ABSTRACT

This study investigates the concentration of heavy metals (Zn, Pb, Cd and As) in the soil and leachate from the unlined dumpsite at Ubakala, Umuahia South L.G.A, Abia State, Nigeria. Soil samples from different layers; 0-15cm, 15-30cm and 30-45cm, were collected from three sampling locations, PA, PB. PC and a control site 300M away from the dumpsite, PD. Leachate samples were also collected from leachate pools at the three sampling locations; A, B, C. The soil and leachate samples were analysed using Atomic Absorption Spectrophotometer, SPECTRA AA100. The mean concentration of heavy metals for soil samples across the three sampling locations of the dumpsite ranged from; 7.68±0.10 to 12.40±0.20mg/kg for Zinc, 0.60±0.10 to 3.29±0.10mg/kg for Lead, 0.60±0.10 to 9.45±0.20mg/kg for Cadmium and Arsenic ND (not detected). The mean concentrations for leachate samples across the three sampling locations of the dumpsite ranged from; 0.049±0.001 to 0.061±0.001mg/L for Zinc, 0.023±0.001 to 0.056±0.001mg/L for Lead, 0.037±0.001 to 0.050±0.002mg/L for Cadmium, and Arsenic (ND) not detected. The mean concentration of the heavy metals in the soil sample from the control site ranged from 0.34±0.19 to 1.13±0.03mg/kg for Zinc, 0.74±0.05 to 1.45±0.14mg/kg for Lead, 0.33±0.09 to 1.70±0.07mg/kg for Cadmium and Arsenic was not also detected. The concentrations of heavy metals in the soil and leachate samples display the following decreasing trend Zn˃ Cd˃ Pd. From the results, it was found that the mean concentrations of the heavy metals in the soil of the control site was significantly (p≤0.05) lower than their concentrations in the dumpsite soil and there were also significant differences in the heavy metal concentrations among the three sampling locations PA, PB and PC of the dumpsite, indicating uneven distribution of heavy metals across the dumpsite.. There is high mobility of the heavy metals down the soil profile (as the mean concentrations increased down the soil depth) which indicates possible underground water contamination. The results of this work have revealed that the mean concentration of heavy metals investigated in the soil samples were within the maximum tolerable levels proposed for agricultural soil by WHO (1993) with the exception of cadmium which was higher than the maximum tolerable limits (0.02-0.5mg/kg), while the heavy metals found in leachate were exceeding the allowable limits for Nigerian Standard for Drinking Water Quality set by SON (2007) except for Zinc which is within the allowable limit. These observations suggest that there is tendency of accumulation of these metals in the future as the dumpsite represents a significant source of heavy metal contamination of soil and underground water.