Distribution and mobility of arsenic in soils of a mining area (Western Spain) Original Research Article

High levels of total and bioavailable As in soils in mining areas may lead to the potential contamination of surface water and groundwater, being toxic to human, plants, and animals. The soils in the studied area (Province of Salamanca, Spain) recorded a total As concentration that varied from 5.5 mg/kg to 150 mg/kg, and water-soluble As ranged from 0.004 mg/kg to 0.107 mg/kg, often exceeding the guideline limits for agricultural soil (50 mg/kg total As, 0.04 mg/kg water-soluble As). The range of As concentration in pond water was < 0.001 μg/l–60 μg/l, with 40% of samples exceeding the maximum permissible level (10 μg/l) for drinking water. Estimated bioavailable As in soil varied from 0.045 mg/kg to 0.760 mg/kg, around six times higher than water-soluble As fraction, which may pose a high potential risk in regard to its entry into food chain. Soil column leaching tests show an As potential mobility constant threatening water contamination by continuous leaching. The vertical distribution of As through soil profiles suggests a deposition mechanism of this element on the top-soils that involves the wind or water transport of mine tailings. A similar vertical distribution of As and organic matter (OM) contents in soil profiles, as well as, significant correlations between As concentrations and OM and N contents, suggests that type and content of soil OM are major factors for determining the content, distribution, and mobilization of As in the soil. Due to the low supergenic mobility of this element in mining environments, the soil pollution degree in the studied area is moderate, in spite of the elevated As contents in mine tailings.