Binding and Activity of Tetrabromobisphenol A Mono-Ether Structural Analogs to Thyroid Hormone Transport Proteins and Receptors

Assessing plasmatic transport inhibitors of thyroid hormone in mammals in the Xenopus Eleutheroembryonic Thyroid Assay (XETA)

The Xenopus Eleutheroembryonic Thyroid Assay (XETA, OECD TG 248) was established as an alternative to the Amphibian Metamorphosis Assay (AMA, OECD TG 231) for the analysis of (anti-)thyroid activity of chemicals. The XETA is a New Approach Method (NAM) since the embryonic life stages used in the assay are not yet feeding independently, which renders the assay to be considered a non-animal test under many national laws. Physiologically, the used embryos are not fully developed yet, and thus there are limitations to the XETA for detecting certain mechanisms along the hypothalamic-pituitary-thyroid (HPT) axis. However, the plasmatic transport inhibition of thyroid hormone should physiologically be detectable in the XETA but has not yet been sufficiently investigated. Here, we tested three substances that are known, amongst others, to inhibit thyroid hormone transport by competitive binding to transthyretin in mammalian studies, namely pentachlorophenol (PCP), tetrabromo bisphenol A (TBBPA), and mefenamic acid. Following the test guideline, X. laevis eleutheroembryos of Nieuwkoop-Faber stage 45 were exposed for 72 h at 21 °C in 6-well plates to different concentrations of the test substances. For PCP and TBBPA, the XETA showed a decrease in fluorescence intensity, which would be expected for thyroid hormone transport inhibition amongst other, similar modes of action, while for the lower potency substance mefenamic acid, a trend was visible, but no statistically significant inhibition was detected. Overall, the results indicate that in the XETA, the plasmatic transport inhibition of thyroid hormone should be detectable alongside other inhibitory modes of action on the HPT axis.

Optimized methods for measuring competitive binding of chemical substances to thyroid hormone distributor proteins transthyretin and thyroxine binding globulin

Transthyretin (TTR) and thyroxine-binding globulin (TBG) are two major thyroid hormone (TH) distributor proteins in human plasma, playing important roles in stabilizing the TH levels in plasma, delivery of TH to target tissues, and trans-barrier transport. Binding of xenobiotics to these distributor proteins can potentially affect all these three important roles of distributor proteins. Therefore, fast and cost-effective experimental methods are required for both TTR and TBG to screen both existing and new chemicals for their potential binding. In the present study, the TTR-binding assay was therefore simplified, optimized and pre-validated, while a new TBG-binding assay was developed based on fluorescence polarization as a readout. Seven model compounds (including positive and negative controls) were tested in the pre-validation study of the optimized TTR-binding assay and in the newly developed TBG-binding assay. The dissociation constants of the natural ligand (thyroxine, T4) and potential competitors were determined and compared between two distributor proteins, showing striking differences for perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA).

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).

In silico models for the screening of human transthyretin disruptors

The use of New Approach Methodologies (NAMs), such as Quantitative Structure-Activity Relationship (QSAR) models, is highly recommended by international regulations to speed up hazard and risk assessment of Endocrine Disruptors, which are known to be linked to a wide spectrum of severe diseases on humans and wildlife. A very sensitive target for these chemicals is the thyroid hormone system, which plays a key role in regulating metabolic and cognitive functions. Several chemicals have been demonstrated to compete with the thyroid hormone thyroxine (T4) for binding to human thyroid hormone distributor protein transthyretin (hTTR). In this work, we generated three new datasets composed by T4-hTTR competing potencies of more than 200 heterogeneous chemicals measured by three different in vitro assays. These datasets were used for the development of new regression QSAR models. The best models were thoroughly validated by internal and external validation procedures. The mechanistic interpretation of the selected molecular descriptors provided information on structural features which are relevant to characterise hTTR binders, such as the presence of hydroxylated and halogenated aromatic rings. PCA analysis was used to rank the studied chemicals according to their increasing T4-hTTR competing potency. Hydroxylated and halogenated bicyclic aromatic compounds are ranked as the strongest hTTR binders. The new QSARs are useful to screen potential Thyroid Hormone System-Disrupting Chemicals (THSDCs), and to support the identification of sustainable alternatives to hazardous chemicals.

Temperature dependent cholinergic synapse induced by triphenyl phosphate and tris(1.3-dichloroisopropyl) phosphate via thyroid hormone synthesis in Cyprinus carpio

Triphenyl phosphate (TPHP) and tris(1.3-dichloroisopropyl) phosphate (TDCIPP) are emerging contaminants that pervade diverse ecosystems and impair the thyroid and neural signaling pathways. The intricate interactions between thyroid and neurodevelopmental effects mediated by TPHP and TDCIPP remain elusive. This study integrates in vivo, in vitro, and in silico approaches to elucidate these mechanisms in Cyprinus carpio at varying temperatures. It showed that TPHP and TDCIPP hindered fish growth, particularly at low temperatures, by interfering with thyroid hormone synthesis and transport processes. Both compounds have been identified as environmental hormones that mimic thyroid hormone activity and potentially inhibit acetylcholinesterase, leading to neurodevelopmental disorders characterized by brain tissue damage and disrupted cholinergic synapses, such as axon guidance and regeneration. Notably, the bioaccumulation of TPHP was 881.54 % higher than that of TDCIPP, exhibiting temperature-dependent variations with higher levels of TDCIPP at low temperatures (20.50 % and 250.84 % above optimum and high temperatures, respectively), suggesting that temperature could exacerbate the toxicity effects of OPEs. This study sheds new light on the mechanisms underlying thyroid endocrine disruption and neurodevelopmental toxicity in C. carpio. More importantly, these findings indicate that temperature affects the environmental fate and effects of TPHP and TDCIPP, which could provide an important basis for ecological environmental zoning control of emerging contaminants in the future.

Key characteristics of carcinogens meet hallmarks for prevention-cutting the Gordian knot

The complexity of cancer requires a comprehensive approach to understand its diverse manifestations and underlying mechanisms. Initially outlined by Hanahan and Weinberg in 2000 and updated in 2010, the hallmarks of cancer provide a conceptual basis for understanding inherent variability in cancer biology. Recent expansions have further elucidated additional hallmarks, including phenotypic plasticity and senescent cells. The International Agency for Research on Cancer (IARC) has identified the key characteristics of carcinogens (KCCs) to evaluate their carcinogenic potential. We analyzed chemicals of concern for environmental exposure that interact with specific receptors to induce genomic instability, epigenetic alterations, immune suppression, and receptor-mediated effects, thereby contributing to chronic inflammation. Despite their varying degrees of carcinogenicity, these chemicals have similar KCC profiles. Our analysis highlights the pivotal role of receptor binding in activating most other KCCs, underscoring their significance in cancer initiation. Although KCCs are associated with early molecular or cellular events, they do not encompass processes directly linked to full cellular malignancy. Thus, there is a need to integrate clear endpoints that anchor KCCs to the acquisition of a complete malignant phenotype into chemical testing. From the perspective of toxicology and cancer research, an all-encompassing strategy that incorporates both existing and novel KCCs and cancer hallmarks is essential to enable the targeted identification of prevalent carcinogens and facilitate zone-specific prevention strategies. To achieve this goal, collaboration between the KCC and cancer hallmarks communities becomes essential.

Assessment of the disruption effects of tetrabromobisphenol A and its analogues on lipid metabolism using multiple in vitro models

Tetrabromobisphenol A (TBBPA), a widely-used brominated flame retardant, has been revealed to exert endocrine disrupting effects and induce adipogenesis. Given the high structural similarities of TBBPA analogues and their increasing exposure risks, their effects on lipid metabolism are necessary to be explored. Herein, 9 representative TBBPA analogues were screened for their interference on 3T3-L1 preadipocyte adipogenesis, differentiation of C3H10T1/2 mesenchymal stem cells (MSCs) to brown adipocytes, and lipid accumulation of HepG2 cells. TBBPA bis(2-hydroxyethyl ether) (TBBPA-BHEE), TBBPA mono(2-hydroxyethyl ether) (TBBPA-MHEE), TBBPA bis(glycidyl ether) (TBBPA-BGE), and TBBPA mono(glycidyl ether) (TBBPA-MGE) were found to induce adipogenesis in 3T3-L1 preadipocytes to different extends, as evidenced by the upregulated intracellular lipid generation and expressions of adipogenesis-related biomarkers. TBBPA-BHEE exhibited a stronger obesogenic effect than did TBBPA. In contrast, the test chemicals had a weak impact on the differentiation process of C3H10T1/2 MSCs to brown adipocytes. As for hepatic lipid formation test, only TBBPA mono(allyl ether) (TBBPA-MAE) was found to significantly promote triglyceride (TG) accumulation in HepG2 cells, and the effective exposure concentration of the chemical under oleic acid (OA) co-exposure was lower than that without OA co-exposure. Collectively, TBBPA analogues may perturb lipid metabolism in multiple tissues, which varies with the test tissues. The findings highlight the potential health risks of this kind of emerging chemicals in inducing obesity, non-alcoholic fatty liver disease (NAFLD) and other lipid metabolism disorders, especially under the conditions in conjunction with high-fat diets.

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.

Identification of Hydrocarbon Sulfonates as Previously Overlooked Transthyretin Ligands in the Environment

Incidences of thyroid disease, which has long been hypothesized to be partially caused by exposure to thyroid hormone disrupting chemicals (TDCs), have rapidly increased in recent years. However, known TDCs can only explain a small portion (∼1%) of in vitro human transthyretin (hTTR) binding activities in environmental samples, indicating the existence of unknown hTTR ligands. In this study, we aimed to identify the major environmental hTTR ligands by employing protein Affinity Purification with Nontargeted Analysis (APNA). hTTR binding activities were detected in all 11 indoor dust and 9 out of 10 sewage sludge samples by the FITC-T4 displacement assay. By using APNA, 31 putative hTTR ligands were detected including perfluorooctanesulfonate (PFOS). Two of the most abundant ligands were identified as hydrocarbon surfactants (e.g., dodecyl benzenesulfonate). Moreover, another abundant ligand was surprisingly identified as a disulfonate fluorescent brightener, 4,4'-bis(2-sulfostyryl)biphenyl sodium (CBS). CBS was validated as a nM-affinity hTTR ligand with an IC50 of 345 nM. In total, hydrocarbon surfactants and fluorescent brighteners explain 1.92-17.0 and 5.74-54.3% of hTTR binding activities in dust and sludge samples, respectively, whereas PFOS only contributed <0.0001%. Our study revealed for the first time that hydrocarbon sulfonates are previously overlooked hTTR ligands in the environment.

Mechanism of tartaric acid mediated dissipation and biotransformation of tetrabromobisphenol A and its derivatives in soil

Biotransformation is a major dissipation process of tetrabromobisphenol A and its derivatives (TBBPAs) in soil. The biotransformation and ultimate environmental fate of TBBPAs have been widely studied, yet the effect of root exudates (especially low-molecular weight organic acids (LMWOAs)) on the fate of TBBPAs is poorly documented. Herein, the biotransformation behavior and mechanism of TBBPAs in bacteriome driven by LMWOAs were comprehensively investigated. Tartaric acid (TTA) was found to be the main component of LMWOAs in root exudates of Helianthus annus in the presence of TBBPAs, and was identified to play a key role in driving shaping bacteriome. TTA promoted shift of the dominant genus in soil bacteriome from Saccharibacteria_genera_incertae_sedis to Gemmatimonas, with a noteworthy increase of 24.90-34.65% in relative abundance of Gemmatimonas. A total of 28 conversion products were successfully identified, and β-scission was the principal biotransformation pathway for TBBPAs. TTA facilitated the emergence of novel conversion products, including 2,4-dibromophenol, 3,5-dibromo-4-hydroxyacetophenone, para-hydroxyacetophenone, and tribromobisphenol A. These products were formed via oxidative skeletal cleavage and debromination pathways. Additionally, bisphenol A was observed during the conversion of derivatives. This study provides a comprehensive understanding about biotransformation of TBBPAs driven by TTA in soil bacteriome, offering new insights into LMWOAs-driven biotransformation mechanisms.

First insights into the bioaccumulation, biotransformation and trophic transfer of typical tetrabromobisphenol A (TBBPA) analogues along a simulated aquatic food chain

Tetrabromobisphenol A (TBBPA) analogues have been investigated for their prevalent occurrence in environments and potential hazardous effects to humans and wildlife; however, there is still limited knowledge regarding their toxicokinetics and trophic transfer in aquatic food chains. Using a developed toxicokinetic model framework, we quantified the bioaccumulation, biotransformation and trophic transfer of tetrabromobisphenol S (TBBPS) and tetrabromobisphenol A di(allyl ether) (TBBPA-DAE) during trophic transfer from brine shrimp (Artemia salina) to zebrafish (Danio rerio). The results showed that the two TBBPA analogues could be readily accumulated by brine shrimp, and the estimated bioconcentration factor (BCF) value of TBBPS (5.68 L kg-1 ww) was higher than that of TBBPA-DAE (1.04 L kg-1 ww). The assimilation efficiency (AE) of TBBPA-DAE in zebrafish fed brine shrimp was calculated to be 16.3%, resulting in a low whole-body biomagnification factor (BMF) in fish (0.684 g g-1 ww). Based on the transformation products screened using ultra-high-performance liquid chromatograph-high resolution mass spectrometry (UPLC-HRMS), oxidative debromination and hydrolysis were identified as the major transformation pathways of TBBPS, while the biotransformation of TBBPA-DAE mainly took place through ether bond breaking and phase-II metabolism. Lower accumulation of TBBPA as a metabolite than its parent chemical was observed in both brine shrimp and zebrafish, with metabolite parent concentration factors (MPCFs) < 1. The investigated BCFs for shrimp of the two TBBPA analogues were only 3.77 × 10-10 - 5.59 × 10-3 times of the theoretical Kshrimp-water based on the polyparameter linear free energy relationships (pp-LFERs) model, and the BMF of TBBPA-DAE for fish was 0.299 times of the predicted Kshrimp-fish. Overall, these results indicated the potential of the trophic transfer in bioaccumulation of specific TBBPA analogues in higher trophic-level aquatic organisms and pointed out biotransformation as an important mechanism in regulating their bioaccumulation processes. ENVIRONMENTAL IMPLICATION: The internal concentration of a pollutant in the body determines its toxicity to organisms, while bioaccumulation and trophic transfer play important roles in elucidating its risks to ecosystems. Tetrabromobisphenol A (TBBPA) analogues have been extensively investigated for their adverse effects on humans and wildlife; however, there is still limited knowledge regarding their toxicokinetics and trophic transfer in aquatic food chains. This study investigated the bioaccumulation, biotransformation and trophic transfer of TBBPS and TBBPA-DAE in a simulated di-trophic food chain. This state-of-art study will provide a reference for further research on this kind of emerging pollutant in aquatic environments.

CatNet: Sequence-based deep learning with cross-attention mechanism for identifying endocrine-disrupting chemicals

Endocrine-disrupting chemicals (EDCs) pose significant environmental and health risks due to their potential to interfere with nuclear receptors (NRs), key regulators of physiological processes. Despite the evident risks, the majority of existing research narrows its focus on the interaction between compounds and the individual NR target, neglecting a comprehensive assessment across the entire NR family. In response, this study assembled a comprehensive human NR dataset, capturing 49,244 interactions between 35,467 unique compounds and 42 NRs. We introduced a cross-attention network framework, "CatNet", innovatively integrating compound and protein representations through cross-attention mechanisms. The results showed that CatNet model achieved excellent performance with an area under the receiver operating characteristic curve (AUCROC) = 0.916 on the test set, and exhibited reliable generalization on unseen compound-NR pairs. A distinguishing feature of our research is its capacity to expand to novel targets. Beyond its predictive accuracy, CatNet offers a valuable mechanistic perspective on compound-NR interactions through feature visualization. Augmenting the utility of our research, we have also developed a graphical user interface, empowering researchers to predict chemical binding to diverse NRs. Our model enables the prediction of human NR-related EDCs and shows the potential to identify EDCs related to other targets.

Tetrabromobisphenol A induces neuronal cytotoxicity by inhibiting PINK1-Parkin-mediated mitophagy via upregulating ATF3 expression

Tetrabromobisphenol A (TBBPA), as a widely used brominated flame retardant, has been implicated as a potential neurotoxicant. However, the mechanism of TBBPA-induced neurotoxicity has not been fully elucidated yet. In this study, using mouse hippocampal neuron cell HT22 as the in vitro model, the neuronal cytotoxicity of TBBPA and the mechanism by focusing on mitophagy have been studied. We found that neuronal cytotoxic effects were indeed induced by TBBPA exposure at concentrations of >20 μM for 24 h, including decreased cell viability (to 92.38 % at 20 μM; 18.25 % at 80 μM), enhanced ROS (enhanced 53.26 % at IC50 of 60 μM, compared with that in the control group) and mitochondrial ROS (mtROS) levels (enhanced 24.12 % at 60 μM), reduced mitochondrial membrane potential (MMP) (decreased 33.60 % at 60 μM). As a protective mechanism in cells, autophagy was initiated; however, mitophagy was inhibited, where PINK1 (PINK1-Parkin activation is critical in the depolarized MMP-induced mitophagy) expression was found to be repressed and decreased, further leading to the failure of Parkin recruitment to the damaged mitochondria. Mitophagy activator, nicotinamide mononucleotide (β-NMN) that activates the PINK1-Parkin pathway, could alleviate TBBPA-induced mitophagy deficiency and further reduce the neuronal cytotoxicity, demonstrating that TBBPA-induced PINK1-Parkin-mediated mitophagy deficiency contributed to the neuronal cytotoxicity. Furthermore, we found TBBPA caused the upregulation of Atf3 (activating transcription factor 3) gene transcription and expression levels, alongside reduced Pink1 levels; whereas enhanced Pink1 transcript levels were observed after ATF3 depletion even under TBBPA treatment, demonstrating TBBPA-induced overexpression of ATF3 should be responsible for the reduced PINK1 expression. Therefore, for the first time, here we demonstrate that TBBPA can inhibit PINK1-Parkin-mediated mitophagy via upregulating ATF3 expression, which further contributes to its neuronal cytotoxicity. This study should be able to improve our understanding of the mechanism of TBBPA-induced neuronal cytotoxicity.

Eight novel brominated flame retardants in indoor and outdoor dust samples from the E-waste recycling industrial park: Implications for human exposure

As alternatives for legacy brominated flame retardants, novel brominated flame retardants (NBFRs) have a wide array of applications in the electronic and electrical fields. The shift of recycling modes of electronic and electrical waste (e-waste) from informal recycling family workshop to formal recycling facilities might come with the change the chemical landscape emitted including NBFRs, however, little information is known about this topic. This study investigated the occurrence characteristics, distribution, and exposure profiles of eight common NBFRs and their derivatives in an e-waste recycling industrial park in central China and illustrated the differences in various functional zones in the recycling park. The highest level of ΣNBFRs in dust samples was found in e-waste storage area at median concentration of 27,400 ng/g, followed by e-waste dismantling workshops (23,300 ng/g), workshop outdoor area (7770 ng/g), and residential area outdoor (536 ng/g). In the e-waste dismantling associated dust samples, tetrabromobisphenol A bis(2,3-dibromopropyl ether) (TBBPA-BDBPE), tetrabromobisphenol A (TBBPA) and 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ) were the predominant components. This paper presented the first evidence regarding the occurrence characteristic and distribution of tetrabromobisphenol S (TBBPS), tetrabromobisphenol A bismethyl ether (TBBPA-BME) and tetrabromobisphenol S bis(2,3-dibromopropyl ether) (TBBPS-BDBPE) in the e-waste associated dust samples. By comparing with previous studies performed in China, this paper also noticed the significant decrease of TBBPA concentrations in the dust probably due to the shift of e-wastes sources and recycling modes. We further assessed the risk of occupational workers exposure to NBFRs. The median EDI (estimated daily intake) value of ΣNBFRs among e-waste dismantling workers was 9.71 ng/kg BW/d with the maximum EDI value being 19.6 ng/kg BW/d, hundreds of times higher than those exposed by general population. The study raises great concern for the health risk of occupational exposure to NBFRs in the e-waste recycling industrial park.

Extended exposure to tetrabromobisphenol A-bis(2,3-dibromopropyl ether) leads to subfertility in male mice at the late reproductive age

Tetrabromobisphenol A-bis(2,3-dibromopropyl ether) (TBBPA-BDBPE), a commonly used brominated flame retardant as a decabromodiphenyl ether substitute, has been detected in various environmental compartments, but its health hazards remain largely unknown. Our recent study showed that low-dose exposure of male mice to TBBPA-BDBPE from postnatal day (PND) 0 to 56 caused remarkable damage to the microtubule skeleton in Sertoli cells and the blood-testis barrier (BTB) but exerted little effect on conventional reproductive endpoints in adulthood. To investigate whether TBBPA-BDBPE may cause severe reproductive impairments at late reproductive age, here, we extended exposure of historically administrated male mice to 8-month age and allowed them to mate with non-treated females for the evaluation of fertility, followed by a general examination for the reproductive system. As expected, we found that 8-month exposure to 50 μg/kg/d as well as 1000 μg/kg/d TBBPA-BDBPE caused severe damage to the reproductive system, including reduced sperm counts, increased sperm abnormality, histological alterations of testes. Moreover, microtubule damage and BTB-related impairment were still observed following 8-month exposure. Noticeably, high-dose TBBPA-BDBPE-treated mice had fewer offspring with a female-biased sex ratio. All results show that long-term exposure to TBBPA-BDBPE caused severe reproductive impairment, including poor fertility at late reproductive age. It is therefore concluded that slight testicular injuries in early life can contribute to reproductive impairment at late reproductive age, highlighting that alterations in certain non-conventional endpoints should be noticed as well as conventional endpoints in future reproductive toxicity studies.

Cross-species applicability of an adverse outcome pathway network for thyroid hormone system disruption

Thyroid hormone system disrupting compounds are considered potential threats for human and environmental health. Multiple adverse outcome pathways (AOPs) for thyroid hormone system disruption (THSD) are being developed in different taxa. Combining these AOPs results in a cross-species AOP network for THSD which may provide an evidence-based foundation for extrapolating THSD data across vertebrate species and bridging the gap between human and environmental health. This review aimed to advance the description of the taxonomic domain of applicability (tDOA) in the network to improve its utility for cross-species extrapolation. We focused on the molecular initiating events (MIEs) and adverse outcomes (AOs) and evaluated both their plausible domain of applicability (taxa they are likely applicable to) and empirical domain of applicability (where evidence for applicability to various taxa exists) in a THSD context. The evaluation showed that all MIEs in the AOP network are applicable to mammals. With some exceptions, there was evidence of structural conservation across vertebrate taxa and especially for fish and amphibians, and to a lesser extent for birds, empirical evidence was found. Current evidence supports the applicability of impaired neurodevelopment, neurosensory development (eg, vision) and reproduction across vertebrate taxa. The results of this tDOA evaluation are summarized in a conceptual AOP network that helps prioritize (parts of) AOPs for a more detailed evaluation. In conclusion, this review advances the tDOA description of an existing THSD AOP network and serves as a catalog summarizing plausible and empirical evidence on which future cross-species AOP development and tDOA assessment could build.

Linking Transthyretin-Binding Chemicals and Free Thyroid Hormones: In Vitro to In Vivo Extrapolation Based on a Competitive Binding Model

Large numbers of pollutants competitively inhibit the binding between thyroid hormones and transthyretin (TTR) in vitro. However, the impact of this unintended binding on free thyroid hormones in vivo has not yet been characterized. Herein, we established a quantitative in vitro to in vivo extrapolation (QIVIVE) method based on a competitive binding model to quantify the effect of TTR-binding chemicals on free thyroid hormones in human blood. Twenty-five TTR-binding chemicals including 6 hydroxyl polybromodiphenyl ethers (OH-PDBEs), 6 hydroxyl polychlorobiphenyls (OH-PCBs), 4 halogenphenols, 5 per- and polyfluorinated substances (PFASs), and 4 phenols were selected for investigation. Incorporating the in vitro binding parameters and human exposure data, the QIVIVE model could well predict the in vivo effect on free thyroid hormones. Co-exposure to twenty-five typical TTR-binding chemicals resulted in median increases of 0.080 and 0.060% in circulating levels of free thyroxine (FT4) and free triiodothyronine (FT3) in the general population. Individuals with occupational exposure to TTR-binding chemicals suffered 1.88-32.2% increases in free thyroid hormone levels. This study provides a quantitative tool to evaluate the thyroid-disrupting risks of TTR-binding chemicals and proposes a new framework for assessing the in vivo effects of chemical exposures on endogenous molecules.

Sensitive method for simultaneous determination of TBBPA and its ten derivatives

Tetrabromobisphenol A (TBBPA) and its derivatives are regarded as new contaminants, raising much attention on their environmental occurrence and fates. However, the sensitive detection of TBBPA and its main derivatives is still a great challenge. This study investigated a sensitive method for simultaneous detection of TBBPA and its ten derivatives using high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (HPLC-MS/MS) with atmospheric pressure chemical ionization (APCI) source. The method exhibited much better performance than previously reported methods. Furthermore, it was successfully applied in determining complicated environmental samples, including sewage sludge, river water and vegetable samples with concentration range from undetected (n.d.) to 25.8 ng g^-1 dry weight (dw). For sewage sludge, river water and vegetable samples, the spiking recoveries of TBBPA and its derivatives ranged from 69.6 ± 7.0% to 86.1 ± 12.9%, 69.5 ± 13.9% to 87.5 ± 6.6%, and 68.2 ± 5.6% to 80.2 ± 8.3%, respectively; the accuracy ranged from 94.9 ± 4.6% to 113 ± 5%, 91.9 ± 10.9% to 112 ± 7%, and 92.1 ± 5.1% to 106 ± 6%, and the method quantitative limits ranged from 0.00801 to 0.224 ng g^-1 dw, 0.0104-0.253 ng L^-1, and 0.00524-0.152 ng g^-1 dw, respectively. Moreover, the present manuscript describes for the first time the simultaneous detection of TBBPA and ten derivatives from various environmental samples, providing fundamental work for further research on their environmental occurrences, behaviors and fates.

Proliferation toxicity and mechanism of novel mixed bromine/chlorine transformation products of tetrabromobisphenol A on human embryonic stem cell

Mixed bromine/chlorine transformation products of tetrabromobisphenol A (Cl_yBr_xBPAs) are mixed halogenated-type compounds recently identified in electronic waste dismantling sites. There are a lack of toxicity data on these compounds. To study their development toxicity, the proliferation toxicity was investigated using human embryonic stem cells (hESC) exposed to the lowest effective dose of two Cl_yBr_xBPA analogues (2-chloro-2',6-dibromobisphenol A and 2,2'-dichloro-6-monobromobisphenol A). For comparison, tetrabromobisphenol A, 2,2',6-tribromobisphenol A, and bisphenol A were also assessed. It was observed that Cl_yBr_xBPAs inhibited hESCs proliferation in a concentration-dependent manner. The cell bioaccumulation efficiency of Cl_yBr_xBPAs was higher than that of tetrabromobisphenol A. Also, Cl_yBr_xBPAs were more toxic than tetrabromobisphenol A, with 2,2'-dichloro-6-monobromobisphenol A exhibiting the most potent toxicity. Furthermore, flow cytometry and oxidative stress results showed that increased reactive oxygen species raised the degree of apoptosis and reduced DNA synthesis. Metabolomics analysis on the effect of Cl_yBr_xBPAs on metabolic pathway alteration showed that Cl_yBr_xBPAs mainly interfered with four metabolic pathways related to amino acid metabolism and biosynthesis. These results provide an initial perspective on the proliferation toxicity of Cl_yBr_xBPAs, indicating development toxicity in children.

Daily exposure to low concentrations Tetrabromobisphenol A interferes with the thyroid hormone pathway in HepG2 cells

Tetrabromobisphenol A (TBBPA) is a flame retardant that adversely affects the environment and human health. The present study exposed HepG2 cells to low concentrations of TBBPA daily to investigate the changes in gene regulation, mainly related to pathways associated with the endocrine system. The quantitative polymerase chain reaction (qPCR) confirmed that prolonged exposure gradually activated the thyroid hormone and parathyroid hormone signaling pathways. The expression levels of genes related to the thyroid hormone signaling pathway were upregulated (1.15-8.54 times) after five generations of exposure to 1 and 81 nM TBBPA. Furthermore, co-exposure to 81 nM TBBPA and 0.5 nM thyroid hormone receptor antagonist for five generations significantly reduced the expression of thyroid hormone and parathyroid hormone receptors. Meanwhile, 81 nM TBBPA inhibited the activation of the Ras pathway and downregulated Ras gene expression level (3.7 times), indicating the association between the toxic effect and thyroid hormone receptors. Additionally, our experiments revealed that the thyroid hormone pathway regulated the induction of the Ras signaling pathway by TBBPA. The study thus proves that daily exposure to TBBPA interferes with the thyroid hormone signaling pathway and subsequently the endocrine system.

Binding, activity and risk assessment of bisphenols toward farnesoid X receptor pathway: In vitro and in silico study

Bisphenols have been identified as emerging environmental pollutants of high concern with potential adverse effects through interactions with receptor-mediated pathways. However, their potential mechanism of action and health risks through the farnesoid X receptor (FXR) pathway remain poorly understood. In the present study, we aimed to explore the potential disruption mechanism of bisphenols through the FXR signalling pathway. Receptor binding assays showed that bisphenols bound to FXR directly, with tetrabromobisphenol A (TBBPA; 34-fold), tetrachlorobisphenol A (TCBPA; 8.7-fold), bisphenol AF (BPAF; 2.0-fold), and bisphenol B (BPB; 1.9-fold) showing a significantly stronger binding potency than bisphenol A (BPA). In receptor transcriptional activity assays, bisphenols showed agonistic activity toward FXR, with BPAF, BPB, and bisphenol F (BPF) exhibiting higher activity than BPA, but TBBPA and TCBPA showing significantly weaker activity than BPA. Molecular docking results indicated that the number of hydrogen bonds dictated their binding strength. Intracellular concentrations of bisphenols were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in receptor activity assays, and it was found that the intracellular concentrations of TBBPA and TCBPA were 40-fold lower than those of BPA. Using the bioactivity concentrations in the FXR receptor activity assay, the liver concentrations of bisphenols were estimated using physiologically-based pharmacokinetic (PBPK) models through their serum concentrations, and the hazard quotient (HQ) values were calculated. The results suggest a potentially high concern for the risk of activating the FXR pathway for some populations with high exposure. Overall, these results indicate that bisphenols can bind to and activate FXR receptors, and that the activation mechanism is dependent on cellular uptake and binding strength. This study provides important information regarding the exposure risk of bisphenols, which can promote the development of environmentally friendly bisphenols.

Binding and Activation of Estrogen-Related Receptor γ: A Novel Molecular Mechanism for the Estrogenic Disruption Effects of DDT and Its Metabolites

DDT and its metabolites (DDTs) can induce estrogenic effects. Previous mechanistic investigations mainly concentrated on activating the genomic transcription of estrogen receptor (ER) pathways. Here, we identified whether estrogen-related receptor γ (ERRγ), an orphan nuclear receptor, is a potential target of DDTs by receptor binding, transcriptional activity, and receptor-mediated pathway assays. Fluorescence polarization-based binding assays showed that all eight DDTs bound to ERRγ directly, with K_d values ranging from 0.73-168.82 μM. Among them, 2,2-bis(4-chlorophenyl)ethanol (4,4'-DDOH) exhibited the highest binding affinity, which was 2.5-fold stronger than GSK4716, a well-known ERRγ agonist. Eight DDTs exhibited agonistic activity toward the ERRγ pathway, with 4,4'-DDOH showing the strongest potency. In silico studies revealed that DDTs tended to bind with ERRγ in the agonistic conformation. Using a SKBR3 breast cancer cell model, we further found that nanomolar or micromolar levels of DDTs significantly activated the ERRγ pathway in cells and induced cell proliferation through the ERRγ-modulated cell cycle. These results indicated that the binding and activation of DDTs to ERRγ might serve as molecular initiating events for subsequent ERRγ-mediated signaling pathways and adverse outcomes. Overall, our results demonstrated that ERRγ might be a crucial pathway involved in the estrogenic disruption effects of DDTs.

Identification and occurrence of TBBPA and its debromination and O-methylation transformation products in sediment, fish and whelks from a typical e-waste dismantling site

Tetrabromobisphenol A (TBBPA) and its debromination (∑BBPA) and O-methylation (∑MeO-TBBPA) products were widely detected in matched sediments, fish, and whelks samples collected from a typical electronic waste (e-waste) dismantling site in Southern China, with concentrations ranging from 19.8 to 1.52 × 10⁴, 8.05 to 1.84 × 10³, and 0.08 to 11.9 ng/g dry weight in sediments, and 6.96 to 1.97 × 10⁵, 3.84 to 7.07 × 10³, and 3.42 to 472 ng/g lipid in biotas, for TBBPA, ∑BBPA, and ∑MeO-TBBPA, respectively. Significantly higher concentrations of these targets were found in samples collected close to the e-waste site, indicating their potential e-waste sources. Tri-BBPA was the most abundant debromination products in sediments, whereas diMeO-TBBPA was the dominant O-methylation product in biotas. Relatively higher levels of diMeO-TBBPA found in liver and kidneys, suggesting these chemicals might be mainly derived from the in vivo biotransformation. Furthermore, significantly higher biota-sediment accumulation factor values were found for diMeO-TBBPA than these of TBBPA, indicating that O-methylation would increases their accumulation in aquatic organisms. Our study provides insights into the accumulation and biotransformation of TBBPA in aquatic systems. Further studies should pay attention to the occurrence as well as potential health risks of these transformation products.

Environmentally relevant exposure to TBBPA and its analogues may not drastically affect human early cardiac development

Tetrabromobisphenol A (TBBPA) and its substitutes and derivatives have been widely used as halogenated flame retardants (HFRs), in the past few decades. As a consequence, these compounds are frequently detected in the environment, as well as human bodily fluids, especially umbilical cord blood and breast milk. This has raised awareness of their potential risks to fetuses and infants. In this study, we employed human embryonic stem cell differentiation models to assess the potential developmental toxicity of six TBBPA-like compounds, at human relevant nanomolar concentrations. To mimic early embryonic development, we utilized embryoid body-based 3D differentiation in presence of the six HFRs. Transcriptomics data showed that HFR exposure over 16 days of differentiation only interfered with the expression of a few genes, indicating those six HFRs may not have specific tissue/organ targets during embryonic development. Nevertheless, further analyses revealed that some cardiac-related genes were dysregulated. Since the heart is also the first organ to develop, we employed a cardiac differentiation model to analyze the six HFRs' potential developmental toxicity in more depth. Overall, HFRs of interest did not significantly disturb the canonical WNT pathway, which is an essential signal transduction pathway for cardiac development. In addition, the six HFRs showed only mild changes in gene expression levels for cardiomyocyte markers, such as NKX2.5, MYH7, and MYL4, as well as a significant down-regulation of some but not all the epicardial and smooth muscle cell markers selected. Taken together, our results show that the six studied HFRs, at human relevant concentrations, may impose negligible effects on embryogenesis and heart development. Nevertheless, higher exposure doses might affect the early stages of heart development.

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.

Preself-Feeding Medaka Fry Provides a Suitable Screening System for in Vivo Assessment of Thyroid Hormone-Disrupting Potential

Endocrine-disrupting chemicals are assessed based on their physiological potential and their potential associated adverse effects. However, suitable end points for detection of chemicals that interfere with the thyroid hormone (TH) system have not been established in nonmammals, with the exception of amphibian metamorphosis. The aims of the current study were to develop an in vivo screening system using preself-feeding medaka fry (Oryzias latipes) for the detection of TH-disrupting chemicals and elucidate the underlying molecular mechanism. 17α-Ethinylestradiol (EE2: <100 ng/L) did not induce mRNA expression of estrogen-responsive genes, vitellogenins (vtgs) mRNA. Meanwhile, coexposure with thyroxin (T4) induced an increase of vtg expression. TH-disrupting chemicals (thiourea (TU), perfluorooctanoic acid (PFOA), and tetrabromobisphenol A (TBBPA)) significantly suppressed EE2 (1,000 ng/L)-induced vtg1 expression, while T4 rescued their expression as well as that of thyroid hormone receptor α (tRα) and estrogen receptors (esrs). These results were supported by in silico analysis of the 5'-transcriptional regulatory region of these genes. Furthermore, the esr1 null mutant revealed that EE2-induced vtg1 expression requires mainly esr2a and esr2b in a TH-dependent manner in preself-feeding fry. Application of preself-feeding medaka fry as a screening system might help decipher the in vivo mechanisms of action of TH-disrupting molecules, while providing an alternative to the traditional animal model.

Effects of postnatal exposure to tetrabromobisphenol A on testis development in mice and early key events

Whether or not tetrabromobisphenol A (TBBPA) has reproductive developmental toxicity remains controversial. Here, we evaluated the effects of postnatal TBBPA exposure of dams (before weaning) and pups through drinking water (15, 150, 1500 ng/mL) on testis development in mice. On postnatal day (PND) 56, we found that TBBPA exerted little effects on testis weight, anogenital distance, sperm parameters, and the serum testosterone level, but resulted in dose-dependent reductions in the seminiferous tubule area coupled with decreased Sertoli cells and spermatogonia and the number of stage VII-VIII seminiferous tubules, and cytoskeleton damage in Sertoli cells, along with down-regulated expression of marker genes for Sertoli cells, spermatogonia and spermatocyte. Further study revealed that the reduced tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression also occurred in TBBPA-treated testes on PND 7, along with reduced cell proliferation and disordered arrangement of Sertoli cell nuclei. On PND 15, most of these testicular alterations were still observed in TBBPA-treated males, and cytoskeleton damage in Sertoli cells became observable. All observations convincingly demonstrate that postnatal exposure to TBBPA disturbed testis development in early life and ultimately caused adverse outcomes in adult testes, and that cell proliferation inhibition, the reduction in the seminiferous tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression, and cytoskeleton damage in Sertoli cells, are early events contributing to adverse outcomes in adult testes. Our study improves the understanding of reproductive developmental toxicity of TBBPA, highlighting its risk for human health.

An adverse outcome pathway based in vitro characterization of novel flame retardants-induced hepatic steatosis

A wide range of novel replacement flame retardants (nFRs) is consistently detected in increasing concentrations in the environment and human matrices. Evidence suggests that nFRs exposure may be associated with disruption of the endocrine system, which has been linked with the etiology of various metabolic disorders, including nonalcoholic fatty liver disease (NAFLD). NAFLD is a multifactorial disease characterized by the uncontrolled accumulation of fats (lipids) in the hepatocytes and involves multiple-hit pathogenesis, including exposure to occupational and environmental chemicals such as organophosphate flame retardants (OPFRs). In the present study we aimed to investigate the potential mechanisms of the nFRs-induced hepatic steatosis in the human liver cells. In this study, we employed an in vitro bioassay toolbox to assess the key events (KEs) in the proposed adverse outcome pathways (AOP) (s) for hepatic steatosis. We examined nine nFRs using AOP- based in vitro assays measuring KEs such as lipid accumulation, mitochondrial dysfunction, gene expression, and in silico approach to identify the putative molecular initiating events (MIEs). Our findings suggest that several tested OPFRs induced lipid accumulation in human liver cell culture. Tricresyl phosphate (TMPP), triphenyl phosphate (TPHP), tris(1,3-dichloropropyl) phosphate (TDCIPP), and 2-ethylhexyl diphenyl phosphate (EHDPP) induced the highest lipid accumulation by altering the expression of genes encoding hepatic de novo lipogenesis and mitochondrial dysfunction depicted by decreased cellular ATP production. Available in vitro data from ToxCast and in silico molecular docking suggests that pregnane X receptor (PXR) and peroxisome proliferator-activated receptor gamma (PPARγ) could be the molecular targets for the tested nFRs. The study identifies several nFRs, such as TMPP and EHDPP, TPHP, and TDCIPP, as potential risk factor for NAFLD and advances our understanding of the mechanisms involved, demonstrating the utility of an AOP-based strategy for screening and prioritizing chemicals and elucidating the molecular mechanisms of toxicity.

Thyroid hormone system disrupting chemicals

The thyroid hormone system is a main target of endocrine disruptor compounds (EDC) at all levels of its intricately fine-tuned feedback regulation, synthesis, distribution, metabolism and action of the 'prohormone' thyroxine and its active metabolites. Apart from classical antithyroid effects of EDC on the gland, the majority of known and suspected effects occurs at the pre-receptor control of T3 ligand availability to T3 receptors exerting ligand modulated thyroid hormone action. Tissue-, organ- and cell-specific expression and function of thyroid hormone transporters, deiodinases, metabolizing enzymes and T3-receptor forms, all integral components of the system, may mediate adverse EDC effects. Established evidence from nutritional, pharmacological and molecular genetic studies clearly support the functional, biological, and clinical relevance of these targets. Iodine-containing thyroid hormones and the organization of this system are highly conserved during evolution from primitive aquatic life forms, amphibia, birds throughout all vertebrates including humans. Mechanistic studies from various animal experimental models strongly support cause-effect relationships upon EDC exposure, hazards and adverse effects of EDC across various species. Retrospective case-control, cohort and population studies linking EDC exposure with epidemiological data on thyroid hormone-related (dys-)functions provide clear evidence that human development, especially of the fetal and neonatal brain, growth, differentiation and metabolic processes in adult and aging humans are at risk for adverse EDC effects. Considering that more than half of the world population still lives on inadequate iodine supply, the additional ubiquitous exposure to EDC and their mixtures is an additional threat for the essential thyroid hormone system, the health of the human population and their future progenies, animal life forms and our global environment.

Different co-culture models reveal the pivotal role of TBBPA-promoted M2 macrophage polarization in the deterioration of endometrial cancer

Tetrabromobisphenol A (TBBPA), an emerging organic pollutant widely detected in human samples, has a positive correlation with the development of endometrial cancer (EC), but its underlying mechanisms have not yet been fully elucidated. Tumor-associated macrophages (TAM), one of the most vital components in tumor microenvironment (TME), play regulatory roles in the progression of EC. Consequently, this study mainly focuses on the macrophage polarization in TME to unveil the influence of TBBPA on the progression of EC and involved mechanisms. Primarily, low doses of TBBPA treatment up-regulated M2-like phenotype biomarkers in macrophage. The data from in vitro co-culture models suggested TBBPA-driven M2 macrophage polarization was responsible for the EC deterioration. Results from in vivo study further confirmed the malignant proliferation of EC promoted by TBBPA. Mechanistically, TBBPA-mediated miR-19a bound to the 3'-UTR regions of SOCS1, resulting in down-regulation of SOCS1 followed by the phosphorylation of JAK and STAT6. The present study not only revealed for the first time the molecular mechanism of TBBPA-induced EC's deterioration based on macrophage polarization, but also established co-culture models, thus providing a further evaluation method for the exploration of environmental pollutants-induced tumor effects from the role of TME.

Toxicity of Tetrabromobisphenol A and Its Derivative in the Mouse Liver Following Oral Exposure at Environmentally Relevant Levels

As typical brominated flame retardants (BFRs), tetrabromobisphenol A (TBBPA) and its derivative TBBPA-bis(2,3-dibromopropyl ether) (TBBPA-BDBPE) are ubiquitous in various environmental compartments. However, the potential health risk posed by these compounds, especially at environmentally relevant levels, remains unclear. In this study, using adult male mice, we investigated the toxicity of orally administered TBBPA and TBBPA-BDBPE at an environmentally relevant dose (57 nmol/kg body weight). After a single exposure and daily exposure, we assessed lipid metabolism homeostasis, the transcriptome, and immune cell components in the liver. We found that the single exposure to TBBPA or TBBPA-BDBPE alone increased the number of hepatic macrophages, induced alterations in the levels of lipids, including triacylglycerol and free fatty acids, and caused transcriptome perturbation. The results from the daily administration groups showed that TBBPA and TBBPA-BDBPE both significantly increased the triacylglycerol content; however, the elevation of hepatic macrophages was observed only in the TBBPA-BDBPE treatment group. This study confirmed that environmentally relevant levels of TBBPA and TBBPA-BDBPE are toxic to the liver. Our findings revealed that dysfunction of the liver is a health concern, following exposure to BFRs, even at very low concentrations. The chronic effects induced by TBBPA and its derivatives should be further investigated.

Covalent organic frameworks with tunable pore sizes enhanced solid-phase microextraction direct ionization mass spectrometry for ultrasensitive and rapid analysis of tetrabromobisphenol A derivatives

Selective adsorption via the size matching effect is one of the most effective strategies for separating and analyzing low levels of organic molecules. Herein, multicomponent covalent organic frameworks (MC-COFs) with tunable pore sizes are constructed by using one knot (1,3,5-triformylphloroglucinol, Tp) and two organic linkers (p-phenylenediamine, Pa; benzidine, BD). The pore sizes of the MC-COFs composed of TpPaBD_X (X = [BD]/([Pa] + [BD]) × 100 = 0, 25, 50, 75, and 100) range from 0.5-1.5 to 0.5-2.2 nm due to variations in the initial organic linker ratios. When coupling TpPaBD_X-based solid-phase microextraction (SPME) with constant flow desorption ionization mass spectrometry (CFDI-MS), these MC-COFs feature better selective adsorption performance for tetrabromobisphenol A (TBBPA) derivatives than TpPa with a smaller pore size, TpBD with a larger pore size and even some commercial fibers (e.g., polydimethylsiloxane/divinylbenzene (PDMS/DVB)-, polyacrylate (PA)- and PDMS-coated fibers). The improved method involving MC-COF TpPaBD₅₀ also presents favorable stability with relative standard deviations (RSD, 1 μg L^-1) for single fibers of 5.5-7.9% (n = 7) and fiber-to-fiber of 6.6-7.8% (n = 7). Due to the decreased limits of detection and quantification (0.5-12 and 1.6-40 ng L^-1), and reduced separation and detection time (7 min), ultratrace levels of TBBPA derivatives in real water samples are successfully detected. The proposed method shows great potential for the rapid tracing of the distribution, transportation and transformation of TBBPA derivatives to better understand their ecotoxicological effects in environmental media.