Anomalous concentrations of fluoride in groundwater were identified in 19 drilling wells in the Salto-Indaiatuba region, São Paulo State, with an average concentration of 3.03 mg dm-3 and a maximum of 6.95 mg dm-3, which constitute a restriction for the water's usage in terms of human consumption. The wells exploit water from the Tubarão Aquifer (sedimentary, granular) and Crystalline Aquifer (granitic, fractured), used for sanitary or industrial purposes. These groundwaters are typically HCO3 and HCO3-SO4 types, with high concentrations of HCO3-and Na+ and high pH-values between 7.5 and 10.0. The highest concentrations of F- are associated to the Tubarão and Tubarão/Crystalline aquifer drilling wells. The presence of F- in groundwater is controlled by these high pH-values, alkalinity, and fluorine availability. The source of fluoride in the Tubarão and Crystalline Aquifers can be related to the percolation of hydrothermal fluids associated with Mesozoic lava flow, emplaced due to the opening of Atlantic Ocean and/or hydrolysis of fluorine-rich minerals and clay minerals.
Fluoride; groundwaters; Tubarão Aquifer; Crystalline Aquifer
