Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs in human serum from Shanghai, China: a study on their presence and correlations

Identification of serum metabolites associated with polybrominated diphenyl ethers (PBDEs) exposure in papillary thyroid carcinoma: a case-control study

As the most common endocrine cancer, thyroid cancer (TC) has sharply increased globally over the past three decades. The growing incidence of TC might be counted by genetics, radiation, iodine, autoimmune disease, and exposure to environmental endocrine-disrupting chemicals (EDCs). Polybrominated diphenyl ethers (PBDEs), being typical EDCs, have been widely utilized in plastics, electronics, furniture, and textiles as flame retardants since the 1980s, and research has indicated a significant correlation between their exposure and the risk of TC. Even so, PBDEs exposure impact on the metabolic signature for TC remains unexplored. In this study, eight congeners of PBDEs were determined in serum from 111 patents with papillary thyroid cancer (PTC) and 111 healthy participants based on case-control epidemiology using gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (GC-APCI-MS/MS). Based on the tertile distribution of total PBDEs concentrations in 59 participants, metabolomics analysis was further performed by ultra-high performance liquid chromatography coupled to hybrid quadrupole-Orbitrap MS. In the partial correlation analysis, the 29 identified metabolites were correlated with PBDEs exposure (P < 0.05). In addition, PBDEs disrupted the metabolism of glycerophospholipids, sphingolipids, taurine, and hypotaurine, indicating that neurotransmitters, oxidative stress, and inflammation are the vulnerable pathways affected in PTC. Furthermore, (±)-octopamine and 5-hydroxyindole, both of which modulate the actions of neurotransmitters, emerged as potential disturbed metabolite markers for TC following exposure to PBDEs. This study analyzed the impact of PBDEs on PTC in terms of the metabolic changes and further explored possible biomarkers, which helped us have a deep understanding of the possible mechanism of the effects of PBDEs on TC.

Developmental hazards of 2,2',4,4'-tetrabromodiphenyl ether induced endoplasmic reticulum stress on early life stages of zebrafish (Danio rerio)

Polybrominated diphenyl ether flame retardants are known to have adverse effects on the development of organisms. We investigated the molecular mechanisms associated with the developmental hazards of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in zebrafish, as well as the behavioral and morphological alterations involved, focusing on endoplasmic reticulum stress (ERS), oxidative stress, and apoptosis. Our study revealed behavioral alterations in zebrafish exposed to BDE-47, including impaired motor activity, reduced exploration, and abnormal swimming patterns. In addition, we observed malformations in craniofacial regions and other developmental abnormalities that may be associated with ERS-induced cellular dysfunction. BDE-47 exposure showed apparent changes in ERS, oxidative stress, and apoptosis biomarkers at different developmental stages in zebrafish through gene expression analysis and enzyme activity assays. The study indicated that exposure to BDE-47 results in ERS, as supported by the upregulation of ERS-related genes and increased activity of ERS markers. In addition, oxidative stress-related genes showed different expression patterns, suggesting that oxidative stress is involved in the BDE-47 toxic effects. Moreover, an assessment of apoptotic biomarkers revealed an imbalance in the expression levels of pro- and anti-apoptotic genes, suggesting that BDE-47 exposure activated the apoptotic pathway. These results highlight the complex interactions between ERS, oxidative stress, apoptosis, behavioral alterations, and morphological malformations following BDE-47 exposure in zebrafish. Understanding the mechanisms of toxicity of developmental hazards is essential to elucidate the toxicological effects of environmental contaminants. The knowledge can help develop strategies to mitigate their adverse effects on the health of ecosystems and humans.

Persistent immune injury induced by short-term decabromodiphenyl ether (BDE-209) exposure to female middle-aged Balb/c mice

Decabromodiphenyl ether (BDE-209), widely used in various industries for its excellent flame-retardant performance, could be enriched in humans and is closely associated with immune impairment. In addition, immune system is gradually declined and becoming more sensitive to environmental pollutants in the ageing process. Therefore, the immunotoxicity of BDE-209 (4, 40, and 400 mg/kg/day) to middle-aged mice and its recovery and susceptibility was first to be comprehensively investigated in this study. The results showed that BDE-209 exposure could lead to oxidative injury to immune organs (spleen, thymus, and liver), impair humoral (immunoglobulins), cellular (lymphopoiesis), and non-specific immunity, and disturb the expressions of the genes related to Th1/Th2 balance (T helper cells) in the middle-aged mice. In addition, Integrated Biomarker Response (IBR) indicated that BDE-209-induced immune impairment was challenging to self-regulated, and even exacerbated after 21 days of recovery and oxidative injury in immune organs could be the main reason. Furthermore, factorial analysis showed that middle-aged mice exposed to BDE-209 suffered from greater immune impairment than adult mice, and the immune impairment in aged mice is more difficult to be self-repaired than that in adult mice. It can be seen that the aged tend to suffer from BDE-209-induced persistent immune impairment and health threats.

Serum polybrominated diphenyl ether exposure and influence factors in blood donors of Wuxi adults from 2013 to 2016

Polybrominated diphenyl ethers (PBDEs) have been used as brominated flame retardants worldwide and are correlated with extensive environmental pollution and human health concerns. This study is aimed at analyzing the concentrations of PBDEs and at evaluating their temporal trends among a population of blood donors (n = 33) over a 4-year period. A total of 132 serum samples were used for PBDE detection. Nine PBDE congeners were quantified in serum samples by gas chromatography with mass spectrometry (GC-MS). The median concentrations of Σ₉PBDEs in each year were 33.46, 29.75, 30.85, and 35.02 ng/g lipid, respectively. Most of the PBDE congeners showed a downward trend from 2013 to 2014 and then increased after 2014. No correlations between age and PBDE congener concentrations were observed, while concentrations of each congener and Σ₉PBDE were nearly always lower in females than in males, especially in BDE-66, BDE-153, BDE-183, BDE-190, and Σ₉PBDE. We also found that the intake of fish, fruit, and eggs in the daily diet was related to the exposure level of PBDEs. Our results suggest that, as deca-BDE is still produced and used in China, diet is an important exposure pathway for PBDEs, and follow-up studies will be required to improve our understanding of the behaviors of PBDE isomers in humans and the exposure levels.

Exposure to Polybrominated Diphenyl Ethers and Phthalates in China: A Disease Burden and Cost Analysis

Increasing evidence indicates that endocrine-disrupting chemicals (EDCs) cause a variety of adverse health outcomes and contribute to substantial disease burden. This study summarized the exposure status of polybrominated diphenyl ethers (PBDEs) and phthalates (PAEs) in China and evaluated the disease burden attributable to PBDEs and PAEs in 2015. The results showed that PBDE and PAE concentrations were higher in coastal areas. The disease burden attributable to PBDEs was 0.77 million cases, and the economic costs were CNY 18.92 billion. Meanwhile, 3.02 million individuals suffered from diseases attributable to PAEs, and the economic costs were CNY 49.20 billion. The economic burden caused by PBDEs and PAEs accounted for 0.28% and 0.72% of China's Gross Domestic Product (GDP) in 2015, respectively. When comparing China's results from 2010, it was determined that the GDP ratio of economic costs caused by PAEs in 2015 (0.72%) was lower than in 2010 (1.42%). Finally, compared with the results of the European Union and North America, the GDP ratios of economic costs caused by PAEs in 2015 were 0.19% in Canada (lower than China), 0.29% in the United States (lower than China), and 1.44% in the European Union (higher than China). This study provides important reference values for China's health governance, and further research should be conducted in the future.

New Insights into Human Biotransformation of BDE-209: Unique Occurrence of Metabolites of Ortho-Substituted Hydroxylated Higher Brominated Diphenyl Ethers in the Serum of e-Waste Dismantlers

Extremely high levels of decabromodiphenyl ether (BDE-209) are frequently found in the serum of occupationally exposed groups, such as e-waste dismantlers and firefighters. However, the metabolism of BDE-209 in the human body is not adequately studied. In this study, 24 serum samples were collected from workers at a typical e-waste recycling workshop in Taizhou, Eastern China, and the occurrence and fate of these higher brominated diphenyl ethers (PBDEs) were investigated. The median concentration of the total PBDEs in the serum was 199 ng/g lipid weight (lw), ranging from 125 to 622 ng/g lw. Higher brominated octa- to deca-BDEs accounted for more than 80% of the total PBDEs. Three ortho-hydroxylated metabolites of PBDEs─6-OH-BDE196, 6-OH-BDE199, and 6'-OH-BDE206─were widely detected with a total concentration (median) of 92.7 ng/g lw. The concentrations of the three OH-PBDEs were significantly higher than their octa- and nona-PBDE homologues, even exceeding those of the total PBDEs in several samples, indicating that the formation of OH-PBDEs was a major metabolic pathway of the higher brominated PBDEs in occupationally exposed workers. An almost linear correlation between 6-OH-BDE196 and 6-OH-BDE199 (R = 0.971, P < 0.001) indicates that they might undergo a similar biotransformation pathway in the human body or may be derived from the same precursor. In addition, the occurrence of a series of penta- to hepta- ortho-substituted OH-PBDEs was preliminarily identified according to their unique "predioxin" mass spectral profiles by GC-ECNI-MS. Taken together, the tentative metabolic pathway for BDE-209 in e-waste dismantlers was proposed. The oxidative metabolism of BDE-209 was mainly observed at the ortho positions to form 6'-OH-BDE-206, which later underwent a consecutive loss of bromine atoms at the meta or para positions to generate other ortho-OH-PBDEs. Further studies are urgently needed to identify the chemical structures of these ortho-OH-PBDE metabolites, and perhaps more importantly to clarify the potentially toxic effects, along with their underlying molecular mechanisms.

Determination of polybrominated diphenyl ethers in serum using isotope internal standard-gas chromatography-high resolution dual-focus magnetic mass spectrometry

建立了同位素内标-气相色谱-高分辨双聚焦磁质谱(GC-HRMS)同时测定人体血清中14种多溴联苯醚(PBDEs)的方法。血清样品解冻后,取0.5 mL与¹³C标记的内标物进行混合,加入甲醇沉淀样品中的蛋白质,比较了3种酸化条件下的去脂效果和回收率,结果显示硫酸去脂效果最好;使用液液萃取法提取样品中的目标物,比较了不同萃取溶剂对回收率的影响,结果显示以正己烷(6 mL)-甲基叔丁基醚(6 mL)作为萃取溶剂效果最好;提取液经固相萃取柱净化和洗脱,比较了不同固相萃取柱和洗脱溶剂的净化效果和回收率,结果显示采用硅胶柱净化和用正己烷-二氯甲烷(1:1, v/v)洗脱时效果最好;洗脱液经氮吹近干后用正己烷复溶,经GC-HRMS测定。目标物经Rtx-1614色谱柱(30 m×0.25 mm×0.1 μm)分离,电压选择离子检测(VSIR)模式测定。BDE-209在0.40~25 μg/L、其他13种多溴联苯醚在0.08~5 μg/L范围内线性关系良好,相关系数>0.995,方法检出限为0.01~0.51 μg/L,定量限为0.04~1.70 μg/L,加标回收率为75.5%~120.7%,日内精密度为3.8%~10.9%(n=6),日间精密度为4.2%~12.4%(n=6)。应用该方法对采集的某地区15份青少年血清样本进行检测,结果显示14种PBDEs中,BDE-47检出率为100%,其他组分均未检出,说明该人群存在一定的PBDEs暴露。与现有文献报道方法相比,本方法样本需求量少,灵敏度、准确度较高,可对人血清中包括BDE-209在内的14种PBDEs同时测定,有效提高检测效率。本方法的建立可为我国开展多溴联苯醚对人群健康的影响提供技术支撑。

Critical review of analytical methods for the determination of flame retardants in human matrices

Human biomonitoring is a powerful approach in assessing exposure to environmental pollutants. Flame retardants (FRs) are of particular concern due to their wide distribution in the environment and adverse health effects. This article reviews studies published in 2009-2020 on the chemical analysis of FRs in a variety of human samples and discusses the characteristics of the analytical methods applied to different FR biomarkers of exposure, including polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), novel halogenated flame retardants (NHFRs), bromophenols, incl. tetrabromobisphenol A (TBBPA), and organophosphorous flame retardants (PFRs). Among the extraction techniques, liquid-liquid extraction (LLE) and solid phase extraction (SPE) were used most frequently due to the good efficiencies in the isolation of the majority of the FR biomarkers, but with challenges for highly lipophilic FRs. Gas chromatography-mass spectrometry (GC-MS) is mainly applied in the instrumental analysis of PBDEs and most NHFRs, with recent inclusions of GC-MS/MS and high resolution MS techniques. Liquid chromatography-MS/MS is mainly applied to HBCD, bromophenols, incl. TBBPA, and PFRs (including metabolites), however, GC-based analysis following derivatization has also been used for phenolic compounds and PFR metabolites. Developments are noticed towards more universal analytical methods, which enable widening method scopes in the human biomonitoring of FRs. Challenges exist with regard to sensitivity required for the low concentrations of FRs in the general population and limited sample material for some human matrices. A strong focus on quality assurance/quality control (QA/QC) measures is required in the analysis of FR biomarkers in human samples, related to their variety of physical-chemical properties, low levels in most human samples and the risk of contamination.

Human Biomonitoring of Environmental and Occupational Exposures by GC-MS and Gas Sensor Systems: A Systematic Review

Environmental chemicals and contaminants coming from multiple external sources enter the human body, determining a potential risk for human health. Human biomonitoring (HBM), measuring the concentrations of biomarkers in human specimens, has become an emerging approach for assessing population-wide exposure to hazardous chemicals and health risk through large-scale studies in many countries. However, systematic mapping of HBM studies, including their characteristics, targeted hazardous pollutants, analytical techniques, and sample population (general population and occupationally exposed workers), has not been done so far. We conducted a systematic review of the literature related to airborne hazardous pollutants in biofluids to answer the following questions: Which main chemicals have been included in the literature, which bodily fluids have been used, and what are the main findings? Following PRISMA protocol, we summarized the publications published up to 4 February 2021 of studies based on two methods: gas-chromatography/mass spectrometry (GC/MS) and electronic noses (e-noses). We screened 2606 records and 117 publications were included in the analysis, the most based on GC/MS analysis. The selected HBM studies include measurements of biomarkers in different bodily fluids, such as blood, urine, breast milk, and human semen as well as exhaled air. The papers cover numerous airborne hazardous pollutants that we grouped in chemical classes; a lot of hazardous and noxious compounds, mainly persistent organic pollutants (POPs) and volatile organic compounds (VOCs), have been detected in biological fluids at alarming levels. The scenario that emerged from this survey demonstrates the importance of HBM in human exposure to hazardous pollutants and the need to use it as valid tool in health surveillance. This systematic review represents a starting point for researchers who focus on the world of pollutant biomonitoring in the human body and gives them important insights into how to improve the methods based on GC/MS. Moreover, it makes a first overview of the use of gas sensor array and e-noses in HBM studies.

Emerging environmental pollutants hydroxylated polybrominated diphenyl ethers: From analytical methods to toxicology research

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are of particular concern due to their ubiquitous distribution and adverse health effects. Significant progress has been made in the characterization of OH-PBDEs by using mass spectrometry (MS). In this review, we summarize applications of MS-based techniques in detection, environmental and biota distribution, and potential health risk effects, hoping to unfold an overall picture on account of current knowledge of OH-PBDEs. The analytical methodologies are discussed from sample pretreatment to MS analysis. The methods including gas chromatography-MS (GC-MS), liquid chromatography-MS (LC-MS), and ion mobility spectrometry-MS (IMS-MS) are discussed. GC-MS is the most frequently adopted method in the analysis of OH-PBDEs due to its excellent chromatographic resolution, high sensitivity, and strong ability for unknown identification. LC-MS has been widely used for its high sensitivity and capability of direct analysis. As a newly developed technique, IMS-MS provides high specificity, which greatly facilitates the identification of isomers. OH-PBDEs pervasively existed in both abiotic and biotic samples, including humans, animals, and environmental matrices. Multiple adverse health effects have been reported, such as thyroid hormone disruption, estrogen effects, and neurotoxicity. The reported potential pathological mechanisms are also reviewed. Additionally, MS-based metabolomics, lipidomics, and proteomics have been shown as promising tools to unveil the molecular mechanisms of the toxicity of OH-PBDEs. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Exploring reproductive associations of serum polybrominated diphenyl ether and hydroxylated brominated diphenyl ether concentrations among women undergoing in vitro fertilization

STUDY QUESTION

Are serum concentrations of polybrominated diphenyl ethers (PBDEs) and hydroxylated brominated diphenyl ethers (OH-BDEs) associated with IVF endpoints?

SUMMARY ANSWER

Positive associations were observed for BDE153 and several OH-BDEs with IVF endpoints.

WHAT IS KNOWN ALREADY

PBDEs have been voluntarily phased out of production in the USA and EU due to their persistence and toxicity to humans and ecosystems. PBDEs have been associated with implantation failure among women undergoing IVF, yet some animal studies suggest greater toxicity from their metabolites, OH-BDEs.

STUDY DESIGN, SIZE, DURATION

We evaluated a subset of 215 women (contributing 330 IVF cycles) enrolled between 2005 and 2016 in a longitudinal cohort based at Massachusetts General Hospital Fertility Center.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The following PBDEs were quantified: 47, 99, 100, 153 and 154 and the following OH-BDEs: 3-OH-BDE47, 5-OH-BDE47, 6-OH-BDE47 and 4-OH-BDE49. Clinical endpoints of IVF treatments were abstracted from electronic medical records. Associations of log-transformed PBDEs and OH-BDEs with IVF outcomes were assessed using multivariable generalized mixed models and cluster weighted generalized estimating equation models adjusted for lipids, age, BMI, race, year of sample collection, IVF protocol and FSH levels. Outcomes were adjusted to represent a percent change in outcome with an increase equal to the magnitude of the difference between the 75th and 25th percentiles for each specific compound (interquartile range (IQR) increase).

MAIN RESULTS AND THE ROLE OF CHANCE

Detection frequencies were highest for congeners 47 and 153 (82% ≥ method detection limit (MDL)) and metabolites 3 and 5-OH-BDE47 and 4-OH-BDE49 (92% > MDL). PBDE and OH-BDE geometric mean concentrations declined by up to 80% between participants recruited in 2005 and those recruited in 2016. An IQR increase of BDE153 was associated with an increase in the probability of implantation (relative risk (RR) = 1.26, 95% CI: 1.16, 1.36), clinical pregnancy (RR = 1.32, 95% CI: 1.19, 1.46) and live birth (RR = 1.34; 95% CI: 1.15, 1.54). An IQR increase in 3 and 5-OH-BDE47 was associated with increased probabilities of implantation (RR = 1.52; 95% CI: 1.11, 2.09), clinical pregnancy (RR = 1.66; 95% CI: 1.17, 2.36), and live birth (RR = 1.61; 95% CI: 1.07, 2.40). When models were stratified by race (White (86%)/Other race (14%)), associations remained positive for White women, yet inverse associations were observed for Other race women. An IQR increase in BDE47 was associated with a 46% decreased probability of clinical pregnancy (95% CI: 0.31, 0.95) for Other race women.

LIMITATIONS, REASONS FOR CAUTION

Despite the long half-lives of PBDEs and OH-BDEs, exposure misclassification is possible for women who underwent multiple treatment cycles over several months or years. It is also possible another medium, such as follicular fluid would be optimal to characterize exposure. We also tested associations for multiple congeners and metabolites with multiple outcomes.

WIDER IMPLICATIONS OF THE FINDINGS

Detections of serum concentrations of PBDEs and OH-BDEs were highest in the early years of the study and suggests that the phase-out of these compounds has contributed to a decrease in exposure. The negative associations found for PBDEs and IVF outcomes among other race women suggests the potential for racial disparity. Potential racial disparities in PBDE exposure and exploration of alternative flame retardants with reproductive health outcomes should be the focus of future investigations.

STUDY FUNDING/COMPETING INTEREST(S)

Funding for this research was supported by the National Institutes of Environmental Health Sciences (NIEHS) [R01 ES009718, ES022955, ES000002 and 009718T32ES007069]. The authors have no conflicts of interest.

Polybrominated diphenyl ethers in serum from residents living in a brominated flame retardant production area: Occurrence, influencing factors, and relationships with thyroid and liver function

Polybrominated diphenyl ethers (PBDEs) have been used as flame retardants (FRs) in China for decades, even after they were identified as persistent organic pollutants. In this study, serum samples were collected from 172 adults without occupational exposure who were residents of a well-known FR production region (Laizhou Bay, north China), and PBDE congeners were measured to assess their occurrence, congener profile and influencing factors in serum. Moreover, the relationships between serum concentrations of PBDEs and thyroid/liver function indicators were analyzed to evaluate whether human exposure to PBDEs would lead to thyroid/liver injury. All 8 PBDE congeners were detected at higher frequencies and serum concentrations than those found in general populations. The median levels of ∑PBDEs, BDE-209 and ∑_3-7PBDEs (sum of tri-to hepta-BDEs) were 64.5, 56.9 and 7.2 ng/g lw (lipid weight), respectively, which indicated that deca-BDE was the primarily produced PBDE in Laizhou Bay and that the lower brominated BDEs were still ubiquitous in the environment. Gender was a primary influencing factor for some BDE congeners in serum; their levels in female serum samples were significantly lower than those in male serum samples. Serum PBDE levels showed a downward trend with increased body mass index (BMI), which might reflect the increasing serum lipid contents. Serum levels of some BDE congeners were significantly positively correlated with certain thyroid hormones and antibodies, including free triiodothyronine (fT3), total triiodothyronine (tT3), total thyroxine (tT4) and thyroid peroxidase antibody (TPO-Ab). Levels of some congeners were significantly negatively correlated with some types of serum lipid, including cholesterol (CHOL), low density lipoprotein (LDL) and total triglyceride (TG). Other than serum lipids, only two liver function indicators, total protein (TP) and direct bilirubin (DBIL), were significantly correlated with certain BDE congeners (BDE-100 and BDE-154). Our results provide new evidence on the thyroid-disrupting and hepatotoxic effects of PBDEs.

Comprehensive binding analysis of polybrominated diphenyl ethers and aryl hydrocarbon receptor via an integrated molecular modeling approach

Polybrominated diphenyl ethers (PBDEs) are often suspected to activate the signal transduction pathway of aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, for the induction of toxicity. Hence, the binding property of PBDEs with AhR is assumed to be associated with the ligand-dependent activation of AhR that may introduce many drug-metabolizing enzymes of genes encoding. However, the binding mechanism and the structural effect of PBDEs on their binding properties of AhR still need to be unraveled for toxicology research. A comprehensive study of the PBDEs-AhR binding mechanism was investigated using an integrated molecular modeling approach with two-dimensional quantitative structure-activity relationships (2D-QSAR), three-dimensional QSAR (3D-QSAR), and molecular docking simulation. Molecular docking revealed the differences in binding domains among 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-AhR complex and two PBDE-AhR complexes. A 2D-QSAR model was developed to analyze the overall structural effects of PBDEs on the binding affinity of AhR. It provided an insight into major physico-chemical properties by multiple linear regression based on genetic algorithm with reasonable results. The 3D-QSAR modeling discovered the detailed interaction features of binding sites, configurations and interaction fields of AhR with different PBDE ligands. This study demonstrated that the descriptors of Smin69 and MoRSEC15 were related to electronic properties and had a great effect on the relative binding affinities. The position of Br substitutions exhibited a significant influence on the interactions between AhR and PBDEs, including halogen interaction, π-S interaction, π-π stacking interaction, and hydrophobic effect. This integrated molecular modeling approach provided a comprehensive analysis of the structural effects of PBDEs on their binding properties with AhR at molecular level.

Antagonistic effects of multi-walled carbon nanotubes and BDE-47 in zebrafish (Danio rerio): Oxidative stress, apoptosis and DNA damage

In natural environments, organisms are often exposed to several environmental pollutants at any one time, and the potential effects of such co-exposures on human and environmental health are of considerable concern. It is thought that multi-walled carbon nanotubes (MWCNTs) may interact with other pollutants in aquatic systems and induce considerably different effects compared with exposure to a single contaminant. The objective of this study was to evaluate the potential acute combined effects of mixtures of MWCNTs and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on embryonic development stages, oxidative stress, apoptosis and DNA damage in developing zebrafish (Danio rerio). The embryos were treated with BDE-47 (5, 10, and 50 μg/L) and MWCNTs (50 mg/L), either combined or individually, for 96 h. Following exposure, BDE-47 induced significant acute toxicity, while the MWCNTs exhibited slight toxicity. When compared with BDE-47-only exposure, the inhibited growth induced by BDE-47 was weakened in the presence of MWCNTs. Similarly, the levels of oxidative stress biomarkers (reactive oxygen species, superoxide dismutase, catalase activities and malondialdehyde), apoptosis (apoptosis rate, caspase-3 and caspase-9 activities) and DNA damage (comet assay and comet olive tails) decreased in the presence of MWCNTs compared to those exposed to BDE-47 alone. These results demonstrate that MWCNTs can weaken the developmental inhibition, oxidative stress, apoptosis and DNA damage induced by BDE-47 in the early stages of zebrafish development.

Spatial distribution, source analysis, and ecological risk assessment of PBDEs in river sediment around Taihu Lake, China

The distribution and composition of organic pollutants in sediment are affected by the source and regional environment. To understand the characteristics and risk of polybrominated diphenyl ethers (PBDEs) in the area around Taihu Lake, composite sediment samples (n = 41) were collected in rivers around Taihu Lake to explore the level, spatial distribution, and source of PBDEs. The results showed that the most abundant BDE congener in river sediment was BDE209, followed by BDE99 and BDE47, with median values of 48.7, 2.17, and 1.52 ng g^-1, respectively. Concentrations of PBDEs in sediments from northern rivers were significantly higher than those from other areas, but the overall risk was at a moderate-lower level compared with research results in other references. Results of principle component analysis (PCA) and source characteristics analysis revealed that most of PBDEs in river sediments around Taihu Lake were mixture of multiple sources, which mainly originated from atmospheric deposition, industrial wastewater, and municipal sewage. TOC showed good correlations with most PBDEs, which implied that PBDE components were influenced by sediment organic matter. Meanwhile, the risk of PBDEs in river sediments in this study area is a moderate-lower level.

Occupational and dietary differences in hydroxylated and methoxylated PBDEs and metals in plasma from Puget Sound, Washington, USA region volunteers

Electronic waste (E-waste) recycling is a rapidly growing occupation in the USA with the potential for elevated exposure to flame retardants and metals associated with electronic devices. We previously measured polybrominated diphenyl ethers (PBDEs) in plasma from E-waste workers and found them similar to non-E-waste workers. This study focused on structurally related PBDE derivatives, the hydroxylated (OH-PBDEs) and methoxylated (MeO-PBDEs) forms along with metals known to occur in E-waste. Humans can metabolize PBDEs and some MeO-PBDEs into OH-PBDEs, which is a concern due to greater health risks associated with OH-PBDEs. We measured 32 different OH-PBDEs and MeO-PBDEs in plasma samples provided by 113 volunteers living in the greater Puget Sound region of Washington State, USA. We measured 14 metals in a subset of 10 E-waste and 10 non-E-waste volunteers. Volunteers were selected based on occupational and dietary habits: work outdoors and consume above average amounts of seafood (outdoor), electronic waste recycling (E-waste) or non-specific indoor occupations (indoor). A two-week food consumption diary was obtained from each volunteer prior to blood sampling. OH-PBDEs were detected in all volunteers varying between 0.27 and 102 ng/g/g-lipid. The MeO-PBDEs were detected in most, but not all volunteers varying between n.d. - 60.4 ng/g/g-lipid. E-waste recyclers had OH-PBDE and MeO-PBDE plasma levels that were similar to the indoor group. The outdoor group had significantly higher levels of MeO-PBDEs, but not OH-PBDEs. Comparison of plasma concentrations of BDE-47 with its known hydroxylated metabolites suggested OH-PBDE levels were likely determined by biotransformation and at least two subpopulations identified differing in their apparent rates of OH-PBDE formation. The metals analysis indicated no significant differences between E-waste workers and non-E-waste workers. Our results indicate E-waste workers do not have elevated plasma levels of these contaminants relative to non-E-waste workers.

A density functional theory/time-dependent density functional theory study of the structure-related photochemical properties of hydroxylated polybrominated diphenyl ethers and methoxylated polybrominated diphenyl ethers and metal ion effects

As the derivatives and structural analogs of polybrominated diphenyl ethers (PBDEs), hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs) have attracted increasing concern. However, knowledge of the photochemical behaviors of OH-PBDEs and MeO-PBDEs in water is limited. Here, we used density functional theory and time-dependent density functional theory to examine the structure-related photochemical properties of OH-PBDEs and MeO-PBDEs in water and the effects of metal ions as environmental factors. Eight 6-OH-PBDEs with 1-8 bromine substituents and eight 6-MeO-PBDEs with 1-8 bromine substituents were selected for this study. The optimized geometries of the selected congeners and their complexes with metals in the lowest excited triplet state (T₁) showed that one C-Br bond moderately or significantly elongated. The elongated C-Br bond in the T₁ state was shown in the ortho-position for the 6-OH-PBDE congeners and the ortho-position or the meta-position for the 6-MeO-PBDE congeners. For the selected congeners, there were significant positive linear correlations between the number of bromine atoms (N_Br) and the calculated average atomic charge of bromine and maximum electronic absorbance wavelength (λ_max), and a negative linear correlation between the N_Br and average bond dissociation energy of C-O bonds (BDE_C-O). The photoreactivities of the 6-OH-PBDEs and 6-MeO-PBDEs increased with an increase in the bromination degree with or without metal ions. The calculated average atomic charge of bromine and BDE_C-O of the complexes with Mg²⁺/Zn²⁺ was higher and lower than those of the corresponding monomers, respectively, indicating that the presence of Mg²⁺/Zn²⁺ increased the photoreactivity (debromination and dissociation of C-O bond) of the selected 6-OH-PBDEs and 6-MeO-PBDEs. The effects of the coordination of Mg²⁺/Zn²⁺ may be overestimated due to their missing explicit solvation shell. These results provide vital insight into the photochemical properties of OH-PBDEs and MeO-PBDEs in water.

Levels and distribution of polybrominated diphenyl ethers in humans and environmental compartments: a comprehensive review of the last five years of research

Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardants (BFRs), present in the environment, animals, and humans. Their levels, distribution, and human exposure have been studied extensively, and over the last decade, various legal measures have been taken to prohibit or minimize their production and use due to the increasing amount of evidence of their harmful effects on human and animal health.Our aim here was to make a comprehensive and up-to-date review of the levels and distribution of PBDEs in the aquatic environment, air, and soil, in indoor dust, and in humans. To fulfill this, we searched through Web of Science for literature data reported in the last five years (2015-2019) on levels of at least six key PBDE congeners in abovementioned matrices. According to our summarized data, significant PBDE mass concentrations/fractions are still being detected in various sample types across the world, which implies that PBDE contamination is an ongoing problem. Secondary sources of PBDEs like contaminated soils and landfills, especially those with electronic and electrical waste (e-waste), represent a particular risk to the future and therefore require a special attention of scientists.

Oxidative and nitrosative stress in the neurotoxicity of polybrominated diphenyl ether-153: possible mechanism and potential targeted intervention

Polybrominated diphenyl ethers (PBDEs) have been known to exhibit neurotoxicity in rats; however, the underlying mechanism remains unknown and there is no available intervention. In this study, we aimed to investigate the role of oxidative and nitrosative stress in the neurotoxicity in the cerebral cortex and primary neurons in rats following the BDE-153 treatment. Compared to the untreated group, BDE-153 treatment significantly induced the neurotoxic effects in rats, as manifested by the increased lactate dehydrogenase (LDH) activities and cell apoptosis rates, and the decreased neurotrophic factor contents and cholinergic enzyme activities in rats' cerebral cortices and primary neurons. When compared to the untreated group, the oxidative and nitrosative stress had occurred in the cerebral cortex or primary neurons in rats following the BDE-153 treatment, as manifested by the increments in levels of reactive oxygenspecies (ROS), malondialdehyde (MDA), nitric oxide (NO), and neuronal nitric oxide synthase (nNOS) mRNA and protein expressions, along with the decline in levels of superoxide dismutase (SOD) activity, glutathione (GSH) content, and peroxiredoxin I (Prx I) and Prx II mRNA and protein expressions. In addition, the ROS scavenger N-acetyl-l-cysteine (NAC) or NO scavenger NG-Nitro-l-arginine (L-NNA) significantly rescued the LDH leakage and cell survival, reversed the neurotrophin contents and cholinergic enzymes, mainly via regaining balance between oxidation/nitrosation and antioxidation. Overall, our findings suggested that oxidative and nitrosative stresses are involved in the neurotoxicity induced by BDE-153, and that the antioxidation is a potential targeted intervention.

Polybrominated diphenyl ethers in the environment and human external and internal exposure in China: A review

Polybrominated diphenyl ethers (PBDEs) are widely used as brominated flame retardants. Because of their toxicity and persistence, some PBDEs were restricted under the Stockholm Convention in 2009. Since then, many studies have been carried out on PBDEs in China and in many other countries. In the present review, the occurrences and contamination of PBDEs in air, water, sediment, soil, biota and daily food, human blood, hair, and other human tissues in China are comprehensively reviewed and described. The human exposure pathways and associated health risks of PBDEs are summarized. The data showed no obvious differences between North and South China, but concentrations from West China were generally lower than in East China, which can be mainly attributed to the production and widespread use of PBDEs in eastern regions. High levels of PBDEs were generally observed in the PBDE production facilities (e.g., Jiangsu Province and Shandong Province, East China) and e-waste recycling sites (Taizhou City, Zhejiang Province, East China, and Guiyu City and Qingyuan City, both located in Guangdong Province, South China) and large cities, whereas low levels were detected in rural and less-developed areas, especially in remote regions such as the Tibetan Plateau. Deca-BDE is generally the major congener. Existing problems for PBDE investigations in China are revealed, and further studies are also discussed and anticipated. In particular, non-invasive matrices such as hair should be more thoroughly studied; more accurate estimations of human exposure and health risks should be performed, such as adding bioaccessibility or bioavailability to human exposure assessments; and the degradation products and metabolites of PBDEs in human bodies should receive more attention. More investigations should be carried out to evaluate the quantitative relationships between internal and external exposure so as to provide a scientific basis for ensuring human health.

Multicenter biomonitoring of polybrominated diphenyl ethers (PBDEs) in colostrum from China: Body burden profile and risk assessment

Polybrominated diphenyl ethers (PBDEs) were listed in the Stockholm Convention due to their persistent and toxic nature. In utero exposure to PBDEs might affect fetal development as it is sensitive when exposed to even low dose of xenobiotic substances during the pregnancy. In this study, a multi-centre human biomonitoring study of tri-to hexa-BDEs was conducted in three Chinese cities using 60 colostrum samples from local residents. The patterns and influencing factors, correlation with the birth outcome, and potential health risks during the breastfeeding of tri-to hexa-BDEs in the colostrum samples were assessed. The median concentration of tri-to hexa-BDEs was 9.1 (Interquartile range: 3.1-19.5) ng g^-1 lipid weight, and BDE-153 contributed 68% of the detected PBDEs. The PBDE levels were mostly associated with maternal age and drinking water sources, while correlations with other factors including weight gain, BMI, parity and the number of aborted pregnancies was not significant. The level of BDE-28 was positively correlated with the birth weight, while the BDE-99 was positively correlated with the head circumference, using multilinear regression. For the total hazard quotients, 60% of the infants have an estimated value higher than 1, showed potential chronic hazard for future development and possible adverse health effects to the babies from the exposure to PBDE congeners. Alternative food source seems to have a lower risk for neonates than the colostrum, but the advantages of breastfeeding undoubtedly outweigh the risks and potential adverse health effects caused by environmental PBDEs and other xenobiotic chemical exposure.

Sponge-derived polybrominated diphenyl ethers and dibenzo-p-dioxins, irreversible inhibitors of the bacterial α-d-galactosidase

An integrated in vitro and in silico approach was applied to evaluate the potency of hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and spongiadioxins (OH-PBDDs) isolated from Dysidea sponges on the activity of the recombinant α-d-galactosidase of the GH36 family. It was revealed for the first time that all compounds rapidly and apparently irreversibly inhibited the bacterial α-d-galactosidase. The structure-activity relationship study in the series of OH-PBDEs showed that the presence of an additional hydroxyl group in 5 significantly enhanced the potency (IC50 4.26 μM); the increase of bromination in compounds from 1 to 3 increased their potency (IC50 41.8, 36.0, and 16.0 μM, respectively); the presence of a methoxy group decreased the potency (4, IC50 60.5 μM). Spongiadioxins 6, 7, and 8 (IC50 16.6, 33.1, and 28.6 μM, respectively) exhibited inhibitory action comparable to that of monohydroxylated diphenyl ethers 1-3. Docking analysis revealed that all compounds bind in a pocket close to the catalytic amino acid residues. Molecular docking detected significant compound-enzyme interactions in the binding sites of α-d-galactosidase. Superimposition of the enzyme-substrate and the enzyme-inhibitor complexes showed that their binding sites overlap.

Sulfonation and glucuronidation of hydroxylated bromodiphenyl ethers in human liver

Hydroxylated bromodiphenyl ethers (OH-BDEs) can arise from monooxygenation of anthropogenic BDEs or through natural biosynthetic processes in marine organisms, and several OH-BDEs have been shown to be toxic. OH-BDEs are expected to form sulfate and glucuronide conjugates that are readily excreted, however there is little information on these pathways. We examined the human hepatic glucuronidation and sulfonation of 6-OH-BDE47, 2-OH-BDE68, 4-OH-BDE68 and 2-OH-6'methoxy-BDE68. Human liver microsomes and cytosol were from de-identified female and male donors aged 31 to 75 under an exempt protocol. Recombinant human SULT1A1, 1B1, 1E1 and 2A1 enzymes were prepared from bacterial expression systems. Sulfonation and glucuronidation of each OH-BDE were studied using radiolabeled co-substrates, 3'phosphoadenosine-5'phospho-³⁵S-sulfate or uridine diphospho-β-D-¹⁴C-glucuronic acid in order to quantify the sulfated or glucuronidated products. The OH-BDEs studied were more efficiently glucuronidated than sulfonated. Of the compounds studied, 2-OH-BDE68 was the most readily conjugated, and exhibited an efficiency (V_max/K_M) of glucuronidation of 0.274 ± 0.125 mL/min/mg protein, mean ± S.D., n = 3, while that for sulfonation was 0.179 ± 0.030 mL/min/mg protein. For both pathways, all K_m values were in the low μM range. Studies with human SULT enzymes showed that sulfonation of these four substrates was readily catalyzed by SULT1B1 and SULT1E1. Much lower activity was found with SULT1A1 and SULT2A1. Assuming that the glucuronide and sulfate conjugates are non-toxic and readily excreted, as is the case for most such conjugates, these studies suggest that OH-BDEs should not accumulate in people to the same extent as the parent BDEs.

Polybrominated Diphenyl Ethers Quinone Induced Parthanatos-like Cell Death through a Reactive Oxygen Species-Associated Poly(ADP-ribose) Polymerase 1 Signaling

Polybrominated diphenyl ethers (PBDEs) are emerging organic environmental pollutants, which were accused of various toxic effects. Here, we studied the role of a potential PBDEs quinone metabolite, PBDEQ, on cytotoxicity, oxidative DNA damage, and the alterations of signal cascade in HeLa cells. PBDEQ exposure leads to reactive oxygen species (ROS) accumulation, mitochondrial membrane potential (MMP) loss, lactate dehydrogenase (LDH) release, increasing terminal transferase-mediated dUTP-biotin nick end labeling (TUNEL) positive foci, and the elevation of apoptosis rate. Furthermore, we showed PBDEQ exposure result in increased DNA migration, micronucleus frequency, and the promotion of 8-OHdG and phosphorylation of histone H2AX (γ-H2AX) levels. Mechanism study indicated that PBDEQ caused poly(ADP-ribose) polymerase 1 (PARP-1) activation and apoptosis-inducing factor (AIF) nuclear translocation. All together, these results confirmed the occurrence of parthanatos-like cell death upon PBDEQ exposure.