Occurrence, health risks, and geochemical mechanisms of fluoride and nitrate in groundwater of the rock-dominant semi-arid region, Telangana State, India

Highly contaminated groundwater can affect the human health and constrain the economic development of a country. For this study 105 groundwater samples were collected in rock-dominant semi-arid (RDSA) region, India and analyzed for hydrochemical parameters including major ions, fluoride, and nitrate. The human health risks due to groundwater fluoride and nitrate contamination were also assessed. The analysis reveals that most of the groundwater samples are alkaline in nature. Hydrochemical types of groundwater in the study area are mainly Ca.Mg-HCO3 and Na-HCO3 types and a few samples belong to Ca.Mg-Cl and Na-Cl types in the RDSA region. Fluoride concentration ranges from 0.5 to 3.5 mg/L, and predominantly eastern part of the study region has higher concentrations of fluoride with comparison to the western part. About 49% of the groundwater samples have fluoride concentration above 1.5 mg/L in groundwater, indicating a high health risk to residents. Eventually, water-rock interactions are the main processes to elevate the fluoride concentration in eastern part of the study area. Nitrate concentration ranges from 12 to 212 mg/L, and northern and southern parts of the study region have much higher nitrate concentrations than the central region of the study area, where nitrate concentration is below 45 mg/L. In terms of nitrate, 55% and 17% of the groundwater samples are under high risk and very high risk categories, respectively, which are not suitable for drinking purposes in the study region. Fertilizer application for crop yields could be one of the reasons for elevated nitrate concentration. The total hazard index for adults ranges from 0.87 to 7.08, and for children 1.17 to 9.57, which suggests that children are at higher health risk than adults in the study region. Therefore, contaminants filters and rainwater harvesting are suggested as measures to reduce the health risk in the area.