Heavy-ion irradiation effects on uranium-contaminated soil for nuclear waste

Transcriptome analysis of damage mechanism of Candida utilis under U(VI) stress

Marine radioactive pollution has a great impact on Marine microorganisms, but the damage mechanism by hexavalent uranium (U(VI)) exposure has been rarely known. In this study, Candida utilis (C. utilis) were exposed to U(VI) for 50, 100 and 150 mg/L, and then morphologic change and RNA-Seq in C. utilis were determined. U(VI) exposure significantly induced the changes of morphological characteristics of C. utilis. There were 39 DEGs in the 50 mg/L treated group, including 30 up-regulated genes and 9 down-regulated genes. There were 196 DEGs, 31 up-regulated and 165 down-regulated in the 100 mg/L treated group. The 150 mg/L treated group had 272 DEGs, 74 up-regulated and 198 down-regulated, compared with the control group. The results showed that the number of DEGs increased dose-dependently with U(VI) treatment. The results of this study provide a theoretical basis for the mechanism of radioactive wastewater damage to Marine microorganisms.

Effects of irradiation behavior on physicochemical properties of glassy radioactive contaminated soil containing various contents of actinides nuclear waste

The evaluation of radiation resistance of the treated radioactive contaminated soil is crucial. The irradiation behavior of simulated radioactive soil waste irradiated with 1.5 MeV Xe20+ ions at fluences of 1 × 1012-1 × 1015 ions/cm2 was studied. Before the irradiation experiment, all the samples were sintered by microwave. The results showed that microwave sintering may be used to treat radioactive contaminated soil. In addition, the irradiation experiment results show that when the Nd2O3 content was low (<20 wt.%), the irradiation has little effect on the sample. When the Nd2O3 content was higher, the Vickers hardness of the sample (25 wt.%) decreased by 7 % at a fluence of 1 × 1015 ions/cm2, which may be due to the high Nd2O3 content that destroyed the overall stability of the glass waste form. The low normalized leaching rate of the irradiated sample (LRNd, ∼10-6 g·m-2·d-1) also proved that it had good aqueous durability. Moreover, the radiation resistance of the sample was illustrated by studying the influence mechanism of 1.5 MeV Xe20+ irradiation on radioactive contaminated soil. This work can help to study the environmental pollution problems of radioactive contaminated soil containing various contents of actinide nuclear waste.

Enhanced mechanism of calcium towards uranium incorporation and stability in magnetite during electromineralization

Doping uranium into a room-temperature stable Fe₃O₄ lattice structure effectively reduces its migration. However, the synergistic or competitive effects of coexisting ions in an aqueous solution directly affect the uranium mineralization efficiency and the structural stability of uranium-bearing Fe₃O₄. The effects of calcium, carbonate, and phosphate on uranium electromineralization were investigated via batch experiments and theoretical calculations. Calcium incorporated into the Fe₃O₄ lattice increased the level and stability of doped uranium in Fe₃O₄. Uranium and calcium occupied the octahedral and tetrahedral sites of Fe₃O₄, respectively; the formation energy was only -10.23 eV due to strong hybridization effects between Fe1s, U4f, O2p, and Ca3d orbitals. Compared to the uranium-doped Fe₃O₄, uranium leaching ratios decreased by 19.2 % and 48.9 % under strongly acidic and alkaline conditions after 120 days. However, high concentrations of phosphate inhibited Fe₃O₄ crystallization. These results should provide new avenues for the development of multi-metal co-doping technologies and mineralization optimization to treat uranium-containing complex wastewater.

Response of Vicia faba to short-term uranium exposure: chelating and antioxidant system changes in roots

Uranium (U) phytotoxicity is an inherently difficult problem in the phytoremediation of U-contaminated environments. Plant chelating and antioxidant systems play an authoritative role in resistance to abiotic stress. To reveal the toxicity of U, the changes of chelating system, osmoregulatory substances and antioxidant systems in Vicia faba roots were studied after short-term (24 h) U exposure. The results indicated that the development of lateral roots and root activity of V. faba were significantly inhibited with U accumulation. Compared with the control, plant chelating systems showed significant positive effects after U exposure (15 - 25 μM). Osmoregulatory substances (proline and soluble protein) increasingly accumulated in roots with increasing U concentration, and O2- and H2O2 rapidly accumulated after U exposure (15 - 25 μM). Thus, the contents of malondialdehyde (MDA), a marker of lipid peroxidation, were also significantly increased. Antioxidant systems were activated after U exposure but were inhibited at higher U concentrations (15 - 25 μM). In summary, although the chelating, osmotic regulation and antioxidant systems in V. faba were activated after short-term U exposure, the antioxidases (CAT, SOD and POD) were inhibited at higher U concentrations (15 - 25 μM). Therefore, the root cells were severely damaged by peroxidation, which eventually resulted in inhibited activity and arrested root development.

In vivo appraisal of oxidative stress response, cell ultrastructural aberration and accumulation in Juvenile Scylla serrata exposed to uranium

In vivo studies were performed to evaluate the organ specific tissue accumulation and cellular toxicity of uranium to mud crab Scylla serrata. The specimens were acclimated in natural seawater and the exposure to 50-250 μg/L uranium was investigated up to 60 days. The present study examined the effects of concentration and duration of uranium exposure in the tissue of S. serrata at cellular and subcellular level using scanning electron microscopy and bright field transmission electron microscopy in addition to histological analysis. The results indicated that accumulation of U in S. serrata was organ specific and followed the order gills > hepatopancreas > muscle. The response of key antioxidant enzyme activities such as SOD, GPx and CAT in different organs of crabs indicated oxidative stress due to U in the ambient medium and tissue. At 50 and 100 μg/L of U exposure, individuals were able to acclimate the oxidative stress and withstand the uranium exposure. This acclimation could not be sustained at higher concentrations (250 μg/L), affecting the production of CAT in the tissues. Cellular and subcellular changes were observed in the hemocytes with reduction in their number in consonance with the antioxidant enzymes. Histological aberrations like lamellar disruption of gill, necrosis of hepatopancreas, disruption and rupture of muscle bundles were observed at different concentrations and were severe at higher concentration (250 μg/L). Necrosis was observed in the electron micrographs of tissues shortly after 15 days of exposure. SEM micrograph clearly shows disrupted lamellae, folding of marginal canal and reduction of inter lamellar spaces in the gills of crab exposed to high concentration of uranium. Mitochondrial anomalies are reported for the first time in the present study in addition to the subcellular changes and vacuoles on exposure uranium in the cells of gill and hepatopancreas.

Diamidoximated cellulosic bioadsorbents from hemp stalks for elimination of uranium (VI) and textile waste in aqueous systems

Selective abolition of hazardous U(VI) ions from nuclear power plants and removal of toxic colorants from textile industries pose great challenge. The work aims to develop cellulosic bioadsorbents from waste stalks of local weed, Cannabis sativa, commonly known as hemp. Cellulose nanofibers (PCFs) were chosen as substrates owing to their unique characteristics like surface hydroxyl groups, large surface to volume ratio and excellent mechanical properties. PCFs were isolated from hemp stalks and their structural characterization using FTIR, TGA and XRD ensured retrieval of pure crystalline cellulose. PCFs were modified via copolymerization to obtain diaminomaleonitrile adorned cellulose grafts (DAMNC) and further converted to get diamidoxime functionalized cellulose (DAOC). DAOC exhibited exceptional affinity with uranium (VI) ions, safranin-o and methylene blue dyes due to presence of two amidoxime groups. Sorption capability was ascertained for optimization of parameters like contact time, pH selectivity, adsorbent dosage and concentration. Sorption followed Pseudo second-order kinetic model with maximum sorption of 220 mg/g, 19.01 mg/g and 46.4 mg/g for U(VI) ions, SO and MB, respectively. EDX mapping revealed uniform adsorption of all the three pollutants on DAOC while XPS ascertained that the sorption originated from multiple interactions between the adsorbent and the pollutants.

Uranium (U) source, speciation, uptake, toxicity and bioremediation strategies in soil-plant system: A review

Uranium(U), a highly toxic radionuclide, is becoming a great threat to soil health development, as returning nuclear waste containing U into the soil systems is increased. Numerous studies have focused on: i) tracing the source in U contaminated soils; ii) exploring U geochemistry; and iii) assessing U phyto-uptake and its toxicity to plants. Yet, there are few literature reviews that systematically summarized the U in soil-plant system in past decade. Thus, we present its source, geochemical behavior, uptake, toxicity, detoxification, and bioremediation strategies based on available data, especially published from 2018 to 2021. In this review, we examine processes that can lead to the soil U contamination, indicating that mining activities are currently the main sources. We discuss the relationship between U bioavailability in the soil-plant system and soil conditions including redox potential, soil pH, organic matter, and microorganisms. We then review the soil-plant transfer of U, finding that U mainly accumulates in roots with a quite limited translocation. However, plants such as willow, water lily, and sesban are reported to translocate high U levels from roots to aerial parts. Indeed, U does not possess any identified biological role, but provokes numerous deleterious effects such as reducing seed germination, inhibiting plant growth, depressing photosynthesis, interfering with nutrient uptake, as well as oxidative damage and genotoxicity. Yet, plants tolerate U toxicity via various defense strategies including antioxidant enzymes, compartmentalization, and phytochelatin. Moreover, we review two biological remediation strategies for U-contaminated soil: (i) phytoremediation and (ii) microbial remediation. They are quite low-cost and eco-friendly compared with traditional physical or chemical remediation technologies. Finally, we conclude some promising research challenges regarding U biogeochemical behavior in soil-plant systems. This review, thus, further indicates that the combined application of U low accumulators and microbial inoculants may be an effective strategy for the bioremediation of U-contaminated soils.