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

The time course of exposure to p-nonylphenol (NP) from two different source s was compared to equalivent exposures of 17-beta -estradiol (E2) and a sol vent control (ethanol;;EtOH). Japanese medaka were exposed for 4 days to a nominal concentration of 20 mug/l of either NP-I (Schenectady International , Inc.), NP-II (Aldrich), or E2, and were then placed in untreated water fo r 5 days. Tissue samples were taken at two time points during the 4-day exp osure and two time points during the 5 days following exposure. Liver homog enates were analyzed using a western blot to detect vitellogenin (VTG) and quantified by measuring the optical density for each lane. Preliminary resu lts indicate that E2 significantly increased VTG staining above the level o bserved in EtOH-treated controls for both males and females. A two-way anal ysis 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; Tuke y pairwise tests, all P< 0.008). A significant increase in VTG was observed in Ea-treated males and females the first day following transfer into toxi cant-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-leve l exposures may represent a significant factor for sampling scenarios follo wing pulsitile exposure. (C) 2000 Elsevier Science Ltd. All rights reserved .