MODELING PHOTODEGRADATION KINETICS OF THREE SYSTEMIC NEONICOTINOIDS – DINOTEFURAN, IMIDACLOPRID AND THIAMETHOXAM IN AQUEOUS AND SOIL ENVIRONMENT Sudarshan Kurwadkar, Amanda Evans, Dustan DeWinne, Peter White, and Forrest Mitchell

Environmental presence and retention of commonly used neonicotinoid insecticides such as dinotefuran (DNT), imidacloprid (IMD), and thiamethoxam (THM) is a cause for concern and prevention due to their potential toxicity to non-target species. In the present study the kinetics of the photodegradation of these insecticides were investigated in water and soil compartments under natural light conditions. Results suggest these insecticides are fairly unstable in both aqueous and soil environments when exposed to natural sunlight. All three insecticides exhibit strong first-order degradation rate kinetics in the aqueous phase, with rate constants kDNT, kIMD, and kTHM of 0.20 hr, 0.30 hr, and 0.18 hr respectively. However in the soil phase, the modeled photodegradation kinetics appear to be bi-phasic, with optimal rate constants of k1DNT and k2DNT 0.0198 hr and 0.0022 hr and k1THM and k2THM as 0.0053 hr and 0.0014 hr, respectively. Differentially, in the soil phase, IMD appears to follow the first-order rate kinetics with a kIMDof 0.0013 hr. These results indicate that all three neonicotinoids are photodegradable, with higher degradation rates in aqueous environments relative to soil environments. Additionally, soil-encapsulated IMD appears to degrade slowly compared to DNT and THM and does not emulate the faster degradation rates observed in the aqueous phase. This article is protected by copyright. All rights reserved