Geochemical Partitioning of Heavy Metals in Roadside Surface Soils of Different Grain Size along Major Roads in Kano Metropolis, Nigeria

Abstract

This study evaluates the effect of grain size on levels of metal in roadside surface soils collected along high traffic roads in Kano Metropolis as a consequence of increase in automobile over the years. Composite surface soil samples were collected along ten different roads. Samples were analysed for soil physicochemical parameters, heavy metals (Cd, Cr, Ni, Pb, Cu and Zn) content. On an average a six sequential extraction of roadside surface soils showed that Cd, Cr, Ni, Pb, Cu and Zn are predominantly occur in the Fe-Mn oxide, residual, residual, carbonate bound, organic and residual fractions respectively. It was found that concentrations in the water soluble and exchangeable fractions were generally low for most of the studied metals. Considering the proportion of metals bound to the water soluble to the exchangeable and the carbonate bound fractions, the comparative mobility of metals showed the order; Ni > Cd > Pb > Cr > Cu > Zn. Highest mobility factor (MF) for all studied metals was obtained in 150µm samples with exception of Ni, Pb and Cu where highest percentage MF was obtained in 1400µm samples and 355µm for Zn. This could indicate other sources than fine particulate emission form vehicles responsible. With toxicity it appears that Cd, Cr, Ni, Pb and Cu pollution along the roadside is of concern.