Assessment of Microplastic Pollution: Morphological and Polymer Characterisation of Microplastics in the Lubigi Wetland Ecosystem, Uganda

Abstract

Urban wetlands are increasingly exposed to microplastic contamination driven by rapid urbanisation, inadequate waste management and expanding wastewater discharges. This study presents a comprehensive assessment of microplastics in the Lubigi Wetland (Kampala, Uganda). Water and sediment samples were collected from nine sites spanning upstream, midstream and downstream zones and from four vertical strata (surface, middle, bottom water and 0–10 cm sediment). Samples were processed by density separation (saturated NaCl), peroxide digestion and vacuum filtration; particles were morphologically classified by stereomicroscopy and polymer types confirmed by Fourier Transform Infrared Spectroscopy (FTIR). A total of 1,118 microplastic particles were recorded: microbeads dominated (58.7%), followed by pellets (15.9%) and fragments (11.4%). Transparent particles comprised 42.8% of the assemblage and 61% of particles were < 0.001), with midstream sediment layers (notably Namungona and Nabweru) identified as depositional hotspots. FTIR confirmed polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC) and Nylon6, with PET and PP more frequent in water and PE, PS and PVC more common in sediments. The dominance of microbeads and the polymer signature implicate urban and domestic sources (personal care products, packaging, wastewater and textile effluents) and reflect transport and depositional processes governed by hydrodynamics and wetland geomorphology. These findings align with regional and global observations that freshwater and wetland systems are important sinks and conduits for microplastics and underscore the need for targeted waste management, wastewater controls and routine monitoring to protect wetland ecosystem services and public health.