Arsenic in soils and waters and its relation to geology and mining activities (Salamanca Province, Spain)

Abstract

Arsenic has been determined in a large number of water, rock, soil and stream sediment samples from around an area of former mining activity in Spain. Concentrations of As in different rock types (granites, metamorphic and sedimentary rocks) are generally within the normal global ranges. However, in some relatively abundant granitic and metamorphic zones, hydrothermally altered, the As contents are higher, which could be of local importance as a source of As in the contamination process of soils and waters. The nature of the soil parent material appears to be the main factor determining the As concentration in soils, although due to its low supergene mobility, the soils are slightly enriched in As compared with their soil parent rocks. Soils situated near the mine spoils contain extreme levels of As (>1000 mg/kg); nevertheless the geochemical dispersion halos around the mine sites are not very wide (<500 m). The low solubility of scorodite and the great As adsorption capacity of Fe oxyhydroxides could be the cause. Overall, groundwater presents low As contents. Only some samples show anomalous As concentrations (>10 μg/l), which could be caused by the presence of sulphide minerals in the altered granites or metamorphic rocks of some aquifers occurring into fractured zones of these rock types. In surface waters, high As contents were found in some samples close to mining areas.