Distribution and Health Risk Assessment of Microplastics in Fishes, Water and Sediment from Nigerian Inland Rivers during the Rainy Season

This study investigates the distribution, characteristics, and potential human health risks of microplastics (MPs) in water, sediments, and fish from seven Nigerian inland rivers during the rainy season of 2023. MP abundance was significantly influenced by seasonal hydrology, with higher concentrations observed in fish, reaching 58 ± 0.58 particles/g in River Benue, and water, reaching 48 ± 8.12 particles/50 mL in River Argungu, compared with dry-season levels. These increases were attributed to enhanced runoff and mobilization of land-based plastics. Sediments showed reduced MP levels during the rainy season because of resuspension and downstream transport. Fibres dominated in fish (48.5%) and sediments (49.3%), whereas fragments prevailed in water (60.3%). Fifteen polymer types were identified by Fourier transform infrared spectroscopy. Polystyrene showed apparent bioaccumulation in fish, increasing from 27.8% in gills to 52.4% in guts; polypropylene was prevalent across compartments; and ethylene vinyl acetate dominated water samples at 68%. Principal component analysis revealed distinct compartmental associations, with fish and sediment samples clustering together and indicating transfer pathways. Estimated daily intake through fish and water consumption was low, with fish constituting the primary exposure route and River Benue posing the highest potential risk. Although estimated daily intake values were substantially below global estimates, the capacity of MPs to act as vectors for chemical contaminants raises potential long-term health concerns. The findings demonstrate that the rainy season exacerbates MP pollution in Nigerian freshwater systems and support the need for targeted mitigation strategies.