Heavy Metals Distribution and Speciation in Soils around a Mega Cement Factory in North-Central Nigeria

Abstract

Surface and sub-surface soils were sampled in the neighbourhood environment of an ultra-modern and largest cement factory in Nigeria. The five geochemical fractions investigated were exchangeable, carbonate, Fe-Mn oxide, organic matter and residual. All fractions were subsequently analyzed for lead (Pb), copper (Cu), zinc (Zn), manganese (Mn) and iron (Fe) using atomic absorption spectrophotometer. The average total metals concentrations (mg/Kg) in the surface soil were 1063.8± 261 for Fe, 30.29 ± 19.25 for Mn, 24.15 ± 21.69 for Cu, 15.08 ± 11.95 for Pb and 8.54 ± 3.18 for Zn. Relatively lower mean concentrations were measured in the sub-surface soil samples. The percent distribution concentration of the various metals in the residual fraction ranged from 0.23 to 69.48% for Pb, 0.85 to 75.30% for Cu, 36.02 to 83.86% for Zn, 12.97 to 44.04% for Mn and 18.11 to 57.25% for Fe. Factor analysis revealed that while Pb, Cu and Zn would majorly be of anthropogenic origin, Mn and Fe are mainly of natural origin. Pb was found to be the most mobile with mobility factor of 71.8% while Fe has the least mobility factor of 3.62%. Regression analysis (r² = 0.71) further showed that Cu is correlated with Pb. Soil pollution indices revealed that the surface soil is slightly contaminated in lead and zinc, and moderately contaminated in copper.

Key words: Heavy metals speciation, Mobility factor, Soil pollution, Cement industry