title: Sonolytic degradation of dimethoate: kinetics, mechanisms and toxic intermediates controlling.
abstract: The sonolytic degradation of aqueous solutions of dimethoate, O,O-dimethyl S-[2-(methylamino)-2-oxoethyl]dithiophosphate, was examined. Optimal degradation rates were obtained at 619 kHz for continuous sonolysis and 406 kHz for pulse sonolysis. The primary pathways for degradation include hydroxyl radical oxidation, hydrolysis and pyrolysis on collapsing cavitation bubble interfaces. Reaction mechanisms coupled with the corresponding kinetic models are proposed to reproduce the observed concentration versus time profiles for dimethoate, omethoate and N-(methyl) mercaptoacetamide during sonolysis. The oxidation and hydrolysis of dimethoate and omethoate occurred at the water-bubble interface was the rate-determining step for sonolytic overall degradation of dimethoate. More than 90% toxicity of dimethoate was reduced within 45 min ultrasonic irradiation. Ferrous ion at micro molar level can significantly enhance the sonolytic degradation of dimethoate and effectively reduce the yields of toxic intermediate omethoate.
authors.affiliation: Key Laboratory of Three Gorges Reservoir Regions Eco-Environment, Ministry of Education, Chongqing University, Chongqing 400045, China. yao_juanjuan@yahoo.cn
authors.forename: Juan-Juan
authors.initials: JJ
authors.lastname: Yao
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hoffmann
authors.forename: Nai-Yun
authors.initials: NY
authors.lastname: Gao
authors.forename: Zhi
authors.initials: Z
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Li
mesh_terms: D000081:Acetamides / Q000737:chemistry; D004117:Dimethoate / Q000737:chemistry* / Q000633:toxicity*; D004583:Electrons; D008401:Gas Chromatography-Mass Spectrometry; D007700:Kinetics; D016018:Least-Squares Analysis; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D013010:Sonication / Q000379:methods*; D013997:Time Factors; D014465:Ultrasonics
chemical_list: D000081:Acetamides; D004117:Dimethoate