Origin of High Fluorine Contents in Drinking Water in the Province Capital of Isparta, SW Turkey

Volcanic rocks consist primarily of pyroxenes, hornblendes, sphenes, biotites, fluorites, fluorapatites, and glassy groundmass as potential fluorine carriers. This fluorine-bearing groundmass is an essential reason for the high fluorine contents of drinking waters of the province capital Isparta with about 250.000 inhabitants. In shallow aqueous systems within the volcanic rocks of the Gölcük area in Isparta, high fluorine contents up to 6.0 mg/l were detected which are higher than those of sedimentary rocks. Fluorine ions are leached mainly from glassy groundmass of the Na and K alkaline volcanic rocks, lesser from fluorine carriers such as pyroxenes, hornblendes, biotites, phlogopites, and fluorapatites. Fluorine contents in groundwaters within these volcanic rocks of Gölcük area are limited by the solubility of fluorite, i. e., also by Ca²⁺ values. Due to low pCO₂ in the barren soils of pyroclastic tuffs such as friable tuffs, pumice tuffs, and ignimbrites, calcite dissolution is limited. Low Ca²⁺ concentrations are enhanced by Na⁺ versus Ca²⁺ ion exchanges. Moreover, F⁻ versus OH⁻ ion exchange is at high pH values due to calcite dissolution with low pCO₂. Finally, it can be deduced that not one single reason is responsible for the high fluorine contents in shallow aqueous systems of the Gölcük area, but a concurrence of several natural factors.