title: Kinetics and mechanism of degradation of dichlorvos in aqueous solutions containing reduced sulfur species.
abstract: Reactions of dichlorvos with five reduced sulfur species (hydrogen sulfide, bisulfide, thiosulfate, thiophenol, and thiophenolate) were examined in well-defined anoxic aqueous solutions to investigate their role in its degradation. Reactions were monitored at varying concentrations of reduced sulfur species over pH range to obtain the second-order reaction rate constants. Experiments at 25 degrees C demonstrated that degradation of dichlorvos promoted by bisufide, thiosulfate, and thiophenolate were of much greater importance than hydrolysis under the experimental conditions in our study. In contrast, hydrogen sulfide and thiophenol were not effective in the degradation of dichlorvos. The activation parameters of the reaction of dichlorvos with bisulfide, thiosulfate, and thiophenolate were also determined from the measured second-order rate constants over a temperature range of 12-50 degrees C. The relative reactivity of the reduced sulfur species decreases in the following order: PhS- > HS- approximately equal to S2O3(2-). When the second-order rate constants at 25 degrees C are multiplied by the environmentally relevant concentration of the reduced sulfur species, predicted half-lives of dichlorvos ranged from hours to days. The results indicated that reduced sulfur species could play a very important role in the chemical fate of dichlorvos in coastal marine environments.
authors.affiliation: Chemistry Department, the City College of New York, 138th Street & Convent Avenue, New York, New York 10031, USA.
authors.forename: Qiu
authors.initials: Q
authors.lastname: Gan
authors.forename: Raphael M
authors.initials: RM
authors.lastname: Singh
authors.forename: Tong
authors.initials: T
authors.lastname: Wu
authors.forename: Urs
authors.initials: U
authors.lastname: Jans
mesh_terms: D004006:Dichlorvos / Q000737:chemistry*; D006862:Hydrogen Sulfide / Q000737:chemistry; D007700:Kinetics; D009267:Naled / Q000737:chemistry; D010636:Phenols / Q000737:chemistry; D012996:Solutions; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013447:Sulfites / Q000737:chemistry; D013457:Sulfur Compounds / Q000737:chemistry*; D013885:Thiosulfates / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D010636:Phenols; D012996:Solutions; D013438:Sulfhydryl Compounds; D013447:Sulfites; D013457:Sulfur Compounds; D013885:Thiosulfates; D014867:Water; C042983:thiophenol; D004006:Dichlorvos; C042345:hydrogen sulfite; D009267:Naled; D006862:Hydrogen Sulfide