Thermodynamic Evaluation of the Adsorption of Pharmaceutical Compounds in Aquatic Sediments for Environmental Risk Assessment

Abstract

Pharmaceutical compounds are increasingly recognized as emerging contaminants in aquatic environments due to their continuous release from domestic, hospital, and industrial sources. The interaction of these contaminants with aquatic sediments plays a fundamental role in determining their environmental fate, mobility, persistence, and ecological risk. This study evaluated the thermodynamic adsorption behavior of three widely detected pharmaceutical compounds—diclofenac, carbamazepine, and ibuprofen—in aquatic sediments under different temperature conditions (298, 308, and 318 K). Batch adsorption experiments were conducted to determine equilibrium adsorption capacity and distribution coefficients. Thermodynamic parameters, including Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), were calculated using the Van’t Hoff approach. The results demonstrated that adsorption increased with temperature, indicating an endothermic process. Negative ΔG° values confirmed the spontaneous nature of adsorption, while positive ΔS° values suggested increased molecular disorder at the sediment–solution interface. Diclofenac exhibited the highest adsorption affinity among the studied compounds. Significant positive correlations were observed between adsorption coefficients and sediment organic matter content, total organic carbon, and clay fraction. The findings indicate that aquatic sediments act as important reservoirs for pharmaceutical contaminants and should be considered in environmental monitoring and risk assessment programs. Thermodynamic analysis provides valuable information for understanding contaminant behavior and supporting sustainable management strategies for aquatic ecosystems.