Size- and Polymer-Specific Assessment of Micro- and Nanoplastics in a European Wastewater Treatment System

The unchecked littering and mismanagement of plastics, coupled with their rising production and usage, have escalated them into one of the most pressing environmental pollutants. Among them, microplastics (<5 mm) and nanoplastics (<1 µm) have emerged as critical contaminants, with micro-and nanoplastics (MNPs) posing the greatest risks due to their ability to penetrate and contaminate water sources. While MPs are globally found to contaminate every freshwater ecosystem, it is reasonable to expect NPs to be similarly widespread as a result of MPs degradation with impacts still unknown. Importantly, land-based sources (wastewater systems) release MNPs into rivers ultimately contribute to the growing plastic pollution load in oceans, linking inland sources directly to marine contamination. Globally, numerous studies have examined the abundance, pathways, and removal efficiencies of MPs in wastewater treatment plants (WWTPs); however, systematic assessments of NPs remain scarce. Despite growing awareness of plastic pollution in European aquatic environments, size- and polymer-resolved data on MNPs in wastewater treatment systems and their subsequent release into receiving rivers remain scarce. To address this knowledge gap, the present study investigated the occurrence, size distribution, and polymer composition of MNPs across different treatment stages of a WWTP. Raw influent and treated effluent samples were collected from multiple treatment units and analysed using thermal desorption–proton transfer reaction–mass spectrometry (TD-PTR-MS). MNPs digestion and extraction followed a validated cascade filtration protocol employing membranes with pore sizes of 2700 nm (glass fibre), 1200 nm (silver), 200 nm (Anodisc), and 20 nm (Anodisc), enabling size-resolved characterization from the micro- to nanoscale. A diverse range of polymer types was detected, including polystyrene (PS), polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), with tyre wear particles representing a notable non-conventional plastic fraction. To minimize potential contamination during field sampling and laboratory analyses, appropriate field, procedural, and system blanks were included. Significant variations in polymer composition and size classes were observed across treatment stages, allowing quantification of treatment-specific, size fraction, and polymer-specific MNPs removal efficiencies of the studied WWTP. This study provides a comprehensive dataset of MNPs accumulation within a European wastewater treatment system and their subsequent discharge into receiving aquatic environments.