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Atmospheric Behaviour and Environmental Fate of Semivolatile Pesticides; Heterogeneous Oxidation and Photochemical Degradation

Final Activity Report Summary - AESP_HOP (Atmospheric Behavior and Environmental Fate of Semivolatile Pesticides; Heterogeneous Oxidation and Photochemical Degradation)

The present project investigates the atmospheric interactions of two commonly used pesticides (methyl parathion and cypermethrin) in order to better understand their environmental fate. For this purpose, a novel experimental apparatus combing two FTIR techniques was set, allowing simultaneous real-time monitoring of both condensed and gaseous phases.

The heterogeneous oxidation of thin cypermethrin film by ozone was investigated, including determination of reaction rate constants, identification of volatile and non-volatile products and checking the effect of relative humidity and gaseous ozone levels on the reaction in order to better evaluate its mechanism. The results indicate that oxidation of sorbed cypermethrin by ozone cannot be neglected in the overall environmental fate cycle for this material and that several of the yielded products (condensed and gaseous) are toxic and may pose further environmental problems. The ozonolysis of methyl parathion was found to be very slow and insignificant relative to its other degradation processes.

The photo-degradation of thin films of cypermethrin and methyl parathion under artificial UV light (254, 302, and 365 nm) and solar radiation was also investigated. As part of these studies we examined the effect of radiation wavelength, substrate type and the presence of gaseous oxygen on the photolysis quantum yield and products formation. The photochemical degradation rates of thin films of these pesticides were found to be much faster than in aqueous solutions, and indicate that photolysis is a major degradation path for both compounds. No significant difference was found in the degradation rates of methyl parathion on artificial and natural surfaces (i.e. glass, quartz, apple leaves and peach leaves).

Changes in water uptake by the pesticides films following exposure to ozone or UV radiation were measured in a separate set of experiments using quartz crystal microbalance (QCM). The results suggest that such atmospheric aging cause the pesticides residue to become more hygroscopic and possibly results in increase exposure of the substrate material.