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Investigation of the heterogeneously catalyzed hydrolysis of organophosphorus pesticides

Dannenberg, A., Pehkonen, S.O.
Journal of agricultural and food chemistry 1998 v.46 no.1 pp. 325-334
diazinon, disulfoton, thiometon, iron oxides, goethite, ferrihydrite, aluminum hydroxide, hydrolysis, adsorption, kinetics, pH, temperature
The hydrolysis of four organophosphorus pesticides (demeton S, diazinon, disulfo ton, and thiometon) in the presence or absence of three iron oxides (hematite, g oethite, and ferrihydrite) and aluminum hydroxide has been investigated. Metal o xide surfaces can catalyze as well as inhibit the hydrolysis of organophosphorus insecticides and thus significantly affect the fate of these compounds in the e nvironment. Adsorption of the organophosphorus pesticides onto the metal oxides seems to take place at specific binding sites, and the fraction adsorbed can be as high as 0.4. Activation parameter studies show that the rate-determining step of the mechanism of surface catalysis is complex formation between the pesticid e and the oxide when the catalysis takes place only at low temperatures. Product studies show that hazardous, persistent compounds can be formed. An example is 1,2-bis(ethylthio)ethane, a previously unreported and persistent product of inse cticide hydrolysis. The research also shows that different products can be forme d depending on the reaction conditions (e.g., dissolved oxygen and pH), especial ly when the reactants contain alkyl sulfide moieties as their primary leaving gr oup.