Reactivity of neonicotinoid insecticides with carbonate radicals

The reaction of three chloronicotinoid insecticides, namely Imidacloprid (IMD), Thiacloprid (THIA) and Acetamiprid (ACT), with carbonate radicals (CO3−) was investigated. The second order rate constants (4 ± 1) × 106, (2.8 ± 0.5) × 105, and (1.5 ± 1) × 105 M−1 s−1 were determined for IMD, THIA and ACT, respectively. The absorption spectra of the organic intermediates formed after CO3− attack to IMD is in line with those reported for α-aminoalkyl radicals. A reaction mechanism involving an initial charge transfer from the amidine nitrogen of the insecticides to CO3− is proposed and further supported by the identified reaction products. The pyridine moiety of the insecticides remains unaffected until nicotinic acid is formed. CO3− radical reactivity towards IMD, ACT, and THIA is low compared to that of HO• radicals, excited triplet states, and 1O2, and is therefore little effective in depleting neonicotinoid insecticides. [Display omitted] ► Cloronicotinoid insecticides show low reactivity towards carbonate radicals. ► The reaction involves an initial charge transfer from the insecticide to CO3−. ► After prolonged irradiation chloronicotinic acid is formed. ► Hydroxyl and sulphate radicals are among the most effective in degrading the insecticides.