Low pressure UV/H2O2 treatment for the degradation of the pesticides metaldehyde, clopyralid and mecoprop - Kinetics and reaction product formation

WATER RESEARCH

卷:91

Article

Semitsoglou-Tsiapou, Sofia^1,2  Templeton, Michael R.¹  Graham, Nigel J. D.¹  Leal, Lucia Hernandez²  Martijn, Bram J.³  Royce, Alan⁴  Kruithof, Joop C.² 

[1] Univ London Imperial Coll Sci Technol & Med, Dept Civil & Environm Engn, London, England

[2] European Ctr Excellence Sustainable Water Technol, Wetsus, Leeuwarden, Netherlands

[3] PWN Technol, Velserbroek, Netherlands

[4] Trojan Technol, London, ON, Canada

关键词: Metaldehyde;    Clopyralid;    Mecoprop;    LP-UV/H2O2;    Kinetics;    Reaction products;   

DOI  :  10.1016/j.watres.2016.01.017

来源: Elsevier

【 摘 要 】

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 x 10(8), 2.0 x 10(8) and 1.1 x 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. (C) 2016 Elsevier Ltd. All rights reserved.

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