Biological effects of uranium in water, soil and rice in uranium deposits in southern China

Mitigation of uranium toxicity in rice by Sphingopyxis sp. YF1: Evidence from growth, ultrastructure, subcellular distribution, and physiological characteristics

Uranium (U) contamination of rice is an urgent ecological and agricultural problem whose effective alleviation is in great demand. Sphingopyxis genus has been shown to remediate heavy metal-contaminated soils. Rare research delves into the mitigation of uranium (U) toxicity to rice by Sphingopyxis genus. In this study, we exposed rice seedlings for 7 days at U concentrations of 0, 10, 20, 40, and 80 mg L-1 with or without the Sphingopyxis sp. YF1 in the rice nutrient solution. Here, we firstly found YF1 colonized on the root of rice seedlings, significantly mitigated the growth inhibition, and counteracted the chlorophyll content reduction in leaves induced by U. When treated with 1.1 × 107 CFU mL-1 YF1 with the amendment of 10 mg L-1 U, the decrease of U accumulation in rice seedling roots and shoots was the largest among all treatments; reduced by 39.3% and 32.1%, respectively. This was associated with the redistribution of the U proportions in different organelle parts, leading to the alleviation of the U damage to the morphology and structure of rice root. Interestingly, we found YF1 significantly weakens the expression of antioxidant enzymes genes (CuZnSOD,CATA,POD), promotes the up-regulation of metal-transporters genes (OsHMA3 and OsHMA2), and reduces the lipid peroxidation damage induced by U in rice seedlings. In summary, YF1 is a plant-probiotic with potential applications for U-contaminated rice, benefiting producers and consumers.

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.

Emerging paradigms into bioremediation approaches for nuclear contaminant removal: From challenge to solution

The release of radionuclides, including Cesium-137 (137Cs), Strontium-90 (90Sr), Uranium-238 (238U), Plutonium-239 (239Pu), Iodine-131 (131I), etc., from nuclear contamination presents profound threats to both the environment and human health. Traditional remediation methods, reliant on physical and chemical interventions, often prove economically burdensome and logistically unfeasible for large-scale restoration efforts. In response to these challenges, bioremediation has emerged as a remarkably efficient, environmentally sustainable, and cost-effective solution. This innovative approach harnesses the power of microorganisms, plants, and biological agents to transmute radioactive materials into less hazardous forms. For instance, consider the remarkable capability demonstrated by Fontinalis antipyretica, a water moss, which can accumulate uranium at levels as high as 4979 mg/kg, significantly exceeding concentrations found in the surrounding water. This review takes an extensive dive into the world of bioremediation for nuclear contaminant removal, exploring sources of radionuclides, the ingenious resistance mechanisms employed by plants against these harmful elements, and the fascinating dynamics of biological adsorption efficiency. It also addresses limitations and challenges, emphasizing the need for further research and implementation to expedite restoration and mitigate nuclear pollution's adverse effects.

Characterization relationship between multinuclide nonequilibrium gamma radiation dose rate and 226Ra activity concentration in contaminated soil around uranium mines

According to the characteristics of contaminated soil around uranium mines, combined with the pollution path of soil, the response relationship between the gamma radiation dose rate and radium activity concentration in contaminated soil was proposed by using a numerical model and subequilibrium theory. The results showed that the topsoil (depth 20 cm) made the mainly contribution of gamma dose rate (above 88%), and the main nuclide of concern was radium. Additionally, the uranium-radium equilibrium coefficient between 0 and 0.3 had a great influence on the gamma dose rate. The method proposed in this study could quickly identify the radium activity concentration in topsoil by using on-site gamma dose rate monitoring data. Compared with the actual monitoring results within ±10% error control, which had strong operability. This method could quickly identify the location and scope of contaminated soil and guide the on-site monitoring points around uranium mines.

Insight into microbial functional genes' role in geochemical distribution and cycling of uranium: The evidence from covering soils of uranium tailings dam

There exists a research gap on microbial functional genes' role in U geochemical behavior and cycling in U contaminated soils, which has been poorly understood. Herein, 16S rRNA sequencing gene amplifiers and metagenome analysis were applied to probe microbial community structure and functional metabolism of different depth layers of covering soils in U tailings dam. Results showed that the soils were highly enriched with U (47.5-123.3 mg/kg) and a remarkable portion of 35-70% was associated with the labile fractions. It was found that U geochemical distribution was notably interacted with functional genes from N, S, Fe and P related microbes. Importantly, diminution in gene NirK and amplification in nrfH involving in nitrate reduction could induce microbial tolerance to U. Moreover, gene Sat in microbial sulfate reduction, NosZ and NorB in nitrate reduction, phnD, upgA and upgC in P transportation and phnI, phnK, phoA and opd in microbial organic P mineralization, were all closely linked to U geochemical distribution, species and cycling. All these findings disclose the functional genes that may control the transfer and transformation behavior of U in soil environment, which provides important and novel indications for the bio-remediation strategies towards U polluted sites.

Waterborne Diseases and Wastewater Treatment in Iraq

Iraq is a desert country with access to large river resources and an extensive aquifer, but these have already been overdrawn for domestic, industry and agriculture use. The diminished flow of the Tigris and Euphrates rivers has allowed seawater intrusion from the Persian Gulf 110 km up as far as Basra, the county's third largest city. In addition, water distribution systems are overloaded and wastewater treatment plants (WWTPs) need upgrading, and fresh water sources polluted by lack of sanitation, agricultural runoff, household and industrial waste, and including the irrigation of vegetables with sewage water, have led to episodes of bacterial, viral and parasitic diseases. Also, there have been increases in many types of cancer since the early 1990s, and based on clinical and epidemiological data, these increases could be attributable to exposure to depleted uranium in the environment arising from conflict in Iraq and particularly during the Iraqi War started 20 years ago. The population affected would like government action to reduce their health concerns, and policies that have been proposed for improving water availability and quality, as well as but have not been followed up sufficiently to tackle these, including increasing the capacity and efficiency of WWTP; promoting the most efficient irrigation techniques for the local growing conditions; reducing the use of chemical fertilizers and pesticides that can decrease the water quality; reducing saline intrusion challenges; building compact desalination units; constructing water storage facilities to address water scarcity challenges; and establishing public education plans for consumers to reduce the water demand during the hot season. Whether the government rises to the task remains to be seen. Also, do those countries that used the DU have a responsibility to remove or otherwise dispose of the fragments that remain?

Influence of thermal air oxidation on the chemical composition and uranium binding property of intrinsic dissolved organic matter from biochar

In this work, uranium (U(VI)) binding characteristics of the intrinsic dissolved organic matters (DOM) from the biochars prepared under thermal air oxidation (TAO) and non-TAO conditions were studied using synchronous fluorescence spectra (SFS) and Fourier transform infrared (FTIR) in conjunction with the general two-dimensional correlation spectroscopy (2D-COS), heterospectral 2D-COS and moving-window (MW) 2D-COS. The chemical compositions of the intrinsic DOMs from biochars with/without TAO were investigated by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that the preferential binding of U(VI) to functional groups followed the order: 937 (carboxyl γ_C-OH), 981 (carboxyl γ_C-OH), 1511 (aromatic v_C = C), 1108 (esters or ethers v_C-O), 1282 (esters or carboxyl v_C-O), 1698 (saturated carboxylic acid or ketone v_C = O) cm^-1 for biochar DOM after TAO (OB600), and 937 (carboxyl γ_C-OH), 1484 (lipids δ_C-H or phenolic v_C-O), 1201 (esters or carboxyl v_C-O), 1112 (esters or ethers v_C-O), 1706 (saturated aldehyde, carboxylic acid or ketone v_C = O), 1060 (phenolic, esters or ethers v_C-O), 1014 (phenolic, esters or ethers v_C-O) cm^-1 for the pristine biochar (B600). Fulvic-like substances at 375 nm in the biochar DOM showed a preferential binding with U(VI) after TAO, while humic-like substances played a more critical role in the U(VI) complexation with biochar DOM obtained from non-TAO condition. The results also indicated that TAO increased the content of fluorescent DOM and the chemical stability of DOM-U(VI) complexes. The FT-ICR MS results showed an increase in the relative abundance of protein-like, carbohydrates-like, tannins-like, unsaturated hydrocarbons, and condensed aromatic structure and a decrease in the relative abundance of lipid-like and lignin-like after TAO. Consequently, although biochar after TAO had a much poorer content of intrinsic DOM, its intrinsic DOM showed a much higher capacity in U(VI) precipitation. Therefore, the TAO substantially changed the chemical composition, binding property and environmental behavior of intrinsic DOM from biochar.

A strategy for bioremediation of nuclear contaminants in the environment

Radionuclides released from nuclear contamination harm the environment and human health. Nuclear pollution spread over large areas and the costs associated with decontamination is high. Traditional remediation methods include both chemical and physical, however, these are expensive and unsuitable for large-scale restoration. Bioremediation is the use of plants or microorganisms to remove pollutants from the environment having a lower cost and can be upscaled to eliminate contamination from soil, water and air. It is a cheap, efficient, ecologically, and friendly restoration technology. Here we review the sources of radionuclides, bioremediation methods, mechanisms of plant resistance to radionuclides and the effects on the efficiency of biological adsorption. Uptake of radionuclides by plants can be facilitated by the addition of appropriate chemical accelerators and agronomic management, such as citric acid and intercropping. Future research should accelerate the use of genetic engineering and breeding techniques to screen high-enrichment plants. In addition, field experiments should be carried out to ensure that this technology can be applied to the remediation of nuclear contaminated sites as soon as possible.

Occurrence characteristics of uranium mineral-related substances in various environmental media in China: A critical review

The high demand and extensive exploitation of uranium resources resulted in the ubiquity and high detection levels of uranium mineral-related substances in various environment media in China. The potential adverse effects of uranium mineral-related substances on environment and human health have received extensive attention. Therefore, we reviewed the occurrence and spatial distribution of uranium mineral-related substances in various basins and environmental media in China to obtain an overall understanding. We collected information from over 70 papers reporting the occurrence and distribution of uranium mineral-related substances in multiple environments and 183 articles on the genesis of uranium deposits in China from 2001 to 2021. Then the occurrence of uranium mineral-related substances and corresponding correlation in different basins, environmental media and depth ranges were compared in detail. And this review assessed the uranium mineral-related pollution in China based on various environmental quality standards of China, EPA and WHO, and proposed the priority uranium mineral-related heavy metals and radioactive substances based on cluster analysis. This review showed that there were obvious differences in the occurrence characteristics of various uranium mineral-related substances in different environmental media, especially in the surrounding environment of sandstone type and hard rock type uranium deposits. These results will guide us to tackle the challenge of uranium mineral-related pollution in China. The correlation analysis of uranium mineral-related pollutants in different environmental media and the identification of priority pollutants will also provide instructions for us to control uranium mineral-related pollution. Finally, we put forward a series of urgent and practical suggestions on risk management and control of uranium mining according to the current situation of uranium mining environment in China, which is of guiding significance for the realization of "green uranium mining".

A Novel Triphenylamine-Based Flavonoid Fluorescent Probe with High Selectivity for Uranyl in Acid and High Water Systems

Developing a fluorescent probe for UO₂²⁺, which is resistant to interference from other ions such as Cu²⁺ and can be applied in acidic and high-water systems, has been a major challenge. In this study, a "turn-off" fluorescent probe for triamine-modified flavonoid derivatives, 2-triphenylamine-3-hydroxy-4H-chromen-4-one (abbreviated to HTPAF), was synthesized. In the solvent system of dimethyl sulfoxide:H₂O (abbreviated to DMSO:H₂O) (v/v = 5:95 pH = 4.5), the HTPAF solution was excited with 364 nm light and showed a strong fluorescence emission peak at 474 nm with a Stokes shift of 110 nm. After the addition of UO₂²⁺, the fluorescence at 474 nm was quenched. More importantly, there was no interference in the presence of metal ions (Pb²⁺, Cd²⁺, Cr³⁺, Fe³⁺, Co²⁺, Th⁴⁺, La³⁺, etc.), especially Cu²⁺ and Al³⁺. It is worth noting that the theoretical model for the binding of UO₂²⁺ to HTPAF was derived by more detailed density functional theory (DFT) calculations in this study, while the coordination mode was further verified using HRMS, FT-IR and ¹HNMR, demonstrating a coordination ratio of 1:2. In addition, the corresponding photo-induced electron transfer (PET) fluorescence quenching mechanism was also proposed.

Metal-Organic-Framework Based Functional Materials for Uranium Recovery: Performance Optimization and Structure/Functionality-Activity Relationships

Uranium recovery has profound significance in both uranium resource acquisition and pollution treatment. In recent years, metal-organic frameworks (MOFs) have attracted much attention as potential uranium adsorbents owing to their tunable structural topology and designable functionalities. This review explores the research progress in representative classic MOFs (MIL-101, UiO-66, ZIF-8/ZIF-67) and other advanced MOF-based materials for efficient uranium extraction in aqueous or seawater environments. The uranium uptake mechanism of the MOF-based materials is refined, and the structure/functionality-property relationship is further systematically elucidated. By summarizing the typical functionalization and structure design methods, the performance improvement strategies for MOF-based adsorbents are emphasized. Finally, the present challenges and potential opportunities are proposed for the breakthrough of high-performance MOF-based materials in uranium extraction.

Sources of and Control Measures for PTE Pollution in Soil at the Urban Fringe in Weinan, China

The environment of the urban fringe is complex and frangible. With the acceleration of industrialization and urbanization, the urban fringe has become the primary space for urban expansion, and the intense human activities create a high risk of potentially toxic element (PTE) pollution in the soil. In this study, 138 surface soil samples were collected from a region undergoing rapid urbanization and construction—Weinan, China. Concentrations of As, Pb, Cr, Cu, and Ni (Inductively Coupled Plasma Mass Spectrometry, ICP-MS) and Hg (Atomic Fluorescence Spectrometry, AFS) were measured. The Kriging interpolation method was used to create a visualization of the spatial distribution characteristics and to analyze the pollution sources of PTEs in the soil. The pollution status of PTEs in the soil was evaluated using the national environmental quality standards for soils in different types of land use. The results show that the content range of As fluctuated a small amount and the coefficient of variation is small and mainly comes from natural soil formation. The content of Cr, Cu, and Ni around the automobile repair factory, the prefabrication factory, and the building material factory increased due to the deposition of wear particles in the soil. A total of 13.99% of the land in the study area had Hg pollution, which was mainly distributed on category 1 development land and farmland. Chemical plants were the main pollution sources. The study area should strictly control the industrial pollution emissions, regulate the agricultural production, adjust the land use planning, and reduce the impact of pollution on human beings. Furthermore, we make targeted remediation suggestions for each specific land use type. These results are of theoretical significance, will be of practical value for the control of PTEs in soil, and will provide ecological environmental protection in the urban fringe throughout the urbanization process.