A megascale survey of heavy metal contamination from mining dust from the Cerro de Pasco Mining District (Peru)

Large scale mining results in severe land-surface modification and poses many ecological and human health threats. Silver mining at Cerro de Pasco has been extensive since pre-colonial times, but the completion of a railroad and central smelter in 1897 and 1931 allowed for a shift to large scale copper (Cu) then lead (Pb) production. Inadequate waste management associated with the mine expansion is the suspect cause for basin scale soil contamination via mining dust. Researchers and volunteer citizen samplers collected 375 surface soil samples from various locations within Junín and Pasco provinces. Acid extractions were performed on the entire sample set to analyze twenty different heavy metals with ICP-MS. In addition, a sequential extraction procedure designed for geochemical speciation of metals in mine tailings was modified and performed on a study set of samples to evaluate what soil fractions are retaining metal contaminants. Metal concentration data reveals elevated levels of heavy metals in samples from within a 13.8 km radius from the center of the mining district with furthest extent of contamination at 24.2 km Southwest, downwind of the mining district. Soil metal concentrations reach up to 630 ppb As, 2500 ppb Cu, and 21000 ppb Pb while background levels at uncontaminated sites are in the range of 5-50 ppb As, 5-100 ppb Cu, and 20-300 ppb Pb. The absence of a spatial trend in silver (Ag) concentrations suggests that soil contamination may only record modern and recent mining activity.