Comparative Study of Heavy Metal Levels in Fish Species from Two Rivers in Kogi State

Heavy metal bioaccumulation in freshwater fish poses direct risks to human consumers who depend on inland fisheries for protein nutrition, particularly in regions where industrial and artisanal mining activities introduce metals into river systems. This comparative study analyses heavy metal (cadmium, lead, zinc, copper, chromium, and iron) concentrations in muscle and gill tissues of three fish species landed from the Niger River (Lokoja section) and the Benue-Niger confluence, Kogi State, North Central Nigeria. A total of 90 fish specimens of Clarias gariepinus, Oreochromis niloticus, and Synodontis schall are collected from local fish markets representing each river system. Tissues are digested using a microwave-assisted acid digestion procedure and analysed by atomic absorption spectrophotometry. Metal concentrations are compared between species, tissues, and river systems using analysis of variance and post-hoc tests. Bioaccumulation factors and hazard quotients for human health risk are calculated according to Food and Agriculture Organization guidelines. Concurrent sediment and water samples characterise environmental metal exposure levels for correlation with fish tissue concentrations. Results are expected to show significantly higher cadmium and lead in gill tissues of Clarias gariepinus from the more industrially exposed Niger River section near Ajaokuta Steel Complex. Recommendations address fish consumption advisories for high-risk communities and regulatory improvements for the mining sector. Keywords: heavy metals, bioaccumulation, freshwater fish, Kogi State, river pollution