Hydrogeochemical Characteristics, Groundwater Quality, and Health Risks from Hexavalent Chromium and Nitrate in Groundwater of Huanhe Formation in Wuqi County, Northwest China

This study was carried out to investigate the current status of groundwater quality in Wuqi County, northwest China. The health risk assessment was also performed to quantify the negative impacts of hexavalent chromium (Cr6+) and nitrate (NO3-) in groundwater on human health by fully considering the gender and age of local residents. For this study, thirty groundwater samples were collected from wells and boreholes distributed in the study area and analyzed for pH, total dissolved solids (TDS), total hardness (TH), major ions (Na++K+, Ca2+, Mg2+, HCO3-, SO42-, and Cl-), NO3-, nitrite (NO2-), and Cr6+. Statistical analysis and graphical approaches were adopted to delineate the physicochemical parameters and hydrochemistry of groundwater. Fuzzy comprehensive method was applied in this study to appraise overall groundwater quality. The model recommended by the Ministry of Environmental Protection of the People's Republic of China was selected to assess the non-carcinogenic and carcinogenic risks caused by Cr6+ and NO3- through drinking water intake. Indicated by statistical mean values, the order of cations is Na++K+>Ca2+>Mg2+, and that of anions is SO42->Cl->HCO3-. The averages of TH, TDS, NO3-, and NO2- are 432, 1253, 23.2, and 0.099mg/L, respectively. Piper diagram indicates that groundwater in the study area is SO4Cl-Na type, SO4Cl-CaMg type, and HCO3-Na type. Gibbs diagrams suggest that the major ion chemistry of groundwater in the area is governed by rock weathering and water-rock interaction, while evaporation plays a minor role. According to the results of groundwater quality assessment, over one-third (36.67%) of the groundwater samples are of poor or very poor quality. Through oral pathway, female and male adults in the study area face acceptable non-carcinogenic risks, while children face unacceptable non-carcinogenic risks caused by Cr6+ and NO3-. Both children and adults face unacceptable carcinogenic risks from Cr6+. In addition, children face higher carcinogenic risks than females and males owing to smaller body weight than adults. This study may provide local authorities with insights into making scientific decisions for sustainable groundwater exploitation and efficient groundwater environmental protection.