Determination of levels of some metal contaminants in the freshwater environments of Osun State, Southwest Nigeria: A risk assessment approach to predict health threat.

This study evaluated levels of heavy metals and macro-elements in ten major rivers in Osun State, Southwest Nigeria. Triplicate water samples collected from selected rivers were analyzed for metal pollutants by atomic absorption spectrophotometry. Concentrations were obtained as follows: iron: 60-960 μg L-1; manganese: ND - 3 μg L-1; chromium 0-2100 μg L-1; aluminium: 0-800 μg L-1; copper: 0-1350 μg L-1; zinc: 10-650 μg L-1; calcium: 6400-232000 μg L-1 and magnesium: 2000-71000 μg L-1 but lead was not detected. While most of the parameters fell within the threshold values for drinking water, iron, chromium, aluminium and calcium exceeded at some locations. The pollution order of the rivers, especially with heavy metals had the order: R8 > R3 > R2 > R5 > R10 > R6 > R4 > R1 > R7 > R9; which implies that R8 and R3 are the most polluted. The health risk assessment results revealed that hazard quotient and hazard index were below the acceptable limit of 1.0, suggesting no substantial non-carcinogenic effect would arise from individual exposure to the elements. However, the carcinogenic risks were 3.18 × 10-6 and 4.43 × 10-6 for adults and children, respectively at R8, implying that 1 person in 314,206 adults and 225,836 children drinking from the water may be at risk of having cancer correspondingly. Hence, there is need to moderate the levels of these pollutants in these waterbodies to safeguard public health.