Fate of Clothianidin and Phoxim in Fresh Corn and Corn Grain: Storage Stability and Human Health Risk Assessment

Corn is a critically important agricultural crop, with different parts consumed at specific growth stages—notably, fresh corn and corn grain. The field residue behaviors of clothianidin and phoxim in fresh corn and corn grain were investigated by using a QuEChERS technique combined with UPLC-MS/MS, and the dietary exposure risks of the insecticides were evaluated. Field trials were conducted under the recommended application conditions (2250 g active ingredient per hectare of 2% clothianidin and phoxim granules, applied once) at 12 agricultural regions across China under various climatic conditions to study the residue levels of pesticides. The samples were collected at harvest of fresh corn and corn grain, separately. The results indicated that the residues of the phoxim remained stable in all samples stored at −20 °C for 6 months (180 days). At harvest, the concentrations of clothianidin in fresh corn ranged from <0.01 to 0.027 mg/kg (below the MRL of 0.1 mg/kg established by Japan); the concentrations of phoxim in fresh corn were all below 0.01 mg/kg (below the Chinese MRL of 0.1 mg/kg). In corn grain, clothianidin residues ranged from <0.01 to 0.018 mg/kg (below the Chinese MRL of 0.02 mg/kg), while phoxim residues were below 0.01 mg/kg (below the Chinese MRL of 0.1 mg/kg). Dietary risk assessment based on Chinese pesticide registration status and the per capita dietary structure of Chinese residents showed that the national estimated daily intake (NEDI) of clothianidin for the general population was 0.49 mg, accounting for 7.8% of the adult acceptable daily intake (ADI), while NEDI of phoxim for the general population was 0.048 mg, accounting for 19.2% of adult ADI. The results suggest that the associated health risks are acceptable for the general population. On the basis of these findings, it is recommended to establish an MRL for clothianidin in fresh corn in China at 0.1 mg/kg. This study provided basic data on the use and safety of clothianidin and phoxim in fresh corn and corn grain to help the Chinese government formulate a maximum residue level for clothianidin in fresh corn.