Sorption of Pharmaceuticals onto Polyethylene Terephthalate and Medium-Density Polyethylene: Influence of Plastic Polymer Type and Water Medium

The growing accumulation of microplastics in marine ecosystems, coupled with the presence of emerging contaminants such as pharmaceuticals, represents an environmental problem that has received little attention to date. The present study evaluates the potential of microplastics to act as transport vectors for pharmaceuticals through their adsorption onto two plastic polymers widely used today: polyethylene terephthalate (PET) and medium-density polyethylene (MDPE) in seawater. As a control, the same experiments were conducted in ultrapure water (Milli-Q). Both plastics were exposed to a mixture of 29 pharmaceuticals belonging to different therapeutic classes over a 28-day period, with sampling conducted at various time intervals. The identification, quantification, and characterization of the compounds were performed using ultra-high-performance liquid chromatography coupled with mass spectrometry detection. Statistical analysis was performed using R-Studio software. Outcomes reveal that the type of polymer significantly influences adsorption, with MDPE being more efficient than PET. In contrast, the type of water and the therapeutic class of the drugs were not identified as determining factors. Furthermore, a positive, albeit moderate, correlation was observed between the hydrophobicity of the pharmaceutical and its adsorption efficiency on MDPE. These findings suggest that hydrophobic interactions play a key role in the adsorption of drugs onto microplastics, providing a solid foundation for future research, such as predictive models or mitigation strategies in aquatic ecosystems.