Minor and trace element investigations have been performed on groundwaters of Ischia Island, which is located at the western edge of the bay of Naples. Ischia is formed entirely of Quaternary volcanic rocks. Intense seismicity, widespread fumaroles and thermal springs witness the persistent state of activity of its magmatic system. Groundwater samples, 58 from shallow thermal wells and 15 from thermal springs, were analysed for 72 elements by ICP-MS; temperature, pH and electrical conductivity (EC) were measured at the sampling site. Analytical data indicate clearly that the concentrations in the water of some elements, such as As, Be, Cu, Fe, Mn, Sb, Se and Tl, are often higher and sometimes much higher than the intervention limits fixed by the Italian Law DM 471 (25/10/1999) for water. Worthy of mention are the very high As values, reaching >1,000 lg/l in some wells. By means of R-mode factor analysis, 30 of 72 analysed elements were grouped as elemental associations representative of lithological type, water composition and, possibly, mineralization. Ischia thermal groundwaters are the result of mixing, in variable amounts, of deep magmatic fluids that are rich in metallic elements, with marine and/or meteoric waters. R-mode factor analysis and elemental association factor score distributions of the four-factor model confirm the existence of flux of magmatic mineralised fluids with marine and/or meteoric waters. Recharge by seawater intrusions occurs mostly in the north-western area of the island whereas the influence and control of magmatic mineralised fluids is clearly accentuated in the areas of Panza-Citara, Porto di Forio-Fango and Citara- Lido dei Maronti fracture alignments. The observedcompositional variability of the analysed groundwaters, even in wells lying close to one another, is due to the local hydrodynamic conditions, controlled mostly by complex fault and fracture systems, which may represent preferential thermal water outflow routes. In general, the average minor and trace element compositions of Ischia thermal waters, when compared with the composition of sea and river water, show an enrichment in metallic elements such as As, Sc, V, Cr, Zn, Mo, U, W, Au, Hg. This paper points out that, in addition to the anthropogenic source, natural contribution also plays an important role in determining the high concentrations of toxic elements in groundwaters, which create health and acceptability problems.
|Titolo:||Natural contribution of harmful elements in thermal groundwaters of Ischia island (southern Italy)|
|Data di pubblicazione:||2003|
|Appare nelle tipologie:||1.1 Articolo in rivista|
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