Estrogenic activity and estrogenic chemicals in landfill leachate were investigated by yeast two-hybrid assay and chemical analysis. Leachate sample extracted by liquid–liquid extraction with dichloromethane at pH 7.0 showed a higher dose–response curve than sample extracted at pH 3.0, or than sample extracted by solid phase extraction at either pH 7.0 or 3.0. The fraction extracted at pH 3.0 specifically inhibited not only growth of yeast but also estrogenic activity in this assay, suggesting that it contained anti-estrogenic chemicals. The greatest contributor to estrogenic activity among the chemicals identified in leachate extract was bisphenol A, with an estimated contribution ratio of 84%. The contribution ratios of 4-nonyl phenol (4-np) and 4-tert-octyl phenol (4-t-op) were estimated at 1.0% and 0.1%, respectively, while natural estrogens such as 17β-estradiol or estrone were below detection limit, so that their contribution ratio was estimated at no more than 10%. The estrogenic activity of leachate was decreased by aeration treatment alone after 7 days, and was no longer detected after 22 days. Concentrations of bisphenol A, 4-np and 4-t-op likewise decreased with aeration.
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