Arsenic and polymetallic anomalies in the Neogene- Quaternary sequence of La Botte borehole in the Scarlino Plain (Grosseto) - Southern Tuscany - Italy

摘要

Following the initial discovery of elevated As levels in soils (up to 1000 mg/kg) and groundwater (up to 2000 mg/L) in the surroundings of the industrial plant for sulfuric acid production by pyrite roasting in Scarlino Plain - Southern Tuscany - more extensive surveys were conducted to determine the source of As. The obtained results suggested that on a large scale As anomaly has a geogenic origin, linked to natural processes of weathering and erosion of As-rich mineralizations which are present in the hinterland, thus leading to dispersion of As in the environment. Otherwise there is convincing evidence that soils and groundwater around the industrial plant have been severely polluted by As related to waste residues of pyrite roasting stored close to the plant. To better define the source of As in the Scarlino Plain and in particular to evaluate the possible influence of the industrial activity on the As distribution in the subsoil, a 147 m long borehole was drilled 800 m far from the industrial plant and the As-rich waste piles. The sediment analyses have revealed anomalous As contents from the topographic surface until 130 m b.s. (up to 1060 mg/kg). Below this depth, As concentration values show a decreasing towards the average crustal concentration of 1.8 mg/kg. Arsenic was detected by using SEM/EDS analysis in association with Fe oxy-hydroxides and in few cases in pyrite. In conclusion, the chemical and mineralogical data from the borehole would seem to support that in Scarlino Plain the primary As geogenic anomaly has been overprinted by an anthropogenic input.