Brominated Flame Retardants:

216797

Brominated FlameRetardants:Assessing DecaBDE Debromination in the EnvironmentHEATHER M. STAPLETON (PhD, MS, BS)MAY 200628 Boulevard Charlemagne1000 Brussels (Belgium)Tel.: +32 2 234 3640Fax.: +32 2 234 3649info@env-health.orgwww.env-health.org

About the AuthorHeather Stapleton's expertise is in the fate andbiotransformation of organic contaminants inaquatic systems, focusing on persistent organicpollutants (POPs), such as polychlorinatedbiphenyls (PCBs) and polybrominated diphenylethers (PBDEs). She is presently carrying outresearch on DecaBDE debromination at DukeUniversity, Nicholas School Faculty, EnvironmentalSciences and Policy Division in her capacity as anEnvironmental Chemist.I. Context from European Public HealthAlliance - Environment Network.The draft addendum environmental risk assessmentreport for decabromodiphenyl ether (DecaBDE)was distributed to the Technical Committee forNew and Existing Substances (TC NES) on August11, 2005 (The addendum can be found at theEuropean INventory of Existing Commercialchemical Substances (EINECS),[http://ecb.jrc.it/existing-chemicals/]) . Theprevious risk assessment, agreed in May 2004, hadconcluded that further information was requiredbefore definitive conclusions could be drawn on theconcerns from DecaBDE to the environment. One of the key areas identified for furtherclarification was the extent and importance of thedebromination of DecaBDE in the environment.The conclusion in the draft addendum prepared bythe UK government highlights that it is still notpossible to give a reliable assessment of the overallsignificance of debromination based on expertjudgment. Although the conclusions state that thepublished data on debromination heightened theconcern, it did not necessary mean thatdebromination was a significant pathway in theenvironment. This view was also elaborated in aTNO report commissioned by the BrominatedScience Environment Forum1, an industry basedassociation. 1 A.O. Hanstveit MSc, Dr. C.T. Bowmer, Dr. A.P. Freidig. TNONetherlands Organisation for Applied Scientific Research. A review ofthe anaerobic and abiotic degradation of the flame retardantdecabromodiphenyl ether (CAS # 1163-19-5) in the context of an EUenvironmental risk assessment report, customer BSEF - BromineScience and Environmental Forum & The International Organization ofthe Bromine Chemical Industry. 17 August 2005 (ECB TRACKINGNO. COM013_ENV_IND 09)The intent of this overview is to provide a summaryon the significance and extent of DecaBDEdebromination in the environment. If DecaBDE isa 'significant' pathway for the formation of lowerbrominated congeners, there are both potentialadverse environmental and health consequences.The potential persistency and bioaccumulationproperties of the lower congeners must be takeninto consideration in the risk assessment.Moreover, there may be legal implications forputting on the market indirectly through DecaBDEand into the environment these lower congeners,such as PentaBDE and OctBDE, which are alreadyrestricted under existing EU regulation. II. IntroductionDecabromodiphenyl ether (BDE 209) is a multi-halogenated organic chemical used primarily as aflame retardant in a commercial mixture known asDecaBDE. It has been used as an additive flameretardant since the late 1970s, and because it is wellsuited to flame retard in particular plastics, itsmarket demand has increased significantly over thepast few decades with the increasing use of plasticsin electrical goods 1. Commercially producedDecaBDE consists primarily of BDE 209 (<97%)with minor contributions (0.3 to 3.0%) of octa- andnonaBDE congeners (or iso-forms), which areimpurities in the technical mixture. A particularconcern regarding BDE 209 is the potential fordegradation via debromination. Debromination is aprocess by which bromine atoms are sequentiallyremoved or cleaved from an organic compound,resulting in a smaller lower brominated moleculewhich is slightly more water soluble. These lowerbrominated congeners have the potential to be morepersistent and more bioaccumulative than theirlarger parent chemical. III. Environmental Levels of DecaBDENumerous studies have investigated the prevalenceof polybrominated diphenyl ether (PBDE)congeners in the environment 2, 3.

BDE 209 is a fully brominated PBDE congenercontaining ten bromine atoms (See Figure 1). Amajority of environmental samples, specifically Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 2

human and biological samples, contain PBDEcongeners that are dominated by congeners withfour to six bromine atoms 4, 5. PentaBDE andOctaBDE are two additional commercialbrominated flame retardant mixtures containingPBDE congeners with four to eight bromine atoms(see Table 1), and are believed to be the source ofthese congeners in biological samples. However,debromination of BDE 209 cannot be ruled out as asource of these lower brominated congeners. BDE 209 has been measured in house dust 6-8 atconcentrations up to 10,000 ppb, which could be apotential pathway of human exposure, particularlyfor young children. Toddlers have a predispositionto put dirty hands and toys in their mouth andinadvertently ingest larger amounts of house dust.This predilection has been responsible for largecases of lead poisoning in U.S. children,9-11 due tothe high lead levels in house dust. No studies haveinvestigated the levels of PBDEs in children underthe age of 5; however, modeling studies suggesttoddlers are receiving greater exposure to PBDEsthan adults because of the high levels in house dust12. In some homes studied, BDE 209 comprises90% of the total PBDE burden,7 therefore, BDE209 exposure could be unique to young children. ConclusionDebromination of BDE 209 cannot be ruled out asa source of lower brominated congeners. DecaBDE is mainly found in dust in the indoorenvironment including our homes and cars whichmay result in elevated exposures in children.IV. Photolytic Debromination of BDE 209

exposed BDE 209 spiked house dust to sunlight andfound that the half-life was approximately 220 hoursof continuous sunlight exposure, or assuming 10hours of sunlight a day, approximately 22 days.However, it is difficult to assess the magnitude andduration of sunlight that house dust would beexposed to in an average home. Most windows willblock out UV wavelengths of light which wouldhinder degradation. In contrast, car dust hasrecently been found to contain elevated levels ofBDE 209(http://www.ecocenter.org/releases/20060111_autotoxics.shtml), which is susceptible to greatersunlight exposure and in which debromination canbe expected to occur significantly. The degradation products of BDE 209 photolysisare primarily lower brominated PBDE congenersformed via debromination. In soils, sediment andhouse dust, the primary congeners identified arehepta-, octa- and nonaBDE congeners 13-15, and verylittle degrades to congeners with fewer than sixbromine atoms. When dissolved in water orBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 3 O2

3 4 5 2' 3' 4' 5' 66'

Polybrominated Diphenyl Ether (PBDE)

Brn n=1-10 Figure 1. Structure of PBDE molecule.

organic solvents, BDE 209 degrades quite rapidlyand leads to greater formation of the lowerbrominated congeners, including tri-, tetra- andpentaBDE congeners, and also polybrominateddibenzofurans (PBDFs) 13, 16, 17. In the environment,it is expected that BDE 209 will be found primarilybound to solids in the water column, and bound toparticles in the atmosphere. Therefore, degradationof BDE 209 dissolved in water (or organic solvents)is not expected to be of environmental relevance. ConclusionIt is difficult to assess the degree of BDE 209photolytic debromination in house dust, soils andsediments when exposed to light. However, in carsdebromination can be expected to occur moresignificantly. Debromination in water is notexpected to be of environmental relevance. V. Microbial and Reductive Debromination ofBDE 209One published study has investigated the microbialmediated debromination of BDE 209 underanaerobic (no oxygen) conditions. Gerecke et al. 18

used microflora from sewage sludge to examine thebacterial mediated degradation of BDE 209. Theirresults indicated that debromination of BDE 209did occur, leading to the formation of nona- andoctaBDE congeners. The observed first orderdegradation rate, 1.0 x 10-3 day-1, is equivalent to ahalf life of approximately 690 days. However, thisdegradation rate was accelerated by the use ofprimers to increase degradation potential. Withoutthe use of primers, the observed degradation ratewas 50% lower, resulting in a half-life ofapproximately 3.8 years. Therefore, anaerobicbacteria can initiate debromination of BDE 209,albeit at a slower rate than photolyticdebromination. Given the hydrophobic nature ofBDE 209, and the large volumes that enter watertreatment facilities, anaerobic degradation may beimportant in sewage sludge digesters. However, thetime that BDE 209 spends in the sewage sludge(residence time) will greatly impact it's ability toanaerobically degrade. Reductive debromination of BDE 209 has also beenreported to occur with mineral catalysts. Keum andLi 19 documented a stepwise debromination processusing zero-valent iron and sulfide minerals. Zero-valent iron was a good oxidant for degradation,resulting in a BDE 209 half-life of about one day.The use of iron sulfide and sodium sulfide reducedthe debromination/degradation rate to 2 and 33%of the rate observed for zero-valent iron. Both theiron and sulfides resulted in debromination down tocongeners with two and three bromines. In allexperiments, the initial rate of degradation was rapidand then decreased over time as lower brominatedcongeners were formed that appeared to be morestable. While this study demonstrates the possibilityand feasibility of reductive debromination byminerals, this process is unlikely to occur naturallyin the environment. PBDEs will have a greatertendency to be bound to natural organic matter andsoils in the environment before binding directly tothe mineral surface, which is necessary for themineral to act as an oxidant. ConclusionIn sewage anaerobic bacteria can initiatedebromination of BDE 209, albeit at a slower ratethan photolytic debromination, but due to the largevolumes of DecaBDE in sewage sludge this may besignificant. VI. Metabolic DebrominationDebromination of BDE 209 has also been observedin laboratory in vivo studies with fish and rats,suggesting it is metabolized. In four separatestudies, fish fed food spiked withdecabromodiphenyl ether were found to accumulatelower brominated congeners 20-23. The assimilationand debromination of BDE 209 varied among thethree fish species examined, which included rainbowtrout, common carp and lake trout. Common carpaccumulated no BDE 209 in their tissues, but theydid accumulate one penta-, three hexas-, two heptas-and one octaBDE congener that appeared to resultfrom the debromination of BDE 209. In twoseparate and independent research studies onrainbow trout, accumulation of BDE 209 wasobserved, although the uptake was less than 1% inboth studies. However, both studies observed anincrease in hexa-, hepta-, octa- and nonaBDEcongeners over time that comprised a higherpercentage of the PBDE body burden relative to theBDE 209 body burden. One study found anaccumulation of 0.13% of the BDE 209 dose 20,

while the second study observed an uptake of 3.2%of the BDE 209 dose 23. Lake trout were found toBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 4

accumulate approximately 5% of the BDE 209 doseand debromination was hypothesized to occur.However, the diet in this latter study consisted of acocktail of 13 BDEs and it was impossible tocharacterize debromination of BDE 209. Stapleton et al., 23 recently conducted several in vitroexperiments using fish liver microsomes tocharacterize metabolic biotransformation of BDE209. Microsomes are cell fractions which containactive enzymes from fish that typically metabolizeendogenous compounds (i.e. natural hormones).Using carp and rainbow trout liver microsomes,Stapleton found that as much as 65% of BDE 209was debrominated in a twenty four hour period.Carp microsomes rapidly debrominated as much as30% of the BDE 209 mass to form BDE 155 andBDE 154 (hexaBDEs). In contrast, rainbow troutdebrominated only 22% of the BDE 209 massprimarily to octa- and nonaBDE congeners. Thisstudy demonstrates that there are species specificdifferences in the biotransformation/debrominationcapacity of fish, and possibly, other organisms.Stapleton hypothesizes that thyroid hormoneenzymes are responsible for this observeddebromination, which is similar to endogenousmetabolism of thyroid hormones. In rats, metabolism of BDE 209 appears to occurthrough different mechanisms. Two studies haveexamined the uptake of BDE 209 in rats and bothidentified hydroxyl- and methoxyBDE congeners intissues and plasma and only trace levels ofnonaBDE congeners. This suggests that rats mayinitially debrominate BDE 209, but then othermetabolic pathways become more dominant,resulting in the formation of more polar metabolitesthat are likely to be excreted. ConclusionSome fish appear capable of debrominating BDE209 through metabolism. The extent of themetabolism varies among fish and it is difficult todetermine the extent of debromination that wouldoccur in the wild. VII. Human Debromination PotentialIn a recent study, Thuresson et al.24 measuredPBDE levels in workers occupationally exposed toBDE 209. Analysis of their serum identified severalhepta- and octa-BDE congeners that were notpresent in the decaBDE commercial mixture nor inthe reference groups. The congener patternobserved in these workers was very similar to thecongener pattern observed in the rainbow trout byStapleton et al.23. A follow up study examined theBDE concentrations in these workers when theyhad taken a vacation and reduced their exposure toBDE 209 24. This study found that while BDE 209concentrations decreased in these workers with ahalf life of approximately 15 days, concentrations ofthe hepta- and octaBDE congeners increased,suggesting that debromination of BDE 209 wasoccurring in humans. More studies are needed to determine if BDE 209debromination does occur in human tissues.Exposure to BDE 209 is suggested to be greater foryoung children relative to adults, due to the higherlevels present in house dust and thus, may need tobe investigated further. ConclusionStudies suggest that DecaBDE debrominates inhumans however, more studies are needed toconfirm this analysis.VIII. SummaryTable 1 compares the PBDE congeners that arepresent in the commercial mixtures to the congenersthat have been identified as products of BDE 209debromination. As evident in the table, all thecongeners present in the commercial products alsocan be formed via debromination of DecaBDE. Ofparticular concern in human and environmentalsamples is the accumulation of lower brominatedcongeners (i.e. tetra-, penta- and hexaBDEs). Basedon the current data available, the potential forsignificant formation of these congeners in theenvironment due to debromination is low. The onlystudies demonstrating formation/production ofthese congeners from debromination occurred whenBDE 209 was dissolved in organic solvents andexposed to sunlight and/or UV sources, which isnot environmentally relevant. Additionally,reductive debromination catalyzed by iron and ironsulfides also can lead to these congeners. However,the likelihood of BDE 209 being directly bound toBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 5

these types of mineral surfaces in the environment isalso low. In contrast, the formation of hexaBDE congeners(e.g. BDE 153, BDE 154 and BDE 155) fromdebromination of DecaBDE has more realisticprobabilities. Metabolic debromination resulted inthe formation of several hexaBDE congeners,including BDE 154, in several fish species 20, 21, 23. Inthese studies, less than 1% of the BDE 209exposure debrominated to the hexaBDE congeners,but as much as 2% debrominated into hepta-, octa-and nonaBDE congeners. In the past year, a fewstudies have documented a shift in the PBDEcongener patterns in human tissues. In moststudies, BDE 47 (tetraBDE) was the largestcontributor to the PBDE body burden; howeverrecent studies suggests some populations have aPBDE body burden dominated by BDE 153, ahexaBDE 25, 26. The reason for this is unknown butcould be related to debromination of BDE 209,exposure to different PBDE commercial sources, orto longer half-lives for BDE 153 relative to BDE47. Photolyitic debromination of DecaBDE in dust,soils and sediments also leads to the formation ofseveral hepta-, octa- and nonaBDE congeners,which is environmentally relevant. Because house,office and car dust are enriched in BDE 209, thepotential for debromination is high when exposedto sunlight. Current studies suggest that photolyticdebromination of BDE 209 leads to significantaccumulation of hepta-, octa- and nonaBDEcongeners which are persistent and potentiallybioaccumulative. There are very few studies whichhave investigated the bioaccumulation potential andenvironmental levels of hepta- through nonaBDEcongeners, which makes an assessment of their fatedifficult. More studies are needed to determine thelevels of these congeners in the environment(particularly in sediment and dust) in order todetermine if debromination of BDE 209 isoccurring. ConclusionThe potential for significant formation of BDE 47,BDE 99 and BDE 100 in the environment due todebromination is low as the only study showing thisis not environmentally relevant. The formation ofhexaBDE has more realistic probability and couldbe related to debromination of DecaBDE inhumans. Photolyitic debromination of DecaBDE indust, soils and sediments, leading to the formationof hepta-, octa- and nonaBDE congeners isenvironmentally relevant; not withstanding moreresearch on the significance of these lowercongeners fate in the environment.Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 6

Table 1. PBDE congeners identified in commercial mixtures and in debromination studies.Congener identifications in the PentaBDE and OctaBDE commercial mixtures are from reference27.

SubstitutionCongenerPentaBDEOctaBDEDecaBDEFormed FromDebrominationReference2,4,4'-tribromoBDE 28XX17,19

2,2',4,4'-tetrabromoBDE 47XX17,13,19

2,2',4,5'-tetrabromoBDE 49XX17

2,3',4,4'-tetrabromoBDE 66XX19

2,2'3,4,4'-pentabromoBDE 85XX14,17

2,2',4,4',5-pentabromoBDE 99XX17,13,19

2,2',4,4',6-pentabromoBDE 100XX17,19

2,2',3,4,4',5'-hexabromoBDE 138XX17,19

2,2',4,4',5,5'-hexabromoBDE 153XX17,13,19

2,2',4,4',5,6'-hexabromoBDE 154XX17,13,19,21, 232,2',4,4',6,6'-hexabromoBDE 155XX21, 232,2',3,4,4',5',6-heptabromoBDE 183XXX14,17,13,19

2,2',3,4,4',6,6'-heptabromoBDE 184X23

2,2',3,3',4,4',5,6'-octabromoBDE 196XX14,17,18

2,2',3,3',4,4',6,6'-octabromoBDE 197XX14,17,18

2,2',3,3',4,5',6,6'-octabromoBDE 201X23

2,2',3,3',5,5',6,6'-octabromoBDE 202X23

2,2',3,3',4,5,5',6-octabromoBDE 203XXX18

2,2',3,3',4,4',5,5',6-nonabromoBDE 206XXX14,17,13

2,2',3,3',4,4',5,6,6'-nonabromoBDE 207XXX14,17,13,18

2,2',3,3',4,5,5',6,6'-nonabromoBDE 208XXX14,17,13,18

2,2',3,3',4,4',5,5',6,6'-decabromoBDE 209XX

Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 7

Table 2. Photolytic half-lives of BDE 209 under various conditions.Light SourceSubstrateHalf Life (Reference)UV lampOrganic Solvent<0.25 H13;

UV lampSilica Gel<0.25 H13;

UV lampSand12 H13;

UV lampSediment40-60 H13; 150 D14;

UV lampSoil150-200 H13

UV lampMethanol/water0.5 H16

UV lampMinerals36 D - 3.9 Y14

SunlightHydrated on Quartz35 H28;

SunlightHydrated with Humics on Quartz70 H28

SunlightHumic Acid Coated Sand435 H28

SunlightHexane<0.25 H17

SunlightMinerals261-990 D14

SunlightSand13-37 H13

SunlightSediment30-80 H13

SunlightHouse Dust220 H 15

H- Hours; D- Days; Y- YearsBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 8

REFERENCES

(1)W.H.O. Brominated Diphenyl Ethers; World Health Organization: Vammala, 1994.(2)Hale, R. C.; Alaee, M.; Manchester-Neesvig, J. B.; Stapleton, H. M.; Ikonomou, M. G. Environment International 2003, 29, 771-779.(3)Hites, R. A. Environmental Science & Technology 2004, 38, 945-956.(4)Sjodin, A.; Jones, R. S.; Focant, J. F.; Lapeza, C.; Wang, R. Y.; McGahee, E. E.; Zhang, Y. L.; Turner, W. E.; Slazyk, B.;Needham, L. L.; Patterson, D. G. Environmental Health Perspectives 2004, 112, 654-658.(5)Schecter, A.; Vuk, M. P.; Papke, O.; Ryan, J. J.; Birnbaum, L.; Rosen, R. Environmental Health Perspectives 2003, 111, 1723-1729.(6)Sharp, R. L., S.; ; Environmental Working Group, 2004, pp 1-57.(7)Stapleton, H. M.; Dodder, N. G.; Offenberg, J. H.; Schantz, M. M.; Wise, S. A. Environmental Science & Technology 2005, 39,

925-931.(8)Wilford, B. S., M.; Harner, T.; Zhu, J.; Jones, K. C. Environmental Science & Technology 2005, 39, 7027-7035.(9)Charney, E.; Sayre, J.; Coulter, M. Pediatrics 1980, 65, 226-231.(10)Kranz, B. D.; Simon, D. L.; Leonardi, B. G. Journal of Exposure Analysis and Environmental Epidemiology 2004, 14, 300-311.(11)Rhoads, G. G.; Ettinger, A. S.; Weisel, C. P.; Buckley, T. J.; Goldman, K. D.; Adgate, J.; Lioy, P. J. Pediatrics 1999, 103, 551-555.(12)Jones-Otazo, H. A.; Clarke, J. P.; Diamond, M. L.; Archbold, J. A.; Ferguson, G.; Harner, T.; Richardson, G. M.; Ryan, J. J.;Wilford, B. Environmental Science & Technology 2005, 39, 5121-5130.(13)Soderstrom, G.; Sellstrom, U.; De Wit, C. A.; Tysklind, M. Environmental Science & Technology 2004, 38, 127-132.(14)Ahn, M. Y.; Filley, T. R.; Jafvert, C. T.; Nies, L.; Hua, I.; Bezares-Cruz, J. Environmental Science & Technology 2006, 40, 215-220.(15)Stapleton, H. M. In Degradation of Decabromodiphenyl Ether (BDE 209) in House Dust Following Sunlight Exposure A Report Prepared for the Environment Agency, C. A. S., Ed.; Duke University, 2005, pp 1-22.(16)Eriksson, J.; Green, N.; Marsh, G.; Bergman, A. Environmental Science & Technology 2004, 38, 3119-3125.(17)Bezares-Cruz, J.; Jafvert, C. T.; Hua, I. Environmental Science & Technology 2004, 38, 4149-4156.(18)Gerecke, A. C.; Hartmann, P. C.; Heeb, N. V.; Kohler, H. P. E.; Giger, W.; Schmid, P.; Zennegg, M.; Kohler, M.Environmental Science & Technology 2005, 39, 1078-1083.(19)Keum, Y. S.; Li, Q. X. Environmental Science & Technology 2005, 39, 2280-2286.(20)Kierkegaard, A.; Balk, L.; Tjarnlund, U.; De Wit, C. A.; Jansson, B. Environmental Science & Technology 1999, 33, 1612-1617.(21)Stapleton, H. M.; Alaee, M.; Letcher, R. J.; Baker, J. E. Environmental Science & Technology 2004, 38, 112-119.(22)Tomy, G. T.; Palace, V. P.; Halldorson, T.; Braekevelt, E.; Danell, R.; Wautier, K.; Evans, B.; Brinkworth, L.; Fisk, A. T.Environmental Science & Technology 2004, 38, 1496-1504.(23)Stapleton, H. M., Brazil, B., Holbrook, R.D., Benedict, R., Konstantinov, A, Mitchelmore, C. Environmental Science &Technology 2006, Submitted.

(24)Thuresson, K.; Bergman, A.; Jakobsson, K. Environmental Science & Technology 2005, 39, 1980-1986.(25)Johnson-Restrepo, B.; Kannan, K.; Rapaport, D. P.; Rodan, B. D. Environmental Science & Technology 2005, 39, 5177-5182.(26)Fangstrom, B.; Hovander, L.; Bignert, A.; Athanassiadis, I.; Linderholm, L.; Grandjean, P.; Weihe, P.; Bergmant, A.Environmental Science & Technology 2005, 39, 9457-9463.(27)Korytar, P.; Covaci, A.; de Boer, J.; Gelbin, A.; Brinkman, U. A. T. Journal of Chromatography A 2005, 1065, 239-249.(28)Hua, I.; Kang, N.; Jafvert, C. T.; Fabrega-Duque, J. R. Environmental Toxicology and Chemistry 2003, 22, 798-804.Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 9

Brominated FlameRetardants:Assessing DecaBDE Debromination in the EnvironmentHEATHER M. STAPLETON (PhD, MS, BS)MAY 200628 Boulevard Charlemagne1000 Brussels (Belgium)Tel.: +32 2 234 3640Fax.: +32 2 234 3649info@env-health.orgwww.env-health.org

About the AuthorHeather Stapleton's expertise is in the fate andbiotransformation of organic contaminants inaquatic systems, focusing on persistent organicpollutants (POPs), such as polychlorinatedbiphenyls (PCBs) and polybrominated diphenylethers (PBDEs). She is presently carrying outresearch on DecaBDE debromination at DukeUniversity, Nicholas School Faculty, EnvironmentalSciences and Policy Division in her capacity as anEnvironmental Chemist.I. Context from European Public HealthAlliance - Environment Network.The draft addendum environmental risk assessmentreport for decabromodiphenyl ether (DecaBDE)was distributed to the Technical Committee forNew and Existing Substances (TC NES) on August11, 2005 (The addendum can be found at theEuropean INventory of Existing Commercialchemical Substances (EINECS),[http://ecb.jrc.it/existing-chemicals/]) . Theprevious risk assessment, agreed in May 2004, hadconcluded that further information was requiredbefore definitive conclusions could be drawn on theconcerns from DecaBDE to the environment. One of the key areas identified for furtherclarification was the extent and importance of thedebromination of DecaBDE in the environment.The conclusion in the draft addendum prepared bythe UK government highlights that it is still notpossible to give a reliable assessment of the overallsignificance of debromination based on expertjudgment. Although the conclusions state that thepublished data on debromination heightened theconcern, it did not necessary mean thatdebromination was a significant pathway in theenvironment. This view was also elaborated in aTNO report commissioned by the BrominatedScience Environment Forum1, an industry basedassociation. 1 A.O. Hanstveit MSc, Dr. C.T. Bowmer, Dr. A.P. Freidig. TNONetherlands Organisation for Applied Scientific Research. A review ofthe anaerobic and abiotic degradation of the flame retardantdecabromodiphenyl ether (CAS # 1163-19-5) in the context of an EUenvironmental risk assessment report, customer BSEF - BromineScience and Environmental Forum & The International Organization ofthe Bromine Chemical Industry. 17 August 2005 (ECB TRACKINGNO. COM013_ENV_IND 09)The intent of this overview is to provide a summaryon the significance and extent of DecaBDEdebromination in the environment. If DecaBDE isa 'significant' pathway for the formation of lowerbrominated congeners, there are both potentialadverse environmental and health consequences.The potential persistency and bioaccumulationproperties of the lower congeners must be takeninto consideration in the risk assessment.Moreover, there may be legal implications forputting on the market indirectly through DecaBDEand into the environment these lower congeners,such as PentaBDE and OctBDE, which are alreadyrestricted under existing EU regulation. II. IntroductionDecabromodiphenyl ether (BDE 209) is a multi-halogenated organic chemical used primarily as aflame retardant in a commercial mixture known asDecaBDE. It has been used as an additive flameretardant since the late 1970s, and because it is wellsuited to flame retard in particular plastics, itsmarket demand has increased significantly over thepast few decades with the increasing use of plasticsin electrical goods 1. Commercially producedDecaBDE consists primarily of BDE 209 (<97%)with minor contributions (0.3 to 3.0%) of octa- andnonaBDE congeners (or iso-forms), which areimpurities in the technical mixture. A particularconcern regarding BDE 209 is the potential fordegradation via debromination. Debromination is aprocess by which bromine atoms are sequentiallyremoved or cleaved from an organic compound,resulting in a smaller lower brominated moleculewhich is slightly more water soluble. These lowerbrominated congeners have the potential to be morepersistent and more bioaccumulative than theirlarger parent chemical. III. Environmental Levels of DecaBDENumerous studies have investigated the prevalenceof polybrominated diphenyl ether (PBDE)congeners in the environment 2, 3.

BDE 209 is a fully brominated PBDE congenercontaining ten bromine atoms (See Figure 1). Amajority of environmental samples, specifically Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 2

human and biological samples, contain PBDEcongeners that are dominated by congeners withfour to six bromine atoms 4, 5. PentaBDE andOctaBDE are two additional commercialbrominated flame retardant mixtures containingPBDE congeners with four to eight bromine atoms(see Table 1), and are believed to be the source ofthese congeners in biological samples. However,debromination of BDE 209 cannot be ruled out as asource of these lower brominated congeners. BDE 209 has been measured in house dust 6-8 atconcentrations up to 10,000 ppb, which could be apotential pathway of human exposure, particularlyfor young children. Toddlers have a predispositionto put dirty hands and toys in their mouth andinadvertently ingest larger amounts of house dust.This predilection has been responsible for largecases of lead poisoning in U.S. children,9-11 due tothe high lead levels in house dust. No studies haveinvestigated the levels of PBDEs in children underthe age of 5; however, modeling studies suggesttoddlers are receiving greater exposure to PBDEsthan adults because of the high levels in house dust12. In some homes studied, BDE 209 comprises90% of the total PBDE burden,7 therefore, BDE209 exposure could be unique to young children. ConclusionDebromination of BDE 209 cannot be ruled out asa source of lower brominated congeners. DecaBDE is mainly found in dust in the indoorenvironment including our homes and cars whichmay result in elevated exposures in children.IV. Photolytic Debromination of BDE 209

exposed BDE 209 spiked house dust to sunlight andfound that the half-life was approximately 220 hoursof continuous sunlight exposure, or assuming 10hours of sunlight a day, approximately 22 days.However, it is difficult to assess the magnitude andduration of sunlight that house dust would beexposed to in an average home. Most windows willblock out UV wavelengths of light which wouldhinder degradation. In contrast, car dust hasrecently been found to contain elevated levels ofBDE 209(http://www.ecocenter.org/releases/20060111_autotoxics.shtml), which is susceptible to greatersunlight exposure and in which debromination canbe expected to occur significantly. The degradation products of BDE 209 photolysisare primarily lower brominated PBDE congenersformed via debromination. In soils, sediment andhouse dust, the primary congeners identified arehepta-, octa- and nonaBDE congeners 13-15, and verylittle degrades to congeners with fewer than sixbromine atoms. When dissolved in water orBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 3 O2

3 4 5 2' 3' 4' 5' 66'

Polybrominated Diphenyl Ether (PBDE)

Brn n=1-10 Figure 1. Structure of PBDE molecule.

organic solvents, BDE 209 degrades quite rapidlyand leads to greater formation of the lowerbrominated congeners, including tri-, tetra- andpentaBDE congeners, and also polybrominateddibenzofurans (PBDFs) 13, 16, 17. In the environment,it is expected that BDE 209 will be found primarilybound to solids in the water column, and bound toparticles in the atmosphere. Therefore, degradationof BDE 209 dissolved in water (or organic solvents)is not expected to be of environmental relevance. ConclusionIt is difficult to assess the degree of BDE 209photolytic debromination in house dust, soils andsediments when exposed to light. However, in carsdebromination can be expected to occur moresignificantly. Debromination in water is notexpected to be of environmental relevance. V. Microbial and Reductive Debromination ofBDE 209One published study has investigated the microbialmediated debromination of BDE 209 underanaerobic (no oxygen) conditions. Gerecke et al. 18

used microflora from sewage sludge to examine thebacterial mediated degradation of BDE 209. Theirresults indicated that debromination of BDE 209did occur, leading to the formation of nona- andoctaBDE congeners. The observed first orderdegradation rate, 1.0 x 10-3 day-1, is equivalent to ahalf life of approximately 690 days. However, thisdegradation rate was accelerated by the use ofprimers to increase degradation potential. Withoutthe use of primers, the observed degradation ratewas 50% lower, resulting in a half-life ofapproximately 3.8 years. Therefore, anaerobicbacteria can initiate debromination of BDE 209,albeit at a slower rate than photolyticdebromination. Given the hydrophobic nature ofBDE 209, and the large volumes that enter watertreatment facilities, anaerobic degradation may beimportant in sewage sludge digesters. However, thetime that BDE 209 spends in the sewage sludge(residence time) will greatly impact it's ability toanaerobically degrade. Reductive debromination of BDE 209 has also beenreported to occur with mineral catalysts. Keum andLi 19 documented a stepwise debromination processusing zero-valent iron and sulfide minerals. Zero-valent iron was a good oxidant for degradation,resulting in a BDE 209 half-life of about one day.The use of iron sulfide and sodium sulfide reducedthe debromination/degradation rate to 2 and 33%of the rate observed for zero-valent iron. Both theiron and sulfides resulted in debromination down tocongeners with two and three bromines. In allexperiments, the initial rate of degradation was rapidand then decreased over time as lower brominatedcongeners were formed that appeared to be morestable. While this study demonstrates the possibilityand feasibility of reductive debromination byminerals, this process is unlikely to occur naturallyin the environment. PBDEs will have a greatertendency to be bound to natural organic matter andsoils in the environment before binding directly tothe mineral surface, which is necessary for themineral to act as an oxidant. ConclusionIn sewage anaerobic bacteria can initiatedebromination of BDE 209, albeit at a slower ratethan photolytic debromination, but due to the largevolumes of DecaBDE in sewage sludge this may besignificant. VI. Metabolic DebrominationDebromination of BDE 209 has also been observedin laboratory in vivo studies with fish and rats,suggesting it is metabolized. In four separatestudies, fish fed food spiked withdecabromodiphenyl ether were found to accumulatelower brominated congeners 20-23. The assimilationand debromination of BDE 209 varied among thethree fish species examined, which included rainbowtrout, common carp and lake trout. Common carpaccumulated no BDE 209 in their tissues, but theydid accumulate one penta-, three hexas-, two heptas-and one octaBDE congener that appeared to resultfrom the debromination of BDE 209. In twoseparate and independent research studies onrainbow trout, accumulation of BDE 209 wasobserved, although the uptake was less than 1% inboth studies. However, both studies observed anincrease in hexa-, hepta-, octa- and nonaBDEcongeners over time that comprised a higherpercentage of the PBDE body burden relative to theBDE 209 body burden. One study found anaccumulation of 0.13% of the BDE 209 dose 20,

while the second study observed an uptake of 3.2%of the BDE 209 dose 23. Lake trout were found toBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 4

accumulate approximately 5% of the BDE 209 doseand debromination was hypothesized to occur.However, the diet in this latter study consisted of acocktail of 13 BDEs and it was impossible tocharacterize debromination of BDE 209. Stapleton et al., 23 recently conducted several in vitroexperiments using fish liver microsomes tocharacterize metabolic biotransformation of BDE209. Microsomes are cell fractions which containactive enzymes from fish that typically metabolizeendogenous compounds (i.e. natural hormones).Using carp and rainbow trout liver microsomes,Stapleton found that as much as 65% of BDE 209was debrominated in a twenty four hour period.Carp microsomes rapidly debrominated as much as30% of the BDE 209 mass to form BDE 155 andBDE 154 (hexaBDEs). In contrast, rainbow troutdebrominated only 22% of the BDE 209 massprimarily to octa- and nonaBDE congeners. Thisstudy demonstrates that there are species specificdifferences in the biotransformation/debrominationcapacity of fish, and possibly, other organisms.Stapleton hypothesizes that thyroid hormoneenzymes are responsible for this observeddebromination, which is similar to endogenousmetabolism of thyroid hormones. In rats, metabolism of BDE 209 appears to occurthrough different mechanisms. Two studies haveexamined the uptake of BDE 209 in rats and bothidentified hydroxyl- and methoxyBDE congeners intissues and plasma and only trace levels ofnonaBDE congeners. This suggests that rats mayinitially debrominate BDE 209, but then othermetabolic pathways become more dominant,resulting in the formation of more polar metabolitesthat are likely to be excreted. ConclusionSome fish appear capable of debrominating BDE209 through metabolism. The extent of themetabolism varies among fish and it is difficult todetermine the extent of debromination that wouldoccur in the wild. VII. Human Debromination PotentialIn a recent study, Thuresson et al.24 measuredPBDE levels in workers occupationally exposed toBDE 209. Analysis of their serum identified severalhepta- and octa-BDE congeners that were notpresent in the decaBDE commercial mixture nor inthe reference groups. The congener patternobserved in these workers was very similar to thecongener pattern observed in the rainbow trout byStapleton et al.23. A follow up study examined theBDE concentrations in these workers when theyhad taken a vacation and reduced their exposure toBDE 209 24. This study found that while BDE 209concentrations decreased in these workers with ahalf life of approximately 15 days, concentrations ofthe hepta- and octaBDE congeners increased,suggesting that debromination of BDE 209 wasoccurring in humans. More studies are needed to determine if BDE 209debromination does occur in human tissues.Exposure to BDE 209 is suggested to be greater foryoung children relative to adults, due to the higherlevels present in house dust and thus, may need tobe investigated further. ConclusionStudies suggest that DecaBDE debrominates inhumans however, more studies are needed toconfirm this analysis.VIII. SummaryTable 1 compares the PBDE congeners that arepresent in the commercial mixtures to the congenersthat have been identified as products of BDE 209debromination. As evident in the table, all thecongeners present in the commercial products alsocan be formed via debromination of DecaBDE. Ofparticular concern in human and environmentalsamples is the accumulation of lower brominatedcongeners (i.e. tetra-, penta- and hexaBDEs). Basedon the current data available, the potential forsignificant formation of these congeners in theenvironment due to debromination is low. The onlystudies demonstrating formation/production ofthese congeners from debromination occurred whenBDE 209 was dissolved in organic solvents andexposed to sunlight and/or UV sources, which isnot environmentally relevant. Additionally,reductive debromination catalyzed by iron and ironsulfides also can lead to these congeners. However,the likelihood of BDE 209 being directly bound toBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 5

these types of mineral surfaces in the environment isalso low. In contrast, the formation of hexaBDE congeners(e.g. BDE 153, BDE 154 and BDE 155) fromdebromination of DecaBDE has more realisticprobabilities. Metabolic debromination resulted inthe formation of several hexaBDE congeners,including BDE 154, in several fish species 20, 21, 23. Inthese studies, less than 1% of the BDE 209exposure debrominated to the hexaBDE congeners,but as much as 2% debrominated into hepta-, octa-and nonaBDE congeners. In the past year, a fewstudies have documented a shift in the PBDEcongener patterns in human tissues. In moststudies, BDE 47 (tetraBDE) was the largestcontributor to the PBDE body burden; howeverrecent studies suggests some populations have aPBDE body burden dominated by BDE 153, ahexaBDE 25, 26. The reason for this is unknown butcould be related to debromination of BDE 209,exposure to different PBDE commercial sources, orto longer half-lives for BDE 153 relative to BDE47. Photolyitic debromination of DecaBDE in dust,soils and sediments also leads to the formation ofseveral hepta-, octa- and nonaBDE congeners,which is environmentally relevant. Because house,office and car dust are enriched in BDE 209, thepotential for debromination is high when exposedto sunlight. Current studies suggest that photolyticdebromination of BDE 209 leads to significantaccumulation of hepta-, octa- and nonaBDEcongeners which are persistent and potentiallybioaccumulative. There are very few studies whichhave investigated the bioaccumulation potential andenvironmental levels of hepta- through nonaBDEcongeners, which makes an assessment of their fatedifficult. More studies are needed to determine thelevels of these congeners in the environment(particularly in sediment and dust) in order todetermine if debromination of BDE 209 isoccurring. ConclusionThe potential for significant formation of BDE 47,BDE 99 and BDE 100 in the environment due todebromination is low as the only study showing thisis not environmentally relevant. The formation ofhexaBDE has more realistic probability and couldbe related to debromination of DecaBDE inhumans. Photolyitic debromination of DecaBDE indust, soils and sediments, leading to the formationof hepta-, octa- and nonaBDE congeners isenvironmentally relevant; not withstanding moreresearch on the significance of these lowercongeners fate in the environment.Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 6

Table 1. PBDE congeners identified in commercial mixtures and in debromination studies.Congener identifications in the PentaBDE and OctaBDE commercial mixtures are from reference27.

SubstitutionCongenerPentaBDEOctaBDEDecaBDEFormed FromDebrominationReference2,4,4'-tribromoBDE 28XX17,19

2,2',4,4'-tetrabromoBDE 47XX17,13,19

2,2',4,5'-tetrabromoBDE 49XX17

2,3',4,4'-tetrabromoBDE 66XX19

2,2'3,4,4'-pentabromoBDE 85XX14,17

2,2',4,4',5-pentabromoBDE 99XX17,13,19

2,2',4,4',6-pentabromoBDE 100XX17,19

2,2',3,4,4',5'-hexabromoBDE 138XX17,19

2,2',4,4',5,5'-hexabromoBDE 153XX17,13,19

2,2',4,4',5,6'-hexabromoBDE 154XX17,13,19,21, 232,2',4,4',6,6'-hexabromoBDE 155XX21, 232,2',3,4,4',5',6-heptabromoBDE 183XXX14,17,13,19

2,2',3,4,4',6,6'-heptabromoBDE 184X23

2,2',3,3',4,4',5,6'-octabromoBDE 196XX14,17,18

2,2',3,3',4,4',6,6'-octabromoBDE 197XX14,17,18

2,2',3,3',4,5',6,6'-octabromoBDE 201X23

2,2',3,3',5,5',6,6'-octabromoBDE 202X23

2,2',3,3',4,5,5',6-octabromoBDE 203XXX18

2,2',3,3',4,4',5,5',6-nonabromoBDE 206XXX14,17,13

2,2',3,3',4,4',5,6,6'-nonabromoBDE 207XXX14,17,13,18

2,2',3,3',4,5,5',6,6'-nonabromoBDE 208XXX14,17,13,18

2,2',3,3',4,4',5,5',6,6'-decabromoBDE 209XX

Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 7

Table 2. Photolytic half-lives of BDE 209 under various conditions.Light SourceSubstrateHalf Life (Reference)UV lampOrganic Solvent<0.25 H13;

UV lampSilica Gel<0.25 H13;

UV lampSand12 H13;

UV lampSediment40-60 H13; 150 D14;

UV lampSoil150-200 H13

UV lampMethanol/water0.5 H16

UV lampMinerals36 D - 3.9 Y14

SunlightHydrated on Quartz35 H28;

SunlightHydrated with Humics on Quartz70 H28

SunlightHumic Acid Coated Sand435 H28

SunlightHexane<0.25 H17

SunlightMinerals261-990 D14

SunlightSand13-37 H13

SunlightSediment30-80 H13

SunlightHouse Dust220 H 15

H- Hours; D- Days; Y- YearsBrominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 8

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