Photochemical Decomposition of Pesticide Chemicals in Aerosol Particles and Thin Films Relevant to Environmental Conditions

Abstract

Contamination of the environment by pesticides is the inevitable aftermath of plant protection, and a substantial portion of pesticide pollutants exists in the form of aerosol particles levitated in the air and deposited on plants, and as the pesticide residues (thin films) on the surface of plant leaves. The sunlight photolysis could be the resource for the accelerated photochemical decomposition of pesticide compounds to minimize the long-term environmental contamination. The rates of photochemical decomposition of pesticide chemicals propiconazole (commercial formulation Tilt) and haloxyfop-ethoxyethyl (Zellek) were measured in particles of 0.12-1.3 μm in diameter and in films 0.04-0.2 μm thick. A specific polyaromatic sensitizer Shirvanol was used to induce accelerated decomposition of the above pesticide particulates under both the solar radiation and the artificial UV light. It was established that propiconazole decomposes by the sensitized photo-oxidation only, but haloxyfop-ethoxyethyl reacts in both the oxygen (air) and oxygen-free mediums via both the direct and sensitized reactions. The photochemical mechanisms are hypothesized and argued for the oxidative and non-oxidative decompositions. The haloxyfop-ethoxyethyl (Zellek) residues formed on foliage upon pesticide treatments of agricultural fields would essentially decompose under sunlight via a direct photoreaction in 4-6 weeks, but the propiconazole (Tilt) contaminants probably need more time.