EVALUATION OF HEAVY METAL CONTAMINATION OF SOIL AND WATER SAMPLES IN TWO MINING SITES IN IJERO EKITI, NIGERIA.

Abstract

Heavy metal contamination of soils has been a long-standing environmental problem in many parts of the world, and poses enormous threats to ecosystem and human health. Speciation of heavy metals in soils is crucial to assessing environmental risks from contaminated soils. In this study, total concentrations and speciation of Cr, Cu, Zn, Pb and Ni were measured for soil samples on two mining sites in Ijero Ekiti, Nigeria. Soil samples were collected randomly within the mining area at depth of 0 -15cm with a hand auger. Three water samples were collected in clean plastic bottles around the gold mining site. Soil samples were air dried, sieved through a 0.8mm mesh and stored in clean polythene bags. Metal concentrations were determined by atomic absorption spectrophotometer (AAS, Buck Scientific 210 VGP). Metal concentration ranges obtained for Ile efun (feldspar mining area) are as follows: Cr; 10.33 – 51.50 mg/kg, Cu; 13.17 – 36.33 mg/kg, Zn; 56.17 – 74.50 mg/kg, Pb; 23.50 – 43.50 mg/kg and Ni; 10.17 – 22.33 mg/kg while the values obtained for Oke kusa (gold mining area) are as follows: Cr; 8.67 – 16.00 mg/kg, Cu; 6.50 – 10.67 mg/kg, Zn; 52.67 – 67.00 mg/kg, Pb; 23.50 – 40.34 mg/kg and Ni; 12.00 – 22.17 mg/kg. pH range was 5.20 – 6.29 and 4.47 – 5.40 for the two sites respectively. Percentage nitrogen and phosphorus for the two sites are small, percentage organic matter are higher than the control soil but with lower cation exchange capacity. The metals are associated with the residual fraction of sequential extraction; Cr, Zn and Ni are present in this fraction for the two mining sites. Pb is associated mainly with the Fe – Mn fraction for the two sites. Degree of contamination and pollution load indices are calculated for the two sites and their values are greater than unity suggesting intervention of the Government on the sites based on the present study.Physico-chemical parameters of the water samples were found to conform to the standards set by the two regulatory bodies used (WHO & SON). Concentration of chromium was found to be very low and only detected in one sample. Copper recorded the highest concentration of 0.13 mg/l in one of the water samples.