UV Degradation Kinetics of Estrogens by Direct Photolysis

The occurrence and behavior of natural and synthetic estrogens in the environment is presently of great concern. In this study, the direct photolysis of two natural estrogens, estrone (E1) and 17β-estradiol (E2), and one synthetic estrogen, 17α-ethinylestradiol (EE2) in aqueous solutions by ultraviolet (UV) irradiation was investigated. The experimental results showed both the apparent concentration and estrogenic activity of all three investigated estrogens in aqueous solutions decreased with direct UV irradiation. At the dosage similar to those used in UV disinfection of wastewater effluents, significant E1 removal was observed. The removal of E1 was much quicker than E2 and EE2 with initial concentration both at mg/L and μg/L ranges. With 2 mins exposure of UV light, at the initial concentration of 1 mg/L, 76% of E1 was removed, while less than 20% of E2 and EE2 were removed. The degradation of the three estrogens by UV irradiation follows pseudo first order reaction kinetics. The degradation rate constants of E1 were approximately 5-10 times higher than those of E2 and EE2 at various initial concentrations. The estrogenic activities of the intermediate products are negligible and there is no secondary risk to increase the estrogenic activity as a result of photolysis of estrogens in water under the experimental conditions in this study. Further research needs to be carried out to test the feasibility of direct UV irradiation as an alternative treatment process for estrogens removal from wastewater.