title: Kinetics and mechanism of dimethoate chlorination during drinking water treatment.
abstract: Dimethoate (DMT), a commonly used organophosphorus pesticide, is of great concern because of its toxicity and potentially harmful effects on water sources. The elimination of DMT as well as the toxicity and persistence of the byproducts formed during DMT degradation is most important for the safety of drinking water. This study first determined the reaction kinetics of DMT with free chlorine (FC) under typical water treatment conditions. The reaction between DMT and FC proceeded rapidly, exhibiting first-order with respect to each reactant. The degradation of DMT by FC was highly pH dependent, and the pseudo-first-order rate constant decreased obviously from 0.13 to 0.02 s(-1) with an increase in pH from 7.0 to 8.3. Bromide ion accelerated the reaction by acting as a catalyst, and the accelerated reaction rate was linearly proportional to the bromide concentration. As a ubiquitous component in natural waters, humic acid also increased the reaction rate. However, the presence of ammonium inhibited the degradation of DMT due to its rapid converting FC to chloramines. Omethoate (OMT) was identified as an important byproduct of DMT chlorination, but only accounted for ca. 28% of the DMT degraded; and other two organic byproducts were also identified. The acute toxicity of DMT solution increased after treatment with FC due to the formation of more toxic byproducts (e.g. OMT).
authors.affiliation: School of Environment, Tsinghua University, Beijing 100084, China; School of Environmental Engineering, Nanjing Institute of Technology, Nanjing 211167, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Tian
authors.affiliation: School of Environment, Tsinghua University, Beijing 100084, China. Electronic address: wjliu@tsinghua.edu.cn.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Liu
authors.affiliation: School of Environment, Tsinghua University, Beijing 100084, China; School of Environmental Engineering, Nanjing Institute of Technology, Nanjing 211167, China.
authors.forename: Guang
authors.initials: G
authors.lastname: Guo
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuang-qing Road, Beijing 100085, China.
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Qiang
authors.affiliation: Institute of Disease Control and Prevention, Academy of Military Medical Science, Beijing 100071, China.
authors.forename: Can
authors.initials: C
authors.lastname: Zhang
mesh_terms: D002700:Chloramines / Q000737:chemistry; D004117:Dimethoate / Q000031:analogs & derivatives / Q000737:chemistry*; D060766:Drinking Water / Q000737:chemistry*; D054879:Halogenation; D007700:Kinetics; D010575:Pesticides / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D002700:Chloramines; D060766:Drinking Water; D010575:Pesticides; D014874:Water Pollutants, Chemical; C002302:dimethoxon; D004117:Dimethoate
keywords: Chlorine; Dimethoate; Kinetics; Mechanism; Toxicity; Water disinfection