Assessment and spatial distribution of natural radionuclides and some rare earth elements in the surface sediments of TuyenLam Lake, Central Highlands, Vietnam.

This study investigates the spatial distribution, contamination status, and radiological implications of rare earth elements (REEs: La, Ce, Nd, Sm, Eu, Tb) and natural radionuclides (226Ra, 232Th, 40K) in surface sediments from TuyenLam Lake, Central Highlands of Vietnam. Thirty-five sediment samples were classified into three hydrologically distinct groups based on dominant inflow sources and catchment characteristics. Group 1, influenced by urban development and agricultural runoff, exhibits significantly higher concentrations of La, Ce, Nd, Sm, and Tb, together with elevated activities of 226Ra and 232Th, compared with Group 2, representing predominantly forested catchments, exhibits comparatively lower REE concentrations and radionuclide activities. Group 3, located near the dam outlet, shows intermediate characteristics, reflecting sediment mixing processes. Pollution indices (Igeo and PLI) indicate generally low to moderate relative enrichment, with localized enrichment observed at several sites, particularly within Group 1, whereas enrichment factor values suggest that REE distributions are predominantly controlled by natural geological sources. Radiological hazard assessment shows that, although radium equivalent activity and the external hazard index remain below recommended reference values at most sampling sites, several radiological indices exceed commonly adopted global reference levels at some locations, identifying areas where continued environmental monitoring is warranted. Multivariate statistical analyses reveal strong associations between REEs and the natural radionuclides 226Ra and 232Th, whereas 40K exhibits distinct spatial behavior. Overall, the observed spatial variability is consistent with the combined influence of the regional geological setting, sediment provenance, catchment scale sediment transport processes, and recent land use disturbances, providing a valuable geochemical baseline for sustainable catchment management.