Heavy metal migration along a rural highway route: Ilesha-Akure roadside oil, Southwestern, Nigeria

This paper present migration of some selected heavy metal (zinc, lead, copper, chromium and nickel) of roadside soil samples from along Ilesa-Akure highway with a view to assess the degree of contamination such soils contain and the likelihood that this contamination can be remobilized. Soil samples were collected from 5 locations (Ilesa, Ipetu-ijesa, JABU, Ilara-mokin and FUTA north gate) at depths of 0-5, 15-20, 35-40 and 55-60cm and analysed for the five selected heavy metals in the bulk sample and clay fraction. Their concentrations and distributions in four different road verge zones (5m, 30m, 60m and 110m) were determined. The 5m zone had the highest mean concentration of the five metals whereas the 110m zone exhibited the lowest mean concentration. Zinc and lead exhibited a significant decrease in the roadside soils with the increasing distance from the road while chromium and nickel showed significant increase, copper on the other hand showed no significant difference. Quantitative assessment of the heavy metal contamination using the I_geo and PI indexes showed that the selected heavy metals were in the order of Cu < Pb < Zn < Ni <Cr for both Indexes. Soil characteristics (which include pH, Cation exchange capacity {CEC}, organic matter and other basic geotechnical tests) responsible for the mobility and vertical distributions of these heavy metals from the road side soil were also assessed.