February 12, 2005
This picture was taken during a scientific expedition in January, 1995 to the Argentinian-Chilean Andes. The location was a semi-desert high-altitude area studded by volcanoes. The "Cerro Peinado" ("Combed Mountain"), whose top is 5,740 m (about 18,840 ft), is a perfectly conic, dormant volcano located north of "Paso de San Francisco." Visible remains of past eruptive activity are easy to identify here. The rock chute at center is an example of magma buried in a sandy background, close to an arsenic-laden lake (foreground).
Arsenic (As) can be of natural origin but is a cancer-related environmental toxic trace element. Suggested As concentrations in drinking water should be less than 10 micrograms/liter. Arsenic rarely is found in a free state -- it's generally combined with sulphur, oxygen and iron. As can occur in both organic and inorganic forms. For example, it's present in coal, lead, zinc, gold and copper ores. The commonly existing species in groundwater are in two forms: arsenite [As (III)] -- the reduced state of inorganic arsenic, and arsenate [As (V)] -- the oxidized state of inorganic arsenic. As (III) is more mobile and toxic than is As (V) for living organisms.Related Links: