Novel octabrominated phenolic diphenyl ether identified in blue mussels from the Swedish West Coast.

Hydroxylated (OH-) and methoxylated (MeO-) polybrominated diphenyl ethers (PBDEs) are compounds present in the marine environment and OH-PBDEs are of toxicological concern and are therefore of interest to monitor in the environment. A phenolic octaBDE was tentatively identified in the phenolic fraction of previously analyzed mussel samples after methylation of the halogenated phenolic compounds (HPCs). The aim of the present study was to confirm the identity of this compound in blue mussels and investigate whether the analyte is diOH- and/or OH-MeO-octaBDE. Two reference standards, 6,6'-dimethoxy-2,2',3,3',4,4',5,5'-octabromodiphenyl ether (6,6'-diMeO-BDE194) and 6-ethoxy-6'-methoxy-2,2',3,3',4,4',5,5'-octabromodiphenyl ether (6-EtO-6'-MeO-BDE194) were prepared via O-arylation of 2,3,4,5-tetrabromo-6-methoxyphenol and 2,3,4,5-tetrabromo-6-ethoxyphenol, respectively, with a novel unsymmetrical diaryliodonium salt, 2,3,4,5-tetrabromo-6-methoxydiphenyliodonium triflate. The GC retention time and GC/MS spectrum of the synthesized 6,6'-diMeO-BDE194 correspond well with the analyte in the methylated phenolic fraction of a mussel extract from a previous study. Structural analysis performed in this study indicate that the synthesized 6,6'-diMeO-BDE194 and 6-EtO-6'-MeO-BDE194 correspond well with 6-hydroxy-6'-methoxy-2,2',3,3',4,4',5,5'-octabromodiphenyl ether (6-OH-6'-MeO-BDE194) after methylation and ethylation, respectively, of the HPCs in the mussel extracts. The compound 6-OH-6'-MeO-BDE194 was identified and quantified in new mussels, sampled in 2012 from two locations on the Swedish west coast, with geometric mean concentrations of 3700 and 410 ng/g fat, respectively.

Disruption of oxidative phosphorylation (OXPHOS) by hydroxylated polybrominated diphenyl ethers (OH-PBDEs) present in the marine environment.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are of growing concern, as they have been detected in both humans and wildlife and have been shown to be toxic. Recent studies have indicated that OH-PBDEs can be more toxic than PBDEs, partly due to their ability to disrupt oxidative phosphorylation (OXPHOS), an essential process in energy metabolism. In this study, we determined the OXPHOS disruption potential of 18 OH-PBDE congeners reported in marine wildlife using two in vitro bioassays, namely the classic rat mitochondrial respiration assay, and a mitochondrial membrane potential assay using zebrafish PAC2 cells. Single OH-PBDE congeners as well as mixtures were tested to study potential additive or synergistic effects. An environmental mixture composed of seven OH-PBDE congeners mimicking the concentrations reported in Baltic blue mussels were also studied. We report that all OH-PBDEs tested were able to disrupt OXPHOS via either protonophoric uncoupling and/or inhibition of the electron transport chain. Additionally we show that OH-PBDEs tested in combinations as found in the environment have the potential to disrupt OXPHOS. Importantly, mixtures of OH-PBDEs may show very strong synergistic effects, stressing the importance of further research on the in vivo impacts of these compounds in the environment.

Polybrominated diphenyl ethers and their hydroxylated analogs in plasma of bottlenose dolphins (Tursiops truncatus) from the United States east coast.

Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs (OH-PBDEs) were determined in plasma of free-ranging bottlenose dolphins (Tursiops truncatus) from Charleston (CHS), South Carolina, and the Indian River Lagoon (IRL), Florida, U.S.A. Significantly lower sums (sigma) of PBDE concentrations (sum of 12 congeners) were found in animals from the IRL (arithmetic mean, 5.45 +/- 4.63 ng/g wet wt) compared with those from CHS (30 +/- 40 ng/g wet wt). Brominated diphenyl ether (BDE)-47 was the predominant PBDE in dolphins from the IRL (50% of the sigma PBDEs) and CHS (58%). The sigma PBDE concentrations in plasma of dolphins were negatively correlated with age at both locations. Fifteen and sixteen individual OH-PBDE congeners could be quantified in plasma of dolphins from IRL and CHS, respectively. Similar to sigma PBDE, mean sigma OH-PBDE concentrations were significantly higher in plasma of dolphins at CHS (1150 +/- 708 pg/g wet wt) compared with those at IRL (624 +/- 393 pg/g wet wt). The predominant congener at both locations was 6-OH-PBDE-47 (IRL, 384 +/- 319 pg/g wet wt; CHS, 541 +/- 344 pg/g wet wt), representing 61.5% of total sigma OH-PBDE at IRL and 47.0% at CHS. Concentrations of sigma OH-PBDEs were weakly negatively correlated with age in dolphins from both locations (p < 0.05; IRL, r2 = 0.048; CHS, r2 = 0.021). In addition to the OH-PBDE congeners identified with technical standards, eight and four unidentified OH-PBDEs were detected and quantified, respectively, in animals from CHS (sum of unidentified OH-PBDEs = 1.35 +/- 0.90 pg/g wet wt) and IRL (0.73 +/- 0.40 pg/g wet wt). Results of the present study suggest that, unlike OH-PCBs, OH-PBDEs in bottlenose dolphins are minor products in plasma relative to sigma PBDEs and a significant proportion may be a consequence of the dietary uptake of naturally produced methoxylated- and OH-PBDEs.

Polybrominated diphenyl ethers (PBDEs) and bioaccumulative hydroxylated PBDE metabolites in young humans from Managua, Nicaragua.

OBJECTIVE: Our aim was to investigate exposure to polybrominated diphenyl ethers (PBDEs) in a young urban population in a developing country, with focus on potentially highly exposed children working informally as scrap scavengers at a large municipal waste disposal site. We also set out to investigate whether hydroxylated metabolites, which not hitherto have been found retained in humans, could be detected. METHODS: We assessed PBDEs in pooled serum samples obtained in 2002 from children 11-15 years of age, working and sometimes also living at the municipal waste disposal site in Managua, and in nonworking urban children. The influence of fish consumption was evaluated in the children and in groups of women 15-44 years of age who differed markedly in their fish consumption. Hydroxylated PBDEs were assessed as their methoxylated derivates. The chemical analyses were performed by gas chromatography/mass spectrometry, using authentic reference substances. RESULTS: The children living and working at the waste disposal site showed very high levels of medium brominated diphenyl ethers. The levels observed in the referent children were comparable to contemporary observations in the United States. The exposure pattern was consistent with dust being the dominating source. The children with the highest PBDE levels also had the highest levels of hydroxylated metabolites. CONCLUSIONS: Unexpectedly, very high levels of PBDEs were found in children from an urban area in a developing country. Also, for the first time, hydroxylated PBDE metabolites were found to bioaccumulate in human serum.

Effect of sewage sludges contaminated with polybrominated diphenylethers on agricultural soils.

The fate of polybrominated diphenyl ethers (PBDEs) in sewage sludge after agricultural application was analysed. This study was based on the analysis of sewage sludge and sludge amended soil samples collected during 2005. PBDE concentrations in sewage sludge ranged from 197 to 1185ng/g dry weight (dw), being deca-BDE-209 the predominant congener. PBDE levels in soils ranged between 21 and 690ng/g dw, being BDE-209 also the predominant congener in all soil samples. Sewage-sludge amendment at the research stations increased concentrations of all BDE congeners 1.2- to 45-fold, with the highest increases for BDE-209. Results obtained evidenced the cumulative effect of the sludge application rates. Moreover, high levels found at soils four years after the last sludge application indicate persistence of PBDEs in soils, including deca-BDE-209.

Identification and quantification of new polybrominated dimethoxybiphenyls (PBDMBs) in marine mammals from Australia.

Marine mammals from Queensland, Australia, are bioaccumulating elevated concentrations of a range of polybrominated natural products. In this study, we detected three new polybrominated dimethoxybiphenyls (PBDMBs) in the blubber of selected marine mammal samples which were identified as 2,6'-dimethoxy-3,3',5-tribromobiphenyl (2,6'-diMeO-BB 36), 2,2'-dimethoxy-3,3'-dibromobiphenyl (2,2'-diMeO-BB 36), and 6,6'-dimethoxy-3,3'-dibromobiphenyl (6,6'-diMeO-BB 11). These three PBDMBs are structurally related to the known natural product 2,2'-dimethoxy-3,3',5,5'-tetrabromobiphenyl (2,2'-diMeO-BB 80). In the first part of this study, 2,2'-diMeO-BB 80 was photochemically debrominated under UV irradiation. This resulted in seven of eight possible mono- to triBDMBs as debromination products. In the second part of this study, the structure of all PBDMBs debromination products was investigated. This was supported by synthesis of two diBDMB and one triBDMB via bromination and subsequent methylation of 2,2'-biphenyldiol. Structures of the remaining PBDMBs were tentatively assigned by considering the retention times, mass spectra and amounts formed during UV irradiation of 2,2'-diMeO-BB 80 . In the third part of this study, blubber of marine mammals from Australia was analysed for PBDMBs using gas chromatography in combination with electron ionization mass spectrometry (GC/EI-MS) in the selected ion monitoring mode. In these samples, 2,2'-diMeO-BB 80 was found at concentrations of 200-1800ngg(-1) lipid weight (lw). The latter represents the highest concentration reported for this compound in environmental samples. 6,6'-diMeO BB 11, 2,2'-diMeO BB 36, and 2,6'-diMeO BB 36 were present at approximately 7ngg(-1) lipids, or 0.43-1.5% of diMeO-BB 80. No further PBDMBs were detected in the samples. The di- and triBDMBs identified in marine mammal blubber have not been reported as natural products. They may represent either new natural products or transformation products of 2,2'-diMeO-BB 80.

Decabrominated diphenyl ether in river fish and sediment samples collected downstream an industrial park.

Fish, sediment and water samples from different places along the Spanish River Vero, a tributary of the Cinca River in the Ebro River basin, were collected in two different sampling campaigns, the first one during November 2004 and the second one in November 2005. The samples were collected up- and downstream from an industrial park. A total of 29 fishes, 6 sediments and 3 water samples were analyzed for polybrominated diphenyl ethers (PBDEs). Analytical work included 23 congeners, from tri- to deca-BDEs. The highest values for both sediment and fish samples were found downstream of the industrial park. High BDE-209 contamination was found in these sediment samples, with values up to 12 microg g(-1) dry weight. Moreover, BDE-209 was detected in 14 out of 15 biota samples collected downstream the industrial park, at concentration levels ranging from 20 to 707 ng g(-1) lipid weight, whereas it was not detected in samples collected upstream. These fish concentrations proved the bioavailability of BDE-209 and represented the highest deca-BDE values found in aquatic biota. The analysis of industrial effluents revealed that some industries contribute in some way to the BDE-209 contamination found in this area, but the industry focused on the polyamide polymerization is the main responsible.

Gas chromatography and mass spectrometry of methoxylated polybrominated diphenyl ethers (MeO-PBDEs).

Twenty-six methoxylated polybrominated diphenyl ethers (MeO-PBDEs) were characterized by gas chromatography (GC) on four different GC columns with different lengths and polarities, as well as by mass spectrometry using three ionization techniques, electron ionization (EI), electron capture negative ionization (ECNI) and positive ion chemical ionization (PICI). MeO-PBDE congeners with similar retention times on a nonpolar GC column were separated when analyzed on a polar GC column. EI can be used to determine the position of the methoxy substituent (ortho, meta or para) relative to the diphenyl ether oxygen in the MeO-PBDEs. The PICI ionization technique is shown to be valuable to generate structural information of the MeO-PBDEs, i.e. the degree of bromination on both the methoxy-substituted ring and the entirely brominated phenyl ring can be obtained. This structure information can also be achieved for certain MeO-PBDEs with the methoxy group in ortho position to the diphenyl ether bond in ECNI mode. Like other brominated compounds ECNI is preferable when analyzing environmental samples for quantification of MeO-PBDEs because of the formation of bromide ions, which enables low detection limits.

Neonatal exposure to higher brominated diphenyl ethers, hepta-, octa-, or nonabromodiphenyl ether, impairs spontaneous behavior and learning and memory functions of adult mice.

Polybrominated diphenyl ethers (PBDEs), used as flame retardants, have been shown to be increasing in the environment and in human mother's milk. We have earlier reported that lower brominated PBDEs, such as tetra-, penta-, and hexa-brominated diphenyl ethers, can cause developmental neurotoxic effects in mice. Recently, this was also observed with the full-brominated PBDE, deca-brominated diphenyl ether (PBDE 209), although it was suggested that the effects were caused by a (possibly debrominated) metabolite thereof. The present study revealed that 2,2',3,3',4,4',5,5',6-nonabromodiphenyl ether (PBDE 206), 2,2',3,4,4',5,5',6-octabromodiphenyl ether (PBDE 203), and to a minor extent also 2,2',3,4,4',5',6'-heptabromodiphenyl ether (PBDE 183) can induce developmental neurotoxic effects. Neonatal Naval Medical Research Institute male mice were exposed on postnatal day 3 or 10 to PBDE 206, PBDE 203, or PBDE 183, given as a single oral dose of 21 mumol/kg body weight. At the adult age of 2-3 months, the mice were observed for performance in a spontaneous behavior test and the Morris water maze test. PBDE 203 and PBDE 206, when administered on neonatal day 10, caused disturbances in spontaneous behavior, leading to disrupted habituation and a hyperactive condition in adults at the age of 2 months. These behavioral changes were also seen in 2-month-old mice exposed to PBDE 203 on neonatal day 3. Furthermore, exposure to PBDE 203 on neonatal day 10 affected learning and memory functions in adult mice. The developmental neurotoxic effects were most pronounced in mice exposed to PBDE 203. These developmental neurobehavioral defects were in agreement with those we observed previously with lower brominated PBDEs and with PBDE 209. It is important to consider the fact that different PBDE congeners can have differing degrees of potency, when comparing levels of PBDEs in the environment and in mother's milk.

Identification of hydroxylated metabolites in 2,2',4,4'-tetrabromodiphenyl ether exposed rats.

Faeces from day 1-5 of orally administered 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in rat have been analysed for hydroxylated metabolites. Six hydroxylated tetrabrominated diphenyl ethers, as well as three hydroxylated tribrominated diphenyl ethers found, were structurally identified. They were 2'-hydroxy-2,4,4'-tribromodiphenyl ether, 3'-hydroxy-2,4,4'-tribromodiphenyl ether, 4'-hydroxy-2,2',4-tribromodiphenyl ether, 6-hydroxy-2,2',4,4'-tetrabromodiphenyl ether, 2'-hydroxy-2,3',4,4'-tetrabromodiphenyl ether, 3-hydroxy-2,2',4,4'-tetrabromodiphenyl ether, 5-hydroxy-2,2',4,4'-tetrabromodiphenyl ether, 4'-hydroxy-2,2',4,5'-tetrabromodiphenyl ether and 4-hydroxy-2,2',3,4'-tetrabromodiphenyl ether. The analysis was performed using gas chromatography-mass spectrometry (GC-MS). The identification of the hydroxylated polybrominated diphenyl ether (OH-PBDE) metabolites in the rat faeces was supported by similar relative retention times (RRTs) versus 2,2',3,4,4',5-hexabromodiphenyl ether (BDE-138) on two columns of different polarities compared to the authentic references. The identification of the OH-PBDE metabolites was also supported by full scan electron ionisation mass spectra. Two of the identified OH-PBDE metabolites have identical structures as natural products, which previously have been isolated from marine sponges and an ascidian.

Methods for synthesis of nonabromodiphenyl ethers and a chloro-nonabromodiphenyl ether.

Polybrominated diphenyl ethers (PBDEs) have been used extensively as brominated flame retardants (BFRs) in textiles, upholstery and electronics. They are ubiquitous contaminants in wildlife and humans. A low concentration of nonabrominated diphenyl ethers (nonaBDEs) is present in commercial DecaBDE and they are also abiotic and biotic debromination products of decabromodiphenyl ether (BDE-209). The objective of the present work was to develop methods for synthesis of the three nonaBDEs, 2,2',3,3',4,4',5,5',6-nonabromodiphenyl ether (BDE-206), 2,2',3,3',4,4',5,6,6'-nonabromodiphenyl ether (BDE-207) and 2,2',3,3',4,5,5',6,6'-nonabromodiphenyl ether (BDE-208), with the intention of making them available as authentic standards for analytical, toxicological and stability studies, as well as studies regarding physical-chemical properties. Two methods were developed, one based on perbromination of phenoxyanilines and the other via reductive debromination of BDE-209 by sodium borohydride followed by chromatographic separation of the three nonaBDE isomers formed. An additional nonabrominated compound, 4'-chloro-2,2',3,3',4,5,5',6,6'-nonabromodiphenyl ether (Cl-BDE-208), was also synthesized in the present work. Cl-BDE-208, prepared by the perbromination of 4-chlorodiphenyl ether, may be used as an internal standard in analysis of highly brominated diphenyl ethers. BDE-206, BDE-207, BDE-208 and Cl-BDE-208 were characterized by 1H NMR, 13C NMR, electron ionization mass spectra and by their melting points. The structures of all three nonaBDEs have been characterized previously by X-ray crystallography.

Spectral characterization of two bioaccumulated methoxylated polybrominated diphenyl ethers.

Two methoxylated polybrominated diphenyl ethers (MeO-PBDEs) were isolated from a True's beaked whale (Mesoplodon mirus) and identified by NMR (1H, 1H-1H and 1H-13C) and high resolution mass spectrometry as 2-(2',4'-dibromophenoxy)-3,5-dibromoanisole (6-MeO-BDE47) and 2-(2',4'-dibromophenoxy)-4,6-dibromoanisole (2'-MeO-BDE68). Previously the structures of these bioaccumulated compounds have been determined by comparison of their mass spectra and gas chromatographic (GC) retention times with those of authentic standards. While this method is accepted and generally successful, NMR of the isolated compounds allows us to definitively identify the congeners. Our characterizations are consistent with those made for MeO-PBDEs in other organisms, identified by chromatographic methods.

Human hydroxylated metabolites of BDE-47 and BDE-99 are glucuronidated and sulfated in vitro.

Polybrominated diphenyl ethers (PBDEs) were used worldwide as additive flame retardants and are classified as persistent, bioaccumulable and toxic environmental pollutants. In humans, the hydroxylated metabolites of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) formed in vitro have also been detected in vivo. To further characterize the metabolism of BDE-47 and BDE-99 and to identify candidate markers for monitoring the human exposure to PBDEs using non-invasive approaches, glucuronidation and sulfation of hydroxylated metabolites of BDE-47 and BDE-99 were investigated using human liver microsomes and cytoplasm, respectively. The formed Phase II metabolites were analyzed by liquid chromatography-tandem mass spectrometry using a novel approach to develop analytical methods in absence of authentic standards. All available standards for hydroxylated metabolites of BDE-47 and BDE-99 were glucuronidated and sulfated, showing that glucuronidation and sulfation are part of the metabolism pathway of BDE-47 and BDE-99 in vitro. The major glucuronidated and sulfated analogs of hydroxylated metabolites of BDE-47 were (a) 2,4-DBP-Gluc and 5-Gluc-BDE-47, and (b) 2'-Sulf-BDE-28, 4-Sulf-BDE-42 and 3-Sulf-BDE-47, respectively. The major glucuronidated and sulfated analogs of hydroxylated metabolites of BDE-99 were (a) 2,4,5-TBP-Gluc and 6'-Gluc-BDE-99, and (b) 3'-Sulf-BDE-99 and 5'-Sulf-BDE-99, respectively. Apparent Km values associated with the formation of sulfated metabolites of BDE-47 and BDE-99 were ten times lower than those of the corresponding glucuronidated metabolites, suggesting that sulfated rather than glucuronidated metabolites of OH-PBDEs might be used as markers of human exposure to PBDEs using a non-invasive approach based on urine sample collection.

Synthesis and tentative identification of novel polybrominated diphenyl ether metabolites in human blood.

Hydroxylated polybrominated diphenyl ethers (OH-PDBEs) are exogenous, bioactive compounds that originate, to a large extent, from anthropogenic activities, although they are also naturally produced in the environment. In the present study nine new authentic OH-PBDE reference standards and their corresponding methyl ether derivatives (MeO-PBDEs) were synthesised and characterised by NMR spectroscopy and mass spectrometry. Seven of the authentic reference standards prepared were thereafter tentatively identified in a pooled human blood sample. The tentatively identified OH-PBDEs were 3-hydroxy-2,2',4,4',6-pentabromodiphenyl ether, 3'-hydroxy-2,2',4,4',6-pentabromodiphenyl ether, 3-hydroxy-2,2',4,4',5-pentabromodiphenyl ether, 3-hydroxy-2,2',4,4',5,6'-hexabromodiphenyl ether, 3'-hydroxy-2,2',4,4',5,6'-hexabromodiphenyl ether, 3-hydroxy-2,2',4,4',5,5'-hexabromodiphenyl ether and 4-hydroxy-2,2',3,4',5,5',6-heptabromodiphenyl ether. An additional seven OH-PBDEs were tentatively identified in the pooled human blood sample, of which one OH-PBDE, 4'-hydroxy-2,2',4,5,5'-pentabromodiphenyl ether, has not been identified in human blood before. The identification was performed using gas chromatography-mass spectrometry (GC-MS) recording the bromine ions m/z 79, 81. The tentative identification was supported by the peaks relative retention times (RRTs) compared to authentic references on two GC columns of different polarities for the hexa-, and heptabrominated OH-PBDEs, and three different GC columns for the pentabrominated OH-PBDEs. The OH-PBDE congeners most likely originate from human metabolism of a flame retardant, i.e. polybrominated diphenyl ethers (PBDEs), due to the relatively high concentrations of PBDEs in the same human blood sample and the fact that these PBDEs could form the tentatively identified OH-PBDEs via metabolic direct hydroxylation or via 1,2-shift.

New approaches to assess the transthyretin binding capacity of bioactivated thyroid hormone disruptors.

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl-ethers (PBDEs) are metabolized into hydroxylated metabolites (OH-PCBs/PBDEs), which can disrupt the thyroid hormone homeostasis. Binding of these metabolites to transport proteins such as transthyretin (TTR) is an important mechanism of their toxicity. Several methods to quantify the competitive thyroxine (T(4)) displacement potency of pure metabolites exist. However, quantification of the potency of in vitro metabolized PCBs and PBDEs has drawbacks related to the coextraction of compounds disturbing the T(4)-TTR competitive binding assay. This study identifies and quantifies the major coextractants namely cholesterol, saturated and nonsaturated fatty acids (SFA and NSFA) at levels above 20 nmol per mg equivalent protein following various extraction methods. Their TTR binding potency was analyzed in a downscaled, nonradioactive fluorescence displacement assay. At concentration factors needed for TTR competitive binding, at least 10µM of these coextracts is present, whereas individual SFA and NSFA disturb the assay from 0.3µM. The effectiveness of the in vitro metabolism and extraction of the model compounds CB 77 and BDE 47 was chemically quantified with a newly developed chromatographic method analyzing silylated derivatives of the OH-metabolites and coextractants. A new method to selectively extract metabolites and limit coextraction of disturbing compounds to less than 5 nmol per mg equivalent protein is presented. It is now possible to make a dose-response curve up to 50% inhibition with bioactivated CB 77 and BDE 47. The toxic potencies of bioactivated persistent organic pollutants (POPs) should be taken into account to prevent serious underestimation of their hazard and risk.

Characterization of an abundant and novel methyl- and methoxy-substituted brominated diphenyl ether isolated from whale blubber.

A previously unidentified yet abundant substituted polybrominated diphenyl ether (PBDE) was isolated from a northern bottlenose whale (Hyperoodon ampullatus) found dead in the Skagerrak, North Sea. A combination of gas chromatography, high and low resolution mass spectrometry and nuclear magnetic resonance spectroscopy (NMR) ((1)H, (1)H-(1)H and (1)H-(13)C) after isolation with preparative capillary gas chromatography (PCGC) lead to the identification of the unknown substance as 6-MeO-5-Me-2,2',3,4'-tetrabromo diphenyl ether (6-MeO-5-Me-BDE42). To our knowledge this is only the second time PCGC has been used to isolate individual organohalogen compounds present in trace amounts for identification with NMR. The concentration of this novel bioaccumulated compound was estimated to be about 100 ng g(-1) lipid, which was 2.5 times higher compared with the most abundant MeO-PBDE congeners.

Synthesis of polybrominated diphenyl ethers via symmetrical tetra- and hexabrominated diphenyliodonium salts.

Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardants (BFRs) which have become widespread environmental pollutants due to their persistence and bioaccumulativeness. Pure authentic PBDE congeners are required for chemical analysis, assessments of their chemical/physical properties and toxicological studies. We here report an improved method for synthesis of authentic PBDE congeners applying bromophenols and symmetrical brominated diphenyliodonium salts as building blocks. Altogether, 13 PBDEs were synthesized of which seven are new. The improved coupling reaction between the bromophenol and the brominated diphenyliodonium salts resulted in enhanced yields for PBDEs substituted with more than six bromine atoms. Also, improvements in iodonium salt synthesis made it possible to synthesize symmetrical hexabromodiphenyliodonium salts for the first time, i.e. 2,2',3,3',4,4'-, 2,2',4,4',5,5'- and 2,2',4,4',6,6'-hexabromodiphenyliodonium salts and they made it possible to prepare octabrominated PBDEs via the actual coupling method. All synthesized compounds were characterized by (1)H NMR, (13)C NMR spectra and by their melting points. Also, all products except for the diphenyliodonium salts were characterized by mass spectra in electron ionization mode.

Inhibition of human placental aromatase activity by hydroxylated polybrominated diphenyl ethers (OH-PBDEs).

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants in many different polymers, resins and substrates. Due to their widespread production and use, their high binding affinity to particles, and their lipophilic properties, several PBDE congeners can bioaccumulate in the environment. As a result, PBDEs and their hydroxylated metabolites (OH-PBDEs) have been detected in humans and various wildlife samples, such as birds, seals, and whales. Furthermore, certain OH-PBDEs and their methoxylated derivatives (MeO-PBDEs) are natural products in the marine environment. Recently, our laboratory focused on the possible effects on steroidogenesis of PBDEs and OH-PBDEs, e.g. in the human adrenocortical carcinoma (H295R) cell line indicating that some OH-PBDEs can significantly influence steroidogenic enzymes like CYP19 (aromatase) and CYP17. In the present study, human placental microsomes have been used to study the possible interaction of twenty two OH-PBDEs and MeO-PBDEs with aromatase, the enzyme that mediates the conversion of androgens into estrogens. All OH-PBDE derivates showed significant inhibition of placental aromatase activity with IC(50) values in the low micromolar range, while the MeO-PBDEs did not have any effect on this enzyme activity. Enzyme kinetics studies indicated that two OH-PBDEs, 5-hydroxy-2,2',4,4'-tetrabromodiphenyl ether (5-OH-BDE47) and 6-hydroxy-2,2',4,4'-tetrabromodiphenyl ether (6-OH-BDE47), had a mixed-type inhibition of aromatase activity with apparent K(i)/K(i)' of 7.68/0,02 microM and 5.01/0.04 microM respectively. For comparison, some structurally related compounds, a dihydroxylated polybrominated biphenyl, which is a natural product (2,2'-dihyroxy-3,3',5,5'-tetrabromobiphenyl (2,2'-diOH-BB80)) and its non-bromo derivative were also included in the study. Again inhibition of aromatase activity could be measured, but their potency was significantly less than those observed for the OH-PBDEs. These results show that a wide range of OH-PBDEs have the potential to disturb steroidogenesis and indicate a potential mechanism of action of these brominated flame retardant derivatives as endocrine disruptors in humans and wildlife.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) in the abiotic environment: surface water and precipitation from Ontario, Canada.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have been identified as metabolites of PBDEs, and also as compounds of natural origin in the marine environment; however, there has only been very limited study of their presence in the abiotic environment. In the present study, OH-PBDEs were determined in samples of surface water and precipitation (rain and snow) collected from sites in Ontario, Canada. OH-PBDEs were detected in all the samples analyzed, although half of the observed peaks did not correspond to any of the 18 authentic standards available. Fluxes of sigmaOH-PBDEs ranged from 3.5 to 190 pg/m2 in snow and from 15 to 170 pg/m2/day in rain, and those were higher at three of the southern Ontario locations relative to a single northern remote site. Concentrations of sigmaOH-PBDEs ranged from 2.2 to 70 pg/L in water and from < 1 to 420 pg/g in particulate organic carbon (POC), and higher values were found near sewage treatment plant (STP) outfalls in Lake Ontario. Partition coefficients (log K(oc)) for OH-PBDEs ranged from 4.0 to 5.1. The results in this study suggest that OH-PBDEs are ubiquitous in the abiotic environment and most likely are produced through reaction of PBDEs with atmospheric OH radicals. As well, they may be present in surface waters near STPs due to oxidation of PBDEs and inflows from metabolism by humans and animals.

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.