Brominated dioxins/furans and hydroxylated polybrominated diphenyl ethers: Occurrences in commercial 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) and 2,4,6-tribromophenol, and formation during synthesis of BTBPE

The effects and mechanisms of the new brominated flame retardant BTBPE on thyroid toxicity

As an alternative to octabromodiphenyl ether (octa-BDE), 1, 2-bis (2,4, 6-tribromophenoxy) ethane (BTBPE) has been widely used in a variety of combustible materials, such as plastics, textiles and furniture. Previous studies have demonstrated the thyroid toxicity of traditional brominated flame retardants for example octa-BDE clearly. Nevertheless, little is known about the thyroid toxicity of alternative novel brominated flame retardants BTBPE. In this study, it was demonstrated that BTBPE in vivo exposure induced FT4 reduction in 2.5, 25 and 250 mg/kg bw treated group and TT4 reduction in 25 mg/kg bw treated group. TG, TPO and NIS are key proteins of thyroid hormone synthesis. The results of Western blot and RT-PCR from thyroid tissue showed decreased protein levels and gene expression levels of TG, TPO and NIS as well as regulatory proteins PAX8 and TTF2. To investigate whether the effect also occurred in humans, anthropogenic Nthy-ori 3-1 cells were selected. Similar results were seen in vitro condition. 2.5 mg/L BTBPE reduced the protein levels of PAX8, TTF1 and TTF2, which in turn inhibited the protein levels of TG and NIS. The results in vitro experiment were consistent with that in vivo, suggesting possible thyrotoxic effects of BTBPE on humans. It was indicated that BTBPE had the potential interference of T4 generation and the study provided more evidence of the effects on endocrine disorders.

Occurrence and carcinogenic potential of airborne PBDD/Fs and PCDD/Fs around a large-scale municipal solid waste incinerator: A long-term passive air sampling study

Municipal solid waste incinerator (MSWI) not only is deemed one of the uppermost sources of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs), but also produces substantial amount of polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) owing to the existence of brominated flame retardants (BFRs) in the waste. So far, however, PBDD/Fs in the vicinal environments of MSWI and their associated risks remain rarely studied. Based on a one-year passive air sampling (PAS) scheme, we investigated airborne PBDD/Fs and PCDD/Fs around a large-scale MSWI that has been operated for multi-years. Both the concentrations of PBDD/Fs and PCDD/Fs showed spatially decreasing trends with the distance away from the MSWI, confirming the influence of the MSWI on the dioxin levels in its ambient air. But its influence on PBDD/Fs was less because PBDD/Fs exhibit lower volatility and therefore lower gaseous concentrations than PCDD/Fs. Compared to the existing global data of airborne PCDD/Fs and PBDD/Fs, our data of the MSWI vicinity were at medium levels, despite PAS samples only represent the concentrations of gaseous dioxins in theory. The seasonal data suggest that meteorological conditions exerted apparent influences over the concentrations and sources of airborne dioxins around the MSWI. As for PCDD/Fs, the MSWI was diagnosed as their uppermost source, followed by local traffic and volatilization/deposition. Whereas the top three PBDD/F sources were related to PBDEs, bromophenol/bromobenzene, and traffic vehicles, respectively. The bioassay-derived TEQs based on the aryl hydrocarbon receptor activation of airborne dioxins around the MSWI were one or two orders of magnitudes higher than their concentration-based TEQs, and the corresponding carcinogenic risks at some MSWI-vicinal sites exceeded the acceptable threshold proposed by the U. S. EPA (10-6 ∼ 10-4) and deserve continuous attention.

Polybrominated dibenzo-p-dioxins/furans and their chlorinated analogues in sediments from a historical hotspot for both brominated flame retardants and organochlorine pesticides

Polybrominated dibenzo-p-dioxin/furans (PBDD/Fs) and polychlorinated dibenzo-p-dioxin/furans (PCDD/Fs) in the environment are closely related to their precursors, brominated flame retardants (BFRs) and organochlorine pesticides (OCPs). However, their change trends following the regulation of BFRs and OCPs remain incompletely characterized. Here, we examined PBDD/Fs and PCDD/Fs in sediments from a historical hotspot for both BFRs and OCPs, namely the Pearl River Delta (PRD), China. PBDD/Fs showed ubiquity in these samples but significantly lower concentrations than PCDD/Fs. Spatially, the occurrence of PBDD/Fs was positively correlated with local development levels and sediments from highly urbanized/industrialized areas showed higher and increasing PBDD/F concentrations. Polybrominated diphenyl ether (PBDE)-related products/industries were the greatest PBDD/F contributors to the PRD, followed by bromo-phenol/benzene-related products/industries. PCDD/Fs in PRD sediments showed significant positive correlations with local grain planting area, yield, and pesticide consumption. The historical use of pentachlorophenol (PCP)/PCP-Na and biomass open-burning were the leading PCDD/F sources of the PRD agricultural/rural areas, where the concentrations and toxic equivalent quantities (TEQs) of PCDD/Fs in sediments changed very little over the past decade. Anthropogenic thermal processes involved in metallurgy, waste incineration, and vehicles were the greatest PCDD/F contributors in the PRD urban/industrial areas, where the PCDD/F concentrations in sediments almost doubled over the last decade. This finding indicates the increasing PCDD/F contributions of industrial and municipal activities in the PRD, despite the implementation of strict emission standards. Over sixty percent of the samples showed TEQs that surpassed the low-risk threshold specified for mammalian life by the U.S. EPA (2.5 pg TEQ g^-1) and warrant continuous attention.

Occurrence and formation pathways analysis of PBDD/Fs from 2,4,6-tribromophenol under thermal reaction conditions

Polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) are highly toxic and persistent compounds that provoke a wave of publicity. Bromophenols are important precursors for forming PBDD/Fs, and their reaction path has always been a research hotspot. In this study, the formation characteristic of PBDD/Fs from 2,4,6-TBP were studied. The yields of 2,3,7,8-substituted PBDD/Fs and 2,4,6,8-TBDF for the different thermal products ranged from 0.067 to 10.3 ng/g and 0.207-9.68 ng/g, respectively. The effects of adding Cu, Fe, and Sb₂O₃ were investigated and found to be more inclined to accelerate the formation of ortho-substituted PBDD/Fs than 2,3,7,8-PBDD/Fs. The formation pathways of 2,3,7,8-substituted PBDD/Fs and 2,4,6,8-TBDF were also proposed. 2,4,6,8-TBDF is generated in the C-C coupling reactions of some radical intermediates from the debromination of 2,4,6-TBP. The 2,3,7,8-PBDD/Fs are produced through more complex debromination, bromine substitution, and bromine rearrangement reactions. In addition, various catalytic effects on PBDD/F formation pathways were found, and the catalytic effect of Cu by the Ullmann reaction was the highest, while bromophenol oxidation by Fe was the highest. These results proved that both 2,3,7,8-substituted and non-2,3,7,8-substituted PBDD/Fs would be generated from 2,4,6-TBP, and the effects of the catalyst on the Br substituted position of 2,3,7,8-substituted PBDD/Fs were much lower than the Br-substituted position on bromophenol.

Using In Vitro and Machine Learning Approaches to Determine Species-Specific Dioxin-like Potency and Congener-Specific Relative Sensitivity among Birds for Brominated Dioxin Analogues

There is a paucity of experimental data regarding dioxin-like toxicity of polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs) and non-ortho polybrominated biphenyls (PBBs). In this study, avian aryl hydrocarbon receptor 1 (AHR1)-luciferase reporter gene assays were used to determine their species-specific dioxin-like potencies (DLPs) and congener-specific interspecies relative sensitivities in birds. The results suggested that DLPs of the brominated congeners for chicken-like (Ile324_Ser380) species did not always follow World Health Organization toxicity equivalency factors of their chlorinated analogues. For ring-necked pheasant-like (Ile324_Ala380) and Japanese quail-like (Val324_Ala380) species, the difference in DLP for several congeners was 1 or even 2 orders of magnitude. Moreover, molecular docking and molecular dynamics simulation were performed to explore the interactions between the brominated congeners and AHR1-ligand-binding domain (LBD). The molecular mechanics energy (E_MM) between each congener and each individual amino acid (AA) residue in AHR1-LBD was calculated. These E_MM values could finely characterize the final conformation of species-specific AHR1-LBD for each brominated congener. Based on this, mechanism-driven generalized linear models were successfully built using machine learning algorithms and the spline approximation method, and these models could qualitatively predict the complex relationships between AHR1 conformations and DLPs or avian interspecies relative sensitivity to brominated dioxin-like compounds (DLCs). In addition, several AAs conserved among birds were found to potentially interact with species-specific AAs, thereby inducing species-specific interactions between AHR1 and brominated DLCs. The present study provides a novel strategy to facilitate the development of mechanism-driven computational prediction models for supporting safety assessment of DLCs, as well as a basis for the ecotoxicological risk assessment of brominated congeners in birds.

Environmental characteristics and formations of polybrominated dibenzo-p-dioxins and dibenzofurans

Polybrominated dibenzo-p-dioxins and furans (PBDD/Fs) are emerging persistent organic pollutants (POPs) that have similar or higher toxicities than the notorious dioxins. Toxicities, formation mechanisms, and environmental fates of PBDD/Fs are lacking because accurate quantification, especially of higher brominated congeners, is challenging. PBDD/F analysis is difficult because of photolysis and thermal degradation and interference from polybrominated diphenyl ethers. Here, literatures on PBDD/F analysis and environmental occurrences are reviewed to improve our understanding of PBDD/F environmental pollution and human exposure levels. Although PBDD/Fs behave similarly to dioxins, different congener profiles between PBDD/Fs and dioxins in the environment indicates their different sources and formation mechanisms. Herein, potential sources and formation mechanisms of PBDD/Fs were critically discussed, and current knowledge gaps and future directions for PBDD/F research are highlighted. An understanding of PBDD/F formation pathways will allow for development of synergistic control strategies for PBDD/Fs, dioxins, and other dioxin-like POPs.

Dietary exposure assessment of a nursing mother-infant cohort to legacy and novel brominated flame retardants: Results of a 3-day duplicate diet study in Beijing, China

In a 3-day duplicate diet study of a nursing mother-infant cohort (n = 20), the levels of polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD), and 5 novel brominated flame retardants (BFRs) were measured in 60 24-h duplicate diet samples and 20 breast milk samples provided by the mothers. The dietary BFR intake and related health risks of the mothers and their babies due to food consumption or human milk ingestion were subsequently assessed. At median concentrations of 284, 264 and 177 pg/g wet weight (ww) in the diet, decabrominated diphenyl ethers (BDE-209), decabromodiphenyl ethane (DBDPE) and HBCDD were predominant among the total BFRs. In human milk, HBCDD was the most abundant BFR, followed by BDE-209 and DBDPE, which indicates that BDE-209 and HBCDD have remained ubiquitous in the environment because of their continuous production and use in China. Meanwhile, concentrations of DBDPE were comparative to those of PBDEs and HBCDD in both diet and human milk, and DBDPE also had much higher concentrations than any other NBFRs, which indicates that the BFR consumption pattern in China is shifting from legacy BFRs to NBFRs. The median estimated dietary intakes (EDIs) of BDE-209, HBCDD and DBDPE for the mothers were 6.83, 3.73 and 5.44 ng/kg bw/day, respectively, and EDIs for their nursing babies were 24.7, 41.9 and 7.83 ng/kg bw/day, respectively. The nursing infants showed higher BFR body burden than the mothers. However, the EDIs obtained for both mothers and their babies discloses a low health risk to this mother-infant cohort.

Detection of high PBDD/Fs levels and dioxin-like activity in toys using a combination of GC-HRMS, rat-based and human-based DR CALUX® reporter gene assays

Brominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) are increasingly reported at significant levels in various matrices, including consumer goods that are manufactured from plastics containing certain brominated flame retardants. PBDD/Fs are known ligands for the aryl hydrocarbon receptor (AhR) but are not yet considered in the hazard assessment of dioxin mixtures. The aim of the present study was to determine if PBDD/Fs levels present in plastic constituents of toys could pose a threat to children's health. PBDD/Fs, unlike their chlorinated counterparts (PCDD/Fs), have not been officially assigned toxic equivalence factors (TEFs) by the WHO therefore, we determined their relative potency towards AhR activation in both human and rodent cell-based DR CALUX® bioassays. This allowed us to compare GC-HRMS PBDD/F congener levels, converted to total Toxic Equivalents (TEQ) by using the PCDD/F TEFs, to CALUX Bioanalytical Equivalents (BEQ) levels present in contaminated plastic constituents from children's toys. Finally, an estimate was made of the daily ingestion of TEQs from PBDD/Fs-contaminated plastic toys by child mouthing habits. It is observed that the daily ingestion of PBDD/Fs from contaminated plastic toys may significantly contribute to the total dioxin daily intake of young children.

The formation of PBDFs from the ortho-disubstituted phenol precursors: A comprehensive theoretical study on the PBDD/Fs formation from 2,4,6-tribromophenol

Bromophenols are known as direct precursors of the notorious polybrominated dibenzo-p-dioxin/dibenzofurans (PBDD/Fs). There is a long-held viewpoint that only the more toxic dioxin-type products could be formed from the ortho-disubstituted phenols, totally contrary to the experimental observations that both PBDDs and PBDFs are generated. To tackle the issue, the gaseous formation mechanism of PBDD/Fs from 2,4,6-tribromophenol (TBP), a typical ortho-disubstituted phenol, was investigated in this study. Firstly, the reactions between TBP and the active H radical produce three key radical species including the bromophenoxyl radical, the substituted phenyl radical and phenoxyl diradical. The self- and cross-combinations of these radical species and TBP yield not only the dioxin-type products 1,3,6,8-TeBDD and 1,3,7,9-TeBDD, but also the brominated dibenzofurans 1,3,6,8-TeBDF and 2,4,6,8-TeBDF. Notably, the reactions involving the phenyl C sites in the substituted phenyl and phenoxyl diradicals are demonstrated to be both thermodynamically and kinetically more favorable than those involving the bromophenoxyl radical and the TBP molecule. Most importantly, the findings of the present work are of great importance as it provides feasible pathways to form less toxic dibenzofuran-type products from the ortho-disubstituted phenols. These results will improve the understanding of the PBDD/Fs formation mechanism from phenol precursors.

Organophosphate compounds, polybrominated diphenyl ethers and novel brominated flame retardants in European indoor house dust: Use, evidence for replacements and assessment of human exposure

52 pollutants including organophosphate flame retardants and plasticizers (OPs), polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (NBFRs) were evaluated in household dust from Belgium, Italy and Spain. Pollutant pattern was dominated by ∑OPs (12.8 μg/g; median) followed in decreasing order by ∑PBDEs (229 ng/g), decabromodiphenyl ethane (DBDPE, 130 ng/g), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE, 1.35 ng/g), hexabromobenzene (HBB, 0.28 ng/g) and finally pentabromoethylbenzene (PBEB, 0.03 ng/g). Country differences and substitution of regulated chemicals by unregulated ones were explored. Results clearly reflected a decrease in c-penta and c-octaBDE commercial mixtures, which are mainly substituted by OPs, BTBPE and PBEB. On the other hand, c-decaBDE concentrations increased in Spanish case. However, positive correlations with its proposed substitute (DBDPE) and recent restricted policies make it possible to assume that this trend will change in the coming years. On the basis of the relationship between pollutants, house characteristics and inhabitant habits, potential sources were studied. Finally, data obtained were used to determine estimated daily intakes (EDI) via house dust ingestion and dermal absorption for toddlers and adults at central and upper percentiles. Calculated EDI levels even at worst case scenario were below available reference dose (RfD) values in all cases.

Release and Transformation of BTBPE During the Thermal Treatment of Flame Retardant ABS Plastics

Thermal scenarios inevitably occur during the lifecycle of engineering plastics laden with brominated flame retardants (BFRs). However, little information on the fate of embedded BFRs during the thermal processes is available. In this study, we measured the release and transformation of a typical BFR, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), during the thermal treatment of acrylonitrile butadiene styrene (ABS) plastics. The possible thermal scenarios were simulated by varying the heating temperature and atmosphere. The maximum release rate of BTBPE was observed at 350 °C. A release kinetic model was developed to explore the mechanism of BTBPE release while heating ABS. Material-phase diffusion was found to be the rate-determining step during release. According to the developed release model, it was estimated that 0.04-0.17% of embedded BTBPE could be released to air during the industrial processing of ABS plastics. When the heating temperature was ≥350 °C, approximately 15-56% of embedded BTBPE decomposed to bromophenols (BPs) and 1,3,5-tribromo-2-(vinyloxy) benzene (TBVOB), and the decomposition followed a first-order kinetics at 350 °C. Polybrominated dibenzo- p-dioxins and dibenzofurans (PBDD/Fs) were also significantly formed at ≥350 °C from BPs and TBVOB via a precursor mechanism. A higher temperature (≥450 °C) was favorable for the formation of PBDFs.

Determination of polybrominated diphenyl ethers and novel brominated flame retardants in human serum by gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry

The accurate detection of brominated flame retardants (BFRs) in humans is an area of high scientific interest and regulatory need due to their potential toxicity. The instrumental analysis of BFRs was commonly performed on gas chromatography-mass spectrometry (GC-MS) operating in electron ionization (EI) or negative chemical ionization (NCI) modes. However, soft ionization techniques, such as atmospheric pressure chemical ionization (APCI), may be more suitable for the analysis of BFRs because the BFRs show high fragmentation in EI and low selectivity in NCI. Additionally, accurate quantifications of BFRs in complex matrices is challenging due to their low concentrations and therefore, a highly sensitive technique is desperately needed. In this study, a new methodology based on gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (GC-APCI-MS/MS) analysis was developed for the determination of thirteen BFRs (eight usually monitored polybrominated diphenyl ethers (PBDEs) congeners and five additional novel BFRs) in human serum. The primary task was to evaluate the potential of the GC-APCI-MS/MS technique for the trace analysis of BFRs in human serum. The results of the spiked recovery test using fetal bovine serum showed that mean recoveries of the analytes ranged from 83.4% to 118% with reduced swing differential signaling (RSDs) of ≤21.1%. The methodological limits of detection (mLOD) of the analytes ranged from 0.04 to 30 pg/mL, and these values were at least one order of magnitude lower than those estimated by the authors in a previous study using GC-NCI-MS or GC-EI-MS/MS, indicating that GC-APCI-MS/MS is more sensitive. Specially, compared to GC-NCI-MS and GC-EI-MS/MS, when GC-APCI-MS/MS was used for the detection of highly brominated BFRs, such as BDE-209 and decabromodiphenyl ethane (DBDPE), a notable improvement in sensitivity and reliability was obtained using a deactivated capillary column connected to the analytical column as the transfer line and maintaining a high temperature to improve the chromatographic behaviors. The developed methodology was successfully used for the analysis of BFRs in human serum collected from residents living in a BFR production area and Beijing.

Legacy and novel brominated flame retardants in indoor dust from Beijing, China: Occurrence, human exposure assessment and evidence for PBDEs replacement

Levels of legacy brominated flame retardants (BFRs), including tetrabromobisphenol A (TBBPA), hexabromocyclododecane isomers (HBCDs) and polybrominated diphenyl ethers (PBDEs), and six currently used novel BFRs were determined in house dust and office dust collected from a community in Beijing, China. This is the first study where the three kinds of legacy BFRs and novel BFRs were all measured in dust samples from China. HPLC-MS/MS was used for the detection of TBBPA and HBCDs, and the other BFRs were tested on a GC-NCI/MS. Decabromodiphenyl ethane (DBDPE), PBDEs, HBCD and TBBPA were found to be the main BFRs in the dust samples, with median levels of 709, 241, 199 and 26.7ng/g dust, respectively. Due to the high density of electronic equipment used in offices, levels of BFRs in office dust were found to be higher than those in house dust. DBDPE, as a replacement of PBDEs, was the predominant BFR, and the median level of DBDPE was not only several orders of magnitude higher than that of other novel BFRs but also 3 to 27 times higher than that of the three legacy BFRs, indicating that the consumption pattern of BFRs in the Chinese market has shifted from PBDEs to PBDE alternatives. Median estimated daily intakes (EDIs) of BFRs through dust ingestion for adults (>20years) and toddlers (<2years) were in the range of 2.8×10^-5-0.201ng/kg body weight (bw)/day and 5.7×10^-4-2.52ng/kg bw/day, respectively. The body burden of BFRs for toddlers was far higher than that for adults; however, a comparison between EDIs and threshold values suggested that daily intakes of BFRs for both adults and toddlers were unlikely to raise significant health concerns.

Environmental concentrations and toxicology of 2,4,6-tribromophenol (TBP)

2,4,6-Tribromophenol is the most widely produced brominated phenol. In the present review, we summarize studies dealing with this substance from an environmental point of view. We cover concentrations in the abiotic and biotic environment including humans, toxicokinetics as well as toxicodynamics, and show gaps of the current knowledge about this chemical. 2,4,6-Tribomophenol occurs as an intermediate during the synthesis of brominated flame retardants and it similarly represents a degradation product of these substances. Moreover, it is used as a pesticide but also occurs as a natural product of some aquatic organisms. Due to its many sources, 2,4,6-tribromophenol is ubiquitously found in the environment. Nevertheless, not much is known about its toxicokinetics and toxicodynamics. It is also unclear which role the structural isomer 2,4,5-tribromophenol and several degradation products such as 2,4-dibromophenol play in the environment. Due to new flame retardants that enter the market and can degrade to 2,4,6-tribromophenol, this compound will remain relevant in future years - not only in aquatic matrices, but also in house dust and foodstuff, which are an important exposure route for humans.