PRELIMINARY ASSESSMENT OF MERCURY CONTAMINATION DUE TO GOLD MINING IN THE RIO RAMIS-LAKE TITICACA WATERSHED, PERU

摘要

In developing countries throughout the world, gold ores are being processed by mercury amalgamation, a technique long banned in the U.S. ― unless a retort operation is used for mercury recovery ― due to mercury toxicity and its effects on the environment. Amalgamation is a simple process that involves contacting a ground, slurried concentrate or ore with mercury in a slightly agitated vessel, usually for several hours. The amalgamated mercury is separated by gravity and then filtered through a fine cloth to collect the gold amalgam as a sponge, which is then fired to remove the final remnants of mercury and produce high quality gold. However, in Peru and other developing countries in South America and throughout the world, tailings are simply discarded into uncontrolled drainages and ponds and the sponge is fired in the open air. Clearly, in this case, amalgamation is not environmental friendly and, to make matters worse, is typically conducted by family members of all ages without proper protection. Furthermore, the technique is inefficient, yielding approximately 50% gold recovery. For the past two years, faculty members from Montana Tech in Butte, MT, USA and the Universidad Nacional del Altiplano in Puno, Peru have teamed to study the La Rinconada Mine Complex located in southern Peru approximately 100 kilometers north of Lake Titicaca and 25 kilometers west of Bolivia. The mining complex is over 5,000 meters above sea level and exists at the foot of a receding glacier in the Andes Mountains. A suite of soil and water samples collected in 2001 documented extensive Hg contamination in the Rinconada area. The present paper summarizes results of a follow-up investigation in July-2002, in which water samples were collected at numerous locations along the 200 km length of the Rio Ramis, from the Rinconada mine complex to Lake Titicaca. In addition, we report new results of Hg analyses of fish from Lake Titicaca. The results of this study have relevance to safety and health concerns for the miners as well as people in downstream communities.