Numerous environmental chemicals possess estrogen-like properties. At elevated doses, natural estrogens and environmental estrogen-like chemicals are known to produce adverse effects on humans and wildlife. Sources of potential exposure to endocrine disrupting compounds have to be identified for risk and hazard assessment. Extracts prepared from 16 selected water samples taken in Flemish rivers, effluents of municipal wastewater treatment plants and reservoirs for drinking water production were analysed for estrogenic activity with a cellular bioassay. Yeast cells, which are stably transfected with the DNA sequence of hER and which contain expression plasmids with the reporter gene lac-Z, encoding the enzyme b-galactosidase, were used to measure receptor binding. Flemish rivers showed the highest estrogenic potency, compared to effluents of waste water treatment plants and reservoirs which showed low induction factors (β-galactosidase production) relative to solvent control conditions. By comparison with a standard curve for 17β-estradiol (E2), estrogenic potency in water samples was calculated as E2-equivalents and ranged from below detection limit (˜ 2.75 ng E2/l) up to 81.4 ng/l E2-equivalents. About 7 water samples had more than 10 ng/l E2-equivalents. These elevated levels of E2-equivalents are likely to exert significant adverse effects on reproduction success of wildlife, which should be verified with in vivo studies.

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