Degradation of imidacloprid insecticide in a binary mixture with propylene glycol by conventional fenton process

Imidacloprid is one of the most widely used insecticides in agriculture. The fate of this highly recalcitrant pollutant and its by-product of incomplete degradation in water is of great concern due to the hazardous effects usually associated to pesticides. In the present manuscript, imidacloprid degradation by hydroxyl radical produced in-situ by conventional Fenton process is discussed. Furthermore, it has been studied the influence of propylene glycol, which is a usual excipient found in the commercial pesticides containing imidacloprid, on the conventional Fenton process performance. A two-stage degradation kinetics was observed: (i) a rapid initial decay on the first 5 min of treatment, followed by (ii) a slower kinetics defined by the Fenton-like reaction of Fe²⁺ catalyst regeneration. The influence of several variables on the abatement of imidacloprid such Fe²⁺ and H₂O₂ initial concentration or propylene glycol ratios have been evaluated. Experimental results demonstrate that complete imidacloprid abatement is attained under optimal conditions of 8.0mM of H₂O₂ and 0.8mM of Fe²⁺ after 120 min of treatment at acidic pH. However, increasing concentrations of propylene glycol diminishes the overall performance due to the competitive consumption of hydroxyl radicals.