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Ocean & Coastal Management 43 (2000) 689±712
Anthropogenic marine radioactivity
Hugh D. Livingston, Pavel P. Povinec
International Atomic Energy Agency, Marine Environment Laboratory, MC-98012, Monaco
Abstract
The present sources of anthropogenic radionuclides in the marine environment, consisting
of global fallout, nuclear weapons testing, releases from nuclear facilities, radioactive waste
dumping, the Chernobyl accident and nuclear submarine and aircraft accidents, are reviewed.
90
Sr; 137 Cs and Pu isotopes have been chosen as representative of anthropogenic radionuclides
to study their distribution and behaviour in the marine environment. The data on their
concentrations and inventories in seawater and sediment are presented and discussed. For
dose assessment, 137 Cs and 210 Po were chosen as they are the most representative of
anthropogenic (137 Cs) and natural (210 Po) marine radioactivity on a global scale. The average
annual individual doses from ingestion of marine food estimated for the world population for
the year 2000 are of the order of 0.03 mSv from 137 Cs and 9 mSv from 137 Cs. The annual dose
of 137 Cs for a hypothetical critical group living on the NE Atlantic coast and consuming
100 kg of ®sh and 10 kg of shell®sh per year would be 3 mSv, while the contribution from
210
Po would be 160 mSv. These values are well below the accepted value for the public of
1 mSv. # 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
Concentrations of anthropogenic radionuclides generally vary from region to
region, according to the location and magnitude of the di€erent sources of
contamination. Radionuclides have been released to the environment from a
multiplicity of sources, both planned and accidental. The main contribution to
anthropogenic marine radioactivity, as in the terrestrial environment, is still from
global fallout from nuclear tests performed in the atmosphere, particularly in the
1950s and 1960s. However, in some regions, like the Irish and North Seas,
concentrations of anthropogenic radionuclides in the marine environment have been
signi®cantly in¯uenced by discharges from European reprocessing plants. On the
other hand, the Baltic and Black Seas were the seas most a€ected by the Chernobyl
accident. In all these latter regions the spatial and temporal trends in the
concentrations of anthropogenic radionuclides have been quite dynamic. They are
0964-5691/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
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a result of changing source terms and marine processes including horizontal and
vertical transport in the water column, sedimentation, resuspension from sediment,
biological uptake, and food-chain transfer. Given that more than 70% of the surface
of the Earth is ocean, it is not surprising that much of the anthropogenic
radionuclides now reside there.
The interest in the distribution and behaviour of radionuclides in the ocean derives
from a variety of issues. Firstly, the fate of radionuclides needs to be clearly
understood to assess possible environmental or human health consequences. This
accumulated knowledge then provides a critical basis for rapid assessment of the
impact of future releases } especially unplanned. These include accidents involving
the release of radionuclides from such sources as coastal nuclear facilities, nuclear
waste sites or from the transport of plutonium fuel or high-level waste through the
ocean. Finally, radionuclides are powerful tracers providing basic insights into a
variety of marine processes. Because of the relatively well-de®ned temporal and
spatial aspects of the introduction of radionuclides into the ocean, their movement
within the ocean provides many insights into a large number of processes in the
water column, and in biological and sedimentary systems.
The spectrum of anthropogenic radionuclides released to the marine environment
is very large. Both ®ssion and activation products were released in such quantities
that they have dominated their environmental levels. The anthropogenic radionuclides present in the marine environment can be sorted into two groups. The ®rst
contains those radionuclides which could have possible radiological impacts, e.g.
90
Sr, 137 Cs, 238 Pu, 239 Pu, 240 Pu and 241 Am. The second group is represented by
radionuclides such as 3 H, 14 C, 99 Tc and 129 I which have mainly been used as
radioactive tracers to study marine processes.
Considerable di€erences in the marine behaviour of these radionuclides were
observed. 3 H, 14 C, 90 Sr, 99 Tc, 129 I and 137 Cs are typical representatives of elements
which are soluble in seawater and have been widely used for studies of water
dynamics. Their particle reactivity is very low in comparison to e.g. Pu isotopes and
241
Am, which lie at the other extreme, in a group of elements having low solubility
and high particle reactivity. Pu and Am isotopes will eventually be transferred to
ocean sediments through their association with particles. This process is dynamically
a function of particle density in the ocean. At the present time, this means that in
coastal regions, these isotopes are to a large extent rapidly removed from the water
column. This contrasts with their behaviour in oligotrophic open ocean areas where
the majority of the existing inventory still resides in the water column.
137
Cs is the radionuclide which has been the most intensely used in studies of
marine processes and radiological assessment on both regional and worldwide scales.
Its behaviour in the oceans has been studied over a long period with reference to its
fallout from nuclear weapons tests and discharges from nuclear reprocessing plants.
In particular, discharges from Sella®eld have been extensively used to study water
and sediment dynamics in the Irish, North, Norwegian and Barents Seas. The
radiocaesium from weapons test fallout was exclusively 137 Cs. 134 Cs, however, was
present in Sella®eld discharges as well as in Chernobyl debris, although the
134
Cs=137 Cs ratios were di€erent. Caesium from Chernobyl was thus readily
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distinguishable from other sources by its di€erent 137 Cs=134 Cs activity ratio of about
1 : 2. The ratio provides a reliable means of di€erentiating between reprocessing
discharges, weapons test fallout and Chernobyl debris. Various removal processes
have to be taken into account when studying radiocaesium behaviour in the marine
environment, e.g. radioactive decay, distribution, sedimentation, resuspension,
biological removal, etc. It has been established from nuclear test fallout studies
that 137 Cs has behaved conservatively in Atlantic surface waters with an e€ective
half-life of about 25 years IAEA [1].
In the present paper, the main sources of anthropogenic radioactivity in the
marine environment, namely global fallout, nuclear test sites, reprocessing plants,
dumping of radioactive wastes and nuclear accidents are reviewed and the present
situation of radionuclide contamination of the marine environment is discussed.
2. Global fallout
Hamilton et al. [2] reported that 423 nuclear weapons tests have taken place
between 1945 and 1980 with a total ®ssion yield of 217 MT. About 90% of this
®ssion yield came from USA, UK and USSR tests. Fallout from these tests,
introduced to the Earth's surface from the stratosphere, has been the major source of
anthropogenic radioactivity released to the marine and terrestrial environment. The
cumulative global deposit of 90 Sr by the end of 1990 was 311 PBq. The comparable
®gure for 137 Cs can be estimated to be 1.5 times the 90 Sr ®gure (from the ratio of their
®ssion yields). Aarkrog estimated that 13 PBq of 239;240 Pu was delivered to the
Earth's surface via global fallout [3]. Approximately 76% of the fallout arrived in the
Northern hemisphere and 24% in the Southern hemisphere. Fallout is maximal at
mid-latitudes (30±608) and minimal at the equator and poles. Given the large area of
the Earth covered by ocean, much of the delivered fallout was delivered there. For
example, Hamilton et al. [2] estimated that by 1990, the Paci®c Ocean alone received
147 PBq of 137 Cs and 3.8 PBq of 239;240 Pu. Presumably this implies 98 PBq of 90 Sr,
i.e. about 1/3 of the global delivery.
3. Nuclear weapons test sites
The main nuclear weapons test sites which have contributed to the radionuclide
contamination of the marine environment are: (i) Novaya Zemlya, (ii) the Marshall
Islands, (iii) Christmas Island, (iv) French Polynesia, (v) Lop Nop. Others include
Semipalatinsk, Johnson Atoll and the Nevada test site.
The Novaya Zemlya testing grounds were used for large-scale atmospheric tests
(mainly in 1961 and 1962) in which nuclear debris reached the stratosphere and was
distributed as global fallout. The contribution to local contamination of the marine
environment was found to be negligible [4]. A similar situation was observed at
Christmas Island after the nuclear tests there. The atmospheric tests performed at the
Marshall Islands and in French Polynesia had both stratospheric and tropospheric
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inputs (nuclear debris reaches the stratosphere after the explosion of at least 1 Mt of
TNT). However, the total yield of the atmospheric tests in the Marshall Islands was
an order of magnitude greater than that from the French tests. The smaller number
and yield of tests carried out at the Lop Nop test site only added a small increment to
the contamination of the marine environment.
3.1. The Marshall Islands
The early programme of US military testing was carried out in the western
equatorial North Paci®c. Between 1946 and 1958, 66 nuclear tests took place with a
combined explosive yield of 107 Mt [5]. These tests were especially signi®cant in
terms of radioactive contamination of the marine environment for several reasons.
Firstly, the test series represented about 20% of the total yield from all atmospheric
nuclear testing. As such, they were one of the main source terms for man-made
radioactivity in the oceans. Secondly, as a consequence of the high proportion of
tests conducted at or near ground level, a substantial amount of the radioactivity
produced was delivered regionally as ``close-in'' fallout. Several authors have
addressed this issue with respect to input to the Paci®c in excess of global fallout.
Glasstone [6] estimated that 119 PBq of 90 Sr was deposited by early 1956 as ``closein'' fallout. Bowen et al [7] referred to the fact that the 28% of known ®ssion yields
from nuclear testing gave rise to ``close-in'' fallout } most produced at the Marshall
Islands and shown in North Paci®c inventories of 137 Cs, 90 Sr and 239;240 Pu often up
to two times that expected from global fallout alone. Aarkrog [3] estimated that local
fallout from Paci®c tests must have nearly doubled Paci®c Pu inventories. Whitehead
[8] estimated North Paci®c 137 Cs input as being only slightly less from ``close-in''
fallout as compared with global fallout. Finally, the local marine environment in the
lagoons of the atolls of Bikini and Enewetak contains radioactive contamination,
mostly in sediments, which makes them still quite contaminated (several tens of TBq
for several long-lived radionuclides) but nevertheless of minor radiological
consequence (the total radiological dose from marine pathways is still dominated
by natural radionuclides such as 210 Po and 210 Pb) [5].
3.2. French Polynesia
The IAEA has recently completed an international project to assess the
environmental impact of nuclear weapons tests both surface and underground at
Mururoa and Fangataufa Atolls in French Polynesia (the South Paci®c Ocean).
While the contribution to the marine environment from underground tests can only
be evaluated over a long time scale, the impact from surface tests has already been
seen. The main source of radioactive contamination of the marine environment at
both atolls is Pu buried in lagoon sediments. The total 238;239;240 Pu inventory in both
lagoons has been estimated at about 30 TBq [9]. Contributions from 60 Co, 137 Cs,
155
Eu and 241Am are between 0.6 and 1.1 TBq. The estimated radionuclide release
rates from the lagoons to the open ocean are 5.7 TBq aÿ1 for 3H, 27 GBq aÿ1 for
90
Sr, 11 GBq aÿ1 for 137 Cs and 11 GBq aÿ1 for 238;239;240 Pu. During a hypothetical
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cyclone crossing Mururoa lagoon, the maximum 239;240 Pu release would be about
0.7 TBq [10].
The annual release rates of the radionuclides from the lagoons do not signi®cantly
increase the radionuclide concentrations in the open ocean. 3 H; 90 Sr, 137 Cs and
239;240
Pu levels observed around the atolls at a distance of about 12 nautical miles are
similar to those observed in the South Paci®c Ocean (Fig. 1). Calculated water
column inventories (60 kBq mÿ2 for 3 H, 0.6 kBq mÿ2 for 90 Sr, 1.0 kBq mÿ2 for
137
Cs and 10 Bq mÿ2 for 239;240 Pu) were within a factor of two of those expected
from the global deposition densities for latitudes 208±308S. The 238 Pu=239;240 Pu
activity ratios in surface water (from 0.1 to 0.2) showed signi®cant variations
between sites, con®rming the lagoon origin of the observed Pu.
Fig. 1. 3 H; 90 Sr; 137 Cs and 239;240 Pu water pro®les in the open ocean at about 12 nautical miles from
Mururoa and Fangataufa atolls.
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Radionuclide concentrations in ocean biota were low, only tracer amounts of
Co, 137 Cs and 239;240 Pu were found. Maximum levels observed in lagoon ®sh were
below 2 Bq kgÿ1 for 60 Co, 0.7 Bq kgÿ1 for 137 Cs and 5 Bq kgÿ1 for 239;240 Pu (wet
weight).
Computer modelling of the dispersion of radionuclides to the open ocean using
compartmental and world ocean circulation models has shown that even for a
hypothetical worst case scenario (a rock slide with direct release of radionuclides
from underground), the maximum elevations in radionuclide concentrations above
present background levels at Tureia, the closest atoll (130 km north of Mururoa),
would be a factor of 10 for 3 H, 1 for 137 Cs and 0.1 for 239;240 Pu [10].
As the observed and predicted radionuclide concentrations in lagoon water (and
biota) are low, the estimated radiation doses to hypothetical inhabitants of Mururoa
and Fangataufa Atolls would be below 0.01 mSv per year [11].
60
4. Releases from nuclear plants
Basically, there are two classes of coastally located nuclear plants which can
contribute to the input of arti®cial radionuclides to the ocean through discharges
associated with their normal operating procedures. These discharges are regulated
and monitored by the appropriate national authorities, taking into account both
national and international standards in respect to radiological safety. The two classes
include coastally located nuclear power plants and nuclear fuel reprocessing plants.
The former involve nuclear reactors operated to generate electricity and generally are
not associated with other than minor releases of radionuclides which have usually
very low and very localised radiological impacts. The latter involve chemical
treatment of spent nuclear fuel to extract, typically, plutonium for future use as a
nuclear fuel and generate large quantities of radioactive waste. Depending on the
design of these plants, these reprocessing operations have been associated with
signi®cant discharges of small fractions of waste products to the sea.
Only three nuclear fuel reprocessing plants have resulted in signi®cant direct
releases to the ocean. They are the Sella®eld plant on the Irish Sea on the northwest
coast of England, the La Hague facility on the northwest coast for France and the
plants at Trombay (Bombay Harbour) and Tarapur on the west coast of India. Some
nuclear plants are located on rivers and make indirect and relatively very small
impacts on the ocean, e.g. Savannah River Laboratory, South Carolina, USA;
Krasnoyarsk, Tomsk and Mayak facilities on Siberian rivers; Marcoule on the
Rhone river in France etc.
Some comparative reports of discharges from Sella®eld and La Hague have been
summarised recently [12]. For most radionuclides, the releases from Sella®eld have
historically been more signi®cant although releases, in general, have declined in
recent years (with some exceptions for radiologically less signi®cant radionuclides
like 99 Tc or 129 I). The fate of discharged radioactivity, in the Irish Sea, English
Channel and waters into, around and out of the Arctic Ocean, has been extensively
studied in numerous papers and is beyond the scope of this review. The releases from
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the Indian nuclear reprocessing plants were relatively small compared to the
Sella®eld/La Hague releases and have declined since their higher levels in the 1960s
[13].
5. Dumping of radioactive wastes
The IAEA has compiled information on radioactive waste dumping sites in the
world's oceans and regional seas [14]. The radioactive wastes with the highest
activities at the time of dumping were dumped in the Atlantic Ocean (45 PBq), the
Arctic Ocean (38 PBq) and the Paci®c Ocean (1.4 PBq) and their marginal seas.
These wastes were mainly low-level wastes packed in containers (Atlantic and Paci®c
dumping sites), but also full reactor assemblies with spent nuclear fuel (Novaya
Zemlya bays in the Kara Sea) or reactor assemblies without fuel (the Sea of Japan).
Radioactive wastes were also released as liquids, mainly in the Barents Sea and the
Sea of Japan. Following the London Convention of 1972, the dumping of
radioactive wastes in the sea was banned although dumping continued in some
areas (e.g. the Kara Sea, the Sea of Japan). Liquid radioactive wastes were dumped
in the Sea of Japan as late as 1993.
The IAEA's Marine Environment Laboratory in Monaco (IAEA-MEL) has been
engaged in marine radioactivity assessment programmes related to radioactive waste
dumping in the oceans since 1992 [4,15,16]. Its sta€ has participated in several
expeditions to the Atlantic, Arctic and Paci®c Oceans to sample seawater, biota and
sediment for radiological assessment studies. Di€erent radiometrics (low-level alpha,
beta and gamma-spectrometry) and mass spectrometry (ICPMS, AMS) techniques
were used for radionuclide analysis of marine samples.
5.1. NE Atlantic Ocean
The total activity dumped in the NE Atlantic dumping sites was at the time of the
dumping of the highest one (45 PBq), however, the wastes were mainly of low
activity. In general, 98% of the total activity dumped comprised beta/gamma
emitters, the quantities of alpha-emitting nuclides were much smaller. At the two
main sites in the NE Atlantic (468000 N, 168450 W and 468150 N, 178250 W) a total
activity of more than 30 PBq was disposed of. The expected inventory of alpha
emitting radionuclides at these sites would be of the order of 0.5 PBq [14].
Wastes were dumped into the NE Atlantic dumping sites until 1982. Previously
and subsequently, they were subject to radiological survey, usually on an annual
basis. Marine radioactivity assessment work was carried out in the framework of the
Coordinated Research and Environmental Surveillance Programme (CRESP)
organised by the OECD/NEA. The radiological impact of the dumped radioactive
wastes on the marine environment was found to be negligible. The estimated
collective radiation doses to the world population from low-level radioactive wastes
dumped in the NE Atlantic has been estimated to be 3000 man Sv over 1000 years
and 1 man Sv over 50 years [17].
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In the past, the IAEA-MEL has regularly co-operated with the OECD/NEA and
its Member States on the analytical quality assurance aspects of the CRESP
surveillance programme. From 1992, however, IAEA-MEL participated in several
cruises to sample seawater, sediment and biota at the NE Atlantic dumping sites,
organised by the German Government (Bundesforchungsanstalt fuÈr Fischerei). The
visited sites were: 468000 ± 468080 N, 168410 ±178000 W and around 468050 N±178100 W.
Interest centred on the measurement of 137 Cs; 238 Pu; 239;240 Pu and 241 Am in
bottom waters around the dumping sites, in water pro®les as well as sediment and
biota. Results from the 1992 cruise show enhancements of 5±7 times in 238 Pu
concentrations in seawater collected at dumping sites relative to those at the
background station. The 238 Pu=239;240 Pu activity ratio, a strong indicator of the
origin of plutonium in the marine environment, at the background station
(0.0290.008) is similar to that expected from global fallout in the Northern
hemisphere. On the other hand, 238 Pu=239;240 Pu activity ratios observed in water
samples taken a few tens of meters above the dumping site were considerably higher
(from 0.080.01 to 0.130.01). These results suggest that measurable leakage was
occurring at the sites visited. However, the highest observed activities (below
0.6 Bq mÿ3 for 137 Cs and 20 mBq mÿ3 for 239;240 Pu) were very small (higher
concentrations of these radionuclides from global fallout were observed in surface
waters). Preliminary results from the 1996 and 1998 expeditions (the analysis of
samples has not yet been completed) do not show signi®cant di€erences between the
radionuclide levels observed at the dumping sites and the background stations.
Therefore, it can be concluded that at the dumping sites visited, no leakages of
radionuclides of any radiological signi®cance were observed.
5.2. Arctic Ocean
The IAEA has recently carried out the International Arctic Seas Assessment
Project (IASAP) to address concerns over the potential environmental impact of
high level radioactive wastes dumped in the Kara Sea, mostly in the shallow bays of
Novaya Zemlya, in the form of nuclear reactors with fuel and containers [18]. The
highest contribution to the inventory of radionuclides is due to 137 Cs (1 PBq), 90 Sr
(0.95 PBq), 63 Ni (0.3 PBq), 60 Co (0.1 PBq), 241 Pu (78 TBq) and 239;240 Pu (8.9 TBq).
The radionuclide release rates, calculated using the best estimate scenario and
combined for all sources, peak at approximately 3 TBq yearÿ1 within the next
100 years with a second peak of about 2 TBq yearÿ1 in approximately 300 years.
From 1992 to 1995, IAEA-MEL participated in ®ve expeditions to the Kara Sea
to assess the radiological situation at the sites. The programme included sampling of
seawater, sediment and biota, in situ measurements using underwater gamma
spectrometers, laboratory analyses of collected samples, the development of a Global
Marine Radioactivity Database (GLOMARD), the evaluation of distribution
coecients and concentration factors, modelling and radiation dose assessment.
Radiometric investigations have shown that no radiologically signi®cant environmental contamination has occurred. Leakages which have led to locally increased
levels of radionuclides in sediment have only been observed in Stepovoy and
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697
Abrosimov Bays within a few meters of the containers. Radionuclide concentrations
observed were generally low and similar to those in the open Kara Sea (see Table 1),
which is relatively uncontaminated, the main source of radionuclides being global
fallout and discharges from western European reprocessing plants and nuclear
facilities on the Ob and Yenisey rivers. As can be seen from Fig. 2 which shows that
the present concentrations of 90 Sr and 137 Cs in the Barents Sea surface water and the
Kara Sea surface and bottom waters, as extracted from the GLOMARD, have
actually been decreasing in recent years.
As there is no evidence at present of signi®cant leakage from the reactor
components and other wastes disposed of in the Kara Sea, the major residual issue
regarding these disposals is not what has happened to date, but what could happen
in the future. Dispersion and radiological modelling which was carried out on three
geographical scales, namely local (bays), regional (the Kara Sea) and global, has
shown that only radiological e€ects on a local scale may be of interest. Doses of up
to 4 mSv yearÿ1 have been estimated for a hypothetical critical group subsisting on
®sh caught in the Novaya Zemlya Bays. Projected future doses to members of the
public in typical local population groups living on the Kara Sea coast will be below
1 mSv yearÿ1. These estimations were done for the worst case scenario during which
110 TBq is released after disruption of the barriers [18].
5.3. NW Paci®c Ocean
According to the IAEA [1] about 456 TBq of liquid radioactive waste and
252 TBq of solid waste were dumped over the last three decades in the Sea of Japan
(the East Sea), the Sea of Okhotsk and the western North Paci®c Ocean, mainly by
the former Soviet Union and the Russian Federation. The reactor assemblies
dumped in the Sea of Japan did not contain nuclear fuels. The Japanese contribution
to dumped low solid radioactive wastes east of central Japan was estimated as
15.1 TBq. The inventory of wastes dumped in the Sea of Japan by the Republic of
Korea was negligible in comparison to the total activity of wastes dumped in this sea.
Recent dumping of radioactive wastes was done by the Russian Federation in 1992
and 1993, mainly in the Sea of Japan with a total activity of about 1.4 TBq.
Unfortunately, information on the radionuclide composition of the wastes is missing
[14].
Although the total activity dumped in the NW Paci®c Ocean is lower by a factor
of about 6 in comparison to the dumping sites in the Arctic Ocean, the high level of
consumption of marine foods in the Far Eastern region has brought about interest in
the possible radiological consequences.
Since 1994, the IAEA's Marine Environment Laboratory has been engaged in an
assessment programme related to these disposals by participating in the Japanese±
Korean±Russian joint expeditions in 1994 and 1995 [19,20], by taking part in
the analyses of radionuclides in seawater and sediment samples collected during the
expeditions [21,22], by estimating the possible dispersion of radionuclides from the
dumping sites [23] and the resultant doses by computer modelling [24]. Usually,
surface and bottom waters were taken at each station (including background
Abrosimov Fjord
Stepovoy Fjord
Tsivolka Fjord
Novaya Zemlya Trough
Open Kara Sea
Site
Cs
4±7
3±9
4±6
4±7
3±8
Surface
4±9
6±32
6±14
7±14
8±20
Bottom
Water (Bq mÿ3)
137
9±8.410
7±109103
4±30
7±30
2±33
3
Sediment
(Bq kgÿ 1 dw)
Sr
2±4
2±7
4±6
2±3
3±11
Surface
2±4
3±26
3±4
2±4
4±6
Bottom
Water (Bq mÿ3)
90
0.3±3.510
0.4±300
0.4±1
0.8
0.3±0.8
3
Sediment
(Bq kgÿ1 dw)
Pu
3±7
2±5
4±10
3±4
2±8
Surface
3±5
2±18
5±8
7±12
5±16
Bottom
Water (mBq mÿ3)
239‡240
Table 1
Range of concentrations of radionuclides in Kara Sea waters and surface sediments (0±2 cm) (1992±1994)
1±18
0.1±15
0.03±0.5
1
0.4±1.3
Sediment
(Bq kgÿ1 dw)
Co
51±66
0.1±3.1103
51±4
52
Sediment
(Bq kgÿ1 dw)
60
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H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
699
Fig. 2. 90 Sr and 137 Cs in the Barents Sea surface waters (above) and the Kara Sea surface and bottom
waters (below) as extracted from the GLOMARD database.
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H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
stations). Two water pro®les were sampled, one in the Sea of Japan (N2) and one
east of Kamchatka (R4). At a few stations, surface sediments and sediment cores
were collected as well [19,20].
5.3.1. Sea of Japan
3
H; 90 Sr; 137 Cs and 239;240 Pu concentrations in surface and near bottom waters of
the Sea of Japan did not show signi®cant di€erences between the dumping sites and
the corresponding background stations. Typical vertical pro®les of 3 H; 90 Sr; 137 Cs
and 239;240 Pu with decreasing concentrations with depth are shown in Fig. 3. The
239;240
Pu pro®le is di€erent showing a surface minimum, mid-depth maximum at
800 m and a gradual decrease with increasing depth, since plutonium is scavenged
in the euphotic zone and is subsequently associated with sinking particles and
re-solubilized at depth.
The observed higher surface concentrations of radionuclides found in the Sea of
Japan in comparison with the NW Paci®c Ocean could be explained by speci®c
Fig. 3. 3 H; 90 Sr; 137 Cs and 239;240 Pu water pro®les in the central Sea of Japan station N2, sampled in 1994
during the joint Japan±Korea (Republic of )±Russian Federation expedition.
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701
oceanographic conditions in the Sea of Japan [25]. The higher radionuclide
concentrations found in deep waters suggest recycling on a shorter time scale than
in the NW Paci®c. All these observations suggest that a large part of the
anthropogenic radionuclides is stored in deep waters as the vertical mixing in the
Sea of Japan is much quicker than in the NW Paci®c Ocean.
The observed pro®les have been used to estimate fallout depositions by calculating
the water column inventories. In order to compare these inventories with the
deposition densities estimated by UNSCEAR [26], sediment inventories should also
be considered. Although, for 90 Sr and 137 Cs this addition will be only marginal, for
plutonium it could be more signi®cant. For 3 H; 90 Sr and 137 Cs, the water column
inventories of 270, 3.3 and 4.8 kBq mÿ2 were obtained and are similar to integrated
deposition densities of 250, 3.2 and 5.1 kBq mÿ2, respectively, as obtained from
UNSCEAR data [26].
For the 239;240 Pu inventory in water, a value of 0.12 kBq mÿ2 was obtained, which
is higher by about a factor of 2 than that expected from global fallout. This
estimation is consistent with previous data [27] explaining the additional input from
close-in fallout transported from the tropics to the North Paci®c Ocean.
Radionuclide concentrations in sediment di€er signi®cantly between sampling
sites, the main reason being the higher removal rates in shallow waters. Generally,
90
Sr; 137 Cs and 239;240 Pu concentrations in sediment at shallower water depths show
higher values, as expected. The 239;240 Pu inventories in sediment are lower than in the
water column by about a factor of 2; however, the variation in the total water and
sediment inventories between sampling sites is very small.
The 238 Pu=239;240 Pu activity ratios in all samples analyzed (arithmetic mean
0.0240.08) indicate no statistically signi®cant deviation from the expected global
fallout derived values. These data, with other observations, con®rm the conclusion
that at the sites visited there is no evidence of the release of 3 H; 90 Sr; 137 Cs and
239;240
Pu from radioactive wastes dumped in the Sea of Japan.
5.3.2. Sea of Okhotsk
Surface water concentrations of 3 H; 90 Sr and 137 Cs show moderate variations
between the sampling stations (less than a factor of two). There is no signi®cant
di€erence in concentrations between the dumping sites and nearby background
stations. For bottom water, the concentrations of 3 H; 90 Sr and 137 Cs are generally
lower and more variable between the sampling stations, re¯ecting the di€erence in
water depths. However, at comparable water depths, the dumping site data compare
well with the background station data.
239;240
Pu in surface waters of the shallow Sea of Okhotsk (100 ±1300 m) show
values between 0.6 and 2.6 mBq kgÿ1, comparable with the NW Paci®c data. Higher
concentrations observed in bottom waters could be explained by the high removal
rates in productive shallow waters. The 238 Pu=239;240 Pu activity ratios did not di€er
statistically from the values expected from global fallout. Similar conclusions could
be drawn for 239;240 Pu concentrations in sediment. The data for the shallow stations
in the Sea of Okhotsk show signi®cantly higher sediment inventories than in the Sea
of Japan or the NW Paci®c. However, the total inventories (water and sediment) did
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H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
not di€er considerably. Therefore, a similar conclusion can be made as for the Sea of
Japan: at the sites visited no evidence was found of any contribution from
radioactive wastes dumped in the Sea of Okhotsk.
5.3.3. NW Paci®c Ocean
Fig. 4 shows the 3 H; 90 Sr, 137 Cs and 239;240 Pu vertical concentration pro®les for the
station east of Kamchatka (R4). Pro®les are similar to the pro®les observed in the
NW Paci®c Ocean during the IAEA '97 expedition [27]. The 239;240 Pu pro®le shows a
maximum at around 750 m water depth, with a subsequent decrease down to the sea
¯oor. As mentioned earlier, the surface radionuclide concentrations are much lower
than in the Sea of Japan. When comparing the Sea of Japan pro®le (N2) with the
NW Paci®c pro®le (R4), the penetration of radionuclides to deep waters is much
quicker in the ®rst case. Water column inventories estimated from Fig. 4 are 130,
0.71 and 1.47 kBq mÿ2 for 3 H; 90 Sr and 137 Cs, respectively. The 239;240 Pu water
column inventory is estimated to be 53 Bq mÿ2. The other stations where only
surface and bottom water samples were taken, showed the expected results.
Fig. 4. 3 H; 90 Sr; 137 Cs and 239;240 Pu water pro®les east of Kamchatka, station R2, sampled in 1995 during
the joint Japan±Korea (Republic of )±Russian Federation expedition.
H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
703
Radionuclide concentrations in surface sediment vary by about a factor of ten
between stations. Most of the activity is found in the top layers of sediment. 137 Cs
and 239;240 Pu sediment inventories calculated for station R4 are 0.09 and
0.05 kBq mÿ2, respectively. The 239;240 Pu inventory is higher than for the stations
in the Sea of Japan and in central parts at mid-latitudes of the NW Paci®c Ocean.
When comparing the total inventories of 3 H; 90 Sr and 137 Cs of 130, 0.71 and
1.56 kBq mÿ2 with the deposition densities (estimated from UNSCEAR data [26]) of
110, 1.3 and 2.0 kBq mÿ2, respectively, the di€erences found for 90 Sr and 137 Cs are
greater than expected. The lower inventories observed may be due to the e€ect of
horizontal advection and the bottom topography of the ocean, as the deposition
from global fallout occurred about three decades ago [28]. The total 239;240 Pu
inventory is 107 Bq mÿ2, about twice the expected value for the 50±608N latitude
belt estimated from global fallout. This surplus in the inventory could be explained
by high biological productivity in these areas with subsequent scavenging of Pu to
deep waters and sediment.
The distributions and inventories of radionuclides observed at sites sampled in the
NW Paci®c area seemed consistent with known nuclear weapons fallout sources
(global and local) and with the natural oceanographic processes controlling the
behaviour of radionuclides in this part of the ocean.
6. Nuclear accidents
In the past there have been several accidents, at nuclear plants, with satellites,
aircraft and nuclear submarines, in which radioactive material has been dispersed (or
could be dispersed in the future) into the marine environment. The most important
was the Chernobyl accident which caused worldwide distribution of some of the
radionuclides released (e.g. 137 Cs). Other nuclear accidents which have occurred in
coastal sea areas (e.g. in Vladivostok Bay) or inland (e.g. at Chelyabinsk) have had
only regional e€ects on the radionuclide concentrations of the marine environment.
6.1. The Chernobyl accident
The Chernobyl nuclear accident in April 1986 was the largest nuclear accident to
occur so far and had signi®cant impacts on both the terrestrial and marine
environments. The total activity of nuclear debris released was high (about
1100 PBq) and the radioactive fallout was widely distributed after the accident
and dominated environmental radionuclide levels in various parts of the world. The
total release of 137 Cs was estimated to be about 85 PBq; 10 PBq for 90 Sr and
0.055 PBq for 239;240 Pu [29].
Of the more than 20 radionuclides which were released in signi®cant quantities
during the Chernobyl accident, only a few have been studied in the marine
environment. Among the most important are 90 Sr; 134 Cs; 137 Cs and 239;240 Pu. Other
radionuclides like 131 I, have half-lives which are too short to be investigated in the
marine environment, or had very low concentrations (e.g. 129 I). As the plutonium
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H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
input to the oceans following the Chernobyl accident was small and localized, this
paper will concentrate on discussing the impact of Chernobyl radiocaesium on the
marine environment. The caesium isotopes were both the most widespread and most
abundant of those released.
Radiologically, the sea the most a€ected by the Chernobyl accident was the Baltic
Sea, as the ®rst radioactive clouds from Chernobyl travelled to the north and caused
high deposition over the Scandinavian region. Atmospheric deposition played a
dominant role in the radioactivity of this sea. The 137 Cs inventory in the Baltic Sea
due to the Chernobyl accident increased to about 5 PBq, at least by a factor of 10
higher in comparison with the pre-Chernobyl value [30]. The mean 137 Cs
concentration in surface waters estimated for the reference year 1990 was highest
in the Baltic Sea (125 Bq mÿ3) [1]. Because of the closed nature of this sea and its
small exchange of water with the North Sea, the levels of 137 Cs have remained the
highest in Europe. 137 Cs contours shown on the map of the Baltic Sea (Fig. 5) for the
period 1986±1988, as extracted from the GLOMARD (most of the data were
supplied by the Federal Maritime and Hydrographic Agency, Hamburg, Germany),
illustrate the enhancement of 137 Cs concentrations in seawater, with clear evidence of
the e€ect of run-o€ from land, particularly from Sweden. The measured range in
1986 was from a few to 2400 Bq mÿ3, i.e. two-three orders of magnitude higher than
in other European seas.
The second most perturbed sea following the Chernobyl accident was the Black
Sea. The 137 Cs inventory in the Black Sea due to the Chernobyl accident increased to
about 3 PBq, higher by about a factor of 2 in comparison with the pre-Chernobyl
Fig. 5. 137 Cs contours of Baltic Sea surface waters after the Chernobyl accident (for the period 1986±1988)
as extracted from the GLOMARD database.
H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
705
value [31]. The mean 137 Cs concentration in seawater in 1990 was 52 Bq mÿ3,
comparable to that in the Irish Sea [1]. The highest deposited activity was observed
in 1986 in its northernmost area, about 500 Bq mÿ3, i.e. 30 times higher than preaccident values. The distribution of 137 Cs observed in the Western Black Sea in 1988
is shown in Fig. 6 using data stored in the GLOMARD (mostly supplied by the
Institute of Biology of the Southern Seas, Sevastopol, Ukraine). Two years after the
accident, 137 Cs levels of up to 130 Bq mÿ3 were observed not only in the Dniester
estuary, but also in the open sea with direct deposition of 137 Cs from the atmosphere.
90
Sr activity measured in 1988 in surface waters of the western Black Sea was mostly
between 10 and 50 Bq mÿ3. 90 Sr and 137 Cs surface concentrations in waters of the
Aegean Sea were much lower, between 5 and 11 Bq mÿ3. The distribution patterns
of 90 Sr and 137 Cs observed in surface waters of the Black Sea can be explained in
terms of two main sources, a short-term atmospheric deposition which dominated
after the accident, and a long-term transfer from the Kiev Reservoir and the
catchment area of the Dniepr, Dniester and Danube rivers.
For the Mediterranean Sea, the main contribution from Chernobyl was from
atmospheric deposition. Papucci et al. [32] estimated that at least 2.8 PBq of 137 Cs
was deposited in the Mediterranean Sea (it could be more as data for the southern
Mediterranean are missing). The contribution from the Black Sea was estimated by
Egorov et al. [31] to be about 0.03 PBq/years, i.e. 0.4 PBq up to the year 2000. The
mean 137 Cs concentration in surface water estimated for 1990 was 5.7 Bq mÿ3. The
137
Cs levels in regional seas, as estimated for 1990 by the CEC's MARINA-MED
project, ranged from 2.9 to 9 Bq mÿ3, clearly showing a west-east trend towards the
highest values in the Aegean Sea [33].
Fig. 6. 137 Cs contours of western Black Sea surface waters after the Chernobyl accident in 1988 as
extracted from the GLOMARD database.
706
H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
Generally, it can be concluded that the Chernobyl accident has had a measurable
impact on the marine environment. Radionuclide levels (mainly 137 Cs ) were 2±3
orders of magnitude higher than the pre-Chernobyl levels at locations receiving high
fallout after the accident.
6.2. Satellites and aircraft
There were a few satellites equipped with radionuclide power generators which
burned up in the atmosphere. The most important was the SNAP satellite carrying
0.5 PBq of 238 Pu which burned up at a high altitude over the Mozambique Channel
in 1964. Although this accident did not have any radiological consequences, it
increased the 238 Pu=239;240 Pu activity ratio in the Southern hemisphere from the
global fallout value of 0.025 by about a factor of 10.
Among the accidents of aircraft carrying nuclear weapons, a crash which occurred
in January 1966 near Palomares, Spain, on the southeastern Mediterranean coast
should be mentioned. The debris from the two nuclear weapons carried by the
aircraft was distributed over the land. Although 10 cm of soil was removed during
cleaning operations, heavy rains transported Pu and Am to the Mediterranean
continental shelf. The Pu inventory estimated from sediment cores collected on the
continental shelf was about 1.4 TBq [32].
Another accident involving an aircraft carrying nuclear weapons took place in
January 1968 at Thule in Greenland. Most of the Pu released to the environment
from the four unarmed nuclear weapons was recovered from the ice, however, some
Pu passed through the ice, entered the water and was buried in sediment. The
estimated 238;239;240 Pu inventory in sediment in 1979 was about 1 TBq [34]. The
source has been accurately located and its contribution to the Pu inventory in water
outside the area of impact is negligible.
6.3. Nuclear submarines
There were several accidents involving nuclear submarines which sank in the
world's oceans, mainly in the Atlantic at depths of several kilometres below sea level.
The greatest interest was caused by the nuclear submarine ``Komsomolets'' which
sank on 7 April 1989 to a depth of 1685 m at 738430 1600 N, 138150 5200 E, southwest of
Bear Island in the Norwegian Sea, about 300 nautical miles from the Norwegian
coast. The relatively shallow depth, the fact that the area is an important ®shing
ground and close to the Norwegian coast, were the reasons for the various
assessments of the impact of any leakage to the marine environment. The wreck
contains one nuclear reactor and two nuclear warheads, partially fractured. The
radionuclide inventory includes 1.6 PBq of 90 Sr, 2 PBq of 137 Cs, about 16 TBq of
239
Pu in the two warheads and 5 TBq of actinides in the reactor core [35]. Several
expeditions were organized by the Russian Federation to cover the holes in the doors
and torpedo tubes of the submarine with titanium metal caps; to sample water,
sediment and biota and to install resin packages for in situ sampling of
radionuclides. IAEA-MEL participated in some of the expeditions and analysed
H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
707
samples brought to the laboratory. Traces of radionuclides over background levels
were found in water and sediment samples, which suggest that a small leakage has
occurred. Preliminary computer modelling of the dispersion of radionuclides from
the submarine has shown that the radionuclides will be driven by prevailing currents
to the Arctic Ocean [36].
7. Global distribution of
137
7.1. Global distribution of
Cs and dose assessment
137
Cs
In the framework of the Coordinated Research Programme ``Sources of
radioactivity in the marine environment and their relative contributions to overall
dose assessment from marine radioactivity (MARDOS)'', IAEA-MEL coordinated a
marine radioactivity study with the aim of comparing concentrations of 137 Cs in the
world's oceans and radiation doses delivered to the human population through
ingestion of anthropogenic 137 Cs and natural 210 Po in sea food [1]. These two
radionuclides were chosen, as they are the most representative of each of the two
classes of marine radioactivity on a global scale. 137 Cs is the most abundant
anthropogenic radionuclide in the marine environment and 210 Po is the main
contributor to doses from natural radionuclides by ingestion of seafood.
Concentrations of 137 Cs and 210 Po in seawater and biota (®sh and shell®sh) have
been estimated for the FAO ®shing areas on the basis of measurements carried out in
recent years. While 210 Po is uniformly distributed in seawater at a concentration of
about 1 Bq mÿ3, 137 Cs concentrations in the world's oceans and seas di€er
considerably (Fig. 7). The data presented in Fig. 7 has been up-dated to the year
2000 from the MARDOS report [1] using an e€ective half-life of 137 Cs in surface
water of 25 years. The main source of 137 Cs in the marine environment is still global
fallout. Higher 137 Cs concentrations observed in the NE Atlantic Ocean (the Irish,
North and Barents Seas) are due to the release and transport of 137 Cs from Sella®eld
and La Hague reprocessing plants. The Baltic Sea and the Black Sea (as well as the
Mediterranean Sea) were the main reservoirs for radionuclides released after the
Chernobyl accident.
Data concerning 137 Cs in the oceans seem to be quite reliable. The behaviour of
this radionuclide in the marine environment is well known, its concentration factors
are well established, and predictions of its fate in the case of accidental releases can
be easily achieved. Data on 210 Po are much less abundant and concentration factors
from the literature do not seem to be supported adequately by ®eld studies, at least in
some cases. A wide range of 210 Po concentrations in the marine environment can be
observed and the reason for such ranges of values is not yet suciently understood.
7.2. Dose assessment
Collective doses were calculated for each FAO area using radioactivity data for
water and biota. A reasonably good agreement has been found between the results
708
H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
Fig. 7. Average 137 Cs concentrations in surface waters of the world's oceans and seas adjusted to the year
2000.
calculated by both methods. The collective doses calculated for each ®shing area
from 137 Cs and 210 Po (water data) due to ®sh and shell®sh consumption are shown in
Fig. 8 (adjusted to the year 2000) taken from the MARDOS report [1]. The collective
e€ective dose commitment for 137 Cs in marine food estimated for the year 2000 is
about 120 man Sv with an estimated uncertainty of 50%. The corresponding dose
from 210 Po is about 30 000 man Sv with an estimated uncertainty within a factor of 5.
The average annual individual doses estimated for the world population are of the
order of 0.03 mSv from 137 Cs and 9 mSv from 210 Po. The annual dose of 137 Cs for a
hypothetical critical group living on the NE Atlantic coast and consuming 100 kg of
®sh and 10 kg of shell®sh per year would be 3 mSv, while the contribution from 210 Po
would be 160 mSv. These values are well below the value of 1 mSv accepted for the
public. The results con®rm that the dominant contribution to doses comes from
natural 210 Po in ®sh and shell®sh and that the contribution of anthropogenic 137 Cs is
negligible (100±1000 times lower).
The global collective dose commitments from 137 Cs in sea foods contaminated by
liquid discharges from Western European civil nuclear sites until 1984 have been
estimated to be approximately 3000 man Sv and the corresponding dose
commitment from the Chernobyl accident to be 2000 man Sv. On the other hand,
the total collective dose commitment from 137 Cs in sea foods due to all nuclear
weapons tests in the atmosphere can be estimated to be 9000 man Sv [37]. Hence, the
total dose commitment from marine-derived 137 Cs from these three sources is
1.4104 man Sv, which corresponds to half the dose received in one year from 210 Po
in marine foods. It should also be noted that there are other natural radionuclides
like 210 Pb and 226 Ra, which contribute to population exposure. Although leading to
doses signi®cantly lower than 210 Po, they can still result in exposures more important
than those due to 137 Cs.
H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
709
Fig. 8. Average 137 Cs and 210 Po concentrations in surface waters of the world's oceans and seas and
collective e€ective dose commitments for the world population from ingestion of 137 Cs and 210 Po in ®sh
and shell®sh adjusted to the year 2000.
The results obtained in the framework of the MARDOS project have provided the
most complete data set available to Member States on radionuclide levels in the
marine environment and on doses to the world population from marine radioactivity
through ingestion of marine foods. The results have been used as the international
reference source on the average radionuclide levels in the marine environment and
corresponding doses from ®sh and shell®sh consumption.
8. Conclusions
Global fallout is still the main source of anthropogenic radionuclides in the marine
environment, although in some regions like the Irish and North Seas, authorized
releases from nuclear reprocessing facilities dominate. In the Baltic and Black Seas,
the dominant source of radioactivity is the Chernobyl accident. The Baltic Sea still
has the highest concentration of 137 Cs worldwide (about 100 Bq mÿ3). Potential
sources, such as dumping sites, nuclear weapons test sites, sunken nuclear
submarines or lost nuclear weapons only represent sources of local importance with
negligible radiological impact.
An up-to-date estimate of doses to the public from anthropogenic 137 Cs
(originating from global fallout, the Chernobyl accident and authorized discharges)
and from natural 210 Po through consumption of marine food, has been presented.
710
H.D. Livingston, P.P. Povinec / Ocean & Coastal Management 43 (2000) 689±712
The estimated collective e€ective dose commitment for 137 Cs in marine food (®sh and
shell®sh) in 2000 from the Mediterranean and Black Seas was 5 man Sv, much
smaller than the 1100 man Sv derived from 210 Po ingestion. The highest doses (56
man Sv) in the world's oceans due to 137 Cs were found in the North Atlantic area,
which also includes the Irish, North, Baltic, Norwegian and Barents Seas. However,
they are still negligible in comparison with the 3300 man Sv derived from 210 Po
ingestion. The average annual individual doses estimated for the world population
for the year 2000 are of the order of 0.03 mSv from 137 Cs and 9 mSv from 210 Po. The
annual dose of 137 Cs for a hypothetical critical group living on the NE Atlantic coast
and consuming 100 kg of ®sh and 10 kg of shell®sh per year would be 3 mSv, while
the contribution from 210 Po would be 160 mSv. These values are well below the
accepted value for the public of 1 mSv.
From a radioactivity point of view, the world's oceans and seas are only slightly
contaminated by anthropogenic radionuclides with negligible radiological impact on
the world population.
Acknowledgements
The authors are greatly indebted to the Governments of Germany, Japan,
Norway, Korea (Republic of ), the Russian Federation and the USA for their
various invitations to and support of IAEA-MEL's participation in the international
investigatory cruises, as well as to several institutes supplying radionuclide data and
for their collaboration in the development of the GLOMARD database. The work
presented here was partially carried out in the framework of the project ``Research
on Worldwide Marine Radioactivity'' and the support of this project by the Science
and Technology Agency of Japan is highly acknowledged. IAEA-MEL operates
under an agreement between the IAEA and the Government of the Principality of
Monaco.
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