Pb contamination and isotopic composition of urban soils in Hong Kong

In the urban environment, intense human activities can lead to degradation of environmental quality and have potential long-term effects on human health. In the present study, Pb contamination of urban soil cores in Hong Kong was investigated using a combination of the 'total' concentration, chemical partitioning and isotopic composition of Pb in the soils. The analytical results showed that urban soil cores in close vicinity to high traffic volumes ( > 40 000 vehicles per day) were usually contaminated with Pb, suggesting atmospheric deposition of Pb as a consequence of vehicular emissions arising from the combustion of leaded gasoline in the past. Increasing Pb concentrations were generally associated with decreasing Pb-206/Pb-207 ratios of the contaminated soil cores, offering strong evidence of accumulation of Pb derived from anthropogenic sources. In selected contaminated soil cores, the Pb-206/Pb-207 ratios tended to increase in the order: carbonate < exchangeable < Fe-Mn oxide < organic < residual fractions. The distribution of the Pb-206/Pb-207 ratios in the five operationally defined chemical fractions showed that the Pb-206/Pb-207 ratios generally increased with increasing stability, demonstrating preferential association of anthropogenic Pb with the carbonate, exchangeable, Fe-Mn oxide and organic fractions in the soils. (C) 2003 Elsevier B.V. All rights reserved.