There is gold and silver in the ground, and also antimony, tin, zinc, copper, bismuth and lead. The rock formations under the Bolivian town of Oruro, at the heart of the Andes Cordillera, harbour substantial amounts of precious and commercially prized metals. The silver deposits were already known by the Incas. Large-scale mining though began in the XVIth Century, with the arrival of the Spanish settlers. Since then the mines and foundries developed considerably, according to the needs of the countries of the North and the raw materials prices, as did the urban agglomeration.
The city is perched 3700 m on the Altiplano and now has 220 000 inhabitants. These people are exposed to contamination by a number of metals generated by current and past mining and metallurgical industries. In five centuries, these activities have generated at least two million tonnes of mining waste, piled on spoil heaps open to the air at the foot of the Oruro hills. These masses of waste are sources of pollution.
The impact of these mining activities on health and the environment has been known for decades, or even centuries. Yet they are difficult to quantify exactly, owing to the naturally rich concentrations of metals in the region's soils and the multiple sources of contamination that exist (from mines, foundries, spoil tips, and so on). To remedy the problem of quantity estimation, the multidisciplinary project ToxBol, launched in 2006 by IRD scientists and their partners1, is working to determine the origin, dispersion mechanisms and the impact of metal pollution on the environment and people's health in Oruro. The team involves geochemists, ecologists, epidemiologists, geographers and sociologists.
Hydrological network contaminated
Greenish-yellow waters ejected by mine gallery pumping2 or flowing down from eroding slagheaps in the wet season, pass through the city and eventually into Lake Uru-Uru and Lake Poopó further downstream. This hydrological system is quite unusual. It finds no outlet to the sea. But also its high altitude and the salinity and strong mineralization of its waters makes the ecological and hydrological balance of this region particularly fragile.
The scientific investigations have shown the lake waters to have concentrations in heavy metals -like cadmium, lead, mercury, antimony, nickel, cobalt, chromium, zinc, copper and arsenic- far in excess of standard limits for drinking water. The team's biologists also revealed high levels of contamination in fish, particularly cadmium and sometimes lead, in Lake Poopó. They also detected a process of mercury accumulation3 in the aquatic food web of Lake Uru-Uru, one of Oruro administrative Department's main fishing areas. Moreover, an indicator of the water quality in the rivers by analysis of their fish communities was developed for the Andes. This confirms the strong impact of mining in the Oruro area.
Air also polluted
Wind erosion of the spoil heaps and transport of ore by uncovered trucks or trains, or even in taxis or private cars, from the mines to the processing plants and foundries outside the town, spread metal trace elements in the form of particles. These, often extremely fine and the most highly toxic form, are dispersed over quite long distances.
In some districts where buildings are soundly constructed, the house roofs and door and window frames are dustproof. However, in other areas housing Is more insecure. Corrugated iron roofs without false ceilings allow large quantities of dust to penetrate inside the buildings, giving higher risks of exposure.
Children, primary population at risk
The contamination does not affect all of the population, but groups at risk such as families living near a source of pollution or who bring their working tools home from the mine, sacks of ore or concentrates of metal. Small children are the most vulnerable to this kind of pollution, owing to the dust they ingest by putting their hands or objects to their mouths and because of their small size and immature physiology.
A team of geochemists measured the quantities of heavy metals in the air and tap water in housing areas and at five schools in different districts of Oruro: in the centre, in a rural area, the suburbs, near the mine and near the foundry. The results show some wide differences in the degree of exposure, especially to lead and arsenic, between the children in miners' housing areas, more severely hit, and those in the better-off areas. Similarly, boys, who go outside more often, appear to be more strongly affected than girls who, for cultural reasons, stay inside the home more.
In parallel, Bolivian scientists from the Universidad Mayor de San Andrés in La Paz and epidemiologists from the Hydrosciences laboratory in Montpellier4 conducted a study in two of the city's hospitals on the effect of exposure to metal pollutants on child development in the first year. On the clinical side, some minor symptoms statistically associated with exposure to lead, such as emotional instability or irritability, were observed in infants in the first weeks of life. However, at one year old, the children's development was found to be normal.
Unawareness of the risk in the community
The geographers and sociologists of the Laboratoire Population, Environnement, Développement (LPED) 5, linked up potential sources of pollution, vulnerability of populations and their perception of risk. This perception is mainly local and immediate, with no representation of pollution as a problem generalized throughout the town. The problem from mining is often underestimated by most of the players, including institutional ones, because it is difficult to observe the concrete effects. Further, a strong identity has been forged around the mine (a lucrative industry, with traditions, way of life, complete with carnival and so on). Finally, the absence of planning policies and real information on the dangers lead to situations where housing and some of the industrial activities are located right next to accumulations of mining waste.
For economic, political or social reasons, the authorities have often neglected health risks and restoration of polluted sites, in Oruro as in other mining towns of the Bolivian Cordillera and Altiplano. These four years of multidisciplinary research, as part of ToxBol, provide scientific information for political decision-makers. The data on biological exposure can enable them to set in place legislation on the mining activities creating risks and to improve protection of communities and their environment. The IRD and its partners have communicated the results of these investigations to the people concerned in Aymara and Quechua languages.
1.The Universidad Mayor de San Andrés in La Paz and the Universidad Mayor de San Simón in Cochabamba, Bolivia, Universidad de Chile in Santiago, Chile, Université Paul Sabatier, Toulouse and the Centre for Research in Environmental Epidemiology in Barcelona, Spain. The ToxBol project has been financed by the French Agence Nationale de la Recherche (ANR).
2.Continuous pumping must be conducted to prevent flooding in the mine galleries.
3.The pollutant concentration in the organism rises at each link of the food chain.
4.UMR IRD/ Universités Montpellier 1 and 2/ CNRS
5.UMR IRD / Université de Provence, Aix-Marseille 1
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