Geochemical evaluation of fluoride enrichment in the complexe terminal aquifer and its implications for human health in Oued Souf, Algerian Sahara

This research evaluates the geochemical processes responsible for high fluoride concentrations in the Complex Terminal (CT) aquifer and the associated health risks related to water consumption in the Oued Souf region. Twenty groundwater samples were analyzed to measure pH, electrical conductivity (EC), total dissolved solids (TDS), major ions, and fluoride. Mineralogical, petrographic, and geochemical analyses were also conducted on reservoir rock samples. The study adopted a multidisciplinary approach, utilizing water quality indices (EWQI and PGI), a health risk assessment method (HRA), and various hydrogeochemical tools, such as Piper, Gibbs, and Chadha diagrams, as well as chloro-alkaline indices, saturation indices, and statistical analysis. The results reveal that the groundwater is highly mineralized, very hard, and contains fluoride levels ranging from 1.86 to 2.65 mg/L, exceeding the potable water threshold of 1.5 mg/L. The application of the Entropy Water Quality Index (EWQI) method indicates that TC water is of very poor quality, while the Groundwater Pollution Index (PIG) method highlights significant to very significant pollution. The hydrogeochemical study identified two main water types: Na–Cl and Mg–Ca–SO₄. Furthermore, fluoride enrichment is primarily due to geogenic sources such as the dissolution of evaporites and carbonates, silicate weathering, and cation exchange. The health risk assessment (HRA) shows a higher health risk for children, who are more exposed to fluoride toxicity through drinking water compared to adults. Consequently, this study calls for more effective water management strategies and the implementation of treatment techniques to ensure a safe and sustainable water supply in Oued Souf.