Resumo

VILLARROEL, Lionel F. et al. Heavy metals contamination of the Rio Chilco-Rio Tupiza drainage system, southern Bolivia. Ecología en Bolivia [online]. 2007, vol.42, n.1, pp.48-71. ISSN 1605-2528.

Historic mining operations are known to have released significant, but unquantified, amounts of sediment-borne trace metals into the headwaters of the Rio Tupiza of southern Bolivia. This investigation utilized a geomorphological-geochemical approach to determine the impact of mining on sediment quality within the river system. Spatial patterns in sediment-borne trace metal concentrations indicate that Pb, Zn, Cu, Sb, Sn, and As are predominantly derived from three tributary basins possessing the Abaroa, Chilcobija, and Tatasi-Portugalete mining districts. Downstream of each tributary, geographical patterns in trace metal concentrations reflect local geomorphic processes that change along the river valley. Trace metal concentrations in upstream areas drained by the Rio Chilco decrease rapidly downvalley as a result of dilution by uncontaminated sediments and storage of metal enriched particles (e.g., sulfide minerals) in the channel bed as a result of an ongoing episode of channel bed aggradation. These processes significantly reduced the dispersal and, thus, the potential environmental affects of mining related trace metals released to the basin, including those associated with tailings eroded from the AbarÃa Mine during a flood in 2003. In contrast, downstream changes in concentration are minimal in channel sediments located along downstream reaches of the Rio Tupiza where larger quantities of trace metals are stored in floodplain deposits and aggradation has been less significant. Moreover, soils developed on the floodplains in this area locally contain Pb, Zn, and Sb concentrations that exceed Canadian, German, and Dutch guidelines for agricultural use.

Palavras-chave : Heavy metals; Geomorphic response; Rio Tupiza; Bolivia.

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