Hysteretic Behavior of Imidacloprid Sorption-Desorption in Soils of Croatian Coastal Regions

Sorption and desorption are important processes that influence the transport, transformation, and bioavailability of imidacloprid in the soils. Equilibrium batch experiments were carried out using six coastal Croatian soils. The equilibrium sorption and desorption experimental data showed the best fit to the Freundlich equation. Sorption parameters predicted with the Freundlich model, K-F(sor) and 1/n ranged from 2.92 to 5.74 (mg/kg)/(mg/L)(1/n), and 0.888 to 0.919, respectively. The sorption of imidacloprid was found to be sensitive to organic carbon (OC) content. The highest sorption was observed in Krk soil (OC 4.74%) and the lowest in Zadar soil (OC 1.06%). Fitted desorption parameter values, K-F(des), were consistently higher than those associated with sorption. The opposite trend was observed for the exponential parameter 1/n. Results also suggested that imidacloprid sorption-desorption by soil is concentration-dependent, i.e. at lower imidacloprid concentrations a greater sorption percentage and lower desorption percentage occurred. Desorption studies revealed that there was a hysteresis effect in all the tested soils. Hysteresis coefficient values (H) varied from 0.656 to 0.859. The study results emphasize that the controlled application of imidacloprid is obligatory, especially in soils with a low organic carbon content, in order to minimize a risk of environmental and groundwater pollution.