Heavy metal contamination and ecological risk assessment of soils around the pegmatite mining sites at Olode area, Ibadan southwestern Nigeria

Abstract

Twenty four soil samples were collected from the pegmatite mining sites at Olode and it’s environs within Ibadan, Southwestern Nigeria in order to determine concentrations and contamination assessment of heavy metals such as Pb, Zn, Cu, Ni, Co, Fe, Mn and Cr. The average values are: 17.92 (Pb), 81.67 (Zn), 76.33 (Cu), 22.33 (Ni), 19.21 (Co), 3.77 (Fe), 924.21 (Mn) and 77.92 (Cr) mg/kg, respectively. The order of abundance followed this pattern Mn > Zn > Ba > Cu > Cr > Ni > Co > Fe > Pb > Sr > V>Th. The analysed value of the heavy metals exceeded the background values revealing that mining activities have an adverse impact on the study area, evidenced from the high correlation values (0.6) between Nickel-Vanadium, Nickel-Chromium, Cobalt-Manganese and Vanadium-Chromium. On accessing the soil quality in the study area, based on enrichment factor (EF), the Olode soils have very high enrichment for Mn, Ni and Cr. According to contamination factor (CF) values, Ni and Cr are probably responsible for the high contamination. The degree of contamination (CD) and the pollution load index (PLI), revealed high degree of contamination for all the soil samples while according to Igeo, the Olode soils are moderately to strongly polluted by Zn, Ni, Cr and Co. Nickel may probably be the key controlling factor causing the potential Eri. These findings have provided valuable information for making suitable ecological management approach to alleviate the influence of heavy metal pollution generated from an active and abandoned mining site in Nigeria and other similar areas.