Degradation and ecological risk of a novel neonicotinoid insecticide imidaclothiz in aquatic environments: Kinetics, photodegradation and hydrolysis pathways, mechanism and metabolites toxicity evaluation.

Neonicotinoid insecticides residuals pose a threat to aquatic ecosystems and human health. Imidaclothiz, as a novel neonicotinoid pesticide, the metabolic mechanisms in aquatic environments was unclear. This study investigated the degradation characteristics of imidaclothiz in both pure and actual water, and analyzed the photodegradation and hydrolysis metabolites of imidaclothiz in aquatic environments and assessed their toxicity. The hydrolysis of imidaclothiz was not affected by temperature, pH, and metal ions. In non-sterilized Tai Lake water, the half-life of imidaclothiz were 72-187 d, with biodegradation being the primary process. Additionally, lighting was the key factor to influencing the degradation of imidaclothiz in aquatic environment. Electron Spin Resonance (ESR) results indicated that O and ·OH played crucial roles in the photodegradation of imidaclothiz. Density functional theory (DFT) calculations revealed that the maximum electrostatic potential of the imidaclothiz molecule was located at the electron-donating group (-NH-) on the oxadiazole ring, making it more prone to oxidation reactions. High-resolution mass spectrometry (HRMS) was employed to identify the photolysis and hydrolysis products of imidaclothiz. Toxicity assessment revealed that the oxidized metabolite M217 of imidaclothiz exhibited higher toxicity to aquatic organisms than the parent compound. Meanwhile, both imidaclothiz and its photodegradation and hydrolysis products posed noteworthy chronic toxicity to fish, daphnid and green algae. These finding provided theoretical guidance for the risk assessment and safe use of imidaclothiz.