Assessment of Micro-Plastic Contamination in Urban River Systems: A Case Study Using UK Catchment Data

Microplastic contamination in urban river systems represents a growing environmental concern with implications for freshwater quality, ecosystem health, and downstream marine pollution. This study presents a systematic review of microplastic occurrence, distribution, and transport mechanisms in urban river catchments in the United Kingdom. Following PRISMA 2020 guidelines, 97 peer-reviewed studies published between 2012 and 2024 were systematically conducted, incorporating inter-reviewer validation, quality assessment criteria, and bias control measures to ensure methodological robustness. The results reveal pronounced spatial and temporal heterogeneity in microplastic contamination driven by urban land use, wastewater infrastructure, hydrological variability, and methodological inconsistency. Elevated concentrations were consistently associated with wastewater discharge points, combined sewer overflows, and high-flow events, while riverbed sediments act as long-term sinks and secondary sources. Polymer composition was dominated by polyethylene, polypropylene, and polyethylene terephthalate, with microfibres particularly prevalent in urbanised catchments. Analytical synthesis demonstrates that variation in sampling design, particle size thresholds, and polymer identification techniques significantly influences reported abundances and limits cross-study comparability. Interpreting the findings through a source–pathway–receptor and catchment systems framework highlights the need for integrated monitoring strategies and infrastructure-focused mitigation. The review emphasises the prioritisation of wastewater and stormwater controls within catchment management frameworks to reduce microplastic inputs to freshwater systems.