Characterization and Ecological Risk Assessment of Microplastics in Sediments of a Tropical West African Lagoon Ecosystem

The accumulation of mismanaged plastics has continued as a significant threat to the health and ecological functions of coastal ecosystems globally. This study examined microplastic (MP) contamination and ecological risks of twenty-four sediment samples from four locations characterized by significant anthropogenic activities along the Lagos Lagoon. Physicochemical properties of sediment were analyzed using standard methods, while morphological classification of microplastics and polymer identification was carried out using a stereomicroscope and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) following pretreatment with 30% H₂O₂ and density flotation with ZnCl2. Microplastic abundance ranged from 9.17 ± 6.05 to 12.17 ± 7.55 microplastics/kilogram (MPs/kg), while morphological analysis revealed predominance of fibers (41.4%) and black microplastics (49%). Polyethylene terephthalate (PET) was the most abundant polymer in sediments, suggesting indiscriminate disposal of single-use plastic bottles. One-way ANOVA showed no significant differences among sampling locations for pH (F3, 16 = 1.29, p = 0.31), electrical conductivity (F3, 16 = 1.10, p = 0.37), total organic carbon (F3, 16 = 1.10, p = 0.37), or microplastic abundance (F3, 16 = 0.31, p = 0.82), suggesting relatively uniform sediment conditions. The detection of potentially toxic polymers raises concern over long-term ecological risks. The Polymer Risk Index (PRI) indicates varying ecological risk, with level IV (high) and V (very high) as the predominant categories. This suggests the potential for significant adverse effects to aquatic organisms and ecosystem health. The result emphasizes the urgent need for improved waste management practices, stricter regulation of single-use plastics, sustained monitoring and effective mitigation strategies around the Lagoon’s catchments.