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 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 cl˙-2 with MT and DM, respectively. A reaction mechanism involving an initial charge transfer from the sulfide groups of the insecticides 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 cl˙-2 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. [Copyright &y& Elsevier]