Meso- and microplastics accumulate and transfer hazardous contaminants from wastewater treatment plants to the environment

The ubiquitous presence of meso- and microplastics (M-MPs) in aquatic systems, together with their capacity to act as vectors for contaminants, poses growing concerns for ecosystem and human health. Municipal wastewater treatment plants (WWTPs) play a dual role, partially mitigating but also redistributing M-MPs through effluent discharge and sludge management. This study investigated the association of M-MPs with organic and inorganic micropollutants, including metal(loid)s, synthetic musk fragrances (SMFs), UV filters, pharmaceuticals, organophosphate flame retardants, and pesticides, across WWTP streams. Contaminant partitioning between suspended particulate matter (SPM) and the dissolved phase was evaluated in influent and effluent, and dewatered sludge was also assessed. Results indicated relevant emissions of metal(loid)s, SMFs, and UV filters via treated wastewater. In the effluent, hydrophobic compounds were mostly associated with SPM, while hydrophilic compounds remained predominantly dissolved. M-MPs carried measurable pollutant loads per unit mass, with polystyrene microspheres (500-1000 μm) exhibiting the highest concentrations among the polymers analyzed, reaching 5.2 mg/kg for pharmaceuticals, 283.7 mg/kg for SMFs, and 991.5 mg/kg for UV filters-values comparable to those found on bulk SPM in this study. However, because of their lower abundance, polystyrene particles contributed less to the overall micropollutant flux than polyethylene and polypropylene, which dominated the discharged plastic mass. These results show that M-MPs, as a component of the suspended particulate fraction, constitute a relevant pathway for micropollutant transport in WWTP effluents and underline the need for size-inclusive monitoring and advanced treatment technologies to limit environmental releases.