MAJOR AND TRACE-ELEMENTS GEOCHEMISTRY IN THE GROUND WATERS OF A VOLCANIC AREA - MOUNT-ETNA (SICILY, ITALY)

Thirty-five ground-water samples have been collected from wells, sprin gs and drainage galleries on Mt Etna volcano for the determination of major, minor and trace elements in solution. Attention has been focuse d in particular on dissolved minor add trace elements, for most of whi ch no data were available in the studied area. In general, dissolution of solids into Etna's ground waters follows from strong interaction b etween water of meteoric origin, CO2 gas of magmatic origin and the vo lcanic rocks of the aquifers. However, the R-mode analysis allowed to distinguish several sources of solutes: Al, Co, Ni, Fe, Si, As would d erive mainly from alteration of the volcanic rocks of Etna; SO4=, K, N a, V, Sr, Mo, Cr and calculated p(CO2) would instead indicate a major contribution of volcanic gases (mostly CO2 and SO2); and TDS, HCO3=, L i Mg, B and Cl- would indicate a derivation from both these sources. S e, Hg, Cu and Mn would derive from hydrothermal fluids, and Ca would d erive both from this latter contribution and from rock alteration. The comparison between trace elements abundance in Etna's ground waters a nd that in the ground waters of other areas of Italy showed that, in g eneral, Etna's waters, like other volcanic ground waters, are enriched in Li, Mn, Si, V, As and Mo. Furthermore, in the areas of Mt Etna whe re the contribution of volcanic gas to the aquifers is greatest, groun d waters are also enriched in B, Se, Co, Hg, Al, Fe and Ni. The obtain ed results show clearly that, in active volcanic areas, many dissolved elements can attain levels that can be appreciably different from tho se indicated by WHO for drinking water. Therefore, the local geologica l factors which can influence the geochemical behaviour of these eleme nts in solution should be taken into account when establishing nationa l standards for drinking-water quality. In consideration of the local natural background values, concentrations of dissolved elements that d iffer from the guideline values should be accepted in areas with pecul iar geological characteristics, provided that the elements under consi deration do not have a direct influence on health. (C) 1998 Elsevier S cience Ltd. All rights reserved.