This paper presents new data on the baseline concentrations of ten potentially harmful elements (As, Cd, Co, Cr, Cu, Pb, Sb, Tl, V and Zn) in volcanic soils collected over the whole Ischia volcanic island (46.5 km2). A total of 198 residual soil samples were collected during the spring of 2001 with a sample grid of 500 × 500 m. The < 150 μm fraction was analysed (after aqua regia digestion) by ICP-AES for 30 elements. In addition to elemental analysis, gamma-ray spectrometry data were collected (for a total of 159 measurements) using a hand-held Scintrex GRS-500 spectrometer.
For the compilation of baseline geochemical maps, a recently developed multifractal inverse distance weighted interpolation method and spectral analysis using a new geochemistry-dedicated GIS (GeoDAS) have been applied. The geochemical baseline includes the geogenic natural content (background) and the anthropogenic contribution in the soils. In order to obtain background values, to be used as reference values for the environmental Italian law DM 471/1999, the concentration-area fractal method has been applied. R-mode factor analysis helped in interpreting data controlled by anthropogenic sources as opposed to those controlled by geogenic sources.