Behavior and fate of a novel neonicotinoid cycloxaprid in water–sediment systems through position-specific C-14 labeling

[Display omitted] •Cycloxaprid was transferred from water phase to sediment.•Bound residues formation was greater in the high TOC concentration of sediment.•Short persistence and low mineralization of cycloxaprid was detected.•Three metabolites were identified by 14C labeling and HPLC-QTOF-MS.•The degradation pathways of cycloxaprid in the water–sediment system were inferred. Neonicotinoid insecticides are ubiquitous worldwide, are problematic for pollinators and other nontarget creatures and affect the stability of the environment. These negative impacts prompt the ongoing development of alternatives. Cycloxaprid, a novel cis-nitromethylene neonicotinoid, exhibits high efficacy against imidacloprid-resistant pests and is viewed as a promising alternative candidate. However, information about the fate of cycloxaprid in water–sediment systems is limited. To bridge this knowledge gap, radioactive isotope-labeled 14C-cycloxaprid was employed to determine the formation of residues, transformation products, and degradation pathways. First, the mass balance analysis of residue was investigated. The extractable residue of cycloxaprid accounted for 100–40% of the total radioactive residue; cycloxaprid could transform into bound residue (0–54%) and mineralization (0–0.015%). It was partitioned from the water phase to sediments with dissipation half-lives of 6.62 d in the Dianshan Lake sample and 4.61 d in the Jinhui Port sample. Three degradation products were then detected and identified by liquid chromatography coupled to mass spectrometry. Its main metabolite, 2-chloro-5-[(2-(nitromethylene)-1-imidazolidinyl)methyl]pyridine, was more toxic than the parent compound and should be given priority in monitoring. Ring opening, carboxylation, and reduction of nitro groups were confirmed as the primary degradation pathways. The present study assessed the fate of cycloxaprid in two different water–sediment systems for the first time, and this information could provide insight into the potential ecological impacts of cycloxaprid and more precisely into evaluating its environmental risks in the future.