Chloride anion effect on the advanced oxidation processes of methidathion and dimethoate: role of Cl2- radical

Abstract

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)x 108 and (1.1 ± 0.4) x 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 by-products 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.