Anthropogenic Influence on the Water Quality in the lake Poopó Area, Bolivia

Abstract: Problem Definition: For several hundreds of years, mining in Bolivia has been an important part of the economy. The mining activity has a negative effect on both the environment and the health of the people. Previous studies conducted in the Lake Poopó area show elevated concentrations of heavy metals and ions harmful to people and nature. Also, previous studies indicate that the contamination from mining activities is significant for the water quality. Four larger rivers flow through the studied area; the Poopó, Pazña, Urmiri and Antequera Rivers. A large quantity of mines but also farms and villages are situated in the basins of some of these rivers. This, together with the geological composition of the bedrock, highly pollutes the water that in turn is used by the people in these villages. Objectives: The main objective of this thesis is to gather knowledge of the present environmental condition of the Poopó, Pazña, Urmiri, and Antequera River basins, with focus on heavy metal concentrations in superficial waters. Also, to increase the understanding of how the heavy metal concentrations have changed during the years of studies conducted in the area. The questions to answer include: • What are the concentrations of the heavy metals cadmium, copper, zinc, manganese, iron, arsenic, and lead in the Poopó, Pazña, Urmiri, and Antequera River basins? • Do the heavy metal concentrations change over time? • How much of the heavy metal concentrations are caused by anthropogenic and natural contamination, respectively? • How is the water quality compared to the health-based WHO guidelines for drinking-water? Our hope with this study is that the gained knowledge will help in the effort of developing long-term sustainable plans for remediation and water resource management that will benefit the people living in the Poopó, Pazña, Urmiri, and Antequera River basins. Method: This thesis summarizes information from previous studies as well as analyzes data values from a field trip conducted in June 2013. During the field trip samples of surface water were collected and analyzed. In the field, the parameters pH, Eh, temperature, conductivity, TDS, and alkalinity were measured and the water samples were divided into two bottles for further analysis in laboratory. At the San Andrés University in La Paz the water was analyzed regarding concentrations of the ions nitrate, sulfate, chloride, sodium, potassium, calcium, and magnesium and the concentrations of the heavy metals lead, manganese, arsenic, iron, copper, zinc, and cadmium. Data from previous studies were collected, organized and compared in order to see if and how the heavy metal concentrations change over time. Results and Conclusion: Current Situation The samples collected during the field trip in June 2013 make up the current situation analysis. The concentrations for nitrate, cadmium and arsenic all exceed the WHO health-based guideline values for drinking-water in the Antequera River. A thermal spring that leaks into the Urmiri River, together with the natural bedrock weathering, affects the water and elevates temperature, chloride, sodium, and cadmium concentrations. Since there is no larger mine activity contaminating the water in the Urmiri River, a comparison between the Antequera and Urmiri River gives an approximate indication of how much the mines affect the water quality. This comparison indicates that the Antequera River is highly polluted due to contamination from mines, especially regarding cadmium. The results also indicate that the characteristics of Pazña River are a mixture of those of Urmiri and Antequera River. Furthermore, it seems as though the mine-influenced sampling site MAD1, a tributary of the Poopó River, impairs the water quality of the main river to a great extent. Historical Situation The data from previous studies have been divided into dry and rainy period, respectively, where an analysis of heavy metal contamination has been made only of the dry season data values. This study, similar to the study of the current situation, indicates that the area north east of the Lake Poopó is polluted and that Antequera River is the river most affected by mining activity. In that particular river, the concentrations for cadmium, iron, zinc and manganese exceed the WHO guideline values at almost every sampling site and date. Especially cadmium vastly exceeds the WHO limit. Meanwhile, the values for the Urmiri River rarely exceed the WHO guideline values. The heavy metal values for Pazña River are also often above the WHO guideline values, probably due to the inflow from Antequera River. The sampling site MAD1 greatly affects the Poopó River and elevates the heavy metal concentrations. A clear trend for all four rivers is the constantly elevated concentrations of cadmium that is neither increasing nor decreasing up to June 2013. For sampling sites PAZR1 and POR3, where the data sampling starts as early as 2001, the arsenic and lead concentrations are high above the WHO guideline values until June 2007. After this, the levels seem to have stabilized close to or below the WHO guideline values. Sampling site MAD1 does not, however, follow this pattern but instead has extremely elevated arsenic and lead concentration up to June 2013. The sampling site AVR1 has only been studied since 2007. There, the levels of arsenic and lead have historically had one peak each but otherwise stay around the WHO guideline values for drinking-water.