Efficient degradation of clothianidin and thiamethoxam in contaminated soil by peroxymonosulfate process

The widespread use of neonicotinoids has led to their frequent detection in the environment and potential environmental risk in recent years. Clothianidin (CLO) and thiamethoxam (TMX), as the second generation of neonicotinoid insecticides, are usually used as seed agents with a high risk of residue in the soil. Efficient degradation of CLO and TMX in soil using peroxymonosulfate (PMS) process was investigated in the present study. The degradation efficiencies of CLO and TMX reached 91.4% and 98.6% in 60 min with the addition of 20 mM PMS at pH 5.5 and 25℃. High degradation efficiencies of CLO were achieved with a high PMS dosage and temperature or a low CLO concentration and initial pH. The degradation of CLO was reduced in the presence of high concentration of inorganic anions (Cl^-, HCO₃^-). Soil organic matter might be one critical factor in the degradation of CLO and TMX. Radical scavenger experiments confirmed SO₄^•- and ¹O₂ were the dominant reactive species on the CLO and TMX degradation. Based on the detected degradation intermediates, the degradation pathways of CLO and TMX include dichlorination, hydroxylation, cleavage of C-N or C-C bond and further oxidation in the PMS-based soil. Overall, the PMS process is one effective and economical method for the remediation of the neonicotinoid contaminated soil.