Adsorption-desorption behavior of difenoconazole onto soils: Kinetics, isotherms, and influencing factors

Abstract

Difenoconazole (DFC) is a commonly used triazole fungicide known for its high efficiency and environmental persistence. A thorough understanding of its environmental behavior, particularly sorption in soil, is critical to obtain a comprehensive assessment of the ecological risk of DFC. In this study, three soils with distinct physicochemical properties (brown soil, cinnamon soil, and fluvo-aquic soil) were used to elucidate the adsorption mechanisms of DFC on soil. A combination of adsorption kinetics, isotherms, analysis of soil physicochemical properties, Fourier transform infrared spectroscopy (FT-IR), and fluorescence spectroscopy was utilized to characterize the behavior, influencing factors, and mechanisms of adsorption. The Freundlich model best described the sorption isotherms (R2 = 0.910–0.963). The adsorption coefficients kf of the three soils were 15.25 (brown soil), 11.82 (cinnamon soil), and 26.85 (fluvo-aquic soil). The kf values were positively correlated with soil pH and organic matter contents and negatively correlated with clay contents and cation exchange capacities. The FT-IR analysis revealed a general decline in the hydroxyl absorption peak, indicating the formation of ionic bonds between DFC and soil polar functional groups, primarily on the carboxyl group and hydroxyl group of humic acids in the fluvo-aquic soil. Further characterization of dissolved organic matter supported the idea that humic acids in the fluvo-aquic soil dominated the sorption of DFC. The findings of this study clearly explained the sorption mechanisms of DFC in soil and supported optimized pesticide application strategies, improved risk assessment, and informed regulatory decisions.