Surface Mediated Transformation of Pesticides

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The mineral-water interface strongly influences the overall biogeochemistry of soil environments. Minerals provide reactive surfaces for the adsorption of organic and inorganic solutes, colloids or microorganisms, but also facilitate hydrolysis or electron transfer reactions of the sorbates. In contrast to non-polar, hydrophobic pesticides of the past modern organic agrochemicals typically are highly functionalized. For such pesticides, specific interactions with mineral surfaces contribute to or even may dominate their fate in soils. The overall goal of the proposed research is to elucidate on a mechanistic basis the effects of mineral surfaces (oxides, clays) representative of those present in A and B horizons of natural soils on surface mediated thermochemical reactions of pesticides. To this end, we have chosen a set of pesticides (Fenhexamid, Bentazone, Metalaxyl) that contain reactive structural features typical for modern agrochemicals. More specifically, we propose to evaluate in laboratory batch model systems to what extent sorption to and/or interactions with mineral surfaces i) affects the rates, reaction mechanisms and product spectrum of pesticide hydrolysis. ii) may be stereoselective and thus may affect the transformation rates and the product spectrum (isomer ratios) of chiral pesticides Besides hydrolysis , we will also consider iii) surface mediated oxidative transformation reactions of amino moieties present in pesticides and iv) surface mediated reductive transformation reactions of sulfur moieties present in pesticides. We expect that the results of this research will help to predict the significance of abiotic transformation reactions to the overall degradation rates and mechanisms of pesticides in soil.