HIGASHITANI * and H. TANAKA*

Abstract For examination of multiple effects from individual endocrine disrupters (EDs) to wildlife, we measured the estrogenic activities of major river water by DNA recombinant yeast involving human estrogen receptor gene. This study could show that the estrogen-like activities of the river water ranged 0.01～31ng/L, and averaged 1.6ng/L. The average and maximum values of the river water were lower than those of untreated wastewater and discharge from sewage treated plants (STP) (Yakou et al., 1999; Tanaka et al., 2001). Comparing the estrogen-like activity among each seasons at the same sampling points showed seasonal variations, especially estimated higher activity in winter than the other seasons. Theoretical activity of estrogen-like substances showed that most of the theoretical activities were higher than those of the yeast method. These results are similar to other studies of untreated wastewater and STP discharges (Yakou et al., 1999; Tanaka et al., 1999 and 2001). Moreover, the differences between the theoretical activity and the estrogen-like activity imply that unknown substances and/or antagonists may exist in river water in the same case of STP discharge and untreated wastewater