Towards a comprehensive understanding of malathion degradation: theoretical investigation of degradation pathways and related kinetics under alkaline conditions

Abstract

Malathion is a commercially available insecticide that functions by acting as an acetylcholinesterase inhibitor. Of more significant concern, if left in the environment, some of the products observed from the degradation of malathion can function as more potent toxins than the parent compound. These compounds may threaten human life if they are present in high quantities during operation in contaminated or industrial areas. Several experimental studies have been performed to elucidate the possible degradation products of malathion under various conditions to probe both the application of potential remediation methods and the environmental fate of the degradation products. However, only limited computational studies have been reported to delineate the mechanism by which malathion degrades under environmental conditions and how these degradation mechanisms are intertwined with one another. Herein, M06-2X DFT computations were employed to develop comprehensive degradation pathways from the parent malathion compound to a multitude of experimentally observed degradation products. These data corroborate experimental observations that multiple degradation pathways (ester hydrolysis and elimination) are in competition with each other, and the end-products can therefore be influenced by environmental factors such as temperature. Furthermore, the products resulting from any of the initial degradation pathways (ester hydrolysis, elimination, or P–S hydrolysis) can continue to degrade under the same conditions into compounds that are also reported to be toxic.