title: Degradation and sorption of pirimiphos-methyl in two Nigerian soils.
abstract: This research is a continuation of a study on the behavior of hydrophobic organic compounds in the environment and describes the simultaneous abiotic degradation and sorption of pirimiphos-methyl (O-2-diethylamino-6-methylpyrimidin-4-yl O,O-dimethylphosphorothioate) under controlled conditions in soil/water slurries. A microfiltration-HPLC technique was employed to follow these processes in two well-characterized soils from the Middle Belt region of Nigeria. Rapid sorption of the pesticide occurs during the first 10 min of equilibration and accounted for 37% of the original pirimiphos-methyl in the Rhodic Kandiustalf soil and for 41% of the original concentration in Aquic Ustropept soil. Subsequent slow processes were followed during the remaining 30 days of the experiment. During this time, first-order rate constants for disappearance from solution of pirimiphos-methyl were found to have values of 6.1 x 10(-)(7) and 9.8 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively. Similarly, rate constants for production of the product, pyrimidinol, were calculated to be 6.0 x 10(-)(7) and 9.4 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively, giving pesticide degradation half-lives of 13 and 8.5 days. Disappearance of the pesticide is discussed in terms of a scheme involving both sorptive uptake by the soil and degradation by hydrolysis in the presence of the soil matrix. The labile sorption capacities for pirimiphos-methyl in the Rhodic and Aquic soils were found to be 0.75 and 0.90 micromol g(-)(1), respectively.
authors.affiliation: Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: Ishaq S
authors.initials: IS
authors.lastname: Eneji
authors.forename: Erwin
authors.initials: E
authors.lastname: Buncel
authors.forename: Gary W
authors.initials: GW
authors.lastname: vanLoon
mesh_terms: D000327:Adsorption; D002851:Chromatography, High Pressure Liquid; D005374:Filtration; D006207:Half-Life; D006868:Hydrolysis; D007306:Insecticides / Q000032:analysis / Q000737:chemistry*; D007700:Kinetics; D009549:Nigeria; D009946:Organothiophosphorus Compounds / Q000032:analysis / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D014867:Water / Q000032:analysis
chemical_list: D007306:Insecticides; D009946:Organothiophosphorus Compounds; D012987:Soil; D014867:Water; C014153:pirimiphos methyl