Groundwater quality characteristics and health risk assessment in the valley plain area of the western Qinghai-Tibet plateau.

Accurate evaluation of groundwater chemistry, quality, and human health risk could provide detailed and robust evidence of groundwater utilization. Gaer County is an important residential area in western Tibet. A total of 52 samples were collected from the Shiquan River Basin in Gaer County in 2021. Principal component analysis, ratiometric analysis of major ions, and geochemical modeling were conducted to clarify the characteristics of hydrogeochemical compositions and the controlling factors. The groundwater chemistry type is dominated by HCO3-Ca, and its ion concentration from high to low is Ca2+ > Na+ > Mg2+ > K+ and HCO3- > SO42- > Cl- > NO3- > F-. The groundwater compositions were determined by calcite and dolomite dissolution with cation exchange reaction. The human activity causes nitrate contamination, while arsenic contamination is attributed to surface water recharge. According to the Water Quality Index, 99% of the samples meet the requirements of drinking water. Groundwater quality is affected by the arsenic, fluoride, and nitrate concentrations. According to the human health risk assessment model, the cumulative noncarcinogenic risk (HITotal) values for children and the CR values of arsenic (CRArsenic) for adults are higher than 1 and 1E-6, respectively, which are unacceptable risk values. Therefore, appropriate remedial measures are recommended to reduce nitrate and arsenic concentrations in groundwater sources for protecting against further health risks. This study can provide theoretical support and effective groundwater management experience for ensuring groundwater safety in Gaer County and other similar regions around the world.