Residue degradation and influencing factors of three neonicotinoids insecticides in soil

A new method using HPLC-MS/MS was developed to analyze imidacloprid, acetamiprid and thiamethoxam residues in soil. Samples were extracted with acetonitrile, cleaned up by QuEChERS method, and detected by HPLC-MS/MS with quantification by external standard method. Result shows that when the soil samples were spiked with the above mentioned three neonicotinoids pesticides at levels between 0.01 and 1.0 mg/kg, the average recoveries and the relative standard deviations(RSD) are in conformity with the guideline on pesticide residue analysis method. The limit of quantity (LOQ) of imidacloprid, acetamiprid and thiamethoxam in soil samples were all 0.01 mg/kg. By using this new method, the effects of soil microorganism, temperature, soil humidities and the initial concentration on degradation of imidacloprid, acetamiprid and thiamethoxam were studied under laboratory conditions. The results showed that the soil microorganism was the primary factor influencing the degradation of pesticide, and the degradation rate in sterilized soil was obviously lower than that in the none-sterilized soil. Besides, the degradation rate of pesticide was also influenced by temperature, soil humilities and initial concentration. It was optimal for the degradation of the above three neonicotinoids pesticide when the soil humilities was around 60% FC, and the half-life of imidacloprid, acetamiprid and thiamethoxam were 15.6, 7.2 and 25.8 d, respectively under that condition. The higher the initial concentration, the slower the degradation of the above three neonicotinoids pesticide; The degradation was accelerated significantly when the temperature increased from 5℃ to 35℃.