Origin of hydroxylated brominated diphenyl ethers: natural compounds or man-made flame retardants?

Metabolism of polybrominated diphenyl ethers and tetrabromobisphenol A by fish liver subcellular fractions in vitro

Polybrominated diphenyl ethers (PBDEs) and tetrabromobisphenol A (TBBPA) are two major flame retardants that accumulate in fish tissues and are potentially toxic. Their debrominated and oxidated derivatives were also reported in fish tissues although the sources of theses derivatives were unidentified. Our study was to determine whether PBDEs and TBBPA could be metabolized by fish liver subcellular fractions in vitro and to identify what types of metabolites were formed. Liver microsomes and S9 fractions of crucian carp (Carassius auratus) were exposed to 4,4'-dibromodiphenyl ether (BDE 15), 2,2',4,4'-tetrabromodiphenyl ether (BDE 47) or TBBPA solutions for 4h. Exposure of liver subcellular fractions to BDE 15 resulted in the formation of bromophenol and two monohydroxylated dibromodiphenyl ether metabolites. Neither in microsomes nor in S9 studies has revealed the presence of hydroxylated metabolites with BDE 47 exposure which indicated that the oxidation reactions in vitro were hindered by the increased number of bromine substituents on the PBDEs. TBBPA underwent an oxidative cleavage near the central carbon of the molecule, which led to the production of 2,6-dibromo-4-isopropyl-phenol and three unidentified metabolites. Another metabolite of TBBPA characterized as a hexa-brominated compound with three aromatic rings was also found in the liver subcellular fractions. These results suggest that the biotransformation of BDE 15 and TBBPA in fish liver is mediated by cytochrome P450 (CYP450) enzymes, as revealed by the formation of hydroxylated metabolites and oxidative bond cleavage products. Moreover, further studies on the identification of specific CYP450 isozymes involved in the biotransformation revealed that CYP1A was the major enzyme responsible for the biotransformation of BDE 15 and TBBPA in fish liver subcellular fractions and CYP3A4 also played a major role in metabolism of TBBPA.

Assessment of the binding of hydroxylated polybrominated diphenyl ethers to thyroid hormone transport proteins using a site-specific fluorescence probe

Polybrominated diphenyl ethers (PBDEs) have been shown to disrupt thyroid hormone (TH) functions on experimental animals, and one of the proposed disruption mechanisms is the competitive binding of PBDE metabolites to TH transport proteins. In this report, a nonradioactive, site-specific fluorescein-thyroxine (F-T4) conjugate was designed and synthesized as a fluorescence probe to study the binding interaction of hydroxylated PBDEs to thyroxine-binding globulin (TBG) and transthyretin (TTR), two major TH transport proteins in human plasma. Compared with free F-T4, the fluorescence intensity of TTR-bound conjugate was enhanced by as much as 2-fold, and the fluorescence polarization value of TBG-bound conjugate increased by more than 20-fold. These changes provide signal modulation mechanisms for F-T4 as a fluorescence probe. Based on fluorescence quantum yield and lifetime measurements, the fluorescence intensity enhancement was likely due to the elimination of intramolecular fluorescence quenching of fluorescein by T4 after F-T4 was bound to TTR. In circular dichroism and intrinsic tryptophan fluorescence measurements, F-T4 induced similar spectroscopic changes of the proteins as T4 did, suggesting that F-T4 bound to the proteins at the T4 binding site. By using F-T4 as the fluorescence probe in competitive binding assays, 11 OH-PBDEs with different levels of bromination and different hydroxylation positions were assessed for their binding affinity with TBG and TTR, respectively. The results indicate that the binding affinity generally increased with bromine number and OH position also played an important role. 3-OH-BDE-47 and 3'-OH-BDE-154 bound to TTR and TBG even stronger, respectively, than T4. With rising environmental level and high bioaccumulation capability, PBDEs have the potential to disrupt thyroid homeostasis by competitive binding with TH transport proteins.

Gastrointestinal absorption, metabolic debromination, and hydroxylation of three commercial polybrominated diphenyl ether mixtures by common carp

The gastrointestinal absorption, metabolic debromination, and hydroxylation of three commercial brominated diphenyl ether (BDE) mixtures were separately studied in juvenile common carp. The absorption rate of penta-BDE was higher than that of octa- and deca-BDE, likely because of the lower molecular volumes of its major congeners. However, no significantly positive relationships were found between the number of bromine atoms and the absorption rate, especially for congeners with a bromine atom number larger than six. The major congeners in fish carcass were, respectively, BDE-47 and BDE-100 in the penta-BDE exposure; BDE-154, -155, -149, and BDE-153 in the octa-BDE exposure; and BDE-154, -155, -149, -188, -179, and BDE-202 in the deca-BDE exposure. Congeners with at least one meta- or para- doubly flanked bromine atom easily undergo metabolic debromination in fish. None of the targeted MeO-polybrominated diphenyl ether (PBDE) congeners were detected in serum samples, implying that the methylation of OH-PBDE is not likely occurring in fish. Eleven OH-PBDEs and several unidentified OH-PBDE congeners were found in penta-BDE-exposed fish. The similar level among three mono-OH-BDE47 congeners suggested that the position of OH in the phenyl ring is not selective. The hydroxylation is not a significant metabolic pathway compared with debromination. No OH-PBDE congeners were found in the serum samples from deca-BDE-exposed fish, which may attributable to the low level of PBDE precursors in fish.

Polybrominated diphenyl ethers and decabromodiphenylethane in sediments from twelve lakes in China

Sediment cores from 12 Chinese lakes were analyzed to investigate the historical inputs of polybrominated diphenyl ethers (PBDEs) and decabromodiphenylethane (DBDPE) during the past few decades. Concentrations of ΣPBDE(1) (sum of tri- to hepta-BDEs), ΣPBDE(2) (sum of nona- to deca-BDEs) and DBDPE in the surface sediments were 0.02-0.29 ng g(-1), 0.46-46.6 ng g(-1) and 1.02-3.64 ng g(-1), respectively. The temporal trends of PBDEs and DBDPE followed a general increase from the bottom to the surface. The calculated fluxes for ΣPBDE(1), ΣPBDE(2) and DBDPE were 0.001-0.09, 0.03-4.24, and 0.05-0.31 ng cm(-2) yr(-1), and the inventories were 0.09-7.86, 0.91-461, and 3.83-24.6 ng cm(-2), respectively. The urbanization and industrialization are highly related to the contamination of PBDEs and DBDPE in sediments. The DBDPE input in recent years was still lower than ΣPBDE(2) but the temporal trends indicated that the contamination would increase with the increasing usage of DBDPE in the future.

Regional variation and possible sources of brominated contaminants in breast milk from Japan

This study focuses on the regional trends and possible sources of brominated organic contaminants accumulated in breast milk from mothers in southeastern (Okinawa) and northwestern (Hokkaido) areas of Japan. For persistent brominated flame retardants, polybrominated diphenyl ethers (PBDEs; major components, BDE-47 and BDE-153) were distributed at higher levels in mothers from Okinawa (mean, 2.1 ng/g lipid), while hexabromobenzene (HeBB) and its metabolite 1,2,4,5-tetrabromobenzene were more abundantly detected in mothers from Hokkaido (0.86 and 2.6 ng/g lipid), suggesting that there are regional differences in their exposure in Japan. We also detected naturally produced brominated compounds, one of which was identified as 2'-methoxy-2,3',4,5'-tetrabromodiphenyl ether (2'-MeO-BDE68) at higher levels in mothers from Okinawa (0.39 ng/g lipid), while the other was identified as 3,3',4,4'-tetrabromo-5,5'-dichloro-2,2'-dimethyl-1,1'-bipyrrole in mothers from Hokkaido (0.45 ng/g lipid). The regional variation may be caused by source differences, i.e. southern seafood for MeO-PBDEs and northern biota for halogenated bipyrroles in the Japanese coastal water.

Occurrences and fates of hydroxylated polybrominated diphenyl ethers in marine sediments in relation to trophodynamics

While occurrences and origins of hydroxylated (OH-) polybrominated diphenyl ethers (PBDEs) in organisms have been reported, the fates of these compounds in abiotic matrixes and related trophodynamics are unclear. The present study measured concentrations of nine OH-PBDEs, twelve methoxylated (MeO-) PBDEs, and eleven PBDEs in marine sediments and explored the trophodynamics of OH-PBDEs in five invertebrates, eight fish, and two species of birds from Liaodong Bay, north China. While concentrations of PBDEs were less than the limit of quantification in sediments, concentrations of ΣOH-PBDEs and ΣMeO-PBDEs were 3.2-116 pg/g dry weight (dw) and 3.8-56 pg/g dw, respectively. When the detected compounds were incubated in native marine sediments the interconversion between 6-OH-BDE47 and 6-MeO-BDE47 was observed. This result is consistent with the similar spatial distributions and significant correlation between the concentrations of these naturally occurring compounds. 6-OH-BDE47 and 2'-OH-BDE68 were detected as the two major congeners in organisms collected from Liaodong Bay, and concentrations were 0.24 ± 0.005 ng/g lw (lipid weight) and 0.088 ± 0.006 ng/g lw, respectively. Biota-sediment accumulation factors (BSAFs) for invertebrates of 6-OH-BDE47 and 2'-OH-BDE68 were 0.017-0.96 and 0.19-1.5 (except for short-necked clam: 6.3), respectively. Lipid-normalized concentrations of 6-OH-BDE47 and 2'-OH-BDE68 decreased significantly with trophic level with TMFs of 0.21 and 0.15, respectively. The fates of OH-PBDEs in sediment together with their trophodynamics in marine food webs suggested that OH-PBDEs are partitioned into sediment and undergo biodilution in the marine food web.

Bioaccumulation, depuration and biotransformation of 4,4'-dibromodiphenyl ether in crucian carp (Carassius auratus)

Polybrominated diphenyl ethers (PBDEs) are extensively used as a class of flame retardants and have become ubiquitous environmental pollutants. Significant biotransformation of some PBDEs via reductive debromination has been observed. However, little is known about the fate of lower brominated BDEs in fish. In this study, the tissue distribution, excretion, depuration and biotransformation of 4,4'-dibromodiphenyl ether (BDE 15) were investigated in crucian carp (Carassius auratus) which were exposed to spiked water solution at different concentrations for 50d, followed by a 14-d depuration period. Bioaccumulation parameters were calculated and the results showed that BDE 15 was mainly concentrated in the gill and liver. In particular, five biotransformation products of BDE 15 in carp were identified using GC-MS/MS. Besides two debrominated metabolites, three of the metabolites were mono-OH-BDE 15, diOH-BDE 15 and bromophenol. Our results unequivocally suggested that BDE 15 oxidation did occur via the formation of hydroxylated (OH-) metabolites in crucian carp exposed in vivo. These findings will be useful for determination of the metabolic pathways of PBDEs in freshwater fish, especially about their oxidation metabolism.

Toxicogenomic mechanisms of 6-HO-BDE-47, 6-MeO-BDE-47, and BDE-47 in E. coli

Cytotoxicity of 6-HO-BDE-47 and its two analogues, BDE-47 and 6-MeO-BDE-47, and the associated molecular mechanisms were assessed by use of a live cell reporter assay system which contains a library of 1820 modified green fluorescent protein (GFP) expressing promoter reporter vectors constructed from E. coli K12 strains. 6-HO-BDE-47 inhibited growth of E. coli with a 4 h median effect concentration (EC50) of 22.52 ± 2.20 mg/L, but neither BDE-47 nor 6-MeO-BDE-47 were cytotoxic. Thus, 6-HO-BDE-47 might serve as an antibiotic in some living organisms. Exposure to 6-HO-BDE-47 resulted in 65 (fold change >2) or 129 (fold change >1.5) genes being differentially expressed. The no observed transcriptional effect concentration (NOTEC) and median transcriptional effect concentration (TEC50) based on transcriptional end points, of 6-HO-BDE-47 were 0.0438 and 0.580 mg/L, respectively. The transcriptional responses were 514- and 39-fold more sensitive than the acute EC50 to inhibit cell growth. Most of the genes that were differentially expressed in response to 6-HO-BDE-47 were not modulated by BDE-47 or 6-MeO-BDE-47. These results suggest that cytotoxicity of 6-HO-BDE-47 to E. coli was via a mechanism that was different from that of either BDE-47 or 6-MeO-BDE-47. Gene expression associated with metabolic pathways was more responsive to 6-HO-BDE-47, which suggests that this pathway might be the primary target of this compound.

Marine sponge: a potential source for methoxylated polybrominated diphenyl ethers in the Asia-Pacific food web

Marine sponges collected in Palau, Micronesia, were investigated for hydroxylated or methoxylated analogues of brominated diphenyl ethers (BDEs), brominated dibenzo-p-dioxin (BDD), and brominated biphenyls. The neutral fractions of Haliclona sp. and Callyspongia sp. contained 2'-methoxy-2,3',4,5'-tetraBDE, 6-methoxy-2,2',4,4'-tetraBDE, 2',6-dimethoxy-2,3',4,5-tetraBDE 2,2'-dimethoxy-3,3',5,5'-tetrabromobiphenyl, several methoxy-triBDEs, and dimethoxy-penta-/hexaBDEs. The methoxylated BDEs in sponges were strikingly similar to those of local fish living in the western Pacific Ocean. The total concentrations of these compounds (ΣMeO-PBDE) in both sponges were 63.5 μg/g extractable organic matter (EOM) for Haliclona sp. and 36.5 μg/g EOM for Callyspongia sp., which were about 2 orders of magnitude higher than the levels seen in tropical coral reef fish (unicornfish or surgeonfish) (280-290 ng/g lipid) and groupers (550 ng/g lipid) from Okinawan coastal waters. The phenolic fractions of both sponges contained hydroxy-methoxy tetra-/pentaBDEs as well as hydroxy-tetraBDD, in addition to the corresponding phenolic tetraBDE analogues. Although the total concentrations of phenolic products (27-80 μg/g EOM) in both sponges fell within a range comparable to the methoxylated products, ΣOH-PBDE in local fish were trace level (less than 10 ng/g lipid of) or undetectable. This survey indicates that marine sponges are a possible source of the MeO-PBDE analogues that biomagnify via the food chain to the higher trophic organisms in the western Pacific, whereas the distribution of the corresponding hydroxylated analogues is limited.

New evidence for toxicity of polybrominated diphenyl ethers: DNA adduct formation from quinone metabolites

This study investigated the formation of DNA adducts of polybrominated diphenyl ethers (PBDEs) and the possible mechanisms. DNA adduction was conducted by in vitro reaction of deoxyguanosine (dG) and DNA with PBDE-quinone (PBDE-Q) metabolites, and DNA adducts were characterized by using electrospray ionization tandem mass spectrometry. The results suggested DNA adduction involved Michael Addition between the exocyclic NH(2) group at the N-2 position of dG and the electron-deficient carbon of quinone, followed by reductive cyclization with loss of (bromo-)1-hydroperoxy-benzene or water to form a type I or type II adduct. PBDE-Q with substituted bromine on the quinone ring was proven to be a favorable structure to form a type I adduct, while the absence of bromine on the quinone ring resulted in a type II adduct. Lower reactivity of adduction was also observed with increasing the number of bromine atoms on the phenoxyl ring. Our data clearly demonstrated PBDEs could covalently bind to DNA mediated by quinone metabolites, depending on the degree of bromine substitution. This study opened a new view on the mechanism of toxicity of PBDEs and reported the structure of PBDE-DNA adducts, which might be valuable for the evaluation on potential in vivo formation of PBDE-DNA adducts.

Anthropogenic and naturally occurring polybrominated phenolic compounds in the blood of cetaceans stranded along Japanese coastal waters

We determined the residue levels and patterns of hydroxylated polybrominated diphenyl ethers (OH-PBDEs), and related compounds, such as PBDEs, methoxylated PBDEs (MeO-PBDEs), and bromophenols (BPhs) in the blood of eleven cetacean species stranded along the Japanese coasts. The dominant OH- and MeO-PBDE isomers found in all cetaceans were 6OH-BDE47 and 6MeO-BDE47. Additionally, 2,4,6-triBPh was dominant isomer in all cetaceans. In contrast, specific differences in the distribution of para- and meta- OH-PBDE isomers and some BPhs (potential PBDEs metabolites) were found among the cetaceans. Residue levels of ΣMeO-PBDEs and 6OH-BDE47 + 2'OH-BDE68, and 2,4,6-triBPh and 6OH-BDE47 + 2'OH-BDE68 showed a significant positive correlation. These results may suggest that the large percentages of OH-PBDEs, MeO-PBDEs and 2,4,6-triBPh might share common source (i.e. biosynthesis by marine organisms), or metabolic pathway in cetacean species. Significant correlations were found between the concentrations of BDE99 and 2,4,5-triBPh. This result suggested that 2,4,5-triBPh in cetaceans could be a metabolite of BDE99.

Endocrine effects of methoxylated brominated diphenyl ethers in three in vitro models

Methoxylated brominated diphenyl ethers (MeO-BDEs) in aquatic environments have been found to be primarily of natural origin in the marine environment and not from biotransformation of synthetic PBDEs. Two of the eight MeO-PBDEs (2'-MeO-BDE-68 and 6-MeO-BDE-47) that were detected in anchovy from the Yangtze River Delta, were natural products from marine organisms. So 2'-MeO-BDE-68 and 6-MeO-BDE-47 were chosen to study the potential to modulate androgen, estrogen, or thyroid hormone receptor- (AR, ER, ThR) mediated responses by use of reporter gene assays. 2'-MeO-BDE-68 was antiandrogenic at 50 μM, estrogenic at 10 μM and antiestrogenic at 10 and 50 μM (IC50=4.88 μM). 2'-MeO-BDE-68 enhanced luciferase expression by 5 nM T3 at 50 μM. 6-MeO-BDE-47 exhibited potent antiandrogenicity at 1 μM and greater (IC50=41.8 μM) and possessed estrogenic activity at 10 μM and antiestrogenic activity at 10 and 50 μM (IC50=6.02 μM).

Structure-activity relationship study on the binding of PBDEs with thyroxine transport proteins

Molecular docking and three-dimensional quantitative structure-activity relationships (3D-QSAR) were used to develop models to predict binding affinity of polybrominated diphenyl ether (PBDE) compounds to the human transthyretin (TTR). Based on the molecular conformations derived from the molecular docking, predictive comparative molecular similarity indices analysis (CoMSIA) models were developed. The results of CoMSIA models were as follows: leave-one-out (LOO) cross-validated squared coefficient q² (LOO) = 0.827 (full model, for all 28 compounds); q² (LOO) = 0.752 (split model, for 22 compounds in the training set); leave-many-out (LMO) cross-validated squared coefficient q² (LMO, two groups) = 0.723 ± 0.100 (full model, for all 28 compounds); q² (LMO, five groups) = 0.795 ± 0.030 (full model, for all 28 compounds); and the predictive squared correlation coefficient r²(pred)  = 0.928 (for six compounds in the test set). The developed CoMSIA models can be used to infer the activities of compounds with similar structural characteristics. In addition, the interaction mechanism between hydroxylated polybrominated diphenyl ethers (HO-PBDEs) and the TTR was explored. Hydrogen bonding with amino acid residues Asp74, Ala29, and Asn27 may be an important determinant for HO-PBDEs binding to TTR. Among them, forming hydrogen bonds with amino acid residues Asp74 might exert a more important function.

Organohalogen compounds and their metabolites in the blood of Japanese amberjack (Seriola quinqueradiata) and scalloped hammerhead shark (Sphyrna lewini) from Japanese coastal waters

Information on accumulation of polychlorinated biphenyl metabolites (OH-PCBs) and hydroxylated polybrominated diphenyl ethers (OH-PBDEs) in the blood of marine fish is limited. The present study, we determined the residue levels and patterns of PCBs, OH-PCBs, PBDEs, OH-PBDEs and methoxylated PBDEs (MeO-PBDEs) in the blood collected from scalloped hammerhead shark (Sphyrna lewini) and Japanese amberjack (Seriola quinqueradiata), species of predatory fish at Japanese coastal waters. The predominant homologues found in Japanese amberjacks were mono- and di-chlorinated OH-PCBs, and scalloped hammerhead sharks were octa-chlorinated OH-PCBs. The predominant OH-PCB isomers were lower-chlorinated OH-PCBs such as 6OH-CB2 and 2'OH-CB9 in Japanese amberjacks. This result suggests that exposure of Japanese amberjacks to lower-chlorinated OH-PCBs might be from the ambient aquatic environment. In scalloped hammerhead sharks, 4,4'diOH-CB202, 4OH-CB201 and 4OH-CB146 were the predominant isomers accounting for approximately 60% of the total OH-PCBs. The predominant MeO-PBDE isomers were 6MeO-BDE47 followed by 2'MeO-BDE68 in both species. As for OH-PBDE isomers, 6OH-BDE47 was predominant followed by 2'OH-BDE68 in Japanese amberjacks and scalloped hammerhead sharks. Residue levels of ΣMeO-PBDEs and ΣOH-PBDEs showed a significant positive correlation (p=0.029). This result suggests that MeO-PBDEs and OH-PBDEs share a common source or a metabolic pathway in fishes. Characteristic differences found in the profiles of OH-PCBs and OH-PBDEs in Japanese amberjack and scalloped hammerhead shark show the need for further studies on the differences in exposure profiles, metabolic capacities and toxic effects in fish.

Exposure of Hong Kong residents to PBDEs and their structural analogues through market fish consumption

High concentrations of polybrominated diphenyl ethers (PBDEs) and their structural analogues (such as methoxylated (MeO) and hydroxylated (OH) PBDEs) had been observed in environmental samples and human tissues. This study evaluated the occurrence, potential source and human exposure of these organobrominated compounds via market fish consumption in Hong Kong. The contamination of 22 PBDEs, 7 MeO-BDEs, 15 OH-BDEs and 3 bromophenols (BRPs) were analyzed in 20 fish species (279 samples). The estimated daily intakes of PBDEs, MeO-BDEs, OH-BDEs and BRPs via fish consumption ranged from 4.4 to 14, 0.50 to 4.3, 0.02 to 0.43 and 0 to 0.21 ng/kg day for Hong Kong residents, respectively, based on 50(th) and 95(th) centile concentrations. BDE-47 and 99 were found to be the major PBDE congeners while 2'-MeO-BDE-68, 6-MeO-BDE-47 and 3-MeO-BDE-47 were the dominant MeO-BDEs. Concentrations of OH-BDEs and BRPs were 10-100-fold less than those of PBDEs, with small frequencies of detection (max 36.7%). Dietary intake of PBDEs via fish consumption by Hong Kong residents was greater than many developed countries, such as the USA, UK, Japan and Spain. To our knowledge, this is the first report to estimate the dietary intake of MeO/OH-BDEs and BRPs via fish consumption. Our results indicated that the toxicity potential of these compounds should not be neglected.

In vitro profiling of endocrine disrupting potency of 2,2',4,4'-tetrabromodiphenyl ether (BDE47) and related hydroxylated analogs (HO-PBDEs)

The potential of 2,2',4,4'-tetrabromodiphenyl ether (BDE47) and its related hydroxylated analogs (2'-HO-BDE28, 6-HO-BDE47, 4'-HO-BDE17, and 4'-HO-BDE49) to modulate estrogen/thyroid/androgen receptor-(ER, TR, AR), mediated responses were investigated by use of reporter gene assays. Exposure to 1 or 10 μM, 4'-HO-BDE17 significantly up-regulated expression of Luc, whereas other four chemicals did not induce Luc expression under control of the ER. Anti-estrogenic potency was observed for 4'-HO-BDE17 (IC50=1.14 μM)>6-HO-BDE47 (IC50=2.65 μM)>2'-HO-BDE28 (IC50=9.49 μM)>BDE47 (IC50=21.11 μM). No anti-estrogenic effect of 4'-HO-BDE49 was observed. Both 4'-HO-BDE17, 4'-HO-BDE49 resulted in greater responses of Luc expression induced by T3. BDE47, 2'-HO-BDE28, 6-HO-BDE47 did not show any effect on the expression of Luc induced by 5 nM T3. 6-HO-BDE47 (IC50=0.34 μM)>4'-HO-BDE17 (IC50=1.41 μM)>BDE47 (IC50=3.83 μM)>2'-HO-BDE28 (IC50=29.22 μM) exhibited anti-androgenic potency, while 4'-HO-BDE49 did not show androgenic transcriptional activity.

Formation of 2'-hydroxy-2,3',4,5'-tetrabromodipheyl ether (2'-HO-BDE68) from 2,4-dibromophenol in aqueous solution under simulated sunlight irradiation

Hydroxylated polybrominated diphenyl ethers (HO-PBDEs) have received significant attention due to their toxicities and universal presence in the environmental matrices. However, their origins are not fully understood. We explored the feasibility of the generation of HO-PBDEs through photochemical processes from bromophenol, a commonly detected pollutant with anthropogenic source in freshwater and natural source in the marine environment. The results showed that when 2,4-dibromophenol (2,4-diBP) was irradiated in aquatic solutions under simulated sunlight, significant amounts of 2'-hydroxy-2,3',4,5'-tetrabromodipheyl ether (2'-HO-BDE68) were rapidly formed as the dimeric product of 2,4-diBP. The formation of 2'-HO-BDE68 intensified with the increase of light intensity and with the initial concentration increase of 2,4-diBP, whereas it weakened with an increase in pH. Moreover, Fe(III) and fulvic acid played important roles in the formation of 2'-HO-BDE68. This study provides important insight into a possible source of HO-PBDEs from bromophenols in natural aquatic systems through photochemical approaches.

Seasonal variations of hydroxylated and methoxylated brominated diphenyl ethers in blue mussels from the Baltic Sea

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs) found at high levels in the Baltic biota are mainly natural products, but can also be formed through metabolism or abiotic oxidation of polybrominated diphenyl ethers (PBDEs). The formation of OH-PBDEs is of concern since there is growing evidence of phenolic toxicity. This study investigates seasonal variations in levels of OH-PBDEs and MeO-PBDEs, focusing on an exposed species, the blue mussel (Mytilus edulis), sampled in the Baltic Sea in May, June, August and October of 2008. Both the OH-PBDE and MeO-PBDE levels in the mussels showed seasonal variations from May to October, the highest concentration of each congener appearing in June. The seasonal variation was more marked for OH-PBDEs than in MeO-PBDEs, but all congeners showed the same trends, except 6-MeO-BDE47 and 2'-MeO-BDE68, which did not significantly decline in concentrations after June. Biotic or abiotic debromination is suggested as a possible reason for the rapid decrease in methoxylated penta- and hexa-BDE concentrations observed in blue mussels from June to August, while the tetraBDE concentrations were stable. In addition, 1,3,7/1,3,8-tribrominated dibenzo-p-dioxins showed the same seasonal variation. The seasonal variations indicates natural formation and are unlikely to be due to transformation of anthropogenic precursors. The levels of PBDEs were fairly constant over time and considerably lower than those of the OH-PBDEs and MeO-PBDEs. The timing of the peaks in concentrations suggests that filamentous macro-algae may be important sources of these compounds found in the blue mussels from this Baltic Sea location.

Neurotoxicity of brominated flame retardants: (in)direct effects of parent and hydroxylated polybrominated diphenyl ethers on the (developing) nervous system

BACKGROUND/OBJECTIVE

Polybrominated diphenyl ethers (PBDEs) and their hydroxylated (OH-) or methoxylated forms have been detected in humans. Because this raises concern about adverse effects on the developing brain, we reviewed the scientific literature on these mechanisms.

DATA SYNTHESIS

Many rodent studies reported behavioral changes after developmental, neonatal, or adult exposure to PBDEs, and other studies documented subtle structural and functional alterations in brains of PBDE-exposed animals. Functional effects have been observed on synaptic plasticity and the glutamate-nitric oxide-cyclic guanosine monophosphate pathway. In the brain, changes have been observed in the expression of genes and proteins involved in synapse and axon formation, neuronal morphology, cell migration, synaptic plasticity, ion channels, and vesicular neurotransmitter release. Cellular and molecular mechanisms include effects on neuronal viability 
(via apoptosis and oxidative stress), neuronal differentiation and migration, neurotransmitter release/uptake, neurotransmitter receptors and ion channels, calcium (Ca²⁺) homeostasis, and intracellular signaling pathways.

DISCUSSION

Bioactivation of PBDEs by hydroxylation has been observed for several endocrine end points. This has also been observed for mechanisms related to neurodevelopment, including binding to thyroid hormone receptors and transport proteins, disruption of Ca²⁺ homeostasis, and modulation of GABA and nicotinic acetylcholine receptor function.

CONCLUSIONS

The increased hazard for developmental neurotoxicity by hydroxylated (OH-)PBDEs compared with their parent congeners via direct neurotoxicity and thyroid disruption clearly warrants further investigation into a) the role of oxidative metabolism in producing active metabolites of PBDEs and their impact on brain development; b) concentrations of parent and OH-PBDEs in the brain; and c) interactions between different environmental contaminants during exposure to mixtures, which may increase neurotoxicity.

Bioaccumulation and maternal transfer of PBDE 47 in the marine medaka (Oryzias melastigma) following dietary exposure

The bioaccumulation and maternal transfer of 2,2',4,4'-tetrabromodiphenyl ether (PBDE 47) were investigated in the marine medaka (Oryzias melastigma) following dietary exposure, in which PBDE 47 was bioencapsulated into brine shrimp (Artemia sp.) and fed daily to male-female pairs of medaka. In the accumulation experiment, each 2-month-old (pre-breeding) medaka were provided with dietary PBDE 47 at 1.3±0.2 μg/day for 21 days. Growth-corrected concentrations of PBDE 47 in the medaka increased over the 21 days of exposure and there were no significant differences between males and females at any of the sampling times. Final concentrations were similar for males and females after 21 days (230±30 and 250±30 μgg(-1) wet weight, respectively), accounting for 84-100% of the PBDE 47 provided in the diet. In the maternal transfer experiment, 3-month-old (breeding) medaka were provided with dietary PBDE 47 at 1.2±0.2 μg/day for 18 days, and reached body concentrations of 76±3 (males) and 61±6 (females)μgg(-1) wet weight. Female growth-corrected PBDE 47 concentrations were significantly lower than males by day 12 (P<0.05), and egg PBDE 47 concentrations were up to 25 ng/egg by day 18. Our results showed that maternal transfer is an important offloading mechanism for female fish. The fact that lipid normalized egg:female PBDE ratios did not significantly deviate from 1 further indicated that the maternal transfer of PBDE 47 is associated with lipid mobilization during egg production.

PBDEs and methoxylated analogues in sediment cores from two Michigan, USA, inland lakes

Polybrominated diphenyl ethers (PBDEs) have been widely studied in sediments from the North American Great Lakes; however, no studies have been conducted of occurrences of methoxylated (MeO-) PBDEs in abiotic compartments in this region. In the present study, 23 tri- to hepta-PBDEs and 12 MeO-PBDEs were analyzed in dated sediment cores collected from two inland lakes (White Lake and Muskegon Lake) in Michigan, USA. Concentrations of Σ(23) PBDEs ranged from 3.9 × 10(-1) to 2.4 × 10(0) and from 9.8 × 10(-1) to 3.9 × 10(0) ng/g dry weight in White Lake and Muskegon Lake, respectively. The historical trends of tri- to hepta-PBDEs in the two lakes were different, possibly because of different input and remediation histories. The tri- to hepta-PBDE profiles were similar in the two lakes, with BDE-47 as the predominant congener, followed by BDE-99 and BDE-183. A different temporal trend for BDE-183 was found compared with other PBDEs, which is consistent with debromination of high-brominated PBDEs during sedimentation and aging. Methoxylated-PBDEs were detected only in Muskegon Lake (3.6 × 10(-3) to 1.2 × 10(-1) ng/g dry wt). Methoxylated PBDEs showed different temporal trends compared with tri- to hepta-PBDEs. The differences in patterns of concentrations of MeO-PBDEs in the two lakes might be due to different aquatic communities in each lake. The occurrences of MeO-PBDEs could be the major source of hydroxylated-polybrominated diphenyl ethers (OH-PBDEs) observed in organisms collected in these freshwater systems.

Genotoxicity of several polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs, and their mechanisms of toxicity

Polybrominated diphenyl ethers (PBDEs) have been extensively utilized as flame retardants, and recently there has been concern about potential adverse effects in humans and wildlife. Their hydroxylated analogs (OH-BDEs) have received increasing attention due to their potential for endocrine and neurological toxicities. However, the potentials and mechanisms of genotoxicity of these brominated compounds have scarcely been investigated. In the present study, genotoxicity of tetra-BDEs, penta BDE, octa-BDE, deca-BDE, and tetra-OH-BDEs were investigated by use of chicken DT40 cell lines including wild-type cells and a panel of mutant cell lines deficient in DNA repair pathways. Tetra-BDEs have greater genotoxic potential than do the other BDEs tested. OH-tetra-BDEs were more genotoxic than tetra-BDEs. DT40 cells, deficient in base excision repair (Polβ(-/-)) and translesion DNA synthesis (REV3(-/-)) pathways, were hypersensitive to the genotoxic effects of tetra-BDEs and OH-tetra-BDEs. The observation of chromosomal aberrations and gamma-H2AX assay confirmed that the studied brominated compounds caused double strand breaks. Pretreatment with N-acetyl-l-cysteine (NAC) significantly rescued the Polβ(-/-) and REV3(-/-) mutants, which is consistent with the hypothesis that PBDEs and OH-BDEs cause DNA damage mediated through reactive oxygen species (ROS). Some tetra-BDEs and OH-tetra-BDEs caused base damage through ROS leading to replication blockage and subsequent chromosomal breaks.

Contemporary 14C radiocarbon levels of oxygenated polybrominated diphenyl ethers (O-PBDEs) isolated in sponge-cyanobacteria associations

Considerable debate surrounds the sources of oxygenated polybrominated diphenyl ethers (O-PBDEs) in wildlife as to whether they are naturally produced or result from anthropogenic industrial activities. Natural radiocarbon ((14)C) abundance has proven to be a powerful tool to address this problem as recently biosynthesized compounds contain contemporary (i.e. modern) amounts of atmospheric radiocarbon; whereas industrial chemicals, mostly produced from fossil fuels, contain no detectable (14)C. However, few compounds isolated from organisms have been analyzed for their radiocarbon content. To provide a baseline, we analyzed the (14)C content of four O-PBDEs. These compounds, 6-OH-BDE47, 2'-OH-BDE68, 2',6-diOH-BDE159, and a recently identified compound, 2'-MeO-6-OH-BDE120, were isolated from the tropical marine sponges Dysidea granulosa and Lendenfeldia dendyi. The modern radiocarbon content of their chemical structures (i.e. diphenyl ethers, C(12)H(22)O) indicates that they are naturally produced. This adds to a growing baseline on, at least, the sources of these unusual compounds.

Polybrominated diphenyl ethers and their hydroxylated/methoxylated analogs: environmental sources, metabolic relationships, and relative toxicities

Brominated compounds are ubiquitous in the aquatic environment. The polybrominated diphenyl ether (PBDE) flame retardants are anthropogenic compounds of concern. Studies suggest that PBDEs can be biotransformed to hydroxylated brominated diphenyl ethers (OH-BDE). However, the rate of OH-BDE formation observed has been extremely small. OH-BDEs have also been identified as natural compounds produced by some marine invertebrates. Another class of compounds, the methoxylated BDEs (MeO-BDEs), has also been identified as natural compounds in the marine environment. Both the OH-BDEs and MeO-BDEs bioaccumulate in higher marine organisms. Recent studies have demonstrated that MeO-BDEs can be biotransformed to OH-BDEs and this generates greater amounts of OH-BDEs than could be generated from PBDEs. Consequently, MeO-BDEs likely represent the primary source of metabolically derived OH-BDEs. Given that for some endpoints OH-BDEs often exhibit greater toxicity compared to PBDEs, it is prudent to consider OH-BDEs as chemicals of concern, despite their seemingly "natural" origins.

Dietary exposure of juvenile common sole (Solea solea L.) to polybrominated diphenyl ethers (PBDEs): Part 2. Formation, bioaccumulation and elimination of hydroxylated metabolites

The uptake, elimination and transformation of six PBDE congeners (BDE-28, -47, -99, -100, -153, -209) were studied in juvenile common sole (Solea solea L.) exposed to spiked contaminated food over a three-month period, and then depurated over a five-month period. Methoxylated (MeO-) and hydroxylated (OH-) PBDEs were determined in fish plasma exposed to PBDEs and compared to those obtained in control fish. While all MeO- and some OH- congeners identified in fish plasma were found to originate from non-metabolic sources, several OH- congeners, i.e., OH-tetraBDEs and OH-pentaBDEs, were found to originate from fish metabolism. Among these, 4'-OH-BDE-49 was identified as a BDE-47 metabolite. Congener 4'-OH-BDE-101, identified here for the first time, may be the result of BDE-99 metabolic transformation. Our results unequivocally showed that PBDEs are metabolised in juvenile sole via the formation of OH- metabolites. However, this was not a major biotransformation route compared to biotransformation through debromination.

Neutral and phenolic brominated organic compounds of natural and anthropogenic origin in northeast Atlantic Greenland shark (Somniosus microcephalus)

In the present study, muscle and liver tissue from 10 female Greenland sharks (Somniosus microcephalus) collected in Icelandic waters were analyzed for neutral and phenolic brominated organic compounds, including polybrominated diphenyl ethers (PBDEs) and the structurally related methoxylated (MeO) and hydroxylated (OH) PBDEs. Hydroxylated PBDEs exist both as natural products and as metabolites of the anthropogenic PBDEs, whereas MeO-PBDEs appear to exclusively be of natural origin. Other compounds examined were 2',6-dimethoxy-2,3',4,5'-tetrabromodiphenyl ether (2',6-diMeO-BDE68), 2,2'-dimethoxy-3,3',5,5'-tetrabromobiphenyl (2,2'-diMeO-BB80), 2,4,6-tribromoanisol (2,4,6-TBA) and 2,4,6-tribromophenol, all of natural origin, although 2,4,6-TBA and its phenolic counterpart may also be of anthropogenic origin. The major brominated organic compound was 6-MeO-BDE47, and ΣMeO-PBDE ranged from 49 to 210 ng/g fat in muscle and from 55 to 200 ng/g fat in liver tissue. Total concentrations of PBDEs were lower than ΣMeO-PBDE, in all but one sample, ranging between 7.3 to 190 and 9.9 to 200 ng/g fat in muscle and liver, respectively, and major congeners were BDE-47, BDE-99, and BDE-100. Polybrominated diphenyl ethers were analyzed using both high- and low-resolution mass spectrometry (MS) as a quality assurance, and the results from this comparison were acceptable. In accordance with previous work on Greenland sharks, no size/age-related accumulation was observed. Differences seen in concentrations were instead assumed to be a reflection of different feeding habits among the individuals. Phenolic compounds were only formed/retained in trace amounts in the Greenland shark. Among the phenolic compounds studied were 6-OH-BDE47, 2'-OH-BDE68, and 2,4,6-tribromophenol, all detected in liver and the latter two in muscle.

Trophodynamics of polybrominated diphenyl ethers and methoxylated polybrominated diphenyl ethers in a marine food web

The current study measured the concentrations of 14 polybrominated diphenyl ethers (PBDEs) and eight methoxylated polybrominated diphenyl ethers (MeO-PBDEs) in a marine food web and estimated their trophic magnification factors (TMFs), to highlight the differences between invertebrates, fish, and seabirds. Concentrations of PBDEs were orders of magnitude greater in seabirds (184.07 ± 161.63 ng/g lipid wt) compared with invertebrates and fish (19.01 ± 14.14 ng/g lipid wt). Although the congener profiles in invertebrates, fish, and juvenile seabirds were dominated by BDE-47, the contributions of BDE-99 and BDE-153 in adult seabirds were also significant. Unlike PBDEs, however, higher average MeO-PBDE concentrations were detected in fish (126.27 ± 189.27 ng/g lipid wt) and bivalves (15.96 ± 11.82 ng/g lipid wt) than in seabirds (2.61 ± 2.87 ng/g lipid wt). Correlations between lipid-normalized PBDE concentrations and trophic levels confirmed that seven PBDE congeners were magnified in the invertebrate-fish-seabird food web and that PBDE concentrations increased at a much greater rate across trophic levels in seabirds than in invertebrates and fish. This result indicates that estimating TMFs of PBDEs separately for seabirds, invertebrates, and fish is preferable. For MeO-PBDEs, no significant relationships were obtained in the invertebrate-fish-seabird food web.

Interconversion of hydroxylated and methoxylated polybrominated diphenyl ethers in Japanese medaka

Polybrominated diphenyl ethers (PBDEs), hydroxylated (OH) and methoxylated (MeO), have been widely detected in aquatic environments. However, relationships among these structurally related compounds in exposed organisms are unclear. To elucidate biotransformation relationships among BDE-47, 6-OH-BDE-47, and 6-MeO-BDE-47, dietary accumulation, maternal transfer, and tissue distribution of these compounds and their transformation products were investigated in sexually mature Japanese medaka (Oryzias latipes). In addition, transformation of each compound was determined in vitro using liver microsomes of medaka. OH-PBDEs and MeO-PBDEs were not detected in fish exposed to BDE-47. However, significant concentrations of 6-OH-BDE-47 were detected in medaka or microsomes exposed to 6-MeO-BDE-47. Significant concentrations of 6-MeO-BDE-47 were also measured in fish exposed to 6-OH-BDE-47, but 6-MeO-BDE-47 was not detected in microsomes exposed to 6-OH-BDE-47. Similar patterns of transformation products were observed in medaka eggs from adult fish during exposure. This study presents direct in vivo evidence of biotransformation of 6-MeO-BDE-47 to 6-OH-BDE-47. In addition, this is the first study to demonstrate biotransformation of 6-OH-BDE-47 to 6-MeO-BDE-47. Demethylation of 6-MeO-BDE-47 was the primary transformation pathway leading to formation of 6-OH-BDE-47 in medaka, while the previously hypothesized formation of OH-PBDEs from synthetic BDE-47 did not occur. Biotransformation products formed in adult female medaka were transferred to eggs.

pK(a) values of the monohydroxylated polychlorinated biphenyls (OH-PCBs), polybrominated biphenyls (OH-PBBs), polychlorinated diphenyl ethers (OH-PCDEs), and polybrominated diphenyl ethers (OH-PBDEs)

The SPARC software program aqueous pK(a) prediction module was validated against corresponding experimental acidity constants for chlorinated and brominated phenols and the limited experimental aqueous pK(a) data sets for monohydroxylated polychlorinated biphenyls (OH-PCBs), polychlorinated diphenyl ethers (OH-PCDEs), and polybrominated diphenyl ethers (OH-PBDEs). pK(a) values were then estimated for all 837 monohydroxylated mono- through nona-halogenated congeners in each of the OH-PCB, OH-PCDE, and OH-PBDE classes, as well as for the monohydroxylated polybrominated biphenyls (OH-PBBs), giving a total of 3348 compounds. Large intrahomolog pK(a) variation by up to six units is expected within each contaminant class, with pK(a) values ranging from about 4 to 11 dependent on the degree and pattern of halogenation. Increasing halogenation generally decreased the average pK(a) within each homolog group. Significant intrahomolog differences in pK(a) values exist between OH-PCB, OH-PBB, OH-PCDE, and OH-PBDE congeners, including large acidity constant variation between isomers with equivalent halogenation patterns but varying location of the hydroxy moiety. Congener specific pH dependent investigations into the partitioning and degradation behaviors of these compounds are necessary, including greater consideration of analyte ionization effects during their extraction and analysis.

Brominated phenols, anisoles, and dioxins present in blue mussels from the Swedish coastline

INTRODUCTION

Naturally occurring hydroxylated polybrominated diphenyl ethers (OH-PBDEs), their methoxylated counterparts (MeO-PBDEs), and polybrominated dibenzo-p-dioxins (PBDDs), together with their potential precursors polybrominated phenols (PBPs) and polybrominated anisoles (PBAs), were analyzed in blue mussels (Mytilus edulis) gathered along the east coast (bordering the Baltic Sea) and west coast of Sweden (bordering the North Sea). Brown algae (Dictyosiphon foenicolaceus) and cyanobacteria (Nodularia spumigena) from the Baltic Sea, considered to be among the primary producers of these compounds, were also analyzed for comparison.

MATERIALS AND METHODS

The samples were liquid-liquid extracted, separated into a phenolic and a neutral fraction, and subsequently analyzed by gas chromatography-mass spectrometry (GS-MS).

RESULTS AND DISCUSSION

The levels of OH-PBDEs, MeO-PBDEs and PBDDs were significantly higher in Baltic Sea mussels than in those from the west coast, whereas the levels of PBPs and PBAs displayed the opposite pattern. The blue mussels from the Baltic Sea contained high levels of all analyzed substances, much higher than the levels of, e.g., polybrominated diphenyl ethers. In addition, the GC-MS chromatogram of the phenolic fraction of the west coast samples was dominated by four unknown peak clusters, three of which were tentatively identified as dihydroxy-PBDEs and the other as a hydroxylated-methyl-tetraBDE.

CONCLUSIONS

Clearly, all of the compounds analyzed are natural products, both in the Baltic and the North Sea. However, the geographical differences in composition may indicate different origin, e.g., due to differences in the occurrence and/or abundance of various algae species along these two coasts or possibly a more extensive dilution on the west coast.

Contribution of synthetic and naturally occurring organobromine compounds to bromine mass in marine organisms

An extraction, separation, and purification method was developed for the identification and quantification of total bromine (TBr), extractable organobromine (EOBr), and five classes of identified EOBrs. Instrumental neutron activation analysis (INAA) was utilized to quantify EOBr and TBr. The method was then applied to liver samples of tuna, albatross, and polar bear collected from remote marine locations. Polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), bromophenols (BRPs), hydroxylated (OH-) and methoxylated (MeO-) PBDEs were analyzed as identified EOBr. The majority of the bromine in these marine organisms was nonextractable or inorganic, with EOBr accounting for 10-28% of the TBr. Of the identified EOBr, in tuna and albatross, naturally occurring compounds, including MeO-PBDEs, OH-PBDEs, and BPRs, were prevalent. However, the identifiable EOBr in polar bears consisted primarily of synthetic compounds, including PBDEs and PBBs. Overall, 0.08-0.11% and 0.008-0.012% of EOBr and TBr, respectively, were identified. The proportion of EOBr that was identified in marine organisms was relatively small compared to the proportions for organofluorine and organochlorine compounds. This could be related to the great diversity of naturally occurring organobromine compounds in the environment. Naturally occurring brominated fatty acids were estimated to be the predominant compounds in the EOBr fraction.

On enumeration of congeners of common persistent organic pollutants

Congeners are molecules based on the same carbon skeleton but different by the number of substituents and/or a substitution pattern. Various Persistent Organic Pollutants (POPs) exist in the environment as families of halogen substituted congeners and/or their hydroxyl and methoxy substituted derivatives. Numbers of possible congeners resulting from substitution of a parent POP molecule with only one type of chemical group are generally available. At the same time, numbers of mixed-substituent congeners have not been counted and presented yet, although there is an increasing interest in such as is the increasing number of research articles presenting results on already identified Cl-/Br-mixed type congeners and/or their HO-/CH(3)O-mixed metabolites. We have enumerated and counted possible mixed-substituent congeners of common POPs. This article presents the obtained numbers for congener families of benzene, naphthalene, biphenyl, diphenyl ether, dibenzo-p-dioxin, dibenzofuran, anthracene, pyrene and others and obtained by substitution of up to five chemical group types.

Tissue concentrations of polybrominated compounds in Chinese sturgeon (Acipenser sinensis): origin, hepatic sequestration, and maternal transfer

Information on concentrations of polybrominated compounds in various tissues of wild fish is limited. Concentrations of polybrominated diphenyl ethers (PBDEs), methoxylated PBDEs (MeO-PBDEs), and hydroxylated PBDEs (OH-PBDEs) were measured in 12 organs and eggs of 17 female Chinese sturgeon (Acipenser sinensis). The highest concentrations of PBDEs (42.8+/-39.4 ng/g ww), and MeO-PBDEs (135+/-63.6 pg/g ww) occurred in adipose followed by liver (PBDEs: 25.0+/-27.0 ng/g ww, MeO-PBDEs: 32.3+/-29.1 pg/g ww) and eggs (PBDEs: 21.2+/-19.4 ng/g ww, MeO-PBDEs: 120+/-119 pg/g ww), and the highest concentration of OH-PBDEs was observed in liver (185+/-174 pg/g ww) and eggs (178+/-294 pg/g ww). The lack of in vitro transformation of 6-MeO-BDE47 or BDE47 by microsomes prepared from Chinese sturgeon liver suggests that most 6-OH-BDE47 was directly accumulated as a natural product. Lipid-normalization revealed preferential accumulation of PBDEs in liver, and ratios of concentrations between eggs and liver were 0.10+/-0.11 to 0.22+/-0.26, which was lower than that for MeO-PBDEs (6-MeO-BDE47: 0.57+/-0.60, 2'-MeO-BDE68: 0.65+/-0.85) and 6-OH-BDE47 (0.59+/-0.51). Concentrations of PBDEs were negatively correlated with age, but no significant relationships between concentrations of OH-PBDEs or MeO-PBDEs and age were observed.

Hydroxylated polybrominated diphenyl ethers and bisphenol A in pregnant women and their matching fetuses: placental transfer and potential risks

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are suspected endocrine disruptors, which can pass through the mammalian placenta and accumulate in the human maternal-fetal-placental unit. However, little is known about mechanisms of placental transfer and the associated risk(s). Ten OH-PBDE congeners, bisphenol A (BPA), total 17beta-estradiol (E2), and total thyroxine (T4) were quantified in blood serum from 26 pregnant women and 28 matching fetuses, including three pairs of twins from South Korea. Only 6-OH-BDE-47, a naturally occurring OH-PBDE, was detected at relatively great concentrations (maternal serum: 17.5 +/- 26.3 pg/g ww, fetal cord blood serum: 30.2 +/- 27.1 pg/g ww), which suggests that exposure was related to diets among Korean women. Concentrations of 6-OH-BDE-47 in maternal and cord serum were positively correlated, with concentrations being significantly greater in cord blood serum. The placental transfer ratio between fetal and maternal blood serum for 6-OH-BDE-47 (F/M ratio: 1.4 +/- 1.1) was different than the observed placental transfer ratio of BPA and previously reported values for hydroxylated polychlorinated biphenyls (OH-PCBs). This result is possibly due to large affinities to T4 transport proteins. Lesser concentrations of E2 and T4 were detected in cord blood serum (E2: 4.7 +/- 2.2 ng/mL, T4: 8.5 +/- 1.7 microg/dL) compared to maternal blood serum (E2: 8.0 +/- 3.0 ng/mL, T4: 9.7 +/- 1.8 microg/dL). A major effect of OH-PBDE exposure might be a decrease in serum T4 concentrations. Potential risks associated with disruption of T4 transport to the developing fetus such as negative consequences for fetal neurological development should be considered in further studies.

Historical contaminants, flame retardants, and halogenated phenolic compounds in peregrine Falcon (Falco peregrinus) nestlings in the Canadian Great Lakes Basin

Concentrations and spatial patterns of persistent organic (chlorinated) pollutants (POPs), polybrominated diphenyl ether (PBDE), hexabromocyclododecane (HBCD), other flame retardants, and hydroxylated (OH) PBDE and PCB compounds were determined in nestling peregrine falcons across the Canadian Great Lakes Basin. The highest geometric mean plasma POP concentrations (ng/g ww) were sum (Sigma)PCBs (35.16), SigmaPBDEs (15.38), and SigmaOH-PCB (8.77) with the lowest mean levels in nestlings from urban versus remote nests. PBDE congeners derived from PentaBDE and OctaBDE technical mixtures had the highest concentrations, sometimes exceeding 100 ng/g wet weight (ww); BDE-99, -153, -47, -100, and -183 comprised 92.7% of the Sigma(14)PBDE levels. BDE-209 proportions were minimal (<1%). North Shore (Lake Superior) nestlings had the highest Sigma(14)PBDE concentrations, with BDE-99, -153, and -47 dominant. Urban nestlings had higher BDE-99:BDE-153 ratios, higher BDE-183 proportions, and the only detectable HBCD concentrations, suggesting greater and more localized exposure to HBCD and PBDEs derived from OctaBDEs. Spatial patterns reflected differences in diet, local contaminant sources, and/or atmospheric deposition. Metabolism of PCBs and PBDEs likely occurred in these nestlings: OH-PCB metabolites were detected, and 4-OH-CB187 was the most abundant of these metabolites. Low ppb levels of putative OH-PBDE metabolites, dominated by 6'-OH-BDE47, were also detected in the peregrine nestlings.

Hormone activity of hydroxylated polybrominated diphenyl ethers on human thyroid receptor-beta: in vitro and in silico investigations

BACKGROUND

Hydroxylated polybrominated diphenyl ethers (HO-PBDEs) may disrupt thyroid hormone status because of their structural similarity to thyroid hormone. However, the molecular mechanisms of interactions with thyroid hormone receptors (TRs) are not fully understood.

OBJECTIVES

We investigated the interactions between HO-PBDEs and TRbeta to identify critical structural features and physicochemical properties of HO-PBDEs related to their hormone activity, and to develop quantitative structure-activity relationship (QSAR) models for the thyroid hormone activity of HO-PBDEs.

METHODS

We used the recombinant two-hybrid yeast assay to determine the hormone activities to TRbeta and molecular docking to model the ligand-receptor interaction in the binding site. Based on the mechanism of action, molecular structural descriptors were computed, selected, and employed to characterize the interactions, and finally a QSAR model was constructed. The applicability domain (AD) of the model was assessed by Williams plot.

RESULTS

The 18 HO-PBDEs tested exhibited significantly higher thyroid hormone activities than did PBDEs (p < 0.05). Hydrogen bonding was the characteristic interaction between HO-PBDE molecules and TRbeta, and aromaticity had a negative effect on the thyroid hormone activity of HO-PBDEs. The developed QSAR model had good robustness, predictive ability, and mechanism interpretability.

CONCLUSIONS

Hydrogen bonding and electrostatic interactions between HO-PBDEs and TRbeta are important factors governing thyroid hormone activities.

Absorption and biotransformation of polybrominated diphenyl ethers DE-71 and DE-79 in chicken (Gallus gallus), mallard (Anas platyrhynchos), American kestrel (Falco sparverius) and black-crowned night-heron (Nycticorax nycticorax) eggs

We recently reported that air cell administration of penta-brominated diphenyl ether (penta-BDE; DE-71) evokes biochemical and immunologic effects in chicken (Gallus gallus) embryos at very low doses, and impairs pipping (i.e., stage immediately prior to hatching) and hatching success at 1.8mugg(-1) egg (actual dose absorbed) in American kestrels (Falco sparverius). In the present study, absorption of polybrominated diphenyl ether (PBDE) congeners was measured following air cell administration of a penta-BDE mixture (11.1mug DE-71g(-1) egg) or an octa-brominated diphenyl ether mixture (octa-BDE; DE-79; 15.4mug DE-79g(-1) egg). Uptake of PBDE congeners was measured at 24h post-injection, midway through incubation, and at pipping in chicken, mallard (Anas platyrhynchos), and American kestrel egg contents, and at the end of incubation in black-crowned night-heron (Nycticorax nycticorax) egg contents. Absorption of penta-BDE and octa-BDE from the air cell into egg contents occurred throughout incubation; at pipping, up to 29.6% of penta-BDE was absorbed, but only 1.40-6.48% of octa-BDE was absorbed. Higher brominated congeners appeared to be absorbed more slowly than lower brominated congeners, and uptake rate was inversely proportional to the log K(ow) of predominant BDE congeners. Six congeners or co-eluting pairs of congeners were detected in penta-BDE-treated eggs that were not found in the dosing solution suggesting debromination in the developing embryo, extraembryonic membranes, and possibly even in the air cell membrane. This study demonstrates the importance of determining the fraction of xenobiotic absorbed into the egg following air cell administration for estimation of the lowest-observed-effect level.

Recombinant albumin and transthyretin transport proteins from two gull species and human: chlorinated and brominated contaminant binding and thyroid hormones

Environmentally relevant concentrations of selected polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) flame retardant congeners and their hydroxylated (OH) and methoxylated (MeO) analogues that can perturb thyroid hormone-dependent processes were comparatively examined with respect to competitive binding with thyroxine (T(4)) and 3,5,3'-triiodothyronine (T(3)) thyroid hormones (THs) on recombinant human and gull albumin and transthyretin transport proteins. The liver tissue was from glaucous gulls (Larus hyperboreus) from Norway and herring gulls (Larus argentatus) from the Great Lakes of North America. We isolated, cloned, sequenced, purified, and expressed the cDNA (cDNA) of albumin from liver of herring and glaucous gull. Albumin amino acid sequences were identical for both gull species. Concentration-dependent, competitive binding curves were generated for T(4) and T(3) binding alone and for selected substrates using gull and human recombinant albumin (recALB). Human recALB had high preference for T(4) relative to T(3), whereas it was reversed for gull recALB. Binding assays with recALB and recTTR gull proteins showed that relative to 2,2',4,4'-tetrabromoDE (BDE-47) and 2,2',3,4',5,5',6-heptaCB (CB-187) and the MeO-substituted (4-MeO-CB187 and 6-MeO-BDE47) analogues, 4-OH-CB187, 6-OH-BDE47, and 4'-OH-BDE49 had the greatest binding affinity and potency, and that competitive binding was greater for T(3) relative to T(4). These results indicate that xenobiotic ligand binding to human ALB or TTR cannot be used as a surrogate for gull binding interactions. The combination of TH-like brominated diphenyl ether backbone (relative to the chlorinated biphenyl backbone), and the presence of OH-group produced a more effective competitive ligand on human and gull recALB and recTTR relative to both T(3) and T(4). This suggests the possibility that OH-substituted organohalogen contaminants may be an exposure concern to the thyroid system in free-ranging gulls as well as for humans.