Environmentally relevant concentrations of tris(2-chloroethyl) phosphate disrupt zebrafish...

Tris(2-chloroethyl) phosphate (TCEP) is a widely used chlorinated organophosphorus flame retardant, that has been frequently detected in aquatic organisms and surface water. While previous studies have shown the potential endocrine disrupting effects of TCEP, its long-term reproductive toxicities at environmentally relevant concentrations remain unclear. This study comprehensively analyzed the reproductive toxicity and mechanisms of TCEP in zebrafish. Zebrafish were exposed to TCEP (0.2-200 µg/L) from embryo to adult stages for 120 days. Results showed significant alterations in reproductive indicators, including decreased body length and weight, reduced tissue indices and impaired gonadal development. Notably, TCEP altered sex hormone levels, with decreased 17β-estradiol (E2) and vitellogenin (VTG) in females, increased E2 and VTG in males, and reduced testosterone in both sexes. A female-biased sex ratio was observed at 22.01 and 241.84 µg/L TCEP, with reduced spawning and impaired F1 offspring development. Transcriptomic analysis revealed significant alterations in hypothalamus-pituitary-gonad-liver (HPGL) axis gene expression, such as hsd17b12a. Molecular docking simulations suggested that TCEP may interfere with sex hormone receptor binding and cytochrome P450 (CYP450) enzyme function. This study reveals new insights into the reproductive toxicity mechanisms of TCEP in zebrafish. The toxic effects follow an inverted U-shaped curve, with peak toxicity occurring at approximately 2.62 µg/L. These findings underscore the importance of regulating this emerging contaminant in freshwater ecosystems.