Degradation of 17β-Estradiol and its Metabolites by Sewage Bacteria.

Natural estrogens (e.g., 17β-estradiol or 1,3,5[10]-estratriene-3,17β-diol) have been suggested as one of the major groups of substances that cause endocrine disruption in wildlife. There is little information in the open literature on the fate of natural estrogens in the environment, a fact that hinders the assessment of their ultimate impact on the ecosystem. Aerobic and anaerobic batch experiments involving a 17β-estradiol-degrading culture and a supernatant of activated sludge from a local sewage treatment plant (Burlington, Ontario) were undertaken to assess the persistence of 17β-estradiol (E2) and its 5 metabolites. The batch experiments showed that E2 and the metabolites were not persistent and could be rapidly degraded by sewage bacteria. Biodegradation of E2 by sewage bacteria appeared to initiate at the D ring of E2, leading to the formation of the major metabolite estrone (E1). No other major degradation products were noted. However, during the very early stages of E2 degradation by sewage bacteria, a previously unreported metabolite, X1 (5-hydroxy-15-methyl-13-oxatetracyclo[8.7.0.0 <2,7> .0. <11,15>]-heptadeca-2(7),3,5-trien-14-one), was observed. X1 appeared to be a labile metabolite with a lactone structure, but its significance in the biodegradation of E2 remained to be elucidated. With the observation of the new metabolite X1, a metabolic pathway of E2 by sewage bacteria was proposed. Conditions (e.g., aerobic and anaerobic environment) governing the persistence of E2 in sewage were also investigated. Results in this study suggest that the risk of extensive accumulation of natural estrogens normally found in sewage effluents in the environment is small, due to their ready biodegradation. [ABSTRACT FROM AUTHOR]

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