Assessment of Microplastic Contamination in Surface Water and Sediments of Lake Chad Basin Tributaries in Borno State, North East Nigeria

Microplastic contamination in freshwater systems is a rapidly emerging environmental concern in sub-Saharan Africa, yet quantitative baseline studies for the Lake Chad basin, one of Africa's most ecologically and socioeconomically significant inland water systems, are virtually absent from the published literature. This study assesses microplastic distribution, morphotype composition, and polymer identity in surface water and sediment samples from five Lake Chad basin tributary rivers in Borno State, North East Nigeria. Water samples are collected using 330-micrometre neuston trawls and sediment samples by stainless steel corers at three depths per station. Samples are processed using hydrogen peroxide digestion to remove organic matter and density separation with saturated sodium chloride solution for polymer isolation. Microplastics are counted and classified by size (100-300, 300-1000, and greater than 1000 micrometres), shape (fragment, fibre, film, pellet, foam), and colour under a stereomicroscope. Polymer identification is performed by micro-Fourier transform infrared spectroscopy on randomly selected particles. Spatial distribution patterns are mapped and related to land use, population density, and seasonal flow regime. Statistical analysis applies the Kruskal-Wallis test for inter-station comparisons. Ecological risk assessment follows the pollution load index and risk quotient approach. Findings establish the first spatially resolved microplastic contamination baseline for the Nigerian portion of the Lake Chad basin, providing data urgently needed for transboundary pollution monitoring and conservation planning. Keywords: microplastics, Lake Chad basin, freshwater contamination, polymer identification, Borno State