Baseline studies of some heavy metals in top soils around the Iron - ore Mining Field Itakpe North Central Nigeria

Abstract

The baseline concentration levels of cadmium(Cd), manganese(Mn), chromium(Cr), nickel(Ni), copper(Cu) zinc(Zn) and lead(Pb) were determined in the top soil around the iron ore deposit at Itakpe North Central Nigeria in order to define benchmark concentrations as a basis for future environmental monitoring and pollution control for sustainable environmental protection. One hundred and sixty soil samples were randomly collected over an area of 5x5km2 between December 2003 and November 2005. The soil samples were subjected to standard methods and analysed using Unicam 969 flame atomic absorption spectrophotometer. The pH and organic carbon concentration of the soil ranged 4.28-7.46 (6.56±0.70) and 2.60-5.60% (2.85±1.00%) respectively. The mean concentration levels of heavy metals ranged: Zn, 43.89±9.06-75.29±15.74 mg/kg; Cu, 33.48±7.44-51.50±7.35 mg/kg; Pb, 18.73±2.87-33.31±4.31 mg/kg; Mn, 6.39±1.07-20.31±3.42 mg/ kg; Cr, 8.18–14.89 mg/ kg; Ni, 11.99±2.71-20.84±2.09 mg/kg; and Cd, 0.10±0.05-0.21±0.07 mg/kg. The soil metals concentration sequence was Zn > Mn > Pb > Ni > Cu > Cr > Cd, with Zn having the highest relative abundance in topsoil in respect to the measured metals while Cd had the least. There was decreasing gradient in the heavy metals concentrations from top soil (0–15cm) to depth 110cm. Zinc concentration level decreased by 23.92% from 67.65 mg/kg top soil to 13.06 mg/ kg at 100–110 cm; Mn, 21.5% from 20.30-4.30 mg/kg; Cr, 14.09% from 14.89-1.84 mg/kg; Ni, 16.65% from 16.88-2.41 mg/ kg; and Cu, 19.54% from 45.99-7.52 mg/ kg, from top soils to depth of 100–110 cm respectively. Cadmiumand lead were found below the instruments detection limit (i.e. < 0.002, Cd and < 0.05, Pb) at depth 50–110 cm and 100-110 cm respectively. Apparently, the soil environments are yet to be impacted negatively by heavy metals because heavy metal levels around Itakpe iron ore deposit and beneficiation plant were within natural concentration levels, and are therefore regarded as not polluted.