A Critical Review of the Occurrence, Characteristics and Consequences of Micro-and Nano-plastics in Environmental Waters

Abstract Plastic pollution poses a significant and pervasive threat to aquatic and terrestrial ecosystems globally. This review provides an integrated assessment of Micro- and nano-plastics (MNPs) by linking their sources, pathways, occurrence, and environmental impacts across interconnected aquatic systems. The synthesis reveals that MNPs distribution is driven by multiple pathways, including wastewater discharges, surface runoff, and atmospheric deposition, with sediments and wetlands acting as both sinks and secondary sources. A key finding of this review is that methodological differences in sampling, digestion, density separation, and analytical techniques significantly influence reported concentrations and size distributions, often leading to the underrepresentation of smaller particles, particularly nano-plastics. While advanced analytical tools such as FTIR, Raman spectroscopy, and Py-GC/MS have improved detection and characterization, challenges remain in achieving standardized and comparable measurements across studies. Wastewater treatment plants play a dual role as both partial barriers and pathways for MNPs. Although advanced treatment processes can achieve high removal efficiencies, smaller particles often escape into receiving waters, highlighting limitations in current treatment systems. Beyond occurrence, this review emphasizes the broader ecological implications of MNPs, including their toxicological effects on aquatic organisms, disruption of ecosystem processes, and role as vectors other contaminants. Finally, this review highlights the need for standardized methodologies, improved detection of smaller particles, and integrated, system-level management strategies to better understand and mitigate the environmental risks associated with MNPs pollution.