Heterogeneous photo-oxidation of pesticides and its implication to their environmental fate

The environmental fate and impact of pesticides strongly depend on their post application degradation processes. While most existing knowledge on pesticides degradation refers to processes within bulk soil and water, applied pesticides may remain on treated surfaces (and on airborn particles) for long duration, exposed to atmospheric oxidants and solar radiation. The resulting photo-oxidation processes may have significant effect on their fate, especially in semiarid regions where pesticide applications take place during the long dry season and targeted irrigation is common.

Here we present our studies on heterogeneous photo-oxidation of few commonly used pesticides (e.g., cypermethrin, methyl parathion, and chlorpyrifos), using novel laboratory setups enabling simultaneous monitoring of both phases. Experiments focused on kinetics, quantum yields, and identification of gaseous and condensed products. In addition, the reactivity of the selected pesticides was investigated as a function of their matrix (analytical vs. commercial formula), their phase (thin film vs. airborne aerosols), and the substrate they are sorbed on (leaf, soil, and glass).

Complimentarily to these laboratory studies, field measurements of selected pesticides concentrations in few streams in northern Israel during the first rain events were also conducted and showed the important role of surface processes on these pesticides fate and transport in semi-arid climate.