Urban soil contamination in Salerno (Italy): Concentrations and patterns of major, minor, trace and ultra-trace elements in soils

This work discusses the results of a geochemical survey conducted in the Salerno urban area to determine the sources patterns of major, minor, trace and ultra-trace elements in soils. In particular, the study focused on elements that are potentially toxic and listed in the environmental Italian legislation (D.L. 152/06), in order to effectively monitoring an important aspect of environment health. A total of 151 topsoil samples were collected, air-dried and sieved (<2 mm). After aqua regia digestion the samples were analyzed for 42 elements by ICP-MS and ICP-AES. Geostatistical analyses were carried out in order to show the single element spatial distribution and the distribution of factor scores elemental associations from R-mode factor analysis. In performing factor analysis, the additive logratio (alr) transformation was applied to the whole dataset in order to deal with the closure effects of the investigated geochemical data, avoiding artefacts and spurious correlation. The use of alr-transformed data instead of the normal data in the factor analysis allowed for a better interpretation of the distribution patterns, since this produced four factor models which, once mapped, were easier to interpret. The study revealed that major and minor elements (Al, Ca, Fe, K, Mg, Na, P, S and Ti) have a perfectly natural distribution with no discernible association to any human activity or presence. In contrast, many trace and ultra-trace elements (Ag, As, Au, Ba, Be, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Pd, Pt, Rh, Sb, Sn, Tl, V and Zn) show anomalous concentration values located almost exclusively in highly inhabited areas, industrial sites and along high traffic roads. Other trace and ultra-trace elements (B, Bi, Ga, La, Sc, Se, Sr, Te, Th, Tl, U and W) show concentrations compatible with the natural background levels. Some potentially toxic elements (e.g. Pb and Zn) reach concentration levels tens of times higher than the legal limits in the busiest areas of the city. Exposure to high concentrations of these contaminants may cause health problems to people living in these zones.