Freundlich, Langmuir, Temkin, Elovich, Redlich-Peterson, and Halsey Models of Fenitrothion Adsorption-Desorption Isotherm onto Two Different Soil Textures

Abstract

This study is concerned with studying the adsorption and desorption isotherms of fenitrothion in clay and sandy clay loam soils, while verifying appropriate mathematical models. The average adsorption and values of Kd, log Kom, log Koc and log Kclay were greater in the clay soil than in the sandy clay loam soil. The adsorption was largely irreversible from clay soil but largely reversible from sandy clay loam soil. Thus, the amount of fenitrothion desorbed from clay soil was lower than that desorbed from sandy clay loam soil. The adsorption and desorption behavior of the insecticide fenitrothion on clay soil and sandy clay loam soil can be well described using the Freundilch and Halsey isotherm models, which produce high R2 values and low values of Δqe% and SSE. Additionally, the points corresponding to the data predicted by the two models are located almost consistent with the experimental data. The Langmuir model is limited to describing the experimental adsorption and desorption data at low concentrations of fenitrothion. The Temkin, Elovich and Redlich-Peterson isotherm models are unable to describe the experimental data of adsorption and desorption in clay soil and sandy clay loam soil. The slope (1/n) values of the adsorption isotherms for fenitrothion on sandy clay loam soil were greater than unity, suggesting an S-type isotherm, which reflects a low adsorbent-adsorbate affinity at low concentrations, and the soil surface has a greater affinity for water than for pesticide molecules at low concentrations.