Exposure to tetrabromobisphenol A (TBBPA) in Wistar rats: Neurobehavioral effects in offspring from a one-generation reproduction study

Tetrabromobisphenol A induced p38-MAPK/AMPKα activation downstream-triggered CHOP signal contributing to neuronal apoptosis and death

Tetrabromobisphenol A (TBBPA), a brominated flame retardant (BFR), has been implicated as the neurotoxic effects in mammalian. However, the exact mechanisms underlying TBBPA-induced neurotoxicity remain unclear. In the present study, Neuro-2a cells, a mouse neural crest-derived cell line, were used to examine the mechanism of TBBPA-induced neuronal cytotoxicity. TBBPA exposure caused alterations in cell viability and mitochondrial membrane potential (MMP) and induction of apoptotic events, such as increased apoptotic cell population and cleaved caspase-3, -7, -9, and poly (ADP-ribose) polymerase (PARP) protein expression). TBBPA exposure triggered CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) activation. Transfection with CHOP-specific small interfering RNA (siRNA) obviously prevented the expression of CHOP protein and markedly attenuated MMP loss, and caspase-3 and -7 activation in TBBPA-exposed Neuro-2a cells. In addition, TBBPA exposure significantly evoked the phosphorylation of c-Jun N-terminal kinase (JNK), extracellular-signal regulated kinase1/2 (ERK1/2), p38-mitogen-activated protein kinase (p38-MAPK), and AMP-activated protein kinase (AMPK)α proteins. Pretreatment of cells with pharmacological inhibitors of p38-MAPK (SB203580) and AMPK (compound C), but not inhibitors of JNK (SP600125) or ERK1/2 (PD98059), effectively prevented the increase in caspase-3 activity, MMP loss, and activated CHOP and cleaved caspase-3 and -7 protein expression in TBBPA-treated cells. Notably, transfection with either p38α-MAPK- or AMPKα1/2-specific siRNAs markedly attenuated the expression of CHOP, and cleaved caspase-3 and -7. Interestingly, transfection with each siRNA significantly reduced the TBBPA-induced phosphorylation of p38-MAPK and AMPKα proteins. Collectively, these findings suggest that CHOP activation-mediated mitochondria-dependent apoptosis contributes to TBBPA-induced neurotoxicity. An interdependent p38-MAPK and AMPKα signaling-regulated apoptotic pathway may provide new insights into the mechanism understanding TBBPA-elicited neurotoxicity.

Molecular mechanisms of tetrabromobisphenol A (TBBPA) toxicity: Insights from various biological systems

Tetrabromobisphenol A (TBBPA) is a ubiquitous brominated flame retardant extensively incorporated into a wide range of products. As its utilization has escalated, its environmental exposure risks have concomitantly increased. The molecular properties of TBBPA allow it to persist in the environment and within organisms. In this review, we comprehensively examine the toxicity of TBBPA across different organ systems and elucidate the underlying molecular mechanisms. We particularly emphasize TBBPA's impact on biological signaling pathways, protein functionality, cellular architecture, and epigenetic regulation, which collectively lead to disruptions in endocrine, hepatic, neurological, reproductive, and other biological systems. The analysis of these toxicological phenomena and their fundamental molecular mechanisms has substantially enhanced our understanding of TBBPA's hazardous characteristics. This review also examines potential avenues for future research, with a focus on uncovering novel molecular mechanisms and assessing the toxicological impacts of TBBPA exposure, particularly in relation to interactions with other environmental contaminants. We propose a greater focus on examining the toxic effects and molecular mechanisms of long-term TBBPA exposure at environmentally relevant concentrations to facilitate more accurate assessments of human health risks.

A critical review to identify data gaps and improve risk assessment of bisphenol A alternatives for human health

Bisphenol A (BPA), a synthetic chemical widely used in the production of polycarbonate plastic and epoxy resins, has been associated with a variety of adverse effects in humans including metabolic, immunological, reproductive, and neurodevelopmental effects, raising concern about its health impact. In the EU, it has been classified as toxic to reproduction and as an endocrine disruptor and was thus included in the candidate list of substances of very high concern (SVHC). On this basis, its use has been banned or restricted in some products. As a consequence, industries turned to bisphenol alternatives, such as bisphenol S (BPS) and bisphenol F (BPF), which are now found in various consumer products, as well as in human matrices at a global scale. However, due to their toxicity, these two bisphenols are in the process of being regulated. Other BPA alternatives, whose potential toxicity remains largely unknown due to a knowledge gap, have also started to be used in manufacturing processes. The gradual restriction of the use of BPA underscores the importance of understanding the potential risks associated with its alternatives to avoid regrettable substitutions. This review aims to summarize the current knowledge on the potential hazards related to BPA alternatives prioritized by European Regulatory Agencies based on their regulatory relevance and selected to be studied under the European Partnership for the Assessment of Risks from Chemicals (PARC): BPE, BPAP, BPP, BPZ, BPS-MAE, and TCBPA. The focus is on data related to toxicokinetic, endocrine disruption, immunotoxicity, developmental neurotoxicity, and genotoxicity/carcinogenicity, which were considered the most relevant endpoints to assess the hazard related to those substances. The goal here is to identify the data gaps in BPA alternatives toxicology and hence formulate the future directions that will be taken in the frame of the PARC project, which seeks also to enhance chemical risk assessment methodologies using new approach methodologies (NAMs).

Two novel in vitro assays to screen chemicals for their capacity to inhibit thyroid hormone transmembrane transporter proteins OATP1C1 and OAT4

Early brain development depends on adequate transport of thyroid hormones (THs) from the maternal circulation to the fetus. To reach the fetal brain, THs have to cross several physiological barriers, including the placenta, blood-brain-barrier and blood-cerebrospinal fluid-barrier. Transport across these barriers is facilitated by thyroid hormone transmembrane transporters (THTMTs). Some endocrine disrupting chemicals (EDCs) can interfere with the transport of THs by THTMTs. To screen chemicals for their capacity to disrupt THTMT facilitated TH transport, in vitro screening assays are required. In this study, we developed assays for two THTMTs, organic anion transporter polypeptide 1C1 (OATP1C1) and organic anion transporter 4 (OAT4), both known to play a role in the transport of THs across barriers. We used overexpressing cell models for both OATP1C1 and OAT4, which showed an increased uptake of radiolabeled T4 compared to control cell lines. Using these models, we screened various reference and environmental chemicals for their ability to inhibit T4 uptake by OATP1C1 and OAT4. Tetrabromobisphenol A (TBBPA) was identified as an OATP1C1 inhibitor, more potent than any of the reference chemicals tested. Additionally perfluorooctanesulfonic acid (PFOS), perfluoroctanic acid (PFOA), pentachlorophenol and quercetin were identified as OATP1C1 inhibitors in a similar range of potency to the reference chemicals tested. Bromosulfophthalein, TBBPA, PFOA and PFOS were identified as potent OAT4 inhibitors. These results demonstrate that EDCs commonly found in our environment can disrupt TH transport by THTMTs, and contribute to the identification of molecular mechanisms underlying TH system disruption chemicals.

Tetrabromobisphenol A exerts thyroid disrupting effects but has little overt impact on postnatal brain development and neurobehaviors in mice

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant. There is evidence showing that TBBPA can exert thyroid disrupting effects in mammals, but different results were also reported, along with inconsistent reports regarding its neurotoxicity. Here, we investigated thyroid disrupting effects and neurotoxicity of TBBPA (5, 50, 500 µg/(kg·day)) to male mice following maternal and direct exposure through drinking water, with the anti-thyroid drug propylthiouracil (PTU) as the positive control. On postnatal day (PND) 15, we expectedly observed severe thyroid compensatory hyperplasia and cerebellar developmental retardation in PTU-treated pups. The highest dose of TBBPA also caused thyroid histological alteration but had no effects on cerebellar development in terms of Purkinje cell morphology and the thickness of the internal granular layer and the molecular layer of the cerebellum. During puberty and adulthood, the thyroid morphological alterations became more pronounced in the TBBPA-treated animals, accompanied by decreased serum thyroid hormone levels. Furthermore, the 50 and 500 µg/(kg·day) TBBPA groups showed a significant decrease in the serum level of serotonin, a neurotransmitter associated with anxiety behaviors. Correspondingly, the highest dose group displayed anxiety-like behaviors in the elevated plus-maze test on PND 35, but this neurobehavioral alteration disappeared on PND 56. Moreover, no changes in neurobehavioral parameters tested were found in TBBPA-treated animals at puberty and adulthood. Altogether, all observations show that TBBPA can exert thyroid disrupting effects but has little overt impact on brain development and neurobehaviors in mice, suggesting that thyroid disruption does not necessarily cause overtly adverse neurodevelopmental outcomes.

Update of the scientific opinion on tetrabromobisphenol A (TBBPA) and its derivatives in food

The European Commission asked EFSA to update its 2011 risk assessment on tetrabromobisphenol A (TBBPA) and five derivatives in food. Neurotoxicity and carcinogenicity were considered as the critical effects of TBBPA in rodent studies. The available evidence indicates that the carcinogenicity of TBBPA occurs via non-genotoxic mechanisms. Taking into account the new data, the CONTAM Panel considered it appropriate to set a tolerable daily intake (TDI). Based on decreased interest in social interaction in male mice, a lowest observed adverse effect level (LOAEL) of 0.2 mg/kg body weight (bw) per day was identified and selected as the reference point for the risk characterisation. Applying the default uncertainty factor of 100 for inter- and intraspecies variability, and a factor of 3 to extrapolate from the LOAEL to NOAEL, a TDI for TBBPA of 0.7 μg/kg bw per day was established. Around 2100 analytical results for TBBPA in food were used to estimate dietary exposure for the European population. The most important contributors to the chronic dietary LB exposure to TBBPA were fish and seafood, meat and meat products and milk and dairy products. The exposure estimates to TBBPA were all below the TDI, including those estimated for breastfed and formula-fed infants. Accounting for the uncertainties affecting the assessment, the CONTAM Panel concluded with 90%-95% certainty that the current dietary exposure to TBBPA does not raise a health concern for any of the population groups considered. There were insufficient data on the toxicity of any of the TBBPA derivatives to derive reference points, or to allow a comparison with TBBPA that would support assignment to an assessment group for the purposes of combined risk assessment.

Perturbation of lipid metabolism in 3T3-L1 at different stages of preadipocyte differentiation and new insights into the association between changed metabolites and adipogenesis promoted by TBBPA or TBBPS

Tetrabromobisphenol A (TBBPA) and tetrabromobisphenol S (TBBPS) are widely distributed brominated flame retardants. While TBBPA has been demonstrated to stimulate adipogenesis, TBBPS is also under suspicion for potentially inducing comparable effects. In this study, we conducted a non-targeted metabolomics to examine the metabolic changes in 3T3-L1 cells exposed to an environmentally relevant dose of TBBPA or TBBPS. Our findings revealed that 0.1 µM of both TBBPA and TBBPS promoted the adipogenesis of 3T3-L1 preadipocytes. Multivariate analysis showed significant increases in glycerophospholipids, sphingolipids, and steroids relative levels in 3T3-L1 cells exposed to TBBPA or TBBPS at the final stage of preadipocyte differentiation. Metabolites set composed of glycerophospholipids was found to be highly effective predictors of adipogenesis in 3T3-L1 cells exposed to TBBPA or TBBPS (revealed from the receiver operating characteristic curve with an area under curve > 0.90). The results from metabolite set enrichment analysis suggested both TBBPA and TBBPS exposures significantly perturbed steroid biosynthesis in adipocytes. Moreover, TBBPS additionally disrupted the sphingolipid metabolism in the adipocytes. Our study presents new insights into the obesogenic effects of TBBPS and provides valuable information about the metabolites associated with adipogenesis induced by TBBPA or TBBPS.

Composition, Release, and Transformation of Earthworm Tissue-Bound Residues of Tetrabromobisphenol A in Soil

Earthworms accumulate organic pollutants to form earthworm tissue-bound residues (EBRs); however, the composition and fate of EBRs in soil remain largely unknown. Here, we investigated the fate of tetrabromobisphenol A (TBBPA)-derived EBRs in soil for 250 days using a 14C-radioactive isotope tracer and the geophagous earthworm Metaphire guillelmi. The EBRs of TBBPA in soil were rapidly transformed into nonextractable residues (NERs), mainly in the form of sequestered and ester-linked residues. After 250 days of incubation, 4.9% of the initially applied EBRs were mineralized and 69.3% were released to extractable residues containing TBBPA and its transformation products (TPs, generated mainly via debromination, O-methylation, and skeletal cleavage). Soil microbial activity and autolytic enzymes of earthworms jointly contributed to the release process. In their full-life period, the earthworms overall retained 24.1% TBBPA and its TPs in soil and thus prolonged the persistence of these pollutants. Our study explored, for the first time, the composition and fate of organic pollutant-derived EBRs in soil and indicated that the decomposition of earthworms may release pollutants and cause potential environmental risks of concern, which should be included in both environmental risk assessment and soil remediation using earthworms.

Long-Term Tetrabromobisphenol A Exposure Induces Gut Microbiota Imbalance and Metabolic Disorders via the Peroxisome Proliferator-Activated Receptor Signaling Pathway in the Regenerated Gut of Apostichopus japonicus

Tetrabromobisphenol A (TBBPA), a commonly utilized brominated flame retardant, is found in many types of abiotic and biotic matrices. TBBPA can increase oxidative stress, disrupt the endocrine system, cause neurodevelopmental disorders and activate peroxisome proliferator-activated receptors to modulate lipid deposits in aquatic animals. However, the toxic mechanism of TBBPA on the gut microbiota and intestinal health remains unclear. Apostichopus japonicus is an ideal model for studying the relationship between environmental contaminants and intestinal health due to its unique capacity for evisceration and quickly regenerated intestine. In the present study, we investigated the toxic mechanism of TBBPA on the gut microbiota and intestinal health in the regenerated intestine of A. japonicus. The results show that TBBPA exposure decreased the health of the regenerated intestine and the enzymatic activities, alpha diversity indices, and the relative abundance of the gut microbiota. Transcriptome analysis shows that TBBPA exposure affected lipid metabolism via the PPAR signaling pathway during the process of intestinal regeneration in A. japonicus, suggesting that TBBPA exposure can affect the composition and function of the gut microbiota and intestinal health in the regenerated intestine of A. japonicus. These results provide a basis for further research on the potential toxicity of TBBPA to the intestinal health in animals.

Transcriptomic and metabolomic insights into the defense response to HFRs in Arabidopsis

Tetrabromobisphenol A (TBBPA), Tetrachlorobisphenol A (TCBPA), Tetrabromobisphenol S (TBBPS) and their derivatives as the most widely used halogenated flame retardants (HFR), had been employed in the manufacturing industry to raise fire safety. HFRs have been shown to be developmentally toxic to animals and also affect plant growth. However, little was known about the molecular mechanism responded by when plants were treated with these compounds. In this study, when Arabidopsis was exposed to four HFRs (TBBPA, TCBPA, TBBPS-MDHP, TBBPS), the stress of these compounds had different inhibitory effects on seed germination and plant growth. Transcriptome and metabolome analysis showed that all four HFRs could influence the expression of transmembrane transporters to affect ion transport, Phenylpropanoid biosynthesis, Plant-pathogen interaction, MAPK signalling pathway and other pathways. In addition, the effects of different kinds of HFR on plants also have variant characteristics. It is very fascinating that Arabidopsis shows the response of biotic stress after exposure to these kinds of compounds, including the immune mechanism. Overall, the findings of the mechanism recovered by methods of transcriptome and metabolome analysis supplied a vital insight into the molecular perspective for Arabidopsis response to HFRs stress.

Tetrabromobisphenol A and hexabromocyclododecane, brominated flame retardants, trigger endoplasmic reticulum stress and activate necroptosis signaling in PC12 cells

Tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) are brominated flame retardants commonly used in a variety of industrial and consumer products. In this study, we performed RNA sequencing analysis of PC12 cells to clarify the mechanisms by which TBBPA and HBCD induce neurotoxicity. Differential expression analysis demonstrated that 636 and 271 genes were differentially expressed after TBBPA and HBCD treatment, respectively. Gene Ontology (GO) enrichment analysis revealed that genes annotated with the GO term "endoplasmic reticulum unfolded protein response" were upregulated in both TBBPA- and HBCD-treated groups. Furthermore, protein expression of endoplasmic reticulum stress markers, such as HSPA5 and DDIT3, as well as cleaved caspase-3, an apoptosis marker, were induced by TBBPA and HBCD. We also found that the cytotoxicity induced by TBBPA and HBCD was blocked by necrostatin-1, a necroptosis inhibitor, indicating the contribution of necroptosis. Our findings provide new insight into the mechanisms of toxicity induced by these chemicals.

The joint effects of nanoplastics and TBBPA on neurodevelopmental toxicity in Caenorhabditis elegans

Both of nanoplastics (NPs) and Tetrabromobisphenol A (TBBPA) are organic pollutants widely detected in the environment and organisms. The large specific surface area of NPs makes them ideal vectors for carrying various toxicants, such as organic pollutants, metals, or other nanomaterials, posing potential threats to human health. This study used Caenorhabditis elegans (C. elegans) to investigate the neurodevelopmental toxicity induced by combined exposure of TBBPA and polystyrene NPs. Our results showed that combined exposure caused synergistic inhibitory effects on the survival rate, body length/width, and locomotor ability. Furthermore, the overproduction of reactive oxygen species (ROS), lipofuscin accumulation, and dopaminergic neuronal loss suggested that oxidative stress was involved in induction of neurodevelopmental toxicity in C. elegans. The expressions of Parkinson's disease related gene (pink-1) and Alzheimer's disease related gene (hop-1) were significantly increased after combined exposure of TBBPA and polystyrene NPs. Knock out of pink-1 and hop-1 genes alleviated the adverse effects such as growth retardation, locomotion deficits, dopaminergic loss, and oxidative stress induction, indicating that pink-1 and hop-1 genes play an important role in neurodevelopmental toxicity induced by TBBPA and polystyrene NPs. In conclusion, TBBPA and polystyrene NPs had synergistic effect on oxidative stress induction and neurodevelopmental toxicity in C. elegans, which was mediated through increased expressions of pink-1 and hop-1.

Adsorption behaviour of tetrabromobisphenol A on sediments in Weihe River Basin in Northwest China

Tetrabromobisphenol A (TBBPA) is adsorbed on sediments in river environments, and various environmental factors have distinct effects on its adsorption behaviour. Investigating the adsorption behaviour of TBBPA on the sediments in Weihe River Basin is critical for protecting the water environment and providing a theoretical basis for the prevention and control of brominated flame retardant pollution. In this study, the adsorption behaviour of TBBPA on Weihe River sediment was investigated by conducting batch equilibrium experiments, and the effects of pH, dissolved organic matter, and ionic strength on the adsorption of TBBPA were discussed. The obtained results revealed that rapid adsorption was the main mechanism of the TBBPA kinetic adsorption process. The isothermal adsorption behaviour of TBBPA was well fitted by Freundlich model (R² 99.21%) than Langmuir model (R² 98.59%). The adsorption capacity for TBBPA is 34.13 mg/kg. The thermodynamic results revealed that the adsorption process of TBBPA by the sediment was a spontaneous endothermic reaction. The increase in pH and ionic strength inhibited the adsorption of sediments on TBBPA. With the increase in the humic acid concentration, the adsorption of TBBPA initially increased and subsequently decreased. Synchrotron radiation-Fourier transform infrared spectroscopy indicated that the adsorption mechanism of TBBPA on the surface of sediment was mainly π-π and hydrogen bonds. The obtained results are useful for understanding of TBBPA migration and transformation in river water bodies.

Vascular Response of Tetrabromobisphenol a in Rat Aorta: Calcium Channels Inhibition and Potassium Channels Activation

Tetrabromobisphenol A (TBBPA) is a flame retardant widely used to reduce flammability. It is an endocrine disruptor, and due to constant human exposure, some concerns have been raised regarding its impact on human health. Studies showed that TBBPA affects oxidative stress, cell proliferation and intracellular calcium levels. However, the vascular consequences of TBBPA exposure are still relatively unexplored. Hence, this work aimed to analyse TBBPA effects on rat aortic smooth muscle and its action mechanisms. Through an ex vivo approach, Wistar rat aortas were used in an organ bath to evaluate the vascular effect of TBBPA (0.01-100 μM). Additionally, TBBPA's mode of action was studied through calcium and potassium channel inhibitors. Resorting to in vitro studies, A7r5 cells were used to analyse L-Type voltage-gated calcium channel (VGCC) activity through the whole-cell configuration of the patch clamp technique, and the mRNA expression of proteins and ion channels involved in vascular contractility. The results showed vasorelaxation of rat aorta induced by TBBPA exposure, involving the inactivation of L-Type VGCC and activation of potassium channels, and the modulation of mRNA expression of L-type calcium and large-conductance calcium 1.1 and the BK_Ca 1.1 α- and β₁ -subunit channels, soluble guanylyl cyclase and protein Kinase G.

Towards a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny-part III: how is substance-mediated thyroid hormone imbalance in pregnant/lactating rats or their progeny related to neurodevelopmental effects?

This review investigated which patterns of thyroid- and brain-related effects are seen in rats upon gestational/lactational exposure to 14 substances causing thyroid hormone imbalance by four different modes-of-action (inhibition of thyroid peroxidase, sodium-iodide symporter and deiodinase activities, enhancement of thyroid hormone clearance) or to dietary iodine deficiency. Brain-related parameters included motor activity, cognitive function, acoustic startle response, hearing function, periventricular heterotopia, electrophysiology and brain gene expression. Specific modes-of-action were not related to specific patterns of brain-related effects. Based upon the rat data reviewed, maternal serum thyroid hormone levels do not show a causal relationship with statistically significant neurodevelopmental effects. Offspring serum thyroxine together with offspring serum triiodothyronine and thyroid stimulating hormone appear relevant to predict the likelihood for neurodevelopmental effects. Based upon the collated database, thresholds of ≥60%/≥50% offspring serum thyroxine reduction and ≥20% and statistically significant offspring serum triiodothyronine reduction indicate an increased likelihood for statistically significant neurodevelopmental effects; accuracies: 83% and 67% when excluding electrophysiology (and gene expression). Measurements of brain thyroid hormone levels are likely relevant, too. The extent of substance-mediated thyroid hormone imbalance appears more important than substance mode-of-action to predict neurodevelopmental impairment in rats. Pertinent research needs were identified, e.g. to determine whether the phenomenological offspring thyroid hormone thresholds are relevant for regulatory toxicity testing. The insight from this review shall be used to suggest a tiered testing strategy to determine whether gestational/lactational substance exposure may elicit thyroid hormone imbalance and potentially also neurodevelopmental effects.

Review of the environmental occurrence, analytical techniques, degradation and toxicity of TBBPA and its derivatives

BFRs (brominated flame retardants) are a class of compounds that are added to or applied to polymeric materials to avoid or reduce the spread of fire. Tetrabromobisphenol A (TBBPA) is one of the known BFR used many in industries today. Due to its wide application as an additive flame retardant in commodities, TBBPA has become a common indoor contaminant. Recent researches have raised concerns about the possible hazardous effect of exposure to TBBPA and its derivatives in humans and wildlife. This review gives a thorough assessment of the literature on TBBPA and its derivatives, as well as environmental levels and human exposure. Several analytical techniques/methods have been developed for sensitive and accurate analysis of TBBPA and its derivatives in different compartments. These chemicals have been detected in practically every environmental compartment globally, making them a ubiquitous pollutant. TBBPA may be subject to adsorption, biological degradation or photolysis, photolysis after being released into the environment. Treatment of TBBPA-containing waste, as well as manufacturing and usage regulations, can limit the release of these chemicals to the environment and the health hazards associated with its exposure. Several methods have been successfully employed for the treatment of TBBPA including but not limited to adsorption, ozonation, oxidation and anaerobic degradation. Previous studies have shown that TBBPA and its derivative cause a lot of toxic effects. Diet and dust ingestion and have been identified as the main routes of TBBPA exposure in the general population, according to human exposure studies. Toddlers are more vulnerable than adults to be exposed to indoor dust through inadvertent ingestion. Furthermore, TBBP-A exposure can occur during pregnancy and through breast milk. This review will go a long way in closing up the knowledge gap on the silent and over ignored deadly effects of TBBPA and its derivatives and their attendant consequences.

Environmental pollution, a hidden culprit for health issues

The environmental and health impacts from the massive discharge of chemicals and subsequent pollution have been gaining increasing public concern. The unintended exposure to different pollutants, such as heavy metals, air pollutants and organic chemicals, may cause diverse deleterious effects on human bodies, resulting in the incidence and progression of different diseases. The article reviewed the outbreak of environmental pollution-related public health emergencies, the epidemiological evidence on certain pollution-correlated health effects, and the pathological studies on specific pollutant exposure. By recalling the notable historical life-threatening disasters incurred by local chemical pollution, the damning evidence was presented to criminate certain pollutants as the main culprit for the given health issues. The epidemiological data on the prevalence of some common diseases revealed a variety of environmental pollutants to blame, such as endocrine-disrupting chemicals (EDCs), fine particulate matters (PMs) and heavy metals. The retrospection of toxicological studies provided illustrative clues for evaluating ambient pollutant-induced health risks. Overall, environmental pollution, as the hidden culprit, should answer for the increasing public health burden, and more efforts are highly encouraged to strive to explore the cause-and-effect relationships through extensive epidemiological and pathological studies.

Tetrabromobisphenol A: a neurotoxicant or not?

Although some regulatory agencies have claimed that consumer exposures to tetrabromobisphenol A (TBBPA) are not likely to cause adverse health effects in humans or the environment, the safety of tetrabromobisphenol A (TBBPA) has been questioned. Here, we summarize the literature concerning in vivo and in vitro neurotoxicity of TBBPA over the past decades. Most laboratory rodent studies reported that gavage administration of TBBPA at doses below 1000 mg/kg/day generally exerted no or limited effects on neuropathology and locomotor behaviors, but increased anxiety and auditory impairments were observed in several studies. In fish and amphibians, waterborne exposure to TBBPA was generally reported to disrupt neurodevelopment and lead to neurobehavioral alterations. Moreover, in vitro studies support the observations that TBBPA could exert neurotoxic effects in vertebrates. Thus, we suggest that TBBPA could have adverse effects on the nervous system in vertebrates. Given rapid excretion and low availability of TBBPA in laboratory rodents following single gavage administration, we speculate that single-daily gavage could result in an underestimation of the neurotoxic effects of TBBPA in rodents. Thus, we propose to employ multiple-daily administration routes (such as dermal, inhalation, and drinking water), to further assess the neurotoxic effects of TBBPA in mammals.

New insights into bisphenols induced obesity in zebrafish (Danio rerio): Activation of cannabinoid receptor CB1

Bisphenols (BPs), as widely used plastic additives, penetrate into our daily lives. BPs are considered endocrine disruptors and could potentially induce obesity. In this study, the effects of bisphenol A (BPA) and tetrabromobisphenol A (TBBPA) on food intake and lipid metabolism in zebrafish were determined. Moreover, the impact of BPA and TBBPA on the endocannabinoid system (ECS) of zebrafish was further explored by metabolomics, transcriptomics, and molecular docking analysis. Here we show that exposure to BPA and TBBPA at concentrations commonly found in the environment (20, 100, and 500 μg/L) led to hyperphagia and obesity in adult male zebrafish. Metabolomics and histopathological analysis revealed significant lipid accumulation in the liver of zebrafish exposed to BPA and TBBPA. The expression of ECS-related genes, in conjunction with RNA-Seq results, further indicated that BPA and TBBPA increased appetite and induced obesity by activating cannabinoid receptor type 1(CB1). Furthermore, molecular docking revealed that six representative BPs including BPA and TBBPA could bind to the CB1 receptor. Collectively, these findings indicate that CB1 may be a potential target for BPs to induce obesity.

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.

Developmental co-exposure of TBBPA and titanium dioxide nanoparticle induced behavioral deficits in larval zebrafish

Both tetrabromobisphenol A (TBBPA) and titanium dioxide nanoparticle (TiO₂ NP) have widespread commercial applications, resulting in their ubiquitous co-presence in the environment and biota. Although environmental chemicals exist as mixtures, toxicity studies are nearly always conducted with single chemicals. Few studies explore potential interactions of different chemical mixtures. In this study, we employ the sensitive developing nerve system in zebrafish to assess the neurotoxicity of TBBPA/TiO₂ NP mixtures. Specifically, zebrafish embryos were exposed to solvent control (0.1% DMSO), 2 μM TBBPA, 0.1 mg/L TiO₂ NP, and their mixture from 8 to 120 h post fertilization (hpf), and motor/social behavioral assessments were conducted on embryos/larvae at different developmental stages. Our results showed that TBBPA/TiO₂ NP single or co-exposures increased spontaneous movement, decreased touch response and swim speed, and affected social behaviors of light/dark preference, shoaling, mirror attack and social contact. In particular, many of these phenotypes were manifested with higher magnitude of changes from the mixture exposure. These behavioral deficits were also accompanied with increased cell death in olfactory region and neuromasts in the lateral line system, increased ROS in gallbladder, pancreas, liver, and intestine, as well as increased lipid peroxidation and decreased ATP levels in whole larval tissue homogenates. Further, genes coding for key cell apoptosis marker and antioxidant enzyme were significantly upregulated by these two chemicals, in particular to their mixture. Interestingly, the co-presence of TBBPA also increased the mean particle size of TiO₂ NP in the exposure solutions and the TiO₂ NP content in larval tissue. Together, our analysis suggests that TBBPA/TiO₂ NP induced behavioral changes may be due to physical accumulation of these two chemicals in the target organs, and TiO₂ NP may serve as carriers for increased accumulation of TBBPA. To conclude, we demonstrated that TBBPA/TiO₂ NP together cause increased bioaccumulation of TiO₂, and heightened responses in behavior, cell apoptosis and oxidative stress. Our findings also highlight the importance of toxicity assessment using chemical mixtures.

Sex differences in the auditory functions of rodents

BACKGROUND

In humans, it is well known that females have better hearing than males. The mechanism of this influence of sex on auditory function in humans is not well understood. Testing the hypothesis of underlying mechanisms often relies on preclinical research, a field in which sex bias still exists unconsciously. Rodents are popular research models in hearing, thus it is crucial to understand the sex differences in these rodent models when studying health and disease in humans.

OBJECTIVES

This review aims to summarize the existing sex differences in the auditory functions of rodent species including mouse, rat, Guinea pig, Mongolian gerbil, and chinchilla. In addition, a concise summary of the hearing characteristics and the advantages and the drawbacks of conducting auditory experiments in each rodent species is provided.

DESIGNS

Manuscripts were identified in PubMed and Ovid Medline for the queries "Rodent", "Sex Characteristics", and "Hearing or Auditory Function". Manuscripts were included if they were original research, written in English, and use rodents. The content of each manuscript was screened for the sex of the rodents and the discussion of sex-based results.

CONCLUSIONS

The sex differences in auditory function of rodents are prevalent and influenced by multiple factors including physiological mechanisms, sex-based anatomical variations, and stimuli from the external environment. Such differences may play a role in understanding and explaining sex differences in hearing of humans and need to be taken into consideration for developing clinical therapies aim to improve auditory performances.

Tetrabromobisphenol A (TBBPA): A controversial environmental pollutant

Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants and is extensively used in electronic equipment, furniture, plastics, and textiles. It is frequently detected in water, soil, air, and organisms, including humans, and has raised concerns in the scientific community regarding its potential adverse health effects. Human exposure to TBBPA is mainly via diet, respiration, and skin contact. Various in vivo and in vitro studies based on animal and cell models have demonstrated that TBBPA can induce multifaceted effects in cells and animals, and potentially exert hepatic, renal, neural, cardiac, and reproductive toxicities. Nevertheless, other reports have claimed that TBBPA might be a safe chemical. In this review, we re-evaluated most of the published TBBPA toxicological assessments with the goal of reaching a conclusion about its potential toxicity. We concluded that, although low TBBPA exposure levels and rapid metabolism in humans may signify that TBBPA is a safe chemical for the general population, particular attention should be paid to the potential effects of TBBPA on early developmental stages.

Synthesis and Toxicity of Halogenated Bisphenol Monosubstituted-Ethers: Establishing a Library for Potential Environmental Transformation Products of Emerging Contaminant

As an important branch of halogenated bisphenol compounds, the halogenated bisphenol monosubstituted-ether compounds have received a lot of attention in environmental health science because of their toxicity and variability. In this study, a synthetic method for bisphenol monosubstituted-ether byproduct libraries was developed. By using the versatile and efficient method, tetrachlorobisphenol A, tetrabromobisphenol A, and tetrabromobisphenol S monosubstituted alkyl-ether compounds were accessed in 39-82 % yield. Subsequently, the cytotoxicity of 27 compounds were screened using three different cell lines (HepG2, mouse primary astrocytes and Chang liver cells). Compound 2,6-dibromo-4-[3,5-dibromo-4-(2-hydroxyethoxy)benzene-1-sulfonyl]phenol was more toxic than other compounds in various cells, and the sensitivity of this compound to the normal hepatocytes and cancer cells was inconsistent. The compounds 2,6-dichloro-4-(2-{3,5-dichloro-4-[(prop-2-en-1-yl)oxy]phenyl}propan-2-yl)phenol and 2,6-dibromo-4-(2-{3,5-dibromo-4-[(prop-2-en-1-yl)oxy]phenyl}propan-2-yl)phenol were the most toxic to HepG2 cells, and most of the other compounds inhibited cell proliferation. Moreover, typical compounds were also reproductive and developmental toxic to zebrafish embryos at different concentrations. The synthetic byproduct libraries could be used as pure standard compounds and applied in research on environmental behavior and the transformation of halogenated flame retardants.

Enhanced adsorption of tetrabromobisphenol a (TBBPA) on cosmetic-derived plastic microbeads and combined effects on zebrafish

Microplastics (MPs) pollution and its potential environmental risks have drawn increasing concerns in recent years. Among which, microbeads in personal care and cosmetic products has becoming an emerging issue for their abundance as well as the knowledge gaps in their precise environmental behaviors in freshwater. The present study investigated the sorption process of tetrabromobisphenol A (TBBPA), the most widely applied and frequently encountered flame retardant in aquatic environments, on two sources of polyethylene (PE) particles (pristine PE particles and microbeads isolated from personal care and cosmetic products). Significantly enhanced adsorption capacity of microbeads was observed with up to 5-folds higher than the pristine PE particles. The sorption efficiency was also governed by solution pH, especially for the cosmetic-derived microbeads, indicating the strong adsorption of TBBPA on PE was dominated by both hydrophobic and electrostatic interactions. Additionally, combined effects on redox status of zebrafish were evaluated with two environmental relevant concentrations of PE particles (0.5 and 5 mg L^-1) using integrated biomarker response (IBR) index through a 14-d exposure. Co-exposure induced significant antioxidative stress than either PE or TBBPA alone when exposed to 0.5 mg L^-1 of MPs. After 7-d depuration, the IBR value for combination treatments [TBBPA + PE (L)] was 3-fold compared with that in MP-free groups, indicating the coexistence might exert a prolonged adverse effects on aquatic organisms. These results highlight the probability of risk from microbead pollution in freshwater, where toxic compounds can be adsorbed on microbeads in a considerable amount resulting in potential adverse effects towards aquatic organisms.

Sex-specific behavioral effects following developmental exposure to tetrabromobisphenol A (TBBPA) in Wistar rats

Tetrabromobisphenol A (TBBPA) has become a ubiquitous indoor contaminant due to its widespread use as an additive flame retardant in consumer products. Reported evidence of endocrine disruption and accumulation of TBBPA in brain tissue has raised concerns regarding its potential effects on neurodevelopment and behavior. The goal of the present study was to examine the impact of developmental TBBPA exposure, across a wide range of doses, on sexually dimorphic non-reproductive behaviors in male and female Wistar rats. We first ran a pilot study using a single TBBPA dose hypothesized to produce behavioral effects. Wistar rat dams were orally exposed using cookie treats to 0 or 0.1 mg TBBPA/kg bw daily from gestational day (GD) 9 to postnatal day (PND) 21 to assess offspring (both sexes) activity and anxiety-related behaviors. Significant effects were evident in females, with exposure increasing activity levels. Thus, this dose was used as the lowest TBBPA dose in a subsequent, larger study conducted as part of a comprehensive assessment of TBBPA toxicity. Animals were exposed to 0, 0.1, 25, or 250 mg TBBPA/kg bw daily by oral gavage starting on GD 6 through PND 90 (dosed dams GD 6 - PND 21, dosed offspring PND 22 - PND 90). Significant behavioral findings were observed for male offspring, with increased anxiety-like behavior as the primary phenotype. These findings demonstrate that exposure to environmental contaminants, like TBBPA, can have sex-specific effects on behavior highlighting the vulnerability of the developing brain.

Absence of neurotoxicity and lack of neurobehavioral consequences due to exposure to tetrabromobisphenol A (TBBPA) exposure in humans, animals and zebrafish

Tetrabromobisphenol A (2,2',6,6'-tetrabromo-4,4'-isopropylidenediphenol, CAS no. 79-94-7) (TBBPA) is an effective brominated flame retardant present in many consumer products whose effectiveness is attributable to its ability to retard flames and consequently save human lives. Toxicokinetic studies revealed that TBBPA when absorbed via the gastrointestinal tract is rapidly metabolized to glucuronide or sulfate metabolites which are rapidly eliminated by the kidney. TBBPA does not accumulate in the body and there is no evidence that the parent compound is present in the brain. Although this brominated flame retardant was detected in human breast milk and serum, there was no evidence that TBBPA reached the brain in in vivo animal studies as reflected by the absence of neuropathological, neurotoxic, or behavioral alterations indicating that the central nervous system is not a target tissue. These animal investigations were further supported by use of the larval/embryo observations that TBBPA did not produce behavioral changes in a larval/embryo zebrafish a model of chemical-induced neurotoxicity. Although some protein expressions were increased, deceased or not affected in the blood-brain barrier indicating no evidence that TBBPA entered the brain, the changes were contradictory, or gender related, and behavior was not affected supporting that this compound was not neurotoxic. Taken together, TBBPA does not appear to target the brain and is not considered as a neurotoxicant.

Typical halogenated flame retardants affect human neural stem cell gene expression during proliferation and differentiation via glycogen synthase kinase 3 beta and T3 signaling

2',2',4,4'-tetrabromo diphenyl ether (BDE-47), one of the most abundant congeners of commercial pentaBDE utilized as flame retardants, has been phased out of production due to its potential neural toxicity and endocrine disrupting activities, and yet still present in the environment. Several alternatives to BDE-47, including tetrabromobisphenol A (TBBPA), tetrabromobisphenol S (TBBPS), tetrachlorobisphenol A (TCBPA) and decabromodiphenyl ether (BDE-209), are presently employed without restrictions and their potential toxic effects on human neural development are still unclear. In this study, we utilized a human neural stem cell (hNSC)-based system to evaluate the potential developmental neurotoxic effects of the above-mentioned five chemicals, at environment and human exposure relevant concentrations. We found that those compounds slightly altered the expression of hNSC identity markers (SOX2, SOX3 and NES), without impairing cell viability or proliferation, in part by either modulating glycogen synthase kinase 3 beta (GSK3β) signaling (TBBPS, TCBPA and BDE-47), and slightly disturbing the NOTCH pathway (TBBPA, TBBPS and TCBPA). Moreover, the five chemicals seemed to alter hNSC differentiation by perturbing triiodothyronine (T3) cellular signaling. Thus, our findings suggest that the five compounds, especially TBBPS, TCBPA, and BDE-47, may affect hNSC self-renewal and differentiation abilities and potentially elicit neural developmental toxicity.

Tetrabromobisphenol A: Disposition, kinetics and toxicity in animals and humans

Tetrabromobisphenol A (TBBPA) is a nonregulated brominated flame retardant with a high production volume, and it is applied in a wide variety of consumer products. TBBPA is ubiquitous in abiotic matrices, wildlife and humans around the world. This paper critically reviews the published scientific data concerning the disposition, metabolism or kinetics and toxicity of TBBPA in animals and humans. TBBPA is rapidly absorbed and widely distributed among tissues, and is excreted primarily in the feces. In rats, TBBPA and its metabolites have limited systemic bioavailability. TBBPA has been detected in human milk in the general population. It is available to both the developing fetus and the nursing pups following maternal exposure. It has been suggested that TBBPA causes acute toxicity, endocrine disruptor activity, immunotoxicity, neurotoxicity, nephrotoxicity, and hepatotoxicity in animals. Cell-based assays have shown that TBBPA can induce reactive oxygen species in a concentration-dependent manner, and it promotes the production of inflammatory factors such as TNF α, IL-6, and IL-8. Cells exposed to high levels of TBBPA exhibit seriously injured mitochondria and a dilated smooth endoplasmic reticulum. This review will enhance the understanding of the potential risks of TBBPA exposure to ecological and human health.

Occurrence of two novel triazine-based flame retardants in an E-waste recycling area in South China: Implication for human exposure

The recent increase in the use of alternative flame retardants (FRs) in consumer products has led to emerging contaminants in the environment. Identification of novel FRs is urgently needed because the potential threat posed by these chemicals has provoked considerable attention, but the details of the threat are not yet widely understood. In this study, two novel triazine-based FRs, tris(2,3-dibromopropyl) isocyanurate (TDBP-TAZTO) and 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ), were identified in dust samples from an e-waste recycling area in China. Two legacy FRs, namely, tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCDD), were also analyzed for comparison. The mean level of TDBP-TAZTO in the e-waste dust samples was found to be much higher (2060 ng g^-1) than that of HBCDD (526 ng g^-1), while the mean level of TTBP-TAZ in residential dust samples was moderately higher (119 ng g^-1) than that of HBCDD (35.7 ng g^-1). A comparison of the TDBP-TAZTO and TTBP-TAZ concentrations with those of other alternative and legacy FRs indicated that TDBP-TAZTO is a major FR that is currently used in China. The estimated daily intake of TDBP-TAZTO via dust ingestion for occupational workers was much higher than that of HBCDD and was also much higher than for local adults and children. Exposure to TDBP-TAZTO poses a potentially high risk to the health of the local population, especially for the occupational workers, when the multicomponent chemical 'cocktail' effects are taken into account. More investigations on the environmental behaviors and risk factors of TDBP-TAZTO and TTBP-TAZ in various environmental matrices, as well as their toxicological effects, should be performed in the future.

Embryoid body-based RNA-seq analyses reveal a potential TBBPA multifaceted developmental toxicity

The frequent detection of tetrabromobisphenol A (TBBPA) in the human body, especially in umbilical cord serum and breast milk, has raised concerns about TBBPA potential effects on embryonic development. The differentiation of embryonic stem cells (ESCs) in vitro can serve as a model for the early stages of embryonic development. In this study, we differentiated mouse ESCs via 3D aggregates called embryoid bodies in presence of environment and human relevant TBPPA concentrations for 28 days. We collected samples at different time points and analyzed TBBPA-dependent global gene expression changes by RNA-seq. Our analyses revealed a potential TBBPA multifaceted developmental toxicity with effects on the nervous and cardiac/skeletal muscle systems. Mechanistically, our findings suggest TBBPA endocrine disrupting activities in part via prolactin signaling.

Rapid and simultaneous analysis of tetrabromobisphenol A and hexabromocyclododecane in water by direct immersion solid phase microextraction: Uniform design to explore factors

Direct immersion solid phase microextraction (DI-SPME) coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS) is of significant research interest because of its low solvent consumption, simple design, and efficient, sensitive, fast performance. In this work, a combination of these two methods (DI-SPME-LC-MS) for the determination of tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) in water was developed. Important factors, which included temperature, stirring rate, salt concentration, pH value and adsorption time, were evaluated in for the optimization of solid phase microextraction (SPME) method. The method was developed using spiked natural waters in a concentration range of 0.1-10 ng mL^-1, and showed notable linearity with regression coefficients ranging between 0.992 and 0.999. The limits of detection varied from 0.01 to 0.04 ng mL^-1 (at S/N = 3) and relative standard deviation (RSD < 11%) were obtained showing that the precision of the method was reliable. Recoveries were in relatively high levels for both analytes and ranged from 88% to 108%. Moreover, in comparison with the performance time of traditional sample pretreatment methods such as solid-phase extraction (SPE), accelerated solvent extraction (ASE), and liquid-liquid extraction (LLE), DI-SPME-LC-MS takes only approximately 35 min to perform. The optimized method was successfully applied for monitoring concentrations of TBBPA and HBCD in water.

Ultrafine Bi3TaO7 Nanodot-Decorated V, N Codoped TiO2 Nanoblocks for Visible-Light Photocatalytic Activity: Interfacial Effect and Mechanism Insight

Bi₃TaO₇ is a potential photocatalyst because of its high chemical stability, defective fluorite-type structure, and superior mobility of photoinduced holes. However, few studies have focused on the interfacial effects of Bi₃TaO₇-based photocatalysts. In this work, 0D Bi₃TaO₇ nanodot-hybridized 3D V and N codoped TiO₂ nanoblock (B/VNT) composites were first synthesized for the photocatalytic removal of oxytetracycline hydrochloride, 2,4,6-trichlorophenol, and tetrabromobisphenol A. The fabricated B/VNT had a photocatalytic performance superior to that of pristine components, and probable degradation pathways were proposed according to the primary intermediates identified by a gas chromatography-mass spectrometer. Interestingly, on B/VNT, the transfer of interfacial electrons was observed from V/N-TiO₂ to Bi₃TaO₇, and the formed built-in electronic field led to a direct Z-scheme structure, rather than type II, as confirmed by the generated ^•OH and ^•O₂^- radicals and band structures from the density functional theory calculation. Therefore, the strong interfacial electronic interaction on the B/VNT was significant, which drove faster photogenerated charge transfer, more visible-light adsorption, and active ^•OH and ^•O₂^- generation, thus improving the photocatalytic activity.

Environmental ototoxicants, a potential new class of chemical stressors

Hearing loss is an injury that can develop over time, and people may not even be aware of it until it becomes a severe disability. Ototoxicants are substances that may damage the inner ear by either affecting the structures in the ear itself or by affecting the nervous system. We have examined the possibility that ototoxicants may present a health hazard in association with environmental exposures, adding to existing knowledge of their proven hazards under medical therapeutic conditions or occupational activities. In addition to the already described human environmental ototoxicants, mainly organochlorines such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE), hexachlorocyclohexane (HCH) and hexachlorobenzene (HCB), we have examined the ubiquitous chemical stressors phthalates, bisphenol A/S/F/, PFCs, flame retardants (FRs) and cadmium for potential ototoxic properties, both as single substances or as chemical mixtures. Our literature review confirmed that these chemicals may disturb thyroid hormones homeostasis, activate aryl hydrocarbon receptor (AhR), and induce oxidative stress, which in turn may initiate a chain of events resulting in impairment of cochlea and hearing loss. With regard to auditory plasticity, diagnostics of a mixture of effects of ototoxicants, potential interactions of chemical and physical agents with effects on hearing, parallel deterioration of hearing due to chemical exposures and ageing, metabolic diseases or obesity, even using specific methods as brainstem auditory evoked potentials (BAEP) or otoacoustic emissions (OAEs) registration, may be difficult, and establishment of concentration-response relationships problematic. This paper suggests the establishment of a class of environmental oxotoxicants next to the established classes of occupational and drug ototoxicants. This will help to properly manage risks associated with human exposure to chemical stressors with ototoxic properties and adequate regulatory measures.

Emissions of selected brominated flame retardants from consumer materials: the effects of content, temperature, and timescale

The ubiquitous presence of brominated flame retardants (BFRs) in indoor air, dust, and even in human tissue could be attributed to their emissions from BFR-containing products. Nevertheless, the emission behavior of BFRs, especially novel BFRs from consumer materials, to the indoor environment has still not been well understood. To evaluate the effects of chemical content, temperature, and time on the emissions of BFRs, we used a batch of small glass chambers to conduct emission tests on carpet, computer casings, sound insulation, circuit boards, decorative laminate, and PVC floors at temperatures from 20 to 80 °C, as well as different emission times of up to 35 days. Seven BFRs were extracted from the tested materials with contents ranging from 50 to 35,803 μg g^-1, and four BFRs were detected with emission rates between 5.9 and 418 pg g^-1 h^-1 at room temperature (20 °C); 1,2,5,6,9,10-hexabromocyclododecane (HBCD) was considered to be the dominant compound, which was found in and could be emitted from all of the tested materials. Emission rates are significantly and positively correlated with both the contents of tested materials and the elevated temperature. These results indicate that BFR-containing products have the potential to be a major source of indoor contamination.

TBBPA and Its Alternatives Disturb the Early Stages of Neural Development by Interfering with the NOTCH and WNT Pathways

Tetrabromobisphenol A (TBBPA), as well as its alternatives Tetrabromobisphenol S (TBBPS) and Tetrachlorobisphenol A (TCBPA), are widely used halogenated flame retardants. Their high detection rates in human breast milk and umbilical cord serum have raised wide concerns about their adverse effects on human fetal development. In this study, we evaluated the cytotoxicity and neural developmental toxicity of TBBPA, TBBPS, and TCBPA with a mouse embryonic stem cell (mESC) system, at human body fluid and environmental relevant doses. All the three compounds showed similar trends in their cytotoxic effects. However, while TBBPA and TBBPS stimulated ESC neural differentiation, TCBPA significantly inhibited neurogenesis. Mechanistically, we demonstrated that, as far as the NOTCH (positive regulator) and WNT (negative regulator) pathways were concerned, TBBPA only partially and slightly disturbed them, whereas TBBPS significantly inhibited the WNT pathway, and TCBPA down-regulated the expression of NOTCH effectors but increased the WNT signaling, actions which both inhibited neural specification. In conclusion, our findings suggest that TBBPS and TCBPA may not be safe alternatives to TBBPA, and their toxicity need to be comprehensively evaluated.

Thyroid-disrupting chemicals and brain development: an update

This review covers recent findings on the main categories of thyroid hormone-disrupting chemicals and their effects on brain development. We draw mostly on epidemiological and experimental data published in the last decade. For each chemical class considered, we deal with not only the thyroid hormone-disrupting effects but also briefly mention the main mechanisms by which the same chemicals could modify estrogen and/or androgen signalling, thereby exacerbating adverse effects on endocrine-dependent developmental programmes. Further, we emphasize recent data showing how maternal thyroid hormone signalling during early pregnancy affects not only offspring IQ, but also neurodevelopmental disease risk. These recent findings add to established knowledge on the crucial importance of iodine and thyroid hormone for optimal brain development. We propose that prenatal exposure to mixtures of thyroid hormone-disrupting chemicals provides a plausible biological mechanism contributing to current increases in the incidence of neurodevelopmental disease and IQ loss.

Altered expression of genes involved in programmed cell death in primary cultured rat cerebellar granule cells acutely challenged with tetrabromobisphenol A

In the present study, primary cultures of rat cerebellar granule cells (CGC) and the RT² Profiler PCR array were used to examine the effect of acutely applied brominated flame retardant tetrabromobisphenol A (TBBPA) on the expression of 84 genes related to the main modes of programmed cell death. CGC, at the 7th day of culture, were exposed to 10 or 25μM TBBPA for 30min. Then, 3, 6, and 24h later, the viability of the cells was examined by the staining with propidium iodide (PI) or using the calcein/ethidium homodimer (CA/ET) live/dead kit, and RNA was extracted for the evaluation of gene expression by RT-PCR. At 3, 6 and 24h after the treatment, the number of viable neurons decreased, according to the PI staining method, to 75%, 58% and 41%, respectively, and with the CA/ET method to 65%, 58% and 28%, respectively. In CGC analyzed 3h after the treatment with 25μM TBBPA or 6h after 10μM TBBPA, the only change in the gene expression was a reduction in the expression of Tnf, which is associated with autophagy and may activate some pro-apoptotic proteins. Six hours after 25μM TBBPA, only 2 genes were over-expressed, a pro-apoptotic Tnfrsf10b and Irgm, which is related to autophagy, and the genes that were suppressed included the anti-apoptotic gene Xiap, the necrosis-related Commd4, pro-apoptotic Abl1, 5 genes involved in autophagy (App, Atg3, Mapk8, Pten, and Snca) and 2 genes that participate in two metabolic pathways: Atp6v1g2 (pro-apoptotic and necrosis) and Tnf (pro-apoptotic, autophagy). Autophagy-related Snca and Tnf remained under-expressed 24h after treatment with 25μM TBBPA, which was accompanied by the over-expression of the pro-apoptotic Casp6, the anti-apoptotic Birc3, 2 genes related to autophagy (Htt and Irgm) and 2 genes (Fas and Tp53) that are involved in both apoptosis (pro-apoptotic) and autophagy. These results show a complex pattern of TBBPA-evoked changes in the expression of the genes involved in the programmed neuronal death, indicating no induction of programmed necrosis, an early suppression of the autophagy and anti-apoptotic genes, followed by a delayed activation of genes associated with apoptosis.

In vivo assessment of dermal adhesion, penetration, and bioavailability of tetrabromobisphenol A

Individuals are exposed to brominated flame retardants (BFRs), including tetrabromobisphenol A (TBBPA), on a daily basis because of their widespread usage. These compounds may have adverse effects on human health. In the present study, dermal absorption experiments were conducted in vivo to predict the adhesion, penetration, and bioavailability of TBBPA. TBBPA was administered to Wistar rats for 6 h by repeated dermal exposure at doses of 20, 60, 200, and 600 mg of TBBPA per kg of body weight (bw). The skin adhesion coefficient (AC) was calculated using a difference-value method and ranged from 0.12 to 3.25 mg/cm² and 0.1 to 2.56 mg/cm² for the male and female rats, respectively. The adhesion rate was 70.92%. According to Fick's first law of diffusion, the diffusion constant (D) was 1.4 × 10^-4 cm²/h and the permeation coefficient (K_p) was 1.26 × 10^-5 cm/h for TBBPA. TBBPA levels in the blood, urine, and feces of the male rats were significantly higher than those in the female rats. The dermal bioavailability of TBBPA was 24.71% for male rats and 20.05% for female rats 24 h after exposure.

Excretion characteristics of tetrabromobisphenol-A in Wistar rats following mouth and nose inhalation exposure

Tetrabromobisphenol-A (TBBPA), a brominated flame retardant with the largest production volume worldwide, is employed as a reactive and additive flame retardant, and also as an intermediate in the production of other retardants. The constant release of TBBPA into the environment has attracted increasing attention to its potent health effects. To date, the vast majority of health-related research on TBBPA has focused on oral exposure. This study aims to explore the excretion characteristics of TBBPA in living organisms following inhalation exposure. An inhalation exposure system was established in which the experimental animal model was exposed to inhalable particles (diameter < 10 μm) of TBBPA. The TBBPA aerosol doses used were 12.9, 54.6, 121.6, and 455.0 mg/m³ according to tuning system parameters. Following 14 d (2 h/d) of repeated inhalational exposure, the primary route of elimination was in feces for all exposed groups, and the values showed a significant positive linear relationship with exposure dose. In contrast, the elimination amount in urine was less than 0.4% of the inhaled dose. Trace levels of TBBPA (less than 0.1% of the inhaled dose) were also detected in serum, with amounts varying from 0 to 844 ng (per rat) among all groups.

TBBPA exposure during a sensitive developmental window produces neurobehavioral changes in larval zebrafish

Tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardants (BFRs), is a ubiquitous contaminant in the environment and in the human body. This study demonstrated that zebrafish embryos exposed to TBBPA during a sensitive window of 8-48 h post-fertilization (hpf) displayed morphological malformations and mortality. Zebrafish exposed exclusively between 48 and 96 hpf were phenotypically normal. TBBPA was efficiently absorbed and accumulated in zebrafish embryos, but was eliminated quickly when the exposure solution was removed. Larval behavior assays conducted at 120 hpf indicated that exposure to 5 μM TBBPA from 8 to 48 hpf produced larvae with significantly lower average activity and speed of movement in the normal condition than in those exposed from 48 to 96 hpf. Specifically, 8-48 hpf-exposed larvae spent significantly less time in both activity bursts and gross movements compared to control or 48-96 hpf exposed larvae. Consistent with the motor deficits, TBBPA induced apoptotic cell death, delayed cranial motor neuron development, inhibited primary motor neuron development and loosed muscle fiber during the early developmental stages. To further explore TBBPA-induced developmental and neurobehavioral toxicity, RNA-Seq analysis was used to identify early transcriptional changes following TBBPA exposure. In total, 1969 transcripts were significantly differentially expressed (P < 0.05, FDR < 0.05, 1.5-FC) upon TBBPA exposure. Functional and pathway analysis of the TBBPA transcriptional profile identified biological processes involved in nerve development, muscle filament sliding and contraction, and extracellular matrix disassembly and organization changed significantly. In addition, TBBPA also led to an elevation in the expression of genes encoding uridine diphosphate glucuronyl transferases (ugt), which could affect thyroxine (T4) metabolism and subsequently lead to neurobehavioral changes. In summary, TBBPA exposure during a narrow, sensitive developmental window perturbs various molecular pathways and results in neurobehavioral deficits in zebrafish.