title: Photodegradation of clothianidin under simulated California rice field conditions.
abstract: BACKGROUND
  Photodegradation can be a major route of dissipation for pesticides applied to shallow rice field water, leading to diminished persistence and reducing the risk of offsite transport. The objective of this study was to characterize the aqueous-phase photodegradation of clothianidin under simulated California rice field conditions.
  
  
  RESULTS
  Photodegradation of clothianidin was characterized in deionized, Sacramento River and rice field water samples. Pseudo-first-order rate constants and DT50 values in rice field water (mean k = 0.0158 min(-1) ; mean DT50 = 18.0 equivalent days) were significantly slower than in deionized water (k = 0.0167 min(-1) ; DT50 = 14.7 equivalent days) and river water (k = 0.0146 min(-1) ; DT50 = 16.6 equivalent days) samples. Quantum yield ϕc values demonstrate that approximately 1 and 0.5% of the light energy absorbed results in photochemical transformation in pure and field water respectively. Concentrations of the photodegradation product thiazolymethylurea in aqueous photolysis samples were determined using liquid chromatography-tandem mass spectrometry and accounted for ≤17% in deionized water and ≤8% in natural water.
  
  
  CONCLUSIONS
  Photodegradation rates of clothianidin in flooded rice fields will be controlled by turbidity and light attenuation. Aqueous-phase photodegradation may reduce the risk of offsite transport of clothianidin from flooded rice fields (via drainage) and mitigate exposure to non-target organisms. © 2015 Society of Chemical Industry.
authors.affiliation: Department of Environmental Toxicology, College of Agricultural and Environmental Sciences, University of California, Davis, CA, USA.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Mulligan
authors.affiliation: Department of Environmental Toxicology, College of Agricultural and Environmental Sciences, University of California, Davis, CA, USA.
authors.forename: Zachary C
authors.initials: ZC
authors.lastname: Redman
authors.affiliation: Department of Chemistry, California State University, Chico, CA, USA.
authors.forename: Megan R
authors.initials: MR
authors.lastname: Keener
authors.affiliation: Department of Chemistry, California State University, Chico, CA, USA.
authors.forename: David B
authors.initials: DB
authors.lastname: Ball
authors.affiliation: Department of Environmental Toxicology, College of Agricultural and Environmental Sciences, University of California, Davis, CA, USA.
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Tjeerdema
mesh_terms: D002140:California; D006146:Guanidines / Q000032:analysis / Q000737:chemistry*; D000073943:Neonicotinoids; D012275:Oryza; D010575:Pesticides / Q000032:analysis / Q000737:chemistry*; D010782:Photolysis; D013472:Sunlight; D013844:Thiazoles / Q000032:analysis / Q000737:chemistry*; D014867:Water / Q000032:analysis
chemical_list: D006146:Guanidines; D000073943:Neonicotinoids; D010575:Pesticides; D013844:Thiazoles; D014867:Water; C480342:clothianidin
keywords: clothianidin; neonicotinoid insecticides; pesticide degradation; photodegradation