Investigation of the Heterogeneously Catalyzed Hydrolysis of Organophosphorus Pesticides.

The hydrolysis of four organophosphorus pesticides (demeton S, diazinon, disulfoton, and thiometon) in the presence or absence of three iron oxides (hematite, goethite, and ferrihydrite) and aluminum hydroxide has been investigated. Metal oxide surfaces can catalyze as well as inhibit the hydrolysis of organophosphorus insecticides and thus significantly affect the fate of these compounds in the environment. 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 pesticide 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 insecticide hydrolysis. The research also shows that different products can be formed depending on the reaction conditions (e.g., dissolved oxygen and pH), especially when the reactants contain alkyl sulfide moieties as their primary leaving group.