Abstract
Hydrogeochemical and stable isotope analyses and geochemical modeling were carried out to identify the major geochemical processes controlling the groundwater chemistry and fluoride contamination in the aquifers of the Yuncheng Basin, China, an area with complex hydrogeochemical conditions and severe fluoride contamination of the groundwater. The major findings of this case study include the following: 1) Cation exchange and salt effects are vital controls on the enrichment of fluoride in groundwater in the area by reducing the activity of Ca2+/F- in groundwater via ion complexation. Cation exchange increased the fluoride concentration by 2.7 mg/L when the Na/Ca molar ratio increased from 0.24 to 9.0, while the salt effect led to a ca. 5–10% increase in complex F- in groundwater due to the further dissolution of fluoride-bearing minerals in the aquifers, as suggested by a model calculation. 2) Anthropogenic contamination from pesticide and fertilizer use and industrial waste discharge is also a main source of fluoride in the groundwater. 3) Evaporation and ion effects favor the enrichment of fluoride in groundwater by encouraging the removal of Ca via precipitation. 4) The desorption of fluoride from mineral/organic matter surfaces is enhanced under alkaline conditions and a high HCO3 content in groundwater.
Highlights
Groundwater is becoming increasingly important for the drinking water supply, ecosystem health and economic development as the global population grows
3) Evaporation and ion effects favor the enrichment of fluoride in groundwater by encouraging the removal of Ca via precipitation
Water samples were collected after the in situ physicochemical parameters, including temperature, pH and electrical conductivity (EC), were stable; all the parameters were measured by portable meters
Summary
Groundwater is becoming increasingly important for the drinking water supply, ecosystem health and economic development as the global population grows. Groundwater is fairly ubiquitous, but its conditions vary enormously, and exploitation is often undertaken with a limited understanding of the hydrochemistry and without sufficient evaluation of the resource quality, especially in developing countries. Toxic elements, e.g., fluorine, may reach hazardous concentrations in groundwater as a result of specific hydrogeochemical processes and contamination due to human activities. Elevated concentrations of fluoride in groundwater that exceeded the World Health Organization (WHO) limit of 1.5 mg/L in drinking water have. Geochemical processes controlling groundwater F contamination in area with complex hydrogeochemical conditions no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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