Trace Metals and Hydraulic Characterization of Soils and Groundwater Around Ajakanga Dumpsite in Ibadan Metropolis, Southwest Nigeria.

Abstract

Trace metals concentrations and hydraulic characteristics of soil were studied with a view to assessing the impact of the Ajakanga dumpsite in Ibadan, Southwest Nigeria, on soil and groundwater. Forty one surface soil samples were taken at the depth of 0.2 cm, eleven samples each of disturbed and undisturbed soils along two (2) vertical profiles at up-slope and down-slope pits within the dumpsite premises. Eight groundwater samples were also collected. Digestion of 0.5 gm each of fraction (< 63 µm) of the soil samples was carried out. Both the digested soil and groundwater samples were analysed for Zn, Cu, Mn, Pb, Cd, Ni, As, Co and Cr using Buck Model 205 Atomic Absorption Spectrophotometer (AAS). The undisturbed soils were used for the determination of hydraulic properties. The data collected were interpreted using appropriate qualitative and quantitative statistical techniques. Trace elements results for soil showed average values for Zn (29.30 ± 16.1 mg/L), Pb (14.72 ± 0.84 mg/L), Cd (2.49 ± 0.48 mg/L), Ni (2.03 ± 1.12 mg/L), As (0.84 ± 0.22 mg/L), Co (0.16 ± 0.10 mg/L) and Cr (0.92 ± 1.40 mg/L) that were higher than those of control site values suggesting contamination. Grain size analysis showed that the clay size particles average abundance was higher in the B-level of the down-slope soil profile with mean value of 5.07±0.82 % compared with mean value of 4.85 ± 0.59 % at the up-slope pit. Evaluated results showed that the B-level is more polluted than the A and C levels probably due to adsorbsion effect of clay-sized materials that are more abundant in the B-level. Groundwater trace elements average concentration values were Mn (0.31± 0.74), Pb (0.03 ± 0.04), Cd (0.02 ± 0.03 mg/L), As (0.06 ±0.03 mg/L) and Ni (0.13 ± 0.08mg/L) which were higher than the WHO (2007) permissible levels especially in samples taken close to the dumpsite. The study concluded that the soils and groundwater samples close to Ajakanga open dumpsites were more polluted than those taken far away. The soil contamination was well pronounced within 0 – 3.5 m of the vertical soil profile at the dumpsite vicinity.

Keywords: Trace Metals, Soil, Groundwater, Hydraulic Characteristics, Dumpsite, Environmental Impact.