Sunlight photolysis is an important pathway for the natural transformation of anthropogenic chemicals such as pesticides and pharmaceutical compounds. Although the photochemical fate of these compounds has been widely studied in the aqueous phase, their photolysis on environmental surfaces such as leaf and soil has received much less attention. In this study, we investigated the photochemical behavior of three groups of chemicals on simulated environmental surfaces. First, we showed that the direct photolysis of 2,4-D herbicides on paraffin wax, a simulated leaf surface, had half-lives in the range of 1–6 d, much faster than those previously reported in the aqueous phase. More importantly, these half-lives were on par with the half-life of 2,4-D biodegradation, which is considered as the dominant degradation pathway in the current fate model for these compounds. Our second project investigated the photolysis of the herbicide metolachlor and its safener benoxacor, a pair of agrochemicals used in commercial formulations. Our results showed that benoxacor not only exhibited rapid photodegradation under sunlight, but also sensitized the decay of metolachlor on quartz surface. In addition, the photoproducts of benoxacor were capable of absorbing sunlight and sensitizing metolachlor decay. These findings suggest that the “inert” ingredient in herbicide formulations (safener in this case) can play an important role in the photochemical transformation of the active herbicide compounds. Our third project considers the photochemical fate of pharmaceutical compounds on biosolids. Two model pharmaceuticals naproxen and ibuprofen, both detected at high occurrence and concentrations in biosolids land applied as fertilizers, were selected. Work is ongoing to analyze their photolysis kinetics and products.

Sunlight photolysis of anthropogenic chemicals on simulated environmental surfaces

2019 Fall National Meeting

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