Effect of humic acids on photodegradation of chloroacetanilide herbicides under UV irradiation

• Published in: Journal of environmental science and health. Part B, Pesticides, food contaminants, and agricultural wastes Vol. 42; no. 2; pp. 165 - 171
• Main Authors: Xu, G, Li, F.E, Wang, Q.H
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Taylor & Francis Group 01.02.2007; Taylor & Francis
• Subjects: Acetamides - chemistry; Acetamides - radiation effects; Acetanilides - chemistry; Acetanilides - radiation effects; acetochlor; Biological and medical sciences; butachlor; Chemical control; Chloroacetanilide herbicides; Fundamental and applied biological sciences. Psychology; Gas Chromatography-Mass Spectrometry - methods; humic acids; humic acids (HAs); Humic Substances - analysis; irradiation; Kinetics; Parasitic plants. Weeds; Photolysis; Phytopathology. Animal pests. Plant and forest protection; propisochlor; reaction kinetics; soil pollution; Toluidines - chemistry; Toluidines - radiation effects; ultraviolet radiation; Ultraviolet Rays; UV irradiation; water pollution; Weeds; China; China, People's Rep; Ultraviolet radiation; humic acids (HAs); photolysis; Pesticides; Organic amide; UV irradiation; Kinetics; Humic acid; Herbicide; Photochemical degradation; Chloroacetanilide herbicides
• ISSN: 0360-1234; 1532-4109
• DOI: 10.1080/03601230601123300

The effects of two humic acids (HAs) of different origins on the photodegradation of the chloroacetanilide herbicides acetochlor, propisochlor and butachlor were investigated in this study. One of the tested HAs was a standard sample that was purchased from a commercial source, and the other was isolated from the black soil of Northeast China. The photolysis of all three herbicides followed pseudo-first-order kinetics under ultraviolet (UV) irradiation conditions, regardless of whether HAs were present or not. Both HAs improved the photolysis rates of acetochlor in a dose-reversed way, whereas they inhibited butachlor degradation under all experimental concentrations. The two HAs differed in their effects on propisochlor photolysis, changing from enhancement to inhibition, depending on the origin and concentration of HAs. Element and Fourier Transform Infrared spectroscopy analyses showed that the isolated HAs had more polysaccharides and less aliphatic groups than the commercial HAs, and it was indicated that some characteristic radicals (C═O, O─H and phenolic hydroxyls) in HAs were involved in the photolysis of the herbicides. Gas chromatography/mass spectrometry (GC/MS) analyses indicated that the presence of HAs had no effects on the photolysis pathway and photoproduct species of the three herbicides.