English

Abstract

Intensive mining and processing of silver, lead, tin and zinc ores have occurred in various locations within and around the city of Potosi, Bolivia since 1545. Surface and subsurface waters, stream sediments and soils are contaminated with various heavy metals. Acid mine drainage and processing plant effluent are primary contaminants in the headwaters of the economically vital, yet highly impacted, Rio Pilcomayo watershed. Previous studies have documented downstream heavy metal contamination. The acid mine drainage sources documented in this study help to link downstream pollution to primary origins. Selected acid mine drainage sources, from both operating and abandoned mines contributing to local streams, contained total metal concentrations of 0.284- 977 mg/L Al, 0.03-191 mg/L As, 0.025-50.68 mg/L Cd, 0.03-161 mg/L Cu, 0.15- 7,320 mg/L Fe, 0.3-438 mg/L Mn, 0.03-15.0 mg/L Pb and 1.46-11,760 mg/L Zn, with pH and specific conductance ranging from 2.46-6.39 and 893-19,070 μS/cm, respectively. Data were gathered during the dry season with flows ranging from nil to 4.59 L/s. Metals concentrations and pH values in all mine drainage sources sampled are several orders of magnitude above compliance with Bolivian environmental law.