17α-ethinylestradiol Transformation via Abiotic Nitration in the Presence of Ammonia Oxidizing Bacteria

Abstract

Impacts of trace concentrations of estrogens on aquatic ecosystems are a serious environmental concern, with their primary source being wastewater treatment facility effluents. Increased removal of 17α-ethinylestradiol (EE2) has been reported for activated sludge treatment with long enough solids retention time for nitrification. Previous work based on batch tests with Nitrosomonas europaea and nitrifying activated sludge at high EE2 concentrations (>300 000 ng/L) and high NH₄—N concentrations (>200 mg/L) has led to the hypothesis that ammonia oxidizing bacteria cometabolically degrade EE2. This work investigated EE2 transformation with N. europaea and Nitrosospira multiformis at environmentally relevant EE2 concentrations and LC-MS-MS to observe transformation products. Degradation of EE2 was not observed in batch tests with no NH₄—N addition or with 10 mg/L NH₄—N fed daily. At increased NH₄−N concentrations (200−500 mg/L) EE2 transformation was observed, but the only detected products were nitrated EE2. Abiotic assays with growth medium confirmed EE2 removal by nitration, which is enhanced at low pH and high NO₂—N concentrations. These results suggest that EE2 removal at low concentrations found in municipal treatment activated sludge systems is not due to cometabolic degradation by ammonia oxidizing bacteria, or to abiotic nitration, but most likely due to heterotrophic bacteria.