ABSTRACT
ABSTRACT: Inhabitants of the village of Tlamacazapa display toxic health effects related to arsenic and other metal exposures from shallow well water. Arsenic is present in the dissolved phase up to a concentration of 37g/L, exceeding the World Health Organization guideline of 10g/L. Stable isotope analyses (2Hwater &
18Owater) indicate precipitation is recharging the wells through the soil and shallow groundwater. Soil and rock analyses show that arsenic is present at concentrations up to 56 mg/kg and 26 mg/kg, respectively. High concentrations of Cl, K, Na, NO3 and SO4 suggest sewage or manure contamination in the well water occurs via surface runoff into the unprotected wells or through the thin soil and shallow groundwater. Open air excretion and free-roaming animals are sources of this contamination. Arsenic and sewage contaminant concentrations are strongly correlated and the presence of sewage apparently promotes the release of arsenic from aquifer materials. It is likely that arsenic mobilization is the result of desorption associated with arsenate-phosphate competition for sorption sites.
