Photodegradation rates for 17 steroid hormones and related endocrine-disrupting compounds (EDCs) have been determined over a range of water-quality conditions using simulated solar light. 8 EDCs contain electron-rich phenolic moieties often susceptible to dissolved organic matter (DOM)-driven indirect photolysis. EDC photolysis occurs by direct and indirect pathways, with indirect reactions only important for phenols. Direct photolysis studies indicate that protonated phenol groups dominant at environmentally relevant pH have limited reactivity. At pH7, 9 compounds undergo direct photolysis at non-phenolic sites, with first-order rate constants from 0.2 to 2.3 × 10-4 s-1. Although radical and peroxide chemistries were used to induce EDC degradation, under environmentally realistic solution conditions, indirect photochemical behavior was dominated by excited-state DOM (3DOM*) or singlet oxygen (1O2), photochemically generated from DOM-mediated reactions. Indirect mechanisms were important for phenolic compounds irradiated in solutions containing one of four hydrophobic or transphilic DOM isolates. For these compounds, rates increased with DOM concentration (0 to 15 ppm), but light screening and quenching of photochemically-produced reactive intermediates (PPRIs) attenuated this effect at higher DOM levels. For non-phenolic compounds, the only noticeable effect of DOM was to increase light screening, so degradation rates decreased with DOM concentration. Synthetic PPRI sensitizers and quenchers were added to select experiments to determine which PPRIs were responsible for indirect photochemical processes. These experiments indicate that both 1O2 and 3DOC* were reactive with the compounds of interest, but 3DOC* was responsible for more than 80% of the observed indirect photodegradation. These results were confirmed with laser-flash photolysis, sparging samples with He to remove O2, and conducting experiments in D2Oto increase steady-state [1O2] by slowing the reversion of 1O2 to ground-state 3O2 upon deactivation by the solvent. These results show that 14 of 17 compounds studied can be degraded by sunlight under specific conditions. Of these, 5 do not react with DOM-derived PPRIs so DOM in solution slows photodegradation rate. The remaining 9 EDCs are susceptible to both direct and PPRI-mediated pathways, but the sensitization effect exceeds screening for the isolates and concentrations tested, so DOC increases their photodegradation

Dissolved organic matter-mediated solar degradation of endocrine-disrupting pollutants in natural waters

253rd National Meeting (2017)

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