Vertical distribution of C, Pb, Zn, Cu, Ni, Mn, Fe and P in roadside soils, Caracas, Venezuela

Ten immature soils, probably undisturbed since the road was constructed in stages from 35 to 15 years ago, were sampled along a road with heavy traffic. For eight soil profiles samples were taken at depths of 0-2, 2-4, 4-6, 6-8 and more than 8 cm (the maximum depth varied from 12 to 20 cm). Pb, Zn, Cu, Ni, Mn, Fe, P were analyzed in 1 M HNO3 extracts and total concentrations were determined after digestion with HNO3-HCl-HF. Total C, pH, and mineralogy by XRD were also determined. Pb, Zn and Cu are enriched in surface samples and decrease rapidly with distance from the road, suggesting an anthropic origin. They also show maxima at 3-7 cm depth, roughly coincident with C maxima, allowing estimation of a minimum migration velocity of 1-3 mm/y. Pb concentrations do not show a clear trend with time of road opening, suggesting that other factors are very important.