A\nNovel Organophosphate Ester, Tris(2,4-di<i>tert</i>-butylphenyl)\nPhosphate, Induced Reproductive Toxicity\nin Male Zebrafish at Environmentally Relevant Concentrations

As\na novel organophosphate ester (NOPE), tris(2,4-di<i>tert</i>-butylphenyl) phosphate (TDtBPP) has attracted significant attention\ndue to its unexpectedly high detection in natural environments. However,\nthe ecological toxic effects of environmentally relevant concentrations\nof TDtBPP in organisms remain entirely unknown. In this study, 1 month\nold zebrafish were exposed to 0, 50, 500, or 5000 ng/L TDtBPP for\n150 days, and the reproductive toxicity in male fish was evaluated.\nResults demonstrated that TDtBPP exposure significantly inhibited\nthe maturation of spermatozoa and thus decreased spermatogenesis.\nFurthermore, abnormal sperm morphology and decreased sperm motility\nwere also observed. The decrease in sperm quantity and quality eventually\nresulted in the declining fecundity. Moreover, TDtBPP exposure downregulated\nthe expression of <i>hsd3b1 in vivo</i> and in <i>vitro</i> and subsequently inhibited the synthesis of androgens in zebrafish\ntestes and Leydig cells. This inhibition of androgen synthesis appeared\nto be responsible for the observed reproductive toxicity in male fish.\nMolecular docking and dual-luciferase reporter gene experiments elucidated\nthat TDtBPP inhibited the promotion of vitamin D on <i>hsd3b1</i> transcription by the vitamin D receptor and thus downregulated the\nexpression of <i>hsd3b1</i>. Our findings provide first\ntime evidence that TDtBPP poses a risk to male fish reproduction at\nenvironmentally relevant levels.