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Heterogeneous degradation of pesticides by OH radicals in the atmosphere: Influence of humidity and particle type on the kinetics
- Mattei, Coraline, Wortham, Henri, Quivet, Etienne
- The Science of the total environment 2019 v.664 pp. 1084-1094
- aerosols, cyprodinil, deltamethrin, difenoconazole, environmental factors, fipronil, free radicals, half life, hydrophilicity, hydrophobicity, hydroxyl radicals, oxadiazon, oxidants, pendimethalin, permethrin, relative humidity, silica, tetraconazole, volatile organic compounds
- Pesticides can be adsorbed on the surface of atmospheric aerosol, depending on their physicochemical properties. They can be degraded by atmospheric oxidants such as OH radicals but the influence of some environmental parameters on the degradation kinetics, especially relative humidity and particle surface type, is not well understood. Heterogeneous degradation by OH radicals of eight commonly used pesticides (i.e., difenoconazole, tetraconazole, cyprodinil, fipronil, oxadiazon, pendimethalin, deltamethrin, and permethrin) adsorbed on hydrophobic and hydrophilic silicas at a relative humidity ranging from 0% to 70% was studied. Under experimental conditions, only cyprodinil, deltamethrin, permethrin, and pendimethalin were degraded by OH radical in atmospheric relevant concentration. Second-order kinetic constants calculated for the pesticides degraded by OH radicals ranged from (1.93 ± 0.61) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ (permethrin, hydrophobic silica, 30% RH) to (4.08 ± 0.27) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ (pendimethalin, hydrophilic silica, 0% RH). Results obtained can contribute to improve the understanding of the atmospheric fate of pesticides and other semi-volatile organic compounds in the particulate phase and they highlight the importance of taking humidity and particle type into account for the determination of pesticides atmospheric half-lives.