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?¡À?0.4)?¡Á?108 and (1.1?¡À?0.4)?¡Á?108?M?1?s?1 were determined for the reaction of with MT and DM, respectively. A reaction mechanism involving an initial charge transfer from the sulfide groups of the insecticides to 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 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.