A 28-Day Oral Dose Toxicity Study Enhanced to Detect Endocrine Effects of Hexabromocyclododecane in Wistar Rats

Different Cytotoxicity Induced by Hexabromocyclododecanes on Mouse Neuroblastoma N2a Cells via Oxidative Stress and Mitochondrial Apoptotic Pathway

Hexabromocyclododecane (HBCD) is widely used in polystyrene foams, building materials, and electrical equipment as a brominated flame retardant (BFR) and persists in the environment and human body matrix. It has attracted increased attention since its neuroendocrine disorder effects have been observed in humans and animals. However, studies evaluating the neurotoxicity of HBCD diastereoisomers and the potential mechanisms involved are still limited. In this study, we compared the cytotoxicity induced by the three HBCD diastereoisomers (i.e., α-, β-, and γ-HBCD) in N2a cells and further investigated the underlying molecular mechanism. Our results showed that HBCD diastereoisomers decreased cell viability in the order of β-HBCD > α-HBCD > γ-HBCD. Moreover, α-HBCD and β-HBCD exposure led to different degrees of cell cycle disruption and oxidative stress of N2a cells, implying that oxidative stress-mediated differential cytotoxicity of HBCD diastereoisomers. The expressions of caspases and Bcl-2 were differentially regulated by α-HBCD and β-HBCD, suggesting that the mitochondrial apoptosis pathway may be critical in HBCDs-mediated N2a cell toxicity. Therefore, our studies provided novel evidence for the underlying mechanisms of the distinct cytotoxicity of HBCD diastereoisomers.

Association between brominated flame retardants and risk of endocrine-related cancer: A systematic review and meta-analysis

BACKGROUND

The incidence of endocrine-related cancer, which includes tumors in major endocrine glands such as the breast, thyroid, pituitary, and prostate, has been increasing year by year. Various studies have indicated that brominated flame retardants (BFRs) are neurotoxic, endocrine-toxic, reproductive-toxic, and even carcinogenic. However, the epidemiological relationship between BFR exposure and endocrine-related cancer risk remains unclear.

METHODS

We searched the PubMed, Google Scholar, and Web of Science databases for articles evaluating the association between BFR exposure and endocrine-related cancer risk. The odds ratio (OR) and its corresponding 95% confidence interval (95% CI) were used to assess the association. Statistical heterogeneity among studies was assessed with the Q-test and I2 statistics. Begg's test was performed to evaluate the publication bias.

RESULTS

We collected 15 studies, including 6 nested case-control and 9 case-control studies, with 3468 cases and 4187 controls. These studies assessed the risk of breast cancer, thyroid cancer, and endocrine-related cancers in relation to BFR levels. Our findings indicate a significant association between BFR exposure in adipose tissue and an increased risk of breast cancer. However, this association was not observed for thyroid cancer. Generally, BFR exposure appears to elevate the risk of endocrine-related cancers, with a notable increase in risk linked to higher levels of BDE-28, a specific polybrominated diphenyl ether congener.

CONCLUSIONS

In conclusion, although this meta-analysis has several limitations, our results suggest that BFR exposure is a significant risk factor for breast cancer, and low-brominated BDE-28 exposure could significantly increase the risk of endocrine-related cancers. Further research is essential to clarify the potential causal relationships between BFRs and endocrine-related cancers, and their carcinogenic mechanisms.

Hexabromocyclododecane (HBCD) induced PANoptosis of chondrocytes via activation of the NLRP3 inflammasome and decreased the exercise ability of mice in vivo

Hexabromocyclododecane (HBCD) is a persistent organic pollutant (POP). HBCD is found in the blood and tissues of most populations and causes a range of toxicological damage to tissues and cells. However, the toxicological effects of HBCD on chondrocytes are not fully understood. Here, we evaluated the toxicological effects of HBCD on chondrocytes and cartilaginous tissue. For this, a model of primary cartilage cells was established. Chondrocytes were exposed to different concentrations of HBCD. Western blot, indirect immunofluorescence, ELISA and other biochemical experiments were performed to analyze the toxicological effects of HBCD on chondrocytes/articular cartilage tissue. Cell proliferation assays showed that HBCD caused a reduction in the proliferative capacity of chondrocytes, and further work indicated that HBCD induces chondrocyte death. Further experiments demonstrated that HBCD caused an inflammatory response in chondrocytes by evaluating the levels of inflammatory factors. We found that HBCD led to PANoptosis in chondrocytes by detecting panapoptosis-related marker molecules, and experimental data indicated that apoptosis markers (cleaved caspase-3/7), pyroptosis markers (caspase-1/GSDMD-N) and necroptosis markers (pMLKL/RIPK3) were upregulated after HBCD treatment. Subsequent experiments illustrated that HBCD activated the DAMP sensor NLRP3, which then mediated ZBP1-induced PANoptosis. In the in vivo model, the experimental animals were administered HBCD at 25, 50 and 100 µg/kg/week for 15 weeks. We found that HBCD led to an inflammatory response in articular cartilage tissue. The safranin O-fast green assay showed a certain degree of damage to cartilage tissue under HBCD treatment. Furthermore, HBCD resulted in an increase in MMP13 expression and a downregulation of COL2 expression in chondrocytes/cartilaginous tissues. HBCD decreased the exercise ability of mice in vivo. These data indicate that HBCD leads to chondrocyte damage. In summary, this study lays the foundation for further exploration of the toxicological effects of HBCD on bone and joints.

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.

Mechanisms of cell death induced by hexabromocyclododecane (HBCD) involves apoptosis, autophagy, and ER stress

Hexabromocyclododecane (HBCD), was a widely utilized brominated flame retardant, commonly found in a wide range of household products. The pervasiveness of HBCD has identified the presence of this chemical in foods and in human tissues. Therefore, HBCD has been identified as a chemical of concern. The aim was to investigate the degree of cytotoxicity of HBCD in a range of cell lines derived from different tissues, (including hematopoietic, nerve, liver, and kidney-derived cells) with a view of determining any differential cell type effects. In addition, this study also investigated the mechanism(s) by which HBCD could cause cell death. The results showed that HCBD was considerably more toxic to leukocyte-derived (RBL2H3) and neuronal-derived (SHSY-5Y) cells with LC50 values of 1.5 and 6.1 µM, respectively, compared to cells derived from liver (HepG2) and kidney (Cos-7), which had LC50 values of 28.5 and 17.5 µM, respectively. A detailed investigation of the mechanism(s) of cell death showed that HBCD caused, at least in part, Ca2+ -dependent cell death, caspase-activated apoptosis, and autophagy, but there was little evidence for either necrosis or necroptosis occurring. Furthermore, it was shown that HBCD can also induce the ER stress response which is a known trigger of both apoptosis and autophagy and therefore this could be one of the crucial events by which cell death is initiated. As each of these cell death mechanisms was investigated in at least two different cell lines and no differences were identified, it is likely that the mode of action is not cell-type specific.

The covalent organic framework based nylon membrane extraction coupled with UHPLC-MS/MS for highly efficiency determination of hexabromocyclododecanes in environmental water

Hexabromocyclododecanes (HBCDs) have given their adverse effects on environment and human health, and highly sensitive analysis of HBCDs in water is urgent. In this study, a new method for the determination of trace HBCDs in water was established by covalent organic framework (COF) based nylon membrane extraction (ME) coupled with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The COF had been self-assembled onto the nylon membrane in a gentle strategy to fabricate COF nylon membrane. Several important ME parameters including the dosage of COF, pH, eluent condition and salinity were systematically investigated. The limits of detection and quantification were 0.011-0.014 and 0.038-0.047 ng/L for three HBCDs, respectively. The linear ranges were from 0.04 to 20 ng/L, and the relative standard deviations were 5.7-17.8 % (intra-day) and 5.2-14.1 % (inter-day). In addition, density functional theory (DFT) calculations on adsorption energy proved that the introduction of halogen bond (XB) made a key contribution to high extraction efficiency and excellent selectivity of COF nylon membrane for HBCDs. The 500 mL of samples, including tap water and reservoir water, could be extracted only in 23 min. The established method presented highly sensitive for ultra-trace analysis of HBCDs in environmental water.

Occurrence and Health Effects of Hexabromocyclododecane: An Updated Review

Hexabromocyclododecane (HBCD) is a non-aromatic compound belonging to the bromine flame retardant family and is a known persistent organic pollutant (POP). This compound accumulates easily in the environment and has a high half-life in water. With a variety of uses, the HBCD is found in house dust, electronics, insulation, and construction. There are several isomers and the most studied are α-, β-, and γ-HBCD. Initially used as a substitute for other flame retardants, the polybrominated diphenyl ethers (PBDEs), the discovery of its role as a POP made HBCD use and manufacturing restricted in Europe and other countries. The adverse effects on the environment and human health have been piling, either as a result from its accumulation or considering its power as an endocrine disruptor (ED). Furthermore, it has also been proven that it has detrimental effects on the neuronal system, endocrine system, cardiovascular system, liver, and the reproductive system. HBCD has also been linked to cytokine production, DNA damage, increased cell apoptosis, increased oxidative stress, and reactive oxygen species (ROS) production. Therefore, this review aims to compile the most recent studies regarding the negative effects of this compound on the environment and human health, describing the possible mechanisms by which this compound acts and its possible toxic effects.

Occurrence and tissue-specific partitioning of alternative brominated flame retardants in northwest Atlantic harbor seal pups (Phoca vitulina vitulina)

Brominated flame retardants such as polybrominated diphenyl ethers (PBDEs) have been used for decades until evidence of negative health effects led to bans in many countries. PBDEs have since been replaced by alternative legacy compounds or newly developed chemicals. In this study, eight alternative brominated flame retardants were analyzed in blubber and liver of harbor seal pups (≤6 months) from the Northwest Atlantic collected during 2001-2010 to elucidate concentrations, patterns, contamination trends, potential maternal transfer, and tissue partitioning. All compounds were detected in liver and blubber tissues with hexabromocyclododecane (HBCD) isomers and 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) predominating. Overall, α-HBCD was the dominant HBCD isomer in both tissues although the concentrations of γ-HBCD exceeded those of α-HBCD in seven pups, indicating their mothers may have had alternative dietary patterns or recent exposure to the commercial mixture. Although it was detected in less than half of the samples, to our knowledge, this is the first study to report tetrabromobisphenol A (TBBPA) concentrations in multiple tissues of a top marine predator. For the brominated components of Firemaster® flame retardants, TBB concentrations exceeded bis-(2-ethylhexyl)-tetrabromophthalate (TBPH). This pattern may result from recent exposure to commercial mixtures in which TBB exceeds TBPH 4:1 or from differences in perinatal or lactational transfer efficiency of the two compounds. Between the two tissues, lipid-normalized β-HBCD, γ-HBCD, TBB and decabromodiphenyl ethane (DBDPE) concentrations were significantly higher in liver than blubber. This indicates that the bioaccumulation of these chemicals is not simply related to lipid dynamics but may be linked to blood proteins. This study demonstrates that harbor seal pups from this region are contaminated with alternative flame retardants passed to them via placental or lactational transfer. Given the evidence for negative health effects of these chemicals, this contamination adds additional pressure on the first year survival of these young, developing animals.

The effects of hexabromocyclododecane on the transcriptome and hepatic enzyme activity in three human HepaRG-based models

The disruption of thyroid hormone homeostasis by hexabromocyclododecane (HBCD) in rodents is hypothesized to be due to HBCD increasing the hepatic clearance of thyroxine (T4). The extent to which these effects are relevant to humans is unclear. To evaluate HBCD effects on humans, the activation of key hepatic nuclear receptors and the consequent disruption of thyroid hormone homeostasis were studied in different human hepatic cell models. The hepatoma cell line, HepaRG, cultured as two-dimensional (2D), sandwich (SW) and spheroid (3D) cultures, and primary human hepatocytes (PHH) cultured as sandwich were exposed to 1 and 10 µM HBCD and characterized for their transcriptome changes. Pathway enrichment analysis showed that 3D models, followed by SW, had a stronger transcriptome response to HBCD, which is explained by the higher expression of hepatic nuclear receptors but also greater accumulation of HBCD measured inside cells in these models. The Pregnane X receptor pathway is one of the pathways most upregulated across the three hepatic models, followed by the constitutive androstane receptor and general hepatic nuclear receptors pathways. Lipid metabolism pathways had a downregulation tendency in all exposures and in both PHH and the three cultivation modes of HepaRG. The activity of enzymes related to PXR/CAR induction and T4 metabolism were evaluated in the three different types of HepaRG cultures exposed to HBCD for 48 h. Reference inducers, rifampicin and PCB-153 did affect 2D and SW HepaRG cultures' enzymatic activity but not 3D. HBCD did not induce the activity of any of the studied enzymes in any of the cell models and culture methods. This study illustrates that for nuclear receptor-mediated T4 disruption, transcriptome changes might not be indicative of an actual adverse effect. Clarification of the reasons for the lack of translation is essential to evaluate new chemicals' potential to be thyroid hormone disruptors by altering thyroid hormone metabolism.

Extruded polystyrene microplastics as a source of brominated flame retardant additives in the marine environment: long-term field and laboratory experiments

Microplastics (MPs) in the environment have become a global concern, not only for the physical effects of the plastic particles themselves but also for being vectors of chemical additives. In this context, little is known about the ability of MPs, particularly extruded polystyrene microplastics (XPS-MPs), to release organic chemical additives in the marine environment. In this study, a series of field and laboratory experiments were carried out to determine the leaching behaviour of organic additives including brominated flame retardants from XPS-MPs into seawater. The conducted experiments confirmed a rapid release of bisphenol A (BPA), 2,4,6-tribromophenol (TBP), tetrabromobisphenol A (TBBPA) and hexabromocyclododecane diastereoisomers (α-, β-, and γ-HBCDD) from the studied MPs followed by a slower rate of release over time. The effects of environmental factors on the leaching rates of these additives were also examined. Increasing Dissolved Organic Matter (DOM) concentrations and the temperature of the seawater enhanced the release of additives by increasing their solubility and polymer flexibility. In contrast, pH tested at 7, 7.5 and 8 was found to have a minor effect on additives leaching; and salinity negatively affected the leaching rate likely due to their reduced solubility and reduced diffusion from the MPs. The present study provides empirical evidence of the behaviour of XPS-MPs as a source of organic additives in the marine environment that merit further investigation.

Maternal Transfer and Apical and Physiological Effects of Dietary Hexabromocyclododecane Exposure in Parental Fathead Minnows (Pimephales promelas)

Hexabromocyclododecane (HBCD) is a persistent organic pollutant that has been characterized as an endocrine disruptor, undergoes maternal transfer, and hinders development and growth in oviparous organisms. The present study examined the apical effects of dietary HBCD (11.5, 36.4, 106 mg/kg, wet wt) on adult fathead minnow exposed for 49 days and the subsequent accumulation and maternal transfer kinetics in adult tissue and eggs, respectively. Exposed adults displayed a significant increase in egg production in the medium treatment group, but no other significant effects were noted. Maternal transfer of dietary HBCD had a similar egg-to-muscle ratios (EMR) in the low and medium treatment groups (1.65 and 1.27 [wet wt], respectively). However, the high treatment group deviated from other treatments with an EMR of 4.2 (wet wt), potentially due to differences in total lipid content in food and/or reaching diffusion/lipid saturation limits in adult tissue, resulting in lower accumulation in the adult muscle tissue. A positive correlation was observed between egg HBCD concentration and time of exposure, which indicates that maternal transfer of HBCD is of concern in fish, and further studies should be conducted to fully elucidate the potential adverse effects that may be observed in the early life stage of oviparous organisms. Environ Toxicol Chem 2023;42:143-153. © 2022 SETAC.

Dietary microplastics: Occurrence, exposure and health implications

The increasing use of plastic materials generates an enormous amount of waste. In the aquatic environment, a significant part of this waste is present in the form of microplastics (MPs)- particles with a diameter of between 0.1 μm and 5 mm. The arrival of these small plastics in the food chain has been recently documented. MPs have been reported in fishery products, drinking water and sea salt among other foods. Their intestinal absorption is considered limited due to their size, however, they contain a mixture of chemicals intentionally added during their manufacture, which could cross the intestinal barrier. Currently there are not enough data to allow an accurate assessment of the risk associated with dietary exposure to MPs. The lack of robust methodologies is undoubtedly one of the main problems. There is limited information on occurrence in dietary sources (drinking water and food), human intake, toxicokinetics and long term toxicity of these contaminants. The present review describes the studies published so far and points to the need for improved knowledge in order to have a more accurate view of the problems posed by MPs.

Discovery of a Colon-Targeted Azo Prodrug of Tofacitinib through the Establishment of Colon-Specific Delivery Systems Constructed by 5-ASA-PABA-MAC and 5-ASA-PABA-Diamine for the Treatment of Ulcerative Colitis

To mitigate the systemic adverse effects of tofacitinib, 5-ASA-PABA-MAC and 5-ASA-PABA-diamine colon-specific delivery systems were constructed, and tofacitinib azo prodrugs 9 and 20a-20g were synthesized accordingly. The release studies suggested that these systems could effectively release tofacitinib in vitro, and the 5-ASA-PABA-diamine system could successfully realize the colon targeting of tofacitinib in vivo. Specifically, compound 20g displayed a 3.67-fold decrease of plasma AUC_{(tofacitinib, 0-∞)} and a 9.61-fold increase of colonic AUC_{(tofacitinib, 0-12h)}, compared with tofacitinib at a molar equivalent oral dose. Moreover, mouse models suggested that compound 20g (1.5 mg/kg) could achieve roughly the same efficacy against ulcerative colitis compared with tofacitinib (10 mg/kg) and did not impair natural killer cells. These results demonstrated the feasibility of compound 20g as an effective alternative to mitigate the systemic adverse effects of tofacitinib, and 5-ASA-PABA-MAC and 5-ASA-PABA-diamine systems were proven to be effective for colon-specific drug delivery.

Bone toxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the retinoid system: A causality analysis anchored in osteoblast gene expression and mouse data

Dioxin exposures impact on bone quality and osteoblast differentiation, as well as retinoic acid metabolism and signaling. In this study we analyzed associations between increased circulating retinol concentrations and altered bone mineral density in a mouse model following oral exposure to 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD). Additionally, effects of TCDD on differentiation marker genes and genes involved with retinoic acid metabolism were analysed in an osteoblast cell model followed by benchmark dose-response analyses of the gene expression data. Study results show that the increased trabecular and decreased cortical bone mineral density in the mouse model following TCDD exposure are associated with increased circulating retinol concentrations. Also, TCDD disrupted the expression of genes involved in osteoblast differentiation and retinoic acid synthesis, degradation, and nuclear translocation in directions compatible with increasing cellular retinoic acid levels. Further evaluation of the obtained results in relation to previously published data by the use of mode-of-action and weight-of-evidence inspired analytical approaches strengthened the evidence that TCDD-induced bone and retinoid system changes are causally related and compatible with an endocrine disruption mode of action.

Health toxicity effects of brominated flame retardants: From environmental to human exposure

Hexabromocyclododecane (HBCD) and Tetrabromobisphenol A (TBBP-A) are brominated flame retardants widely used in variety of industrial and consumer products (e.g., automobiles, electronics, furniture, textiles and plastics) to reduce flammability. HBCD and TBBPA can also contaminate the environment, mainly water, dust, air and soil, from which human exposure occurs. This constant exposure has raised some concerns against human health. These compounds can act as endocrine disruptors, a property that gives them the ability to interfere with hormonal function and quantity, when HBCD and TBBPA bind target tissues in the body. Studies in human and animals suggest a correlation between HBCD and TBBPA exposure and adverse health outcomes, namely thyroid disorders, neurobehavior and development disorders, reproductive health, immunological, oncological and cardiovascular diseases. However, in humans these effects are still poorly understood, once only a few data evaluated the human health effects. Thus, the purpose of this review is to present the toxicity effects of HBCD and TBBPA and how these compounds affect the environment and health, resorting to data and knowledge of 255 published papers from 1979 to 2020.

Hexabromocyclododecanes Are Dehalogenated by CYP168A1 from Pseudomonas aeruginosa Strain HS9

Hexabromocyclododecanes (HBCDs) are widely used brominated flame retardants that cause antidiuretic hormone syndrome and even induce cancer. However, little information is available about the degradation mechanisms of HBCDs. In this study, genomic and proteomic analyses, reverse transcription-quantitative PCR, and gene knockout assays reveal that a cytochrome P450-encoding gene is responsible for HBCD catabolism in Pseudomonas aeruginosa HS9. The CO difference spectrum of the enzyme CYP168A1 was matched to P450 characteristics via UV visibility. We demonstrate that the reactions of debromination and hydrogenation are carried out one after another based on detection of the metabolites pentabromocyclododecanols (PBCDOHs), tetrabromocyclododecadiols (TBCDDOHs), and bromide ion. In the ¹⁸O isotope experiments, PBCD¹⁸OHs were only detected in the H₂¹⁸O group, proving that the added oxygen is derived from H₂O, not from O₂. This study elucidates the degradation mechanism of HBCDs by Pseudomonas. IMPORTANCE Hexabromocyclododecanes (HBCDs) are environmental pollutants that are widely used in industry. In this study, we identified and characterized a novel key dehalogenase, CYP168A1, that is responsible for HBCD degradation from Pseudomonas aeruginosa strain HS9. This study provides new insights into understanding biodegradation of HBCDs.

Update of the risk assessment of hexabromocyclododecanes (HBCDDs) in food

The European Commission asked EFSA to update its 2011 risk assessment on hexabromocyclododecanes (HBCDDs) in food. HBCDDs, predominantly mixtures of the stereoisomers α-, β- and γ-HBCDD, were widely used additive flame retardants. Concern has been raised because of the occurrence of HBCDDs in the environment, food and in humans. Main targets for toxicity are neurodevelopment, the liver, thyroid hormone homeostasis and the reproductive and immune systems. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour in mice can be considered the critical effects. Based on effects on spontaneous behaviour in mice, the Panel identified a lowest observed adverse effect level (LOAEL) of 0.9 mg/kg body weight (bw) as the Reference Point, corresponding to a body burden of 0.75 mg/kg bw. The chronic intake that would lead to the same body burden in humans was calculated to be 2.35 μg/kg bw per day. The derivation of a health-based guidance value (HBGV) was not considered appropriate. Instead, the margin of exposure (MOE) approach was applied to assess possible health concerns. Over 6,000 analytical results for HBCDDs in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary LB exposure to HBCDDs were fish meat, eggs, livestock meat and poultry. The CONTAM Panel concluded that the resulting MOE values support the conclusion that current dietary exposure to HBCDDs across European countries does not raise a health concern. An exception is breastfed infants with high milk consumption, for which the lowest MOE values may raise a health concern.

Occurrence of chemical pollutants in major e-waste sites in West Africa and usefulness of cytotoxicity and induction of ethoxyresorufin-O-deethylase (EROD) in determining the effects of some detected brominated flame retardants and e-waste soil-derived extracts

We investigated the occurrence of chemical pollutants in major e-waste sites in West Africa and usefulness of cytotoxicity and induction of ethoxyresorufin-O-deethylase (EROD) in determining the effects of some detected brominated flame retardants (BFRs) and e-waste soil-derived extracts. Analysis of the e-waste site samples using AAS and GC-MS techniques revealed the presence of a range of toxic metals as well as persistent and toxic organic pollutants, respectively, in the vicinity of the e-waste sites. As expected, the occurrence (%) of all the detected chemical pollutants in experimental soils significantly (P < 0.05) differs from occurrence (%) in control soil. The calculated LC₅₀ values on RBL-2H3 cells of the detected tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) were 3.75 μM and 4.2 μM, respectively. Tribromophenol (TBP), dibromobiphenyl (DBB), and decabromodiphenyl ether (DBDE) were remarkably less toxic on RBL-2H3 cells compared with TBBPA and HBCD as they did not reduce RBL-2H3 cell viability below 50% in the tested concentration range (0-20 μM). The study revealed that TBBPA and HBCD could induce significant RBL-2H3 cell death through caspase-dependent apoptosis. The study further shows that the cytotoxicity of some of these BFRs could increase synergistically when in mixtures and potentially activate inflammation through the stimulation of mast cell degranulation. The e-waste soil-derived extracts induced a concentration-dependent increase in EROD activity in the exposed RTG-W1 cells. Ultimately, nonpolar extracts had higher EROD-inducing potency compared with polar extracts and hence suggesting the presence in higher amounts of AhR agonists in nonpolar e-waste soil-derived extracts than polar extracts. Overall, there is urgent need for actions in order to improve the environmental quality of the e-waste sites.

In Utero and Lactational Exposure to an Environmentally Relevant Mixture of Brominated Flame Retardants Induces a Premature Development of the Mammary Glands

In utero and prepubertal development of the mammary glands occurs minimally in a hormone independent manner until puberty where maturation of the hypothalamic-pituitary-gonadal axis drives an extensive remodeling. Nevertheless, because the immature glands contain functional hormone receptors, they are especially vulnerable to the effects of endocrine disruptors, such as brominated flame retardants (BFRs). BFRs are widespread chemicals added to household objects to reduce their flammability, and to which humans are ubiquitously exposed. We previously reported that in utero and lactational exposure to BFRs resulted in an impaired mammary gland development in peripubertal animals. Here, we assessed whether BFR-induced disruption of mammary gland development could manifest earlier in life. Dams were exposed prior to mating until pups' weaning to a BFR mixture (0, 0.06, 20, or 60 mg/kg/day) formulated according to levels found in house dust. The mammary glands of female offspring were collected at weaning. Histo-morphological analyses showed that exposure to 0.06 mg/kg/day accelerates global epithelial development as demonstrated by a significant increase in total epithelial surface area, associated with a tendency to increase of the ductal area and thickness, and of lumen area. Significant increases of the Ki67 cell proliferation index and of the early apoptotic marker cleaved caspase-9 were also observed, as well as an upward trend in the number of thyroid hormone receptor α1 positive cells. These molecular, histologic, and morphometric changes are suggestive of accelerated pubertal development. Thus, our results suggest that exposure to an environmentally relevant mixture of BFRs induces precocious development of the mammary gland.

Exposure to HBCD promotes adipogenesis both in vitro and in vivo by interfering with Wnt6 expression

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant, and a ubiquitous environmental contaminant. However, effects and mechanisms underlying HBCD and the development of obesity remain largely unknown. Here, we investigated the effects and underlying mechanisms of HBCD on adipogenesis. Our results firstly disclosed that both murine 3T3-L1 and human HPA-V preadipocyte exposed to HBCD displayed markedly enhanced adipogenesis, manifesting with increase of triglyceride accumulation and expression of adipogenic marker genes. HBCD was further identified to play roles mainly during early-stage adipogenesis and increased expression of Pparγ, a key adipogenic regulator. Interestingly, HBCD didn't affect early key event mitotic clonal expansion (MCE), expression and activation of early pivotal factor C/EBPβ. In virtue of RNA sequencing, HBCD was further demonstrated to specially block Wnt6 gene expression and inhibited the Wnt/β-catenin pathway at an early stage of adipogenesis. Consistent with cellular finding, C57BL/6 male mice chronically exposed to HBCD exhibited specially increased epididymal white adipose tissue (eWAT) weight gain, elevated expression of master adipogenic genes and down-regulated expression of Wnt6 in eWAT. Taking together, our findings firstly revealed that HBCD promotes adipogenesis in vitro and in vivo by specifically inhibiting Wnt6 expression, presumably connecting exposure of HBCD to the development of obesity.

The HBCDs biodegradation using a Pseudomonas strain and its application in soil phytoremediation

Hexabromocyclododecanes (HBCDs) are the second-most widely used brominated flame retardants. They cause inappropriate antidiuretic hormone syndrome and can induce cancer. However, little information is available about bacterial degradation of HBCDs. In this study, HBCDs (α-, β- and γ-HBCD) degrading strain Pseudomonas aeruginosa HS9 was isolated, identified, and characterized. The strain HS9 could remove 69% (± 0.05%) of 1.7 mg/L HBCDs in 14 days. Based on identification of metabolites, this bacterium could oxidize HBCDs by two pathways. In the first, HBCDs are sequentially debromized to tetrabromocyclododecene, dibromocyclododecadiene, and then debromized once more to cis, trans, trans-1, 5, 9-cyclododecatriene (CDT). After that, CDT is then oxidized to 1,2-epoxy-5,9-cyclododecadiene. The second identified pathway is a simultaneous debrominating and hydroxylating process based on the detection of 2,5,6,9,10-pentabromocyclododecanols, which were newly identified. The strain's effects on plant-maize growth were tested and bioremediation evaluation trials were performed. The addition of strain HS9 could decrease HBCDs of 4.08 mg/g (87.6% removed) and 0.1 mg/g (25% removed) in soil and plants, respectively. Microbial diversity analysis shows that the addition of strain HS9 can promote the abundance of plant-beneficial bacteria, such as Methylobacillus, Nitrosomonas, Plancoccus, Bacillus, and Rhodococcus. The results provide insights for the bioremediation of HBCDs-contaminated soils.

Gestational and Lactational Exposure to an Environmentally Relevant Mixture of Brominated Flame Retardants Downregulates Junctional Proteins, Thyroid Hormone Receptor α1 Expression, and the Proliferation-Apoptosis Balance in Mammary Glands Post Puberty

Mammary gland development requires hormonal regulation during puberty, pregnancy, and lactation. Brominated flame retardants (BFRs) are endocrine disruptors; they are added to consumer products to satisfy flammability standards. Previously, we showed that gestational and lactational exposure to an environmentally relevant mixture of BFRs disrupts proteins of the adherens junctions in rat dam mammary glands at weaning. Here, we hypothesize that perinatal exposure to the same BFR mixture also disrupts junctional proteins and signaling pathways controlling mammary gland development in pups. Dams were exposed through diet to a BFR mixture based on the substances in house dust; doses of the mixture used were 0, 0.06, 20, or 60 mg/kg/day. Dams were exposed continuously beginning prior to mating until pups' weaning; female offspring were euthanized on postnatal day (PND) 21, 46, and 208. The lowest dose of BFRs significantly downregulated adherens junction proteins, E-cadherin, and β-catenin, and the gap junction protein p-Cx43, as well as thyroid hormone receptor alpha 1 protein at PND 46. No effects were observed on estrogen or progesterone receptors. The low dose also resulted in a decrease in cleaved caspase-3, a downward trend in PARP levels, proteins involved in apoptosis, and an upward trend in proliferating cell nuclear antigen, a marker of proliferation. No effects were observed on ductal elongation or on the numbers of terminal end buds. Together, our results indicate that gestational and lactational exposure to an environmentally relevant mixture of BFRs disrupts cell-cell interactions, thyroid hormone homeostasis and the proliferation-apoptosis balance at PND 46, a critical stage for mammary gland development.

Mass balance study of brominated flame retardants in female captive peregrine falcons

Little is known about brominated flame retardant (BFR) dynamics in birds, especially large molecules such as decabromodiphenyl ether (BDE-209). In particular, bioaccumulation from food and transfer dynamics to eggs are poorly understood. Therefore, an input-output mass balance study of tri-decaBDEs, DBDPE and HBCDD was performed in three female peregrine falcons from a captive breeding program by analyzing their naturally contaminated food (quail, chicken (cockerels)), plasma, feces and eggs. Predominant BFRs in cockerels and quail were BDE-209 and DBDPE, as well as HBCDD in quail. The predominant BFRs found in falcon plasma were BDE-209, -153 and -183, in eggs, HBCDD, BDE-209 and -153 and in feces, BDE-209. Mean absorption efficiencies (AE) for the tetra-octabrominated BDEs ranged from 84-100% and 70% for HBCDD. The AEs for BDE-206, -207, -208 and -209 varied due to the large variability seen for feces fluxes. All egg/plasma ratios for BDEs were similar and greater than one (range 1.1-2.7), including for BDE-209, indicating efficient transfer from females to the eggs. Excretion via egg-laying was approximately 6.0-29% of the initial, pre-breeding body burden of individual penta-decaBDE congeners, (15-45% for BDE-206). HBCDD was not detected in plasma but was found in eggs, also indicating efficient transfer and excretion via eggs. Input fluxes from food exceeded the output fluxes (feces, eggs) indicating considerable metabolism for tetra-octaBDEs, possibly also for the nona-decaBDEs and HBCDD. Bioaccumulation factors calculated from lipid weight concentrations in plasma and food (BAFp) were highest for BDE-208 (31), -153 (23), -209 (19) and -207 (16) and from eggs and food (BAFe), were highest for HBCDD (140), BDE-153 (41), -208 (42), BDE-207 (24) and BDE-209 (21). BAFe and BAFp values were below 10 for BDE-47, -99 and -100. For one falcon, egg results were available from three different years and estimated half-lives were 65 d (BDE-99), 624 d (BDE-153), 31 d (BDE-154), 349 d (BDE-183), 77 d (BDE-196) and 89 d (BDE-197).

A comparison of the thyroid disruption induced by decabrominated diphenyl ethers (BDE-209) and decabromodiphenyl ethane (DBDPE) in rats

In recent years, decabromodiphenyl ethane (DBDPE), a new alternative flame retardant to the decabrominated diphenyl ethers (BDE-209), is widely used in a variety of products. Previous studies have indicated that DBDPE, like BDE-209, could disrupt thyroid function. However, compared with BDE-209, the degrees of thyrotoxicosis induced by DBDPE were not clear. In addition, the mechanism of thyrotoxicosis induced by DBDPE or BDE-209 was still under further investigation. In this study, male rats as a model were orally exposed to DBDPE or BDE-209 by 5, 50, 500 mg/kg bw/day for 28 days. Then, we assessed the thyrotoxicosis of DBDPE versus BDE-209 and explored the mechanisms of DBDPE and BDE-209-induced thyrotoxicosis. Results showed that decreased free triiodothyronine (FT3) and increased thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH) in serum were observed in both 500 mg/kg bw/day BDE-209 and DBDPE group. Decreased total thyroxine (TT4), total T3 (TT3), and free T4 (FT4) were only observed in BDE-209 group but not in DBDPE group. Histological examination and transmission electron microscope examination showed that high level exposure to BDE-209 and DBDPE both caused significant changes in histological structure and ultrastructure of the thyroid gland. Additionally, oxidative damages of thyroid gland (decreased SOD and GSH activities, and increased MDA content) were also observed in both BDE-209 and DBDPE groups. TG contents in the thyroid gland was reduced in BDE-209 group but not in DBDPE group. Both BDE-209 and DBDPE affected the expression of hypothalamic-pituitary-thyroid (HPT) axis related genes. These findings suggested that both BDE-209 and DBDPE exposure could disrupt thyroid function in the direction of hypothyroidism and the underlying mechanism was likely to be oxidative stress and perturbations of HPT axis. However, DBDPE was found to be less toxic than BDE-209.

Towards a dietary-exposome assessment of chemicals in food: An update on the chronic health risks for the European consumer

An informed opinion to a hugely important question, whether the food on the Europeans' plate is safe to eat, is provided. Today, the Europeans face food-borne health risks from non-communicable diseases induced by excess body weight, outbreaks caused by pathogens, antimicrobial resistance and exposures to chemical contaminants. In this review, these risks are first put in an order of importance. Then, not only potentially injurious dietary chemicals are discussed but also beneficial factors of the food. This review can be regarded as an attempt towards a dietary-exposome evaluation of the chemicals, the average European adult consumers could chronically expose to during their life-times. Risk ranking reveals that currently the European adults are chronically exposed to a mixture of potentially genotoxic-carcinogenic contaminants, particularly food process contaminants, at the potential risk levels. Furthermore, several of the contaminants whose dietary exposures pose risks appear to be carcinogens operating with a genotoxic mode of action targeting the liver. This suggests that combined health risks from the exposure to a mixture of the chemical contaminants poses a greater potential risk than the risks assessed for single compounds. Over 100 European-level risk assessments are examined. Finally, the importance of a diversified and balanced diet is emphasized.

Toxicity studies used in registration, evaluation, authorisation and restriction of chemicals (REACH): How accurately are they reported?

Toxicity studies on chemicals registered under the European Union's Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulation are provided as summaries instead of as a full study report. Because the registration data are used by regulatory agencies to identify chemicals of concern, the study summaries must accurately reflect the information in studies. A "study summary" should include sufficient information on the objectives, methods, results, and conclusions in the full study report in order for the relevance of the study to be determined. Sometimes a "robust study summary" is required, which should contain more detailed information to enable an independent assessment of the study. The aim of the present investigation is to examine how well published toxicity papers were reflected in study summaries submitted by registrants under REACH. Summaries of 20 published studies (peer-reviewed studies, including 1 abstract) were examined and broad categories of various types of observed differences were derived. The extent to which information in the published studies was reported, as well as how accurately the information was reflected, varied. How accurately the information was reflected also varied. Differences between the published studies and the summaries included simple typing errors, unclear and incomplete reporting, as well as the omission of information on, for example, study design, results, or interpretation of the results, which in some cases could be considered relevant for the risk assessment. This raises concerns regarding the accuracy of study summaries and their use for decision making. Moreover, the possibility for third parties to independently assess and scrutinize the summaries is limited. Considering that we rely on REACH registration data for chemical safety, all data used for risk assessment should be accessible for thorough examination and fully independent assessment. Integr Environ Assess Manag 2019;00:000-000. © 2019 SETAC.

Hepatic transcriptional dose-response analysis of male and female Fischer rats exposed to hexabromocyclododecane

Hexabromocyclododecane (HBCD) is a brominated flame retardant found in the environment and human tissues. The toxicological effects of HBCD exposure are not clearly understood. We employed whole-genome RNA-sequencing on liver samples from male and female Fischer rats exposed to 0, 250, 1250, and 5000 mg technical mixture of HBCD/kg diet for 28 days to gain further insight into HBCD toxicity. HBCD altered 428 and 250 gene transcripts in males and females, respectively, which were involved in metabolism of xenobiotics, oxidative stress, immune response, metabolism of glucose and lipids, circadian regulation, cell cycle, fibrotic activity, and hormonal balance. Signature analysis supported that HBCD operates through the constitutive androstane and pregnane X receptors. The median transcriptomic benchmark dose (BMD) for the lowest statistically significant pathway was within 1.5-fold of the BMD for increased liver weight, while the BMD for the lowest pathway with at least three modeled genes (minimum 5% of pathway) was similar to the lowest apical endpoint BMD. The results show how transcriptional analyses can inform mechanisms underlying chemical toxicity and the doses at which potentially adverse effects occur. This experiment is part of a larger study exploring the use of toxicogenomics and high-throughput screening for human health risk assessment.

Hexabromocyclododecane: concentrations and isomer profiles from sources to environmental sinks

Concentrations and isomer compositions of hexabromocyclododecane (HBCD) were measured in six matrices in the Czech Republic (HBCD technical mixture; consumer products; indoor and outdoor air at industrial, urban and background locations; soils; and sediments) to provide insight into changes in concentrations and isomer profiles between environmental sources and environmental sinks. A distinct gradient of air concentrations was observed, from 1600 ng/m³ in the industrial area to < 10 pg/m³ in urban and background air. Isomer profiles also showed a distinct gradient in air, from 95% γ-HBCD in industrial air to 40% γ-HBCD in background air, suggesting the influence of differential atmospheric transport and phototransformation of γ- to α-HBCD. Concentrations and isomer compositions in consumer products were highly variable and indicated differences between products with intentional addition of HBCD as a flame retardant versus those with HBCD as an impurity, e.g., from recycled plastic. Understanding the isomer-specific environmental distributions and processes remains important for risk assessment and toxicology, considering the continued use of HBCD and the isomer-specific differences in uptake, metabolism, and toxicity, and further, demonstrates the utility of isomer profiles to better understand environmental processes of HBCDs.

Effects of low-levels of three hexabromocyclododecane diastereomers on the metabolic profiles of pak choi leaves using high-throughput untargeted metabolomics approach

The ecological toxicity of hexabromocyclododecane (HBCD) on animals, including fish and mice, has been reported, but its effects in plants, particularly its toxic mechanism, have rarely been investigated. An untargeted metabolomics approach for comprehensive assessment was selected to study the alterations in the metabolic profiles in pak choi leaves induced by exposure to trace-level amounts of HBCD diastereomers over 30 days. A supervised orthogonal partial least-squares-discriminant analysis (OPLS-DA) was performed to investigate differences between the HBCD and control groups. The discriminating metabolites were identified using public databases. The results indicated that the toxicity of the HBCD diastereomers was ordered as γ-HBCD > α-HBCD > β-HBCD. 13 metabolites were identified as potential biomarkers to discriminate the presence of HBCD toxicity. The lipid, carbohydrate, nucleotide and amino acid metabolic pathways affected were found in accordance with animals and humans, and also HBCD could induce the interference of the secondary metabolite pathways. The system of the stress defences was activated, including signalling pathway, antioxidant defence system, shikimate and phenylpropanoid metabolism. The carbohydrate and amino acid metabolism were disturbed by HBCD intervention, and the lipid, amino acid and secondary metabolite metabolism were regulated for HBCD stress prevention. These results provide insights into the mechanism and degree of HBCD phytotoxicity.

Neuroprotection by Taurine on HBCD-Induced Apoptosis in PC12 Cells

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant (BFR). Because of their presence in human issues, including brain tissue, concern has been raised on their possible neurotoxicity. Presently, we explored the neuroprotection of taurine against HBCD-induced apoptotic damages in PC12 cells. Cells were pre-treated with taurine before HBCD exposure and the viability was assayed via the methyl-thiazolyl-tetrazolium (MTT) method. Apoptotic features were observed with Hoechst 33342 staining. Apoptotic ratio was measured using flow cytometry with Annexin V-FITC coupled propidium iodide (PI) double staining. The changes in the levels of Bcl-2 and Bax proteins were quantitated by the western blot. The activity of caspase-3 was tested and the results revealed that presence of HBCD decreased cell survival and led to apoptosis in the tested cells. Further, exposure of HBCD reduced protein expression of Bcl-2, increased expression in Bax protein and activity of caspase-3. Taurine attenuated HBCD-induced cell viability loss and cell apoptosis. Moreover, taurine significantly prevented from reducing Bcl-2 protein expression and elevating Bax protein expression and caspase-3 activity induced by HBCD. These results demonstrated that taurine can alleviate HBCD-induced apoptosis by altering Bcl-2 expression and Bax protein and Caspase-3 activity in PC12.

Iodoacetic Acid Disrupting the Thyroid Endocrine System in Vitro and in Vivo

Exposure to drinking water disinfection byproducts (DBPs) is potentially associated with adverse developmental effects. Iodoacetic acid (IAA), an unregulated DBP, has been shown to be cytotoxic, mutagenic, genotoxic, and tumorigenic. However, its endocrine-disrupting effects remain unknown. This study evaluated the IAA-induced disruption of the thyroid endocrine system using in vitro and in vivo assays. Rat pituitary tumor GH3 cells were treated with IAA in the presence and absence of triiodothyronine (T3). IAA exposure significantly reduced T3-activated GH3 cell proliferation, indicating the antagonistic activity of IAA in vitro. Sprague-Dawley rats were also subjected to IAA treatment through oral gavage for 28 consecutive days. IAA exposure significantly down-regulated the mRNA expression levels of the thyrotropin receptor (TSHR), the sodium/iodide symporter (NIS), and type I deiodinase and simultaneously reduced the protein expression levels of TSHR and NIS. IAA exposure decreased T3 levels but increased the weights of hypothalamus and the levels of thyrotropin releasing hormone and thyrotropin. In addition, IAA induced the formation of smaller and more depleted follicles or even vacuolization in the thyroid. These results suggested that IAA potentially disrupts the thyroid endocrine system both in vitro and in vivo.

Complete genome sequence of Bacillus sp. HBCD-sjtu, an efficient HBCD-degrading bacterium

Environmental pollution caused by the release of industrial chemicals is currently one of the most important environmental harms. Manufacturing chemicals can be biodegraded, and valuable intermediates can be used as pharmacophores in drug targeting and have several other useful purposes. Hexabromocyclododecane (HBCD), a non-aromatic brominated flame retardant, is a toxic compound that consists of a cycloaliphatic ring of 12 carbon atoms to which six bromine atoms are attached. It is formed by bromination of cis-trans-trans-1,5,9-cyclododecatriene, but its use is now restricted in several countries, because it is an environmental pollutant. Little is known about whether bacteria can degrade HBCD. A bacterial strain that degrades HBCD was recently isolated using enrichment culture techniques. Based on morphological, biochemical and phylogenetic analysis this isolate was categorized as Bacillus cereus and named strain HBCD-sjtu. Maximum growth and HBCD-degrading activity were observed when this strain was grown at 30 °C, pH 7.0 and 200 RPM in mineral salt medium containing 0.5 mm HBCD. The genome of strain HBCD-sjtu, which consists of only one circular chromosome, was sequenced. This whole genome sequence will be crucial for illuminating the molecular mechanisms of HBCD degradation.

Biomagnification of Hexabromocyclododecane (HBCD) in a coastal ecosystem near a large producer in China: Human exposure implication through food web transfer

Hexabromocyclododecane (HBCD) is a widely used brominated flame retardant which is mainly produced in China. Many HBCD facilities are located at the coast and the released HBCD may enter into the coastal ecosystem. There is a risk that HBCD can transfer through the food web to the diet of local population. Therefore, the coastal organisms near one of the biggest HBCD facilities in China were investigated. Variation was observed for the bioaccumulation of HBCD between the detrital food chain and the grazing food chain. In the studied species, the mullet was most contaminated which may be caused by its feeding on detritus. At the same time, the transfer of HBCD along the food web was investigated, and HBCD was biomagnified from the prey to the predator in the grazing food chains. Among the three diastereoisomers, α-HBCD was biomagnified with increasing trophic levels in the food web while β- and γ-HBCD were not. To assess the human dietary exposure, the dietary intake of HBCD from seafood was estimated, and the estimated daily intake (EDI) was 5.22ng/kg/day for adults, and 16.39ng/kg/day for children. The EDI for local residents were tens of times higher than that for general population in China, but the risk through dietary intake was very low in terms of existing reference dose.

Flame retardants, hexabromocyclododecane (HCBD) and tetrabromobisphenol a (TBBPA), alter secretion of tumor necrosis factor alpha (TNFα) from human immune cells

Hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA) are flame retardants, used in a variety of applications, which contaminate the environment and are found in human blood. HBCD and TBBPA have been shown to alter the tumor killing function of natural killer (NK) lymphocytes and the secretion of the inflammatory cytokines interferon gamma (IFNγ) and interleukin 1 beta (IL-1β). The current study examined the effects of HBCD and TBBPA on secretion of the critical pro-inflammatory cytokine tumor necrosis factor alpha (TNFα) from human immune cells. Preparations of human immune cells that ranged in complexity were studied to determine if the effects of the compounds were consistent as the composition of the cell preparation became more heterogeneous. Cell preparations studied were: NK cells, monocyte-depleted (MD) peripheral blood mononuclear cells (PBMCs), and PBMCs. Exposure of NK cells to higher concentrations of HBCD (5 and 2.5 µM) caused decreased secretion of TNFα. However, when the cell preparation contained T lymphocytes (MD-PBMCs and PBMCs) these same concentrations of HBCD increased TNFα secretion as did nearly all other concentrations. This suggests that HBCD's ability to increase TNFα secretion from immune cells was dependent on the presence of T lymphocytes. In contrast, exposures to TBBPA decreased the secretion of TNFα from all immune cell preparations regardless of the composition of the cell preparation. Further, HBCD-induced increases in TNFα secretion utilized the p38 MARK pathway. Thus, both HBCD and TBBPA may have the capacity to disrupt the inflammatory response with HBCD having the potential to cause chronic inflammation.

Hexabromocyclododecanes (HBCDs) in fish: Evidence of recent HBCD input into the coastal environment

Hexabromocyclododecanes (HBCDs) are flame retardants and emerging persistent organic pollutants. In the present study, α-, β-, and γ-HBCDs were measured in several fish species from rivers and an electronic waste (e-waste) recycling site in Pearl River Delta, South China. The concentrations of HBCDs were 12.8 to 640, 5.90 to 115, and 34.3 to 518ng/g lipid weight (lw) in mud carp (Cirrhinus molitorella), tilapia (Tilapia nilotica), and plecostomus (Hypostomus plecostomus), respectively. Plecostomus showed the highest HBCD concentrations among three fish species. The contributions of α-HBCD to total HBCDs were 78% to 97%, 93% to 99%, and 87% to 98% in carp, tilapia, and plecostomus, respectively. Fish samples from a harbor and the e-waste site exhibited the highest HBCD concentrations among all samples. The HBCD concentrations were not significantly correlated with the gross domestic product or population data. e-Waste recycling activities, harbor construction, and shipment might be recent HBCD sources.

Parallel in vivo and in vitro transcriptomics analysis reveals calcium and zinc signalling in the brain as sensitive targets of HBCD neurotoxicity

Hexabromocyclododecane (HBCD) is a brominated flame retardant (BFR) that accumulates in humans and affects the nervous system. To elucidate the mechanisms of HBCD neurotoxicity, we used transcriptomic profiling in brains of female mice exposed through their diet to HBCD (199 mg/kg body weight per day) for 28 days and compared with those of neuronal N2A and NSC-19 cell lines exposed to 1 or 2 µM HBCD. Similar pathways and functions were affected both in vivo and in vitro, including Ca²⁺ and Zn²⁺ signalling, glutamatergic neuron activity, apoptosis, and oxidative stress. Release of cytosolic free Zn²⁺ by HBCD was confirmed in N2A cells. This Zn²⁺ release was partially quenched by the antioxidant N-acetyl cysteine indicating that, in accordance with transcriptomic analysis, free radical formation is involved in HBCD toxicity. To investigate the effects of HBCD in excitable cells, we isolated mouse hippocampal neurons and monitored Ca²⁺ signalling triggered by extracellular glutamate or zinc, which are co-released pre-synaptically to trigger postsynaptic signalling. In control cells application of zinc or glutamate triggered a rapid rise of intracellular [Ca²⁺]. Treatment of the cultures with 1 µM of HBCD was sufficient to reduce the glutamate-dependent Ca²⁺ signal by 50%. The effect of HBCD on zinc-dependent Ca²⁺ signalling was even more pronounced, resulting in the reduction of the Ca²⁺ signal with 86% inhibition at 1 µM HBCD. Our results show that low concentrations of HBCD affect neural signalling in mouse brain acting through dysregulation of Ca²⁺ and Zn²⁺ homeostasis.

Tracking Changes of Hexabromocyclododecanes during the Refining Process in Peanut, Corn, and Soybean Oils

Hexabromocyclododecanes (HBCDs) are harmful compounds, which could be taken up by plants and occur in vegetable oils. In this study, we systematically tracked the changes of HBCDs during different refining processes in peanut, corn, and soybean oils in China. The refining processes were efficient at removing the concentrations of total HBCDs (∑HBCDs), although the levels did increase for peanut and corn oils during the neutralization and bleaching steps. Quite significant reductions in the ∑HBCD concentrations were observed for soybean oils (71-100%) through refining. α-HBCD and ∑HBCD levels were significantly and positively correlated with the peroxidation value (PV), suggesting that PV might be an indicator reflecting the changes of α-HBCD and ∑HBCDs during the oil-refining processes. HBCD intakes from vegetable oils represented a low concern for public health. The results might be helpful for quality and process control with a view to minimize the levels of HBCDs in vegetable oils.

Serum Metabolomic Profiles in Neonatal Mice following Oral Brominated Flame Retardant Exposures to Hexabromocyclododecane (HBCD) Alpha, Gamma, and Commercial Mixture

BACKGROUND

Hexabromocyclododecane (HBCD) is a high production volume brominated flame retardant added to building insulation foams, electronics, and textiles. HBCD is a commercial mixture (CM-HBCD) composed of three main stereoisomers: α-HBCD (10%), β-HBCD (10%), and γ-HBCD (80%). A shift from the dominant stereoisomer γ-HBCD to α-HBCD is detected in humans and wildlife.

OBJECTIVES

Considering CM-HBCD has been implicated in neurodevelopment and endocrine disruption, with expected metabolism perturbations, we performed metabolomics on mice serum obtained during a window-of-developmental neurotoxicity to draw correlations between early-life exposures and developmental outcomes and to predict health risks.

METHODS

Six female C57BL/6 mice at postnatal day (PND) 10 were administered a single gavage dose of α-, γ-, or CM-HBCD at 3, 10, and 30 mg/kg. Nuclear magnetic resonance metabolomics was used to analyze 60 μL serum aliquots of blood collected 4 days post-oral exposure.

RESULTS

Infantile mice exposed to α-, γ-, or CM-HBCD demonstrated differences in endogenous metabolites by treatment and dose groups, including metabolites involved in glycolysis, gluconeogenesis, lipid metabolism, citric acid cycle, and neurodevelopment. Ketone bodies, 3-hydroxybutyrate, and acetoacetate, were nonstatistically elevated, when compared with mean control levels, in all treatment and dose groups, while glucose, pyruvate, and alanine varied. Acetoacetate was significantly increased in the 10 mg/kg α-HBCD and was nonsignificantly decreased with CM-HBCD. A third ketone body, acetone, was significantly lower in the 30 mg/kg α-HBCD group with significant increases in pyruvate at the same treatment and dose group. Metabolites significant in differentiating treatment and dose groups were also identified, including decreases in amino acids glutamate (excitatory neurotransmitter in learning and memory) and phenylalanine (neurotransmitter precursor) after α-HBCD and γ-HBCD exposure, respectively.

CONCLUSIONS

We demonstrated that 4 days following a single neonatal oral exposure to α-, γ-, and CM-HBCD resulted in different serum metabolomic profiles, indicating stereoisomer- and mixture-specific effects and possible mechanisms of action.

Transformation of hexabromocyclododecane in contaminated soil in association with microbial diversity

This study evaluated the transformation of 1,2,5,6,9,10-hexabromocyclododecane (HBCD) in soil under various conditions. Under anaerobic conditions for 21days, 34% of the total HBCD was reduced from rhizosphere soil containing humic acid, and 35% of the total HBCD was reduced from the non-rhizosphere soil; under aerobic conditions, 29% and 57-60% of the total HBCD were reduced from the same soil types after 40days. Three HBCD isomers (α-, β-, and γ-HBCD) were separately analyzed for their isomeric effects on transformation. In the soils with added glucose as a carbon and energy source, the fraction of γ-HBCD was reduced due to the blooming microbial activity. The population of Gram-positive bacteria decreased during the aerobic treatments of HBCD, whereas the population of several Gram-negative bacteria (e.g., Brassia rhizosphere, Sphingomonas sp.) increased. Humic acid and glucose increased the HBCD removal efficiency and microbial diversity in both rhizosphere and non-rhizosphere soils.

Impairment in the mesohippocampal dopamine circuit following exposure to the brominated flame retardant, HBCDD

Many chemicals have been used to increase the safety of consumer products by reducing their flammability and risk for ignition. Recent focus on brominated flame retardants, such as polybrominated diphenyl ethers (PBDEs) has shown them to contribute to neurobehavioral deficits in children, including learning and memory. As the manufacture and use of PBDEs have been reduced, replacement chemicals, such as hexabromocyclododecane (HBCDD) have been substituted. Our current study evaluated the neurotoxicity of HBCDD, concentrating on dopaminergic innervation to the hippocampus. Using an in vivo model, we exposed male mice to HBCDD and then assessed alterations to the dopamine synapse 6 weeks later. These exposures elicited significant reductions in presynaptic dopaminergic proteins, including TH, COMT, MAO-B, DAT, VMAT2, and alpha-synuclein. In contrast, postsynaptic dopamine receptors were not impaired. These findings suggest that the mesohippocampal dopamine circuit is vulnerable to HBCDD and the dopamine terminal may be a selective target for alteration.