Cumulative health risk assessment of multiple chemicals in groundwater based on deterministic and Monte Carlo models in a large semiarid basin

Intense anthropogenic activities have led to deterioration of groundwater quality worldwide. Scientific assessments of groundwater quality and human health risks are the premise to ensure water safety and residents’ health. Based on 321 groundwater samples collected from the Guanzhong Basin (GB), this study comprehensively assessed the groundwater quality and potential risks of As, F−, NO3–N, and Cr6+ to human health for the first time in GB. With differences in hydrogeological settings and human activities, the chemical composition of groundwater in GB exhibited wide spatial variability. Results of the integrated-weight water quality index (IWQI) showed that Cr6+, As, NO3–N, and F− have stronger effects on groundwater quality than other ions. Except for As, other pollutants (Cr6+, NO3–N, and F−) distributed mainly in the north of the Wei River, with northeast part of GB had much poorer groundwater quality than other areas. The human health risk assessment showed that carcinogenic risks associated with As and Cr6+ were higher for adults than for children, whereas non-carcinogenic risks posed by As, F−, NO3–N, and Cr6+ were higher for children. The primary exposure pathway for both carcinogenic and non-carcinogenic risks was daily oral ingestion. According to the spatial distribution of total carcinogenic and non-carcinogenic hazard indices, both adults and children living in the north of GB are at high risk. Monte Carlo simulations were used to assess model uncertainty and to determine pollutant treatment priority. The probability of non-carcinogenic risk for children is up to 92.25%. Sensitivity analysis results indicated that the main threat to residents' health is the high concentrations of F− and Cr6+ in groundwater. Hydrogeochemical analyses revealed that the poor quality of groundwater in the northeast of GB is mainly controlled by the geological background and extensive evaporation due to long-term irrigation activities. The findings of this study laid the foundation for the rational development and utilization of groundwater resources and the protection of residents' health in GB. It can also be used as references for the study of groundwater environment and human health risks in other similar areas.