Chemical Speciation and Mobility of Some Heavy Metals in Soils around Automobile Waste Dumpsites in Northern Part of Niger Delta, South Central Nigeria

The mobility of some heavy metals (Fe, Co, Ni and Mn) in soils around automobile waste dumpsites in Northern part of Niger Delta was assessed using Tessier et al. five syteps sequential chemical extraction procedure. The results showed that majority of iron and manganese were associated with the residual fraction with the average levels of 29.2% and 24.43% respectively. The exchangeable fraction was the most important fraction for cobalt with the average level of 39.53%, while the organic fraction contained the predominant species of nickel with an average level of 22.97%. For the total concentrations of the metals, iron ranging from (mgkg-1) 768.30 to 2897.00 was the highest followed by manganese ranging from 1.78 to 19.92 and then cobalt and nickel which ranged from 0.28 to 2.42 and 0.084 to 0.512 respectively. The mobility factors for the metals in all the sites ranged from 20.37 to 90.90 for cobalt, 15.83 to 62.07 for nickel, 25.50 to 60.43 for manganese and 16.49 to 32.13 for iron following the order Co>Ni>Mn>Fe. The relatively high mobility factors observed for cobalt in some sites coupled with its comparatively high concentration in the exchangeable fraction, indicates high mobility, lability and bioavailability for cobalt in the soils studied. The other metals (Fe, Ni and Mn) which are strongly bound to soil matrix are not readily availably for introduction into the food chain. The results suggest that there is no serious contamination hazard with the metals studied, considering the geochemical phases in which Fe, Ni and Mn were associated with, and the low total metal concentration of Co, even with its relatively high mobility. @JASEM J. Appl. Sci. Environ. Manage. December, 2010, Vol. 14 (4) 123 - 130