Reductive debromination of polybrominated diphenyl ethers in anaerobic sediment and a biomimetic system

Because of the bioaccumulation of penta- and tetrapolybrominated diphenyl ether (PBDE) flame retardants in biota,the environmental biotransformation of decabromodiphenyl ether (BDE-209) is of interest. BDE-209 accounts for more than 80% by mass of PBDE production and is the dominant PBDE in sediments. Most sediments are anaerobic and reports of microbial reductive dehalogenation of hydrophobic persistent organohalogen pollutants are numerous. Reductive debromination of BDE-209 in the environment could provide a significant source of lesser-brominated PBDEs to biota. Moreover, a recent study showed that BDE-209 debrominates in sewage sludge, and another demonstrated that some halorespiring bacteria will debrominate BDE-209. To determine whether reductive debromination of BDE-209 occurs in sediments, parallel experiments were conducted using anaerobic sediment microcosms and a cosolvent-enhanced biomimetic system. In the biomimetic system, reductive debromination occurred at rates corresponding to bromine substitution levels with a BDE-209 half-life of only 18 s compared with a halflife of almost 60 days for 2,2',4,4'-tetrabromodiphenyl ether. In sediment, the measured debromination half-life of BDE-209 was well over a decade and was in good agreement with the predicted value obtained from the biomimetic experiment. Product congeners were predominantly double para-substituted. BDE-209 debrominated in sediment with a corresponding increase in nona-, octa-, hepta-, and hexa-PBDEs. Nine new PBDE congeners appeared in sediment from reductive debromination. Given the very large BDE-209 burden already in sediments globally, it is important to determine whether this transformation is a significant source of lesser-brominated PBDEs to the environment.     

Pathways for the anaerobic microbial debromination of polybrominated diphenyl ethers

The debromination pathways of seven polybrominated diphenyl ethers (PBDEs) by three different cultures of anaerobic dehalogenating bacteria were investigated using comprehensive two-dimensional gas chromatography (GC x GC). The congeners analyzed were the five major components of the industrially used octa-BDE mixture (octa-BDEs 196, 203, and 197, hepta-BDE 183, and hexa-BDE 153) as well as the two most commonly detected PBDEs in the environment, penta-BDE 99 and tetra-BDE 47. Among the dehalogenating cultures evaluated in this study were a trichloroethene-enriched consortium containing multiple Dehalococcoides species, and two pure cultures, Dehalobacter restrictus PER-K23 and Desulfitobacterium hafniense PCP-1. PBDE samples were analyzed by GC x GC coupled to an electron capture detector to maximize separation and identification of the product congeners. All studied congeners were debrominated to some extent by the three cultures and all exhibited similar debromination pathways with preferential removal of para and meta bromines. Debromination of the highly brominated congeners was extremely slow, with usually less than 10% of nM concentrations of PBDEs transformed after three months. In contrast, debromination of the lesser brominated congeners, such as penta 99 and tetra 47, was faster, with some cultures completely debrominating nM levels of tetra 47 within weeks.     

Microbial reductive debromination of polybrominated diphenyl ethers (PBDEs)

Polybrominated diphenyl ethers (PBDEs) are a class of widely used flame retardants that have recently been detected in environmental samples, diverse biota, human blood serum, and breast milk at exponentially increasing concentrations. Currently, little is known about the fate of these compounds, and in particular, about the microbial potential to degrade them. In this study, debromination of deca-BDE and an octa-BDE mixture is demonstrated with anaerobic bacteria including Sulfurospirillum multivorans and Dehalococcoides species. Hepta- and octa-BDEs were produced by the S. multivorans culture when it was exposed to deca-BDE, although no debromination was observed with the octa-BDE mixture. In contrast, a variety of hepta- through di-BDEs were produced by Dehalococcoides-containing cultures exposed to an octa-BDE mixture, despite the fact that none of these cultures could debrominate deca-BDE. The more toxic hexa-154, penta-99, tetra-49, and tetra-47 were identified among the debromination products. Because the penta-BDE congeners are among the most toxic PBDEs, debromination of the higher congeners to more toxic products in the environment could have profound implications for public health and for the regulation of these compounds.     

Dehalogenation of polybrominated diphenyl ethers and polychlorinated biphenyl by bimetallic, impregnated, and nanoscale zerovalent iron

Nanoscale zerovalent iron particles (nZVI), bimetallic nanoparticles (nZVI/Pd), and nZVI/Pd impregnated activated carbon (nZVI/Pd-AC) composite particles were synthesized and investigated for their effectiveness to remove polybrominated diphenyl ethers (PBDEs) and/or polychlorinated biphenyls (PCBs). Palladization of nZVI promoted the dehalogenation kinetics for mono- to tri-BDEs and 2,3,4-trichlorobiphenyl (PCB 21). Compared to nZVI, the iron-normalized rate constants for nZVI/Pd were about 2-, 3-, and 4-orders of magnitude greater for tri-, di-, and mono-BDEs, respectively, with diphenyl ether as a main reaction product. The reaction kinetics and pathways suggest an H-atom transfer mechanism. The reaction pathways with nZVI/Pd favor preferential removal of para-halogens on PBDEs and PCBs. X-ray fluorescence mapping of nZVI/Pd-AC showed that Pd mainly deposits on the outer part of particles, while Fe was present throughout the activated carbon particles. While BDE 21 was sorbed onto activated carbon composites quickly, debromination was slower compared to reaction with freely dispersed nZVI/Pd. Our XPS and chemical data suggest about 7% of the total iron within the activated carbon was zerovalent, which shows the difficulty with in-situ synthesis of a significant fraction of zerovalent iron in the microporous material. Related factors that likely hinder the reaction with nZVI/Pd-AC are the heterogeneous distribution of nZVI and Pd on activated carbon and/or immobilization of hydrophobic organic contaminants at the adsorption sites thereby inhibiting contact with nZVI.     

食品中多溴联苯醚及其羟基衍生物的研究进展

近年来,由于多溴联苯醚及其羟基衍生物具有毒性和污染持久性,它们的研究越来越受到重视。本文以食品中多溴联苯醚及其羟基衍生物为重点,对多溴联苯醚及其羟基衍生物的性质、主要来源、毒性、以及在食品中的污染水平和分析方法等进行了评述,为我国开展食品领域内多溴联苯醚及其羟基衍生物的限量制定和研究提供参考。      

Electron impact and electron capture negative ionization mass spectra of polybrominated diphenyl ethers and methoxylated polybrominated diphenyl ethers

This review presents the electron impact (EI) and electron capture negative ionization (ECNI) mass spectra of the polybrominated diphenyl ether (PBDE) flame retardants and of their methoxy derivatives. Data from the literature are reviewed, and full spectra from our laboratory are reported to correct some of the errors that have crept into some previously published data. The EI spectra of the PBDEs are dominated by molecular ions and by singly and doubly charged ions due to the loss of Br2 from the molecular ion. The ECNI spectra of PBDEs with seven or less bromines are dominated by Br(-) and by HBr2(-); the spectra of those with eight or more bromines are dominated bytetra- or pentabromophenoxide ions due to cleavage of the phenyl-ether linkage. The EI mass spectra of methoxy-PBDEs can easily distinguish the position of the methoxy group relative to the phenyl-ether linkage. The ECNI spectra of these compounds are also dominated by Br(-) and HBr2(-). In both ionization modes and for both compound groups, there are some subtle features, which often allow one to rule in or out substitution at one or more of the ortho-ring positions.     

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.     

Atmospheric concentrations of polybrominated diphenyl ethers at near-source sites

Concentrations of polybrominated diphenyl ethers (PBDEs) were determined in air samples from near suspected sources, namely an indoors computer laboratory, indoors and outdoors at an electronics recycling facility, and outdoors at an automotive shredding and metal recycling facility. The results showed that (1) PBDE concentrations in the computer laboratorywere higherwith computers on compared with the computers off, (2) indoor concentrations at an electronics recycling facility were as high as 650,000 pg/m3 for decabromodiphenyl ether (PBDE 209), and (3) PBDE 209 concentrations were up to 1900 pg/m3 at the downwind fenceline at an automotive shredding/metal recycling facility. The inhalation exposure estimates for all the sites were typically below 110 pg/kg/day with the exception of the indoor air samples adjacent to the electronics shredding equipment, which gave exposure estimates upward of 40,000 pg/kg/day. Although there were elevated inhalation exposures at the three source sites, the exposure was not expected to cause adverse health effects based on the lowest reference dose (RfD) currently in the Integrated Risk Information System (IRIS), although these RfD values are currently being re-evaluated by the U.S. Environmental Protection Agency. More research is needed on the potential health effects of PBDEs.     

Air-surface exchange of polybrominated diphenyl ethers and polychlorinated biphenyls

Air and leaf-litter samples were collected from a rural site in southern Ontario under meteorologically stable conditions in the early spring, prior to bud burst, over a three-day period to measure the simultaneous diurnal variations in polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs). PBDEs are used in a wide range of commercial products as flame retardants and are being assessed internationally as potential persistent organic pollutants. Total PBDE concentrations in the air ranged between 88 and 1250 pg m(-3), and were dominated primarily by the lighter congeners PBDEs 17, 28, and 47, and concentrations of total PCBs ranged between 96 and 950 pg m(-3), and were dominated by the lower chlorinated (tri- to tetra-) congeners. Slopes of Clausius-Clapeyron plots indicate that both PCBs and PBDEs are experiencing active air-surface exchange. Fugacities were estimated from concentrations in the air and leaf-litter and suggest near equilibrium conditions. Following the three-day intensive sampling period, 40 air samples were collected at 24-hour intervals in an attempt to evaluate the effect of bud burst on atmospheric concentrations. Total PBDE concentrations in the daily air samples ranged between 10 and 230 pg m(-3), and were dominated by the lighter congeners PBDE 17, 28, and 47, whereas concentrations of total PCBs ranged between 30 and 450 pg m(-3) during this period. It is hypothesized thatthe high PBDE concentrations observed at the beginning of the sampling period are the result of an "early spring pulse" in which PBDEs deposited in the snowpack over the winter are released with snowmelt, resulting in elevated concentrations in the surface and air. Later in the sampling period, following bud burst, PBDE concentrations in air fell to 10 to 20 pg m(-3), possibly due to the high sorption capacity of this freshly emerging foliage compartment.     

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 ?rst 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.     

食品中多溴二苯醚类化合物检测技术研究进展

多溴二苯醚是一类持久性有机污染物,普遍应用在日常产品的防火;因其性质具有潜在致癌性且有高疏水性和抗降解性,已成为人类健康和环境的一大问题。在生物体内积累的多溴二苯醚会通过食物富集于人体,从而对健康饮食和人体寿命构成一定威胁。本文综述了近年来常见多溴二苯醚的种类、提取方法、净化方法、检测技术以及多溴二苯醚的生物危害性;探讨了各项分析检测技术的现存劣势。目前国内有多溴二苯醚消费品检测标准,但无相关食品基质检测标准,因其物质种类繁多和迥异的性质导致检测技术存在巨大挑战;文中也对后续的检测技术发展提出展望,以此为食品中多溴二苯醚检测技术发展和研究提供一定的支持。     

Global assessment of polybrominated diphenyl ethers in farmed and wild salmon

We have shown recently that levels of persistent, bioaccumulative contaminants (polychlorinated biphenyls, dioxins, and several chlorinated pesticides) are significantly higher in farmed than in wild salmon and that European farm-raised salmon have significantly greater toxic contaminant loads than those raised in North and South America. In this paper, we extend these results to polybrominated diphenyl ethers (PBDEs) and show that farm-raised salmon have higher levels of these compounds than wild salmon. We also show that farm-raised salmon from Europe have higher PBDE levels than those raised in North America and that both European and North American farm-raised salmon have higher PBDE levels than those farm-raised in Chile. Among the species of wild salmon, chinook had significantly elevated PBDE levels relative to the other wild species. These elevated PBDE levels may be related to chinook's feeding behavior and trophic level. Among all of the wild species we studied, chinook tend to feed higher in the food web throughout their adult life and grow to be larger individuals.     

Higher accumulation of polybrominated diphenyl ethers in infants than in adults

Pooled serum samples collected from 8132 residents in 2002/ 03 and 2004/05 were analyzed to assess human polybrominated diphenyl ether (PBDE) concentrations from specified strata of the Australian population. The strata were defined by age (0-4 years, 5-15 years, < 16 years, 16-30 years, 31-45 years, 46-60 years, and > 60 years); region; and gender. For both time periods, infants and older children had substantially higher PBDE concentrations than adults. For samples collected in 2004/ 05, the mean +/- standard deviation sigmaPBDE (sum of the homologue groups for the mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, and deca-BDEs) concentrations for 0-4 and 5-15 years were 73 +/- 7 and 29 +/- 7 ng g(-1) lipid, respectively, while for all adults > 16 years, the mean concentration was lower at 18 +/- 5 ng g(-1) lipid. A similar trend was observed for the samples collected in 2002/03, with the mean sigmaPBDE concentration for children < 16 years being 28 +/- 8 ng g(-1) lipid and for the adults >16 years, 15 +/- 5 ng g(-1) lipid. No regional or gender specific differences were observed. Measured data were compared with a model that we developed to incorporate the primary known exposure pathways (food, air, dust, breast milk) and clearance (half-life) data. The model was used to predict PBDE concentration trends and indicated that the elevated concentrations in infants were primarily due to maternal transfer and breast milk consumption with inhalation and ingestion of dust making a comparatively lower contribution.     

Complete debromination of tetra- and penta-brominated diphenyl ethers by a coculture consisting of dehalococcoides and desulfovibrio species

Polybrominated diphenyl ethers (PBDEs) are widespread global contaminants due to their extensive usage as flame retardants. Among the 209 PBDE congeners, tetra-brominated diphenyl ether (tetra-BDE) (congener 47) and penta-BDEs (congeners 99 and 100) are the most abundant, toxic, and bioaccumulative congeners in the environment. However, little is known about microorganisms that carry out debromination of these congeners under anaerobic conditions. In this study, we describe a coculture GY2 consisting of Dehalococcoides and Desulfovibrio spp., which is capable of debrominating ～1180 nM of congeners 47, 99, and 100 (88-100% removal) to the nonbrominated diphenyl ether at an average rate of 36.9, 19.8, and 21.9 nM day(-1), respectively. Ortho bromines are preferentially removed during the debromination process. The growth of Dehalococcoides links tightly with PBDE debromination, with an estimated growth yield of 1.99 × 10(14) cells per mole of bromide released, while the growth of Desulfovibrio could be independent of PBDEs. The growth-coupled debromination suggests that Dehalococcoides cells in the coculture GY2 are able to respire on PBDEs. Given the ubiquity and recalcitrance of the tetra- and penta-BDEs, complete debromination of these congeners to less toxic end products (e.g. diphenyl ether) is important for the restoration of PBDE-contaminated environments.     

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

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

气相色谱-串联质谱法测定蔬菜中8种多溴联苯醚

目的 建立气相色谱-串联质谱法测定蔬菜中8种多溴联苯醚方法。方法 样品采用正己烷：丙酮（V:V,1:1）提取,用25 mg N-丙基乙二胺(primary secondary amine, PSA)、150 mg MgSO4净化,利用气相色谱-串联质谱在多反应离子监测模式下进行检测,外标法定量。结果8种溴代阻燃剂的相关系数（r）均大于0.99,方法检出限范围为0.0001-0.0009 mg/kg。在3 种不同蔬菜基质中3 个添加水平（0.005、0.02、0.2 mg/kg）的平均回收率为91.1～114%,相对标准偏差为1.7%～8.7%。结论 该方法前处理简单快速、灵敏度高,具有良好的回收率和稳定性,适用于不同种蔬菜中8种多溴联苯醚的测定。     

Dietary intake and risk evaluation of polybrominated diphenyl ethers in The Netherlands

The current study aims at estimating the dietary intake of PBDEs in the Netherlands and evaluating the resultant risk. Dietary intake was estimated using results of PBDE analyses in Dutch food products from 2003/2004 and consumption data of the third Dutch National Food Consumption Survey (1997/1998). Assuming that non-detects represent levels of half the detection limit, the median long-term intake of the Dutch population of the sum of five major PBDEs (namely PBDEs 47, 99, 100, 153+154) is 0.79 ng/kg body weight bw/day (P97.5: 1.62 ng/kg bw/day). When non-detects are considered as zeros the values are 0.53 (median) and 1.34 (P97.5) ng/kg bw/day. Environmental concentrations of PBDEs in Europe are expected to decline in the near future because of the ban on penta- and octaBDE technical products. However, it will take at least a decade before this will result in lower PBDE concentrations in food products. Hence, a regular monitoring program for PBDEs is recommended. A risk evaluation at the most sensitive endpoints of BDE 99 carried out in this paper indicates that, although the long-term exposure to BDE 99 is well below the human exposure threshold level for neurodevelopmental toxicity, it may be close to that for reproductive toxicity.     

Total consumer exposure to polybrominated diphenyl ethers in North America and Europe

Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants in textiles, polyurethane foams, and plastics. PBDEs exert toxic effects in various organisms, including humans, and are ubiquitous in the outdoor and indoor environment. Here we estimate total daily PBDE doses received by consumers in North America and Europe, along with the most important pathways and congeners, and derive PBDE elimination half-lives for chronic exposure. We estimate distributions for all parameters (PBDE concentrations in exposure media, food consumption rates, etc.) and conduct a probabilistic exposure assessment. We find that Americans are exposed the most, likely due to stricter fire regulations, followed by consumers from the UK and Continental Europe. In the central quantiles of the exposure distributions derived, food is the dominant pathway; in the upper quantiles either food or oral and dermal exposure to dust. This reflects the lipophilic and persistent nature of PBDEs and their use in products for indoor-use. Median elimination half-lives are in a range of 1-3 years except for BDE-153 with about seven years and BDE-209 with 4-7 days.