Adsorptive interaction of antibiotic ciprofloxacin on polyethylene microplastics: Implications for vector transport in water

This study investigates the adsorption behavior of Ciprofloxacin (CPX) antibiotic on polyethylene (PE) microplastics through batch adsorption experiments under various environmental conditions, i.e., ionic strengths, pH and in the presence of dissolved organic matter (DOM). The adsorption of CPX showed a gradual increase with increasing pH reaching the maximum adsorption at pH 6.5–7.5 and then decreased, which is likely due to the redistribution of CPX species with pH. The overall CPX adsorption capacity of PE microplastics decreased with an increase in the ionic strength revealing the hydrophobic and electrostatic interactions. Fourier-transform infrared spectra (FTIR) bands ascribable to −CH₂ and −CH₃ functional groups exhibited non-polar hydrophobic properties of PE microplastics. CPX adsorption kinetics data were compatible with the parabolic diffusion model and the Elovich model in the presence of humic acid, suggesting that the adsorption was assisted through diffusion-controlled processes. The isotherm equilibrium data fitted well for Hill and Dubinin–Radushkevich models implying multilayer adsorption through physical adsorption processes on the heterogeneous PE microplastics surface. Hence, PE microplastics could be a potential vector to transport CPX in a natural aquatic environment where the adsorption mechanism is being influenced primarily by the pH, ionic strength, DOM of the water system, and the properties of the plastic.