Preliminary investigation of the spatio-seasonal distribution of microplastics in the surface water of River Benue, North Central Nigeria

Abstract

Rivers are critical pathways for microplastic (MP) pollution, yet data remain limited on MP presence in Nigeria’s freshwater systems. This study presents the first comprehensive assessment of MP occurrence and associated risks in the River Benue, one of Nigeria’s most important rivers. Surface water samples were collected in September 2023 (rainy season) and January 2024 (dry season), pre-treated with NaCl and H₂O₂ for density separation and wet peroxide oxidation, and analysed using FTIR spectroscopy and SEM–EDS. MP abundance was higher along the southern bank, ranging from 0 to 11 items L⁻¹ in the dry season and 0 to 9 items L⁻¹ in the rainy season. The lower rainy-season concentrations were attributed to improved hydraulic conditions, which enhanced dilution and downstream transport. Particle sizes ranged from 0.5 to 5 mm, with the 1.5–3 mm fraction being most abundant, raising concerns due to their bioavailability. Risk assessment revealed contamination factors of 2–22 and pollution load indices of 2–4.69, indicating sites with moderate to elevated risks. The PLI_zone (3.23) confirmed severe pollution across the river, potentially warranting remediation. MP distribution patterns are strongly associated with anthropogenic activities, including commerce, transportation, and waste disposal. This study provides crucial baseline data on MP pollution in River Benue and supports the development of targeted management strategies. For a more comprehensive understanding, future investigations should explore the collection of larger sample volumes and asses contamination in the sediments and biota. These findings contribute to global efforts in understanding freshwater MP pollution, particularly in understudied tropical river systems.