GEOLOGICAL SETTING, SOURCES, AND HEALTH EFFECTS OF ARSENIC IN GROUNDWATERS OF MEXICO. AN OVERVIEW

Arsenic in groundwaters of Mexico originates from various natural sources related to specific geological settings. Coexistence of active tectonic zones, mineralized belts, volcanic and geothermal areas enhances the likelihood of finding As enrichment in aquifers. On the other hand, the fact that groundwater supplies two thirds of the country's potable water increases the possibility of the population chronic exposure to arsenic. Abundance of As minerals or arsenic-containing ores is one of the main sources of contamination at various locations. High temperature replacement deposits in carbonates and skarn, contain the largest proportion of As minerals. Arsenopyrite is the main mineral that may release As to groundwater in mining zones like Zimapán, central México. Groundwater abstraction regimes also have contributed to increase the concentrations and exposure of the population to As. At Comarca Lagunera, the first location where As health effects were observed, several hypothesis have been proposed to explain water contamination. One of the most recent studies showed its relation with evaporation processes within the granular aquifer. Intense groundwater exploitation resulting from the economic development of the area based on agriculture and dairy production promoted As-bearing water intake. Arsenic is also present in districts with volcanogenic mineralization. In addition, weathering of acid volcanic rocks has also identified to be an As source at other areas. High temperature deep groundwater flow contains As in some regions like the fluoride-polluted aquifer of San Luis Potosí and at Los Altos de Jalisco, north-central, and western México. Epidemiological and toxicological studies have been developed to reveal the potential or actual damage of As-polluted water intake at several towns. Investigations included visual recognition of specific symptoms, identification and measure of biomarkers and genotoxicity tests. Although As presence has been detected in some areas of the country, specific sources, geochemical processes, and environmental effects need to be determined for other areas with favorable geological conditions for groundwater As pollution. This knowledge is essential to develop sustainable measures to avoid exposure of the population to As-tainted water.