Reactivity of hydroxyl radicals with neonicotinoid insecticides: mechanism and changes in toxicity

Abstract

The reactivity of hydroxyl radicals (HO ) towards three neonicotonoid insecticides, namely imidacloprid, thiacloprid and acetamiprid was investigated. These radicals were generated by photolysis of H(2)O(2) solutions. Flash photolysis experiments were used to determine the rate constants of 5.5 x 10(10) M(-1)s(-1), 6 x 10(10) M(-1)s(-1), and 7.5 x 10(10) M(-1)s(-1), for the reactions of HO with acetamiprid, imidacloprid, and thiacloprid, respectively. Continuous irradiation experiments in the absence and presence of H(2)O(2) allowed the identification and toxicity evaluation of the primary photo- and oxidation products of the insecticides. In all cases, the less toxic 6-chloronicotinic acid was found to be the major product at higher degrees of oxidation. The results reported here indicate that the half life of the insecticides due to their reaction with HO radicals in natural aquatic reservoirs may vary between 5 h and 19 days, and therefore the hydroxyl radical-mediated oxidation may be a significant abiotic elimination route. However, elimination of the insecticide under such conditions might not improve the quality of the contaminated water, as the primary products of degradation still show considerable toxicity to Vibrio fischeri assays.

Supported TiO2solar photocatalysis at semi-pilot scale: degradation of pesticides found in citrus processing industry wastewater, reactivity and influence of photogenerated species

“…Photocatalytic treatment of the mixture led to 60% removal of acetamiprid with a Q UV of 5.5 kJ L and was negligible when 0.01 mol L −1 2‐propanol was present, indicating that HO · , which reacts with acetamiprid with a rate constant of k HO· = 5 × 10 10 M −1 s −1 , is probably the main species involved in the photocatalytic degradation of the pesticide, as proposed by Guzsvany et al Surprisingly, when the photocatalytic treatment was applied in the absence of the other two pesticides, the removal of acetamiprid was lower (40% for the same Q UV ), which could indicate that intermediates and/or reactive species generated during the degradation of the other two pesticides exert a positive effect on the elimination of acetamiprid. Figure shows that during the first kJ L −1 , the evolution of acetamiprid over Q UV was practically the same regardless of the presence of the other pesticides, which coincides with the accumulated UV energy needed for total disappearance of both thiabendazole (Fig.…”

Neonicotinoid insecticide hydrolysis and photolysis: Rates and residual toxicity

“…Direct photolysis has also been observed, with large variations in quantum yield between neonicotinoids and half‐lives ranging from 12 min for imidacloprid to 42 h for thiacloprid (Lu et al ). Indirect photolysis has been studied, with half‐life estimates of 5 h to 19 d in aquatic reservoirs, indicating that hydroxyl radicals may play a role in neonicotinoid photolysis (Dell'Arciprete et al ). The comparison of direct and indirect photolysis in the same study, however, has not been reported, and updated actinometry values (Laszakovits et al ) require validation of previously reported quantum yields.…”

Electro-catalytic degradation pathway and mechanism of acetamiprid using an Er doped Ti/SnO2–Sb electrode

“…According to the article, 19 6-chloronicotinic acid (6-CNA) is regarded as the degradation product of ACT by photocatalytic oxidation. ACT has a high water solubility (the solubility is 4200 mg L À1 in water at 293 K and pH ¼ 7) and is highly stable in the sun and in a weak acidic medium.…”