# Technosols Development in an Abandoned Mining Area and Environmental Risk Assessment
## 4 Discussion  
According to the type of the mine tailings deposited, the World Reference Base for Soil Resources [6] allows to classify these soils as Technosols as they contain more than 20% mine artefacts transported and deposited to the surface directly or after transformation by industrial activities. All the investigated soils were classified Technosols toxic having in some layer within 50 cm of the soil surface inorganic materials with high concentrations of toxic elements. Leptic Hyperskeletic Technosols (Toxic) soils were found in those stony areas where soil developed on abandoned mining area (GR1) having \(<\)20% (by volume) fine earth over continuous rock starting \(<\)75 cm from soil surface. Spolic Technosols (Toxic, Transcript) were classified in those areas where soils were characterized by transported mine gangue materials (GR2), containing \(>\)35% (by volume) mine debris that have been transported from the mining area. Isolate Technosols (Toxic,elocatic) were described in those areas where soils were characterized by deposition of mineral flotation materials derived by rock manipulation (GR3), limited to defined areas, and covered and remodeled in situ with fill soil. As underlined by the soil classification, soils were very little developed and were all characterized by the presence of high content of PTEs. The high PTEs concentration was expected as these soils resulted in an abandoned mining area, characterized by pyrite, barite, iron oxide rich in heavy metal [50; 51; 52]. As soils showed acidic pH, there is a serious risk of metals leaching into underground water, with the consequent spread of the metal contamination in the surrounding area. Concern was arisen for the high content of As Pb, Zn and Tl (up to 297, 1096, 1081 and 143 mg kg\({}^{-1}\), respectively), that exceed the threshold limit defined by Italian law [49], but also for the high concentration of other potentially toxic elements such as Ag, Ni and Cu (up to 29, 49 and 135 mg kg\({}^{-1}\) respectively). According to the sequential partitioning of metals in A and AC horizons more information about potential risk linked to the high concentration of PTEs were recorded. Soils of GR1 were characterized by the highest content of Cu, Pb and Zn, linked to the presence of low-weathered pyrites minerals. Pyrite, in fact, is the most common sulfide associated with other sulfide minerals such as sphalerite (ZnS), chalcopyrite (CuFeS2), and galena (PbS) [53] and in this area such minerals are very common as confirmed by [PERSON] et al. [50]. These soils are also characterized by a lower Ba content, probably because they are the only natural mine soils that do not contain anthropic Ba accumulation occurred in the other soils as results of tailings manipulation. Soils of GR2, developed on gangue deposits, recorded the highest content of TOC and P. This result is probably related to the position of these soils, almost located in natural forested area, that promote wild vegetation growth and accumulation of fresh organic matter [54; 55]. In addition, GR2 soils showed the highest content Fe and Mn, which are probably present as oxide and hydroxides, as the results of pyrite oxidation. The steps of pyrite oxidation due e.g., to atmospheric contact, oxygenated waters, soil humidity, etc., may lead to soil acidification [56; 57] and to different reactions according to the activation energy of the site and redox potential. According to [PERSON] et al. [53], the pyrite weathering at low Eh potential and low activation energy, may lead to oxidation of Fe(II) to Fe(III)-OH- species, while in presence of higher activation energy the weathering product may lead to the formation of S=O bond and Fe(II)-OH\({}_{2}\) species. As a result of mineral oxidation, the total concentration of S-linked metal such as Pb and Zn were significantly lower in GR2 compared to GR 1 soils, but their potential availability is higher.