Study of the degradation of an organophosphorus pesticide using electrogenerated hydroxyl radicals or heat-activated persulfate

The use of pesticides and their release into the natural environment constitutes a direct threat for the environment and the living beings especially the human health. Consequently, the development of technics to detoxify the pesticide residues to reduce at least areas and contaminated matrix is needed. In the present work, a comparative study was performed on the chemical oxidation of an organophosphorus compound, the dimethoate (DIM), with sulfate radicals and hydroxyl radicals. Both oxidants are generated in situ, the sulfate radicals were produced by heat-activation of persulfate (PS) and hydroxyl radicals were generated by water electrooxidation using a boron doped diamond anode (BDD). For both cases, the target molecule has disappeared but the selective reaction of sulfate radicals with organics led to the production of intermediates which are less biodegradable than DIM since the ratio between the biological oxygen demand (BOD5) and the chemical oxygen demand (COD) has been divided by 2 within the first hour of the process. Whereas the BOD5/COD ratio during the electrochemical oxidation of DIM via hydroxyl radicals showed that it was possible to render the solution biodegradable without reaching a complete mineralization. However, it has been shown that the presence of chlorides in the solution must be avoided because of the formation of undesired organochlorides during the process.