Sorption and desorption behavior of hydroxychloroquine and ivermectin in WWTP sludge: kinetic and equilibrium insights

BACKGROUND Domestic sewage is one of the main pathways for the introduction of pharmaceutical contaminants into environmental compartments. During the COVID‐19 pandemic, the consumption of medications such as hydroxychloroquine (HCQ) and ivermectin (IVM) increased significantly, resulting in a greater presence of these substances in ecosystems. Considering the existing knowledge gaps regarding the environmental impacts and ecological behavior of these compounds during this period, this study aimed to investigate the sorption and desorption kinetics and equilibrium of HCQ and IVM in sludge from domestic wastewater treatment plants (WWTPs). RESULTS The pseudo‐second‐order model best fit the kinetic sorption data for both HCQ ( R 2 = 0.91–0.99) and IVM ( R 2 = 0.94–0.99), indicating that chemisorption may be the dominant mechanism. Equilibrium data were better described by the Langmuir isotherm ( R 2 = 0.85–0.99 for HCQ and R 2 = 0.94–0.99 for IVM), suggesting monolayer adsorption on a homogeneous surface. The highest specific sorption capacities observed were 20.04 mg g −1 for HCQ and 23.29 mg g −1 for IVM. The maximum desorption percentage was 49.15% for HCQ, while no desorption of IVM was detected under experimental conditions. CONCLUSION Both analytes exhibited sorptive interactions with sewage sludge, with IVM demonstrating a stronger affinity. The findings highlight concerns about the persistence and accumulation of pharmaceutical contaminants in the environment due to discharges from WWTPs.