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Modeling photodegradation kinetics of three systemic neonicotinoids—dinotefuran, imidacloprid, and thiamethoxam—in aqueous and soil environment
Author(s) -
Kurwadkar Sudarshan,
Evans Amanda,
DeWinne Dustan,
White Peter,
Mitchell Forrest
Publication year - 2016
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.3335
Subject(s) - imidacloprid , thiamethoxam , photodegradation , chemistry , kinetics , reaction rate constant , environmental chemistry , aqueous solution , neonicotinoid , degradation (telecommunications) , bioavailability , pesticide , organic chemistry , ecology , biology , pharmacology , telecommunications , physics , photocatalysis , quantum mechanics , computer science , catalysis
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 k DNT , k IMD , and k THM 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 k 1DNT and k 2DNT of 0.0198 h −1 and 0.0022 h −1 and k 1THM and k 2THM 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 k IMD 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