Ecological Risk Assessment of Selected Heavy Metals in Nwaniba River, Akwa Ibom State

Abstract

This study assessed the ecological risk of heavy metals in sediments and evaluated metal transfer between sediments and water in the Nwaniba River. Water and sediment samples were collected from four sites during the rainy season and analyzed for seven metals (Tl, As, Pb, Cd, Cr, Co, Ni) using the Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) technique. Single-element indices indicated sediment pollution ranging from low to high levels: contamination Factor (ND – 12.71), enrichment Factor (ND – 9.48) and geo-accumulation index (-1.98 – 3.08), while multi-element indices revealed elevated ecological risk, with pollution load index (PLI) values of 1.94, 1.92, 0.82, and 1.94, indicating PLI > 1 for the majority of the study area and potential ecological risk index (PERI) values of 406.60, 388.84, 187.00, and 293.79 across the four sites, respectively, indicating moderate to high ecological risk at most locations. Cadmium (Cd) was identified as the primary contributor to the calculated ecological risks. Transfer factor (TF) values determined for metals with measurable concentrations in both water and sediment exceeded 1, (TF >1) suggesting potential metal accumulation and increased ecological risk due to mobility within the river system. These findings confirm that the sediments are contaminated and pose ecological threats, likely influenced by agricultural runoff and unregulated municipal waste. Regular monitoring and sustainable land-use practices are recommended to mitigate ecological risks and protect the Nwaniba River ecosystem. By informing sediment monitoring and risk mitigation in data-scarce, rapidly urbanizing regions, this study contributes to Sustainable Development Goals six and eleven, emphasizing clean aquatic ecosystems and sustainable urban environments.