Spatial distribution of heavy metals in urban soils of Naples city (Italy)

Cu, Cr, Pb and Zn in the surface and sub-surface soils of the Naples city urban area have been studied and compared with historical data. Concentrations of surface and sub-surface soil Cu, Cr, Pb and Zn in the Naples city urban area were measured in 1999. Contour maps were constructed to describe the metals spatial distribution. In the most contaminated soil samples, metals were speciated by means of the European Commission sequential extraction procedure. At twelve sites, Cu, Pb and Zn levels in soil were compared with those from a 1974 sampling. Many surface soils from the urban area as well as from the eastern industrial district contained levels of Cu, Pb and Zn that largely exceeded the limits (120, 100 and 150 mg kg −1 for Cu, Pb and Zn, respectively) set for soils of public, residential and private areas by the Italian Ministry of Environment. Chromium values were never above regulatory limits (120 mg kg −1). Copper apparently accumulates in soils contiguous to railway lines and tramway. Cu and Cr existed in soil mainly in organic forms (∼68%), whereas Pb occurs essentially as residual mineral phases (77%). The considerable presence of Zn in the soluble, exchangeable and carbonate bound fraction (23%) suggests this element has high potential bioavailability and leachability through the soil. Concentrations of Cu, Pb and Zn have greatly increased since the 1974 sampling, with higher accumulation in soils from roadside fields.