Fluoride content in drinking water supply in São Miguel volcanic island (Azores, Portugal)

• Published in: The Science of the total environment Vol. 432; pp. 23 - 36
• Main Authors: Cordeiro, S., Coutinho, R., Cruz, J.V.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.08.2012; Elsevier
• Subjects: Applied sciences; Azores; Chromatography, Ion Exchange; Drinking Water - analysis; Drinking water and swimming-pool water. Desalination; Earth sciences; Earth, ocean, space; Environmental Monitoring; Exact sciences and technology; Fluoride; Fluorides - analysis; Geochemistry; Groundwater - analysis; Groundwater - chemistry; Island hydrology; Mineralogy; Pollution; Portugal; Silicates; Spectrophotometry, Atomic; Volcanic aquifers; Water geochemistry; Water quality; Water Supply; Water treatment and pollution; Azores; Atlantic Ocean Islands; Portugal; Europe; Azores, Sao Miguel, Ponta Delgada; ANE, Atlantic, Azores; ANE, Atlantic, Azores, Sao Miguel; Island hydrology; Fluoride; Azores; Water quality; Volcanic aquifers; Drinking water; Water supply; Geochemistry; Fluorides; Aquifers; Concentration measurement; Hydrology; Hydrochemistry; Ground water
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2012.05.070

High fluoride contents in the water supply of the city of Ponta Delgada, located in the volcanic island of São Miguel (Azores, Portugal) have been reported. Dental fluorosis in São Miguel has been identified and described in several medical surveys. The water supply in Ponta Delgada consists entirely of groundwater. A study was carried out in order to characterize the natural F-pollution of a group of springs (30) and wells (3), that are associated to active central volcanoes of a trachytic nature. Two springs known for their high content in fluoride were sampled, both located in the central volcano of Furnas. The sampled waters are cold, ranging from slightly acidic to slightly alkaline (pH range 6.53–7.60), exhibiting a low electrical conductivity (springs range 87–502μS/cm; wells range 237–1761μS/cm), and are mainly from the Na–HCO3, Na–HCO3–Cl and Na–Cl–HCO3 water types. Results suggest two main trends of geochemical evolution: silicate weathering, enhanced by CO2 dilution, and seawater spraying. Fluoride contents range between 0.17mg/L and 2mg/L, and no seasonal variations were detected. Results in the sources of the water supply system are lower than those of the Furnas volcano, which reach 5.09mgF/L, demonstrating the effect of F-rich gaseous emanations in this area. Instead, the higher fluoride contents in the water supply are mainly due to silicate weathering in aquifers made of more evolved volcanic rocks. ► High fluoride content in volcanic rock aquifers is exploited for public water supply. ► Groundwater composition is modified by water–rock interaction and marine airborne salts. ► Fluoride enrichment in perched aquifers is mainly due to silicate weathering. ► High F contents are observed in mineral discharges with a volcanic source.