Halogenated estrogens are thought to be moderately potent endocrine-disrupting compounds that are formed during chlorine-based wastewater disinfection processes and may represent a significant fraction of the total amount of estrogen delivered from wastewater treatment plants to receiving waters. Yet we lack key information about the photochemical degradation of halogenated estrogens, a process that has important implications for UV-based wastewater treatment and environmental fate modeling. To better understand halogenated estrogen degradation in aquatic environments, we studied the direct and indirect photolysis of 17β-estradiol (E2), 2-bromo-17β-estradiol (monoBrE2), 2,4-dibromo-17β-estradiol (diBrE2), and 2,4-dichloro-17β-estradiol (diClE2) under natural solar irradiance. We found that direct photolysis rate constants increased with successive halogenation as pKa values decreased, molar absorptivity spectra shifted toward higher wavelengths, and quantum yields increased. The rate of diBrE2 (pKa ~ 7.5) photolysis was strongly influenced by pH. At pH 7, diBrE2 degraded on hour time scales due to higher molar absorptivity values of the more abundant phenolate form.  At pH 4, diBrE2 degraded on time scales of days to weeks. Degradation rates were only slightly faster in the presence of Suwannee River humic acid (5 mg/L), and quenching experiments pointed to <sup>3</sup>DOM as the dominant reactive intermediate responsible for the indirect photolysis of diBrE2. Overall, our data suggest that halogenated estrogens are particularly susceptible to photochemical degradation at environmentally relevant pH values due to the red-shifted absorbance characteristics and slightly higher quantum yields of the phenolate form.<br/>

Photochemical degradation of halogenated estrogens

255th National Meeting (2018)

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