Characteristics And Genesis Of High-Fluoride Groundwater In Hengshui City, The North China Plain

Fluoride is an important element for human health. A small amount of fluoride intake can stop dental caries. However, excessive intake can cause endemic fluorosis, such as dental fluorosis, fluorosis. In this study, Hengshui in Hebei Province with high flluorosis is chosen as a representative area. By means of the data collection of geological and hydrogeological characteristics, field investigation, sample collection and test analysis, the distribution characteristics of groundwater fluoride, and the formation mechanisms are studied.Sixty-two groundwater samples, one surface water samples, and fifty sediments samples, and fifty pore water samples were collected and analyzed for chemical and/or isotopic components. The main conclusions are shown as follows.1. Shallow high F- groundwater(F- >1.0 mg/L) belonged to Cl–SO4–Na–Mg,HCO3–Cl–SO4–Na and SO4–Cl–Na–Mg types, while deep high F- groundwater to HCO3–SO4–Cl–Na and Cl–SO4–Na types.2. Results of hydrogen and oxygen isotope show that shallow groundwaters originated from precipitation, and were affected by evaporation. The environment conditions affect the Hydrogen and oxygen isotopes of deep aquifers. The deep groundwater formed time longer, which had lower δD and δ18O values because of low temperature in the process of precipitation recharge. Results of carbon isotope show that DIC of groundwater originated from rock weathering and biodegradation of organic compounds.3. High F- groundwaters mainly occurred at the depths around 30 m, 200 m, and 300 m. Spatially, high F- groundwaters were mainly found in the southeast of the study area.4. Groundwater p H ranged between 7 and 9, showing that slightly alkaline environment was conducive to the enrichment of fluoride. There is positive correlation between Na+ and F- in groundwater. Ca2+ and Mg2+ inhibit the release of fluoride in the water.5. The main hydrogeochemical processes occurring in groundwater systems included dissolution-precipitation, evaporation, ion exchange and adsorption-desorption process. The genesis of high fluoride water was related to the environmental conditions of its occurrence and migration. The high fluoride shallow groundwater is mainly controlled by evaporation. The high fluoride deep groundwater is dominated by dissolution-precipitation, ion exchange, and adsorption-desorption process.