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UNITED
NATIONS
SC
UNEP/POPS/POPRC.9/INF/19
Distr.: General
8 November 2013
Stockholm Convention
on Persistent Organic
Pollutants
English only
Persistent Organic Pollutants Review Committee
Ninth meeting
Rome, 14–18 October 2013
Agenda item 7 (a)
Consideration of chemicals newly proposed for inclusion
in Annexes A, B and/or C to the Convention:
Decabromodiphenyl ether (commercial mixture,
c-decaBDE)
Debromination of decabromodiphenyl ether (BDE-209) in the
environment
Note by the Secretariat
The annex to the present note sets out a paper prepared by Mr. Ian Rae (Australia) entitled
“Debromination of decabromodiphenyl ether (BDE-209) in the environment”. The paper is presented
as received and has not been formally edited.
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Annex
Debromination of decabromodiphenyl ether (BDE-209) in the
environment
Update on relevant literature
Ian D. Rae, August 2013
1.
Introduction
1.
The reductive debromination of decabromodiphenyl ether (BDE-209) was addressed in
discussion paper UNEP/POPS/POPRC.7/INF/18, in which it was concluded that although
debromination took place in the environment, the concentrations so generated of ‘dangerous’ BDEs that is, congeners with 4-8 bromines – did not build up but were continuously metabolised to
substances of less concern.
2.
Research in this area has continued, and the results have been reported in refereed publications.
In addition, there have been regulatory assessments which concluded that the presence in the
environment of debromination products of BDE-209 was significant enough to be one of the several
reasons for removing this flame retardant from commercial use.
3.
The present discussion paper contains an assessment of thirteen articles published in 2009-2012
in which debromination of BDE-209 is reported.
2.
Literature review
2.1
Fish feeding studies
4.
Two articles from the Stapleton group (P.D. Noyes 2011, S.C. Roberts, P.D. 2011) report
feeding experiments with fish in which BDE-209 was metabolised by reductive debromination. In
both cases the most abundant metabolites were BDEs with five or six bromines. The results support a
hypothesis that bromines in certain positions of heavily brominated benzene rings are replaced rapidly
and that further debromination is slow, resulting in some accumulation of BDEs with five or six
bromines which are already listed under the Stockholm Convention. Thyroid hormones were affected
and morphological changes in liver and other tissues were observed.
5.
The outcomes of fish-feeding experiments reported by other researchers are consistent with
these findings. Zeng et al. (4) showed that hexa-BDEs were the main metabolites of of octa- and
deca-BDEs in carp, but that hydroxy-BDEs were also formed. Tetra-BDEs were the main metabolites
detected by Munschy et al. (10) when a mixture of BDEs was added to food of the common sole.
BDE-99 (a penta-BDE) was a major metabolite of BDE-209 in rainbow trout; a number of
methoxy-BDEs were also detected (11). Feng et al. (1) reported degradation of BDE-209 to BDEs of
unstated congener composition, and also the formation of hydroxy- and methoxy-BDEs. Some thyroid
hormone levels were affected, and were negatively correlated with the concentrations of
hydroxyl-BDEs.
6.
BDE-47 (a tetra-BDE) was the major metabolite present in wild fish from an Italian river (5)
and its presence was ascribed to BDE-209 entering the food web. If debromination is indeed
operating, it could have occurred in the fish or lower down the food web, from whence it could enter
the fish by selective uptake.
2.2
Bird eggs
7.
‘Non-commercial’ metabolites detected in the eggs of Californian peregrine falcons (13)
provide evidence that BDE-209 is debrominated, but whether this occurs in the environment, with
metabolites being taken up in food, or in the animals themselves, is unclear. Similar remarks apply to
observed concentrations of penta- and hexa-BDEs which could result from selective uptake from the
environment and not necessarily from debromination of BDE-209.
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2.3
Sediments
8.
Lee et al. (2) detected a range of BDEs in sediments from a river near a Chinese industrial plant
from which flame retardants might be released, and since the major BDE in use is BDE-209 they
deduced that debromination of that substance had taken place in the environment. Most of the
metabolites were still heavily brominated.
9.
There were two reports of experiments with sediment taken from polluted Chinese rivers and
spiked with BDE-209. Qiu et al. (3) reported that concentrations of tetra-, octa- and nona-BDEs
increased as metabolism proceeded. Deng et al. (7) isolated an aerobic bacterium from sediments and
employed it in studies with BDE-209, from which the major metabolite was hexa-BDE.
2.4
Soils
10.
Two articles report results of experiments in which plants were grown in BDE-free soil spiked
with BDE-209. Wang et al. (9) found that major metabolites in the soil were BDEs 206-208, from
which only one or two bromines had been removed, but that rye grass grown in the soil contained
hexa- and tetra-BDEs. It was not clear whether debromination had occurred in the soil, followed by
selective uptake by the plant, or in the plant itself. Similar explanations were advanced in a report (12)
of earlier experiments by these researchers, who detected BDEs and hydroxy-BDEs in plants.
Amounts were correlated with root lipid concentration.
3.
Conclusions
11.
There is evidence that congeners of concern, being those with mid-level bromination, are major
metabolites of BDE-209 that survive in the environment at significant levels. There is also evidence
that shows effects on thyroid hormones might be mediated by hydroxy-BDEs which are metabolites of
BDEs such as BDE-209.
12.
These conclusions add weight to the case for removing decabromodiphenyl ether from
commercial use.
Annotated references
1.
C. Feng, Y. Xu, G. Zhao, J, Zha, F. Wu and Z. Wang, Relationship between BDE-209
metabolites and thyroid hormone levels in rainbow trout (Oncorhynhus mykiss), Aquatic Toxicology,
2012, 122-123, 28-35.
Single injections of BDE-209 in corn oil administered at five nominal gradient concentrations,
50,100, 200, 500 and 1000 ng/g. Liver, blood and kidneys sampled after 21 days’ normal
feeding.
Dose
ng/g
BDE-209 (ng/g)
Total PBDEs (ng/g from graph)
Liver
Blood
Kidneys
Liver
Blood
Kidneys
50
38.51
ND
30.71
110
35
90
100
80.29
ND
41.29
275
80
125
200
57.21
ND
31.15
175
130
115
500
49.03
ND
17.61
160
60
65
1000
48.27
ND
18.09
170
65
70
Hydroxy- and methoxy-BDEs were also detected, the former at concentrations comparable to those of
the BDEs. Thyroid hormone TT3 and TT4 levels were little affected, but levels of FT3 and FT4 were
reduced. The hormone levels were negatively correlated with concentrations of hydroxy-BDEs.
2.
I-S. Lee, K-S. Kim, S-J. Kim, J.H. Yoon, K.H. Choi, S-D. Choi and J-E. Oh, Evaluation of
mono-to deca-brominated diphenyl ethers in riverine sediment of Korea with special reference to the
debromination of DeBDE-209, Science of the Total Environment, 2012, 432, 128-134.
Total BDE concentrations in inland sediments were 0.46-1760 ng/g dry weight, with mean
55±230 and median 12 ng/g. Consolidated data show that the BDEs consisted of BDE-209,
70.9±12.4%; nona- and octa-congeners, 14.6±5.0%; and tetra-, penta- and hepta-congeners
(#47, 99, 183), 1.3-4.3%. Since the lower brominated congeners are now little used in Korea,
their presence in the sediments is ascribed to debromination of deca-BDE, which is the most
common flame retardant of this group.
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3.
M. Qiu, X. Chen, D. Deng, J. Guo, G. Sun, B. Mai and M. Xu, Effects of electron donors on
anaeorbic debromination of polybrominated diphenyl ethers (PBDEs), Biodegradation, 2012, 23,
351-361.
Aliquots (20 g) of sediment containing a range of PBDEs collected near an electronics
recycling plant in China were spiked with 10 μM (9.6 mg) of BDE-209 and selected adjuncts
such as methanol, ethanol, lactate or pyruvate and microbial action was allowed to proceed.
Debromination was monitored by analysis for bromide ion, and the overall rate was shown not
to be affected by the added substances. After 90 days, more than 50% of BDE-209 remained.
Significant increases in the proportions of congeners were observed only for tetra-, octa- and
nona-BDE.
4.
Y-H. Zeng, X-J. Luo, H-S. Chen, L-H. Yu, S-J. Chen and B-X. Mai, Gastrointestinal
absorption, metabolic debromination, and hydroxylation of three commercial polybrominated diphenyl
ether mixtures by common carp, Environmental Toxicology, 2011, 31(4), 731-738.
Groups of 30 fish were fed with food spiked with commercial penta-, octa- and deca-BDE
(mixtures) at rates of 100±10, 120±10 and 150±10 μg/day/fish respectively, for 20 days before
harvesting. Congeners detected after penta-BDE feeding were the same as those in the food
although ratios had changed. Hexa-BDEs were the main degradation products of octa- and
deca-BDEs. Hydroxy BDEs were detected in fish fed with penta-BDE but there was no
change in background levels of methoxy-BDEs.
5.
L. Viganò, C. Roscioli and L. Guzzella, Decabromodiphenyl ether (BDE-209) enters the food
web of the River Po and is metabolically debrominated in resident cyprinid fishes Science of the Total
Environment, 2011, 409, 4966-4972.
Although BDE-209 is present in sediments and invertebrates in the river, there is none in the
fish examined. Instead, less-brominated BDEs are present, several of which are not present in
commercial flame proofing mixtures and are arguably formed from BDE-209 by
debromination. BDE-47 was the major congener detected in livers, making up 75% of the
PBDEs detected (average 185 ng/g of 247 ng/g). BDE-100 (8%) and BDE-154 (5%) were the
next most abundant congeners. Since the original quantities of BDE-209 are not known, no
quantitative data on conversion rates could be reported.
6.
P.D. Noyes, D.E. Hinton and H.M. Stapleton, Accumulation of debromination of
decabromodiphenyl ether (BDE-209) in juvenile fathead minnows (Pimephales promelas) induces
thyroid disruption and liver alternations, Toxicological Sciences, 2011, 122(2), 265-274.
Young fish received BDE-209 at microgram levels in food for 28 days followed by 14 days
depuration before harvesting at 0, 14, 14, 28 and 42 days. Over 28 days, each fish
accumulated approximately 0.45 nM of BDE-209 (429 ng) and summed metabolites were
0.026 nM. Metabolites were penta- to octa-BDEs with hexa-BDE-154 being the most
abundant. Metabolism of BDE-209 appeared to proceed rapidly to penta-BDEs but not
proceed further to less- brominated congeners. De-iodination of thyroid hormones was
reduced, and morphological changes in thyroid and liver were observed.
7.
D. Deng, J. Guo, G. Sun, X. Chen, M. Qiu and M. Xu, Aerobic debromination of deca-BDE:
isolation and characterization of an indigenous isolate from a PBDE contaminated sediment,
International Biodeterioration & Biodegradation, 2011, 65, 465-469.
BDE-209 was exposed to an aerobic bacterium isolated from a heavily polluted river near
electronic dismantling workshops, in media containing carbon sources such as acetate,
pyruvate or lactate. Bromide ion was released, the concentration of BDE-209 was greatly
diminished, octa- and hepta-BDE were detected in the mixture after 36 hours, and after
72 hours the major product was hexa-BDE, suggesting successive debrominations had taken
place.
8.
S.C. Roberts, P.D. Noyes, E.P. Gallagher and H.M. Stapleton, Species-specific differences and
structure-activity relationships in the debromination of PBDE congeners in three fish species,
Environmental Science & Technology, 2011, 45, 1999-2005.
In separate experiments, livers of rainbow trout, common carp and Chinook salmon were
incubated with eleven individual PBDEs with 3-10 bromines. Metabolites were detected from
those congers (99, 153, 183, 303, 208 and 209) that contain at least one bromine in a position
meta to the oxygen. Rates of replacement of bromines in particular positions on the rings of
these six congeners are reported. Carp accumulate BDE-47 and -154, while trout and salmon
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accumulate BDE-99 and -154 to a greater extent. The results support other observations from
this group that debromination in fish stops at the tetra- or penta-BDE level.
9.
S. Wang, S. Zhang, H. Huang and P. Christie, Behaviour of decabromidiphenyl ether
(BDE-209) in soil: effects of rhizosphere and mycorrhizal colonization of ryegrass roots,
Environmental Pollution, 2011, 159, 749-753.
BDE-109 was debrominated in both plant tissue (24 metabolites) and soil (12 metabolites). In
soil, BDE-209 concentration began at 3584.0±201.6 ng/g. BDEs 206-208, which (as
impurities) initially comprised less than 2.3% of the BDE-209, made up about 60% of the
metabolites in soil. Hexa-BDE and, to a lesser extent, tetra-BDE, were the major metabolites
in roots and shoots. The authors suggested that some debromination to these levels might have
taken place in soil, followed by ready uptake into plant tissue.
10.
C. Munschy, K. Héas-Moisan, C. Tixier, N. Olivier, O. Gastineau, N. Le Bayon and V. Buchet,
Dietary exposure of juvenile common sole (Solea solea L.) to polybrominated diphenyl ethers
(PBDEs); Part 1. Bioaccumulation and elimination kinetics of individual congeners and their
debrominated metabolites, Environmental Pollution, 2011, 159, 229-237.
Food for juvenile common sole was spiked with a mixture of BDE-28, 47, 99, 100, 153, and
209 for three months, followed by five months depuration. No steady state concentration for
any congener was observed during the three months. The major metabolites were BDE-49
and an unidentified tetra-BDE.
11.
C. Feng, Y. Xu, Y. He, Q. Luo, J, Zha and Z. Wang, Debrominated and methoxylated
polybrominated diphenyl ether metabolites in rainbow trout (Oncorhynchus mykissi) after exposure to
decabromodiphenyl ether, Journal of Environmental Sciences, 2010, 222(9), 1425-1434.
BDE-209 (100 or 500 ng/g) in corn oil was injected into fish and samples were taken on days
1 and 28. BDEs 206-208 were present in tissue samples. In the low dose group, BDE-99 was
the major metabolite in muscle, but in liver and blood the major metabolites had 1-4 bromines
and this was replicated in the high dose group. Seven methoxy-BDEs were detected.
12.
H. Huang, S. Zhang, P. Christie, S. Wang and M. Xie, Behavior of decabromodiphenyl ether
(BDE-209) in the soil-plant system: uptake, translocation, and metabolism in plants and dissipation in
soil, Environmental Science and Technology, 2010, 44, 663-667.
BDE-209 was accumulated from treated soil by plants (ryegrass, alfalfa, pumpkin, summer
squash, maize and radish), in amounts correlated with root lipid content. Di- to nona-BDEs
were detected in plants together with five hydroxylated BDEs. BDE-206-208 were major
metabolites, while di- to penta-BDEs made up 7.8-21.1 mole % of congeners in plants, but less
in soil, from which it is speculated that lower-brominated congeners might be absorbed by
plants.
13.
A. Holden, J-S.Park, V. Chu, M. Kim, G. Choi and Y. Shi, Unusual hepta- and octabrominated
diphenyl ethers and nonabrominated diphenyl ether profile in California, USA, peregrine falcons
(Falco peregrinus): more evidence for brominated diphenyl ether-209 debromination, Environmental
Toxicology and Chemistry, 2009, 28(9), 1906-1911.
Peregrine falcon eggs have higher concentrations of BDE-202 (octabromo) and an unidentified
hepta-BDE than occur in commercial mixtures, leading to the conclusioin that they arise from
debromination of BDE-209. On a lipid basis the eggs contain (on average) 7.85 ng/g ΣPBDE;
BDE-209, 0.47; nona-BDEs, 0.18; octa-BDEs, 0.80; hepta-BDEs, 0.95; hexa-BDEs, 1.95;
penta-BDEs, 1.90; and tetra-BDEs, 0.54 ng/g.
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