simple struc­
ture of the POPCYCLING-Baltic model. The rate of decrease in the
other water bodies is closely linked to the PCDD/F residence time,
which is in turn linked to the model assumptions regarding the
sur­face area and mixed depth of the surface sediments as well as the
sediment burial rates. Although these assumptions have an empirical
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basis, they are uncertain, and it has not yet been possible to evaluate
their correctness, e.g. by measuring the elimination rate of very
hydrophobic chemicals from these water bodies. In addition, the
residence time may be modified by environmental disturbances such
as intense storms which resuspend accumulation sediments and thus
bring buried PCDD/Fs back into circulation.
g) The rate of decrease in the concentrations in fish will parallel the rate
of decrease in the freely dissolved concentrations in the water bodies.
This conclusion is considered to be very uncertain. The ob­servations
of levels in herring over the last 15 years have shown that this need
not be the case. The decrease in the rate of growth of the herring is
believed to have resulted in stronger bioaccumulation of the PCDD/
Fs, with the consequence that the PCDD/F concentrations in herring
did not decrease during this period, although the freely dissolved
concentrations (presumably) did. Hence it is possible that changes in
the ecosystem may slow down or accelerate the expected response of
the fish to a decrease in the freely dissolved concentra­tions.
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10 Conclusions and future research
10.1 New field measurements
10.1.1 Air and atmospheric deposition measurements
• The highest PCDD/F concentrations (TEQ) were found in air that
had passed over the European continent.
• Air that had passed over the British Isles and air from northerly
direc­tions showed lower concentrations.
• The PCDF concentrations (TEQ) were higher than the PCDD
concentra­tions in air from southwest, south, east, and northeast,
while the opposite was generally true in air from west-northwest.
• The variability in the concentrations was much lower within a
compass sector than it was between the sectors.
• Approximately 40% of the wet deposition of PCDD/F derived from
air that originated from the southwest sector, while ~20% derived
from air from the south sector.
• The PCDD/F bulk deposition was 1.1 pg WHO-TEQ m–2d–1 during a
6‑month study period (winter 2006/2007). Estimates of the origin of
the gaseous deposition to the Baltic Sea indicate that the contributions from various sectors to gaseous deposition were quite comparable.
• A strong correlation between the concentration of particle-bound
PCDD/F and the soot carbon concentration was found, with a
correlation coefficient (r2) of 0.80.
10.1.2 Surface sediments:
• PCDD/F concentrations in offshore areas are approximately 2–3
times higher in the Baltic Proper than in the Bothnian Sea if normalised to dry weight. The organic carbon (OC) levels are on average
substantially higher in Baltic Proper offshore sediments. If normalised to OC, there are no differences in PCDD/F-levels between the
two basins.
• The ΣPCB7 concentrations normalised to dry weight are on average
4-5 times lower in the Bothnian Sea as compared to the Baltic
Proper. This difference is less pronounced if the data are normalised
to OC. The con­centrations of HCB in sediment seem to be quite
similar in the Bothnian Sea and the Baltic Proper.
• The variability of PCDD/F and PCB levels in offshore sediments is
largely explained by variation in OC levels. The OC content explained 80–90% of the PCDD/F and PCB variation, while the BC content ex­plained 50–70% of the variation. If one outlier was excluded,
the BC content could explain 70–90% of the OC level variation.
There was a low correlation between OC content and the concentration of HCB (r2=0.28).
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• The variability in PCDD/F levels and contamination patterns in
coastal zones is large. The coast of the Baltic Sea includes several
heavily industrialized zones, and it has been shown that the Swedish
coast in­cludes a number of PCDD/F hot spots associated with industrial activi­ties.
• There is limited information on PCDD/F time trends in Baltic offshore sediments. While levels are clearly declining in offshore areas
in the Gulf of Finland due to extensive reduction of emissions, the
situations in the Bothnian Sea and the Baltic Proper are unclear.
• During the last 10–20 years, a distinct decrease of PCB concentrations in surface sediments of the Bothnian Sea and the Baltic Proper
has occurred. In the Bothnian Sea, the decrease was on average a
factor of 5.6, while in the Baltic Proper it was a factor of 4.5. These
decreasing PCB concentrations in offshore surface sediments are in
line with the de­creases in PCB concentrations in herring from the
Bothnian Sea and in herring and guillemot egg from the Baltic
Proper. There are also indica­tions of decreasing HCB concentrations
in Baltic sediments.
10.1.3 Surface, deep sea and sediment pore-water:
• Average dioxin concentrations in coastal and offshore waters were
found to be 1.1 and 2.5 pg WHO-TEQ m‑3, respectively, and the
corresponding levels for average ΣPCB7 concentrations were 5.8 and
24 ng m‑3.
• There were no significant concentration differences between surface
and deep sea water, neither in the Baltic Proper nor in the Bothnian
Sea.
• The POP concentrations in the pore-water generally co-varied with
sedi­ment concentrations.
10.1.4 Sediment-water exchange:
• For the coastal stations, the average ratio of the pore-water/overlying
water concentration was 3.6 ± 1.6 and 1.0 ± 0.6 for PCDD/Fs and
PCBs, respectively. This indicates that the coastal sediments act as a
source of PCDD/Fs to the overlying water, whereas for the PCBs
there is no con­centration gradient and the sediments in the coastal
areas constitute neither strong sinks nor strong sources of PCBs.
• At deep water sites, the average ratio of the pore-water/overlying
water was 1.1 ± 0.5 for PCDD/Fs, which suggests that there are no
concentra­tion gradients and that the sediments in the offshore areas
constitute neither strong sinks nor strong sources for the diffusive
exchange of dis­solved PCDD/Fs. For PCBs, this ratio was 0.7 ± 0.3,
suggesting that there is only a slight concentration gradient for PCBs.
The direction of the gradient indicates that the sediments could be a
PCB sink.
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• The binding of PCDD/Fs to Baltic Sea sediments is 10–30 times
stronger than predicted by the equation typically used in risk assessment. The ecotoxicological risk from PCBs and PCDD/Fs in the
Baltic Sea sedi­ments is 10–30 times lower than would be predicted if
the risk assessment would be based on the binding to AOC alone.
Mass balance modelling, Pattern analyses and uncertainty
analyses
Offshore and other pristine areas:
• The atmosphere is the dominant external source of HCB and PCBs
to the Baltic Sea, and the concentrations of HCB and PCBs in the
water column will react quickly to changes in the concentrations in
the atmosphere. These conclusions were considered to be highly
certain for HCB and very certain for PCBs. Good agreement between
predicted and measured concentrations in water and sediment
including time trends supports this. The atmospheric deposition is
much larger than the estimated riverine in­puts and known direct
inputs, and the input to the water column is also clearly larger from
the atmosphere than from the sediments.
• The atmosphere is the major source of PCDD/Fs to the Bothnian Sea
and the Baltic Proper. This conclusion is considered to be quite
certain. The modelling results indicate that the inputs from the
atmosphere are larger than the inputs from other known sources.
They also indicate that the atmospheric inputs are sufficiently large
to explain the current levels of PCDD/Fs in the water column.
Furthermore, the congener pattern analy­sis indicates that the PCDD/
Fs in offshore surface sediments of the Both­nian Sea and the Baltic
Proper are largely of atmospheric origin.
• The freely dissolved PCDD/F concentrations in the Bothnian Sea
and the Baltic Proper will decrease if the PCDD/F concentrations in
the atmo­sphere remain at current levels. This conclusion is considered to be quite certain. The process determining the lag between the
decrease in the con­centrations in air and in water is the transfer of
PCDD/Fs from surface sediment to water. The concentrations in the
surface sediment respond over a period of several decades to changes
in the rate of input due to the long residence time of the PCDD/Fs in
the Baltic Sea system. Thus the flow of PCDD/Fs from the sediment
into the water column also responds over a time period of decades to
changes in the rate of input. The scenario for the decrease in
PCDD/F concentrations in air over the last 20 years is based on
empirical observations and is judged to be quite reli­able. Since the
atmospheric deposition of PCDD/Fs has decreased over the last decades, there is likely to be an ongoing decrease of the freely dissolved
concentrations in the next decades. The major uncertainty associated
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with this conclusion is that there could be other unidentified major
sources of PCDD/Fs that have not decreased over recent years.
• Reducing the PCDD/F concentrations in the atmosphere will accelerate the reduction in the freely dissolved PCDD/F concentrations in
the Both­nian Sea and the Baltic Proper. This conclusion is considered to be quite certain. This is a consequence of atmospheric deposition being the domi­nant source of PCDD/Fs to these basins. The
residual uncertainty lies in the possibility that there are other major
unidentified sources.
• The rate of decrease in the concentrations in fish will parallel the rate
of decrease in the freely dissolved concentrations in the water bodies.
This conclusion is considered to be very uncertain. The observations
of levels in herring over the last 15 years have shown that this need
not be the case. PCDD/F concentrations in herring did not decrease,
although the freely dissolved concentrations (presumably) did. This
is believed to be due to a stronger bioaccumulation of PCDD/Fs as a
result of a decrease in the rate of growth of the herring. Hence
ecosystem changes may slow down or accelerate the expected
response of the fish to a decrease in the freely dissolved concentrations.
Non-pristine areas (e.g. near industries, cities and contaminated land)
• Analyses of surface sediments along the Swedish coast has shown
that the PCDD/F patterns in sediments sampled near urbanised and
industri­alised areas often differ significantly from atmospheric
patterns. For source apportioning, so called receptor modelling has
been shown to be an effective tool for tracing and quantifying PCB
and PCDD/F sources. A receptor modelling study for PCDD/Fs
sources in the Baltic Sea area is under way. Preliminary results
support the findings in this study, namely that the atmospheric inputs
are large for offshore sites, while in coastal zones, the contribution
from various sources is often much more complex and nonatmospheric sources can be significant on a local/regional scale.
Recommendations for future research
The POP pollution situation in the Baltic Sea continues to be a problem, especially for the PCDD/F and dioxin-like PCBs, which contaminate the fish so
that marketing of Baltic fish is restricted in the EU.
Although the current project has contributed to a better understanding of
the contamination situation in the Baltic Sea, several areas for which knowledge is uncertain or lacking have also been identified. It is primarily for the
PCDD/Fs that the uncertainties are high. The major areas of interest include:
• A better understanding of current emissions of PCDD/Fs to air. This
work has clearly demonstrated that the PCDD/F problem in the
Baltic as a whole is caused by long range atmospheric transport,
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•
•
•
•
•
•
•
whereby sources in continental Europe play a major role. Con­
sequently, it is important to establish whether our current under­
standing of PCDD/F emissions is consistent with the atmospheric
input of PCDD/Fs to the Baltic. As an example, a comparison of the
EMEP model predictions of PCDD/F concentrations in air, which are
based on current emissions inventories for European countries, with
the ambient air concentrations measured in this project would be a
good point of departure. This could be followed up by a revision of
the emissions estimates or an assessment of how planned emis­sions
reductions measures can be expected to reduce PCDD/F inputs to the
Baltic Sea in the future (both on a European scale).
A better knowledge of riverine inputs of PCDD/Fs to the Baltic Sea.
This is essential for assessing whether transfer of PCDD/Fs from the
watershed, for instance via soil erosion, is a significant source of
PCDD/Fs to the Baltic that could greatly lengthen the response time
of concentrations in Baltic biota to reductions in PCDD/F emissions
to air. This potential source was not addressed in this report as there
is a lack of data.
A better knowledge of current industrial emissions to Baltic Sea
water. These include industrial effluents and leakage from contami­
nated land. There are large uncertainties in all these categories,
which primarily affect the contamination situation in coastal zones.
It appears as the PCDDs have a better (i.e. declining) trend than the
PCDFs in Baltic biota, blood serum of Swedish men, and possibly
also in Baltic sediments. Is there a shift towards emissions rich in
PCDFs rather than PCDDs, or can this be attributed to other factors?
A better knowledge of trends for PCDD/Fs in Baltic sediments and
Baltic air. This is needed for the evaluation of retrospective and
pro­spective model predictions.
A better knowledge of levels and composition of PCDD/Fs and
dioxin-like PCBs in Baltic surface sediments. Large areas of the
Baltic Sea have never been investigated. Contaminant pattern analy­
sis of surface sediments can be used for tracing sources. Currently,
the data available only allow for source apportionment in limited
parts of the Baltic Sea (along the Swedish coast).
A better understanding of surface sediment accumulation and verti­
cal mixing. This is needed to produce more reliable estimates of the
response time of the Baltic Sea to changes in PCDD/F inputs.
A better understanding of sediment-water-biota contaminant dynam­
ics. Why do we see spatial and temporal variation in PCDD/F levels
in fish from the Baltic Sea? Is it due to biological factors (e.g. growth
rate, feeding habits, etc.), other factors or a combination of factors?
How important are the PCDD/F levels in sediment for the PCDD/F
levels in biota?
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vid svenska massa- och pappersbruk. Draft report to the Swedish EPA by
Malmaeus, M. and Norrström, H.
143
A better knowledge of sources, transport, reservoirs and fate of
persistent organic pollutants (POPs) in the Baltic Sea environment is
crucial for the identification of effective actions against these compounds.
In this report the present situation regarding sources and current
fluxes of persistent pollutants in the Baltic Sea ecosystem is presented.
The compounds selected for the study were: polychlorinated bi­phenyls
(PCBs), hexachlorobenzene (HCB), polychlorinated dibenzo­furans
(PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). These
classes of compounds represent a broad range of physical-­chemical
Based on current knowledge and some new field measurements
in air, sea water and sediments, mass balances for the selected POPs
were calculated. These mass balances indicate that the atmosphere
7
5
4
3
2
1
is the major source of PCDD/Fs to the Bothnian Sea and the Baltic
0
2005
Proper and also the dominant external source of HCB and PCBs to
3
Cdissolved (pg TEQ m-3)
these POPs.
2015
3.5
the Baltic Sea. These fi
­ ndings emphasise the need for further international agreements to ­prevent long-range transboundary transport of
No Change
6
Cair (fg TEQ m-3)
spectrum of most chemicals listed in the Stockholm Convention.
2025
7
2035
1.5
1
0.5
2025
300
Baltic Proper
0
2005
2015
2025
2035
2045
Bothnian Sea
3
Baltic Proper Surface
2.5
Baltic Proper Deep
2
1.5
1
0.5
0
2005
2015
2025
2035
300
2045
Bothnian Sea
250
Baltic Proper
150
150
100
100
50
2015
2025
Year
2035
2045
Report 5912
Naturvårdsverket 106 48 Stockholm. Besöksadress: Stockholm – Valhallavägen 195, Östersund – Forskarens väg 5 hus Ub, Kiruna – Kaserngatan 14.
Tel: +46 8-698 10 00, fax: +46 8-20 29 25, e-post: [email protected] Internet: www.naturvardsverket.se Beställningar Ordertel: +46 8-505 933 40,
orderfax: +46 8-505 933 99, e-post: [email protected] Postadress: CM Gruppen AB, Box 110 93, 161 11 Bromma. Internet: www.naturvardsverket.se/bokhandeln
1
200
200
0
2005
2
2045
Bothnian Sea
250
Csediment (pg TEQ g-1 OC)
2035
REPORT 5912 • JANUARY 2009
3
3.5
Baltic Proper Deep
2015
4
Bothnian Sea
2
0
2005
5
2045
Baltic Proper Surface
2.5
Reduced Air Concentrations
6
50
Air
0
160
2005
140
120
100
80
60
40
20
0
2000
2015
10
8
6
4
2
2025
2035
2045
Year
2001
Water
12
Cdissolved (pg L-1)
properties, and hence their environmental behaviour encompasses the
Sources, transport,
reservoirs and fate of
dioxins, PCBs and HCB in
the Baltic Sea environment
Cair (fg TEQ m-3)
issn 0282-7298
Cdissolved (pg TEQ m-3)
NATURVÅRDSVERKET
isbn 978-91-620-5912-5
Cair (pg m-3) Csediment (pg TEQ g-1 OC)
REport 5912
Sources, transport, reservoirs and fate of dioxins, PCBs and HCB in the Baltic Sea environment
Sources, transport,
reservoirs and fate of
dioxins, PCBs and HCB
in the Baltic Sea
environment
2002
2003
2004
2005