Safeners, so-called "inert" ingredients in herbicide formulations, are widely used agrochemicals, but their environmental fate and effects are largely uninvestigated. Here, we report on the phototransformation of dichloroacetamide herbicide safeners. We establish the primary mechanism of photolysis (i.e., direct versus indirect photolysis), as well as the timescales and major products resulting from phototransformation. Benoxacor is prone to relatively rapid direct photolysis (with a half-life on the order of 0.5 h), yielding a mixture of several transformation products. Other dichloroacetamides (e.g., dichlormid, AD-67, furilazole) are resistant to direct photolysis, and only slowly degraded (~10-25% over 10 h) by indirect processes with environmentally relevant concentrations of sensitizers (e.g., humic substances) and other sources of photooxidants (e.g., nitrate and nitrite). All dichloroacetamide safeners investigated were degraded by UV-254 irradiation, as might be encountered in advanced disinfection systems. In sunlit surface waters, we suggest that photolysis is likely only a significant degradation pathway for benoxacor, whereas modest transformation may occur over several days via indirect photolysis pathways, depending on water quality, for the other dichloroacetamide safeners we investigated.

Environmental photochemistry of dichloroacetamide herbicide safeners

255th National Meeting (2018)

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