Degradation of organic pollutants mediated by extracellular peroxidase in simulated sunlit humic waters: A case study with 17β-estradiol.

A growing body of research indicated that natural processes such as photolysis, biotransformation and sorption contribute to natural attenuation of organic compounds in natural waters. Here we report another potential natural reaction involving induction by extracellular peroxidase (POD) in sunlit humic waters. The degradation behavior of a natural estrogen 17β-estradiol (E2) in waters containing both horseradish peroxidase (HRP) and Suwannee River humic acid (SRHA) were studied under simulated sunlight. Significant enhancement of E2 degradation was observed in the presence of HRP as compared to direct and SRHA-inducted photolysis, resulting from the efficient degradation of E2 induced by HRP using photoproduced HO. The contribution of direct photolysis, indirect photolysis and enzymatic degradation to E2 degradation was calculated as 36.6, 31.7 and 31.7%, respectively. Lower yields of hydroxylation products and several new dimer products in E2+SRHA+HRP system relative to E2+SRHA system indicated that E2 degradation was primarily mediated by HRP, revealing the presence of HRP strongly affected the degradation pathway of E2. Take naturally occurring POD into consideration, enzymatic degradation may be an important attenuation pathway of E2 and other contaminants that are sensitive to peroxidases in certain waters such as humic rich freshwater system.