Assessment of the environmental fate of cycloxaprid in flooded and anaerobic soils by radioisotopic tracing

Abstract

Cycloxaprid (CYC) is a novel broad-spectrum neonicotinoid insecticide that has been developed for agricultural pest control. The fate of the 14C-labeled racemic and enantio-pure CYC isomers in flooded and anaerobic soil was investigated using radioisotope tracing techniques. After 100d of incubation, only a minor portion (<1%) of the applied CYC isomers is mineralized by each of the four tested soil types. The fraction of initially applied radioactive CYC dissipated into the bound or non-extractable residues (BR) increases with increase in the length of the incubation period, reaching up to 53.0–81.6%. The dissipation of the CYC through mineralization or formation of BR is strongly influenced by soil properties, such as humic content, pH value, and retained microbial activity. Amongst the soils studied, the fluvio-marine yellow loamy soil displayed the highest tendency to mineralize CYC while the coastal saline soil exhibited the strongest tendency to form BR. The observation that the water phase retained the large portion(>60%) of the radioactivity attributed to the total extractable residue suggested that under the experimental condition, the initially applied 14C-labeled CYC residues were readily available for leaching or offsite transport. Additionally, no enantiomer-specific behaviors are observed. The results from this study provide a framework for assessing the environmental impact resulting from the use of this pesticide.