Hydrogeochemical heterogeneity, driving forces, and human health risk of groundwater in an arid alluvial fan plain on Tibetan Plateau

Groundwater quality in arid alluvial fan plains on Tibetan Plateau is deteriorating due to human activities, yet relevant health risks remain understudied. This study investigates 37 groundwater samples from a typical alluvial fan plain of Qaidam basin, to explore the spatial variability and genesis of groundwater chemistry and associated health risks in the arid alluvial fan plains on Tibetan Plateau. The groundwater is slightly alkaline, predominantly characterized by the hydrochemical facies of Cl-Mg·Ca and Cl-Na type. Groundwater NO₃⁻, NO₂⁻, and NH₄⁺ exceed the acceptable drinking water limits by 18.92%, 40.52%, and 16.22%, respectively. Natural forces, including silicates and evaporites dissolution, and cation exchange, dominate the groundwater chemistry. Anthropogenic inputs elevate groundwater nitrate levels (max 106.29 mg/L). The EWQI values range from 13.72 to 265.52, and near 84% of groundwater samples are suitable for domestic drinking. Non-carcinogenic health risk assessment on nitrogen is performed considering deterministic and probabilistic perspectives. All populations are facing health risks exposing to nitrogen-polluted groundwater, with the infants being the highest, followed by children, females, and males, and the risks are mainly caused by nitrate. Mitigation measures are urgently needed. This study could contribute to policy-making for groundwater security in the arid alluvial fan plains worldwide.