title: Modeling photodegradation kinetics of three systemic neonicotinoids-dinotefuran, imidacloprid, and thiamethoxam-in aqueous and soil environment.
abstract: Environmental presence and retention of commonly used neonicotinoid insecticides such as dinotefuran (DNT), imidacloprid (IMD), and thiamethoxam (THM) are a cause for concern and prevention because of their potential toxicity to nontarget species. In the present study the kinetics of the photodegradation of these insecticides were investigated in water and soil compartments under natural light conditions. The results suggest that these insecticides are fairly unstable in both aqueous and soil environments when exposed to natural sunlight. All 3 insecticides exhibit strong first-order degradation rate kinetics in the aqueous phase, with rate constants kDNT , kIMD , and kTHM of 0.20 h(-1) , 0.30 h(-1) , and 0.18 h(-1) , respectively. However, in the soil phase, the modeled photodegradation kinetics appear to be biphasic, with optimal rate constants k1DNT and k2DNT of 0.0198 h(-1) and 0.0022 h(-1) and k1THM and k2THM of 0.0053 h(-1) and 0.0014 h(-1) , respectively. Differentially, in the soil phase, imidacloprid appears to follow the first-order rate kinetics with a kIMD of 0.0013 h(-1) . These results indicate that all 3 neonicotinoids are photodegradable, with higher degradation rates in aqueous environments relative to soil environments. In addition, soil-encapsulated imidacloprid appears to degrade slowly compared with dinotefuran and thiamethoxam and does not emulate the faster degradation rates observed in the aqueous phase. Environ Toxicol Chem 2016;35:1718-1726. © 2015 SETAC.
authors.affiliation: Department of Civil and Environmental Engineering, California State University, Fullerton, California, USA.
authors.forename: Sudarshan
authors.initials: S
authors.lastname: Kurwadkar
authors.affiliation: Department of Chemistry and Biochemistry, California State University, Fullerton, California, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Evans
authors.affiliation: Consulting Environmental Engineers, Stephenville, Texas, USA.
authors.forename: Dustan
authors.initials: D
authors.lastname: DeWinne
authors.affiliation: Department of Mathematics, Tarleton State University, Stephenville, Texas, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: White
authors.affiliation: Texas A&M AgriLife Research, Stephenville, Texas, USA.
authors.forename: Forrest
authors.initials: F
authors.lastname: Mitchell
mesh_terms: D006146:Guanidines / Q000032:analysis* / Q000528:radiation effects; D007093:Imidazoles / Q000032:analysis* / Q000528:radiation effects; D007700:Kinetics; D008962:Models, Theoretical; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000032:analysis* / Q000528:radiation effects; D010078:Oxazines / Q000032:analysis* / Q000528:radiation effects; D010782:Photolysis; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D000077922:Thiamethoxam; D013844:Thiazoles / Q000032:analysis* / Q000528:radiation effects; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000528:radiation effects
chemical_list: D006146:Guanidines; D007093:Imidazoles; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010078:Oxazines; D012987:Soil; D012989:Soil Pollutants; D013844:Thiazoles; D014874:Water Pollutants, Chemical; C465368:dinotefuran; C082359:imidacloprid; D000077922:Thiamethoxam
keywords: Agriculture; Environmental fate; Environmental impact; Insecticide; Neonicotinoids