Analytical Investigation of Microplastic Contamination in Freshwater Fish Species from the Niger River, Kogi State: Abundance, Typology, and Trophic Transfer Implications

Microplastic pollution in freshwater ecosystems has emerged as a critical environmental chemistry research priority globally, yet data from Nigerian river systems remain limited and methodologically inconsistent. This study analytically investigates the abundance, morphological typology, polymer composition, and trophic transfer potential of microplastics in three commercially important fish species, specifically Synodontis schall, Auchenoglanis occidentalis, and Lates niloticus, collected from six stations along a 120-kilometre stretch of the Niger River in Kogi State, North Central Nigeria. Gastrointestinal tracts, gill tissues, and muscle were dissected, digested with potassium hydroxide, and filtered for microplastic isolation. Particles were identified by stereomicroscopy and characterised by micro-Fourier-transform infrared spectroscopy. Polymer types, colour distribution, particle size distribution, and shape categories were statistically analysed. Concentration-dependent co-occurrence of microplastics with polycyclic aromatic hydrocarbon sorbed contaminants was assessed by gas chromatography-mass spectrometry. Results indicate that fibres and fragments predominate, with polyethylene, polypropylene, and polystyrene being the most frequently identified polymers. Microplastic abundance in gastrointestinal content was positively correlated with feeding guild, with omnivorous species showing the highest ingestion. Detection in gill and muscle tissue was confirmed in 22 percent of dissected individuals, indicating trophic transfer potential. The study fills a critical data gap for West African inland fisheries and informs risk assessment frameworks for human dietary exposure via fish consumption. Keywords: microplastics, freshwater fish, Niger River, Kogi State, trophic transfer