Occurrence and Health Risk Assessment of Fluoride and Nitrate in the Groundwater of the Xilin Gol Grassland in the Inner Mongolian Plateau: A Case Study of the Shengli Basin, China

Groundwater is the main water supply source especially in arid/semiarid regions, whose quality has been widely concerned. To clarify the spatial distribution, occurrence and the impacts of fluoride (F-) and nitrate (NO3-) in groundwater, 26 groundwater samples were collected from domestic water wells and agricultural irrigation wells in Xilinhot city, a famous tourist city on the Xilin Gol grassland of China. The integration of statistical analysis and hydrochemical diagrams and the model of health risk assessment recommended by the USEPA were carried out in the study. The analysis reveals that the groundwater is weakly alkaline, and the hydrochemical facies are mainly HCO3-Ca<middle dot>Mg and SO4<middle dot>Cl- Na + K, which are controlled by natural processes and anthropogenic factors in the study area. Groundwater with high fluorine is chiefly located in the west of the study area, and high-nitrate groundwater is chiefly located in the middle and southern parts of the study area. Fluoride in groundwater is predominantly derived by the weathering and dissolution of fluoride-bearing minerals and ion exchange. The values of hazard index (HI) of 65.38% groundwater samples were greater than the recommended limit for noncarcinogenic risk (HI = 1) for children, followed by 38.46% for adult females and 30.77% for adult males. The water quality of the urban water supply should be treated. At the same time, contaminant filters and other instruments should be supplied to residents in pastoral area to reduce fluoride and nitrate concentration in drinking water, which will mitigate health risks and ensure the safety of drinking water in the study area.