Pesticides and pharmaceuticals are increasingly common anthropogenic contaminants in natural water systems. One pathway of degradation for some of these contaminants is photolysis. Due to their chemical structures the four target compounds in this study (atorvastatin, carbamazepine, DEET, and venlafaxine) absorb sunlight poorly. Consequently, rather than being significantly impacted by direct photolysis these compounds undergo indirect photodegradation mediated by photochemically-produced reactive intermediates (PPRIs) produced by dissolved organic matter (DOM). These PPRIs are formed through the absorption of sunlight by DOM and include singlet oxygen (1O2), triplet DOM (3DOM*), and hydroxyl radicals. To investigate the kinetics of photolysis of each of the four target compounds under environmental conditions, water samples were collected at various sites along the St. Louis River and spiked individually with each compound. They were then photolyzed in a solar simulator for up to four hours and HPLC was used to track parent compound loss and quantify the first-order rate constant of each compound. Total organic carbon (TOC) was measured for each sample site and used to calculate the rate per unit carbon (rate/hr/mgC) to allow calculation of carbon-normalized rate constants. To investigate the individual effects of each PPRI on the overall rate constants of each compound, a series of quenching experiments was performed by adding furfuryl alcohol (FFA) to quench 1O2, isopropanol (IPA) to quench hydroxyl radicals, and potassium sorbate to quench 3DOM*. Results illustrated that the importance of DOM variability among the water samples and significance of individual PPRI contributions was different for each target contaminant.

Investigation of the impacts of indirect photolysis on select contaminants along the St. Louis River

255th National Meeting (2018)

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