Characteristics and effects of fluorine release from shallow high-fluoride soils

Areas with high fluoride content in shallow groundwater are usually also the areas where drinking-water endemic fluorosis was found, for example, in Gaomi, China. In recent decades, with the development of industry and agriculture and the improvement in living environments, the groundwater level has slowly declined, and the former high-fluoride conditions of shallow water-soil systems has changed. Shallow high-fluoride soils will release a large amount of fluorine downward under the leaching of rainfall, which poses a potential risk to the deep water-soil system. To evaluate the characteristics and effects of fluorine release from shallow high-fluoride soils, five soil samples were collected to conduct a static fluorine release experiment and a soil column leaching experiment. The results indicated that the release of fluorine from soils conforms to the Elovich model, and in the soil profile, the fluorine release gradually moves from up to down along the runoff direction. Components, such as Ca²⁺, Mg²⁺, K⁺, Cl⁻ and HCO₃⁻, together with F⁻, leached from the soil and migrated downward. With increasing leaching time, the concentrations of soluble salt components gradually decreased, the pH values increased, and the dissolution equilibrium of fluorite shifted toward the dissolution direction.