title: Photodegradation of etridiazole by UV radiation during drinking water treatment.
abstract: The photodegradation of etridiazole (ETZ) in water by UV radiation at 254 nm was investigated. Results indicate that the simulated first-order rate constants decreased with the increase of initial ETZ concentration (i.e., 5, 20 and 30 microM), and did not show any pH dependence within the range from 6.0 to 8.0. The quantum yield was 0.46+/-0.02 molE(-1) at pH 7.0. H(2)O(2) was generated at trace levels in the range from 0 to 1.0 microM during photodegradation of ETZ. Direct photodegradation was responsible for the decomposition of ETZ in distilled water by UV radiation. Three organic byproducts were identified: 5-ethoxy-3-dichloromethyl-1,2,4-thiadiazole, 5-ethoxy-1,2,4-thiadiazole-3-carboxylic acid and 5-ethoxy-3-hydroxyl-1,2,4-thiadiazole. About 90% of chloro mass in the initial ETZ was released as Cl(-) at the end of photodegradation. In contrast, the formation of sulfate and nitrate was insignificant. In general, ETZ decayed more quickly in groundwater than in sand-filtered or surface water. It is reasonably deduced that ETZ may not get removed effectively under a typical UV dose of 40 mJcm(-2) at most water treatment plants that employ UV radiation for disinfection.
authors.affiliation: State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences (RCEES), Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Qiang
authors.forename: Fang
authors.initials: F
authors.lastname: Tian
authors.forename: Tao
authors.initials: T
authors.lastname: Zhang
mesh_terms: D004326:Drinking; D005240:Feasibility Studies; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010575:Pesticides / Q000737:chemistry* / Q000302:isolation & purification*; D010782:Photolysis / Q000528:radiation effects*; D013830:Thiadiazoles / Q000737:chemistry* / Q000302:isolation & purification*; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry; D018508:Water Purification / Q000379:methods*
chemical_list: D010575:Pesticides; D013830:Thiadiazoles; D014867:Water; C014547:etridiazol