Unabated acid mine drainage from Cerro Rico de Potosi, Bolivia: uncommon constituents of concern impact the Rio Pilcomayo headwaters

摘要

Intensive mining and processing of the polyme-tallic sulfide ore body of Cerro Rico de Potosi (Bolivia) has occurred since 1545, leading to severe degradation of surface and subsurface waters, stream sediments, and soils at the headwaters of the economically vital, yet highly impacted, Rio Pilcomayo. Previous studies have documented extremely elevated concentrations of a limited suite of metals in local waterways from acid mine drainage (AMD), terrestrial and in-stream tailings, and ore processing plant discharges. However, contamination from a wider variety of ecotoxic metals/metalloids was considered likely due to the highly mineralized poly metallic nature of the ore body. To screen for this broader range of ecotoxic elements in AMD and receiving streams, data were gathered during two sampling events timed for the most extreme periods of the dry and wet seasons of one water-year. Concentrations of Ag, B, Ba, Mo, Sb, Se, Sn and V in AMD and receiving streams were greater than Bolivian discharge limits and receiving water body guidelines as well as international agricultural use standards. Locally, results indicate that contamination from mining Cerro Rico has a larger scope than previously thought and underscore the importance of remediation. Globally, the results raise the possibility that other mining regions could have unqualified hazards from overlooked ecotoxic elements and that screening for a broader range of contaminants may be warranted.