Origin and risk assessment of natural radioactivity in groundwater from the Eastern Gonghe Basin, Tibetan Plateau

This study systematically investigates natural radioactivity in groundwater from the densely populated eastern Gonghe Basin in Qinghai Province, aiming to reveal its spatial distribution, origins, and potential health risks. The characteristics of gross-α and gross-β activities, as well as the concentrations of nuclide including ²³⁸U, ²³²Th, and ²²⁶Ra, have been investigated in groundwater samples from 12 groups encompassing various types such as hot springs and artesian wells across different aquifer systems. Correlation analysis and dose estimation models were applied to preliminary estimate the radiation exposure to local residents and to explore the genesis and hazards of natural radioactivity in groundwater. Results indicate that overall groundwater radioactivity in the Gonghe Basin remains within acceptable limits, with mean gross-α and gross-β activity concentrations of 0.32 <i>Bq/L</i> and 0.27 <i>Bq/L</i>, respectively. Approximately 83.33% of samples comply with relevant national standards. However, two fault-controlled high-temperature spring samples exhibited gross-α activity exceeding regulatory limits, with one also showing elevated gross-β activity surpassing China's Class III groundwater quality standards for radioactivity. Furthermore, single-radionuclide α radioactivity from ²³⁰Th, ²²⁶Ra, ²¹⁰Po, and ²³²Th exceeded regulatory thresholds in some samples, suggesting potential long-term health risks. While most samples complied with effective dose limits, four showed ²¹⁰Po α radioactivity exceedances within controllable risk ranges. The findings suggest that groundwater radioactivity in the region is primarily controlled by geological structures, lithology, and hydrothermal conditions, with fault zones and high-temperature environments serving as key factors in radionuclide enrichment. This research provides scientific foundation for the sustainable development of geothermal resources and the prevention of radioactive water contamination. Continuous monitoring of high-radioactivity hot springs and prudent resource utilization are recommended.