Heavy Metal Concentrations and Ecological and Human Health Risks in Soils Around Osubi and Aladja Waste Dumpsites, Delta State, Nigeria

Open dumping of municipal solid waste can introduce potentially toxic metals into surrounding soils and may create long-term environmental and public-health concerns. This study assessed the concentrations, contamination status, ecological risk and potential human health risks of selected heavy metals in soils around active municipal waste dumpsites at Osubi (Okpe LGA) and Aladja DSC (Udu LGA), Delta State, Nigeria. Soil samples were collected using established field procedures, and cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), copper (Cu) and arsenic (As) were determined using Atomic Absorption Spectrophotometry (AAS). Soil contamination and ecological risk were assessed using the geo-accumulation index (Igeo), contamination factor (CF), degree of contamination (Cdeg), modified degree of contamination (mCd), pollution load index (PLI), ecological risk factor (Er) and potential ecological risk index (RI). Pearson correlation analysis was used to examine relationships among the metals, while non-carcinogenic and carcinogenic risks for adults and children were estimated using the hazard quotient (HQ), hazard index (HI) and lifetime cancer risk (LCR). Nickel and arsenic recorded the highest mean concentrations, whereas cadmium had the lowest. Copper and chromium showed a statistically significant positive correlation (r = 0.534, p = 0.049), suggesting a possible common source or similar behaviour in the soil. Although some localized enrichment was observed, particularly for lead and nickel, all Igeo values were negative and classified the soils as practically uncontaminated. The combined contamination and ecological-risk indices also indicated low contamination and low ecological risk. Based on the reported concentrations, HQ and HI values were below 1 for both adults and children, while the estimated cancer risks were below the stated negligible-risk level. Nevertheless, the continued occurrence of arsenic and nickel indicates the need for preventive monitoring and improved waste-management practices. The study recommends routine soil monitoring, improved waste segregation and recycling, engineered landfill development, and stronger enforcement of environmental regulations around the dumpsites.