Identification of polybrominated dibenzo-p-dioxins in blue mussels (Mytilus edulis) from the Baltic Sea

Polybrominated dibenzo-p-dioxins (PBDDs) are known to be formed as byproducts in connection with the manufacture and combustion of products containing brominated flame retardants. However, to date little is known about the occurrence of PBDDs in biological samples. The aim of the present investigation was to examine the presence of PBDDs in blue mussels (Mytilus edulis) from the Baltic Sea employing a procedure adapted for dioxin analysis. Two triBDDs (1,3,7-triBDD and 1,3,8-triBDD) were identified in biota here for the first time. This identification was based on accurate mass determination and comparison of retention times on three gas chromatographic columns of different polarities (PTE 5, SP-2331, and OV1701/heptakis) with synthesized standards, together with comparisons of electron capture negative ionization (ECNI) and electron ionization (EI) mass spectra. In addition, five PBDDs and one polybrominated dibenzofuran (PBDF) were tentatively identified; altogether, one diBDD, three triBDDs, three tetraBDDs, and one triBDFwere detected in the blue mussels. To our knowledge this is the first time PBDDs have been identified in biota of the Baltic Sea. The sigma triBDD concentration in the blue mussels was estimated to be 170 ng/g lipids. The origin of these PBDDs remains unclear, but a plausible hypothesis could be biogenic formation in the marine environment.     

Formation of environmentally relevant brominated dioxins from 2,4,6,-tribromophenol via bromoperoxidase-catalyzed dimerization

Polybrominated dibenzo-p-dioxins (PBDD) are emerging environmental pollutants with structural similarities to the highly characterized toxicants polychlorinated dibenzo-p-dioxins. The geographical and temporal variations of PBDD in biota samples from the Baltic Sea do not display features that are normally related to anthropogenic sources such as incineration, and therefore the natural formation of PBDDs has been suggested. This study of the bromoperoxidase mediated oxidative coupling of 2,4,6-tribromophenol (an abundant substance that is naturally formed in marine systems) identified the formation of ppb-level yields of 1,3,6,8-tetrabromodibenzo-p-dioxin (1,3,6,8-TeBDD) through direct condensation. Additional TeBDDs (1,3,7,9-TeBDD, 1,2,4,7-TeBDD, and/or 1,2,4,8-TeBDD) and tri-BDDs (1,3,7-TrBDD and 1,3,8-TrBDD) were frequently formed but at lower yields. The formation of these TeBDDs probably proceeds via bromine shifts or Smiles rearrangements, whereas the TrBDDs may result from subsequent debromination processes. Because all of the congeners formed by oxidative coupling and subsequent reactions are also found in Baltic Sea biota, the results support the theory that PBDDs are formed from natural precursors.     

Occurrence of polybrominated biphenyls, polybrominated dibenzo-p-dioxins, and polybrominated dibenzofurans as impurities in commercial polybrominated diphenyl ether mixtures

The objective of this study was to determine the concentrations and compositions of polybrominated biphenyls (PBBs), polybrominated dibenzo-p-dioxins (PBDDs), and polybrominated dibenzofurans (PBDFs) as contaminants in the commercial polybrominated diphenyl ether (PBDE) mixtures DE-71, DE-79, and DE-83 and to ascertain the lot-to-lot variations in the proportions of these contaminants. Commercial PBDE mixtures tested in the present study contained both PBBs and PBDFs, as impurities, at concentrations in the range of several tens to several thousands of nanograms per gram. Concentrations of total PBDFs were greater than those of total PBBs in DE-79 and DE-83 mixtures. PBDDs were not detected at levels above the limit of detection. Profiles of PBB and PBDF congeners varied with the degree of bromination of the commercial PBDE mixtures (i.e., more highly brominated mixtures of PBDEs contained heavily brominated homologues of PBBs and PBDFs). On the basis of the production/ usage of commercial PBDE mixtures in 2001, potential global annual emissions of PBBs and PBDFs were calculated to be 40 and 2300 kg, respectively. Results of our study suggestthat PBDFs can also be formed during the production of commercial PBDE mixtures, in addition to their formation during pyrolysis of brominated flame retardants.     

Brominated dibenzo-p-dioxins: a new class of marine toxins?

Levels of polybrominated dibenzo-p-dioxins (PBDDs) were measured in marine fish, mussels, and shellfish. PBDDs were nondetectable in samples from freshwater environments, and their levels were successively higher in samples from the marine environments of the Bothnian Bay and Bothnian Sea, the West Coast of Sweden, and the Baltic Proper. In Baltic Proper littoral fish the levels of PBDDs generally exceeded those of their chlorinated analogues (PCDDs). This is alarming as some Baltic fish species already are contaminated by chlorinated dioxins to such an extent that they cannot be sold on the European market. By comparing spatial trends in PBDD and PCDD distributions, and PBDD patterns in fish, mussels, and algae, we show that the PBDDs are probably produced naturally, and we propose a route for their biosynthesis. We further show that the levels of PBDDs are high (ng/g wet weight) in mussels, and that the levels increase over time. Finally, we discuss the possibility that the PBDDs have adverse biological effects, and that the levels are increasing as a result of global warming and eutrophication.     

Surface-mediated formation of polybrominated dibenzo-p-dioxins and dibenzofurans from the high-temperature pyrolysis of 2-bromophenol on a CuO/silica surface

We studied the surface-mediated pyrolytic thermal degradation of 2-bromophenol, a model brominated hydrocarbon that may form brominated dioxins in combustion and thermal processes, on silica-supported copper oxide in a 1 mm i.d., fused silica flow reactor at a constant concentration of 88 ppm over a temperature range of 250-550 degrees C. Observed products included dibenzo-p-dioxin (DD), 1-monobromodibenzo-p-dioxin (1-MBDD), dibromo-dibenzo-p-dioxin (DBDD),tribromodibenzo-p-dioxin (TrBDD), 4-monobromodibenzofuran (4-MBDF), dibenzofuran (DF), 2,4,6-tribromophenol, 2,4- and 2,6-dibromophenol, and polybrominated benzenes. These results are compared and contrasted with previous work on surface-catalyzed pyrolysis of 2-chlorophenol. Polybrominated dibenzofurans (PBDFs) are formed by the Langmuir-Hinshelwood mechanism, and the formation of polybrominated dibenzo-p-dioxins (PBDDs) is through an Eley-Rideal mechanism. Yields of PBDDs are at least 16x greater for 2-bromophenol than for analogous PCDDs from 2-chlorophenol. Higher yields of polybrominated phenols and polybrominated benzenes are also observed. This can be attributed to the relative ease of bromination over chlorination and the higher concentration of bromine atoms in the 2-bromophenol system versus chlorine atoms for the 2-chlorophenol system.     

Modeling the importance of biota and black carbon as vectors of polybrominated diphenyl ethers (PBDEs) in the Baltic Sea ecosystem

The POPCYCLING-Baltic model, a nonsteady state spatially resolved mass balance model of chemical transport in the Baltic Sea environment was modified to include black carbon (BC), dissolved organic carbon (DOC) and food-web bioaccumulation. The importance of these modifications to the transport of PBDE congeners BDE-47, -99, -153, and -209 was assessed by comparing time-series simulated with and without black carbon and biota between 1970 and 2005. Inclusion of black carbon improved the model fit to measurements from air, soil, and biota, and had a major effect on the mass balance. Modeled bulk concentrations of PBDEs in sediments and soils increased by a factor of 3 while concentrations in biota decreased by a factor of 2-5. Black carbon also doubled the recovery time of the system due to the limited availability of PBDEs for degradation. In comparison, the inclusion of biota had only a minor effect on the overall mass balance and recovery times. The modified model is constructed as a flexible matrix and can also be applied to persistent organic pollutants in other ecosystems besides the Baltic Sea.     

Characterization of polybrominated dibenzo-p-dioxins and dibenzofurans in different atmospheric environments

Few studies have measured polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) in the atmosphere. In this study,four categories of atmospheric environments, including rural (Kengting national park, Taitung county, and Yilan county), urban (north Kaohsiung city and south Taichung city), industrial (Lin-hai industrial park), and science park (Hsinchu science park) areas were investigated for their characteristics of 2,3,7,8-substituted PBDD/F and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The elevated PCDD/F I-TEQ concentrations and higher ratio of PCDFs to PCDDs in the industrial areas reveal that the metallurgical facilities, including sinter plants, electric arc furnaces, secondary aluminum smelters, and secondary copper smelters, significantly influence their surrounding atmospheric environments. The mean PBDD/F concentrations in the atmosphere of the rural, urban, industrial, and science park areas were 11, 24, 46, and 95 fg/Nm3, respectively, while the corresponding mean TEQ concentrations were 2.7, 6.4, 12, and 31 fg TEQ/Nm3, respectively. The significantly high correlation (r = 0.85, p = 0.034)found betweenthe PBDD/F and PCDD/F concentrations in the atmospheres of the industrial areas reveals that the metallurgical facilities are also the most likely PBDD/F emission sources in the industrial areas. The PBDD/F concentration in the science park area was approximately 2-fold higher than that in the industrial areas, whereas PCDD/F I-TEQ concentration in the area was only 23% of that in the industrial areas. The elevated PBDD/F concentrations in the science park areas may be attributed to the use of polybrominated diphenyl ethers as brominated flame retardants in the electrical and electronics industries, which contribute to direct PBDD/F emissions into the environment. PBDFs were all much more dominant than PBDDs in the atmosphere, and their mass fractions increase with PBDD/F concentrations.     

Pyrolysis study of halogen-containing aromatics reflecting reactions with polypropylene in a posttreatment decontamination process

Halogen-containing aromatics, mainly bromine-containing phenols, are harmful compounds contaminating pyrolysis oil from electronic boards containing halogenated flame retardants. In addition,theirformation increases the potential for evolution of polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs) at relatively low temperature (up to 500 degrees C). As a model compound, 2,4-dibromophenol (DBP) was pyrolyzed at 290-450 degrees C. While its pyrolysis in a nitrogen flow reactor or in encapsulated ampules yields bromine-containing phenols, phenoxyphenols, PBDDs, and PBDFs, pyrolysis of DBP in a hydrogen-donating medium of polypropylene (PP) at 290-350 degrees C mainly results in the formation of phenol and HBr, indicating the occurrence of a facile hydrodebromination of DBP. The hydrodebromination efficiency depends on temperature, pressure, and the ratio of the initial components. This thermal behavior of DBP is compared to that of 2,4-dichlorophenol and decabromodiphenyl ether. A treatment of halogen-containing aromatics with PP offers a new perspective on the development of low-environmental-impact disposal processes for electronic scrap.     

Inhibition of polybrominated dibenzo-p-dioxin and dibenzofuran formation from the pyrolysis of printed circuit boards

Waste printed circuit boards containing brominated flame retardants were pyrolyzed in a high-temperature melting system to observe the formation behaviors of polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs). In this study, the results showed that the formation of PBDD/ Fs during pyrolysis can be destroyed under controlled primary combustion conditions. There were two significant factors that influenced the extent of PBDD/F formation. The first factor was temperature. The results showed that, both the total PBDD/F content in the bottom ash and the total PBDD/F emission factor from the flue gas decrease by approximately 50% with an increase of the pyrolysis temperature from 850 to 1200 degrees C. The second factor was the addition of CaO. The possible mechanism involves the reaction between CaO and HBr to form the solid-phase product CaBr2. Thus, the addition of CaO is effective in adsorbing HBr and results in the inhibition of PBDD/F synthesis by more than 90% and further prevents the acid gases (HCl and HBr) that corrode the equipment. In conclusion, due to the persistence and toxicity of PBDD/Fs, a combined regulation for controlling both PCDD/Fs and PBDD/Fs is of great importance for environmental protection issues.     

PBCDD and PBCDF from incineration of waste-containing brominated flame retardants

Brominated organic flame retardants comprise a large, heterogeneous group of compounds that are useful but also potentially damaging to the environment. In this investigation, three common brominated flame retardants were co-combusted with an artificial municipal solid waste in a pilot-scale fluidized bed incinerator. Combustion conditions ensured degradation of the flame retardants, but stable brominated organic compounds such as polybrominated dibenzo-p-dioxins and polybrominated dibenzofurans were formed in the cooling flue gases. The incineration of fuels that contain both chlorine and bromine leads to the formation of a complex mixture of polybrominated/chlorinated dibenzo-p-dioxins and dibenzofurans. More bromination than chlorination was observed in these experiments, and the chlorination levels increased when bromine was added to the fuel. The most favored reactions led to the formation of dibromodichlorodibenzo-p-dioxin and dibromodichlorodibenzofuran. Theoretical calculations show that there is more Br2 than Cl2 in the flue gas when the two halogens are present at equimolar levels, because chlorine is mainly found in the form of HCl. This may explain the higher bromination level. BrCl is also present, which drives the chlorination observed when bromine is added.     

Identification of hydroxylated and methoxylated polybrominated diphenyl ethers in Baltic Sea salmon (Salmo salar) blood

Methoxylated and hydroxylated polybrominated diphenyl ethers (MeO-PBDEs and OH-PBDEs) have recently been reported to be present in wildlife from Northern Europe. The structures of a majority of these compounds have however been unknown. In the present study, nine OH-PBDEs and six MeO-PBDEs were identified in Baltic Sea salmon (Salmo salar) blood. All OH- and MeO-PBDEs identified were substituted with four or five bromines, and five of these had one chlorine substituent. Fourteen of the OH- and MeO-PBDEs have the methoxy or hydroxy group substituted in the ortho position to the diphenyl ether bond. Identification was done by comparison of relative retention times of authentic reference standards with compounds present in salmon plasma on two gas chromatographic columns of different polarities. The identification was supported by comparisons of full-scan mass spectrometric data: electron ionization (EI) and electron capture negative ionization (ECNI). Nine of the 15 OH- and MeO-PBDEs identified have not previously been reported to occur in the environment. The structures of several identified OH- and MeO-PBDEs support natural origin. However, at least one of the OH-PBDEs may be a hydroxylated metabolite of anthropogenic polybrominated diphenyl ether (PBDE).     

PBDDs/Fs and PCDDs/Fs in the raw and clean flue gas during steady state and transient operation of a municipal waste combustor

Concentrations of polybrominated dibenzo-p-dioxins, and -dibenzofurans (PBDDs/Fs) and polychlorinated dibenzo-p-dioxins, and -dibenzofurans (PCDDs/Fs), were determined in the pre- and post-air pollution control system (APCS) flue gas of a municipal waste combustor (MWC). Operational transients of the combustor were found to considerably increase levels of PBDDs/Fs and PCDDs/Fs compared to steady state operation, both for the raw and clean flue gas; ΣPBDDs/Fs increased from 72.7 to 700 pg dscm(-1) in the raw, pre-APCS gas and from 1.45 to 9.53 pg dscm(-1) in the post-APCS flue gas; ΣPCDDs/Fs increased from 240 to 960 ng dscm(-1) in the pre-APCS flue gas, and from 1.52 to 16.0 ng dscm(-1) in the post-APCS flue gas. The homologue profile of PBDDs/Fs and PCDDs/Fs in the raw flue gas (steady state and transients) was dominated by hexa- and octa-isomers, while the clean flue gas homologue profile was enriched with tetra- and penta-isomers. The efficiency of the APCS for PBDD/F and PCDD/F removal was estimated as 98.5% and 98.7%, respectively. The cumulative TEQ(PCDD/F+PBDD/F) from the stack was dominated by PCDD/F: the TEQ of PBDD/F contributed less than 0.1% to total cumulative toxic equivalency of MWC stack emissions.     

Polybrominated diphenyl ethers, hydroxylated polybrominated diphenyl ethers, and measures of thyroid function in second trimester pregnant women in California

Prenatal exposure to polybrominated diphenyl ethers (PBDEs) may disrupt thyroid function and contribute to adverse neurodevelopmental outcomes. We conducted a pilot study to explore the relationship between serum concentrations of lower-brominated PBDEs (BDE-17 to -154), higher-brominated PBDEs (BDE-183 to -209), and hydroxylated PBDE metabolites (OH-PBDEs) with measures of thyroid function in pregnant women. Concentrations of PBDEs, OH-PBDEs, thyroid-stimulating hormone (TSH), total thyroxine (T(4)), and free T(4) were measured in serum samples collected between 2008 and 2009 from 25 second trimester pregnant women in California. Median concentrations of lower-brominated PBDEs and OH-PBDEs were the highest reported to date in pregnant women. Median concentrations of BDE-47 and the sum of lower-brominated PBDEs (ΣPBDE(5)) were 43.1 ng/g lipid and 85.8 ng/g lipid, respectively, and the sum of OH-PBDEs (ΣOH-PBDE(4)) was 0.084 ng/mL. We observed a positive association between the weighted sum of chemicals known to bind to transthyretin (ΣTTR binders) and TSH levels. We also found positive associations between TSH and ΣPBDE(5), ΣOH-PBDE(4), BDE-47, BDE-85, 5-OH-BDE47, and 4'-OH-BDE49, and an inverse association with BDE-207. Relationships with free and total T(4) were weak and inconsistent. Our results indicate that PBDE exposures are elevated in pregnant women in California and suggest a relationship with thyroid function. Further investigation is warranted to characterize the risks of PBDE exposures during pregnancy.     

Brominated organic contaminants in the liver and egg of the common cormorants (Phalacrocorax carbo) from Japan

The contamination profiles of brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs), biphenyls (PBBs), dibenzo-p-dioxins (PBDDs), and dibenzofurans (PBDFs) were determined in the liver and egg of common cormorants from Japan. PBDEs and PBBs were detected in all the samples; especially the former were detected at elevated levels. PBDDs/PBDFs were also detected in cormorants, albeit the concentrations were lower than those of the PBBs. The total concentration of PBDEs ranged from 330 to 2600 in the liver and from 600 to 3300 in the egg on a nanogram per gram of lipid basis. The concentration of PBBs was in the range from 3.0 to 33 (in the liver) and from 3.4 to 82 (in the egg) on a nanogram per gram of lipid basis. The 2,2',4,4',5,5'-hexabromobiphenyl (BB-153) was the most predominant PBB congener in either organ, which corresponds to a major constituent of the BFR FireMaster BP-6. Concentrations of PBDDs/ PBDFs in the liver (range from 21 to 470) were slightly higher than in the egg (range from 31 to 160) on a picogram per gram of lipid basis. The results of this study imply that common cormorants accumulate a high level of PBDEs and PBBs. Comparing the concentrations of brominated organic compounds with those of chlorinated analogues, good relevance between PBBs and coplanar PCBs (r2 = 0.746 [liver] and 0.715 [egg]) was elucidated. To our knowledge, the present study demonstrates the first report of PBDEs, PBBs, and PBDDs/PBDFs in the common cormorant from Japan.     

Atmospheric transport of polybrominated diphenyl ethers and polychlorinated biphenyls to the Baltic Sea

The atmospheric transport of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) was compared by measuring concentrations in air and deposition on an island located in the central basin of the Baltic Sea. Median sigmaPBDE and sigmaPCB concentrations (gaseous + particle) were 8.6 and 7.4 pg m(-3), respectively. Airborne PCBs were mainly found in the gaseous phase, while most of the PBDEs were detected on particles, which agrees with predicted particle/gas distributions. SigmaPBDE levels were dominated by the decabrominated BDE209 followed bythe tetrabrominated BDE47 and pentabrominated BDE99. BDE209 is a marker for the environmental distribution of the commercial deca-BDE formulation (>99.5% BDE209), whereas BDE47 and BDE99 are markers for the commercial penta-BDE mixture. General correlations between PBDEs and PCBs suggested similarities in sources and transport mechanism, while more detailed examination of the data identified notable behaviors and exceptions. Differences in regression slopes among tetra-, penta-, and decabrominated PBDEs may reflect different transport processes and the change in usage pattern. Tetra- and pentabrominated PBDEs may originate from secondary sources such as air surface exchange in a manner similar to that of the PCBs, while the deca-BDE209 formulation still has primary sources. The tribrominated BDE17 was also detected and is proposed to be a breakdown product due to atmospheric debromination processes. PBDEs had higher washout ratios than PCBs, explaining their higher concentrations compared to PCBs in precipitation (median of 6.0 and 0.5 ng L(-1) for sigmaBDE and sigmaPCB concentrations ("dissolved" + particle), respectively) than in air. The calculated yearly deposition of PBDEs and PCBs indicated that the atmospheric input of PBDEs to the Baltic Proper is currently exceeding that of the PCBs by a factor of 40, while that of the PCBs is decreasing.     

Emerging contaminants in car interiors: evaluating the impact of airborne PBDEs and PBDD/Fs

Air samples from automobile cabins were collected and analyzed for polybrominated diphenyl ethers (PBDEs), polybrominated dibenzofurans (PBDFs), and polybrominated dibenzo-p-dioxins (PBDDs). The concentration of total PBDEs (sigmaPBDE; sum of 19 congeners) varied from 0.4 to 2644 pg m(-3), with a median of 201 pg m(-3), while BDE 47, 99, and 209 collectively accounted for 70 +/- 30% of sigmaPBDE concentrations. Multiple linear regression analysis revealed that sigmaPBDE concentration was significantly influenced by vehicle's age and interior temperature. More specifically, sigmaPBDE decreased over time and increased with the rise of temperature. The daily inhalation intake of PBDEs during commuting was estimated to range from 0.5 to 2909 pg day(-1) (median 221 pg day(-1)) and contributed 29% of the overall daily exposure to PBDEs via inhalation. When excluding BDE 209, a lower contribution was calculated for this source (18%), but this was still comparable with residential exposure (22%). The levels of PBDD/Fs were generally below the limits of detection and only in one case were hepta-BDFs positively detected at a concentration of 61 pg m(-3). This study demonstrates that car interiors, especially when new, contain high levels of airborne PBDEs and represent a potential route of human exposure via inhalation.     

Global pollution monitoring of polybrominated diphenyl ethers using skipjack tuna as a bioindicator

To elucidate the global distribution of polybrominated diphenyl ethers (PBDEs), these chemicals were determined in the muscle of skipjack tuna (Katsuwonus pelamis) collected from offshore waters of various regions in the world (Japan, Taiwan, Philippines, Indonesia, Seychelles, and Brazil, and the Japan Sea, East China Sea, South China Sea, Indian Ocean, and North Pacific Ocean). PBDEs were detected in almost all the skipjack tuna collected from the locations surveyed (from < 0.1 to 53 ng/g of lipid), indicating widespread contamination by these compounds in the marine environment. Residue levels of PBDEs in these samples from the northern hemisphere seem to be higher than those from the southern hemisphere, which is plausibly due to larger usage of these compounds in the northern hemisphere. Higher concentrations of PBDEs were detected in the samples from waters around the East China Sea (up to 53 ng/g of lipid). Developing countries around the East China Sea are supposedly the "hot spots" releasing these chemicals into the marine environment. With regard to the composition of PBDE congeners, the percentage contribution by lower brominated congeners (BDE15, -28, and -47) showed an increasing trend with increasing latitude. On the other hand, higher brominated congeners (BDE153, -154, and -183) showed a reverse trend. These patterns suggest that lower brominated congeners of PBDEs (di-, tri-, and tetra-BDEs) were preferentially transported from pollution sources to northern colder regions through the atmosphere. PBDEs may have a high potency to cause global pollution like PCBs.     

Hydroxylated and methoxylated polybrominated diphenyl ethers in a Canadian Arctic marine food web

Residues of hydroxylated (OH-) and methoxylated (MeO-) polybrominated diphenyl ethers (PBDEs) have been previously detected in precipitation, surface waters, wildlife, and humans. We report measured concentrations of OH-PBDEs, MeO-PBDEs, and Br3-Br7 PBDEs in sediments and biota from a Canadian Arctic marine food web. PBDEs exhibited very low trophic magnification factors (TMFs between 0.1-1.6), compared to recalcitrant PCBs (TMFs between 3 and 11), indicating biotransformation via debromination and/or cytochrome P450 mediated metabolism. OH-PBDEs were not detectable in samples of blood, muscle, and/or liver of fish and marine wildlife. Five OH-PBDEs were detected at very low concentrations (range: 0.01-0.1 ng x g(-1) lipid equivalent) in beluga whale blubber and milk. The data indicate negligible formation/retention of OH-PBDEs in these Arctic marine organisms. Appreciable levels of several MeO-PBDEs were observed in bivalves, Arctic cod, sculpin, seaducks, and beluga whales (mean range 0.1-130 ng x g(-1) lipid equivalent). 2'-MeO-BDE-68 and 6-MeO-BDE-47 exhibited the highest concentrations among the brominated compounds studied (including BDE-47 and BDE-99) and biomagnified slightly in the food web, with TMFs of 2.3 and 2.6, respectively. OH- and MeO-PBDEs in this Arctic marine food web may occur via metabolic transformation of PBDEs or bioaccumulation of PBDE degradation products and/or natural marine products. We observed no evidence of a local natural source of OH- or MeO-PBDEs, as no measurable quantities of those compounds were observed in ambient environmental media (i.e., sediments) or macroalgae. Further investigations of PBDEs and their hydroxylated and methoxylated analogues would be useful to better understand sources, fate, and mechanisms governing biotransformation and bioaccumulation behavior of these compounds.     

Microarray analysis reveals a mechanism of phenolic polybrominated diphenylether toxicity in zebrafish

Polybrominated diphenylethers (PBDEs) are ubiquitous in the environment, with the lower brominated congener 2,2',4,4'-tetrabromodiphenylether (BDE47) among the most prevalent. The phenolic PBDE, 6-hydroxy-BDE47 (6-OH-BDE47) is both an important metabolite formed by in vivo metabolism of BDE47 and a natural product produced by marine organisms such as algae. Although this compound has been detected in humans and wildlife, including fish, virtually nothing is known of its in vivo toxicity. Here we report that 6-OH-BDE47 is acutely toxic in developing and adult zebrafish at concentrations in the nanomolar (nM) range. To identify possible mechanisms of toxicity, we used microarray analysis as a diagnostic tool. Zebrafish embryonic fibroblast (PAC2) cells were exposed to 6-OH-BDE47, BDE47, and the methoxylated metabolite 6-MeO-BDE47. These experiments revealed that 6-OH-BDE47 alters the expression of genes involved in proton transport and carbohydrate metabolism. These findings, combined with the acute toxicity, suggested that 6-OH-BDE47 causes disruption of oxidative phosphorylation (OXPHOS).Therefore, we further investigated the effect of 6-OH-BDE47 on OXPHOS in zebrafish mitochondria. Results show unequivocally that this compound is a potent uncoupler of OXPHOS and is an inhibitor of complex II of the electron transport chain. This study provides the first evidence of the in vivo toxicity and an important potential mechanism of toxicity of an environmentally relevant phenolic PBDE of both anthropogenic and natural origin. The results of this study emphasize the need for further investigation on the presence and toxicity of this class of polybrominated compounds.     

Reductive debromination of polybrominated diphenyl ethers by zerovalent iron

Polybrominated diphenyl ethers (PBDEs) are a new class of global, persistent, and toxic contaminants, which need proper remediation technologies. PBDE degradation in the environment is not well understood. In this study, degradation of PBDEs with zerovalent iron was investigated with six BDEs, substituted with one to 10 bromines. Within 40 days 92% of BDE congener 209 was transformed into lower bromo congeners. During the initial reaction period of BDE 209 (<5 days), hexa- to heptabromo BDEs were the most abundant products, but tetra- to pentabromo congeners were dominant after 2 weeks. The amount of mono- to tribromo BDEs was steadily increased during the experiments. BDEs 28, 47, 66, and 100 also showed a stepwise accumulation of lower bromo congeners. No oxidation products were detected in all experiments. The results showed that a stepwise debromination from n-bromoto (n-1)-bromodiphenyl ethers was the dominant reaction in all congeners. The reaction rate constants of lower bromo BDEs decreased as the number of bromines decreased. The initial reductive debromination rate constants were positively correlated with the heats of formation of BDEs. The preferential accumulation of specific congeners was observed in the experiment with BDEs 28, 47, 66, and 100, where the most abundant products were BDEs 15, 28, 37, and 47, respectively. Reactions proceeded to form more stable and less brominated products that have lower heats of formation. Almost all the possible isomers from a specific parent BDE were found in all the experiments, which was probably due to the small difference of heat of formation between the products (2-5 kcal/mol). Reactions of all congeners proceeded fast at the initial phase (<5 days) followed by a slow reaction. The rate of reductive debromination of BDE 209 was slower with environmentally relevant sulfide minerals (iron sulfide and sodium sulfide). However, the product congener pattern, produced by sulfide mineral catalysis, was nearly similar with that of zerovalent iron treatment. This may be a possible source of lower brominated BDEs in the environment. Debromination of PBDEs by zerovalent iron has high potential values for remediation of PBDEs in the environment.