Article pubs.acs.org/JPCA
Heterogeneous Ozonolysis of Folpet and Dimethomorph: A Kinetic and Mechanistic Study Mariam J. Al Rashidi, Abdelkhaleq Chakir, and Estelle Roth* Groupe de Spectrométrie Moléculaire et Atmosphérique, Unité Mixte de Recherche CNRS 7331, and UFR Sciences Exactes et Naturelles Moulin de la Housse, Université de Reims Champagne Ardenne, B.P. 1039, 51687 Reims, France ABSTRACT: The research study discussed in this paper concerns determination of the kinetic rate constants for heterogeneous degradation of the pesticides folpet and dimethomorph by ozone at room temperature. The study also involves identification of the degradation products of the analyzed compound in the condensed phase by solid-phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS). The heterogeneous O3 reactivity of the identified degradation product of dimethomorph, 4chlorophenyl 3,4-dimethoxyphenyl methanone (CPMPM), is also evaluated experimentally. The obtained results show that the rate constant values of the analytes are (1.7 ± 0.5) × 10−19, (2.1 ± 0.8) × 10−19, (2.6 ± 0.2) × 10−20, and (2.7 ± 0.2) × 10−20 cm3·molecule−1·s−1 for (Z)-dimethomorph, (E)dimethomorph, folpet, and CPMPM, respectively. Such values implicate heterogeneous ozone lifetimes that vary from a few days to several months, meaning that, depending on their reactivity with respect to other atmospheric oxidants, these compounds might be relatively persistent and may be transported to regions far from their point of application.
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INTRODUCTION Pesticide use is an issue of great controversy that has occupied the scientific community for many years. Although this practice helps to enhance agricultural yields, it has been shown to evoke a multitude of environmental and sanitary problems. In fact, pesticide use is associated with many diseases including cancer.1,2 Consequently, various governmental and nongovernmental organizations, such as the Food and Agriculture Organization (FAO) and the Union des Industries pour la Protection des Plantes (UIPP), were established for the purpose of controlling pesticide use locally, nationally, and globally. The control of pesticide use requires information concerning the potential health hazards and the chemical behavior of these species. Therefore, studies regarding such issues are needed. The chemical behavior of pesticides is influenced by the environment in which they are found (soil, water, and atmosphere). Depending on the mode of application as well as the meteorological conditions, up to 90% of the applied pesticides do not reach the targeted pests.3 During and after application, 30−50% of the applied pesticides are lost to the atmosphere4 via spray drift evaporation, volatilization, and wind erosion.3 This loss is governed by a multitude of factors including chemical and physical properties of the pesticide, amount used, mode of application, and weather conditions (temperature, wind speed, and humidity) as well as the nature of the crop and soil characteristics.5 Once in the atmosphere, pesticides partition between the three atmospheric phases: gas, solid, and liquid.6−8 Their atmospheric fate is dictated by a collection of physical and chemical processes of elimination. Physical processes of elimination from the atmosphere include © 2013 American Chemical Society
dry and wet deposition, whereas the chemical processes include photolysis and oxidation by atmospheric oxidants such as OH radicals and ozone. The lifetime of a particular pesticide and its atmospheric transfer potential are governed by the degradation and elimination processes it undergoes. Because pesticides are semivolatile organic compounds with relatively low vapor pressures (
