There is a story about a hillside in the Erzgebirge Mountains of Germany where livestock can safely graze on one side of the hillside, but become ill if they graze on the other side of the hillside on which sits a mine. This scenario is unique because many mines in the Erzgebirge mountain range were established between 600 to 1000 years ago and this extensive amount of time has possibly allowed heavy metals leached from the mine tailings to migrate into the soil now covered in vegetation. In a study conducted in 2012 on the geochemical composition of mine materials in the Freiberg mining district, Stockman et al. found that while the mines were primarily mined for Pb, Zn, and Ag, the dumps also contained mining-related elements of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, S, and Zn. Oxide weathering of these elements yields free acid and dissolves soluble metals from sulfide minerals, mobilizing the indicated chemical elements (Stockman et al. 2013). Soil can be transformed to include heavy metals; the degree of transformation is due to factors including the cation exchange capacity, the pH, and the content of clay minerals, carbonate minerals, oxides, organic matter, and oxygen (U.S. Department of Health Services 1993, 91). When considering that these processes have been occurring for such an extended time period, the surrounding soil has been probably significantly affected and altered. This study focuses on the absorption of mining related elements into the vegetation cover and investigates if plants growing around various mines throughout the Erzgebirge are absorbing heavy metals in greater amounts, thus possibly being toxic to grazing livestock.

References:

Stockmann, M., Hirsch, D., Lippmann-Pipke, J., and Kupsch, H. 2013. "Geochemical study of different-aged mining dump materials in the Freiberg mining district, Germany." Environmental Earth Sciences 68:1153-1168. Accessed February 14, 2014. doi:10.1007/s12665-012-1817-6.

U.S. Department of Health Services. 1993. Toxicological Profile for Cadmium. Atlanta: Agency for Toxic Substances and Disease Registry.