title: Reaction of chlorpyrifos-methyl in aqueous hydrogen sulfide/bisulfide solutions.
abstract: The kinetics of the reactions of chlorpyrifos-methyl, an organophosphorus insecticide, with hydrogen sulfide (H(2)S) and bisulfide (HS(-)) were determined in well-defined aqueous solutions. The resulting pseudo-first-order rate constant for chlorpyrifos-methyl with bisulfide yielded a second-order rate constant of (2.1 +/- 0.3) x 10(-3) M(-1) s(-1). The second-order rate constant for chlorpyrifos-methyl with hydrogen sulfide is significantly slower than the second-order rate constant with bisulfide. The contribution of H(2)S to the observed degradation rate constant of chlorpyrifos-methyl at concentrations of up to 4 mM H(2)S is not significant. The second-order rate constant of chlorpyrifos-methyl with H(2)S was too low to be measured in this study. The results indicate that HS(-) present at environmentally relevant concentrations may represent an important sink for phosphorothionate triesters in a coastal marine environment, while H(2)S reacts too slowly to be environmentally relevant (pH 6-9). Trichloropyridinol, the major product of hydrolysis of chlorpyrifos-methyl, is only a minor product of the reaction of chlorpyrifos-methyl with bisulfide; however, trichloropyridinol was found to be stable under the experimental conditions.
authors.affiliation: Chemistry Department, City College of City University of New York, New York, New York 10031, USA. ujans@ccny.cuny.edu
authors.forename: Urs
authors.initials: U
authors.lastname: Jans
authors.forename: M Hasan
authors.initials: MH
authors.lastname: Miah
mesh_terms: D004390:Chlorpyrifos / Q000031:analogs & derivatives* / Q000737:chemistry*; D006862:Hydrogen Sulfide / Q000737:chemistry*; D006868:Hydrolysis; D007306:Insecticides / Q000737:chemistry*; D007700:Kinetics; D012989:Soil Pollutants / Q000032:analysis; D012996:Solutions; D014867:Water; D014873:Water Pollutants / Q000032:analysis
chemical_list: D007306:Insecticides; D012989:Soil Pollutants; D012996:Solutions; D014873:Water Pollutants; D014867:Water; D004390:Chlorpyrifos; C007031:chlorpyrifos-methyl; D006862:Hydrogen Sulfide