title: Low pressure UV/H2O2 treatment for the degradation of the pesticides metaldehyde, clopyralid and mecoprop - Kinetics and reaction product formation.
abstract: The degradation kinetics of three pesticides - metaldehyde, clopyralid and mecoprop - by ultraviolet photolysis and hydroxyl radical oxidation by low pressure ultraviolet hydrogen peroxide (LP-UV/H2O2) advanced oxidation was determined. Mecoprop was susceptible to both LP-UV photolysis and hydroxyl radical oxidation, and exhibited the fastest degradation kinetics, achieving 99.6% (2.4-log) degradation with a UV fluence of 800 mJ/cm(2) and 5 mg/L hydrogen peroxide. Metaldehyde was poorly degraded by LP-UV photolysis while 97.7% (1.6-log) degradation was achieved with LP-UV/H2O2 treatment at the maximum tested UV fluence of 1000 mJ/cm(2) and 15 mg/L hydrogen peroxide. Clopyralid was hardly susceptible to LP-UV photolysis and exhibited the lowest degradation by LP-UV/H2O2 among the three pesticides. The second-order reaction rate constants for the reactions between the pesticides and OH-radicals were calculated applying a kinetic model for LP-UV/H2O2 treatment to be 3.6 × 10(8), 2.0 × 10(8) and 1.1 × 10(9) M(-1) s(-1) for metaldehyde, clopyralid and mecoprop, respectively. The main LP-UV photolysis reaction product from mecoprop was 2-(4-hydroxy-2-methylphenoxy) propanoic acid, while photo-oxidation by LP-UV/H2O2 treatment formed several oxidation products. The photo-oxidation of clopyralid involved either hydroxylation or dechlorination of the ring, while metaldehyde underwent hydroxylation and produced acetic acid as a major end product. Based on the findings, degradation pathways for the three pesticides by LP-UV/H2O2 treatment were proposed.
authors.affiliation: Department of Civil and Environmental Engineering, Imperial College London, London, UK; Wetsus, European Centre of Excellence for Sustainable Water Technology, Leeuwarden, The Netherlands. Electronic address: s.semitsoglou-tsiapou12@imperial.ac.uk.
authors.forename: Sofia
authors.initials: S
authors.lastname: Semitsoglou-Tsiapou
authors.affiliation: Department of Civil and Environmental Engineering, Imperial College London, London, UK.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Templeton
authors.affiliation: Department of Civil and Environmental Engineering, Imperial College London, London, UK.
authors.forename: Nigel J D
authors.initials: NJ
authors.lastname: Graham
authors.affiliation: Wetsus, European Centre of Excellence for Sustainable Water Technology, Leeuwarden, The Netherlands.
authors.forename: Lucía
authors.initials: L
authors.lastname: Hernández Leal
authors.affiliation: PWN Technologies, Velserbroek, The Netherlands.
authors.forename: Bram J
authors.initials: BJ
authors.lastname: Martijn
authors.affiliation: Trojan Technologies, London, Ontario, Canada.
authors.forename: Alan
authors.initials: A
authors.lastname: Royce
authors.affiliation: Wetsus, European Centre of Excellence for Sustainable Water Technology, Leeuwarden, The Netherlands.
authors.forename: Joop C
authors.initials: JC
authors.lastname: Kruithof
mesh_terms: D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D000079:Acetaldehyde / Q000031:analogs & derivatives / Q000737:chemistry; D006540:Herbicides / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D008975:Molluscacides / Q000737:chemistry; D010084:Oxidation-Reduction; D010782:Photolysis; D010848:Picolinic Acids / Q000737:chemistry; D011312:Pressure; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D006540:Herbicides; D008975:Molluscacides; D010848:Picolinic Acids; D014874:Water Pollutants, Chemical; C011767:clopyralid; D017665:Hydroxyl Radical; C002935:metaldehyde; C008340:mecoprop; D006861:Hydrogen Peroxide; D008456:2-Methyl-4-chlorophenoxyacetic Acid; D000079:Acetaldehyde
keywords: Clopyralid; Kinetics; LP-UV/H(2)O(2); Mecoprop; Metaldehyde; Reaction products