Uranium in groundwater - The importance of hydraulic regime and groundwater flow system's understanding

A systematic review and meta-analysis of radon risk exposure from drinking water resources in Nigeria

Elevated radon concentrations in drinking water pose an increased risk of cancer among nonsmokers. A Monte-Carlo Simulation was employed to assess the effective dose and cancer risk associated with radon exposure in humans, utilizing a systematic review and meta-analysis of related studies. These studies were sourced from databases including PubMed, Web of Science, Scopus, Science Direct, and Google Scholar, focusing on drinking water from Nigeria's six geopolitical zones. The random effects models revealed a 222Rn concentration in drinking water of Nigeria at 25.01, with 95% confidence intervals (CI) of 7.62 and 82.09, indicating significant heterogeneity of (I2 = 100%; p < 0.001). The probabilistic risk of effective dose revealed a best-scenario (P 5%) at Kundiga and Magiro that exceeded the World Health Organization's (WHO) recommended effective dose limit of 200 µSv/y. Conversely, the worst-case scenario (P 95%) indicated concentrations surpassing the recommended limit at Kundiga, Edbe, Magiro, Ekiti, and Abeokuta. Excess Life Cancer Risk for infants, children, and adults attributed to the ingestion and inhalation of radon from various drinking water sources exceeded the recommended values of 0.2 x 10-3 established by the International Commission on Radiological Protection (ICRP) and the United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR). It underscores the necessity for treating radon-polluted water, employing methos such as aeration and granular activated carbon (GAC) processes.

Maternal exposure to dietary uranium causes oxidative stress and thyroid disruption in zebrafish offspring

The contamination of uranium in aquatic ecosystems has raised growing global concern. However, the understanding of its chronic effects on aquatic organisms is limited, particularly with regards to transgenerational toxicity. In this study, we evaluated the maternal transfer risk of uranium using zebrafish. Sexually mature female zebrafish were exposed to 2 and 20 ng/g of uranium-spiked food for 28 days. The induced bioconcentration, thyroid disruption, and oxidative stress in both the adults (F0) and their embryos (F1) were further investigated. Element analysis showed that uranium was present in both F0 and F1, with higher concentrations observed in F1, indicating significant maternal offloading to the offspring. Meanwhile, an increased malformation and decreased swim speed were observed in the F1. Thyroid hormone analysis revealed significant decreases in the levels of triiodothyronine (T3) in both the F0 adults and F1 embryos, but thyroxine (T4) was not significantly affected. Additionally, the activities of antioxidant defenses, including catalase (CAT) and superoxide dismutase (SOD), and the expression of glutathione (GSH) and malondialdehyde (MDA) were significantly altered in the F0 and F1 larvae at 120 hpf. The hypothalamic-pituitary-thyroid (HPT) axis, oxidative stress, and apoptosis-related gene transcription expression were also significantly affected in both generations. Taken together, these findings highlight the importance of considering maternal transfer in uranium risk assessments.

Diatom DNA metabarcoding to assess the effect of natural radioactivity in mineral springs on ASV of benthic diatom communities

Little is still known about the low dose effects of radiation on the microbial communities in the environment. Mineral springs are ecosystems than can be affected by natural radioactivity. These extreme environments are, therefore, observatories for studying the influence of chronic radioactivity on the natural biota. In these ecosystems we find diatoms, unicellular microalgae, playing an essential role in the food chain. The present study aimed to investigate, using DNA metabarcoding, the effect of natural radioactivity in two environmental compartments (i.e. spring sediments and water) on the genetic richness, diversity and structure of diatom communities in 16 mineral springs in the Massif Central, France. Diatom biofilms were collected during October 2019, and a 312 bp region of the chloroplast gene rbcL (coding for the Ribulose Bisphosphate Carboxylase) used as a barcode for taxonomic assignation. A total of 565 amplicon sequence variants (ASV) were found. The dominant ASV were associated with Navicula sanctamargaritae, Gedaniella sp., Planothidium frequentissimum, Navicula veneta, Diploneis vacillans, Amphora copulata, Pinnularia brebissonii, Halamphora coffeaeformis, Gomphonema saprophilum, and Nitzschia vitrea, but some of the ASVs could not be assigned at the species level. Pearson correlation failed to show a correlation between ASV' richness and radioactivity parameters. Non-parametric MANOVA analysis based on ASVs occurrence or abundances revealed that geographical location was the main factor influencing ASVs distribution. Interestingly, ²³⁸U was the second factor that explained diatom ASV structure. Among the ASVs in the mineral springs monitored, ASV associated with one of the genetic variants of Planothidium frequentissimum was well represented in the springs and with higher levels of ²³⁸U, suggesting its high tolerance to this particular radionuclide. This diatom species may therefore represent a bio-indicator of high natural levels of uranium.

Integration of a Shallow Soda Lake into the Groundwater Flow System by Using Hydraulic Evaluation and Environmental Tracers

Lake Velence is a shallow soda lake whose water level and water quality show a severely deteriorating tendency in recent years. Until recently, the groundwater component in the lake’s water budget has not been taken into consideration. To integrate the lake into the groundwater flow system at the regional scale, methods of “basin hydraulics” were applied. In addition, 17 water samples were collected for δ2H and δ18O, and for ΣU, 226Ra and 222Rn activity measurements to use these parameters as environmental tracers of groundwater contribution. Groundwater mapping revealed that groundwater recharges in Velence Hills and the local elevations south of the lake, whereas discharge occurs by the lake’s shoreline and along surface watercourses. The results indicated that Lake Velence is the discharge point of local groundwater flow systems known to be more sensitive to climate changes and anthropogenic activities (e.g., contamination, overexploitation). Groundwater and lake water have similar uranium activity concentrations serving as another sign of groundwater inflow into the lake. Therefore, it is necessary to consider both the groundwater component in the lake’s water management and its vulnerability regarding local and short-term changes in the catchment area.

Use of Biomphalaria glabrata as a bioindicator of groundwater quality under the influence of NORM

The Brazilian northeast is known to have sedimentary areas that contain minerals with anomalous concentrations of naturally occurring radioactive material (NORM). This characteristic can contribute to the elevation of natural radiation in the air, soil, and groundwater. Due to the inefficiency of drinking water distribution in this region, the use of water from wells has become essential for the population. Therefore, the objective of this research was to monitor the concentration of ²³⁸U and ²³²Th associated with biomonitoring with the species of mollusc Biomphalaria glabrata in waters of residential artesian wells, used for domestic consumption, in the municipalities of Abreu e Lima and São José do Sabugi, Brazil. To check the concentration of ²³⁸U and ²³²Th, ICP-MS was used. For biomonitoring, ecotoxicity techniques such as embryotoxicity and genotoxicity were used. The monitoring results confirmed high concentrations of natural uranium in one of the residential artesian wells, the data being above the limit allowed by the Ministry of Health of Brazil, whose study reference is the World Health Organization (WHO). The results of the bioassays showed embryotoxicity, with malformations and deaths in the exposed organisms being observed. The comet assay showed that groundwater caused changes in the mollusc's DNA, indicating genotoxicity. The bioassays suggest that embryotoxicity and genotoxicity were caused mainly by the high concentration of natural uranium. Therefore, the bioindicator B. glabrata was shown to be sensitive to the toxic effects of anomalous concentrations of NORM present in groundwater.

Application Progress of Deinococcus radiodurans in Biological Treatment of Radioactive Uranium-Containing Wastewater

Radioactive uranium wastewater contains a large amount of radionuclide uranium and other heavy metal ions. The radioactive uranium wastewater discharged into the environment will not only pollute the natural environment, but also threat human health. Therefore, the treatment of radioactive uranium wastewater is a current research focus for many researchers. The treatment in radioactive uranium wastewater mainly includes physical, chemical and biological methods. At present, the using of biological treatment to treat uranium in radioactive uranium wastewater has been gradually shown its superiority and advantages. Deinococcus radiodurans is a famous microorganism with the most radiation resistant to ionizing radiation in the world, and can also resist various other extreme pressures. D. radiodurans can be directly used for the adsorption of uranium in radioactive waste water, and it can also transform other functional genes into D. radiodurans to construct genetically engineered bacteria, and then applied to the treatment of radioactive uranium containing wastewater. Radionuclides uranium in radioactive uranium-containing wastewater treated by D. radiodurans involves a lot of mechanisms. This article reviews currently the application of D. radiodurans that directly or construct genetically engineered bacteria in the treatment of radioactive uranium wastewater and discusses the mechanism of D. radiodurans in bioremediation of uranium. The application of constructing an engineered bacteria of D. radiodurans with powerful functions in uranium-containing wastewater is prospected.

Occurrence and Distribution of Uranium in a Hydrological Cycle around a Uranium Mill Tailings Pond, Southern China

Uranium (U) mining activities, which lead to contamination in soils and waters (i.e., leachate from U mill tailings), cause serious environmental problems. However, limited research works have been conducted on U pollution associated with a whole soil-water system. In this study, a total of 110 samples including 96 solid and 14 water samples were collected to investigate the characteristics of U distribution in a natural soil-water system near a U mining tailings pond. Results showed that U concentrations ranged from 0.09 ± 0.02 mg/kg to 2.56 × 10⁴± 23 mg/kg in solid samples, and varied greatly in different locations. For tailings sand samples, the highest U concentration (2.56× 10⁴ ± 23 mg/kg) occurred at the depth of 80 cm underground, whereas, for paddy soil samples, the highest U concentration (5.22 ± 0.04 mg/kg) was found at surface layers. Geo-accumulation index and potential ecological hazard index were calculated to assess the hazard of U in the soils. The calculation results showed that half of the soil sampling sites were moderately polluted. For groundwater samples, U concentrations ranged from 0.55 ± 0.04 mg/L to 3.36 ± 0.02 mg/L with a mean value of 2.36 ± 0.36 mg/L, which was significantly lower than that of percolating waters (ranging from 4.56 ± 0.02 mg/L to 12.05 ± 0.04 mg/L, mean 7.91 ± 0.98 mg/L). The results of this study suggest that the distribution of U concentrations in a soil-water system was closely associated with hydrological cycles and U concentrations decreased with circulation path.

Transient nature of riverbank filtered drinking water supply systems - A new challenge of natural radioactivity assessment

In Hungary the drinking water supply is mainly based on groundwater, in which radionuclides are common components. Since the mobility of the most common radionuclides, uranium and radium, is strongly influenced by the geochemical conditions, knowledge on the geochemical parameters of water is required. This depends on the flow system and the flow regime. Therefore, hydrogeology has a crucial role in revealing the origin of elevated activity concentrations. This research presents a case study in Hungary where the drinking water supply is provided by bank filtered and karst wells. In most of the wells of the research area the gross alpha values are above the screening level, 0.1 Bq L^-1. The aim of this study is to determine which radionuclides may cause the elevated radioactivity and explain their occurrence using the hydrogeological approach. All samples of the study were analysed for (U-238+U-234), Ra-226, Rn-222. Alpha spectrometry applied on Nucfilm discs was used to measure the uranium and radium activity while radon activity was determined by liquid scintillation. The study revealed the correlation between the river water level fluctuation and the uranium content of the wells. The results of this study highlighted the transient nature of river bank filtered systems, which should be taken into account in the monitoring and water supply strategy.