An Assessment of the Concentrations of Heavy Metals in the Soils of Abuja Metropolis, Nigeria

Abstract

This paper explains the mean concentrations of some selected heavy metals in the soils of Abuja metropolis at depth of 15cm. Aqua Regia (HCl/HNO₃) method was employed to evaluate total metal concentrations in Abuja soils samples. Concentration levels of Pb, Cd, Fe, Ni, Zn, Al, Mn, Cu, Cr and As in Abuja Metropolis soil samples collected from motor parks, industrial zones, near auto mechanic zones, residential areas and an urban forest were investigated. Mean concentrations of heavy metals in Abuja urban soil samples were found to be; Pb(0.23±0.07), Cd(0.34±0.07), Fe(33.66±0.01), Ni(3.80±0.007), Zn(136.21±0.02), Al(20.11±1.8), Zn(91.52±0.02), Al(14.63±0.002), Mn(13.31±0.007), Cu(86.95±0.03) \Cr(0.09±0.007)and As(4.82±0.02). Results were below the limit of regulatory authorities. Zn had the highest mean concentrations in Abuja urban soils in the following sequence of decreasing order: Zn>Cu>Fe>Al>Mn>>As>Ni>Cr>Cd>Pb and in the sub-urban soils, it was; Zn>Cu>Fe>Al>Mn>>As>Ni>Pb>Cd>Cr. Zn mean concentration was observed to be highest in Asokoro Forest samples too. Excess Zn like its deficiency in plants, results in Zn phytotoxicity which disrupts plant photosynthesis among other things, this increases the amount of CO₂ in the atmosphere thereby increasing global warming. This implies that Abuja Metropolis is in danger of global warming due to excess of Zn in the soils. Relevant authorities should be conducting periodic environmental risk assessments of Abuja soils in order to checkmate the rising toxic metal build up in the metropolis.