Hydroxylated, methoxylated, and parent polybrominated diphenyl ethers (PBDEs) in the inland environment, Korea, and potential OH- and MeO-BDE source

The concentrations, congener profiles, and phase-specific distribution profiles of 27 polybrominated diphenyl ethers and 10 hydroxylated and 18 methoxylated brominated diphenyl ethers (OH- and MeO-BDEs; later called structural analogues of PBDEs) were determined in surface soil, water, air, and vegetation from the southeastern city of Busan, Korea for 2010-2011. The total PBDE concentrations were 0.18-7.7 ng/g in soil, 6.3-87 pg/L [corrected] in water, 5.3-16 pg/m(3) in air, and 0.06-0.22 ng/g in vegetation. The OH- and MeO-BDE concentrations were lower than the parent PBDE concentrations in soil samples but OH-BDEs were much greater in the water samples and MeO-BDEs were much greater in the air samples. The relative concentrations of the PBDEs and their structural analogues varied depending on the type and homologue of the degradation product, the substituent position, and the characteristics of the environmental medium. In particular, the OH-BDEs were not found in air samples and the OH-penta BDEs were not detected in any of the matrices. The dominance of the ortho-substituted structural analogues found in water and vegetation suggested that they may have natural sources, but different substituent patterns were found in the air and soil samples, suggesting that the structural analogues had different formation mechanisms in these media.

Application of electrokinetic soil flushing to four herbicides: A comparison

In this work, four bench-scale plants containing soil spiked with four herbicides (2,4-Dichlorophenoxyacetic acid (2,4-D), oxyfluorfen, chlorsulfuron and atrazine) undergo treatment consisting of an electrokinetic soil flushing (EKSF). Results clearly demonstrate that efficiency of EKSF depends on the chemical characteristic of the pesticide used. The amount of pesticide collected in the anode well is more significant than that collected in the cathode wells, indicating that the electromigration is much more important than drainage by electro-osmotic flux for this application. After 15 d of treatment, the 2,4-D is the pesticide most efficiently removed (95% of removal), while chlorsulfuron is the pesticide more resilient to the treatment. Additionally, volatilization was found to be a process of the major significance in the application of electrokinetic techniques to soil polluted with herbicides and because of that it should always be taken into account in the future design of full-scale processes.

Correlations of PCBs, DIOXIN, and PBDE with TSH in children's blood in areas of computer E-waste recycling

OBJECTIVE

To study correlations of polychlorinated biphenyls (PCBs), DIOXIN, and polybrominated diphenyl ethers (PBDE) with thyroid stimulating hormone(TSH) in children, and assess the impact on children's health.

METHODS

Three hundred and sixty nine children aged from 6 to 8, including 195 from Luqiao, the computer E-waste recycling area, and 174 from Longyou, the control area, were selected for this investigation to elucidate the correlation of PCBs, DIOXIN, and PBDE with TSH in children's blood samples. The children had a physical examination and their blood levels of PCBs, DIOXIN, PBDE, and TSH were detected after sample collection.

RESULTS

In the E-waste recycling area, the contents of PCBs, PBDE, DIOXIN, and TSH in the blood samples of children were 484.00 ± 84.86 ng·g(-1) lipid weight, 664.28 ± 262.38 ng·g(-1) lipid weight, 26.00 ± 19.58 ng·g(-1) lipid weight and 1.88 ± 0.42 μIU/mL (serum) respectively, while in the control area, the PCBs, PBDE, DIOXIN, and TSH contents were 255.38 ± 95 ng·g(-1) lipid weight, 375.81 ± 262.43 ng·g(-1) lipid weight, 39.64 ± 31.86 ng·g(-1) lipid weight, and 3.31±1.04 μIU/mL respectively.

CONCLUSION

The health status of children in the control area are better than that in the contaminated area. Among children who are exposed to persistent organic pollutants, the pollutant content increases significantly in their serum, and the distribution of TSH levels in their bodies are also affected.

Interaction studies of polybrominated diphenyl ethers (PBDEs) with human serum albumin (HSA): Molecular docking investigations

This work has evaluated the interactions of HSA and typical PBDEs (BDE47, BDE99, BDE100, BDE153 and BDE209) at molecular level by modelling. Apart from the BDE209, PBDEs with higher molecular weight show higher binding energy with the residues of HSA. The BDE209 without H atoms has the lowest binding energy (-ΔG_binding: 4.30calmol^-1) than other PBDEs (-ΔG_binding: 7.93-8.42calmol^-1). The BDE99 shows a higher binding energy than its isomer (BDE100). On the other hand, the lgK_ow-depth plotting figure shows that a higher K_ow value (hydrophobicity) of PBDEs is accompanied by a deeper binding site within the central channel of HSA. This work may provide a theoretical method to assess the transport and distribution of PBDEs in human body.

Leaching characteristics of heavy metals and brominated flame retardants from waste printed circuit boards

Leaching assessment on five heavy metals (copper, zinc, lead, nickel and cadmium) and two brominated flame retardants (BFRs), polybrominated diphenyl ethers (PBDEs) and tetrabromobisphenol A (TBBPA), from waste printed circuit boards (WPCBs) were conducted using various leaching methods. The mean leaching concentrations of copper were the highest in both toxicity characteristic leaching procedures (TCLP) and synthetic precipitation leaching procedures (SPLP) tests at 8.6 mg/L and 1.1mg/L, while only lead (6.2mg/L) exceeded the TCLP criteria and Chinese EPA regulatory limit (both 5.0mg/L). However, PBDEs and TBBPA were not detected in TCLP and SPLP tests. Then the BFRs leaching trends and potential leachabilities were further investigated in actual landfill leachates using a modified method. Leaching characteristics that fast-leaching initially followed by slow-desorption over time were generally observed. In landfill leachate tests, the highest leaching concentrations of PBDEs and TBBPA were determined at 30.39 and 12.27 μg/L. Meanwhile, the highest leaching rates were estimated to reach 0.08% and 1.00%, respectively, which were significantly influenced by the dissolved organic carbon contents of extracts, the hydrophobicities of target BFRs and the specific surface areas of WPCBs materials. These results proved that leaching from WPCBs was a significant emission source of BFRs in landfill and electronic waste recycling dumpsite.

Binding and activity of polybrominated diphenyl ether sulfates to thyroid hormone transport proteins and nuclear receptors

Polybrominated diphenyl ethers (PBDEs) can be metabolized to hydroxylated PBDEs (OH-PBDEs), which play important roles in their disruption effects on the thyroid hormone (TH) system. Recently, multiple in vitro studies suggested that OH-PBDEs might be further metabolically transformed to PBDE sulfates. However, information about the bioactivity of PBDE sulfate metabolites is limited. In the present study, we explored the possible disruption effects of PBDE sulfates to the TH system by studying their binding and activity towards TH transport proteins and nuclear receptors. We found PBDE sulfates could bind to two major TH transport proteins (thyroxine-binding globulin and transthyretin). Besides, PBDE sulfates could also bind to two subtypes of TH nuclear receptors (TRα and TRβ) and showed agonistic activity towards the subsequent signaling pathway. Moreover, the PBDE sulfates showed higher binding potency to TH transport proteins and TRs compared with their corresponding OH-PBDE precursors. Molecular docking results showed that replacement of hydroxyl groups with sulfate groups might lead to more hydrogen bond interactions with these proteins. Overall, our study suggested that PBDE sulfates might disturb the TH system by binding to TH transport proteins or TRs. Our finding indicated a possible mechanism for the TH system disruption effects of PBDEs through their sulfate metabolites.

UV-induced formation of bromophenols from polybrominated diphenyl ethers

Bromophenols (BPs) are both man-made industrial compounds and naturally produced secondary metabolites of algae and sponges. This study explored the formation of BPs by UV irradiation of polybrominated diphenyl ethers (PBDEs). Simulated sunlight (10-80 min) and natural sunlight irradiations (5 days) of BDE-153, BDE-154, BDE-183, BDE-196, and technical octabromodiphenyl ether (DE-79) generated hydrodebrominated PBDEs along with up to 0.7-4 mass % BPs. UV absorption spectra were recorded to show that the para-substituted PBDEs and BPs are those predominately transformed because this structural feature causes a significant bathochromic shift of λmax to higher wavelength. A decrease of higher brominated BPs in favor of lower brominated BPs was observed with time. All possible substitution patterns on the BPs formed by the cleavage of the parent PBDEs and respective hydrodebromination products were observed. The main di- and tribromophenols detected were 2,4-diBP > 2,5-diBP and 2,4,6-triBP > 2,4,5-triBP on average. The irradiation conditions were similar to real-world scenarios and emphasized the environmental relevance of these photolysis products of PBDEs. The meta-substituted BPs can be used as markers to distinguish photolytic PBDE transformation products from naturally produced BPs, which exclusively feature bromo-substitutents in ortho- and para-positions.

Toxicity of Bromkal 70-5DE, a technical mixture of polybrominated diphenyl ethers, following 28 d of oral exposure in rats and impact of analysed impurities

The subacute toxicity of a commercial polybrominated diphenyl ether (PBDE) preparation, Bromkal 70-5DE, was investigated. In addition to a vehicle control, the mixture was given orally to male and female Sprague-Dawley rats for 28 d at three dose levels; 2.5, 25 and 250 mg kg(-1) b.w.d(-1). The observed effects include increased hepatic EROD activity (from 2.5 mg kg(-1)d(-1)); increased liver weight (males), increased PROD activity and depletion of hepatic retinoids (from 25 mg kg(-1)d(-1)); and increased liver weight (females), marked histological changes in the liver and lungs, as well as increased serum parameters such as total protein, cholesterol and albumin (from 250 mg kg(-1)d(-1)). Chemical analysis of the PBDE mixture with gas chromatography/mass spectrometry (GS/MS) showed impurities of polybrominated dibenzofurans and to a lesser extent dibenzodioxins, in total levels of about 7.0 microg g(-1) of Bromkal technical mixture. The animals were thereby exposed to an estimated dose of dioxin-like equivalents corresponding to 1.3-131 ng TEQ kg(-1) b.w.d(-1). It cannot be ruled out that this level of impurities can explain the hepatic EROD induction and hepatic retinoid depletion, which are considered typical markers of toxicity mediated via the aryl hydrocarbon receptor (AhR).

Liposome and protein-water partitioning of polybrominated diphenyl ethers (PBDEs)

Bioaccumulation of polybrominated diphenyl ethers (PBDEs) in marine and terrestrial organisms is of great environmental concern. Understanding the partitioning of PBDEs to biological phases is crucial for elucidating their bioaccumulation behavior. In this study, partitioning coefficients of PBDEs from water to phospholipid liposomes (K(lipw)) and to bovine serum albumin (BSA) (K(BSAw)) were measured using a polymer depletion method. K(lipw) values measured in two laboratories are in an excellent agreement (within 0.14 log units), indicating a high method repeatability. The values of log K(lipw) and log K(BSAw) are in the range of 6.3-8.2 and 5.1-7.0, respectively, representing the highest of these partition coefficients measured to date. Log K(lipw) values for PBDEs are similar to the log of the octanol-water partition coefficients (K(ow)) (log K(lipw)-log K(ow)=-0.06±0.23; mean±SD of 7 congeners), consistent with the data of chlorobenzenes and polychlorinated biphenyls (PCBs) reported in the literature. No hydrophobicity cutoff was observed for partitioning to the liposome membrane. Log K(BSAw) values for PBDEs increase linearly with log K(ow) and do not follow the non-linear trend observed for polycyclic aromatic hydrocarbons (PAHs). This difference between PBDEs and PAHs suggests specific binding mechanisms to serum albumin even for hydrophobic compounds.

Oxidative transformation of polybrominated diphenyl ether congeners (PBDEs) and of hydroxylated PBDEs (OH-PBDEs)

BACKGROUND, AIM, AND SCOPE

The historical and widespread use of polybrominated diphenyl ethers (PBDEs) as flame retardants in consumer products worldwide has caused PBDEs to now be regarded as pervasive environmental contaminants. Most recently, hydroxylated PBDEs (OH-PBDEs) and methoxylated PBDEs (MeO-PBDEs) have emerged as environmentally relevant due to reports of their natural production and metabolism. An important parameter for assessing the environmental impact of a chemical substance is persistence. By formulating the concept that persistence is the result of the substance's physicochemical properties and chemical reactivity, Green and Bergman have proposed a new methodology to determine the inherent persistence of a chemical. If persistence could be predicted by straightforward methods, substances with this quality could be screened out before large-scale production/manufacturing begins. To provide data to implement this concept, we have developed new methodologies to study chemical transformations through photolysis; hydrolysis, substitution, and elimination; and via oxidation. This study has focused on adapting an oxidative reaction method to be applicable to non-water soluble organic pollutants.

MATERIALS AND METHODS

PBDEs and one MeO-PBDE were dissolved in tetrahydrofuran/methanol and then diluted in alkaline water. The OH-PBDEs were dissolved in alkaline water prior to reaction. The oxidation degradation reaction was performed at 50 degrees C using potassium permanganate as described elsewhere. The pH was maintained at 7.6 with disodium hydrogen phosphate and barium hydrogen phosphate, the latter also serving as a trapping agent for manganate ions. The oxidation reactions were monitored by high-performance liquid chromatography and reaction rates were calculated.

RESULTS

The OH-PBDEs have very fast oxidative transformation rates compared to the PBDEs. The reaction rates seem to be primarily dependent on substitution pattern of the pi-electron-donating bromine substituents and of bromine content. There are indications that further reactions of OH-PBDEs, e.g., methylation to the MeO-PBDEs, decrease the oxidation rates, and thereby generate more persistent substances.

DISCUSSION

The resistance of PBDEs to oxidation, a major degradation pathway in air, should be further investigated, since these compounds do undergo long range transport. With slight modifications, the original method has been adapted to include a larger variety of chemical substances, and preliminary data are now available on the oxidative transformation rates for PBDEs and of OH-PBDEs.

CONCLUSIONS

The original oxidation degradation method can now include non-water soluble compounds. This modification, using low concentrations of test chemicals, allows us to measure oxidative transformation rates, for some of the lower brominated DEs, data that can be used to assess their persistence in future model calculations. Oxidative transformation rates for PBDEs are slow compared to those for the OH-PBDEs. This suggests that OH-PBDEs, when released into the environment, undergo faster oxidative metabolism and excretion than the PBDEs.

RECOMMENDATIONS AND PERSPECTIVES

To evaluate the modified method, more degradation reactions with non-water soluble compounds should be investigated. Recent studies show that OH-PBDEs are present in rats and in humans and, because of their activity as endocrine disruptors, determining their subsequent environmental fate is of importance. The resistance of PBDEs to oxidative degradation should be acknowledged as of possible future concern. Several other compound classes (such as polychlorinated biphenyls (PCBs), hydroxylated polychlorinated biphenyls (OH-PCBs), and pharmaceuticals) need to be subjected to this screening method to increase the database of transformation rates that can be used with this model.

Bromination of 2-methoxydiphenyl ether to an average of tetrabrominated 2-methoxydiphenyl ethers

Brominated 2-phenoxyanisoles (2-methoxydiphenyl ethers, 2-MeO-BDEs) are a class of halogenated natural products, produced by algae and sponges. Especially two tetrabrominated isomers, i.e. 2'-MeO-BDE 68 (BC-2) and 6-MeO-BDE 47 (BC-3), have also been frequently determined in environmental and food samples. In addition, 2-MeO-BDEs are under discussion as metabolites of polybrominated diphenyl ethers (PBDEs). In this study, we synthesized the backbone 2-methoxydiphenyl ether and brominated it to an average degree of four bromine substituents. The reaction mixture only contained one major product (∼90%) along with three further MeO-BDEs and ∼5% hydroxylated BDEs. In all likelihood, the HO-BDEs were formed in a side reaction by cleavage of the methoxy group. The major MeO-BDE was identified as 6'-methoxy-2,3',4,4'-tetrabromodiphenyl ether (6'-MeO-BDE-66). The HO-BDEs were separated by KOH/n-hexane partitioning, and the resulting 2-MeO-BDEs were fractionated by means of high-speed counter-current chromatography (HSCCC). Due to the excellent enrichment facilities of HSCCC, some 15 MeO-BDEs, mainly present at traces only, could be detected in 26 fractions, and eight of them could be characterized by nuclear magnetic resonance spectroscopy (NMR). Only two of the compounds--2'-MeO-BDE 68 and 6-MeO-BDE 123--had been characterized as natural products while the prominent halogenated natural product 6-MeO-BDE 47 was not detected at all in the reaction product. The "non-natural" 2-MeO-BDEs may be useful internal standards in trace analysis.

Peculiar and rapid photocatalytic degradation of tetrabromodiphenyl ethers over Ag/TiO2 induced by interaction between silver nanoparticles and bromine atoms in the target

As a typical moderately-brominated diphenylethers, 2,2',4,4'-tetrabromodiphenyl ether (BDE47) is hardly debrominated by a conventional TiO2-mediated photocatalysis. However, its reductive debromination was rapid achieved over silver nanoparticle-loaded TiO2 (Ag/TiO2) in UV-irradiated anoxic acetonitrile-water within 13 min. An "Ag-promoted electron transfer and C-Br cleavage" concept was proposed based on experimental results and density functional theory calculations. Ag(0) exerted affinity interaction with bromine atoms, and the storing of electrons on Ag(0) increased the binding interaction, which elongated the C-Br bond of BDE47 and facilitated its cleavage. The initiating of the BDE47 debromination on Ag(0) required an induction period to enrich a critical amount of electrons, leading to a stronger driving force for both injecting electron to BDE47 and stretching the C-Br bond. Stronger photo-excitation, higher polar solvent, and a moderate Ag(0) load strengthened the interfacial electron transfer over Ag/TiO2, and thereby shortening the induction time and accelerating the BDE47 degradation.

Levels of polybrominated diphenyl ethers in Brazilian food of animal origin and estimation of human dietary exposure

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants, commonly used as flame retardants in a wide variety of products. In the last years, the concentration of PBDEs is increasing in the environment, turning human exposure more common. Since the diet is the primary source of human exposure, several surveys evaluate the levels of PBDEs in foods to estimate the dietary intake and the hazard index (HI). However, this data is limited in Brazil. Thus, this study aims to determine the level of seven PBDE congeners (BDE-28, 47, 99, 100, 153, 154, 183) in Brazilian food of animal origin. The total concentration of PBDE (∑PBDE) determined in the food samples were 2.29 (0.92-4.85) ng/g wet weight (ww), 1.98 (1.23-3.12) ng/g ww, 1.91 (1.23-3.12) ng/g ww, and 4.42 (1.26-8.42) ng/g ww in eggs, fish, seafood, and milk, respectively. BDE-47 was the most abundant compound. Based on consumer habits and the found levels of PBDEs in Brazilian food, we estimated the daily intake of ∑PBDEs as 3.25 (0.02-2.19) ng/kg bw per day. Surprisingly, the PBDE levels in milk samples were higher than those found in reported studies in other countries, and the consumption of milk products give a higher relative contribution to PBDEs exposure. The HI was <1. A complete risk assessment of the human exposure to PBDEs most likely could be evaluated considering all commercial PBDEs congeners and other exposure sources of these contaminants.

Sorption of PBDE in low-density polyethylene film: implications for bioavailability of BDE-209

The coefficients of partitioning (K(pew) ) between low-density polyethylene (LDPE) film (50-µm thickness) and water for 23 polybrominated diphenyl ether (PBDE) congeners were determined based on a regression analysis of sorption kinetics over an extended exposure period (up to 365 d). A curvilinear relationship between log K(pew) and log K(OW) (octanol-water partition coefficient) was obtained for the target BDE congeners with the turning point at log K(OW) approximately 8. Previously obtained dietary uptake efficiencies of BDE congeners in common carp (Cyprinus carpio) were also found to relate curvilinearly to log K(OW) . In addition, field-measured relative abundances of BDE-209 compiled from previous investigations conducted in the Pearl River Delta of South China were significantly (p < 0.001) higher in abiotic samples (n = 79 from 11 matrices) than in biotic samples (n = 73 from 12 matrices), suggesting the likelihood for reduced bioavailability of BDE-209 in certain biota. Finally, a molecular-scale analysis indicated that the curvilinear relationship between log K(pew) and log K(OW) can be attributed to the energy barrier that a molecule has to overcome as it attempts to diffuse into the LDPE structure, which can become significant for larger molecules. Similarly, the reduced bioavailability of BDE-209 in many biological species can be regarded as a reflection of the magnitude of molecular interactions between cell membranes and BDE-209.

Debrominated, hydroxylated and methoxylated metabolism in maize (Zea mays L.) exposed to lesser polybrominated diphenyl ethers (PBDEs)

A hydroponic experiment was conducted to investigate the debrominated, hydroxylated and methoxylated metabolism of polybrominated diphenyl ethers (PBDEs, BDE-15, -28 and -47) in maize. A total of six debrominated metabolites (de-PBDEs), seven hydroxylated PBDEs (OH-PBDEs, including two unidentified OH-di-PBDEs and one unidentified OH-tri-PBDE) and four methoxylated PBDEs (MeO-PBDEs) were determined in the exposed plants. The metabolic products were detected in maize only after 12h of exposure to the PBDEs. However, the concentration of each type of the metabolites (de-PBDEs, OH-PBDEs or MeO-PBDEs) decreased at the later exposure time, possibly due to further metabolism. The removal of a bromine atom or the introduction of a hydroxyl/methoxy group was easier at the ortho-positions on the biphenyl structure than at the para-positions. Concentration ratios of the total debrominated, hydroxylated or methoxylated metabolites to the parent congener (BDE-28 or -47) generally followed the order of leaves>stems>>roots, and MeO-PBDEs>de-PBDEs>>OH-PBDEs. These results suggest that metabolism occurred preferentially in leaves and stems than in roots. Less transformation and shorter elimination half-life of OH-PBDEs would contribute to the lower concentrations of OH-PBDEs than of de-PBDEs or MeO-PBDEs in maize.

Environmental fractionation of PCBs and PBDEs during particle transport as recorded by sediments in coastal waters

The Strait of Georgia (British Columbia, Canada) is a hydrologically complex inland sea with a rich abundance and diversity of species of aquatic life. Marine sediments, as both a sink for hydrophobic contaminants and a potential source for aquatic food webs, were collected from 41 sites throughout the 6,900-km(2) Strait of Georgia. The congener-specific concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), including BDE-209, were measured. Urban harbors represented hotspots for both PCBs and PBDEs, whereas PBDEs were also found at high concentrations near municipal outfalls. Patterns of PCB distribution were consistent with historical point source emissions in urban areas and environmental distillation toward lighter profiles in remote sites over time. The single congener BDE-209 dominated the PBDEs, accounting for 52% of the average total concentration. However, nonurban deep-water sediment PBDE profiles were both heavier and had higher concentration-weighted average log K(OW) (octanol-water partition coefficient) values compared to shallow samples (percent BDE-209 of total PBDE, 66 versus 32%; log K(OW) , 9.5 versus 8.2, respectively). Collectively, our results suggest that although source signals largely explain PCB and PBDE hotspots in the Strait of Georgia, the combination of physicochemical properties and environmental processes drive divergent compositional fates for the PCBs and the heavier PBDEs in the sediments of the Strait of Georgia.

Binary toxicity of polystyrene nanoplastics and polybrominated diphenyl ethers to Arctic Cyanobacteria under ambient and future climates

Cyanobacteria are the predominant biota in the Arctic. Interactive effects on Arctic cyanobacteria between climate-change-shifting parameters and anthropogenic contaminants are largely unknown. We utilized a fractional factorial experiment and Arctic cyanobacteria Pseudanabaena biceps Strain PCCC_O-153 to capture the complexity of interacting climate factors, nano-polystyrene (nano-PS) and 2,2´,4,4´-tetrabromodipenyl ether (BDE-47). The short-term binary toxicity of nano-PS and BDE-47 was then examined through experiments, toxicity units, and reference models. The toxic mechanism was further revealed through biochemical analyses and multivariate statistics. We found that BDE-47 and nano-PS had more hazardous effects than changing climate conditions. The mixture had antagonistic effects on PCCC_O-153, attributing to the aggregation of nano-PS, the adsorption of BDE-47, and the wrapping of both contaminants by released extracellular polymeric substances. Binary toxicity was caused by the chain reactions triggered by combining individual contaminants. Total protein was a sensitive target and positively correlated to chlorophyll pigment. Oxidative stress for the mixture mainly resulted from the presence of nano-PS. This is the first study to access the hazardous effects of a mixture of anthropogenic contaminants on Arctic cyanobacteria under ambient and future climates.

Analysis of Ah receptor binding affinities of polybrominated diphenyl ethers via in silico molecular docking and 3D-QSAR

Polybrominated diphenyl ethers (PBDEs) have become ubiquitous contaminations due to their use as flame retardants. The structural similarity of PBDE to some dioxin-like compounds suggested that they may share similar toxicological effects: they might activate the aryl hydrocarbon receptor (AhR) signal transduction pathway and thus might have adverse effects on wildlife and humans. In this study, in silico computational workflow combining molecular docking and three-dimensional quantitative structure-activity relationship (3D-QSAR) was performed to investigate the binding interactions between PBDEs and AhR and the structural features affecting the AhR binding affinity of PBDE. The molecular docking showed that hydrogen-bond and hydrophobic interactions were the major driving forces for the binding of ligands to AhR, and several key amino acid residues were also identified. The CoMSIA model was developed from the conformations obtained from molecular docking and exhibited satisfactory results as q (2) of 0.605 and r (2) of 0.996. Furthermore, the derived model had good robustness and statistical significance in both internal and external validations. The 3D contour maps generated from CoMSIA provided important structural features influence the binding affinity. The obtained results were beneficial to better understand the toxicological mechanism of PBDEs.

PBDD/F impurities in some commercial deca-BDE

The study presented the concentrations and distributions of polybrominated dibenzo-p-dioxins and polybrominated dibenzofurans (PBDD/Fs) as impurities in some commercial decabromodiphenyl ether (DBDE) mixtures that were produced by several manufacturers. The total concentrations of 12 2,3,7,8-substituted tetra- to octa-BDD/F congeners were found to be in the range of 3.4-13.6 (mean 7.8) μg/g, averagely accounting for 99% of total PBDD/Fs. OBDF was the prevailing congener, followed by 1,2,3,4,6,7,8-HpBDF. In addition, OBDD and 1,2,3,4,7,8-HxBDF were also obviously detectable. The total concentrations of PBDD/Fs varied both between the manufacturers and between the lots. On the basis of the global demand for the commercial DBDE in 2001, the annual potential emissions of PBDD/Fs were calculated coarsely to be 0.43 (range: 0.21-0.78) tons. The major dioxin congeners, OBDF and 1,2,3,4,6,7,8-HpBDF, presenting in DBDE, were estimated to be formed from BDE-209, BDE-206, and/or BDE-207 via an intra-molecular elimination of Br2/HBr.

Photochemical formation of polybrominated dibenzo-p-dioxins from environmentally abundant hydroxylated polybrominated diphenyl ethers

High levels of polybrominated dibenzo-p-dioxins (PBDDs) have been found in Baltic Sea biota, where the toxic load owing to, for example, polychlorinated dibenzo-p-dioxins and other organic pollutants is already high. The levels and geographic pattern of PBDDs suggest biogenic rather than anthropogenic origin, and both biotic and abiotic formation pathways have been proposed. Photochemical formation from hydroxylated polybrominated diphenyl ethers (OH-PBDE) is a proposed pathway for PBDDs in marine environments. Ultraviolet radiation-initiated transformations of OH-BDEs 47, 68, 85, 90, 99, and 123, which all are abundant in the environment, were investigated. It was shown that the most abundant PBDDs in the environment (1,3,7-triBDD and 1,3,8-triBDD) can be formed from the most abundant OH-BDEs (OH-BDE 47 and OH-BDE 68) at high rates and with percentage yields. In fact, most of the PBDDs that have been identified in the Baltic Sea environment were formed with high yield from the six studied OH-PBDE, through initial cyclization and subsequent debromination reactions. The high formation yields point to this route as an important source of PBDDs in biota. However, congeners showing relatively high retention in fish, specifically 1,3,6,8- and 1,3,7,9-tetraBDD, were not formed. These are likely formed by enzymatic coupling of brominated phenols.

Photolytic degradation of decabromodiphenyl ethane (DBDPE)

The photolytic degradation of decabromodiphenyl ethane (DBDPE), an alternative flame retardant to decabromodiphenyl ether, was investigated in a variety of matrixes (n-hexane, tetrahydrofuran, methanol/water, humic acid/water, and silica gel) by irradiation under ultraviolet light and in n-hexane under natural light. Photolytic degradation of DBDPE occurs in all the matrixes investigated within the irradiation period (<320 min). The degradation experiments showed varied reaction rates, dependent on the matrixes, with increasing half-lives (t(1/2)) in the order of tetrahydrofuran (t(1/2)=6.0 min)>n-hexane (t(1/2)=16.6 min)>humic acid/water (30<t(1/2)<60)>silica gel (t(1/2)=75.9 min)>methanol/water (t(1/2)>240 min). The reaction in tetrahydrofuran, n-hexane, and silica gel matrixes can be described by the pseudo first order kinetics. Nevertheless, the matrixes have little effect on the degradation product distributions of DBDPE. A numbers of debrominated intermediates were identified. The degradation involves the initial formation of nona-BDPEs and the subsequent decomposition of these congeners to lower brominated congeners (octa- and hepta-BDPEs) within the irradiation time. To our knowledge, the present work is the first attempt to investigate the photolytic degradation kinetics and the identification of intermediates, as well as the degradation mechanism, during the degradation of DBDPE. Further research is needed to understand the photolytic degradation pattern of DBDPE in the natural environment.

Polybrominated diphenyl ethers in pinnipeds stranded along the southern California coast

Little to no information exists for polybrominated diphenyl ethers (PBDEs) in marine mammals frequenting the highly urbanized southern California (USA) coast. Fourteen PBDE congeners were determined by GC-ECNI-MS in blubber of pinnipeds stranded locally between 1994 and 2006. Total PBDE concentrations (SigmaPBDE) in California sea lion (n = 63) ranged from 0.04 to 33.7 microg/g wet weight (mean: 5.24 microg/g). To our knowledge, these are the highest reported PBDE levels in marine mammals to date. By comparison, mean SigmaPBDE in Pacific harbor seals (n = 9) and northern elephant seals (n = 16) were 0.96 and 0.09 microg/g, respectively. PBDEs in adult males were higher than for adult females, however, no age class differences or temporal trends were observed. As the first PBDE data reported for marine mammals in this region, the elevated levels underscore the need for additional studies on the sources, temporal trends, and potential effects of PBDEs in highly urbanized coastal zones.

The humic acid influenced the behavior and reactivity of Ni/Fe nanoparticles in the removal of deca-brominated diphenyl ether from aqueous solution

The removal of contaminants by iron-based nanomaterials was inevitably affected by the natural organic matter (NOM), which is one of the most abundant material on earth and exists in natural waters. This study was performed to investigate the main influence of humic acid (HA, representing NOM) on the behavior and reactivity of Ni/Fe nanoparticles in the removal of deca-brominated diphenyl ether (BDE209). Generally, the inhibitory effect of HA on the removal of BDE209 by Ni/Fe showed greater significance with an increase of HA concentration. The zeta potential and sedimentation experiments showed that the HA enhanced the dispersion and stabilization of Ni/Fe particles; however, the removal of BDE209 was found to be inhibited. Moreover, the corrosion capacity of the Ni/Fe nanoparticles showed a positive correlation with the effect of HA on the reactivity of Ni/Fe nanoparticles. Meanwhile, typical quinone compounds in HA had an adverse effect on the removal of BDE209. Additionally, the competitive adsorption experiments and characterization illustrated that the adsorption of HA by Ni/Fe nanoparticles was superior to BDE209. Overall, it was proposed that the corrosion of Ni/Fe was reduced as the contact between the nanoparticles and H₂O was hindered due to the surface of Ni/Fe was occupied by the adsorbed HA, and thus inhibited the reactivity of Ni/Fe nanoparticles in the removal of BDE209.

Debromination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by synthetic Pd/Fe0 and Cu/Fe0 in different protic solvents

Polybrominated diphenyl ethers (PBDEs) belong to a class of persistent organic pollutants (POPs), with potential toxicity to the liver, reproductive system, and development of mammals. The highly toxic and concentrated congener, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), was chosen to investigate debromination mechanisms by the two synthetic iron-based bimetals (Pd/Fe⁰ and Cu/Fe⁰) in two protic solvents (water and ethanol). SEM, XPS, and BET analyses showed that the synthetic bimetals Pd/Fe⁰ and Cu/Fe⁰ were spherical with diameters of about 100 nm and loaded with ∼1% (wt%) of Pd and Cu, respectively. GC-MS was used for the analysis of degradation products and the chromatograms showed that both Pd/Fe⁰ and Cu/Fe⁰ bimetals had effective reducing properties in water solvent. In ethanol solvent, debromination of BDE-47 by Pd/Fe⁰ showed a similar high activity, but BDE-47 could be hardly degraded by Cu/Fe⁰. The dominant debromination products of BDE-47 by Pd/Fe⁰ and Cu/Fe⁰ were ortho-substituted and para-substituted BDEs, respectively. Active H-atomic transfer was found to play a key role in the debromination of BDE-47 by Pd/Fe⁰ in both, water and ethanol, with a preference for para-debromination along with the formation of dibenzo-p-furan (DF) as the by-product, mainly in water. In contrast, electron transfer with a preference for ortho-debromination was found to play a predominant role for Cu/Fe⁰ system in water. More importance should be provided to active H-atomic transfer for its high efficiency. In-depth study on the mechanism of formation of by-product DF would be significant for its higher toxicity, possibility of accumulation and migration in the environment.

Simulation research on the natural degradation process of PBDEs in soil polluted by e-waste under increased concentrations of atmospheric O(3)

There have been increased concerns regarding the effect of polybrominated diphenyl ethers (PBDEs) on the environment. These compounds are widely utilized by the electronics industry and also function as fire retardants. More data on the basic characteristics of PBDEs are needed to better understand and used to describe their environmental fate. The aim of this study was to investigate the degradation of BDE-209 with different degrees of bromination under changes in the atmospheric environment. BDE-209 was able to be removed quickly due to the strong oxidizing ability of ozone in the atmosphere environment. Less-brominated BDEs, ranging from BDE-28 to BDE-183, were formed progressively, and the reaction of ozone gradually occupied the main position along with an increase in ozone flow time. Degradation reaction rates of PBDEs increased with increasing ozone concentration but decreased with increasing soil depth. Under UV-irradiation, BDE-209 was quickly transformed into less-brominated BDEs and the photodegradation reactions were faster than solar irradiation. The conditions of high ground temperature in the summer and alkaline soil were both contributors to the degradation of PBDEs. These results could facilitate the improvement of waste treatment designs and lead to better predictions of the outcome of PBDEs in the environment.