The study of organophosphorus pesticides with and without metal ions

Abstract

With the wide application of the organophosphorus pesticides(OPs) throughout the world, the study of the fate and effect on the environment of the Ops appears to be more and more important. Hydrolysis, oxidation, photolysis, and microbial degradation are several major pathways of the transformations of the Ops. Among them, hydrolysis is a significant degradation process for pesticides.Here, three typical Ops are studied: Demeton S, Diazinon, and Chlorpyrifos-methyl. The similarity and difference of molecular structure of them make them show various sensitivity to the change of conditions of hydrolysis, such as changing temperature and pH, and adding divalent metal ions. In this study, three temperatures (30 0C, 40 0C and 47 0C) were applied to study the effect of the temperature on Demeton S. Four pH values (4.3, 5.5, 7.0 and 8.0) were used to compare the hydrolysis rate of selected pesticides in acid and base environment. Two divalent metal ions ( Hg(II) and Cu(II)) were added in the hydrolysis solution to study the catalyst function of ions.Combined with the theory bases of review of previous literature and analysis of experiment results, it was confirmed that the hydrolysis Demeton S and Chlorpyrifos-methyl increase with increasing pH. Hg(II) acts as electrophile to promote hydrolysis and is suggested to be more activity than Cu(II) for degradation. Cu(II) behaves as nucleophile to attack pesticides and enhances the hydrolysis obviously. The postulated mechanisms for hydrolysis of different pesticides at different condition are various. In addition, with the presence of Hg(II), the mercury chloride seems to inhibit the hydrolysis.