Distribution and Abundance of Microplastics in Surface Water of Lake Geriyo, Adamawa State, Nigeria

Abstract

 Microplastic (MP) pollution is an emerging threat to freshwater ecosystems, yet data remain scarce across African inland waters. This study provides the first systematic assessment of microplastic distribution and abundance in the surface water of Lake Geriyo, a shallow tropical lake in the Upper Benue River Basin, Nigeria. Surface water samples were collected in triplicate from three stations over 18 months (September 2024-February 2026). Microplastics were isolated by wet sieving, wet peroxide oxidation, and density separation, and polymers were identified using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). Spatial and temporal differences were tested with one-way ANOVA and Duncan’s multiple range test. A total of 623 microplastic particles were recovered, with mean concentrations of 6 to 19 particles/L. Stations 1 (fishing landing; 12.67 ± 3.48 particles/L) and 2 (settlement runoff; 12.89 ± 2.35 particles/L) recorded significantly higher concentrations than Station 3 (depositional zone; 9.06 ± 1.66 particles/L) (ANOVA: F(2,51) = 11.88, p < 0.001). Concentrations peaked during the late wet season (September-October 2024) and the warm dry season (May-July 2025), with minima in the cool dry season (December-February). Fibres (26.30 %) and fragments (21.10 %) were the dominant morphotypes, and transparent/clear particles constituted 46.20 %. ATR-FTIR confirmed polyethylene, polystyrene, polyamide (nylon), polyethylene terephthalate, and silicone-based polymers. Fishing operations and settlement runoff are the primary drivers of contamination, with seasonal hydrology modulating distribution. These findings establish a critical baseline for microplastic pollution in a tropical African lake and underscore the need for integrated watershed management strategies.