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Estrogens of human and animal origin that reach the aquatic environment may enter human or animal organism and act as endoerine disruptors.To investigate the persistency ofestrogens in laboratory experiments, estrone respectively 17ß-estradiol were added to stream water sampled from river Spree in Berlin. The concentration of estrone and 17ß-estradiol was quantified using enzyme-immuno-assay.The estrone concentration decreased to less than 5 %of the starting concentration at storage temperature of 5 °C within 56 days and at storage temperature of 20 °C within 14 days. If the estrone were added to autoclaved stream water, no biodegradation was observed. Biodegradation was enhanced when activated sludge was added. Escherichia coli, Pseudomonas fluorenscens and Aeromonas hydrophila in monoculture did not degrade estrone in autoclaved stream water.The concentrations of 17ß-estradiol and estrone decreased similarly.The logistic funetion proved to be suitable to describe the course of time for the decrease of concentration.