Assessment of Microplastic Pollution in Lubigi Wetland, Uganda: Spatial Distribution and Source Pathways

Urban wetlands face growing threats from microplastic pollution, yet their function as sinks and conduits for microplastics in sub‑Saharan Africa is poorly characterised. This study examined the spatial and vertical distribution, morphological features, polymer composition, and likely source pathways of microplastics in Lubigi Wetland, Kampala, Uganda. Surface water and sediment samples were taken at nine sites across upstream, midstream and downstream zones, with vertical stratification into surface, middle, bottom and sediment layers. Microplastics were isolated by density separation and oxidative digestion, identified by stereomicroscopy, and chemically characterised by Fourier Transform Infrared Spectroscopy (FTIR). Six morphological categories were recorded: fibres, filaments, films, fragments, microbeads and pellets. Microbeads were dominant (58.7%), especially in sediments and bottom waters, while fibres and fragments were relatively more common in surface layers.

Transparent particles were the most frequent, and particles smaller than 300 μm made up 61% of all counts. Polyethylene terephthalate (PET) and polypropylene (PP) were prevalent in water samples, whereas polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) were more abundant in sediments. Sediments held significantly higher microplastic loads than water (p < 0.001), with midstream sites (Namungona, Nabweru) acting as depositional hotspots. Spatial patterns reflected inputs from urban runoff and wastewater and were shaped by wetland topography. Overall, the wetland shows moderate contamination, with microplastic distribution governed by hydrological and anthropogenic factors. We recommend improved waste management, routine monitoring, and the integration of microplastic control measures into wetland restoration and urban planning.

Microplastic pollution, wetland ecosystems, spatial distribution, sediment and water sampling, environmental risk assessment

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