Occurrence, Controlling Factors and Health Risks of Cr6+ in Groundwater in the Guanzhong Basin of China

Recently, high levels of Cr6+ in groundwater have been found and are threatening public health in the Guanzhong Basin of China. For this reason, this study aims to specify the occurrence and spatial distribution of groundwater Cr6+ and to analyze the favorable hydrogeochemical environment elevating its concentration in the Guanzhong Basin. The impacts of Cr6+ on human health were also estimated based on the health risk assessment model recommended by the USEPA. Results show that 45.40% and 37.36% of the groundwater samples contain Cr6+ concentration lower than 10 μg/L and ranging within 11–50 μg/L, respectively. And they are predominantly of HCO3-Ca and HCO3-Ca(Mg) water type. About 17.24% of the total water samples present Cr6+ concentrations exceeding the acceptable limit for drinking purpose of 50 µg/L, and are mainly classified as HCO3-Na water type. Low Cr6+ groundwater is mainly observed in the alluvial aquifer. Cr6+ concentration in the samples from the loess aquifer is higher due to low groundwater velocity caused by the low permeability of loess, as verified by the relationship between Cr6+ and major ions. The relationship between Cr6+ and pH and molar ratio of Na+/(Na+ + Ca2+) suggest that alkaline environment and cation exchange are beneficial to high concentration of Cr6+ in groundwater. Industrial activities are also responsible for the elevation of Cr6+ to some extent. Health risk assessment results show that the adults and children in the study area face higher carcinogenic risks than non-carcinogenic risk induced by Cr6+.