Adsorption of strobilurin fungicide Kresoxim methyl onto diverse Indian soils: kinetic and mechanistic modeling.

Extensive use of Kresoxim methyl, its ability to bio-concentrate and its carcinogenic nature makes this strobilurin fungicide a prominent leaching contaminant contributing to ground water pollution. Understanding its sorption kinetics is essential for elucidating the sorption mechanisms occurring in soil and for predicting its transport across various kinds of soil. In the current study, adsorption kinetics of kresoxim methyl onto ten soil samples of different geographical regions (Shivalik hills, Bhabhar and Indo-Gangetic plains) were examined. The adsorption of Kresoxim methyl was maximum (16.096 mg kg-1) onto soil with high clay + silt content (86.2%) and minimum (13.813 mg kg-1) onto soil with low clay + silt (44.9%). The kinetic data of Kresoxim methyl for all soil samples aligned well with pseudo-first-order (coefficient of determination (R2) ranging from 0.848 to 0.987) and pseudo-second-order kinetic models (R2 = 1). Mechanistic modelling revealed the applicability of chemisorption-diffusion model for all soils (R2 = 1). Soil properties such as clay + silt compositions, organic matter content and surface complexation of fungicide by exchangeable micronutrient cations can be used to predict the Kresoxim methyl sorption kinetics. This approach can be extended to other pesticides, structurally and physico-chemically analogous to Kresoxim methyl, providing a framework for evaluating their environmental behaviour. Besides the involvement of intra-particle diffusion and chemisorption-diffusion models, the adsorption of Kresoxim methyl was presumably governed by one or more supplementary mechanisms, such as hydrogen bonding.