Chloride anion effect on the advanced oxidation processes of methidathion and dimethoate: Role of Cl2− radical

The reaction of phosphor-containing pesticides such as methidathion (MT) and dimethoate (DM) with dichloride radical anions (Cl2−) was investigated. The second order rate constants (1.3 ± 0.4) × 108 and (1.1 ± 0.4) × 108 M−1 s−1 were determined for the reaction of Cl2− with MT and DM, respectively. A reaction mechanism involving an initial charge transfer from the sulfide groups of the insecticides to Cl2− is proposed and supported by the identified transient intermediates and reaction products. The formation of chlorinated byproducts was determined. The unexpected consequences of an efficient Cl2− reactivity towards MT and DM on the degradation capacity by Advanced Oxidation Procedures applied to polluted waters containing the insecticides and Cl− anions is discussed.

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► Cl atoms and Cl2− radicals efficiently react with methidathion and dimethoate.
► Chlorinated byproducts are formed upon degradation of the pesticides in the presence of Cl−.
► The presence of chloride anions severely affect AOPs pollutant degradation.