Tamoxifen is widely used in the treatment of breast cancer and can enter the aquatic environment in municipal wastewater. To evaluate potential effects on embryonic development of Japanese medaka, fertilized eggs were exposed to tamoxifen at 1-625μg/l for 14 days. Adverse effects on hatchability and time to hatching only occurred at 125 and 625μg/l. Reproductive effects were assessed by exposing adults for 21 days to the same dose range. At all concentrations tested, tamoxifen significantly increased plasma vitellogenin levels in males in a dose-dependent manner. Fecundity and fertility were detrimentally affected at 625μg/l. Additionally, F1 eggs were removed from tamoxifen-contaminated water to evaluate transgenerational effects. Hatchability was affected at 625μg/l but no morphological deformities were observed. A significant dose-dependent increase in the proportion of genotypic males occurred at all concentrations greater than 5μg/l.
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