RELEASE OF ARSENIC AND CHEMICAL ALTERATION OF VOLCANIC ROCKS IN ALKALINE VOLCANIC LAKES

Several volcanic alkaline lakes in El Salvador and other parts of Latin American show high concentrations of arsenic as well as calcium. The rocks forming these basins are calc-alkaline rocks generated during explosive acidic eruptions. Chemical alteration of the ash and rocks forming these basins produce waters rich in calcium and bicarbonate. Significant correlations between calcium and arsenic in the waters of these lakes suggest that arsenic is released to the water by similar chemical processes than the release of calcium. In one of the lakes, Ilopango Lake in El Salvador, a positive correlation between diffuse volcanic gases released from the caldera floor and a negative correlation with the arsenic composition of the sediments are observed. This behavior suggests that alteration of the glass material in the ash by these gases is a possible mechanism for calcium and arsenic release.