Micro- and nanoplastic pollution in urban influenced aquatic environments: Sources, pathways, and remediation strategies

Plastic pollution, particularly microplastics (MPs) and nanoplastics (NPs), is increasingly threatening urban aquatic environments. These particles (25-1000 μm) originate from diverse sources and exhibit complex environmental behavior depending on their physicochemical characteristics and interactions with organic matter. Wastewater treatment plants (WWTPs), though designed to mitigate various contaminants, have demonstrated limited efficiency in removing micro and nanoplastics (MNPs), with effluent concentrations ranging from 0.2 to 180 × 10^6 MPs L and removal rates 40-95 % for MPs, and lower for NPs depending on the treatment process and particle properties. This inefficiency contributes to the persistent dissemination of MNPs into rivers, lakes, and coastal areas. Moreover, ecotoxicological evidence, although limited, indicates oxidative stress and physiological impairments in fish, highlighting substantial knowledge gaps. To address these knowledge gaps, recent scientific efforts have focused on understanding the occurrence, sources, and behavior of MNPs across urban water systems, along with assessing the effectiveness of physical separation and chemical/biological degradation technologies. While methods such as coagulation, filtration, adsorption, and advanced oxidation processes show promise, each presents limitations in terms of operational cost, energy demand, and the potential generation of toxic by-products. Emerging strategies such as upcycling plastic waste and employing nature-based solutions (e.g., riparian vegetation restoration, constructed wetlands) offer complementary benefits but require further investigation and investment. This review critically summarizes current knowledge on the sources, fate, ecological impacts, and management strategies of MNPs in urban waters, identifies region-specific challenges and research gaps, and provides guidance for future monitoring, technological innovation, and policy interventions.