Concentration, characterization, and risk assessment of microplastics in two main rivers in Birnin Kebbi, Nigeria

Background: Dukku and Kalgo rivers in Kebbi, Nigeria, provide essential ecosystem services such as drinking and domestic water, fishing, and farming. However, the safety of these rivers in terms of microplastic pollution has not been investigated. This study aimed to characterize and determine the concentration and associated risks of microplastics in both rivers. Methods: Microplastics were extracted from water samples through filtration and analyzed using spectroscopy and microscopy. Results: Significant concentrations of microplastics were detected in both rivers. Dukku River samples showed concentrations ranging from 125.00 to 160.30 particles/liter, while Kalgo River ranged from 119.30 to 134.70 particles/liter. Both rivers predominantly contained microplastic fibers and fragments, with fibers comprising the highest percentages (61% in the Dukku River and 56% in the Kalgo River). Microplastics in Kalgo River were predominantly sized between 0 and 100 µm, whereas in Dukku River, sizes ranged from 500 to 1000 µm. Polyamide was the dominant polymer, constituting 50% in the Dukku River and 42.50% in the Kalgo River, followed by polyethylene (34% in the Kalgo River and 25.60% in Dukku River), and polyvinyl alcohol (24.40% in Dukku River and 23.50% in Kalgo River). The predominant risk level posed by these polymers was level III (moderate risk), although polyamide posed a level IV risk (high risk). The pollution load index (PLI) for both rivers exceeded one, indicating a high risk. Conclusion: Microplastic pollution in these rivers poses ecological and health risks. Identifying and mitigating sources of microplastic entry into the rivers is crucial to reducing exposure levels.