Anaerobic transformation kinetics and mechanism of steroid estrogenic hormones in dairy lagoon water.

Wastewater from concentrated animal feeding operations (CAFOs) frequently contains high concentrations of steroid estrogenic hormones. Release of these hormones into the environment may occur when CAFO wastewater is applied to agricultural lands as a nutrient and water source for crop production. To assess the potential risk of hormone contaminants derived from animal wastewater, we investigated the transformation kinetics and mechanisms of three natural estrogenic hormones (17α-estradiol, 17β-estradiol, and estrone) in aqueous solutions blended with dairy lagoon water under anaerobic conditions. Initial transformations of the three hormones in the dairy lagoon water were dominated by biodegradation and the degradation rates were temperature-dependent. The total amounts of hormones (initial concentration at 5 mg L(-1)) remaining in the solution after 52 days at 35 °C accounted for approximately 85%, 78%, and 77% of the initial amounts of 17α-estradiol, 17β-estradiol, and estrone, respectively. This observation suggests that these hormones are relatively stable over time and may accumulate in anaerobic or anoxic environments and anaerobic CAFO lagoons. A racemization reaction between 17α-estradiol and 17β-estradiol via estrone was observed in aqueous solutions in the presence of CAFO wastewater under anaerobic conditions. The initial hormone concentrations did not affect this degradation mechanism. A reversible reaction kinetic model was applied to fit the observed transformation dynamics. The degradation and regeneration of the parent hormone and its metabolites were successfully simulated by this model. The information in this study is useful for assessing the environmental risk of steroid hormones released from CAFO wastewater and to better understand why these hormone contaminants persist in many aquatic environments.