Photodegradation of Metolachlor in Water in the Presence of Soil Mineral and Organic Constituents

Photodegradation of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 253.7 nm was carried out in water containing soil minerals (kaolinite, montmorillonite, and goethite) and fulvic acid under two different pH conditions. The rate of photolysis was dependent on the nature of the soil constituents and the initial pH of the medium. Based on the regression analysis, it was shown that the photodegradation followed the first-order kinetics with respect to the metolachlor concentration, and the half-life of the herbicide under UV irradiation was longer in the absence of soil constituents. Hydroxylation, dehalogenation, oxoquinoline formation, and demethylation were the main processes observed during the photolysis of metolachlor. More degradation products were formed in the presence of kaolinite, montmorillonite, and goethite than with fulvic acid and water alone. The major degradation product formed under UV irradiation in all the treatments was identified as 4-(2-ethyl-6-methylphenyl)-5-methyl-3-morpholine. Keywords: Photodegradation; metolachlor; soil minerals; fulvic acid; degradation products