Exposure to environmentally relevant concentrations of different nonylphenol formulations in Japanese medaka

The time course of exposure to p-nonylphenol (NP) from two different sources was compared to equivalent exposures of 17-beta-estradiol (E2) and a solvent control (ethanol; EtOH). Japanese medaka were exposed for 4 days to a nominal concentration of 20 micrograms/l of either NP-I (Schenectady International, Inc.), NP-II (Aldrich), or E2, and were then placed in untreated water for 5 days. Tissue samples were taken at two time points during the 4-day exposure and two time points during the 5 days following exposure. Liver homogenates were analyzed using a western blot to detect vitellogenin (VTG) and quantified by measuring the optical density for each lane. Preliminary results indicate that E2 significantly increased VTG staining above the level observed in EtOH-treated controls for both males and females. A two-way analysis of variance (ANOVA) indicates that NP from both sources, as well as E2, significantly increased VTG staining in males (ANOVA, n = 48, P < 0.001; Tukey pairwise tests, all P < 0.008). A significant increase in VTG was observed in E2-treated males and females the first day following transfer into toxicant-free water (two-way ANOVAs, both n = 48, P < 0.003; Tukey pairwise tests, all P < 0.019). If confirmed, this extended response observed for low-level exposures may represent a significant factor for sampling scenarios following pulsitile exposure.