Feminized responses in fish to environmental estrogens.

Effluent from sewage-treatment works entering British rivers contains an estrogenic chemical, or mixture of chemicals, that stimulates vitellogenin synthesis in male fish. If the effluent constitutes a significant proportion of the flow of the river, lengthy stretches of entire rivers can be estrogenic to fish. The chemical, or chemicals, responsible for this feminizing effect have not yet been identified. However, many man-made chemicals known to be estrogenic to fish (and other vertebrates) are present in effluent, although which of these, if any, is responsible for the effects noted when caged fish are placed in rivers is unclear presently. In laboratory studies, exposure to estrogenic alkylphenolic chemicals caused a reduction in the rate of testicular development in trout undergoing sexual maturation.