| Neonicotinoid insecticides such as Imidacloprid (IMD), Thiamethoxam (THM), and Dinotefuran (DNT) are extensively used in agricultural operations. Their occurrence in the environment can have significant adverse ecological consequences to non-target species. In this research, hydrolysis kinetics of these insecticides were investigated at various pHs (acidic, neutral, and basic) and temperature (room temperature [~25°C], 45°C, and 60°C) conditions. Results indicate that of the three neonicotinoids, THM exhibits higher hydrolysis rate across all temperature and pH conditions, followed by IMD and DNT. Both temperature and pH have pronounced effect on the hydrolysis rate. All three neonicotinoids are unstable at pH 11, 60°C, with their hydrolysis rate constants: kTHM = 10.03 hr-1, kIMD = 0.58 hr-1, and kDNT 0.08 hr-1. Slower hydrolysis rate was observed at room temperature with hydrolysis rate constants: kTHM = 0.09 hr-1, kIMD = 0.01 hr-1 and kDNT 5E-04 hr-1. Reduction in temperature and a change in pH induces the largest effect on the hydrolysis rate of the THM. Across all experimental temperature conditions, the hydrolysis rate is fastest at pH 11, followed by pH 7, and stable at pH 4. The difference in the hydrolysis rates for the neonicotinoids tend to shrink as pH changes from alkaline to neutral, with the most unstable compound experiencing the largest effect. The hydrolysis rates clearly demonstrate that these neonicotinoids are stable towards hydrolysis and may pose serious adverse risk to non-target species. |
