Assessing Groundwater Quality and Health Risks of Nitrogen Pollution in the Shenfu Mining Area of Shaanxi Province, Northwest China

The purpose of this study was to evaluate groundwater quality and health risks of nitrogen pollution in the Shenfu mining area of northwest China. Statistical analysis, Durov diagrams, Gibbs diagrams and correlation analysis were applied to analyse the groundwater chemistry. Entropy weighted water quality index was applied for groundwater quality assessment. The non-carcinogenic risks to adults and children due to drinking nitrogen-contaminated groundwater were assessed using the models recommended by US Environmental Protection Agency. The study shows that the abundances of anions and cations are in the order of HCO3 − > SO4 2− > Cl− and Ca2+ > Na+ > Mg2+, respectively. Gibbs diagrams reveal that groundwater chemistry is mainly controlled by rock weathering. Cation exchange and the dissolution of aluminate minerals, carbonate minerals and halite are the main sources of major ions in the groundwater. More than half of the groundwater in the study area is medium quality, marginally suitable for multiple purposes. NH4–N, NO2–N and organic matter are the main pollutants which mainly derived from agricultural and industrial activities. The mean total hazard index (THI) value of nitrogen for adults and children is 1.563 and 3.126, respectively, which surpasses the permissible limit (THI = 1) recommended by USEPA. Moreover, the NO3–N level in some medium quality water, which is considered suitable for drinking purposes according to Chinese drinking water quality standards, poses high non-carcinogenic risks to adults and children. Therefore, the Chinese government should revise the concentration limit of NO3–N (20 mg/L) in medium quality water so as to ensure the safety of drinking water.