Phototransformation of selected organophosphorus pesticides: Roles of hydroxyl and carbonate radicals

• Published in: Water research (Oxford) 2010-06, Vol.44 (12), p.3585-3594
• Main Authors: Wu, Changlong, Linden, Karl G.
• Format: Article
• Language: English
• Subjects: Advanced oxidation; Applied sciences; bicarbonates; Bicarbonates - chemistry; chlorpyrifos; Chlorpyrifos - radiation effects; environmental fate; Exact sciences and technology; hydrogen peroxide; Hydrogen Peroxide - chemistry; Hydroxyl Radical - chemistry; hydroxyl radicals; ions; Kinetics; Models, Chemical; Organophosphorus Compounds - radiation effects; Other industrial wastes. Sewage sludge; Oxidation-Reduction; parathion; Parathion - radiation effects; Pesticides - radiation effects; Photochemistry; Pollution; Ultraviolet light; Ultraviolet Rays; Wastes; Water treatment; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2010.04.011

The phototransformation of two organophosphorus pesticides, parathion and chlorpyrifos, by hydroxyl radicals and carbonate radicals in aqueous solution were studied. Addition of hydrogen peroxide increased the UV degradation rates of both pesticides and data were simulated through kinetic modeling. The second-order rate constants of parathion and chlorpyrifos with hydroxyl radical were determined to be 9.7 ± 0.5 × 10 9 and 4.9 ± 0.1 × 10 9 M −1 s −1, respectively. The presence of bi/carbonate ions reduced the pesticide degradation rates via scavenging of hydroxyl radical but the formation of carbonate radical also contributed to the degradation of the pesticides with second-order reaction rate constants of 2.8 ± 0.2 × 10 6 and 8.8 ± 0.4 × 10 6 M −1 s −1 for parathion and chlorpyrifos, respectively. The dual roles of bicarbonate ion in UV/H 2O 2 treatment systems, i.e., scavenging of hydroxyl radicals and formation of carbonate radicals, were examined and discussed using a simulative kinetic model. The transformation of pesticides by carbonate radicals at environmentally relevant bi/carbonate concentrations was shown to be a significant contributor to the environmental fate of the pesticides and it reshaped the general phototransformation kinetics of both pesticides in UV/H 2O 2 systems.