Evaluation of the estrogenic activity in sewage treatment works using a medaka vitellogenin assay

The aim of the present study was to determine whether tertiary treatment is effective for decreasing estro-genic activity in a sewage treatment works (STW), using a medaka vitellogenin (VTG) assay. We introduced male Japanese medaka Oryzias latipes into the STW at several points in the treatment process for 2 weeks at a time. Plasma and hepatic VTG levels of the medaka were then determined using an enzyme-linked immunosorbent assay (ELISA) to measure the estrogenic response. Exposure after Activated Sludge Treatment (AS) resulted in elevated plasma and hepatic VTG levels (plasma max., 543,mu g/mL; liver max., 26 mu g/g wet), close to the levels of females (plasma average, 1028 mu g/mL; liver average, 154 mu g/g wet). In contrast, VTG was not detected (detection limit: plasma, 0.4 mu g/mL; liver, 0.1 mu g/g wet) after Stones Contact Oxidization treatment (SC). Furthermore, exposure for 2 weeks activated VTG synthesis more than exposure for 1 week. The plasma and hepatic VTG concentrations correlated well. In addition, we also determined aquatic 17 beta-estradiol and estrone by ELISA, and found them to be treated more efficiently by SC than AS. Consequently, more effective processing is possible when using both AS and SC.