Heavy Metals Speciation and Human Health Risk Assessment of Soil around Prism Steel Mill, Ikirun, Osun State, Nigeria

Abstract

This study determined the trace metal concentrations of soil around the study area and it also estimated the contamination indices of the soil around the factory and assessed the health risk and hazard index of the human population around the factory. Five perimeters at 100, 200, 300, 400 and 500m radii were mapped out around the factory. Within each perimeter, eight soil samples each were collected at random at 0 – 15 cm depth. The samples were added together to form a composite sample for each perimeter radius which gave a total of five composite samples. Similarly, one control sample, about 10 km away from the factory was collected from an undisturbed area. All samples were separately air-dried, sieved and pulverized to ensure homogeneity using standard methods before being kept in the polythene bags for speciation analysis. The worked up samples from above were taken to a standard laboratory for Atomic Absorption Spectroscopy (AAS) analysis of Fe, As, Cd, Cu, Co, Pb and Ni in the samples. From the result of the analysis, the Geo-accumulation (I-geo), the Mobility Factor, the Enrichment Factor and the Health Risk Index were estimated using standard formulae. The data obtained were subjected to appropriate descriptive and inferential statistical analyses. The results showed that the total heavy metal concentration in the soil decreased with distance from the factory. The concentration of the metals for all the distances were also significantly higher (at p ≤ 0.5) than that of the control. The mean levels of metal concentration followed the order (in μgg-1); Pb (395.05 - 500.52) > Co (318.32 - 447.45) > Cu (335.57 - 385.57) > Fe (253.75 - 443.25) > Ni (156.40 - 211.45) > As (147.85 - 170.85) > Cd (95.80 - 101.55). The study concluded that the concentrations of Fe and Pb at 100 m away from the factory were about four times and that of Cd Cu, As, Ni and Co were three times higher than the control. This calls for putting in place remediation steps that could prevent heavy metal-associated health effects to humans and the biota.