Spatial distribution maps of Cu, Pb, Zn, Cr, As and V in rural soils in northern part of Chile: The use of geochemical baseline values as an index in environmental assessment.

Soil pollution is a worldwide concern and several countries are established guidelines. In the case of Chile, the very diverse soils characteristics along the country made difficult to set guidelines to acceptable levels of potentially toxic elements (PTEs) in soils. However, due to several reasons such as anthropogenic contamination, and increment of erosion rates there is urgency in to establish guidelines values to this parameters. In Chile, the most of abandoned mining wastes are located in the northern part which could negatively have impacted the ecosystem and human health. Thus, in absence of guidelines to PTEs in soils, the use of regional geochemical baseline (GBL) as a reference values could be a first approach to preliminary determine pollution levels of PTEs in soils. The objective of this study was to use the calculated GBL values to determine the influence of mining activities on the levels of PTEs in soils and to determine the spatial distribution maps of PTEs. A regional mapping of soils was conducted in northern part of Chile during 2017-2018 and the pH, electrical conductivity, redox potential and concentration of PTEs was determined. A systematic sampling in a 20,000 square-kilometer area was conducted and 467 rural top and sub soil samples were taken to determine their physical and chemical composition. The content of PTEs was determined by ICP-OES. The GBL values were estimated following the upper-whisker limit method. The pH, electrical conductivity, and redox potential of soils were 4.9-9.5, 10.5-56,000 mS/cm, and 89.7-348.3 mV, respectively. The median concentration of Mn (695.9 mgkg^-1) was the highest followed by V (148.4 mgkg^-1), Ni (75.2 mgkg^-1), Zn (59.7 mgkg^-1), Cu (59.0 mgkg^-1), Sb (34.0 mgkg^-1), As (18.3 mgkg^-1), Cr (17.9 mgkg^-1), Sn (17.5 mgkg^-1), Pb (14.6 mgkg^-1), Co (13.0 mgkg^-1), Cd (12.9 mgkg^-1), Hg (3.6 mgkg^-1), and Mo (3.3 mgkg-1). The GBL for Cu, Zn, V, As, Mo, and Sb were higher than the reported average for world soils. The spatial distribution maps of Cu, Pb, Zn, Cr, As and V were used to determine pollution levels. Statistical correlation models showed the influence of either abandoned mining sites or active mining operation on the pollution levels of PTEs in the surrounding soils. The geochemical baseline values could contribute for government decision-makers to choose the best available remediation technologies for the impacted area.