Bolivia, a country located in the center of South America, has in the west part an Andean region, where the Poopo Lake is located. This area has many mineral resources, there, from thousand for years ago; the mining activity has a large importance. However, mainly from the colonial time, the extraction of these resources was indiscriminate and the region of the Poopo Lake, suffers terrible consequences for the environmental contamination. The Poopo basin has been contaminated due to a natural leakage from minerals with toxic contents; another problem is the high levels of salinization and the contamination of organic sewage effluents from the urban sites. Additionally to this, the climate conditions aggravate the problems. The area is semi arid and cold with a big change of temperatures between the day and the night. This region has further two clear seasons: a dry period and a rainy season that affect the environmental conditions. In this study, arsenic and heavy metals have been analyzed in surface waters, sediments, groundwater and biota from the rivers of the Poopo basin, the Poopo and Uru Uru Lakes and wells around the basin. The results show a strong natural contamination from weathering of minerals with high concentrations of lead and arsenic, generally dry conditions which results in high salinity in water and soil and important anthropogenic contamination from the intensive mining and metallurgic activities. The metals are transported from the mines through the rivers to the Poopo Lake. This transport is influenced by the season, if the river flows increase and decrease. A high flow gives a high sediment transport. In addition, some remediation possibilities were studied where the effectiveness of phytofiltration and biogenic sulfide precipitation to remove heavy metals from acid mine drainage was compared. The results show that the most effective sorption material in the phytoremediation is the macro-algae and thereafter the totora. Sulfide producing bacteria were the most effective method for removing heavy metals. Different time-dependent controls, were identified as sources and sinks far dissolved species of arsenic and heavy metals, to cause element-specific seasonal changes in the chemical composition of the surface waters in Poopo basin, where natural and mining-related release of that elements contaminates the basins rivers and results in an accumulation within Poopo Lake, which is receiving these waters. Highest concentrations of Pb in surface waters occur in the rainy season probably caused by dissolution of Pb-containing sulfates and chlorides on the banks of the Poopo Lake and increased erosion by rainfalls leaching Pb and transporting them into the rivers. In contrast, dissolved Cd is only found in the dry season indicating for the rainy season a dilution effect or the existence of a Cd-sink, which removes practically all dissolved Cd from the surface waters. In the Poopo Lake, the highest As-concentrations correspond to the dry season whereas in most rivers maximum As-values are found in the rainy season, indicating for both areas different dominating As-mobility controls: In Poopo Lake dominance of control by evaporation, and a possible uptake by biological sinks, explains the As maximum in dry season, whereas increased erosion and dissolution of weathered solids and transport into rivers explains the As maximum in the rivers in the rainy season. Dissolved Fe and Zn do not show significant seasonal variations.
Article Subject Terms: Arsenic; Basins; Cadmium; Climate; Contamination; Dissolution; Dominance; Drainage; Effluents; Erosion; Evaporation; Heavy metals; Lakes; Leaching; Lead; Leakage; Minerals; Mines; Mining; Precipitation; Rainfall; Rivers; Salinity effects; Seasonal variations; Sediments; Sewage effluents; Sorption; Sulfate; Sulfide; Sulfides; Surface water; Weathering; anthropogenic factors; dry season; heavy metals; phytoremediation; rainy season; Article; Geographic Terms: Bolivia; Bolivia, Oruro, Poopo L.; South America; P 2000 FRESHWATER POLLUTION; K 03340 Effects of Physical &; Chemical Factors