Radionuclide distribution across soil layers and in river sediments: insights from the Aragats Massif, Armenia

Understanding the distribution and mobility of natural and artificial radionuclides in soil and river sediments is crucial for environmental monitoring and radiation risk assessment. This study investigates the vertical distribution of K-40, Ra-226, Th-232, and Cs-137 in the soils and river sediments of the Aragats Massif, Armenia, a region of interest for nuclear energy development. The research aims to establish baseline radionuclide levels, evaluate their mobility, and assess potential environmental implications. Soil and sediment samples were analyzed for radionuclide activity concentrations using gamma spectrometry with HPGe detector. Descriptive statistical methods and non-parametric tests were applied to assess distribution patterns and potential influencing factors. The results indicate that natural radionuclide activity concentrations in soils are consistent across different depths, suggesting a strong geogenic control over their distribution. Cs-137, primarily concentrated in the upper soil layers (0-10 cm), exhibits limited vertical migration with a tenfold decrease in activity observed in deeper layers. Elemental concentrations of potassium, radium, and thorium were predominantly below global average values, and according to the geoaccumulation index of natural radionuclides, the surface soil of Aragats Massif is practically uncontaminated. River sediment analysis reveals higher natural radionuclide activity in fast-flowing mountain rivers, while Cs-137 activity remains below detectable levels near the Armenian Nuclear Power Plant, with the highest concentrations observed in high-altitude sediments, consistent with global radioactive fallout. These findings establish a baseline for future radioecological monitoring in the region, particularly in the context of potential nuclear energy developments in Armenia. The study provides insights into radionuclide behavior in soil and sediments, supporting regional environmental assessments and transboundary water resource management. Further investigations should focus on long-term monitoring and geochemical modeling to improve predictions of radionuclide mobility under changing environmental conditions.