Simultaneous remediation of three neonicotinoids in soil using nanoscale zero-valent iron-activated persulfate process: Performance, effect of process parameters, and mechanisms

Neonicotinoids are commonly used pesticides in agricultural regions all over the world, and their widespread use has caused potential environmental pollution issues in recent years. The simultaneous degradation of three representative neonicotinoids (i.e., imidacloprid (IMI), thiamethoxam (TMX) and dinotefuran (DIN)) in soil by a nanoscale zero-valent iron-activated persulfate (nZVI-activated PS) process was investigated. Under the optimum conditions with 1 mg g−1 nZVI, 10 mM PS at an initial pH value of 6.9 and a water-soil ratio of 1.5, the degradation efficiency of IMI, TMX and DIN reached 89%, 86% and 69% in 15 mins, respectively. Degradation of the three neonicotinoids was fitted with a pseudo first-order kinetic model. High nZVI dosage and PS concentration were found to enhance the neonicotinoids degradation. In contrast, the presence of Cl-, HCO3- and HA reduced the degradation rates of the three neonicotinoids. Soil physicochemical properties showed a significant effect on the degradation efficiencies of the three neonicotinoids. In addition, quenching experiments combined with electron paramagnetic resonance (EPR) showed that free radicals SO4•- and •OH contributed to the degradation of three neonicotinoids in the nZVI-activated PS system. Degradation pathways were proposed based on identified intermediates of IMI, TMX and DIN. Overall, the nZVI-activated PS process is an effective method for remediation of the neonicotinoids contaminated soil.