Assesment of Heavy Metals in Water, Sediment and Aquatic Organisms and Associated Health Risk to Human in Selected Rivers in Osun State, South-Western Nigeria

ABSTRACT Heavy metals are toxic at low concentrations and have relatively high densities. They are naturally present in the Earth's crust and can enter the human body through air, water, and food. Lead, cadmium, and mercury are the most common environmental pollutants that have significant adverse health impacts. Heavy metal contamination in aquatic environments poses significant environmental and health risks. This study assesses the concentration of heavy metals in water, sediment, and selected aquatic organisms from rivers in Osun State, Nigeria, and evaluates the potential human health risks associated with their consumption. Samples were collected from Eko-nde, Kajola, Asejire, and Ofatedo rivers and analyzed using Atomic Absorption Spectroscopy (AAS). The study measured the levels of lead (Pb), cadmium (Cd), chromium (Cr), and arsenic (As) to determine their contamination levels and ecological risks. Statistical analysis revealed mean heavy metal concentrations in water as Pb (0.04 mg/L), Cd (0.04 mg/L), Cr (0.04 mg/L), and As (0.00 mg/L). In sediment, mean values were Pb (0.02 mg/kg), Cd (0.04 mg/kg), Cr (0.03 mg/kg), and As (0.00 mg/kg). For aquatic organisms, mean concentrations were Pb (1.225 mg/kg), Cd (1.011 mg/kg), Cr (0.000 mg/kg), and As (0.894 mg/kg). Some of these levels exceeded WHO and EPA safety limits, particularly for Pb and Cd in fish. The multivariate statistical analysis explained a high percentage of total variance, indicating that both anthropogenic activities (industrial discharge, agricultural runoff, and domestic waste) and natural geological sources contributed significantly to heavy metal contamination. The health risk assessment examined Chronic Daily Intake (CDI) and Hazard Quotient (HQ), highlighting the potential health risks of consuming contaminated fish. The Potential Ecological Risk Index (PERI) classified contamination levels from low to considerable. Given the risks of bioaccumulation, long-term exposure could lead to kidney damage, neurological disorders, and cancer. The study underscores the urgent need for pollution control, strict environmental regulations, and continuous monitoring. Recommendations include improved waste management, policy enforcement, and public awareness initiatives to ensure the sustainability of Osun State’s water bodies and safeguard public health.