The Chemistry and Toxicology of Depleted Uranium

A comparison of the chemo- and radiotoxicity of thorium and uranium at different enrichment grades

Uranium and thorium are heavy metals, and all of their isotopes are radioactive, so it is impossible to study chemical effects entirely independent of the radiation effects. In the present study, we tried to compare the chemo- and radiotoxicity of both metals, taking into account deterministic radiation damages reflected by acute radiation sickness and stochastic radiation damages leading to long-term health impairments (e.g., tumor induction). We made at first a literature search on acute median lethal doses that may be expected to be caused by chemical effects, as even acute radiation sickness as a manifestation of acute radiotoxicity occurs with latency. By simulations based on the biokinetic models of the International Commission on Radiological Protection and using the Integrated Modules for Bioassay Analysis software, we determined the amounts of uranium at different enrichment grades and thorium-232 leading to a short-term red bone marrow equivalent dose of 3.5 Sv considered to cause 50% lethality in humans. Different intake pathways for incorporation were considered, and values were compared to the mean lethal doses by chemotoxicity. To assess stochastic radiotoxicity, we calculated the uranium and thorium amounts leading to a committed effective dose of 200 mSv that is often considered critical. Mean lethal values for uranium and thorium are in the same order of magnitude so that the data do not give evidence for substantial differences in acute chemical toxicity. When comparing radiotoxicity, the reference units (activity in Bq or weight in g) must always be taken into account. The mean lethal equivalent dose to the red bone marrow of 3.5 Sv is reached by lower activities of thorium compared to uranium in soluble compounds. However, for uranium as well as thorium-232, acute radiation sickness is expected only after incorporation of amounts exceeding the mean lethal doses by chemotoxicity. Thus, acute radiation sickness is not a relevant clinical issue for either metal. Concerning stochastic radiation damages, thorium-232 is more radiotoxic than uranium if incorporating the same activities. Using weight units for comparison show that for soluble compounds, thorium-232 is more radiotoxic than low-enriched uranium in the case of ingestion but even more toxic than high-enriched uranium after inhalation or intravenous administration. For insoluble compounds, the situation differs as the stochastic radiotoxicity of thorium-232 ranges between depleted and natural uranium. For acute effects, the chemotoxicity of uranium, even at high enrichment grades, as well as thorium-232 exceeds deterministic radiotoxicity. Simulations show that thorium-232 is more radiotoxic than uranium expressed in activity units. If the comparison is based on weight units, the rankings depend on the uranium enrichment grades and the route of intake.

Not Just Another Methanation Catalyst: Depleted Uranium Meets Nickel for a High-Performing Process Under Autothermal Regime

Ni-based catalysts prepared through impregnation of depleted uranium oxides (DU) have successfully been employed as highly efficient, selective, and durable systems for CO₂ hydrogenation to substituted natural gas (SNG; CH₄ ) under an autothermal regime. The thermo-physical properties of DU and the unique electronic structure of f-block metal-oxides combined with a nickel active phase, generated an ideal catalytic assembly for turning waste energy back into useful energy for catalysis. In particular, Ni/UO_x stood out for the capacity of DU matrix to control the extra heat (hot-spots) generated at its surface by the highly exothermic methanation process. At odds with the benchmark Ni/γ-Al₂ O₃ catalyst, the double action played by DU as a "thermal mass" and "dopant" for the nickel active phase unveiled the unique performance of Ni/UO_x composites as CO₂ methanation catalysts. The ability of the weakly radioactive ceramic (UO_x ) to harvest waste heat for more useful purposes was demonstrated in practice within a rare example of a highly effective and long-term methanation operated under autothermal regime (i. e., without any external heating source). This finding is an unprecedented example that allows a real step-forward in the intensification of "low-temperature" methanation with an effective reduction of energy wastes. At the same time, the proposed catalytic technology can be regarded as an original approach to recycle and bring to a second life a less-severe nuclear by-product (DU), providing a valuable alternative to its more costly long-term storage or controlled disposal.

Cellular transport of uranium and its cytotoxicity effects on CHO-k1 cells

Uranium is a radioactive heavy metal and a significant public health concern; however, its associated underlying toxicological mechanisms remain largely unknown. In this work, the uptake and efflux processes of uranium in CHO-k1 cells were studied and the cytotoxicity effects were explored. It was found that both the uptake and efflux processes took place rapidly and half of the internalized uranium was expelled within 8 h. The uranium exposure caused a decrease of cell viability and adhesion ability in a dose-dependent manner and blocked the cell cycle at the G1 stage. In addition, gene expression analysis revealed relative changes in the transcription of metabolism related genes. Further studies revealed that the cytotoxicity of uranium could be alleviated by exposing cells to a lower temperature or by the addition of amantadine-HCl, an endocytosis inhibitor. Interestingly, after uranium exposure, needle-like precipitates were observed in both intracellular and extracellular regions. These findings collectively suggest that the cellular transport of uranium is a rapid process that disturbs cell metabolism and induces cytotoxicity, and this impact could be reduced by slowing down endocytic processes.

Hydrogeochemical Processes Governing Uranium Mobility: Inferences from the Anthropogenically Disturbed, Semi-arid Region of India

Khetri Copper Belt, Rajasthan, is anthropogenically active and geologically belongs to the Delhi super-group. A study was designed to understand the geochemical processes controlling the elemental mobility in the groundwater. Sampling sites were divided into three zones, i.e. copper, quartzite and granite mine zones depending on the type of mineral excavated. A total of 32 representative groundwater samples were collected and analysed for heavy metals and radionuclide (U) using ICP-MS. A maximum U concentration (average 87 µgL^-1) is observed in the quartzite mine zone, and minimum (average 13 µgL^-1) is found in the copper mine zone samples. A high concentration of U (maximum of 430 µgL^-1) in groundwater is attributed to mineral dissolution due to geogenic and anthropogenic activities. Despite the presence of Jaspura and Gothra granitoid in the copper mine zone, the abundance of U is low suggesting the scavenging of U by sulphides or iron oxides. Additionally, at the confluence of two geological groups, Fe concentration is found high with a low concentration of U which further confirms scavenging of U. It is evident from the results that in the absence of iron-bearing sulphides, U concentration in groundwater would be very high compared to the current concentration. It also indicates low concentration of U in the copper mine zone is due to dissolution of Fe sulphide-rich waste. The present study recommends further research to understand the feasibility of mining waste for the removal of U contamination from groundwater.

Weaponised uranium and adverse health outcomes in Iraq: a systematic review

Background

The US military first deployed depleted uranium (DU) weapons in Iraq during the Gulf War in 1990 and in the 2003 invasion of Iraq. Research into the health impacts of DU has been mired in debate and controversy. Research funded by the US government has denied the health risks posed by DU to the Iraqi population, while opponents have claimed that DU is responsible for increased rates of birth defects and cancers in Iraq. Others assert that the public health impacts of DU weapons remain uncertain. This systematic review identified, appraised and synthesised all human observational studies assessing adverse health outcomes associated with DU exposure among the Iraqi population. To our knowledge, no systematic review has been conducted on the topic previously.

Methods

We searched 11 electronic databases for human observational studies published between 1990 and 2020 that measured association between exposure to weaponised uranium and health outcomes (including cancer, birth defects, immune system function and mortality) among the Iraqi population. We assessed risk of bias using the Navigation Guide’s risk of bias tool and rated certainty of the evidence using the Grading of Recommendations, Assessment, Development and Evaluations approach (PROSPERO: CRD42018108225).

Results

Our searches identified 2601 records, of which 28 met our inclusion criteria. We identified five additional eligible reports from other sources. Two articles reported the results of multiple relevant studies; our final set included 33 articles reporting on 36 eligible studies. Most studies (n=30, 83%) reported a positive association between uranium exposure and adverse health outcomes. However, we found that the reviewed body of evidence suffers from a high risk of bias.

Conclusion

The available evidence suggests possible associations between exposure to depleted uranium and adverse health outcomes among the Iraqi population. More primary research and the release of missing data are needed to design meaningful health and policy interventions in Iraq.

Renal adaptive response to exposure to low doses of uranyl nitrate and sodium fluoride in mice

BACKGROUND

Despite their differences in physicochemical properties, both uranium (U) and fluoride (F) are nephrotoxicants at high doses but their adverse effects at low doses are still the subject of debate.

METHODS

This study aims to improve the knowledge of the biological mechanisms involved through an adaptive response model of C57BL/6 J mice chronically exposed to low priming doses of U (0, 10, 20 and 40 mg/L) or F (0, 15, 30 and 50 mg/L) and then challenged with acute exposure of 5 mg/kg U or 7.5 mg/kg NaF.

RESULTS

We showed that an adaptive response occurred with priming exposures to 20 mg/L U and 50 mg/L F, with decreased levels of the biomarkers KIM-1 and CLU compared to those in animals that received the challenge dose only (positive control). The adaptive mechanisms involved a decrease in caspase 3/7 activities in animals exposed to 20 mg/L U and a decrease in in situ VCAM expression in mice exposed to 50 mg/L F. However, autophagy and the UPR were induced independently of priming exposure to U or F and could not be identified as adaptive mechanisms to U or F.

CONCLUSION

Taken together, these results allow us to identify renal adaptive responses to U and F at doses of 20 and 50 mg/L, probably through decrease apoptosis and inflammatory cell recruitment.

Distribution and Fractionation of Uranium in Weapon Tested Range Soils

Uranium is a chemically toxic and radioactive heavy metal. Depleted uranium (DU) is the byproduct of the uranium enrichment process, with a majority of U as uranium-238, and a lower content of the fissile isotope uranium-235 than natural uranium. Uranium-235 is mainly used in nuclear reactors and in the manufacture of nuclear weapons. Exposure is likely to have an impact on humans or the ecosystem where military operations have used DU. Yuma Proving Ground in Arizona, USA has been using depleted uranium ballistics for 36 years. At a contaminated site in the Proving Grounds, soil samples were collected from the flat, open field and lower elevated trenches that typically collect summer runoff. Spatial distribution and fractionation of uranium in the fields were analyzed with total acid digestion and selective sequential dissolution with eight operationally defined solid-phase fractions. In addition to uranium, other trace elements (As, Ba, Co, Cr, Cu, Hg, Mo, Nb, Pd, Pb, V, Zn, Zr) were also assessed. Results show that the trench area in the testing site had a higher accumulation of total U (12.4%) compared to the open-field soil with 279 mg/kg U. Among the eight solid-phase components in the open-field samples, U demonstrated stronger affinities for the amorphous iron-oxide bound, followed by the carbonate bound, and the residual fractions. However, U in the trench area had a stronger binding to the easily reducible oxide bound fraction, followed by the carbonate-bound and amorphous iron-oxide-bound fractions. Among other trace elements, Nb, As, and Zr exhibited the strongest correlations with U distribution among solid-phase components. This study indicates a significant spatial variation of U distribution in the shooting range site. Fe/Mn oxides and carbonate were the major solid-phase components for binding U in the weapon test site.

Remote Detection of Uranium Using Self-Focusing Intense Femtosecond Laser Pulses

Optical measurement techniques can address certain important challenges associated with nuclear safety and security. Detection of uranium over long distances presents one such challenge that is difficult to realize with traditional ionizing radiation detection, but may benefit from the use of techniques based on intense femtosecond laser pulses. When a high-power laser pulse propagates in air, it experiences collapse and confinement into filaments over an extended distance even without external focusing. In our experiments, we varied the initial pulse chirp to optimize the emission signal from the laser-produced uranium plasma at an extended distance. While the ablation efficiency of filaments formed by self-focusing is known to be significantly lower when compared to filaments produced by external focusing, we show that filaments formed by self-focusing can still generate luminous spectroscopic signatures of uranium detectable within seconds over a 10-m range. The intensity of uranium emission varies periodically with laser chirp, which is attributed to the interplay among self-focusing, defocusing, and multi-filament fragmentation along the beam propagation axis. Grouping of multi-filaments incident on target is found to be correlated with the uranium emission intensity. The results show promise towards long-range detection, advancing the diagnostics and analytical capabilities in ultrafast laser-based spectroscopy of high-Z elements.

A quantitative comparison of the chemo- and radiotoxicity of uranium at different enrichment grades

OBJECTIVE

The radiotoxic effects of uranium are often in the focus of the public fears but the chemical toxic effects of uranium are reported to surpass radiation effects. As there is no uranium isotope that is not radioactive, it is not possible to study chemical effects fully independently from radiation effects. In order to quantitate and compare radio- and chemotoxicity, we determined the median lethal doses of uranium due to its chemical toxicity and calculated the absorbed radiological doses resulting from the ingestion or inhalation of corresponding amounts depending on the isotopic enrichment grade. Committed effective doses over 50 years are related to the stochastic health effects like cancer occurrence and can be converted to a loss of statistical life time (mean loss 0.4 day / mSv). The equivalent doses absorbed within a short time frame permits conclusion on the induction of deterministic effects (e.g. acute radiation sickness).

METHOD

Simulations were based on the biokinetic models of the International Commission for Radioprotection and performed using Integrated Modules for Bioassay Analysis software. Results were compared with the doses given by the calculator of the WISE uranium project. The fractions of the total doses absorbed within different time periods were derived from the respective areas under the activity-time curves in the whole body.

RESULTS

The distribution of the total dose on the organs and tissues depends on the invasion pathway and the solubility of the compound. In the case of inhalation, the absorption of the total dose is more protracted than after ingestion. The incorporation of depleted or natural uranium in lethal amounts due to nephrotoxicity does not lead to deterministic radiation effects and is associated with committed effective doses reaching at most about 200 mSv (proposed possible threshold for therapeutic interventions after accidental radionuclide incorporation). The inhalation of low enriched uranium leads to higher effective doses up to 690 mSv, but they are still insufficient to cause acute deterministic effects. Even highly enriched uranium seems not to induce radiation nephropathy, but deterministic effects on the hematopoetic system cannot be excluded in particularly sensitive patients. But the equivalent doses to the lungs associated with the inhalation of poorly soluble compounds of highly enriched uranium are in a range that may induce radiation pneumonitis.

CONCLUSION

Our findings give clear evidence that for depleted and natural uranium chemical toxicity is much more marked than radiotoxicity. However, this conclusion must not be drawn for enriched and in particular highly enriched compounds that besides stochastic effects may even cause deterministic radiation effects.

Role of PI3K-Akt and MAPK Signaling in Uranyl Nitrate-Induced Nephrotoxicity

Uranium is a heavy metal of considerable environmental and occupational concern. It is well-known that the kidney is the major target organ of uranium exposure. Elucidating the mechanistic basis of uranium interactions is essential for monitoring the health risk. In the present study, we investigated the cellular mechanisms involved in uranyl nitrate-induced nephrotoxicity. Male Swiss albino mice were administrated with a single intraperitoneal dose of 2 and 4 mg/kg of uranyl nitrate at different time points 1, 3, 5, 7, 14, and 28 days. Uranyl nitrate intoxication-induced apoptosis in the kidney tissue was observed by TUNEL assay. To assess the proliferation, immunohistochemistry was performed using Ki67 proliferative marker followed by western blotting to confirm the involvement of key signaling molecules. The number of TUNEL positive nuclei peaked at third day after uranyl nitrate insult. The increased expression of proliferation marker Ki67 suggests the enhanced DNA repair process prominently at seventh day. Uranyl nitrate administration also resulted in activation of extracellular signal-regulated kinases (ERK), Akt, and c-Jun N-terminal kinases (JNK) expression. All these changes were found to be time-dependent. The result of the current study suggests that uranyl nitrate induces acute renal injury by activation of apoptosis through JNK pathway, while the early activation of signaling molecules Akt and ERK promotes the tubular cell proliferation and cell survival.

Depleted uranium assessment and natural radioactivity monitoring in North West of Iraq over a decade since the last Gulf War

For the sake of completeness of the surveillance process concerning the spread of depleted uranium (DU) in the Arabian Gulf region, we have applied a simple gamma spectroscopy technique to evaluate its content in Al Jolan, Nazzal and Askari districts in Al Fallujah area, Iraq for the first time and after more than one decade. The measurements were carried out along the lines of the wars that have been witnessed in Iraq last period and expected to be the region of impact of residuals of a large quantity of DU. The observed radionuclides are ⁴ K and other naturally occurring radioactive members of uranium and thorium series. The obtained results show that, the average specific activity concentrations of ²²⁶Ra, ²³²Th, ⁴ K, ²¹⁰Pb ²³⁸U and ²³⁵U in different soil samples collected from Al Fallujah area, Iraq in range of 20.09 ± 4.0 to 21.94 ± 2.4, 11.51 ± 2.3 to 11.75 ± 3.2, 96.53 ± 8.0 to 112.13 ± 49.8, 19.98 ± 4.6 to 20.76 ± 4.8, 25.4 ± 3.9 to 26.1 ± 6.0 and 1.28 ± 0.18 to 1.34 ± 0.21 respectively. The obtained values of Ra_eq for all the investigated samples are less than the recommended limit of 370 Bq kg^-1 and those for H_ex are less than one. These results have been compared with the previous works and the world mean values specified by the UNSCEAR reports. The mean ratio of ²³⁸U/²³⁵U activity in all cases is about the natural value (21.73) which is less than its value in case of DU (76.92). The present obtained results of DU levels show that although a large amount of DU was released in Iraq during the Gulf wars, the tested samples are DU free. This may be attributed to the reduction of DU from the soil surface by wind or sandstorms and the downward leaching process.

Strong Uranium(VI) Binding onto Bovine Milk Proteins, Selected Protein Sequences, and Model Peptides

Hexavalent uranium is ubiquitous in the environment. In view of the chemical and radiochemical toxicity of uranium(VI), a good knowledge of its possible interactions in the environment is crucial. The aim of this work was to identify typical binding and sorption characteristics of uranium(VI) with both the pure bovine milk protein β-casein and diverse related protein mixtures (caseins, whey proteins). For comparison, selected model peptides representing the amino acid sequence 13-16 of β-casein and dephosphorylated β-casein were also studied. Complexation studies using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy revealed that the phosphoryl-containing proteins form uranium(VI) complexes of higher stability than the structure-analog phosphoryl-free proteins. That is in agreement with the sorption experiments showing a significantly higher affinity of caseins toward uranium(VI) in comparison to whey proteins. On the other hand, the total sorption capacity of caseins is lower than that of whey proteins. The discussed binding behavior of milk proteins to uranium(VI) might open up interesting perspectives for sustainable techniques of uranium(VI) removal from aqueous solutions. This was further demonstrated by batch experiments on the removal of uranium(VI) from mineral water samples.

In Vivo Comparison of the Phenotypic Aspects and Molecular Mechanisms of Two Nephrotoxic Agents, Sodium Fluoride and Uranyl Nitrate

Because of their nephrotoxicity and presence in the environment, uranium (U) and fluoride (F) represent risks to the global population. There is a general lack of knowledge regarding the mechanisms of U and F nephrotoxicity and the underlying molecular pathways. The present study aims to compare the threshold of the appearance of renal impairment and to study apoptosis and inflammation as mechanisms of nephrotoxicity. C57BL/6J male mice were intraperitoneally treated with a single dose of U (0, 2, 4 and 5 mg/kg) or F (0, 2, 5, 7.5 and 10 mg/kg) and euthanized 72 h after. Renal phenotypic characteristics and biological mechanisms were evaluated by urine biochemistry, gene/protein expression, enzyme activity, and (immuno)histological analyses. U and F exposures induced nephrotoxicity in a dose-dependent manner, and the highest concentrations induced severe histopathological alterations as well as increased gene expression and urinary excretion of nephrotoxicity biomarkers. KIM-1 gene expression was induced starting at 2 mg/kg U and 7.5 mg/kg F, and this increase in expression was confirmed through in situ detection of this biomarker of nephrotoxicity. Both treatments induced inflammation as evidenced by cell adhesion molecule expression and in situ levels, whereas caspase 3/7-dependent apoptosis was increased only after U treatment. Overall, a single dose of F or U induced histopathologic evidence of nephrotoxicity renal impairment and inflammation in mice with thresholds under 7.5 mg/kg and 4 mg/kg, respectively.

Passive, non-intrusive assay of depleted uranium

The ability to detect neutrons from the spontaneous fission of ²³⁸U in samples of depleted uranium with organic liquid scintillation detectors is presented. In this paper we introduce a small modular organic liquid scintillator detector array that can detect changes in mass of ²³⁸U between 3.69 g and 14.46 g. To do this, 18-h assays of various masses of 0.3% wt. of depleted uranium dioxide were assessed using four EJ-309 detectors, a mixed field analyser operated in pulse gradient analysis mode, and associated counting components. We observe a background-corrected fast neutron count sensitivity of (2.0 ± 0.3) × 10^-4 n g^-1 s^-1 per detector. This research demonstrates a proof of concept for depleted uranium quantity to be assessed passively on a non-intrusive basis via its spontaneous fission decay.

Speciation in Metal Toxicity and Metal-Based Therapeutics

Metallic elements, ions and compounds produce varying degrees of toxicity in organisms with which they come into contact. Metal speciation is critical to understanding these adverse effects; the adjectives "heavy" and "toxic" are not helpful in describing the biological properties of individual elements, but detailed chemical structures are. As a broad generalization, the metallic form of an element is inert, and the ionic salts are the species that show more significant bioavailability. Yet the salts and other chelates of a metal ion can give rise to quite different toxicities, as exemplified by a range of carcinogenic potential for various nickel species. Another important distinction comes when a metallic element is organified, increasing its lipophilicity and hence its ability to penetrate the blood brain barrier, as is seen, for example, with organic mercury and tin species. Some metallic elements, such as gold and platinum, are themselves useful therapeutic agents in some forms, while other species of the same element can be toxic, thus focusing attention on species interconversions in evaluating metal-based drugs. The therapeutic use of metal-chelating agents introduces new species of the target metal in vivo, and this can affect not only its desired detoxification, but also introduce a potential for further mechanisms of toxicity. Examples of therapeutic iron chelator species are discussed in this context, as well as the more recent aspects of development of chelation therapy for uranium exposure.