Graph Convolutional Network-Enhanced Model for Screening Persistent, Mobile, and Toxic and Very Persistent and Very Mobile Substances.

The global management for persistent, mobile, and toxic (PMT) and very persistent and very mobile (vPvM) substances has been further strengthened with the rapid increase of emerging contaminants. The development of a ready-to-use and publicly available tool for the high-throughput screening of PMT/vPvM substances is thus urgently needed. However, the current model building with the coupling of conventional algorithms, small-scale data set, and simplistic features hinders the development of a robust model for screening PMT/vPvM with wide application domains. Here, we construct a graph convolutional network (GCN)-enhanced model with feature fusion of a molecular graph and molecular descriptors to effectively utilize the significant correlation between critical descriptors and PMT/vPvM substances. The model is built with 213,084 substances following the latest PMT classification criteria. The application domains of the GCN-enhanced model assessed by kernel density estimation demonstrate the high suitability for high-throughput screening PMT/vPvM substances with both a high accuracy rate (86.6%) and a low false-negative rate (6.8%). An online server named PMT/vPvM profiler is further developed with a user-friendly web interface (http://www.pmt.zj.cn/). Our study facilitates a more efficient evaluation of PMT/vPvM substances with a globally accessible screening platform.

Advances and applications of machine learning and deep learning in environmental ecology and health.

Machine learning (ML) and deep learning (DL) possess excellent advantages in data analysis (e.g., feature extraction, clustering, classification, regression, image recognition and prediction) and risk assessment and management in environmental ecology and health (EEH). Considering the rapid growth and increasing complexity of data in EEH, it is of significance to summarize recent advances and applications of ML and DL in EEH. This review summarized the basic processes and fundamental algorithms of the ML and DL modeling, and indicated the urgent needs of ML and DL in EEH. Recent research hotspots such as environmental ecology and restoration, environmental fate of new pollutants, chemical exposures and risks, chemical hazard identification and control were highlighted. Various applications of ML and DL in EEH demonstrate their versatility and technological revolution, and present some challenges. The perspective of ML and DL in EEH were further outlined to promote the innovative analysis and cultivation of the ML-driven research paradigm.

Bisphenol analogues induce thyroid dysfunction via the disruption of the thyroid hormone synthesis pathway.

Bisphenol analogues are widely used in industrial and daily-use consumer products having imperfect thyroid hormones (THs) structures. Widespread exposure interferes with thyroid-related health outcomes in human. The mechanisms of disruption on TH synthesis and subsequent thyroid dysfunction by different bisphenol analogues remain unclear. Here, we evaluated bisphenol-induced thyroid endocrine disruption in C57BL/6 mice at doses of 0.002, 0.02, 2, and 20 mg/kg body weight/day (BW/d) for five consecutive weeks. Administration of 20 mg/kg BW/d bisphenol S (BPS) and 2 mg/kg BW/d tetrabromobisphenol S (TBBPS) significantly increased serum thyrotropin (TSH) levels to 1.21-fold and 1.20-fold of control group, respectively, indicating that bisphenols induced thyroid dysfunction in mice. Height of the thyroid follicle epithelium significantly increased to 1.27-, 1.24-, 1.26-, and 1.36-fold compared to control group with BPA, BPS, TBBPA, and TBBPS at 20 mg/kg BW/d, respectively, indicating impairment of the thyroid gland structure, and TBBPS showed potent effect. Exposure to bisphenol analogues of 0.02 mg/kg BW/d downregulated the protein expression levels of thyrotropin receptor, the sodium/iodide symporter, thyroperoxidase. The TH-dependent effects were further determined using the T-Screen assay at 10-11 M to 10-5 M concentrations. Bisphenol analogues significantly decreased TH-dependent GH3 cell proliferation, indicating the antagonistic activity of bisphenol analogues. The gene responsible for THs synthesis of thyrotropin releasing hormone receptor and TSH were upregulated, but downregulation of thyroid receptor ß was observed. Our results suggest that bisphenol analogues distinctly induce thyroid dysfunction via TH synthesis, implying adverse effect of bisphenol analogues on TH homeostasis and subsequent physiological processes.

Angiogenic Activity and Mechanism for Bisphenols on Endothelial Cell and Mouse: Evidence of a Structural-Selective Effect.

Increased epidemiological evidence indicates the association of bisphenol exposure with human vascular disorders, while the underlying mechanism has not been clarified. Here, we sought to unveil the potential angiogenic effect and the underlying mechanism of bisphenols with different structural features using endothelial cells treated with an environmentally relevant concentration of bisphenols (range: 1 nM to 10 µM) and a C57BL/6 mouse model fed with doses of 0.002, 0.02, 2, and 20 mg/kg BW/day for 5 weeks. Bisphenol A (BPA) and bisphenol S (BPS) at a 1 nM level significantly increased tube formation by 45.1 and 30.2% and induced the microvessel sprouting, while tube length and microvessel sprouting were significantly inhibited by 37.2 and 55.7% after exposure to tetrabromobisphenol S (TBBPS) at 1 µM, respectively. Mechanistically, TBBPA and TBBPS significantly inhibited the interaction between phosphatidylinositol 3-kinase (PI3K) and thyroid receptor (TR), while BPA and BPS favored the interaction between PI3K and estrogen receptor (ER), resulting in abnormal PI3K signaling with consequent distinct angiogenic activity. BPA- and BPS-induced pro-angiogenic effects and TBBPS showed anti-angiogenic effects due to their distinct disruption on the TR/ER-PI3K pathway. Our work provided new evidence and mechanistic insight on the angiogenic activity of bisphenols and expanded the scope of endocrine disruptors with interference in vascular homeostasis.

Embryonic Exposure to UV-328 Impairs the Cell Cycle in Zebrafish (Danio rerio) by Inhibiting the p38 MAPK/p53/Gadd45a Signaling Pathway.

The benzotriazole UV stabilizer UV-328 is well known for its potent antioxidative properties; however, there are concerns about how it may affect signaling nodes and lead to negative consequences. This study identified the key signaling cascades involved in oxidative stress in zebrafish (Danio rerio) larvae and evaluated the cell cycle arrests and associated developmental alternations. Exposure to UV-328 at 0.25, 0.50, 1.00, 2.00, and 4.00 µg/L downregulated gene expression associated with oxidative stress (cat, gpx, gst, and sod) and apoptosis (caspase-3, caspase-6, caspase-8, and caspase-9) at 3 days postfertilization (dpf). The transcriptome aberration in zebrafish with disrupted p38 mitogen-activated protein kinase (MAPK) cascades was validated based on decreased mRNA expressions of p38 MAPK (0.36-fold), p53 (0.33-fold), and growth arrest and DNA damage-inducible protein 45 α (Gadd45a) (0.52-fold) after a 3- and 14-day exposure alongside a correspondingly decreased protein expression. The percentage of cells in the Gap 1 (G1) phase increased from 69.60% to a maximum of 77.07% (p < 0.05) in the 3 dpf embryos. UV-328 inhibited the p38 MAPK/p53/Gadd45a regulatory circuit but promoted G1 phase cell cycle arrest, abnormally accelerating the embryo hatching and heart rate. This study provided mechanistic insights that enrich the risk profiles of UV-328.

Impaired barrier integrity of endothelial cells induced by PEGylated black phosphorus nanosheets.

PEGylated black phosphorus nanosheets (PEG-BPNSs) have shown promising applications in biomedicine and potentially interact with the vasculature following iatrogenic exposures. Whether the exposure to PEG-BPNSs could induce toxic effects on endothelial cells that line the blood vessels remains largely unknown. Herein, we investigate the cellular response and transcriptional profiling of human umbilical vein endothelial cells (HUVECs) after the exposure to BPNSs and PEG-BPNSs. BPNSs and PEG-BPNSs induce cellular elongation and cause significant cytotoxicity to HUVECs at 0.8 µg/mL, with viabilities of 87.8% and 87.7% respectively. The transcriptome analysis indicates that BPNSs and PEG-BPNSs at 0.4 µg/mL cause marked alterations in the expression of genes associated with detection of stimulus, ion transmembrane transport and components of plasma membrane. BPNSs and PEG-BPNSs at 0.4 µg/mL decrease the transendothelial electrical resistance (TEER) across monolayers of HUVECs by 22.8% and 20.3% compared to the control, respectively. The disturbance of tight junctions (TJs) after 24 h exposure to 0.4 µg/mL BPNSs and PEG-BPNSs is indicated with the downregulated mRNA expression of zona occluden-1 (ZO-1) by respective 16.5% and 29.9%, which may be involved in the impairment of endothelial barrier integrity. Overall, the response of HUVECs to PEG-BPNSs and BPNSs has no statistical difference, suggesting that PEGylation does not attenuate the BPNSs-induced endothelial injury. This study demonstrates the detrimental effects of BPNSs and PEG-BPNSs on barrier integrity of HUVECs, contributing to our understanding on the potential toxicological mechanisms.

Machine Learning-Based Models with High Accuracy and Broad Applicability Domains for Screening PMT/vPvM Substances.

Persistent, mobile, and toxic (PMT) substances and very persistent and very mobile (vPvM) substances can transport over long distances from various sources, increasing the public health risk. A rapid and high-throughput screening of PMT/vPvM substances is thus warranted to the risk prevention and mitigation measures. Herein, we construct a machine learning-based screening system integrated with five models for high-throughput classification of PMT/vPvM substances. The models are constructed with 44 971 substances by conventional learning, deep learning, and ensemble learning algorithms, among which, LightGBM and XGBoost outperform other algorithms with metrics exceeding 0.900. Good model interpretability is achieved through the number of free halogen atoms (fr_halogen) and the logarithm of partition coefficient (MolLogP) as the two most critical molecular descriptors representing the persistence and mobility of substances, respectively. Our screening system exhibits a great generalization capability with area under the receiver operating characteristic curve (AUROC) above 0.951 and is successfully applied to the persistent organic pollutants (POPs), prioritized PMT/vPvM substances, and pesticides. The screening system constructed in this study can serve as an efficient and reliable tool for high-throughput risk assessment and the prioritization of managing emerging contaminants.

Promotion of Bladder Cancer Cell Metastasis by 2-Mercaptobenzothiazole via Its Activation of Aryl Hydrocarbon Receptor Transcription: Molecular Dynamics Simulations, Cell-Based Assays, and Machine Learning-Driven Prediction.

2-Mercaptobenzothiazole (MBT) is an industrial chemical widely used for rubber products, corrosion inhibitors, and polymer materials with multiple environmental and exposure pathways. A growing body of evidence suggests its potential bladder cancer (BC) risk as a public health concern; however, the molecular mechanism remains poorly understood. Herein, we demonstrate the activation of the aryl hydrocarbon receptor (AhR) by MBT and reveal key events in carcinogenesis associated with BC. MBT alters conformational changes of AhR ligand binding domain (LBD) as revealed by 500 ns molecular dynamics simulations and activates AhR transcription with upregulation of AhR-target genes CYP1A1 and CYP1B1 to approximately 1.5-fold. MBT upregulates the expression of MMP1, the cancer cell metastasis biomarker, to 3.2-fold and promotes BC cell invasion through an AhR-mediated manner. MBT is further revealed to induce differentially expressed genes (DEGs) most enriched in cancer pathways by transcriptome profiling. The exposure of MBT at environmentally relevant concentrations induces BC risk via AhR signaling disruption, transcriptome aberration, and malignant cell metastasis. A machine learning-based model with an AUC value of 0.881 is constructed to successfully predict 31 MBT analogues. Overall, we provide molecular insight into the BC risk of MBT and develop an effective tool for rapid screening of AhR agonists.

Benzophenone-1 induced aberrant proliferation and metastasis of ovarian cancer cells via activated ERα and Wnt/ß-catenin signaling pathways.

Benzophenone-1 (BP-1) belongs to personal care product-related contaminants of emerging concern and has been recently reported to induce xenoestrogenic effects. However, the underlying mechanisms leading to the activation of target receptors and subsequent various adverse outcomes remain unclear, which is beneficial to safety and health risk assessment of benzophenone-type ultraviolet filters with their widespread occurrence. Herein, we investigated disrupting effects of BP-1 at environmentally relevant concentrations (10-9-10-6 M) on estrogen receptor (ER) α-associated signaling pathways. Molecular dynamics simulations together with yeast-based assays revealed the steady binding of BP-1 to ERα ligand binding domain (LBD) and hence the observed agonistic activity. BP-1 triggered interaction between ERα and ß-catenin in human SKOV3 ovarian cancer cells and caused translocation of ß-catenin from the cytoplasm to the nucleus, leading to aberrant activation of Wnt/ß-catenin. BP-1 consequently induced dissemination of SKOV3 via regulating epithelial-mesenchymal transitions (EMT) biomarkers including minimally downregulating ZO-1 gene to 78.0 ± 10.1% and maximally upregulating MMP9 gene to 144.1 ± 29.7% and promoted 1.03-1.83 fold proliferation, migration and invasion of SKOV3. We provide the first evidence that the BP-1 activated ERα triggers crosstalk between ERα and Wnt/ß-catenin pathway, leading to the abnormal stimulation and progression of SKOV3 cancer cells.

Endothelial barrier dysfunction induced by anthracene and its nitrated or oxygenated derivatives at environmentally relevant levels.

Polycyclic aromatic hydrocarbons (PAHs) are epidemiologically associated with cardiovascular diseases characterized by early key events involving in the disruption of endothelial barrier function. Whether PAHs can induce adverse cardiovascular outcome by directly destabilizing endothelial barrier function remains elusive. Herein, we investigated the effect of anthracene (ANT), 9-nitroanthracene (9-NANT), and 9,10-anthraquinone (9,10-AQ) on vascular endothelial barrier functions in human umbilical vein endothelial cells (HUVECs). The integrity of endothelial barrier in HUVECs was disturbed with a 1.15-1.42 fold increase in fluorescein leakage, and 21.8%-58.3% downregulated transendothelial electrical resistance. ANT, 9-NANT and 9,10-AQ promoted paracellular gap formation as revealed by transmission electron microscope. The disrupted cell junctions after 24 h exposure to ANT, 9-NANT and 9,10-AQ at 0.01 µM were indicated by the downregulated mRNA expression of vascular endothelial cadherin (VE-cadherin), zona occludens-1 (ZO-1) and occludin by 33.2%-71.4%, 19.1%-21.0%, and 31.9% respectively, and the downregulated protein expression of ZO-1 and occludin, and by the internalization of VE-cadherin. We demonstrated that ANT and its derivatives at environmentally relevant concentrations induced endothelial barrier dysfunction via the disruption of cell junctions, providing essential in vitro evidence on the association with their adverse cardiovascular outcomes.

Carcinogenic Risk of 2,6-Di-tert-Butylphenol and Its Quinone Metabolite 2,6-DTBQ Through Their Interruption of RARß: In Vivo, In Vitro, and In Silico Investigations.

Thousands of contaminants are used worldwide and eventually released into the environment, presenting a challenge of health risk assessment. The identification of key toxic pathways and characterization of interactions with target biomacromolecules are essential for health risk assessments. The adverse outcome pathway (AOP) incorporates toxic mechanisms into health risk assessment by emphasizing the relationship among molecular initiating events (MIEs), key events (KEs), and adverse outcome (AO). Herein, we attempted the use of AOP to decipher the toxic effects of 2,6-di-tert-butylphenol (2,6-DTBP) and its para-quinone metabolite 2,6-di-tert-butyl-1,4-benzoquinone (2,6-DTBQ) based on integrated transcriptomics, molecular modeling, and cell-based assays. Through transcriptomics and quantitative real-time PCR validation, we identified retinoic acid receptor ß (RARß) as the key target biomacromolecule. The epigenetic analysis and molecular modeling revealed RARß interference as one MIE, including DNA methylation and conformational changes. In vitro assays extended subsequent KEs, including altered protein expression of p-Erk1/2 and COX-2, and promoted cancer cell H4IIE proliferation and metastasis. These toxic effects altogether led to carcinogenic risk as the AO of 2,6-DTBP and 2,6-DTBQ, in line with chemical carcinogenesis identified from transcriptome profiling. Overall, our simplified AOP network of 2,6-DTBP and 2,6-DTBQ facilitates relevant health risk assessment.

Transcriptome aberration in mice uterus associated with steroid hormone response and inflammation induced by dioxybenzone and its metabolites.

Benzophenone-type UV filters have been implicated in multiple adverse reproductive outcomes, yet the underlying processes and molecular targets on the female reproductive tract remain largely unknown. Herein, we investigated the effect of dioxybenzone, one of the widely used congeners, and its demethylated (M1) and hydroxylated (M2) metabolites on transcriptome profiles of ICR mice uterus and identified potential cellular targets in human endometrial stromal cells (HESCs) separated from normal endometrium tissues. Dioxybenzone, M1 and M2 (20 mg/kg bw/d) significantly induced transcriptome aberration with the induction of 683, 802, and 878 differentially expressed genes mainly involved in cancer, reproductive system disease and inflammatory disease. Compared to dioxybenzone, M1 and M2 exhibited a transcriptome profile more similar to estradiol in mice uterus, and subsequently promoted thicker endometrial columnar epithelial layer through upregulation of estrogen receptor target genes-Sprr2s. Dioxybenzone, M1 and M2 (0.1 or 1 µM) also exhibited estrogenic disrupting effect via increasing the mRNA expressions and production of the growth factors responsible for epithelial proliferation, including Fgfs and Igf-1 in HESCs. Additionally, the mRNA expressions of several inflammatory cytokines especially IL-1ß in mice uterus and HESCs was significantly upregulated by dioxybenzone and its metabolites. Overall, we revealed that dioxybenzone and its metabolites triggered transcriptome perturbation dually associated with abnormal steroid hormone response and inflammation, both as key determinants to reproductive health risks.

Enhanced Disrupting Effect of Benzophenone-1 Chlorination Byproducts to the Androgen Receptor: Cell-Based Assays and Gaussian Accelerated Molecular Dynamics Simulations.

Benzophenone-1 (BP-1), one of the commonly used ultraviolet filters, has caused increasing public concern due to frequently detected residues in environmental and recreational waters. Its susceptibility to residual chlorine and the potential to subsequently trigger endocrine disruption remain unknown. We herein investigated the chlorination of BP-1 in swimming pool water and evaluated the endocrine disruption toward the human androgen receptor (AR). The structures of monochlorinated (P1) and dichlorinated (P2) products were separated and characterized by mass spectrometry and 1H-1H NMR correlation spectroscopy. P1 and P2 exhibited significantly higher antiandrogenic activity in yeast two-hybrid assays (EC50, 6.13 µM and 9.30 µM) than did BP-1 (12.89 µM). Our 350 ns Gaussian accelerated molecular dynamics simulations showed the protein dynamics in a long-time scale equilibrium, and further energy calculations revealed that although increased hydrophobic interactions are primarily responsible for enhanced binding affinities between chlorinated products and the AR ligand binding domain, the second chloride in P2 still hinders the complex motion because of the solvation penalty. The mixture of BP-1-P1-P2 elicited additive antiandrogenic activity, well fitted by the concentration addition model. P1 and P2 at 1 µM consequently downregulated the mRNA expression of AR-regulated genes, NKX3.1 and KLK3, by 1.7-9.1-fold in androgen-activated LNCaP cells. Because chlorination of BP-1 occurs naturally by residual chlorine in aquatic environments, our results regarding enhanced antiandrogenic activity and disturbed AR signaling provided evidence linking the use of personal care products with potential health risks.

2,6-Di-tert-butylphenol and its quinone metabolite trigger aberrant transcriptional responses in C57BL/6 mice liver.

2,6-Di-tert-butylphenol (2,6-DTBP) is used as an antioxidant with wide commercial applications and its residues have been detected in various environmental matrices. 2,6-DTBP may enter human body via ingestion, inhalation or other exposure pathways. However, its susceptibility to biotransformation and potential of the metabolic products to trigger aberrant transcriptional responses remain unclear. Here, we investigated in vitro and in vivo biotransformation of 2,6-DTBP and characterized the RNA-Seq based transcriptional profiling of C57BL/6 mice liver after the exposure to 2,6-DTBP and its metabolites. 2,6-DTBP was metabolized into hydroxylated (2,6-DTBH) and para-quinone (2,6-DTBQ) products with residues detected in serum and liver of C57BL/6 mice. 2,6-DTBP and 2,6-DTBQ induced the aberrant transcription in C57BL/6 mice liver featured with 373-2861 differentially expressed genes (DEGs). They also up-regulated 1.09-2.92 fold mRNA expression of carcinogenesis-related genes such as Ccnd1, TGFß1 and FOS in C57BL/6 mice liver. Our study indicated potential carcinogenic risk of 2,6-DTBP and its metabolites, beneficial to further evaluation of health risk of TBPs-related contaminants.

Dioxybenzone triggers enhanced estrogenic effect via metabolic activation: in silico, in vitro and in vivo investigation.

Dioxybenzone is widely used in cosmetics and personal care products and frequently detected in multiple environmental media and human samples. However, the current understanding of the metabolic susceptibility of dioxybenzone and the potential endocrine disruption through its metabolites in mimicking human estrogens remains largely unclear. Here we investigated the in vitro metabolism of dioxybenzone, detected the residue of metabolites in rats, and determined the estrogenic disrupting effects of these metabolites toward estrogen receptor α (ERα). In vitro metabolism revealed two major metabolites from dioxybenzone, i.e., M1 through the demethylation of methoxy moiety and M2 through hydroxylation of aromatic carbon. M1 and M2 were both rapidly detected in rat plasma upon exposure to dioxybenzone, which were then distributed into organs of rats in the order of livers > kidneys > uteri > ovaries. The 100 ns molecular dynamics simulation revealed that M1 and M2 formed hydrogen bond to residue Leu387 and Glu353, respectively, on ERα ligand binding domain, leading to a reduced binding free energy. M1 and M2 also significantly induced estrogenic effect in comparison to dioxybenzone as validated by the recombinant ERα yeast two-hybrid assay and uterotrophic assay. Overall, our study revealed the potential of metabolic activation of dioxybenzone to induce estrogenic disrupting effects, suggesting the need for incorporating metabolic evaluation into the health risk assessment of benzophenones and their structurally similar analogs.

Pentabromoethylbenzene Exposure Induces Transcriptome Aberration and Thyroid Dysfunction: In Vitro, in Silico, and in Vivo Investigations.

Pentabromoethylbenzene (PBEB), as one of the novel brominated flame retardants (NFBRs), has caused increasing public concern for health risks. Till now, information regarding potential effects of PBEB on thyroid function remains unclear. Herein, we investigated thyroid disruption of PBEB in vitro and in silico and evaluated thyroid dysfunction induced by PBEB using Sprague-Dawley rats. PBEB showed thyroid receptor (TR) ß antagonistic activity with IC50 of 9.82 × 10-7 M in the dual-luciferase reporter gene assay and induced relative reorientation of helix 11 (H11) and H12 of the TR ligand binding domain as revealed by molecular dynamics simulations. PBEB (0.2, 2, 20 mg/kg BW/d) markedly altered the transcriptome profile of thyroid with induction of 17, 42, and 119 differentially expressed genes (DEGs) involved in thyroid hormone signaling and synthesis pathway, of which transthyretin and albumin are common DEGs. The 28-d exposure to PBEB significantly decreased the triiodothyronine level (from 7.23 to 5.67 ng/mL) and increased the thyrotropin level (from 7.88 to 12.86 mU/L) for female rats. PBEB consequently reduced thyroid weight and altered its morphology with more depleted follicles. Overall, our study provides the first account of evidence on PBEB exerted thyroid disruption, transcriptome aberration, and morphological alteration, facilitating health risk assessment of PBEB and structurally related NBFRs.

The molecular mechanism of the antagonistic activity of hydroxylated polybrominated biphenyl (OH-BB80) toward thyroid receptor ß.

Polybrominated biphenyls (PBBs) were widely used as additive brominated flame retardants. Their hydroxylated products (OH-PBBs) have been detected frequently in various marine mammals, causing an increased health risk. Till now, there lacks information on the potential disruption of OH-PBBs toward thyroid hormone receptor (TR) and the molecular characteristics of their interactions remain largely unknown. We herein in vitro and in silico evaluated the disrupting effect of 3,3',5,5'-tetrabromobiphenyl (BB80) and its metabolite 2,2'-dihydroxy- 3,3',5,5'-tetrabromobiphenyl (OH-BB80) toward human TR. The recombinant human TRß two-hybrid yeast assay reveals the moderate antagonistic activity of OH-BB80 with IC20 at 2 µmol/L, while BB80 shows no agonistic or antagonistic activity. OH-BB80 binds at the binding cavity of TRß ligand binding domain (LBD) and forms one hydrogen bond with Phe272. Electrostatic interactions and hydrophobic interactions contribute much to their interactions. The binding of OH-BB80 quenches the intrinsic fluorescence of TRß LBD at static quenching mode. Our study extends knowledge on the endocrine disrupting effect of OH-PBBs and suggests the full consideration of the biotransformation for further health risk assessment of PBBs and related structurally similar emerging contaminants.

Natural sunlight-driven aquatic toxicity enhancement of 2,6-di-tert-butylphenol toward Photobacterium phosphoreum.

The tert-butylphenols (TBPs) are one group of alkylated phenolic compounds with wide applications in UV absorbers and antioxidants. They are becoming contaminants of emerging concern with residues frequently detected in natural surface water or drinking water. The direct sunlight may photolyze TBPs in waters and affect their aquatic toxicities; however, such data are very limited. In the present study, we investigate the photodegradation of 2,6-DTBP by direct sunlight in water and compare the aquatic toxicities of 2,6-DTBP with that of its product toward Photobacterium phosphoreum. 2,6-DTBP is photodegraded by 71.31 ±â€¯2.64% under simulated sunlight following a pseudo-first-order kinetics with rate constant (k) of 0.061 h-1. Density functional theory simulations at M06-2X/def2-SVP level reveal that the photodegradation occurred sequentially through oxidation, photo-isomerization and hydrogenation. The degradation product 2,5-DTBP is toxic to P. phosphoreum (EC50 3.389 × 10-5 mol/L) whereas 2,6-DTBP is not harmful (EC50 3.917 × 10-3 mol/L) as designated by the European Union Standard, indicating the enhanced toxicities driven by the direct sunlight photodegradation. We demonstrate the enhanced toxicities of 2,6-DTBP by natural sunlight, suggesting that negligence of photodegradation of TBPs-related contaminants will underestimate the comprehensive risk of these emerging contaminant in natural waters.

Metabolic Susceptibility of 2-Chlorothioxanthone and Its Toxic Effects on mRNA and Protein Expression and Activities of Human CYP1A2 and CYP3A4 Enzymes.

Thioxanthones (TXs) are photoinitiators widely used in UV curable resins and food packaging, and their residues have been frequently detected in human bodies. Our current understanding of the susceptibility of residual TXs to metabolism and their effects on human health is very limited. The in vitro metabolism of TXs and its toxic effects on cytochrome P450 (CYP) (the key xenobiotic metabolizing enzymes) were examined in this study. 2-Chlorothioxanthone (2-Cl-TX) significantly inhibited the enzymatic activities of CYP1A2 and CYP3A4 with IC50 of 8.36 and 0.86 µM, respectively. The exposure to 2-Cl-TX at 2.5 µM up-regulated the mRNA expression of CYP1A2 and CYP3A4 in human hepatocellular carcinoma cells to 3.03-fold and 2.02-fold, respectively. 2-Cl-TX at 2.5 µM caused 2.19-fold and 1.98-fold overexpression of CYP1A2 and CYP3A4, respectively. In vitro studies revealed that 2-Cl-TX was biotransformed into two metabolites through the sulfoxidation of the sulfur atom, or via the hydroxylation of aromatic carbon. Results from this study, including the metabolic susceptibility of residual 2-Cl-TX, the proposed metabolites and the significant toxic effect on the activities, mRNA, and protein expression of CYP1A2 and CYP3A4, are vital to the human health and safety risk assessment from this ubiquitous xenobiotic.