ARSENIC IN GROUNDWATER OF LATIN AMERICA —A CHALLENGE OF THE 21ST CENTURY

In Latin America, at least 4 million people depend on drinking water with toxic levels of arsenic (As), originating from geogenic sources. In Argentina, As has been reported in groundwater of the Chaco-Pampean Plain, where 1.2-2 million are exposed to As in drinking water (> 50 µg/L). The aquifers comprisesTertiary aeolian loess-type deposits, with water soluble volcanic glass component (~20%) as the principal source of As. In the Andean range, As is predominantly released by weathering/dissolution of volcanic rocks and sulfide ore deposits. This explains the high levels of As in drinking water of northern Chile. In this region, the principal drinking water source are the rivers (200 to 900 µg/L As), which originate at the foots in the Andean mountains. Arsenic is mobilised following the snow melt and rain following dissolution of the Andean volcanic rocks of the chain, and after transporting it as surface water, before the spring in the rivers. The same process explains the As-release into ground and surface waters in Peru and wide parts of the Andean Highland of Bolivia. In Peru, geogenic As contaminants are present in the Aricota lake (Ilo city), which is fed by the rivers Collazas and Salado. In Central America, As in groundwater was reported for the first time in 1996 in Nicaragua, exceeding the national limit of 10 µg/L. The source of As is geogenic and due to dissolution of volcanic rocks and the sediments of their weathering products. Highest concentrations (up to of 1320 µg/L) of As were found in groundwater of El Zapote and Llano La Tejera towns. In Mexico, the release of As into drinking water supplies of Zimapán area of Mexico occurs by both, the natural dissolution/weathering of the As rich rocks and by mining activities (e.g. through tailings with up to 22,000 mg As/kg). As consequence, the groundwater in the area of Zimapán has high concentrations of As (190 to 650 µg /L; average 380 µg/L). The Salamanca aquifer system located in Guanajuato state, is naturally affected by As from geogenic sources. The highest As concentration observed in groundwater of a well was 280 µg/L. It is thus observed that the contamination of ground- and surface water by As of geogenic origin (predominatly to sediments resulting from volcanic rocks, sulfide ore bodies and volcanic rocks) is one important environmental problem in Latin America that poses a severe challenge during the 21st century.