Understanding bioaccumulation and metabolism is critical for evaluating the fate and potential toxicity of compounds in vivo. We recently investigated, for the first time, the bioconcentration and tissue distribution of triphenyl phosphate (TPHP) and its main metabolites in selected tissues of adult zebrafish. To further confirm the metabolites, deuterated TPHP (d-TPHP) was used in the exposure experiments at an environmentally relevant level (20 μg/L) and at 1/10 LC (100 μg/L). After 11-14 days of exposure to 100 μg/L of d-TPHP, the accumulation and excretion of d-TPHP reached equilibrium, at which point the intestine contained the highest d-TPHP (μg/g wet weight, ww) concentration (3.12 ± 0.43), followed by the gills (2.76 ± 0.12) > brain (2.58 ± 0.19) > liver (2.30 ± 0.34) ≫ muscle (0.53 ± 0.04). The major metabolite of d-TPHP, d-diphenyl phosphate (d-DPHP), was detected at significantly higher contents in the liver and intestine, at levels up to 3.0-3.5 times those of d-TPHP. The metabolic pathways of TPHP were elucidated, including hydrolysis, hydroxylation, and glucuronic acid conjugation after hydroxylation. Finally, a physiologically based toxicokinetic (PBTK) model was used to explore the key factors influencing the bioaccumulation of d-TPHP in zebrafish. These results provide important information for the understanding of the metabolism, disposition, and toxicology of TPHP in aquatic organisms.

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Antiviral transformation products (TPs) generated during wastewater treatment are an environmental concern, as their discharge, in considerable amounts, into natural waters during a pandemic can pose possible risks to the aquatic environment. Identification of the hazardous TPs generated from antivirals during wastewater treatment is important. Herein, chloroquine phosphate (CQP), which was widely used during the coronavirus disease-19 (COVID-19) pandemic, was selected for research. We investigated the TPs generated from CQP during water chlorination. Zebrafish (Danio rerio) embryos were used to assess the developmental toxicity of CQP after water chlorination, and hazardous TPs were estimated using effect-directed analysis (EDA). Principal component analysis revealed that the developmental toxicity induced by chlorinated samples could be relevant to the formation of some halogenated TPs. Fractionation of the hazardous chlorinated sample, along with the bioassay and chemical analysis, identified halogenated TP387 as the main hazardous TP contributing to the developmental toxicity induced by chlorinated samples. TP387 could also be formed in real wastewater during chlorination in environmentally relevant conditions. This study provides a scientific basis for the further assessment of environmental risks of CQP after water chlorination and describes a method for identifying unknown hazardous TPs generated from pharmaceuticals during wastewater treatment.

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Polyhalogenated carbazoles (PHCZs) make up a group of persistent, bioaccumulative, and toxic contaminants and are newly identified as chlorinated disinfection byproducts. However, the fates of these compounds in prolonged chlorination are largely unknown, leading to a great threat to the safety of drinking water. This study investigated the transformation of PHCZs during prolonged chlorination by using 3,6-dichlorocarbazole (36-CCZ) as a model congener, providing important information about the fates of PHCZs in drinking water. The degradation kinetics of 36-CCZ showed a strong pH dependency with apparent second-order rate constants of 1.52–5.17 M–1 s–1 at pH 6–10. The degradation rates are comparable to that of pyrene in chlorination. Seven new chlorine-containing products P1–P7 were detected. Transformation pathways, involving electrophilic chlorination, nucleophilic water addition, aromatic ring opening, and HCl elimination, were proposed, and the reaction mechanism was explored. The product evolution versus time showed the first generation of the highly halogenated carbazoles of 1,3,6-trichlorocarbazole (P1) and 1,3,6,8-tetrachlorocarbazole (P2), followed by the generation of hydroxylated products P3–P7. The persistence of the seven products in chlorinated water over 24 h indicated that human exposure to PHCZs and/or their transformation products was highly possible. This study provides novel insights into the behaviors of PHCZs in drinking water.