HEAVY METAL SOIL CONTAMINATION OF THE LAKE JUNÍN BASIN FROM MINE TAILINGS DUST

Activity within the Cerro de Pasco mining district has led to the heavy metal contamination of soils in the Lake Junín basin in Peru’s Junín and Pasco Provinces. 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. Elevated metal concentrations in soils closer to Cerro de Pasco correlate with the more recent mining interests.

Teams of researchers and volunteer citizen samplers collected 154 surface soil samples from various locations around Lake Junín and Cerro de Pasco. To prepare for analysis samples were oven dried, ground, and homogenized. Twenty metals were extracted using 9.5 ml deionized water and 1 ml of 70% nitric acid and analyzed by ICP-MS. Metal concentrations were normalized to aluminum to account for mineralogical effects.

Concentrations reveal 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. Normalized concentrations reveal soils closer to the mine have up to 1000 ppb of As, 4200 ppb of Cu, and 25000 of ppb lead more than background levels of metals in uncontaminated soils from Junín Province. The absence of a spatial trend in silver (Ag) concentrations reveals that the contribution of metals to soils from mining dust is from recent mining activity.