Fluoride levels in water sources inside the crater of Furnas volcano: Potential health implications for local communities and tourists

Fluoride, a naturally occurring mineral, is widely recognized for its dual role in human health. At optimal concentrations, it provides dental benefits; however, excessive fluoride can lead to dental and skeletal fluorosis. Volcanic regions are known for their geothermal water sources that contain elevated levels of fluoride, raising concerns about potential health impacts on local populations. This study focuses on the Furnas volcano region at the Island of São Miguel, Azores, where natural springs are promoted for their therapeutic and medicinal properties. However, these springs also raise concerns about health risks due to fluoride exposure, as they are freely consumed by locals and tourists without any formal treatment or monitoring. Eighteen water samples were collected from natural springs in the village of Furnas. In situ measurements were taken forphysicochemical parameters such as pH, temperature, and conductivity. Fluoride concentrations were quantified using a potentiometric method with a fluoride ion-selective electrode. To assess risks, we estimated daily fluoride intake (DFI) and calculated the Hazard Quotient (HQ) for both children and adults. The fluoride concentrations in the samples ranged from 0.47 mg/L to 5.48 mg/L, with 72 % exceeding the recommended limit of 1.5 mg/L for drinking water. Significant correlations were found between temperature, conductivity, and fluoride concentration. Hazard Quotient values indicated potential health risks for children consuming untreated spring water. Waters categorized as hypothermal exhibited significantly lower fluoride concentrations compared to mesothermal, thermal, and hyperthermal samples. These findings highlight the impact of volcanic activity on fluoride levels in the natural springs of Furnas, emphasizing the need for regular monitoring and public awareness. While these waters are frequently consumed for their perceived health benefits, elevated fluoride levels may pose health risks to residents and tourists, demanding informed decision-making and enhanced water safety measures.