title: Comparison of Direct and Indirect Photolysis in Imazosulfuron Photodegradation.
abstract: Imazosulfuron, a sulfonylurea herbicide used in rice cultivation, has been shown to undergo photodegradation in water, but neither the photochemical mechanism nor the role of indirect photolysis is known. The purpose of this study was to investigate the underlying processes that operate on imazosulfuron during aqueous photodegradation. Our data indicate that in the presence of oxygen, most photochemical degradation proceeds through a direct singlet-excited state pathway, whereas triplet-excited state imazosulfuron enhanced decay rates under low dissolved oxygen conditions. Oxidation by hydroxyl radical and singlet oxygen were not significant. At dissolved organic matter (DOM) concentrations representative of rice field conditions, fulvic acid solutions exhibited faster degradation than rice field water containing both humic and fulvic acid fractions. Both enhancement, via reaction with triplet-state DOM, and inhibition, via competition for photons, of degradation was observed in DOM solutions.
authors.affiliation: Center for Medicinal and Veterinary Entomology, U.S. Department of Agriculture , 1600 S.W. 23rd Drive, Gainesville, Florida 32608, United States.
authors.forename: Caitlin
authors.identifier: http://orcid.org/0000-0003-0577-645X
authors.initials: C
authors.lastname: Rering
authors.affiliation: Environmental Toxicology Department, University of California-Davis , 4138 Meyer Hall, One Shields Avenue, Davis, California 95616, United States.
authors.forename: Katryn
authors.initials: K
authors.lastname: Williams
authors.affiliation: Environmental Toxicology Department, University of California-Davis , 4138 Meyer Hall, One Shields Avenue, Davis, California 95616, United States.
authors.forename: Matt
authors.initials: M
authors.lastname: Hengel
authors.affiliation: Environmental Toxicology Department, University of California-Davis , 4138 Meyer Hall, One Shields Avenue, Davis, California 95616, United States.
authors.forename: Ronald
authors.initials: R
authors.lastname: Tjeerdema
mesh_terms: D006540:Herbicides / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction / Q000528:radiation effects; D010782:Photolysis / Q000528:radiation effects; D011725:Pyridines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*
chemical_list: D006540:Herbicides; D011725:Pyridines; D011743:Pyrimidines; C433346:1-(2-chloroimidazo(1,2-a)pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea; D017665:Hydroxyl Radical
keywords: dissolved organic matter; herbicide; imazosulfuron; indirect photolysis; reactive oxygen species