Trace metal concentration in roadside surface soil and tree back: a measurement of local atmospheric pollution in Abuja, Nigeria.

Cadmium, copper, lead, nickel and zinc concentrations were analysed by atomic absorption spectrophotometry in surface soil and tree bark from different districts of Abuja, Nigeria, in order to determine the atmospheric trace metal input in the area. Elevated concentrations of some of the studied metals were observed in the soil and tree bark samples from the commercial/high traffic areas of the city compared to background values. In soil samples, the average concentration of the metals were 0.6 +/- 0.4, 18.0 +/- 4.0, 281 +/- 39, 16 +/- 4 and 66 +/- 23 microg g(-1) dry weight for Cd, Cu, Pb, Ni and Zn, respectively, whilst the average concentrations in tree bark were 0.3 +/- 0.2, 12 +/- 4, 133 +/- 32, 13 +/- 3 and 61 +/- 10 microg g(-1) dry weight for Cd, Cu, Pb, Ni and Zn, respectively. The trend in trace metal levels suggested that automobile emissions are a major source of these metals as the highest concentrations of Pb and Zn were recorded in the commercial areas of the city known for their high traffic densities. The levels of metal in the study area were relatively low compared to levels found in some larger and older cities in various countries worldwide.