The Link between Nitrification and Biotransformation of 17α-Ethinylestradiol

Abstract

Biological treatment processes are probably important for preventing the proliferation of steroidal compounds in the environment, and a growing number of reports suggest that nitrification may play a role in removing these chemicals from wastewater. The link between nitrification and biotransformation of 17α-ethinylestradiol (EE₂) was investigated using enriched cultures of autotrophic ammonia-oxidizers. Batch experiments showed that ring A of EE₂ is the site of electrophilic initiating reactions, including conjugation and hydroxylation. Ring A was also cleaved before any of the other rings were broken, which is likely because the frontier electron density of the ring A carbon units is higher than those of rings B, C, or D. EE₂ and NH₃ were degraded in the presence of an ammonium monooxygenase (AMO) containing protein extract, and the reaction stoichiometry was consistent with a conceptual model involving a binuclear copper site located at the AMO active site. Continuous tests showed a linear relationship between nitrification and EE₂ removal in enriched nitrifying cultures. Taken together, these results support the notion that EE₂ biotransformation can be cometabolically mediated under operating conditions that allow for enrichment of nitrifiers.