Caffeine has low affinity for polystyrene micro- and nanoplastics in aquatic environments (and vice versa)

Despite the increasing occurrence of microplastics (MPs), nanoplastics (NPs), and pharmaceutically active compounds (PhAC) in the environment, the understanding of their physicochemical interactions in aquatic systems remains limited. We studied the interactions of polystyrene MPs and NPs (PSMP/NPs) with caffeine (CAF) in neutral pH conditions. Namely, the sorption of CAF onto PSMP/NPs was quantified for solutions at low (10 μg/L) and high (100 μg/L) environmentally relevant CAF concentrations. Additionally, we conducted physicochemical characterization of the PSMP/NPs, examining size, charge, and functional groups to evaluate changes occurring before and after interaction with CAF. We determined minimal sorption of CAF and negligible changes to the surface properties of PSMP/NPs under neutral conditions. This study contributes to the understanding of how mixtures of major emergent pollutants (microplastics, nanoplastics, and caffeine) may interact in aquatic ecosystems.