Characterisation of Microplastic Contamination in River Niger Sediments Across North Central Nigeria

Microplastic pollution in freshwater environments has emerged as a significant and largely uncharacterised environmental threat in sub-Saharan Africa, and the River Niger, which passes through multiple states in North Central Nigeria, is particularly vulnerable to microplastic inputs from urban centres, agricultural activities, and inadequate solid waste management. This study characterised microplastic contamination in surface sediments of the River Niger at seven sampling stations across Niger and Kogi States, spanning urban, peri-urban, and rural settings. Sediment samples were collected by grab sampler, processed by density separation using zinc chloride solution, filtered onto stainless steel sieves, and examined under stereomicroscopy. Microplastic particles were characterised by morphology, colour, size, and polymer identity by Fourier-transform infrared spectroscopy with attenuated total reflectance accessory. Microplastic abundance ranged from 48 to 1,240 particles per kilogram dry sediment, with the highest concentrations at the Lokoja urban station. Fibres were the most abundant morphotype at 56 percent of all particles, followed by fragments at 32 percent and films at 12 percent. Polyethylene, polypropylene, polyethylene terephthalate, and nylon were the dominant polymer types identified by infrared spectroscopy. Urban stations showed significantly higher particle abundance and a greater proportion of smaller particles, consistent with secondary fragmentation of plastic waste. This study fills a critical gap in microplastic baseline data for the River Niger and provides the first systematic characterisation of freshwater sediment microplastic contamination in North Central Nigeria, which is essential for risk assessment and policy development.

Keywords: microplastics, River Niger, freshwater sediments, polymer characterisation, North Central Nigeria