Pedo-geochemical background and sediment contamination of metal(loid)s in the old mining-district of Salsigne (Orbiel valley, France)

International audienceThe mining district of Salsigne in the Orbiel valley (Aude, France) was at one time the first gold mine in Europe and the first arsenic mine in the world. However, no scientific studies have evaluated the magnitude of its environmental impact. In this study, the pedo-geochemical background (PGB) was determined for 14 metal (loid) elements, including As. It appears that the PGB values for As and Sb are relatively high with 44±12 and 0.9±1.2 mg kg-1, respectively, because of the geological particularities of this area. In a second step, these PGB values (normalized with Ti concentrations) were used as local references to determine enrichment factors (EFs) of bed river sediments for the Orbiel River and two of its major tributaries (Gresillou and Russec rivers) collected between November 2018 and July 2020. Results showed that riverine sediments are contaminated by past mining activity and/or current storage areas. If we except the major elements (Fe, Ti and at a lesser extent Mn), we observed that As, Cu, Sb, Pb present the highest concentrations relative to the remaining elements (Cd, Co, V, Ni and Cr). In the case of As, EFs can reach 74 in the Orbiel River, 1000 in the Gresillou River and 27 in the Russec River. These calculations were also performed for sediments transported by the extreme flood of October 14, 2018, that killed 15 people and potentially remobilized contamination in the valley. We observed that the As concentrations of suspended samples from Grésillou and Russec rivers have reached 870 mg kg-1. Finally, the As concentrations measured in the river sediments of this valley are of the same order of magnitude than those published in the literature for environments strongly impacted by mining or mineral processing activities