Source apportionment and health risk assessment of fluoride in water resources, south of Fars province, Iran: Stable isotopes (δ18O and δD) and geochemical modeling approaches

Abstract

In this study the key factors influencing fluoride enrichment in water resources, south of Fars province, Iran are investigated. For this purpose, hydrogeochemical, statistical and isotopic studies were conducted on water and dominant rock types. Impact on human health is also considered. The results indicated that fluoride concentrations in water resources range from 0.06 to 4.95 mg/L, while 67.5% of the analysed samples displayed concentrations above the world health organization guidelines for drinking water. Fluoride enrichment is associated with NaCaMgClSO4 water type and the chemical evolution of groundwater along flow path. F/Cl ratio, δ18O and δD results of water samples indicated that evaporation favored F‾ enrichment. Calculated mineral saturation indices and statistical analysis indicated that while the lithological units play a prominent role in fluoride anomalies, anthropogenic sources are negligible. Inverse geochemical modeling and calculated Chloro-Alkaline indices proved the occurrence of reverse ion exchange processes in the groundwater. Conducted leaching tests and X-ray diffraction data on abundant geological formations revealed dolomite and clay minerals as two likely candidates for contributing fluoride to the aquifers. The alkaline nature of water seems to have intensified the F‾ exchange in clay minerals with OH‾ in water. Fluoride exposure risk assessment revealed that children and adults are prone to fluoride-related diseases caused by ingestion of fluoride-rich water. Considering the prevailing climatic conditions and the ongoing geochemical processes, fluoride level in local aquifers will undoubtedly rise with time unless preventive and remediative measures are taken by the responsible authorities.