No abstract

Some physicochemical characteristics and heavy metal levels in soil samples around metal scrap dumps at Abraka and Agbor vicinities of Delta State, Nigeria, were analysed in order to assess the effects of the dumps on the soils. Conventional analytical methods were employed for the determination of these physicochemical parameters while heavy metals in the soil samples where analysed using Atomic Absorption Spectrophotometer. The results of the physicochemical analysis showed that the pH values in all the sites ranged from 7.01 to 7.99 indicating neutrality to slight alkalinity of the soils. The Total Organic Carbon values ranged from 0.38 to 0.54% indicating presence of some organic matter and some microbiological activities in the soil samples. The high conductivity values ranging from 165 to 201µs/cm indicated significant presence of some soluble inorganic salts in soils studied. For all the physicochemical values recorded, the soil samples at Agbor had slightly higher values than those of Abraka. The heavy metal levels for the soils in Abraka and Agbor respectively were (mgkg -1 ) 1.50 and 1.52 for Cd, 5.10 and 4.48 for Ni, 1431 and 1411 for Fe, 74.26 and 97.21 for Zn, 14.31 and 34.21 for Cu, 24.0 and 18 for Cr, 9.73 and 10.54 for Co, and then 12.24 and 14.47 for Pb. The levels were all higher than those recorded in the control sites. A consistent trend showing a decrease in the concentration of heavy metals was observed for soil samples at increased distances from the impact points for the two towns studied. Metal was observed for soil samples at increased distances from the impact point for the two towns studied. The results from the contamination index indicated a significant degree of soil contamination for Pd, Cd, Co, Cu and Zn in the soils studied showing a higher degree of contamination for these metals. These soils therefore constitute a major health risk to the local population. This study successfully related and attributed the presence of heavy metals with anomalous concentration in the soils to anthropogenic inputs from the metal scrap dumps. @JASEM.

The chemical forms of copper, lead, manganese and zinc in soils around five selected municipal waste dumpsites in Asaba metropolis, Delta State, Nigeria, were studied, using the Ma and Rao six-step sequential chemical extraction procedure, with a view to providing information on the bioavailability and mobility of the metals in the soil matrix. The results showed that lead and manganese were speciated into residual fractions with averages of 60.32 and 82.24% respectively, while copper and zinc were associated with organic and Fe -Mn oxide fractions respectively with respective averages of 47.91 and 63.21%. The residual fraction also contained relatively high percentages of copper (33.18%) and zinc (20.81%). Relatively very low levels of the metals were found in the water soluble, exchangeable and carbonate fractions. The mobility factors of all the metals in all the soil profiles were generally low ranging from 1.97 to 39.99 indicating generally low availability as well as mobility. Lead and manganese associated with the residual fraction were strongly bound to soil matrix and were not bioavailable since they were occluded within the crystal lattice layer of silicates and well crystallised oxide minerals. Our results show that the metals do not pose any environmental risk or hazard. However, the soils stand the risk of being contaminated by copper and zinc since metals associated with organic and Fe -Mn oxide fractions could be bioavailable and mobilisable when the soil conditions such as pH and redox potentials change.