Heavy Metal Concentrations in Water, Sediment, and Three Commercially Important Fish Species of the Lower River Niger at Geregu, Ajaokuta, Kogi State - Nigeria

Heavy metal pollution of freshwater ecosystems remains a pressing global environmental and public health concern, particularly in rivers subject to intensifying agricultural, industrial, and domestic pressures. This study evaluated the concentrations of six heavy metals iron (Fe), lead (Pb), nickel (Ni), chromium (Cr), cadmium (Cd), and zinc (Zn) in water, sediment, and three commercially important fish species (Oreochromis niloticus, Citharinus citharus, and Clarias gariepinus) sampled from three stations along the lower River Niger at Geregu, Ajaokuta, Kogi State, Nigeria, between July and December 2025. Samples were analysed in triplicate using an Atomic Absorption Spectrophotometer, and data were subjected to one-way analysis of variance (ANOVA) with means separated by Duncan's Multiple Range Test (p ≤ 0.05). Heavy metal concentrations followed the general order Fe > Zn > Ni/Cr > Pb > Cd across water, sediment, and fish tissue, with pronounced temporal variation and comparatively minor spatial variation among the three stations. Several water-column metals (Pb, Ni, Cr, Cd, Zn) exceeded FAO/WHO maximum permissible limits during the later months of the study (October to December), whereas sediment- and fish-tissue metal concentrations remained largely within FAO/WHO/WHO safety thresholds. Species-specific differences in fish tissue accumulation were also evident, with Oreochromis niloticus accumulating the highest Fe burden and Clarias gariepinus recording the highest Zn burden. The findings indicate moderate but escalating heavy metal contamination driven primarily by seasonal hydrological dynamics and anthropogenic inputs, underscoring the need for sustained environmental monitoring of this ecologically and economically important river system.