Estrogenic potency of chemicals detected in sewage treatment plant effluents as determined by in vivo assays with Japanese medaka (Oryzias latipes)

Gonadal intersex and high prevalences of the female phenotype have been obs erved in fish populations in urbanized areas. Environmental estrogens disch arged in sewage treatment plant effluents may be responsible for feminizati on of fish but many compounds with the potential to induce these responses occur in effluents, including natural and synthetic estrogen hormones, degr adation products of alkylphenol ethoxylate surfactants, and plasticizers. I n this study, the estrogen hormones 17 alpha -ethinylestradiol, 17 beta -es tradiol, estrone, and estriol induced intersex (i.e., testis-ova) and alter ed sex in Japanese medaka (Oryzias latipes) when these fish were exposed to nanogram per liter concentrations of test compounds from hatch to approxim ately 100 d after hatch. A mix of nonylphenol mono- and diethoxylate induce d a weak response and a mix of nonylphenol mono- and diethoxycarboxylate di d not give a response in this assay at microgram per liter concentrations, indicating that these degradation products of nonylphenol ethoxylates have little or no estrogenic activity in fish. Bisphenol A induced testis-ova in medaka exposed to a concentration of 10 mug/L, but diethylhexyl phthalate did not induce a response. Results with the medaka assay were consistent wi th estrogenic responses in the yeast estrogen screening assay. Analyses of monitoring data reported in the literature indicate that concentrations of estrogen hormones detected in the final effluents of sewage treatment plant s are generally greater than the lowest-observed effect levels for alterati ons to gonadal development in medaka.