Environmental dynamics and mobility of pyrazosulfuron-ethyl herbicide in diverse soils and their amendments

The nonionic herbicide pyrazosulfuron-ethyl (PYZE) has low water solubility, yet residues are frequently found in surface and groundwater, raising environmental concerns. Its soil binding and release depend on soil composition. This study examines how soil types influence PYZE sorption-desorption behavior. Four soils were tested, with three treatments on clay loam: removal of organic matter (OM), reduction of clay content (CC), and reapplication of OM to reduced-clay soil. Sorption kinetics followed a pseudo-second-order model, indicating a multi-step mechanism. Sorption and desorption isotherms fit the Freundlich equation, suggesting non-uniform binding. A sharp decline in sorption above 35 °C indicates temperature dependence. Across soils, PYZE showed strong affinity (K_D = 1.51-11.99 mL/g). Modified soils exhibited higher sorption (K_D = 3.15-44.76 mL/g), underscoring OM and CC effects. Desorption was low (≤26.72%) with notable hysteresis (H = 0.01-0.42), emphasizing persistence. Thermodynamic analysis showed sorption was physical (ΔG = -2.41 to -9.51 kJ/mol), endothermic (ΔH = 3.77-7.58 kJ/mol), and spontaneous (ΔS = 0.04-0.53 J mol^-1 K^-1). Overall, PYZE binds strongly to soils, with OM and CC key to retention, though flooding or misapplication may heighten environmental risks.