Modeling Adsorption-Desorption Kinetics of Imidacloprid in Soils

The potential contamination of water resources by pesticides caused by a consequence of extensive agricultural use is a major environmental concern. Imidacloprid is a widely used insecticide because of its relative safety and mode of action. Our goal was to quantify the reactivity (adsorption-desorption) of imidacloprid by soils having different properties. Kinetic batch adsorption experiments were carried out over time and then followed by desorption or release using successive dilution techniques. Freundlich and linear equations provided good predictions of imidacloprid adsorption isotherm at different reaction times (P < 0.01); best descriptions were obtained using the Freundlich model. Adsorption isotherms exhibited kinetic behavior for imidacloprid adsorption for all soils. Soils with highest organic matter and clay content exhibited the strongest affinity for imidacloprid and least kinetic behavior. Desorption or release of imidacloprid showed strong hysteretic behavior. After successive dilutions, the amounts of imidacloprid released or recovered ranged from 32% to 60% of the total amount adsorbed. A multireaction kinetic reaction model was capable of predicting imidacloprid adsorption and desorption or release for all soils and over the entire wide range of input concentrations. The model exhibited robust predictions. One set of model parameters was capable of predicting desorption or release kinetics (i.e., hysteresis) over a wide range of imidacloprid concentrations.