Induction of testis-ova in Japanese medaka (Oryzias latipes) exposed to p-nonylphenol

4-Nonylphenol (NP) is a degradation product of nonylphenol polyethoxylates, a major group of nonionic surfactants. When Japanese medaka, Oryzias latipes were exposed from hatch to 3 months of age to aqueous solutions of NP at nominal concentrations of 10, 50, and 100 mu g/L, 50% of the male fish in the 50-mu g/L treatment and 86% of the males in the 100-mu g/L treatment developed testis-ova, an intersex condition characterized by both testicular and ovarian tissue in the gonad. The ratios of males to females in the control treatment (2:1, M:F) and the 100-mu g/L NP treatment (1:2, M:F) were also significantly different. The LOAEC for induction of testis-ova at a nominal concentration of 50 mu g/L NP is slightly greater than the upper range of concentrations of NP that have been reported in final effluents from municipal sewage treatment plants. Studies on the environmental fate of nonylphenol ethoxylates and degradation products in the aquatic environment are needed to assess the significance of these data in terms of potential reproductive effects in feral fish populations.