Xiaolan Ma

Fluoroquinolone antibiotics are widely detected emerging pollutants, yet their interfacial behavior in the alkaline, calcium-rich sediments of arid inland river basins remains poorly quantified, which limits regional risk assessment. This study selected riverbank calcareous sediments from the Ili River and ofloxacin (OFL), a representative fluoroquinolone, and used batch adsorption–desorption experiments to quantify the retention of OFL and the regulatory roles of pH and coexisting cations. Adsorption was biphasic, with a fast stage ( Ca²⁺ > Na⁺ at matched molarity (0.01 mol L⁻¹), and the inhibition intensified with increasing cation concentration. Because Na⁺ was applied at the same molarity as Mg²⁺ as an ionic-strength control while Ca²⁺ was also applied at a higher concentration, the ranking reflects specific competition by the divalent cations combined with a weaker double-layer (ionic-strength) effect for the monovalent ion. Acidic pH enhanced adsorption and alkaline pH suppressed it, consistent with the change in OFL speciation from cationic through zwitterionic to anionic. This work quantifies the adsorption–desorption behavior of OFL on arid-region calcareous sediments and provides parameter values with uncertainty estimates that support risk assessment and pollution control in the Ili River Basin. From a sustainability perspective, the work converts these site-specific measurements into transferable, uncertainty-bounded parameters (Langmuir and Freundlich capacities, the linear partition coefficient Kd and the hysteresis index) for a sediment type that is widespread in arid inland river basins. It therefore supplies directly usable input for the definition and quantification of water-quality sustainability indicators, the monitoring of the sediment buffering function over time, and the setting of discharge-outlet effluent limits and the seasonal screening of secondary-pollution risk during the warm, low-flow irrigation period, thereby connecting a mechanistic sorption study to the wider objective of sustaining safe water use in a water-scarce region.