Search Results (12)

Bone is a major tissue for uranium deposition in human body. Considering mesenchymal stem cells (MSCs) play a vital role in bone formation and injury recovery, studying the mechanism of MSCs responding to uranium poisoning can benefit the understanding of bone damage and repair after uranium exposure. Cellular structural alterations were analyzed via transmission electron microscopy (TEM). Changes in cellular behaviors were assessed through cellular viability, apoptosis, and the production of DNA double-strand breaks (DSBs). In addition, the influence of gap junctional intercellular communication (GJIC) on uranium toxicity was assessed. The disruption of MSCs was elevated with the increase in uranyl nitrate concentration, as shown by TEM micrograph. This was verified by the results of cellular viability and DSB production. Interestingly, the results of apoptosis assay indicated significant apoptosis occurred, which was accompanied with an obvious disruption of cellular membranes. Furthermore, closely contacted cell confluence groups exhibited resistant to uranium poisoning in contrast to sparse growth groups, which can be eliminated with the pretreatment of a GJIC inhibitor in the close connection group. To verify the association between GJIC and cytotoxic effects of uranyl nitrate, GJIC function was evaluated by wound healing and cellular migration. The results showed an inhibition of the healing ratio and migration ability induced by the exposure of uranyl nitrate. The low transfer efficiency of the dye coupling experiment and depressed expression of gap functional protein connexins confirmed the impairment of GJIC function. These results suggest that uranium toxicity is involved with GJIC dysfunction. Full article

With the rapid development of industrialization, the emission of nitrogen oxides (NO_x) has become a global environmental issue. Uranium is the primary fuel used in nuclear power generation. However, the production of uranium, typically based on the uranyl nitrate method, usually generates large amounts of nitrogen oxides, particularly NO₂, with concentrations in the exhaust gas exceeding 10,000 ppm. High concentrations of nitrogen dioxide are also produced during silver electrolysis processing and the treatment of waste electrolyte solutions. Traditional V-W/TiO₂ NH₃-SCR catalysts typically exhibit high catalytic activity at temperatures ranging from 300 to 400 °C, under conditions of low NO_x concentrations and high gas hourly space velocity. However, their performance is not satisfying when reducing high concentrations of NO₂. This study aims to optimize the traditional V-W/TiO₂ catalysts to enhance their catalytic activity under conditions of high NO₂ concentrations (10,000 ppm) and a wide temperature range (200–400 °C). On the basis of 3 wt% Mo/TiO₂, various loadings of V₂O₅ were selected, and their catalytic activities were tested. Subsequently, the optimal ratios of active component vanadium and additive molybdenum were explored. Simultaneously, doping with WO₃ for modification was selected in the V-Mo/TiO₂ catalyst, followed by activity testing under the same conditions. The results show that: the NO_x conversion rates of all five catalysts increase with temperature at range of 200–400 °C. Excessive loading of MoO₃ decreased the catalytic performance, with 5 wt% being the optimal loading. The addition of WO₃ significantly enhanced the low-temperature activity of the catalysts. When the loadings of WO₃ and MoO₃ were both 3 wt%, the catalyst exhibited the best denitrification performance, achieving a NO_x conversion rate of 98.8% at 250 °C. This catalyst demonstrates excellent catalytic activity in reducing very high concentration (10,000 ppm) NO₂, at a wider temperature range, expanding the temperature range by 50% compared to conventional SCR catalysts. Characterization techniques including BET, XRD, XPS, H₂-TPR, and NH₃-TPD were employed to further study the evolution of the catalyst, and the promotional mechanisms are explored. The results revealed that the proportion of chemisorbed oxygen (O_α) increased in the WO₃-modified catalyst, exhibiting lower V reduction temperatures, which are favorable for low-temperature denitrification activity. NH₃-TPD experiments showed that compared to MoO_x species, surface WO_x species could provide more acidic sites, resulting in stronger surface acidity of the catalyst. Full article

This study focuses on the Medical Isotope Production Reactor (MIPR), an aqueous homogeneous reactor utilized for synthesizing medical isotopes like ⁹⁹Mo. A pivotal aspect of MIPR’s functionality involves the fuel solution’s complex chemical interactions, particularly during reactor operation. These interactions result in the formation of precipitates, notably studtite and columnar uranium ore, which can impact reactor performance. The research presented here delves into the reactions between liquid fuel uranyl nitrate and key radiolytic products, employing simulation calculations complemented by experimental validation. This approach facilitates the identification of uranium precipitate types and their formation conditions under operational reactor settings. Additionally, the article explores strategies to mitigate the formation of specific uranium precipitates, thereby contributing to the efficient and stable operation of MIPR. Full article

The development of microbial biofilms increases the survival of microorganisms in the extreme conditions of ecosystems contaminated with components of liquid radioactive waste (LRW) and may contribute to the successful bioremediation of groundwater. The purpose of this work was to compare the composition of the microorganisms and the exopolysaccharide matrix of the biofilms formed on sandy loams collected at the aquifer from a clean zone and from a zone with nitrate and radionuclide contamination. The aquifer is polluted from the nearby surface repository for liquid radioactive waste (Russia). The phylogenetic diversity of prokaryotes forming biofilms on the sandy loams’ surface was determined during 100 days using high-throughput sequencing of the V4 region of the 16S rRNA genes. Scanning electron microscopy was used to study the development of microbial biofilms on the sandy loams. The ratio of proteins and carbohydrates in the biofilms changed in the course of their development, and the diversity of monosaccharides decreased, depending on the contamination of the sites from which the rocks were selected. The presence of pollution affects biofilm formation and EPS composition along with the dominant taxa of microorganisms and their activity. Biofilms establish a concentration gradient of the pollutant and allow the microorganisms involved to effectively participate in the reduction of nitrate and sulfate; they decrease the risk of nitrite accumulation during denitrification and suppress the migration of radionuclides. These biofilms can serve as an important barrier in underground water sources, preventing the spread of pollution. Pure cultures of microorganisms capable of forming a polysaccharide matrix and reducing nitrate, chromate, uranyl, and pertechnetate ions were isolated from the biofilms, which confirmed the possibility of their participation in the bioremediation of the aquifer from nonradioactive waste components and the decrease in the radionuclides’ migration. Full article

The contamination of groundwater by uranium, nitrate, ammonium, and sulfate near uranium sludge storage sites due to the degradation of engineering safety barriers is an urgent problem during their long-term operation. The purification of such multicomponent contaminants is a complex task and one of the promising methods for this purpose is in situ bioremediation using the metabolic potential of aborigenic microflora. The work focused on the geochemical, geological, and microbiological parameters of groundwater with multi-component contamination near the uranium sludge storage sites of four chemical plants. In conditions of extreme nitrate contamination (up to 15 g/L), denitrifying bacteria were found to be the dominant group of microorganisms. In conditions of nitrate–ammonium contamination, bacteria responsible for the Anammox process were found. In laboratory, optimal conditions were selected to stimulate microflora to promote nitrate removal. For this purpose, sources of carbon (acetate, whey) were added to the water samples in concentrations necessary for the complete removal of nitrate by microbial denitrification. The experiment was carried out at ambient temperature in hermetically sealed vials. Uranyl nitrate was added to the samples at a concentration of 5 mg/L for uranium. It was found that nitrate removal contributes to the cycle of anaerobic processes of authigenic sedimentation because of sulfate and iron reduction processes, which provide the formation of a mineral geochemical barrier for uranium immobilization. As a result of the experiment, after 3–6 months, depending on the concentration of nitrate in the groundwater sample, the uranium content in the liquid phase decreased by 92–98%. Full article

Changes in metabolomics over time were studied in rats to identify early biomarkers and highlight the main metabolic pathways that are significantly altered in the period immediately following acute low-dose uranium exposure. A dose response relationship study was established from urine and plasma samples collected periodically over 9 months after the exposure of young adult male rats to uranyl nitrate. LC-MS and biostatistical analysis were used to identify early discriminant metabolites. As expected, low doses of uranium lead to time-based non-toxic biological effects, which can be used to identify early and delayed markers of exposure in both urine and plasma samples. A combination of surrogate markers for uranium exposure was validated from the most discriminant early markers for making effective predictions. N-methyl-nicotinamide, kynurenic acid, serotonin, tryptophan, tryptamine, and indole acetic acid associated with the nicotinate–nicotinamide and tryptophan pathway seem to be one of the main biological targets, as shown previously for chronic contaminations and completed, among others, by betaine metabolism. This study can be considered as a proof of concept for the relevance of metabolomics in the field of low-dose internal contamination by uranium, for the development of predictive diagnostic tests usable for radiotoxicological monitoring. Full article

A nucleation method based on a composite of uranium dioxide (UO₂) and graphene is presented by in situ synthesis, and the relevant mechanism and fuel properties are investigated. UO₂–graphene composite fuel powders containing graphene volume (2%, 4%, 6%, and 8%) were prepared using a nucleation method through the reactive deposition of uranyl nitrate and aqueous ammonia on graphene by controlling the reaction parameters. The composite fuel pellets were prepared using spark plasma sintering (SPS). The results showed that the uniformity of UO₂–graphene powder prepared by in situ synthesis reached up to 96.39%. An analysis on the relevant phase structure showed that only UO₂ and graphene existed in the sintered pellets at 1723 K, graphene and UO₂ were not destroyed during the reaction, and the pellet densities for the in-situ synthesis were 95.56%TD, 95.32%TD, 95.08%TD, and 94.76%TD for graphene contents of 2%, 4%, 6%, and 8%, respectively. The thermal conductivities of pellets at 293 K increased by 12.27%, 20.13%, 27.47%, and 34.13%, and by 18.36%, 35.00%, 47.07%, and 58.93% at 1273 K for 2%, 4%, 6%, and 8% graphene contents, respectively. The performance of graphene in the fuel was superior at high temperatures, which overcame shortcomings due to the low thermal conductivity of UO₂ at high temperatures. SEM results showed that the grain sizes of the pellets prepared by synthesis in situ were 10–30 μm, and there was no obvious pore at the grain boundary because the grains were closely bound. The graphene was uniformly coated by UO₂, and the thermal conductivity of the pellets improved upon the formation of a bridging heat conduction network. Full article

Uranium (U) is a heavy metal used in military and industrial settings, with a large portion being mined from the Southwest region of the United States. Uranium has uses in energy and military weaponry, but the mining process has released U into soil and surface waters that may pose threats to human and environmental health. The majority of literature regarding U’s human health concern focuses on outcomes based on unintentional ingestion or inhalation, and limited data are available about its influence via cutaneous contact. Utilizing skin dermis cells, we evaluated U’s topical chemotoxicity. Employing soluble depleted uranium (DU) in the form of uranyl nitrate (UN), we hypothesized that in vitro exposure of UN will have cytotoxic effects on primary dermal fibroblasts by affecting cell viability and metabolic activity and, further, may delay wound healing aspects via altering cell proliferation and migration. Using environmentally relevant levels of U found in water (0.1 $\mathsf{\mu }$M to 100 $\mathsf{\mu }$M [UN]; 23.8–23,800 ppb [U]), we quantified cellular mitosis and migration through growth curves and in vitro scratch assays. Cells were exposed from 24 h to 144 h for a time-course evaluation of UN chemical toxicity. The effects of UN were observed at concentrations above and below the Environmental Protection Agency threshold for safe exposure limits. UN exposure resulted in a dose-dependent decrease in the viable cell count; however, it produced an increase in metabolism when corrected for the viable cells present. Furthermore, cellular proliferation, population doubling, and percent closure was hindered at levels ≥10 $\mathsf{\mu }$M UN. Therefore, inadvertent exposure may exacerbate pre-existing skin diseases in at-risk demographics, and additionally, it may substantially interfere in cutaneous tissue repair processes. Full article

In this study, various solid uranium oxycompounds and TiO₂-supported materials based on nanocrystalline anatase TiO₂ are synthesized using uranyl nitrate hexahydrate as a precursor. All uranium-contained samples are characterized using N₂ adsorption, XRD, UV–vis, Raman, TEM, XPS and tested in the oxidation of a volatile organic compound under visible light of the blue region to find correlations between their physicochemical characteristics and photocatalytic activity. Both uranium oxycompounds and TiO₂-supported materials are photocatalytically active and are able to completely oxidize gaseous organic compounds under visible light. If compared to the commercial visible-light TiO₂ KRONOS^® vlp 7000 photocatalyst used as a benchmark, solid uranium oxycompounds exhibit lower or comparable photocatalytic activity under blue light. At the same time, uranium compounds contained uranyl ion with a uranium charge state of 6+, exhibiting much higher activity than other compounds with a lower charge state of uranium. Immobilization of uranyl ions on the surface of nanocrystalline anatase TiO₂ allows for substantial increase in visible-light activity. The photonic efficiency of reaction over uranyl-grafted TiO₂, 12.2%, is 17 times higher than the efficiency for commercial vlp 7000 photocatalyst. Uranyl-grafted TiO₂ has the potential as a visible-light photocatalyst for special areas of application where there is no strict control for use of uranium compounds (e.g., in spaceships or submarines). Full article

Nitrate is a substance which influences the prevailing redox conditions in groundwater, and in turn the behaviour of U. The study of groundwater in an area with low-level radioactive sludge storage facilities has shown their contamination with sulphate and nitrate anions, uranium, and some associated metals. The uranyl ion content in the most contaminated NO₃–Cl–SO₄–Na borehole is 2000 times higher (1.58 mg/L) than that in the background water. At the same time, assessment of the main physiological groups of microorganisms showed a maximum number of denitrifying and sulphate-reducing bacteria (e.g., Sulfurimonas) in the water from the same borehole. Biogenic factors of radionuclide immobilization on sandy rocks of upper aquifers have been experimentally investigated. Different reduction rates of NO₃⁻, SO₄²⁻, Fe(III) and U(VI) with stimulated microbial activity were dependent on the pollution degree. Moreover, 16S rRNA gene analysis of the microbial community after whey addition revealed a significant decrease in microbial diversity and the activation of nonspecific nitrate-reducing bacteria (genera Rhodococcus and Rhodobacter). The second influential factor can be identified as the formation of microbial biofilms on the sandy loam samples, which has a positive effect on U sorption (an increase in Kd value is up to 35%). As PHREEQC physicochemical modelling numerically confirmed, the third most influential factor that drives U mobility is the biogenic-mediated formation of a sulphide redox buffer. This study brings important information, which helps to assess the long-term stability of U in the environment of radioactive sludge storage facilities. Full article

Six novel uranyl nitrate compounds K₃[(UO₂)(NO₃)Cl₃](NO₃) (1, 2), α-Cs₂[(UO₂)(NO₃)Cl₃] (3), [(UO₂)(NO₃)₂(H₂O)₂][(CH₃NH₃)₂(NO₃)₂] (4), Cs₂[(UO₂)(NO₃)₄] (5), and [(UO₂)₂(OH)₂(NO₃)₂(H₂O)₃](H₂O) (6) have been prepared from aqueous solutions. Their structures were analyzed using single-crystal X-ray diffraction technique. Structural studies have shown that the crystals of 1 and 2 are isotypic but differ in the distortion at the counter ion’s sites. The crystal of 3 is a low-temperature polymorph modification of the recently studied compound. The crystal structure of 4 is composed of uranyl-dinitrate-dihydrate and methylamine-nitrate electroneutral complexes linked through the system of H-bonds. The crystal structure of 5 is based on the finite [(UO₂)(NO₃)₄]²⁻ clusters that are arranged in pseudo-chained complexes extended along [100] and are arranged according to a hexagonal packing or rods. The crystal of 6 is also a novel polymorph modification of previously studied compound, the structure of which is based on the very rare topological type of the finite clusters. Nowadays, uranyl nitrate finite clusters of nine various topological types are known. We give herein a short review of their topological features and relationships. Crystallization of uranyl nitrates usually occurs when all other competitive anions in the system have already formed crystalline phases, or the reaction of reagents have slowed down or even stopped. Thus it is suggested that crystallization of uranyl nitrates can be used as a key indicator of the reaction progress, which points to the necessity of the initial concentrations of reagents correction, or to the replacement of reagents and adjustment of the thermodynamic (P,T) parameters of the synthesis. Full article

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. Full article