Environmental occurrence of commonly used neonicotinoid insecticides such as Dinotefuran (DNT), Imidacloprid (IMD) and Thiamethoxam (THM) is a cause of concern due to their potential toxicity to the non-target species. In this photo-degradation kinetic study, persistence of these insecticides is investigated in water and soil compartment under ambient environment. The results suggest that neonicotinoids in both aqueous and soil phase are fairly unstable when exposed to natural UV-light. All three insecticides exhibit strong first-order degradation kinetic in aqueous phase with rate constants kDNT, kIMD, and kTHM of 0.195/hr., 0.299/hr, and 0.181/hr. respectively. In the soil environment however, the modeled photo-degradation kinetics appears to be bi-phasic with optimal rate constants of k1DNT and k2DNT 0.0198/hr. and 0.00220/hr. and k1THM and k2THM as 0.00532/hr. and 0.00142/hr. respectively. Unlike DNT and THM, even in soil environment, IMD appears to follow the first order rate kinetics with kIMD 0.00135/hr. These results clearly demonstrate that all three neonicotinoids are photodegradable, with predictably higher degradation rate in aqueous compared to soil environment. Unlike in aqueous phase where IMD degradation rate is fastest, the soil encapsulated IMD degrades very slowly compared to DNT and THM.

Modeling photo-degradation kinetics of three systemic neonicotinoid insecticides in aqueous and soil environment

247th National Meeting (2014)

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