Environmentally Relevant Concentrations of the Organophosphorus Flame Retardant Triphenyl Phosphate Impaired Testicular Development and Reproductive Behaviors in Japanese Medaka (Oryzias latipes)

While triphenyl phosphate (TPhP) has been frequently detected in surface water and wildlife, its adverse effects on the gonadal development and reproductive behaviors of fish remain unclear. In this study, Japanese medaka (Oryzias latipes) were exposed to TPhP at concentrations of 134.1, 299.1, and 1429.5 ng/L from hatching [0 days posthatching (dph)] to sexual maturity (100 dph). TPhP induced gonadal intersex in male medaka in all exposure groups, and a significant increase was observed in the 1429.5 ng/L exposure group, with an incidence of 26.2% (11 of 42; p < 0.01). TPhP exposure also caused abnormal chasing behavior, with a lowest observable effective concentration (LOEC) of 299.1 ng/L, and reduced the desire of males for females in the 1429.5 ng/L group, demonstrating toxicity for fish reproductive behaviors. The anti-androgenic activity of TPhP via both androgen suppression and AR blocking was proposed to be the major mechanism of the observed effects. On the basis of dose-dependent inhibition of successful mating, fertilization, and hatching of eggs, environmentally relevant concentrations of Tphp pose a risk to fish reproduction.