HEALTH RISK ASSESSMENT OF HEAVY METAL CONTAMINATION IN EKULU AND NYABA RIVERS, SOUTHEAST NIGERIA

Heavy metal contamination of surface waters poses serious ecological and human health concerns, particularly in mining-impacted environments. This study evaluated the concentrations, seasonal variations, sources, and health risks of heavy metals in Ekulu and Nyaba rivers, Southeast Nigeria. Both rivers drain the abandoned Onyeama and Okpara coal mines, which continue to discharge Acid Mine Drainage (AMD) into downstream communities. A total of 34 water samples were collected during wet and dry seasons from upstream, midstream, downstream, mine discharge, and control sites. Samples were analyzed for As, Cd, Co, Fe, Hg, Mn, Ni, Pb, and Se using Atomic Absorption Spectrophotometry (AAS), following APHA protocols. The results revealed that Fe, Pb, Cd, and As concentrations consistently exceeded permissible limits set by WHO, USEPA, and FEPA/NESREA standards. Seasonal variations showed higher concentrations in Ekulu River during the dry season due to reduced dilution, while Nyaba River recorded elevated levels in the wet season as rainfall enhanced leaching from abandoned mine tunnels. Correlation analysis confirmed AMD as the dominant contamination source, with additional contributions from irrigation, laundry, effluent disposal, and sand dredging. Human health risk assessment indicated Hazard Quotient (HQ) and Hazard Index (HI) values above 1 for several metals, signifying non-carcinogenic risks, while Incremental Lifetime Cancer Risk (ILCR) values for As, Cd, Ni, and Pb exceeded the acceptable threshold of 1 × 10⁻⁴. Children were found to be more vulnerable than adults across all exposure pathways. The study concludes that Ekulu and Nyaba rivers are unsafe for direct domestic and agricultural use without treatment. It recommends urgent remediation of abandoned mines, continuous water quality monitoring, provision of alternative safe water supplies, stricter regulation of anthropogenic activities, and targeted public health interventions to safeguard local communities