Pb isotopic fingerprinting of uranium pollution: New insight on uranium transport in stream-river sediments

Uranium mill tailings (UMT) present a significant environmental concern due to high levels of radioactive and toxic elements, including uranium (U), thorium (Th), and lead (Pb), which can pose serious health risks to aquatic ecosystems. While Pb isotopic tracers have been widely utilized in environmental studies to identify elemental sources and geological processes, their application in U geochemistry remains relatively limited. In this study, we investigate the distribution and migration of U in stream-river sediments surrounding a decommissioned U hydrometallurgical area, employing Pb isotopes as tracers. Our findings reveal significant enrichment and ecological risk of U, Pb, and Th in the sediments. Uranium predominantly associates with quartz and silicate minerals, and its dispersion process is influenced by continuous leaching and precipitation cycles of typical U-bearing minerals. Furthermore, we establish a compelling positive relationship (r2 = 0.97) between 208Pb/207Pb and 206Pb/207Pb in the stream-river sediments and sediment derived from UMT. Application of a binary Pb mixing model indicates that anthropogenic hydrometallurgical activities contribute to 2.5–62.7% of the stream-river sediments. Notably, these values are lower than the 6.6–89.6% recorded about 10 years ago, prior to the decommissioning of the U hydrometallurgical activity. Our results underscore the continued risk of U pollution dispersion even after decommission, highlighting the long-term environmental impact of UMT. Environmental Implication Lead (Pb) isotopic tracers have been widely used in environmental studies to identify elemental sources and geological processes. However, their application in uranium (U) geochemistry remains limited. In our study, we employ a binary Pb mixing model and multivariate statistical analysis to investigate the prevalence of uranium-dominated contamination in stream-river sediments around a decommissioned U hydrometallurgical area. Through this approach, we quantitatively identify contamination sources in surface sediments, contributing to a better understanding of U geochemical transport behavior in typical aquatic environments. Our findings suggest that effective remediation countermeasures are urgently required to address the potential risks posed by both toxic and radioactive legacies.