Background and geochemical baseline values of chalcophile and siderophile elements in soils around the former mining area of Abbadia San Salvatore (Mt. Amiata, southern Tuscany, Italy)

Background and geochemical baseline values of Potentially Toxic Elements (PTEs) in soils developed on natural or anthropogenically-affected areas are increasingly important parameters as they represent highly useful tools at local, regional, national and European level. While background values are mostly applied to uncontaminated areas to verify the presence of high to anomalous concentrations of PTEs due to geogenic sources, the geochemical baseline values are better representing those areas where the anthropogenic activities have altered more or less significantly the background values. This is the case of the Municipality of Abbadia San Salvatore, mostly lying above the volcanic products of Mt. Amiata (Tuscany, central Italy) and, subordinately, above sedimentary formations, where >100 years of exploitation of cinnabar (HgS) and production of liquid mercury have affected the environmental matrices, including the pedosphere compartment. Consequently, 51 top-soils and 51 sub-soils, developed on the volcanic and sedimentary domains were collected and analyzed for PTEs (Hg, As, Sb, Cr, Co, Ni, Cu and V). A CoDA (Compositional Data Analysis) approach (robust Principal Component Analysis) combined with geochemical mapping allowed to account for the compositional nature of geochemical data and define the spatial distribution of the investigated chalcophile and siderophile elements. The results obtained by CoDa are useful to understand data variability and relative variations of the elements compared to the barycenter of the total composition. Independently by the substratum (volcanic or sedimentary), the concentrations of Hg, As, Sb, Cr, Co, Ni, Cu and V were highly variable and up to 258, 276, 110, 261, 32, 132, 80 and 173 mg/kg, respectively. Owing to the significant differences between the two geological domains, the two datasets were considered separately in order to define the geochemical baseline values of the analyzed PTEs computed using ProUCL 5.2.0 software. Accordingly, the geochemical baseline values of Hg, As, Cr, Co and V were much higher than the values imposed by the Italian Legislative Decree 152/06, suggesting the importance of exploring the geological features of the investigated territories and their anthropic history, particularly in Italy where poly-metallic sulfide ore deposits have been exploited in many regions since the Etruscan and Roman times.