Deciphering sources of U contamination using isotope ratio signatures in the Loire River sediments: Exploring the relevance of 233U/236U and stable Pb isotope ratios

Uranium's hazardous effects on humans and recent developments in treatment

Uranium, a naturally occurring element, is predominantly recognized for its role as fuel in both civilian and military energy sectors. Concerns have been raised regarding the adverse environmental impacts and health risks associated with uranium mining due to the exposure it causes. Such exposure leads to systemic toxicity, affecting pulmonary, hepatic, renal, reproductive, neurological, and bone health. This review identifies significant research gaps regarding detoxification methods for uranium contamination and recommends further advancements, including genetic modification and exploration of plant compounds. A comprehensive review of published research materials from diverse sources of uranium, including various treatments and hazardous impacts on the human body, was conducted. Additionally, a PRISMA analysis was performed in this study. This review emphasizes the importance of collaboration and the formulation of research-informed regulations to effectively safeguard vulnerable communities from the consequences of contamination. Public discourse often emphasizes the significance of radiotoxicity; however, the non-radioactive chemotoxicity of uranium has been identified as a significant risk factor for environmental exposures, contingent upon species, enrichment, and exposure route. Given these serious health consequences, several methods are being investigated to ameliorate uranium toxicity. In response to these concerns, several techniques, such as phytomedicinal treatments, biochemical approaches, and chelation therapy, have been investigated to minimize the adverse effects of uranium exposure in the human body.

Simultaneous measurement of labile U(VI) concentration and (234U/238U) activity ratio using a Monophos®-based Diffusive Gradients in thin-films sampler

BACKGROUND

In a context of environmental monitoring around installations related to the nuclear fuel cycle, the Diffusive Gradient in Thin-films (DGT) technique captures the integrated concentration of U isotopes in their native environment, yielding comprehensive data on U origin (anthropogenic vs natural), total concentration, and mobility. However, for common deployment times (4-5 days) in moderately basic waters, none of the commercially available binding gels is adapted to measure the total U concentration. So, the development of novel DGT binding gels is timely.

RESULTS

A new DGT sampler, using the Monophos® resin, as well as a new model for the interpretation of the DGT flux, has been successfully developed to measure the labile U concentration (which was also its total concentration) in moderately basic waters (pH ≈ 8). The model accounts for the penetration of uranyl carbonate complexes into the binding gel. Monophos-DGT samplers were able to quantify the total U concentration (accuracy >90 %) in three different mineral basic waters and in a synthetic seawater in laboratory experiments, as well as in situ in the rivers Essonne and Œuf, France. Ion interferences (e.g., Ca2+, Mg2+ and HCO3-), critical when using Chelex and Metsorb resins as binding agents, were overcome by using the new DGT sampler, thus allowing for a longer linear accumulation of U in the tested matrices and, above all, a better detection of U minor isotopes improving the potential of using DGT samplers for water source tracing through isotopic measurements.

SIGNIFICANCE

The use of the new DGT sampler and the new model for the interpretation of DGT flux is recommended to improve the accuracy of total U concentration determinations in field applications. Moreover, simultaneous elemental and isotopic measurements were successfully performed during field application, confirming new perspectives for environmental applications such as identification of U pollution sources by using isotopic signatures.

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.

Temporal trajectories of artificial radiocaesium 137Cs in French rivers over the nuclear era reconstructed from sediment cores

137Cs is a long-lived man-made radionuclide introduced in the environment worldwide at the early beginning of the nuclear Era during atmospheric nuclear testing's followed by the civil use of nuclear energy. Atmospheric fallout deposition of this major artificial radionuclide was reconstructed at the scale of French large river basins since 1945, and trajectories in French nuclearized rivers were established using sediment coring. Our results show that 137Cs contents in sediments of the studied rivers display a large spatial and temporal variability in response to the various anthropogenic pressures exerted on their catchment. The Loire, Rhone, and Rhine rivers were the most affected by atmospheric fallout from the global deposition from nuclear tests. Rhine and Rhone also received significant fallout from the Chernobyl accident in 1986 and recorded significant 137Cs concentrations in their sediments over the 1970-1985 period due to the regulatory releases from the nuclear industries. The Meuse River was notably impacted in the early 1970s by industrial releases. In contrast, the Seine River display the lowest 137Cs concentrations regardless of the period. All the rivers responded similarly over time to atmospheric fallout on their catchment, underlying a rather homogeneous resilience capacity of these river systems to this source of contamination.

Accelerator mass spectrometry measurements of 233U in groundwater, soil and vegetation at a legacy radioactive waste site

Low-level radioactive wastes were disposed at the Little Forest Legacy Site (LFLS) near Sydney, Australia between 1960 and 1968. According to the disposal records, 233U contributes a significant portion of the inventory of actinide activity buried in the LFLS trenches. Although the presence of 233U in environmental samples from LFLS has been previously inferred from alpha-spectrometry measurements, it has been difficult to quantify because the 233U and 234U α-peaks are superimposed. Therefore, the amounts of 233U in groundwaters, soils and vegetation from the vicinity of the LFLS were measured using accelerator mass spectrometry (AMS). The AMS results show the presence of 233U in numerous environmental samples, particularly those obtained within, and in the immediate vicinity of, the trenched area. There is evidence for dispersion of 233U in groundwater (possibly mobilised by co-disposed organic liquids), and the data also suggest other sources of 233U contamination in addition to the trench wastes. These may include leakages and spills from waste drums as well as waste burnings, which also occurred at the site. The AMS results confirm the historic information regarding disposal of 233U in the LFLS trenches. The AMS technique has been valuable to ascertain the distribution and environmental behaviour of 233U at the LFLS and the results demonstrate the applicability of AMS for evaluating contamination of 233U at other radioactive waste sites.