A mixture of the novel brominated flame retardants TBPH and TBB affects fecundity and transcript profiles of the HPGL-axis in Japanese medaka

Aggravated visual toxicity in zebrafish larvae upon co-exposure to titanium dioxide nanoparticles and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate

The bioavailability and toxicity of organic pollutants in aquatic organisms can be largely affected by the co-existed nanoparticles. However, the impacts of such combined exposure on the visual system remain largely unknown. Here, we systematically investigated the visual toxicity in zebrafish larvae after single or joint exposure to titanium dioxide nanoparticles (n-TiO2) and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) at environmentally relevant levels. Molecular dynamics simulations revealed the enhanced transmembrane capability of the complex than the individual, which accounted for the increased bioavailability of both TBPH and n-TiO2 when combined exposure to zebrafish. Transcriptome analysis showed that co-exposure to n-TiO2 and TBPH interfered with molecular pathways related to eye lens structure and sensory perception of zebrafish. Particularly, n-TiO2 or TBPH significantly suppressed the expression of βB1-crystallin and rhodopsin in zebrafish retina and lens, which was further enhanced after co-exposure. Moreover, we detected disorganized retinal histology, stunted lens development and significant visual behavioral changes of zebrafish under co-exposure condition. The overall results suggest that combined exposure to water borne n-TiO2 and TBPH increased their bioavailability, resulted in severer damage to optic nerve development and ultimately abnormal visual behavior patterns, highlighting the higher potential health risks of co-exposure to aquatic vertebrates.

Bis(2-ethylhexyl)-tetrabromophthalate Poses a Higher Exposure Risk and Induces Gender-Specific Metabolic Disruptions in Zebrafish Liver

Bis(2-ethylhexyl)-tetrabromophthalate (TBPH), a typical novel brominated flame retardant, has been ubiquitously identified in various environmental and biotic media. Consequently, there is an urgent need for precise risk assessment based on a comprehensive understanding of internal exposure and the corresponding toxic effects on specific tissues. In this study, we first investigated the toxicokinetic characteristics of TBPH in different tissues using the classical pseudo-first-order toxicokinetic model. We found that TBPH was prone to accumulate in the liver rather than in the gonad, brain, and muscle of both female and male zebrafish, highlighting a higher internal exposure risk for the liver. Furthermore, long-term exposure to TBPH at environmentally relevant concentrations led to increased visceral fat accumulation, signaling potential abnormal liver function. Hepatic transcriptome analysis predominantly implicated glycolipid metabolism pathways. However, alterations in the profile of associated genes and biochemical indicators revealed gender-specific responses following TBPH exposure. Besides, histopathological observations as well as the inflammatory response in the liver confirmed the development of nonalcoholic fatty liver disease, particularly in male zebrafish. Altogether, our findings highlight a higher internal exposure risk for the liver, enhancing our understanding of the gender-specific metabolic-disrupting potential associated with TBPH exposure.

Integrated Studies on Male Reproductive Toxicity of Bis(2-ethylhexyl)-tetrabromophthalate: in Silico, in Vitro, ex Vivo, and in Vivo

Bis(2-ethylhexyl)tetrabromophthalate (TBPH) has been widely detected in the environment and organisms; thus, its toxic effects on male reproduction were systematically studied. First, we found that TBPH can stably bind to the androgen receptor (AR) based on in silico molecular docking results and observed an antagonistic activity, but not agonistic activity, on the AR signaling pathway using a constructed AR-GRIP1 yeast assay. Subsequently, we validated the adverse effects on male germ cells by observing inhibited androgen production and proliferation in Leydig cells upon in vitro exposure and affected general motility and motive tracks of zebrafish sperm upon ex vivo exposure. Finally, the in vivo reproductive toxicity was demonstrated in male zebrafish by reduced mating behavior in F0 generation when paired with unexposed females and abnormal development of their offspring. In addition, reduced sperm motility and impaired germ cells in male zebrafish were also observed, which may be related to the disturbed homeostasis of sex hormones. Notably, the specifically suppressed AR in the brain provides further evidence for the antagonistic effects as above-mentioned. These results confirmed that TBPH affected male reproduction through a classical nuclear receptor-mediated pathway, which would be helpful for assessing the ecological and health risks of TBPH.

Computational Risk Assessment of Persistence, Bioaccumulation, and Toxicity of Novel Flame-Retardant Chemicals

Novel brominated flame retardants (NBFRs) have emerged as chemicals of environmental concern, as they have been widely used as an alternative to polybrominated diphenyl ethers (PBDEs). Considering the similar structural features of NBFRs and PBDEs necessitates a comprehensive investigation to understand the physicochemical relationships of these compounds and their ability to alter biological functions. In this study, we investigated the persistent nature of NBFRs in terms of thyroid-disrupting potential by understanding the structure-stability aspects using density functional theory (DFT)-based reactivity parameters and interactions via molecular docking and molecular dynamics (MD) simulations. The results indicate that the DFT-based stability descriptor (chemical hardness) is associated with the persistent nature of NBFRs. The computed molecular interaction profile revealed prominent interactions between thyroid receptor-β (TR-β) and NBFRs. Stable trajectory and interactions with TR-β were obtained with ATE, p-TBX, PBT, PBEB, and TBBPA-DBPE during 100 ns of MD simulation. The results of these studies have suggested that the presence of a higher number of halogenated atoms increases the stability vis-à-vis the persistence and endocrine disruption potential of NBFRs.

Multi-process regulation of novel brominated flame retardants: Environmentally friendly substitute design, screening and environmental risk regulation

Novel brominated flame retardants (NBFRs), one of the most widely used synthetic flame-retardant materials, have been considered as a new group of pollutants that potentially affect human health. To overcome the adverse effects of NBFRs, a systematic approach for molecular design, screening, and performance evaluation was developed to generate environmentally friendly NBFR derivatives with unaltered functionality. In the present study, the features of NBFRs (long-distance migration, biotoxicity, bioenrichment, and environmental persistence) were determined and characterized by the multifactor comprehensive characterization method with equal weight addition, and the similarity index analysis (CoMSIA) model was constructed. Based on the three-dimensional equipotential diagram of the target molecule 2-ethylhexyl tetrabromobenzoic acid (TBB), 23 TBB derivatives were designed. Of these, 22 derivatives with decreased environmental impact and unaltered functional properties (i.e., flame retardancy and stability) were selected using 3D-QSAR models and density functional theory methods. The health risks of these derivatives to humans were assessed by toxicokinetic analysis; the results narrowed down the number of candidates to three (Derivative-7, Derivative-10, and Derivative-15). The environmental impact of these candidates was further evaluated and regulated in the real-world environment by using molecular dynamics simulation assisted by the Taguchi experimental design method. The relationship between the binding effects and the nonbonding interaction resultant force (TBB derivatives-receptor proteins) was also studied, and it was found that the larger the modulus of the binding force, the stronger the binding ability of the two. This finding indicated that the environmental impact of the designed NBFR derivatives was decreased. The present study aimed to provide a new idea and method for designing NBFR substitutes and to provide theoretical support for restraining the potential environmental risks of NBFRs.

Skeletal effects following developmental flame-retardant exposure are specific to sex and chemical class in the adult Wistar rat

Introduction: Accumulating evidence reveals that endocrine disrupting chemicals (EDCs) can disrupt aspects of metabolic programming, suggesting that skeletal development may be at risk, a possibility that is rarely examined. The commercial flame retardant (FR) mixture, Firemaster 550 (FM 550), has repeatedly been shown to negatively influence metabolic programming, raising concerns that skeletal integrity may consequently be impaired. We have previously shown that gestational and lactational exposure to 1,000 µg FM 550 negatively affected sex-specific skeletal traits in male, but not female, rats assessed at 6 months of age. Whether this outcome is primarily driven by the brominated (BFR) or organophosphate ester (OPFR) portions of the mixture or the effects persist to older ages is unknown. Materials and methods: To address this, in the present study, dams were orally exposed throughout gestation and lactation to either 1,000 μg BFR, 1,000 µg OPFR, or 2,000 µg FM 550. Offspring (n = 8/sex/exposure) were weaned at PND 21 and assessed for femoral cortical and trabecular bone parameters at 8 months of age by high-resolution X-ray micro-computed tomography (micro-CT). Serum levels of serotonin, osteocalcin, alkaline phosphatase, and calcium were quantified. Results: FM 550 affected both sexes, but the females were more appreciably impacted by the OPFRs, while the males were more vulnerable to the BFRs. Conclusion: Although sex specificity was expected due to the sexual dimorphic nature of skeletal physiology, the mechanisms accounting for the male- and female-specific phenotypes remain to be determined. Future work aims to clarify these unresolved issues.

Chronic diflubenzuron exposure causes reproductive toxic effects in female marine medaka (Oryzias melastigma)

Diflubenzuron, an insecticide commonly used in marine fish farming, has been detected in various marine environments. However, its potential impact on marine fish remains largely unknown. This study investigated the reproductive toxicity of chronic diflubenzuron exposure in female marine medaka (Oryzias melastigma). Marine medaka were exposed continuously to environmentally relevant concentrations of diflubenzuron (0.1, 1, and 10 μg/L) or a solvent control from the fertilized egg to adulthood. In exposed female marine medaka, the gonadosomatic index (GSI) and the number of laid eggs were significantly reduced. Moreover, diflubenzuron-exposed female marine medaka showed altered ovarian histopathology, with an increased relative proportion of immature oocytes and atretic follicles and a decreased relative proportion of mature oocytes. Maternal exposure to diflubenzuron also inhibited the development of the F1 generation, significantly reducing the hatching rate of F1 embryos and significantly increasing the malformation rate of F1 larvae. Furthermore, changes in hormone levels and expression of genes along the hypothalamus-pituitary-gonad-liver (HPGL) axis were observed, which may be the fundamental reason for all the reproductive toxic effects mentioned above. These results provide new insights into the impact of diflubenzuron on the female marine medaka reproductive system and underscore the importance of investigating the potential environmental risks of diflubenzuron in the marine environment.

Integrated assessment of endocrine disrupting potential of four novel brominated flame retardants

Novel brominated flame retardants (NBFRs) have emerged as alternatives to the legacy BFRs due to BFRs' persistence, bioaccumulation and evidence of adverse health effects. The increasing production of NBFRs has led to the frequent detection in environmental media and even in organisms. Thus the potential health risks of these novel NBFRs need to be taken into account. Herein, the endocrine disrupting effects of the four NBFRs (α/β-TBCO, PBEB, EHTBB and BEHTBP) were evaluated by constructing an estrogen receptor (ERα), glucocorticoid receptor (GR), and mineralocorticoid receptor (MR) mediated dual-luciferase reporter gene assays on the CHO cells, in combination with steroid experiments on the H295R cells and molecular docking. The results revealed that α/β-TBCO, PBEB and EHTBB induced anti-estrogenic activity at certain concentrations while none of the four NBFRs was agonistic to ERα. For reporter gene assay, only PBEB exhibited GR antagonistic effects. Notably, none of the four NBFRs possess neither agonistic nor antagonistic activity of MR. The molecular docking results were generally consistent with the reporter gene assay, which showed the different binding affinities between NBFRs and the receptors. For steroidogenesis, α/β-TBCO, PBEB, and EHTBB all upregulated genes encoding for steroid synthesis enzymes, including 17βHSD, CYP11B1 and CYP17. Altogether, the data clarified that NBFRs may pose risks of endocrine disruption.

FireMaster® 550 (FM 550) exposure during the perinatal period impacts partner preference behavior and nucleus accumbens core medium spiny neuron electrophysiology in adult male and female prairie voles, Microtus ochrogaster

One of the most widely used flame retardant (FR) mixtures in household products is Firemaster 550 (FM 550). FM 550 leaches from items such as foam-based furniture and infant products, resulting in contamination of the household environment and biota. Previous studies indicate sex-specific behavioral deficits in rodents and zebrafish in response to developmental FM 550 exposure. These deficits include impacts on social and attachment behaviors in a prosocial rodent: the prairie vole (Microtus ochrogaster). The prairie vole is a laboratory-acclimated rodent that exhibits spontaneous attachment behaviors including pair bonding. Here we extend previous work by addressing how developmental exposure to FM 550 impacts pair bonding strength via an extended-time partner preference test, as well as neuron electrophysiological properties in a region implicated in pair bond behavior, the nucleus accumbens (NAcc) core. Dams were exposed to vehicle or 1000 μg of FM 550 via subcutaneous injections throughout gestation, and female and male pups were directly exposed beginning the day after birth until weaning. Pair bond behavior of adult female and male offspring was assessed using a three hour-long partner preference test. Afterwards, acute brain slices of the NAcc core were produced and medium spiny neuron electrophysiological attributes recorded via whole cell patch-clamp. Behavioral impacts were sex-specific. Partner preference behavior was increased in exposed females but decreased in exposed males. Electrophysiological impacts were similar between sexes and specific to attributes related to input resistance. Input resistance was decreased in neurons recorded from both sexes exposed to FM 550 compared to vehicle. This study supports the hypothesis that developmental exposure to FM 550 impacts attachment behaviors and demonstrates a novel FM 550 effect on neural electrophysiology.

New understanding of novel brominated flame retardants (NBFRs): Neuro(endocrine) toxicity

Traditional brominated flame retardants (BFRs) negatively affect the environment and human health, especially in the sensitive (developing) nervous system. Considering the physicochemical similarities between novel brominated flame retardants (NBFRs) and BFRs, more and more evidence reveals the neurotoxic effects of NBFRs. We reviewed the neuro(endocrine) toxic effects of NBFRs in vivo and in vitro and discussed their action mechanisms based on the available information. The neurotoxic potential of NBFRs has been demonstrated through direct neurotoxicity and disruption of the neuroendocrine system, with adverse effects on neurobehavioral and reproductive development. Mechanistic studies have shown that the impact of NBFRs is related to the complex interaction of neural and endocrine signals. From disrupting the gender differentiation of the brain, altering serum thyroid/sex hormone levels, gene/protein expression, and so on, to interfere with the feedback effect between different levels of the HPG/HPT axis. In this paper, the mechanism of neurotoxic effects of NBFRs is explored from a new perspective-neuro and endocrine interactions. Gaps in the toxicity data of NBFRs in the neuroendocrine system are supplemented and provide a broader dataset for a complete risk assessment.

Physical Characterization of Inclusion Complexes of Triphenyl Phosphate and Cyclodextrins in Solution

The goal of this work is to provide physical insights into the formation and stability of inclusion complexes (ICs) in aqueous solution between cyclodextrins (CDs) and a common flame retardant, triphenyl phosphate (TPP). Quantum chemistry calculations reveal the possible energetically favorable geometries of TPP in their 1:1 IC form with α-, β-, and γ-CDs as well as their associated complexation, conformational, and interaction energies. High-resolution mass spectrometry (MS) and tandem MS were used with electrospray ionization to study the soluble ICs formed between TPP and CDs. Successful formation of TPP ICs with both β- and γ-CD in solution was detected in the ratio of 1:1 using high-resolution MS in the positive ion mode. Collision-induced dissociation confirmed the formation of TPP ICs with β- and γ-CDs by generating two product ions, TPP and β- or γ-CD, in both cases. Although quantum chemistry calculations suggest that IC formation with α-CD is energetically possible, an IC with α-CD is not observed in aqueous solution using MS, which aligns with what we also previously observed in the solid state. Since TPP forms stable ICs with β- and γ-CDs both in the solid state and in solution suggests that complexation could be a safer alternative than applying TPP directly to a substrate. In addition, complexation with CDs in solution also opens up new processing methods to create flame-retardant fabrics and foams with TPP.

Sex-specific effects of perinatal FireMaster® 550 (FM 550) exposure on socioemotional behavior in prairie voles

The rapidly rising incidence of neurodevelopmental disorders with social deficits is raising concern that developmental exposure to environmental contaminants may be contributory. Firemaster 550 (FM 550) is one of the most prevalent flame-retardant (FR) mixtures used in foam-based furniture and baby products and contains both brominated and organophosphate components. We and others have published evidence of developmental neurotoxicity and sex specific effects of FM 550 on anxiety-like and exploratory behaviors. Using a prosocial animal model, we investigated the impact of perinatal FM 550 exposure on a range of socioemotional behaviors including anxiety, attachment, and memory. Virtually unknown to toxicologists, but widely used in the behavioral neurosciences, the prairie vole (Microtus ochrogaster) is a uniquely valuable model organism for examining environmental factors on sociality because this species is spontaneously prosocial, biparental, and displays attachment behaviors including pair bonding. Dams were exposed to 0, 500, 1000, or 2000 μg of FM 550 via subcutaneous (sc) injections throughout gestation, and pups were directly exposed beginning the day after birth until weaning. Adult offspring of both sexes were then subjected to multiple tasks including open field, novel object recognition, and partner preference. Effects were dose responsive and sex-specific, with females more greatly affected. Exposure-related outcomes in females included elevated anxiety, decreased social interaction, decreased exploratory motivation, and aversion to novelty. Exposed males also had social deficits, with males in all three dose groups failing to show a partner preference. Our studies demonstrate the utility of the prairie vole for investigating the impact of chemical exposures on social behavior and support the hypothesis that developmental FR exposure impacts the social brain. Future studies will probe the possible mechanisms by which these effects arise.

Underlying mechanisms of reproductive toxicity caused by multigenerational exposure of 2, bromo-4, 6-dinitroaniline (BDNA) to Zebrafish (Danio rerio) at environmental relevant levels

2-bromo-4, 6-dinitroaniline (BDNA) is a mutagenic aromatic amine involved in the production and degradation of Disperse blue 79, one of the most extensively used brominated azo dyes. In our previous study, a multigenerational exposure of BDNA (0.5, 5, 50 and 500 μg/L) to zebrafish from F₀ adult to F₂ larvae including a recovery group in F₂ larvae was conducted. The effects on apical points observed in individuals and the long-term effects predicted on population were all related to reproduction. In this study, we performed molecular analysis to elucidate the underlying mechanisms of the reproductive toxicity of BDNA. In F₁ generation, measurement of vitellogenin and transcription levels of genes associated with hypothalamus-pituitary-gland (HPG) axis, estrogen receptor (ER) and androgen receptor (AR) were conducted. There was a decrease in VTG level in the blood of F₁ female fish and transcription of genes related to ER was more affected than that of genes related to AR. These results were consistent with adverse effects that sexual differentiation was biased towards males and fecundity was impaired in a concentration-dependent manner in adults of F₁ generation after 150 days exposure. In F₂ generation, global gene transcriptions of F₂ larvae were investigated. It was uncovered that processes related to apoptosis, development and DNA damage were strongly affected. Alterations to these biological pathways accounted for the irreversible parental influence on a significant decrease in hatchability and increase in abnormality of F₂ larvae. All evidence suggested that the multigenerational exposure of BDNA posed lasting effects transmitted from parents to offspring that persisted after exposure ceased.

Characterization of the Fundulus heteroclitus embryo transcriptional response and development of a gene expression-based fingerprint of exposure for the alternative flame retardant, TBPH (bis (2-ethylhexyl)-tetrabromophthalate)

Although alternative Flame Retardant (FR) chemicals are expected to be safer than the legacy FRs they replace, their risks to human health and the environment are often poorly characterized. This study used a small volume, fish embryo system to reveal potential mechanisms of action and diagnostic exposure patterns for TBPH (bis (2-ethylhexyl)-tetrabromophthalate), a component of several widely-used commercial products. Two different concentration of TBPH were applied to sensitive early life stages of an ecologically important test species, Fundulus heteroclitus (Atlantic killifish), with a well-annotated genome. Exposed fish embryos were sampled for transcriptomics or chemical analysis of parent compound and primary metabolite or observed for development and survival through larval stage. Global transcript profiling using RNA-seq was conducted (n = 16 per treatment) to provide a non-targeted and statistically robust approach to characterize TBPH gene expression patterns. Transcriptomic analysis revealed a dose-response in the expression of genes associated with a surprisingly limited number of biological pathways, but included the aryl hydrocarbon receptor signal transduction pathway, which is known to respond to several toxicologically-important chemical classes. A transcriptional fingerprint using Random Forests was developed that was able to perfectly discriminate exposed vs. non-exposed individuals in test sets. These results suggest that TBPH has a relatively low potential for developmental toxicity (at least in fishes), despite concerns related to its structural similarities to endocrine disrupting chemicals and that the early life stage Fundulus system may provide a convenient test system for exposure characterization. More broadly, this study advances the usefulness of a biological testing and analysis system utilizing non-targeted transcriptomics profiling and early developmental endpoints that complements current screening methods to characterize chemicals of ecological and human health concern.

Human Sex Hormone Disrupting Effects of New Flame Retardants and Their Interactions with Polychlorinated Biphenyls, Polybrominated Diphenyl Ethers, a Case Study in South China

Even though sex hormone disrupting effects of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are widely understood, similar effects associated with new flame retardants (NFRs) have not been so well studied. This study aimed to explore the sex hormone disruption of NFRs and their interactions with PCBs and PBDEs through the conduct of an ecological study in an e-waste dismantling and control region in South China. Questionnaires and blood samples were collected from local adult residents. Results of generalized additive model and linear regression analyses indicate that several species of NFRs showed similar disrupting effects with PBDE congeners on female follicle-stimulating hormone (FSH) and male testosterone. Judged by the curved shape and statistical significance, ΣNFR (sum of 8 species of NFRs) showed stronger disrupting effects on male testosterone and female FSH compared to ΣPBDE (sum of 13 congeners of PBDEs). The interactions induced by NFRs complicated the original sex hormone disruption led by PCBs and PBDEs. The disrupting effects and interactions induced by NFRs decreased female FSH levels in the exposed group. Comprehensive evaluation is needed to provide the evidence base for judging the health risks arising from the increased usage of NFRs.

Estrogenic potency of MC-LR is induced via stimulating steroidogenesis: In vitro and in vivo evidence

Waterborne microcystin-LR (MC-LR) has been reported to disrupt sex hormones, while its estrogenic potency remains controversial. We hypothesized that MC-LR could induce estrogenic effects via disrupting sex hormone synthesis, and verified this hypothesis by in vitro and in vivo assays. Effects of MC-LR (1, 10, 100, 500, 1000 and 5000 μg/L) on steroidogenesis were assessed in the H295R cells after 48 h. The contents of 17β-estradiol (E2) and testosterone (T) increased in a non-dose-dependent manner, which showed positive correlations with the expression of steroidogenic genes. In the in vivo assay, adult male zebrafish were exposed to 0.3, 1, 3, 10 and 30 μg/L MC-LR for 30 d. Similarly, E2 and T contents in the testis were increased, accompanied by extensive up-regulation of steroidogenic genes, especially cyp19a. Meanwhile, the percentage of spermatid in the testis declined. In the liver, the vtg1 gene was significantly up-regulated while both the transcriptional and protein levels of the estrogenic receptor (ER) declined. These results indicate that MC-LR induced non-dose-dependent estrogenic effects at environmental concentrations, which may result from steroidogenesis stimulation via a non-ER-mediated pathway. Our findings support a paradigm shift in the risk assessment of MC-LR from traditional toxicity to estrogenic risk, particularly at low concentrations, and emphasize the potential threat to the male reproductive capacity of wildlife in bloom areas.

Bioaccumulation and effects of dietary exposure to the alternative flame retardant, bis(2-ethylhexyl) tetrabromophthalate (TBPH), in the Atlantic killifish, Fundulus heteroclitus

Bis(2-ethylhexyl) tetrabromophthalate (TBPH), a high production volume flame retardant chemical used as a replacement for banned flame retardants, has been detected in media and human and wildlife tissues globally. We describe bioaccumulation and biological effects from dietary exposure of TBPH to an estuarine fish, Atlantic killifish, Fundulus heteroclitus. Briefly, adult fish were fed carrier control or chemically amended diets for 28 d, followed by 14 d of control diet feeding. Diets were amended with TBPH (TBPH_LO diet, 139 μg/g dry wt, or TBPH_HI diet, 4360 μg/g dry wt) or a polychlorinated biphenyl congener (PCB153 diet, 13 μg/g dry wt), which was included as a positive control for bioaccumulation. Although bioaccumulation of either chemical correlated with fish size, only a small proportion of the TBPH offered (<0.5% total TBPH) had bioaccumulated into TBPH-treated fish by 28 d. In contrast, 24.5% of the PCB153 offered was accounted for in 28-d PCB-treated fish. Although 28-d bioaccumulated concentrations of TBPH differed by sex and treatment, sexes did not differ in their rates of TBPH bioaccumulation, and the time to achieve 50% of 28 d concentration (T1/2 ) was estimated to be 13 d. Depuration rates of TBPH did not differ by sex or treatment, and the time after exposure to achieve T1/2 was estimated to be 22 d. Independent of treatment, male fish grew faster than female fish, but for both sexes reproductive condition (gonadal somatic index) declined unexpectedly over the experimental period. Across treatments, only the TBPH_LO treatment affected growth, reducing male but increasing female growth rates by small amounts relative to respective controls. In summary, our study used very high concentrations of dietary TBPH to contaminate fish tissues above the highest levels reported to date in wild biota, yet we observed few adverse biological effects. Environ Toxicol Chem 2018;37:2350-2360. © 2018 SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Multigenerational Effects and Demographic Responses of Zebrafish ( Danio rerio) Exposed to Organo-Bromine Compounds

Long-term exposure to toxic chemicals often has deleterious effects on aquatic organisms. In order to support appropriate environmental management of chemicals, a mathematical model was developed to characterize the effects of chemicals on multigenerational population dynamics in aquatic animals. To parametrize the model, we conducted a multigenerational laboratory toxicity test in zebrafish ( Danio rerio) exposed to 2-bromo-4,6-dinitroaniline (BDNA). Long-term exposure to BDNA considerably reduced the fecundity of adult zebrafish (F₀ and F₁) and caused deformities in the offspring (F₂). Life history data, including changes in fecundity and population growth, were then integrated into the model to predict population dynamics of zebrafish exposed to two novel brominated flame retardants, bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB). The model predicted that the fecundity of adult zebrafish would be significantly impaired after exposure to 90.36 μM TBPH and 99.16 μM TBB. Thus, prolonged exposure to such levels over multiple generations could result in population extinction within 20 years. Our results provide an intensive temporal perspective to investigate a keystone that connects with individual response to chemicals, population dynamics, and ultimately ecosystem influences.

Trophodynamics of Emerging Brominated Flame Retardants in the Aquatic Food Web of Lake Taihu: Relationship with Organism Metabolism across Trophic Levels

Despite the increasing use and discharge of novel brominated flame retardants, little information is available about their trophodynamics in the aquatic food web, and their subsequent relationships to compound metabolism. In this study, concentrations of 2,4,6-tribromophenyl allyl ether (ATE), 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), tetrabromo- o-chlorotoluene (TBCT), pentabromobenzyl acrylate (PBBA), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), bis(2-ethylhexyl)-3,4,5,6-tetrabromo-phthalate (TBPH), and decabromodiphenyl ethane (DBDPE) were measured in 17 species, including plankton, invertebrates, and fish from Lake Taihu, South China. Trophodynamics of the compounds were assessed, and metabolic rates were measured in the liver microsomes of crucian (trophic level [TL]: 2.93), catfish (TL: 3.86), and yellow-head catfish (TL: 4.3). Significantly positive relationships were found between trophic levels and lipid-normalized concentrations of ATE, BTBPE, and TBPH; their trophic magnification factors (TMFs) were 2.85, 2.83, and 2.42, respectively. Consistently, the three chemicals were resistant to metabolism in all fish microsomes. No significant relationship was observed for βTBECH ( p = 0.116), and DBDPE underwent trophic dilution in the food web (TMFs = 0.37, p = 0.021). Moreover, these two chemicals showed steady metabolism with incubation time in all fish microsomes. TBCT and PBBA exhibited significant trophic magnifications in the food web (TMF = 4.56, 2.01). Though different metabolic rates were observed for the two compounds among the tested fish species, TBCT and PBBA both showed metabolic resistance in high-trophic-level fish. These results indicated that metabolism of organisms at high trophic levels plays an important role in the assessment of trophic magnification potentials of these flame retardant chemicals.

Occurrence and Source Effect of Novel Brominated Flame Retardants (NBFRs) in Soils from Five Asian Countries and Their Relationship with PBDEs

This paper presents the first comprehensive survey of 19 novel brominated flame retardants (NBFRs) in soil samples collected among five Asian countries. High variability in concentrations of all NBFRs was found in soils with the geometric mean (GM) values ranging from 0.50 ng/g dry weight (dw) in Vietnam to 540 ng/g dw in the vicinity of a BFR manufacturer in China. In urban, rural, and background locations, the GM concentrations of ∑₁₉NBFRs decreased in the order of Japan > South Korea > China > India > Vietnam. Correlations among different NBFR compounds were positive and statistically significant (p < 0.05), suggesting that they originate from similar sources. Evidence for simultaneous application between polybrominated diphenyl ethers (PBDEs) and NBFRs were also noted. Principal component analysis of NBFR concentrations revealed specific pollution sources for different NBFRs coming from urban, BFR-related industrial, and e-waste sites. For the first time, this study demonstrates a "point source fractionation effect" for NBFRs and PBDEs. The concentrations of all NBFRs and PBDEs were negatively and significantly correlated with the distance from BFR-related industrial and e-waste regions. Positive and significant correlation between population density and NBFR concentrations in soils was identified. Our study revealed that the primary sources effects were stronger than the secondary sources effects in controlling the levels and distribution of NBFRs and PBDEs in soils in these five Asian countries.

Effects of novel brominated flame retardant TBPH and its metabolite TBMEHP on human vascular endothelial cells: Implication for human health risks

As a replacement for polybrominated diphenyl ethers, bis-(2-ethylhexyl) tetrabromophthalate (TBPH) is widely used as a novel flame retardant and has been detected in many environmental matrix including human blood. TBPH can be metabolized into mono-(2-ethyhexyl) tetrabromophthalate (TBMEHP) by carboxylesterase. However, their adverse effects on human vascular endothelium and their potential impacts on human cardiovascular disease are unknown. In this study, their adverse effects and associated molecular mechanisms on human vascular endothelial cells (HUVECs) were investigated. A concentration-dependent inhibition on HUVECs' viability and growth was observed for TBMEHP but not for TBPH. TBMEHP induced a marked G₀/G₁ cell cycle arrest and robust cell apoptosis at 1μg/mL by inducing expression of p53, GADD45α and cyclin dependent kinase (CDK) inhibitors (p21and p27) while suppressing the expression of cyclin D1, CDK2, CDK6, and Bcl-2. Unlike TBMEHP, TBPH caused early apoptosis after G₂/M phase arrest only at 10μg/mL via up-regulation of p21 and down-regulation of CDK2 and CDK4. TBMEHP decreased mitochondrial membrane potential and increased caspase-3 activity at 1μg/mL, suggesting that activation of p53 and mitochondrial pathway were involved in the cell apoptosis. The data showed that TBPH and TBMEHP induced different cell cycle arrest and apoptosis through different molecular mechanisms with much higher toxicity for TBMEHP. Our study implies that the metabolites of TBPH, possibly other novel brominated flame retardants, may be of potential concern for human cardiovascular disease.

Effects of food-borne exposure of juvenile rainbow trout (Oncorhynchus mykiss) to emerging brominated flame retardants 1,2-bis(2,4,6-tribromophenoxy)ethane and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate

Brominated flame retardants (BFRs) represent a large group of chemicals used in a variety of household and commercial products to prevent fire propagation. The environmental persistence and toxicity of some of the most widely used BFRs has resulted in a progressive ban worldwide and the development of novel BFRs for which the knowledge on environmental health impacts remains limited. The objectives of this study were to evaluate the effects of two emerging BFRs, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), in diet exposed juvenile rainbow trout (Oncorhynchus mykiss). Both compounds were detected in fish carcasses at 76% and 2% of the daily dosage of BTBPE and EH-TBB, respectively, indicating accumulation of BTBPE and by contrast extensive depuration/metabolism of EH-TBB. Liver gene transcription analysis using RNA-sequencing indicated that the chronic 28-d dietary exposure of trout to EH-TBB down-regulated one single gene related to endocrine-mediated processes, whereas BTBPE impacted the transcription of 33 genes, including genes involved in the immune response, reproduction, and oxidative stress. Additional analysis using qRT-PCR after 48-h and 28-d of exposure confirmed the impact of BTBPE on immune related genes in the liver (apolipoprotein A-I, lysozyme) and the head-kidney (complement c3-4). However, the activity of lysozymes measured at the protein level did not reflect transcriptomic results. Overall, results suggested an impact on immune-related gene transcription in BTBPE exposed fish, as well as oxidative stress and endocrine disruption potentials.

Comparative Toxicogenomic Responses to the Flame Retardant mITP in Developing Zebrafish

Monosubstituted isopropylated triaryl phosphate (mITP) is a major component of Firemaster 550, an additive flame retardant mixture commonly used in polyurethane foams. Developmental toxicity studies in zebrafish established mITP as the most toxic component of FM 550, which causes pericardial edema and heart looping failure. Mechanistic studies showed that mITP is an aryl hydrocarbon receptor (AhR) ligand; however, the cardiotoxic effects of mITP were independent of the AhR. We performed comparative whole genome transcriptomics in wild-type and ahr2^hu3335 zebrafish, which lack functional ahr2, to identify transcriptional signatures causally involved in the mechanism of mITP-induced cardiotoxicity. Regardless of ahr2 status, mITP exposure resulted in decreased expression of transcripts related to the synthesis of all-trans-retinoic acid and a host of Hox genes. Clustered gene ontology enrichment analysis showed unique enrichment in biological processes related to xenobiotic metabolism and response to external stimuli in wild-type samples. Transcript enrichments overlapping both genotypes involved the retinoid metabolic process and sensory/visual perception biological processes. Examination of the gene-gene interaction network of the differentially expressed transcripts in both genetic backgrounds demonstrated a strong AhR interaction network specific to wild-type samples, with overlapping genes regulated by retinoic acid receptors (RARs). A transcriptome analysis of control ahr2-null zebrafish identified potential cross-talk among AhR, Nrf2, and Hif1α. Collectively, we confirmed that mITP is an AhR ligand and present evidence in support of our hypothesis that mITP's developmental cardiotoxic effects are mediated by inhibition at the RAR level.

Gene transcription, metabolite and lipid profiling in eco-indicator daphnia magna indicate diverse mechanisms of toxicity by legacy and emerging flame-retardants

The use of chemical flame-retardants (FR) in consumer products has steadily increased over the last 30 years. Toxicity data exist for legacy FRs such as pentabromodiphenyl ether (pentaBDE), but less is known about effects of new formulations. To address this issue, the toxicity of seven FR chemicals and formulations was assessed on the freshwater crustacean Daphnia magna. Acute 48-h nominal LC50 values for penta- and octabromodiphenyl ether (pentaBDE, octaBDE), Firemaster 550 (FM550), Firemaster BZ-54 (BZ54), bis(2-ethylhexyl) tetrabromophthalate (BEH-TEBP), triphenyl phosphate (TPhP), and nonbrominated BEH-TEBP analog bis(2-ethylhexyl) phthalate (BEHP) ranged from 0.058 mg/L (pentaBDE) to 3.96 mg/L (octaBDE). mRNA expression, (1)H NMR-based metabolomic and lipidomic profiling at 1/10 LC50 revealed distinct patterns of molecular response for each exposure, suggesting pentaPBDE affects transcription and translation, octaBDE and BEH-TEBP affect glycosphingolipid biosynthesis and BZ54 affects Wnt and Hedgehog signal pathways as well as glycosaminoglycan degradation. Brominated components of FM550 (i.e., BZ54) were significantly higher in Daphnia after 48 h following 1/10 LC50 exposure. FM550 elicited significant mRNA changes at five concentrations across a range from 1/10(6) LC50 to 1/2 LC50. Analyses suggest FM550 impairs nutrient utilization or uptake in Daphnia.

Effects of the brominated flame retardant TBCO on fecundity and profiles of transcripts of the HPGL-axis in Japanese medaka

The novel brominated flame retardant, 1,2,5,6-tetrabromocyclooctane (TBCO) is an additive flame retardant which is marketed under the trade name Saytex BCL-48. TBCO has recently been investigated as a potential alternative to the major use brominated flame retardant, hexabromocyclododecane (HBCD), which could have major implications for significant increases in amounts of TBCO used. Yet there is a lack of information regarding potential toxicities of TBCO. Recently, results of in vitro experiments have demonstrated the potential of TBCO to modulate endocrine function through interaction with estrogen and androgen receptors and via alterations to the synthesis of 17-β-estradiol and testosterone. Further research is required to determine potential endocrine disrupting effects of TBCO in vivo. In this experiment a 21-day fecundity assay with Japanese medaka (Oryzias latipes) was conducted to examine endocrine disrupting effects of TBCO in vivo. Medaka were fed a diet containing either 607 or 58μg TBCO/g food, wet mass (wm). Fecundity, measured as cumulative deposition of eggs and fertilization of eggs, as well as abundances of transcripts of 34 genes along the hypothalamus-pituitary-gonadal-liver (HPGL) axis were measured as indicators of holistic endocrine disruption and to determine mechanisms of effects, respectively. Cumulative fecundity was 18% lesser by medaka exposed to 58μg TBCO/g, wm food. However, fecundity of medaka exposed to 607μg TBCO/g, wm food was not significantly different from that of controls. Organ-specific and dose-dependent alterations to abundances of transcripts were observed in male and female medaka. A pattern of down-regulation of expression of genes involved in steroidogenesis, metabolism of cholesterol, and regulatory feedback mechanisms was observed in gonads from male and female medaka which had been exposed to the greater concentration of TBCO. However, these effects on expression of genes were not manifested in effects on fertilization of eggs or fecundity. In livers from male and female medaka exposed to the lesser concentration of TBCO greater expression of genes that respond to exposure to estrogens, including vitellogenin II, choriogenin H, and ERα, were observed. The results reported here confirm the endocrine disrupting potential of TBCO and elucidate potential mechanisms of effects which include specific patterns of alterations to abundances of transcripts of genes in the gonad and liver of medaka.