Estrogenic compounds are widely known to be present in water sources for public water supply and in aquatic environments at trace levels. However, the synergistic interactions of estrogenic chemicals in water have been scarcely reported. Therefore, the effects of p-nonylphenol (NP), bisphenol A (BPA), 17β-estradiol (E2), and their mixture on the induction of serum vitellogenin (VTG) in Japanese medaka were investigated in this study. Mature male medaka was exposed to NP, BPA and E2, and their mixture to evaluate their estrogenic activities by using a water-flow-through a chemical-exposure system installed in a clean room. VTG concentration in the sample was analyzed using a Medaka vitellogenin ELISE kit (Metocean Environment Inc., Transgenic Inc.). The lowest observed effect concentrations (LOEC) of vitellogenin by NP, BPA, and E2 exposures were 50μg·l-1, 500μg·l-1 and 5ng·l-1, respectively. No observed effect concentrations (NOEC) by NP, BPA, and E2 exposures were 10μg·l-1, 200μg·l-1 and 1ng·l-1, respectively. A significant increase in VTG level was observed when medakas were exposed to the mixture of these chemicals at NOEC. In addition, the mixture of these chemicals at LOEC showed a higher rate of VTG induction than single chemicals.
