Effluents from sewage treatment plants can be discharged into rivers with estrogenic contaminants at levels sufficient to induce adverse reproductive and fertility developments in humans and wildlife. Of great concern in recent years are the estrogenic activities of chlorinated by-products (CBPs) in effluents. Simplified cell proliferation tests using the human estrogen receptor-positive MCF-7 ATCC breast cancer cells (E-SCREEN) were performed to investigate the influence of chlorination on the estrogenicity in effluents. It was found that the increase of chlorine dosages from 0 mg/L to 4 mg/L led to the decrease of total content of estrogenic activity: the 17ß-estradiol equivalent concentration (EEQ) from 22.40 to 8.35 ng/L. However, the increase of contact time from 10–30 minutes increased EEQ from 14.04 to 29.97 ng/L. Furthermore, increasing TOC level using humic acid from 5 mg/L to 15 mg/L in effluents correspondingly resulted in an increase of EEQ from 19.69–27.20 ng/L; it was thus confirmed that chlorination of humic acid could produce estrogenic by-products.

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