Document Type : Original Article
Author
Department of Pesticide Chemistry and Technology, Faculty of Agriculture, Alexandria University, Aflaton St., 21545, El-Shatby, Alexandria, Egypt.
Abstract
To achieve the objectives of this study, the batch sorption and desorption kinetic experiments were performed to obtain the equilibrium time for fipronil and thiamethoxam in three types of Egyptian soil (clay soil, sandy clay loam soil and sandy loam soil). Equilibrium between the insecticides solution and the soil for adsorption and desorption appeared at 30, 24, 6 and 30 hr in clay soil, 0.5,12, 12 and 12 hr in sandy clay loam soil and 3, 1, 24 and 30 hr in sandy loam soil for fipronil and thiamethoxam, respectively. The adsorption rate of fipronil was higher and it had stronger affinity to three tested soils compared to thiamethoxam. Nevertheless, both pesticides showed stronger affinity to clay soil than to sandy clay loam soil and sandy loam soil. Using five kinetic models; Elovich, Intraparticle diffusion, modified Freundlich, Pseudo-first-order rate and Pseudo-second-order rate were tested to describe the experimental data.The model that gives a relatively high correlation coefficient was used to test the validity of mathematical models (R2). The best model is Pseudo-second-order rate equation that fits with experimental data for fipronil and thiamethoxam on adsorption and desorption kinetic in three types of soil (R2 ≥ 0.9). Elovich kinetic model fit the experimental data quite well for adsorption in clay soil for two insecticides, adsorption and desorption in sandy clay loam soil for thiamethoxam, adsorption in sandy loam soil for fipronil and desorption in sandy clay loam soil for thiamethoxam with high values of R2 ≥ 0.9.Its application of Intraparticle diffusion, the modified Freundlich model, and the Pseudo-first-order rate equation was limited.
Keywords
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