Adsorption interactions between typical microplastics and enrofloxacin: Relevant contributions to the mechanism

Microplastics (MPs) are increasingly contaminating the environment and they can combine with antibiotics as carriers to form complex contaminants. In this study, we systematically investigated the interactions between the antibiotic enrofloxacin (ENR) and MPs comprising polyethylene (PE), polyvinyl chloride (PVC), and polystyrene (PS). Characterization was performed by using conventional techniques and the mechanisms involved in interactions were initially explored based on adsorption kinetics, isotherms, and resolution experiments, and the adsorption capacities of the MPs were determined. In addition, the extended Derjaguin-Landau-Verwey-Overbeek theory was used to investigate the interaction mechanisms. The results showed that the interactions were weaker in strong acidic and alkaline environments, and the interactions were also inhibited at higher salt ion concentrations. The saturation adsorption amounts of ENR on PVC, PE, and PS were 74.63 μg/g, 103.09 μg/g, and 142.86 μg/g, respectively. The interactions between MPs and ENR were dominated by hydrophobic interactions, followed by van der Waals forces and acid-base forces. This study provides new insights into the adsorption behavior of ENR by MPs.