Assessment of microplastic pollution sources and seasonal distribution in urban river systems using citizen-science sampling and GIS analysis

Project Abstract

This study investigates microplastic pollution sources and seasonal distribution in urban river systems through a citizen-science sampling framework integrated with geographic information system (GIS) analysis to quantify spatial-temporal patterns and identify key contributors. A multi-stage methodology was employed, beginning with the recruitment and training of community volunteers to collect surface and near-sediment microplastics across multiple urban river sites representing varying land-use types (residential, industrial, commercial, and green infrastructure). Standardized sampling protocols were designed to minimize cross-contamination, with parallel expert-led transects conducted to validate citizen-collected data. Samples were analyzed for particle size distribution, polymer type (via FTIR spectroscopy), color, and morphology to differentiate microplastics from natural particulates. Temporal sampling occurred across four seasons to capture fluctuations linked to precipitation, urban runoff, tourism cycles, and waste management practices. GIS-based spatial analyses integrated microplastic concentration data with high-resolution land-use maps, hydrological flow paths, sewer network locations, traffic density, and proximity to known pollution sources. Hotspot analyses identified persistent accumulation zones within river channels, confluences, and downstream Ahmed points where retention and flushing dynamics promote retention of microplastics. Source apportionment combined two-pronged approaches a top-down petrographic and polymer signature analysis to infer likely origins (e.g., packaging debris, synthetic textiles, tire wear particles) and a bottom-up citizen-reported event mapping correlated with storm events, maintenance activities, and anthropogenic activities recorded by volunteers. Statistical models (generalized linear models and mixed-effects models) assessed the influence of land-use category, rainfall intensity, wastewater treatment plant (WWTP) effluent proximity, river width, and urban green space on observed microplastic densities, while controlling for sampling effort and site-specific characteristics. Key findings reveal that urban river systems exhibit pronounced seasonal variability in microplastic abundance, with higher concentrations during and immediately after peak rainfall due to surface runoff and combined sewer overflows in older infrastructure areas. Fibrous elastomeric and polyurethane particles were frequently associated with textile washing emissions and brake/wheel wear, respectively, while fragments and films dominated areas adjacent to commercial corridors and consumer waste disposal hotspots. Chemically, low-density polyethylene and polypropylene were predominant, consistent with consumer packaging proxies. Spatial patterns indicated that downstream segments near WWTP outlets and stormwater outfalls function as convergence zones for microplastics, yet upstream riparian zones with dense traffic and informal dumping exhibited elevated concentrations of microfibers and degraded fragments, suggesting multiple concurrent sources. The study demonstrates the effectiveness of citizen science in expanding sampling coverage and enhancing public awareness, while GIS analysis provides a robust framework for tracing microplastic pathways in complex urban hydrological networks. Implications for policy include recommendations for targeted source reduction (e.g., improved laundry effluent filtration, tire wear particle mitigation, and packaging waste management), infrastructure retrofits to reduce overflows, and strategic placement of green corridors to impede pollutant transport. Limitations identified include potential biases in volunteer sampling, challenges in polymer identification for very small particles, and the need for continuous temporal data to fully characterize episodic pollution events. Future work proposes integrating passive sampling technologies and expanding to freshwater–marine interfaces to scale the assessment.

Project Overview

What This Project Is About

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A simple, clear look at how microplastics enter urban rivers, when they are most abundant, and where they come from. The project uses everyday citizen helpers to collect samples and maps to show patterns over seasons.

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The Problem It Addresses

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Urban rivers carry microplastic waste from everyday products and street litter into the water. There is limited, easy-to-access data on where plastics originate and how their presence changes with seasons. Understanding this helps reduce pollution and protect water life and human health.

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Objectives of the Project

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1. Identify common microplastics in an urban river area.
2. Show how plastic levels change with different seasons.
3. Map likely sources using simple spatial tools.
4. Engage local volunteers in-data collection and awareness.
5. Provide practical steps to reduce plastic inputs from the community.

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What You Will Do Step by Step

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1) Learn basic sampling methods with clear instructions. 2) Collect river water and surface samples in different seasons with volunteers. 3) Sort and record visible plastics and capture basic photos or notes. 4) Use simple maps to show where plastics are found. 5) Analyze patterns to link pollution to land uses or activities. 6) Present results in an easy-to-understand report for community groups.

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Expected Outcome

Clear findings on when and where microplastics appear in the river, a public-facing map showing hotspots, and practical recommendations for reducing plastic entry that local people and authorities can follow.