Metabolic pathways of decabromodiphenyl ether (BDE209) in rainbow trout (Oncorhynchus mykiss) via intraperitoneal injection

Contamination characteristics and dietary intake risk of brominated flame retardants in fishes around a typical e-waste dismantling site in Southern China

Polybrominated diphenyl ethers (PBDEs) and their substitutes, novel brominated flame retardants (NBFRs), are ubiquitously present in the aquatic environment of electronic waste (e-waste) dismantling region, leading to their inevitable absorption and accumulation by aquatic organisms, which can be transferred to human via directly aquatic product consumption or through food chain, thereby posing potential health risks. This study focused on fish samples from Guiyu and its surrounding areas, and found the total PBDEs concentrations were 24-7400 ng/g lw (mean: 1800 ng/g lw) and the total NBFRs concentrations were 14 to 2300 ng/g lw (mean: 310 ng/g lw). Significant positive correlations were found among PBDE congeners, among different NBFRs, and between NBFRs and commercial PBDEs that they replace. ΣPBDEs and ΣNBFRs in the intestine were 620-350,000 and 91-81,000 ng/g lw (mean: 83000 and 12,000 ng/g lw, respectively), significantly exceeding those in the gills, where ΣPBDEs and ΣNBFRs were 14-37,000 and 39-45,000 ng/g lw (mean: 9200 and 2400 ng/g lw, respectively). The ΣPBDEs and ΣNBFRs showed no non-carcinogenic risks to the target population through dietary intake. Despite the significantly higher daily intake of decabromodiphenyl ethane (DBDPE) compared to decabromodiphenyl ether (BDE209), the non-carcinogenic risk associated with BDE209 remained higher than that of DBDPE. Our findings can assist researchers in understanding the presence of BFRs in aquatic organisms, inhabiting e-waste dismantling areas, and in evaluating the associated health risks posed to humans through dietary exposure.

Influence of paternal factors on plastic ingestion and brominated chemical exposure in East Tropical Atlantic Procellariid chicks

The presence of plastic debris and organo-brominated compounds in the marine environment poses a concern to wildlife. Plastic can absorb and release chemical compounds, making their ingestion potentially harmful, while chemical compounds have become omnipresent, with a tendency to bioaccumulate in the food web. Seabirds are often used as indicators of marine plastic pollution, yet studies on the exposure of tropical communities to plastic contamination are still scarce. In this study we monitored the amounts of plastics in faeces and organo-brominated compounds ingested/assimilated in feathers by adults and chicks of Cape Verde shearwaters and Bulwer's petrels from Cabo Verde. Anthropogenic pollutants, polybrominated diphenyl ethers (PBDEs), and naturally generated methoxylated-PBDEs (MeO-PBDEs) were among the probed compounds. The frequency of plastic debris ingestion was similar in both species' adults and chicks, although, the characteristics of the ingested plastic differed. Frequency and number of microplastics increased throughout the nestling season for chicks from both species. All species and age groups showed the presence of PBDEs and MeO-PBDEs. Among PBDEs, Bulwer's petrels exhibited higher concentrations than Cape Verde shearwaters, and chicks had higher concentration profiles than adults. Specifically, Bulwer's petrel chicks showed higher concentrations than Cape Verde shearwater chicks. On the contrary, Cape Verde shearwater adults exhibited higher occurrence and concentrations of MeO-PBDEs when compared to Cape Verde shearwater chicks. We found no effect of plastic loadings or loadings of organohalogen contaminants on body condition or size, although harmful effects may be hidden or reveal themselves in a medium- to long-term. Feather samples from both adults and chicks were shown to be useful for comparing intraspecific contamination levels and appear suitable for the long-term assessment of organohalogen contaminants in seabirds. Species-specific foraging and feeding strategies are likely the drivers of the observed variation in organochlorine contamination burdens among seabird species.

Temporal Trends and Suspect Screening of Halogenated Flame Retardants and Their Metabolites in Blubbers of Cetaceans Stranded in Hong Kong Waters during 2013-2020

Halogenated flame retardants (HFRs) are a large class of chemical additives intended to meet flammability safety requirements, and at present, they are ubiquitous in the environment. Herein, we conducted the target analysis and suspect screening of legacy and novel HFRs and their metabolites in the blubber of finless porpoises (Neophocaena phocaenoides; n = 70) and Indo-Pacific humpback dolphins (Sousa chinensis; n = 35) stranded in Hong Kong, a coastal city in the South China Sea, between 2013 and 2020. The average concentrations of total target HFRs (ΣHFRs) were 6.48 × 10³ ± 1.01 × 10⁴ and 1.40 × 10⁴ ± 1.51 × 10⁴ ng/g lipid weight in porpoises and dolphins, respectively. Significant decreasing temporal trends were observed in the concentrations of tetra-/penta-/hexa-bromodiphenyl ethers (tetra-/penta-/hexa-BDEs) in adult porpoises stranded from 2013-2015 to 2016-2020 (p < 0.05), probably because of their phasing out in China. No significant difference was found for the concentrations of decabromodiphenyl ether and hexabromocyclododecane, possibly due to their exemption from the ban in China until 2025 and 2021, respectively. Eight brominated compounds were additionally identified via suspect screening. A positive correlation was found between the concentrations of tetra-BDE and methyl-methoxy-tetra-BDE (Me-MeO-tetra-BDE) (p < 0.05), indicating that the metabolism of tetra-BDE may be a potential source of Me-MeO-tetra-BDE in marine mammals.

Glucoregulatory disruption in male mice offspring induced by maternal transfer of endocrine disrupting brominated flame retardants in DE-71

Introduction

Polybrominated diphenyl ethers (PBDEs) are commercially used flame retardants that bioaccumulate in human tissues, including breast milk. PBDEs produce endocrine and metabolic disruption in experimental animals and have been associated with diabetes and metabolic syndrome (MetS) in humans, however, their sex-specific diabetogenic effects are not completely understood. Our past works show glucolipid dysregulation resulting from perinatal exposure to the commercial penta-mixture of PBDEs, DE-71, in C57BL/6 female mice.

Methods

As a comparison, in the current study, the effects of DE-71 on glucose homeostasis in male offspring was examined. C57BL/6N dams were exposed to DE-71 at 0.1 mg/kg/d (L-DE-71), 0.4 mg/kg/d (H-DE-71), or received corn oil vehicle (VEH/CON) for a total of 10 wks, including gestation and lactation and their male offspring were examined in adulthood.

Results

Compared to VEH/CON, DE-71 exposure produced hypoglycemia after a 11 h fast (H-DE-71). An increased fast duration from 9 to 11 h resulted in lower blood glucose in both DE-71 exposure groups. In vivo glucose challenge showed marked glucose intolerance (H-DE-71) and incomplete clearance (L- and H-DE-71). Moreover, L-DE-71-exposed mice showed altered glucose responses to exogenous insulin, including incomplete glucose clearance and/or utilization. In addition, L-DE-71 produced elevated levels of plasma glucagon and the incretin, active glucagon-like peptide-1 (7-36) amide (GLP-1) but no changes were detected in insulin. These alterations, which represent criteria used clinically to diagnose diabetes in humans, were accompanied with reduced hepatic glutamate dehydrogenase enzymatic activity, elevated adrenal epinephrine and decreased thermogenic brown adipose tissue (BAT) mass, indicating involvement of several organ system targets of PBDEs. Liver levels of several endocannabinoid species were not altered.

Discussion

Our findings demonstrate that chronic, low-level exposure to PBDEs in dams can dysregulate glucose homeostasis and glucoregulatory hormones in their male offspring. Previous findings using female siblings show altered glucose homeostasis that aligned with a contrasting diabetogenic phenotype, while their mothers displayed more subtle glucoregulatory alterations, suggesting that developing organisms are more susceptible to DE-71. We summarize the results of the current work, generated in males, considering previous findings in females. Collectively, these findings offer a comprehensive account of differential effects of environmentally relevant PBDEs on glucose homeostasis and glucoregulatory endocrine dysregulation of developmentally exposed male and female mice.

Fate and toxicity of legacy and novel brominated flame retardants in a sediment-water-clam system: Bioaccumulation, elimination, biotransformation and structural damage

Due to the characteristics of persistent organic pollutants (POPs), some legacy brominated flame retardants (LBFRs) were prohibited from use, and then gradually replaced by novel brominated flame retardants (NBFRs). However, till now little research focused on the effects of NBFRs on the benthos. In the present study, 0.5, 5, and 50 mg/kg dw of pentabromotoluene (PBT), hexabromobenzene (HBB), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), decabromodiphenyl ethane (DBDPE) and decabromodiphenyl ether (BDE209) were added into sediments to test freshwater clams (Corbicula fluminea). In the 35-day exposure experiment, C. fluminea had different enrichment behaviors in three treatment groups. It was conjectured that in the lower dose group, the clams ingested contaminants and tended to be stable over time. While in higher dose groups, the clams were induced by the chemicals, leading to the changes in physiological activities so that the concentrations showed a downward trend first and then went up. The half-lives of contaminants in freshwater clams were between 0.911 and 11.6 days. DBDPE showed stronger bioaccumulation ability than BDE209 in this study. Parabolic relationships were observed between log BSAF and log K_ow values in clam tissues. Debromination, hydroxylation, and methoxylated products were detected. Additionally, the gill samples of C. fluminea exposed to 50 mg/kg dw of single substance were observed by scanning electron microscope (SEM), indicating that the adhesions, tissue hyperplasia, and messy cilia occurred on the surface. Our research potentially contributes to further evaluations of the environmental risks posed in sediments contaminated by PBT, HBB, BTBPE, DBDPE, and BDE209, particularly the benthic organisms.

Metabolic transformation of environmentally-relevant brominated flame retardants in Fauna: A review

Over the past few decades, production trends of the flame retardant (FR) industry, and specifically for brominated FRs (BFRs), is for the replacement of banned and regulated compounds with more highly brominated, higher molecular weight compounds including oligomeric and polymeric compounds. Chemical, biological, and environmental stability of BFRs has received some attention over the years but knowledge is currently lacking in the transformation potential and metabolism of replacement emerging or novel BFRs (E/NBFRs). For articles published since 2015, a systematic search strategy reviewed the existing literature on the direct (e.g., in vitro or in vivo) non-human BFR metabolism in fauna (animals). Of the 51 papers reviewed, and of the 75 known environmental BFRs, PBDEs were by far the most widely studied, followed by HBCDDs and TBBPA. Experimental protocols between studies showed large disparities in exposure or incubation times, age, sex, depuration periods, and of the absence of active controls used in in vitro experiments. Species selection emphasized non-standard test animals and/or field-collected animals making comparisons difficult. For in vitro studies, confounding variables were generally not taken into consideration (e.g., season and time of day of collection, pollution point-sources or human settlements). As of 2021 there remains essentially no information on the fate and metabolic pathways or kinetics for 30 of the 75 environmentally relevant E/BFRs. Regardless, there are clear species-specific and BFR-specific differences in metabolism and metabolite formation (e.g. BDE congeners and HBCDD isomers). Future in vitro and in vivo metabolism/biotransformation research on E/NBFRs is required to better understand their bioaccumulation and fate in exposed organisms. Also, studies should be conducted on well characterized lab (e.g., laboratory rodents, zebrafish) and commonly collected wildlife species used as captive models (crucian carp, Japanese quail, zebra finches and polar bears).

High-fat diet exacerbated decabromodiphenyl ether-induced hepatocyte apoptosis via intensifying the transfer of Ca2+ from endoplasmic reticulum to mitochondria

Polybrominated diphenyl ether (PBDE) as the flame retardant is heavily used in daily necessities, causing adverse health effects on humans. This study aimed to evaluate the hepatotoxicity of decabromodiphenyl ether (BDE-209), the most widely used PBDE, in lean and high-fat diet (HFD)-treated obese mice and elucidate the underlying mechanism. Firstly, the increasing levels of TG and proinflammatory factors in the liver and ALT and AST in serum demonstrated the hepatic damage caused by BDE-209 and further exacerbated by HFD. Tunel image revealed that BDE-209 induced more severe hepatocyte apoptosis with the assistant of HFD. Next, the mechanism analysis showed that the pro-apoptotic action of BDE-209 was in an endoplasmic reticulum (ER)/Ca²⁺ flux/mitochondria-dependent manner, concluded from the impairment of mitochondrial membrane potential, the enhancive protein expression of p-PERK/PERK, p-IRE1/IRE1, ATF6, CHOP, Bax/Bcl-2, cleaved caspase-3/caspase-3, IP3R1 and Sig-1R, and the over-transfer of Ca²⁺ from ER to mitochondria. Such proposed mechanism was further confirmed by the IP3R1 siRNA transfection cell experiment, where apoptotic rate was reduced in parallel with the reduced mitochondrial Ca²⁺ level. Finally, the higher expression of PACS-2 protein and the expanded ER contributed to the enriched ER-mitochondria interaction, reflected by the closer distance between ER and mitochondria visually displayed in the TEM image in HFD groups. This change was conducive to the rapid delivery of apoptosis signals via Ca²⁺, as proven, mechanically explaining the strengthening effect of HFD on BDE-209 hepatotoxicity. These findings detailedly explained the mechanism of BDE-209 hepatotoxicity and clarified the auxiliary effect of HFD, providing a theoretical basis for further studying other analogs.

Global distribution and trends of polybrominated diphenyl ethers in human blood and breast milk: A quantitative meta-analysis of studies published in the period 2000-2019

Polybrominated diphenyl ethers (PBDEs) are a class of flame-retardants that are found throughout the human body. However, global trends and diversity of the concentrations in human body and the potential risks remain largely unresolved. Based on published data during 2000-2019, we conducted a systematic meta-analysis to understand the burden and risks of PBDEs in humans and their spatiotemporal variations. The report provides a global picture of PBDE concentrations in human blood and breast milk. We found the levels of body PBDE burden in the North American population were higher than those from Asia and Europe. However, high concentrations of blood PBDEs in occupational population from Asia were observed, largely because of poorly controlled e-waste recycling operations. Penta- and deca-BDE were the main contributors in North America and Asia, respectively, reflecting the difference in the production and use of these chemicals. On a global scale, no substantial decreases in the concentrations of PBDEs in the blood and breast milk were observed, although most of the chemicals have been phased out. The results suggested that humans will be exposed to PBDEs with relatively high concentrations in a certain period because of the legacy in products and the environmental media. And the potential health risks necessitate careful study in the future. Our results also remind that the uses of degradation-resistant chemicals should be attached great importance to their safety.

Short-term exposure of decabromodiphenyl ether in female adult Balb/c mice: Immune toxicity and self-recovery

As a typical persistent organic pollutant, decabromodiphenyl ether (BDE-209) is associated with various health risks, especially on immune system, which is sensitive to environmental pollutants. In addition, there is a problem of multi-index estimation and lack of comprehensive evaluation in immune toxicity study. In this study, the immunotoxicity of BDE-209 was systematically estimated from the aspects of immunopathology, humoral immunity, cellular immunity and non-specific immunity, etc., and integrated biomarker responses (IBR) combined with principal component analysis was applied to comprehensively evaluate the immunotoxicity of BDE-209 and its self-recovery after discontinuation. Results showed that BDE-209 exposure could cause immunotoxicity. This response seems to depend on (1) atrophying immune organs (thymus and spleen), hepatomegaly accompanied by increasing aspartate aminotransferase and oxidative stress;(2) changing humoral (immunoglobulins) and cellular (lymphocyte proliferation and cytokine secretion) immunity indices; (3) altering related expressions of genes, and further leading to imbalance of Th1/Th2 (Th, helper T cell). Integrated biomarker responses (IBR) companied with principal component analysis selected five biomarkers (mRNA expression of GATA-3, malondialdehyde level in thymus, count of white blood cell, serum IgG and lipopolysaccharide-induced splenic lymphocyte proliferation) to clarify the immunotoxicity induced by BDE-209. Furthermore, IBR combined with factorial analysis revealed that the effect of BDE-209 could be dose-dependently reduced after withdrawal of BDE-209. Overall results suggested that BDE-209 has immunotoxicity on adult Balb/c mice, whereas this immunotoxicity could be reduced by the self-regulation of organisms to some extent.

Distributions and biomagnification of polybrominated diphenyl ethers in a grassland ecosystem food chain

The concentrations, distributions, and biomagnification of polybrominated diphenyl ethers (PBDEs) in environmental and biological media in a terrestrial grass ecosystem were studied, The total PBDE concentrations in grasses were 4.00 × 10^-2 to 4.28 ng·g^-1. The total PBDE concentration in weasel muscle (23.2 ng·g^-1 l.w.) was the highest concentrations of all animal tissue samples, and the total PBDE concentration in hair from local herdsmen (22.2 ng·g^-1 l.w.) was second highest. Less-brominated PBDEs were found to be more strongly biomagnified than more-brominated PBDEs in the grassland food web. PBDEs were found to be much more strongly biomagnified in the food chains of homothermic animals than heterothermic animals. More-brominated PBDEs were not markedly biomagnified in the grassland food web. For example, BDE-153 was not biomagnified in the grassland wildlife food chain but was clearly biomagnified through the sheep, cattle, or horse hair to human hair route. The biomagnification factors and log K_ows negatively correlated for the toad-snake, lizard-snake, and mouse-weasel food chains. The ability of PBDE congeners to become enriched generally decreased as the log K_ow increased, and this decrease occurred 100-1000 times more strongly for homothermic animals than heterothermic animals.

Absorption, tissue distribution, metabolism, and elimination of decabrominated diphenyl ether (BDE-209) in rats after multi-dose oral exposure

Human and ecological risks of BDE-209 have drawn much attention, particularly with growing e-waste recycling activities in developing countries. To further address the issue of BDE-209 biotransformation, a laboratory-controlled study was conducted. Female Sprague-Dawley rats were dosed orally by gavage at a daily dose of 1 mg kg^-1 body weight for 7 d and a depuration period of 22 d, to characterize absorption, distribution, metabolism, and elimination dynamics of BDE-209 during multi-dose exposures simulating short-term oral exposure of e-waste workers. The concentrations of BDE-209 in all tissues increased exponentially during the 7-d exposure period, indicating that multi-dose exposure could lead to increased accumulation of BDE-209 in rats. The liver accumulated the greatest amount of BDE-209 on a wet-weight basis, while adipose tissue had the highest concentration by the end of the 22-d depuration period. Half-lives of BDE-209, 207, and 197 during depuration were 1.1 ± 0.1, 2.7 ± 0.3, and 10.5 ± 3.1 d in serum and 0.9 ± 0.1, 2.2 ± 0.2, and 11.8 ± 2.3 d in liver, i.e., the half-life increased with decreasing level of bromination from deca- to octa-BDEs and was similar in both serum and liver. By contrast, the half-life of the debromination metabolite BDE-207 (21.7 ± 7.7 d) was longer in small intestine than in serum and liver, suggesting slower depletion of BDE-209 metabolites in small intestine. The metabolism of BDE-209 was not responsible for the occurrence of low brominated BDE congeners and OH and MeO-PBDEs in human tissues.

Dietary exposure assessment of Chinese population to tetrabromobisphenol-A, hexabromocyclododecane and decabrominated diphenyl ether: Results of the 5th Chinese Total Diet Study

Based on the 5th Chinese Total Diet Study (TDS) carried out in 2011, the dietary exposure of Chinese population to three currently used brominated flame retardants (BFRs), tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD) and decabrominated diphenyl ether (BDE-209), was estimated and the related health risks were assessed. Levels of the three BFRs were determined in 80 composite samples from four animal-origin food groups. The average levels of BFRs in various food groups ranged from 0.671 to 5.76 ng/g lipid weight (lw). The levels of TBBPA were lower than those of HBCD but higher than those of BDE-209. Moreover, average contamination levels of TBBPA and HBCD in TDS 2011 were found to be 3 to 30 times higher than those observed in TDS 2007 in the four food groups, indicating an increase in TBBPA and HBCD in the environment during 2007-2011. The average estimated daily intakes (EDIs) of TBBPA, HBCD and BDE-209 via food consumption for a "standard Chinese man" were 1.34, 1.51 and 0.96 ng/kg bw/day, respectively. Meat and meat products were found to be the major contributor to the daily dietary intake because the consumption of meat and meat products were significantly higher than that of other food groups in China. In comparison, the levels and EDIs of BFRs in this study were found to be higher than those in most studies worldwide. However, the large margin of exposure (MOE), with at least 1.1 × 10⁵ calculated following the European Food Safety Authority (EFSA) approach, indicates that the estimated dietary exposure to these three BFRs is unlikely to raise significant health concerns. In addition, a comparison between the contamination levels of TBBPA, HBCD, BDE-209 and some novel BFRs in food samples from TDS 2011 indicated an obvious shift in the industrial production and usage pattern between PBDE and non-PBDE BFRs in China.

Biotransformation of the Flame Retardant 1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) in Vitro by Human Liver Microsomes

The technical mixture of 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH or DBE-DBCH) and the pure β-TBECH isomer were subjected to in vitro biotransformation by human liver microsomes (HLM). After 60 min of incubation, 5 potential metabolites of TBECH were identified in microsomal assays of both the TBECH mixture and β-TBECH using ultraperformance liquid chromatography-Q-Exactive Orbitrap mass spectrometry. These include mono- and dihydroxylated TBECH and mono- and dihydroxylated TriBECH as well as an α-oxidation metabolite bromo-(1,2-dibromocyclohexyl)-acetic acid. Our results indicate potential hepatic biotransformation of TBECH via cyctochrome P450-catalyzed hydroxylation, debromination, and α-oxidation. Kinetic studies revealed that the formation of monohydroxy-TBECH, dihydroxy-TBECH, and monohydroxy-TriBECH were best fitted to a Michaelis-Menten enzyme kinetic model. Respective estimated V_max values (maximum metabolic rate) for these metabolites were 11.8 ± 4, 0.6 ± 0.1, and 10.1 ± 0.8 pmol min^-1 mg protein^-1 in TBECH mixture and 4992 ± 1340, 14.1 ± 4.9, and 66.1 ± 7.3 pmol min^-1 mg protein^-1 in β-TBECH. This indicates monohydroxy-TBECH as the major metabolite of TBECH by in vitro HLM-based assay. The estimated in vitro intrinsic clearance (Cl_int) of TBECH mixture was slower (P < 0.05) than that of pure β-TBECH. While the formation of monohydroxy-TBECH may reduce the bioaccumulation potential and provide a useful biomarker for monitoring TBECH exposure, further studies are required to fully understand the levels and toxicological implications of the identified metabolites.

Current halogenated flame retardant concentrations in serum from residents of Shandong Province, China, and temporal changes in the concentrations

The residents of Shandong Province, China, are exposed to high concentrations of halogenated flame retardants because large amounts of halogenated flame retardants are produced in the province. We determined the concentrations of eight polybrominated diphenyl ether congeners (PBDEs), seven novel brominated flame retardants (NBFRs), and the two dechlorane plus isomers (DPs) in serum from residents of Shandong Province. The aim was to identify temporal trends in the concentrations of these pollutants. The mean total concentrations of PBDEs, NBFRs and DPs were 41, 2.2 and 2.1ng/g lipid in pooled serum samples collected in 2014, and were 32, 3.5 and 3.1ng/g lipid in pooled serum samples collected in 2015, respectively. Decabromodiphenyl ether was the dominant PBDE congener in all of the samples. The novel brominated flame retardant and dechlorane plus concentrations were between one and two orders of magnitude lower than the PBDE concentrations. The PBDE concentrations in serum decreased significantly between 2007 and 2015, but the pentabromobenzene, pentabromotoluene, and dechlorane plus concentrations were relatively stable.