ASSESSMENT OF HEAVY METALS CONTAMINATION FROM POINT SOURCES IN THE ABAROA - TUPIZA BASIN, BOLIVIAN SOUTHERN REGION

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Lionel Franklin Villarroel (Creator)
Institution
Western Carolina University (WCU )
Web Site: http://library.wcu.edu/

Abstract: Heavy metal contamination in rivers downstream from mining operations is an important environmental concern due to the potential release of metals that affect water quality. The downstream transport of particulate bound metals and their subsequent storage in alluvial deposits is of particular concern because they may pose a significant threat to the quality of agricultural crops grown on floodplains. This study examines the downstream transport and storage of contaminated sediment derived from three mining centers in southern Bolivia: the Abaroa, the Chilcobija, and the Tatasi - Portugalete District. It also examines the consequences of erosion of mine tailings impounded within a small river valley at the Abaroa Mine site. Trace metal concentrations (including lead, zinc, and antimony) within the bed sediments of a bedrock constrained channel located immediately downstream of the Abaroa Mine gradually decrease downstream until reaching the Rio Chilco, where concentrations abruptly decrease. Metal concentrations within the bed sediments are similar to background concentrations within approximately 30 km of the Abaroa Mine.However, Pb and Zn concentrations locally increase farther downstream along the Rio Tupiza - San Juan del Oro as a result of the influx of mining debris from polymetallic mining operations within the Rio Tatasi basin and, to a lesser degree, the Rio Chilcobija. Downstream of the tributaries Rio Abaroa, and Rio Tatasi, Pb, Zn, and Sb concentrations decrease gradually until reaching concentrations similar to local background.The spatial distribution of metals in floodplain deposits differs from site to site. In floodplains closest to the mines such as FF-1 and FF-2, relatively elevated metal concentrations were found at sites located near the channel separated 10 and 35 m,whereas lower concentrations occurred at distances greater than 50 m from the channel. The opposite trend was observed in floodplain FF-3, and in the floodplain farthest downstream the difference in metal content was negligible. However, it is difficult to define a particular trend due to the small variations among and within the sites.Vertically, most of the floodplains exhibit the highest concentrations at the surface. Highly variable concentrations exist at greater depths, although the lowest metal concentrations were often at the base of the core. This spatial pattern suggests that sediments contaminated by Pb, Zn, and Sb have been deposited on the floodplain over the past several decades. Concentrations of heavy metals in floodplain deposits are higher than in channel bed sediments. Grain size data demonstrate that silt and clay is more abundant in floodplain deposits (~50%) than in channel sediments (~15%). These differences imply that differences in heavy metal concentrations are due to variations in the abundance of chemically reactive, fine sediments within the deposits. Locally, soil concentrations in floodplain soils exceed Dutch, Canadian, and German guideline values for agricultural use. In fact, the German guidelines are locally exceeded by two orders of magnitude. These data indicate that additional studies related to the accumulation of heavy metals within agricultural products should be conducted to more fully assess the potential impacts of metal contamination on human health.Impacts on human health and the environment caused by the Abar6a dam failure were apparently limited, as indicated by rapid downstream reduction in metal concentrations. The continuous inputs of sediments stored within the floodplain deposits during bank erosion may be a more important source of metals for the rivers.

Additional Information

Publication
Dissertation
Language: English
Date: 2005

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