Adsorption–desorption behaviour of mesosulfuron methyl and iodosulfuron methyl across soils with varying texture, organic carbon and pH

Mesosulfuron methyl and iodosulfuron methyl are sulfonylurea herbicides widely used for weed control in cereal crops. Despite their low mammalian toxicity, their high-water solubility and weakly acidic nature suggest potential risks regarding their environmental mobility and persistence in diverse agricultural soils, particularly those that are alkaline. Since adsorption–desorption dynamics strongly influence their transport and bioavailability, the study aims to quantify and compare their adsorption–desorption behaviour in five agricultural soils differing in texture, organic carbon content and pH. Adsorption kinetics followed a two-stage process, with rapid adsorption during the initial hours, reaching equilibrium within 24 h. The pseudo-second-order kinetic model provided the best fit for experimental data. The adsorption isotherms exhibited C-type behaviour, with data fitting well to both the Freundlich and Langmuir models, indicating heterogeneous adsorption sites with a high correlation to soil composition. K_Fads of mesosulfuron methyl and iodosulfuron methyl were 1.811 ± 0.012 to 9.954 ± 0.056 and 1.068 ± 0.011 to 8.941 ± 0.078 µg¹⁻ⁿ g⁻¹mLⁿ, indicating weak adsorption of iodosulfuron methyl as compared to mesosulfuron methyl on the studied soils. K_Fads of acidic loam 1 soil (K_Fads = 8.941 ± 0.078 to 9.954 ± 0.056 µg¹⁻ⁿ g⁻¹mLⁿ) was about 5.49 to 8.37-fold higher as compared to alkaline loamy sand soil (1.068 ± 0.011 to 1.811 ± 0.012 µg¹⁻ⁿ g⁻¹mLⁿ) and the adsorption of herbicides follows the trend as loam 2 > clay loam > sandy loam > loamy sand. Adsorption decreased with increasing temperature, highlighting the exothermic nature of the process. Desorption studies showed that mesosulfuron methyl exhibited higher retention than iodosulfuron methyl, with desorption being more prominent in alkaline soils due to electrostatic repulsion and entrapment in soil nanopores. These findings contribute to understanding the environmental fate of mesosulfuron methyl and iodosulfuron methyl and may help in predicting their mobility and persistence in agricultural soils.