Arsenic in a village drinking water supply, Mexico

Abstract

Inhabitants of Tlamacazapa, Mexico display toxic health effects related to arsenic and other metal exposure from well-derived drinking water. Dissolved arsenic concentrations reach 37 ug/L, exceeding the World Health Organization guideline of 10 ug/L. Stable isotope data (2H & 18O-H2O, 13C in DIC, 34S-SO4) indicate that precipitation is recharging the wells through the soil and shallow groundwater. Soil and rock analyses exhibit arsenic concentrations up to 110 and 26 mg/kg, respectively. Major ion concentrations indicate that sewage contamination is entering well water by transport through the thin soil and shallow groundwater. Sewage contamination is a result of open-air excretion by humans and free-roaming animals.

Arsenic and sewage contaminant concentrations correlate strongly and the presence of sewage apparently promotes the release of arsenic from aquifer materials. It is likely that arsenic mobilization is the result of competition with phosphate and other sewage-derived anions for sorption sites.