The paradigm of high concentration of metals of natural or anthropogenic origin in soils – The case of Neves-Corvo mine area (Southern Portugal)

Abstract The aim of this study is to evaluate the spatial distribution of arsenic, copper, lead and zinc in soils, often used for agriculture, collected in the vicinity of Neves-Corvo mine, and understand how the geological context and local and natural geochemical anomalies can be differentiated from anthropogenic loads. It was found that mean and median concentrations of arsenic observed in soils used for agriculture in the vicinity of Neves-Corvo mine, exceeded more than twice the recommended value of 11 mg kg − 1 , in accordance with the Ontario Guidelines (OG). Furthermore, at 83% of sampling sites, arsenic in soils exceeded the above-mentioned limit. A similar situation held for copper, whose soil concentrations were above the levels recommended by the OG. In contrast, lead and zinc levels did not exceed OG-recommended levels. In addition, natural geochemical background threshold values were above (As and Cu), below (Zn) and above and/or below (Pb) the OG-recommended levels, indicating that even in the absence of anthropogenic contamination, the area in the vicinity of the mine poses a risk for agriculture. It was concluded that all the areas with the highest probability of the occurrence of concentrations above threshold values were located very close to the mine complex, mainly southeast, and were of anthropogenic origin. Spatial results deriving from probability maps were also consistent with positive Pearson's correlation coefficients.