Water samples were collected in spring, summer and winter from English rivers in urban/industrial (River Aire and River Calder, Yorkshire) and rural environments (River Thames, Oxfordshire) to study the biodegradation potential of the key steroid estrogen 17b-estradiol (E2) and its synthetic derivate ethinylestradiol (EE2). Micro-organisms in the river water samples were capable of transforming E2 to estrone (E1) with half-lives of 0.2-9 days when incubated at 20°C. E1 was then further degraded at similar rates. The most rapid biodegradation rates were associated with the downstream summer samples of the River Aire and River Calder. E2 degradation rates were similar for spiking concentrations throughout the range of 20 ng/l to 500 µg/l. Microbial cleavage of the steroid ring system was demonstrated by release of radiolabeled CO2 from the aromatic ring of E2 (position 4). When E2 was degraded the loss of estrogenicity, measured by the yeast estrogen screen assay (YES), closely followed the loss of the parent molecule. Thus apart from the transient formation of E1, the degradation of E2 does not form other significantly estrogenic intermediates. E2 could also be degraded when incubated with anaerobic bed-sediments. Compared to E2, EE2 was much more resistant to biodegradation, but both E2 and EE2 were susceptible to photodegradation, with half-lives in the order of 10 days under ideal conditions
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