Abstract

Sulfonylureas are among the most used herbicides globally, including regions dominated by volcanic ash-derived soils (VADS), which possess unique physicochemical properties. Despite their high solubility and persistence, the behavior and fate of sulfonylureas in VADS remain poorly understood, limiting accurate risk assessments. We aim to explore the environmental dynamics of sulfonylureas in VADS and identify key VADS descriptors via principal component analysis (PCA) to understand the dominant factors influencing sulfonylurea adsorption in VADS. Using bensulfuron-methyl (BSM) and rimsulfuron (RS) as model sulfonylureas, batch adsorption kinetics and adsorption-desorption studies were conducted in ten different VADS from Chile. The sulfonylurea sorption in VADS and solute transport mechanisms were predicted by combining adsorption kinetics and adsorption-desorption modeling. The pseudo-second-order model elucidated the involvement of variable charge materials in sulfonylurea adsorption, wherein OM content and the halloysite/kaolinite ratio played significant roles in the two and three-step adsorption processes. Freundlich isotherms describe the sulfonylurea adsorption in all soils (K-f values between 0.04 and 171.6 mu g(1-1/n) mL(1/n) g(-1)), indicating non-linear, irreversible adsorption consistent with chemisorption. The PCA effectively identified bulk density, C_EH_aM, C_EH/TOC ratio, cation exchange capacity (CEC), and specific nutrient content as key soil descriptors for explaining sulfonylurea adsorption variability in VADS. This study highlights the need for context-specific management of sulfonylurea application in VADS, emphasizing soil pH adjustment, OM enhancement, and the development of predictive adsorption modeling to mitigate leaching and groundwater contamination risks.