Assessment of radioactivity contents in bedrock groundwater samples from the northern region of Saudi Arabia

Colorimetric sensing for the sensitive detection of UO22+via the phosphorylation functionalized mesoporous silica-based controlled release system

In this study, we developed a simple and sensitive colorimetric sensing method for the detection of UO22+, which was built to release MB from the molybdenum disulfide with a phosphate group (MoS2-PO4) gated mesoporous silica nanoparticles functionalized phosphate group (MSN-PO4) with UO22+ chelating. In the presence of UO22+, MoS2-PO4 can be effectively adsorbed onto the surface of MSN-PO4 based on the coordination chemistry for strong affinity between the P-O bond and UO22+. The adsorbed MoS2-PO4 was then utilized as an ideal gate material to control the release of signal molecules (MB) entrapped within the pores of MSN-PO4, resulting in a detectable decrease in the absorption peak at 663 nm. This colorimetric sensing demonstrated the advantages of simplicity and easy manipulation and exhibited a linear response to the concentration of UO22+ within the range of 0.02-0.2 μM. The detection limit of UO22+ was determined to be 0.85 nM, which was lower than the limit (130 nmol L-1) set by the US Environmental Protection Agency. Furthermore, the proposed colorimetric sensing method has been utilized to determine UO22+ in samples of Xiangjiang River and tap water, and a high recovery rate was achieved. This method shows promising potential in preventing and controlling environmental pollution.

Estimation of gross α-β and tritium activities in groundwater samples using LSC-TDCR technique in and around the geothermal region of Eastern India

The present study is an attempt to assess the radiogenic quality of groundwater on the basis of gross α, gross β and tritium (3H or H-3) activities in the Bakreswar-Tantloi geothermal region of Chotanagpur Plateau, West Bengal and Jharkhand, India. The aforesaid parameters in groundwater samples were measured using liquid scintillation counting triple to double coincidence ratio (LSC-TDCR) technique. Groundwater samples collected from Bakreswar-Tantloi geothermal region show gross α activities from below the minimum detectable activity (BMDA) to 0.5 ± 0.05 Bq/L, gross β activities from BMDA to 0.2 ± 0.01 Bq/L and H-3 activities from BMDA to 63.42 Bq/L. The average gross α, gross β and H-3 activities are also within the permissible limits prescribed by the World Health Organization (WHO). Though the annual effective doses in some samples were higher than the reference dose level of 0.1 mSv, the overall result suggests that the groundwater in the Bakreswar-Tantloi geothermal region is radiologically safe considering the radionuclides covered in this study.

Environmental evaluation of radioactivity levels and associated radiation hazards in groundwater around the WIPP site

Groundwater may contain radioactive substances which can be dangerous to human health. Concentrations of natural radionuclides polonium (Po), thorium (Th), uranium (U), and radium (Ra) isotopes were measured in groundwater samples collected from different locations in the vicinity of the Waste Isolation Pilot Plant (WIPP) site in Carlsbad, New Mexico. The average values of gross activity concentrations of ²¹⁰Po, ²²⁸Th, ²³⁸U, ²³⁴U, ²²⁶Ra and ²²⁸ Ra isotopes were determined to be 1.62 Bq L^-1 in shallow groundwater and 5.88 Bq L^-1 in deep groundwater, respectively. The total radioactivity in deep groundwater was higher than that in shallow groundwater, and most of the radioactivity in the water is from ²²⁶Ra. Furthermore, the effective doses for ingestion of natural radionuclides were about 0.333 mSv y^-1 for shallow groundwater and about 1.338 mSv y^-1 for deep groundwater samples, which are higher than the World Health Organization (WHO, 2017) guideline level (0.1 mSv y^-1) for drinking water. Ra dominated the total ingestion dose, contributing 93.06 % and 75.40 % of the total effective doses to the deep and shallow groundwater, respectively. The ingrowth and decay of natural radionuclides suggested that ²²⁸Ra/²²⁶Ra ratio can be a useful indicator of the source of radioactive contamination. The radioactivity data obtained from the investigated groundwater samples can be used to establish a baseline for radioactivity levels in groundwater around the WIPP site.

Factors controlling groundwater radioactivity in arid environments: An automated machine learning approach

Groundwater resources in the Kingdom of Saudi Arabia (KSA) have high levels of natural radioactivity. Within the northwestern KSA, gross alpha (α) and gross beta (β) levels exceed national and international drinking-water limits. In this study, we developed and used an automated machine learning (AML) approach to quantify relationships between gross α and gross β activities and different geological, hydrogeological, and geochemical conditions. Two AML model groups (group I for gross α; group II for gross β) were constructed, using water samples collected from 360 irrigation and water supply wells, to define a robust model that explains the spatial variability in gross α and gross β activities, as well as variables that control the gross activities. Each group contained four model families: deep neural network (DNN), gradient boosting machine (GBM), generalized linear model (GLM), and distributed random forest (DRF). Model inputs include chemical compositions as well as geological and hydrogeological conditions. Three performance metrics were used to evaluate the models during training and testing: normalized root mean square error (NRMSE), Pearson's correlation coefficient (r), and Nash-Sutcliff efficiency (NSE) coefficient. Results indicate that (1) the GBM model outperformed (training: NRMSE: 0.37 ± 0.10; r: 0.92 ± 0.05; NSE: 0.85 ± 0.09; testing: NRMSE: 0.71 ± 0.08; r: 0.72 ± 0.08; NSE: 0.49 ± 0.12) the DNN, DRF, and GLM models when modelling gross α activities; (2) gross α activities are controlled by pH, stream density, nitrate, manganese, and vegetation index; (3) the DRF model outperformed (training: NRMSE: 0.41 ± 0.05; r: 0.92 ± 0.02; NSE: 0.83 ± 0.04; testing: NRMSE: 0.67 ± 0.09; r: 0.77 ± 0.07; NSE: 0.54 ± 0.12) the GBM, DNN, and GLM models when modelling gross β activities; (4) input variables that affect the gross β actives are pH, temperature, stream density, lithology, and nitrate; and (5) no single model could be used to model both gross α and gross β activities-instead, a combination of AML models should be used. Our computationally efficient approach provides a framework and insights for using AML techniques in water quality investigations and promotes more and improved use of different geological, hydrogeological, and geochemical datasets by the scientific community and decision makers to develop guidelines for mitigation.

A critical review on the occurrence and distribution of the uranium- and thorium-decay nuclides and their effect on the quality of groundwater

This critical review presents the key factors that control the occurrence of natural elements from the uranium- and thorium-decay series, also known as naturally occurring radioactive materials (NORM), including uranium, radium, radon, lead, polonium, and their isotopes in groundwater resources. Given their toxicity and radiation, elevated levels of these nuclides in drinking water pose human health risks, and therefore understanding the occurrence, sources, and factors that control the mobilization of these nuclides from aquifer rocks is critical for better groundwater management and human health protection. The concentrations of these nuclides in groundwater are a function of the groundwater residence time relative to the decay rates of the nuclides, as well as the net balance between nuclides mobilization (dissolution, desorption, recoil) and retention (adsorption, precipitation). This paper explores the factors that control this balance, including the relationships between the elemental chemistry (e.g., solubility and speciation), lithological and hydrogeological factors, groundwater geochemistry (e.g., redox state, pH, ionic strength, ion-pairs availability), and their combined effects and interactions. The various chemical properties of each of the nuclides results in different likelihoods for co-occurrence. For example, the primordial ²³⁸U, ²²²Rn, and, in cases of high colloid concentrations also ²¹⁰Po, are all more likely to be found in oxic groundwater. In contrast, in reducing aquifers, Ra nuclides, ²¹⁰Pb, and in absence of high colloid concentrations, ²¹⁰Po, are more mobile and frequently occur in groundwater. In highly permeable sandstone aquifers that lack sufficient adsorption sites, Ra is often enriched, even in low salinity and oxic groundwater. This paper also highlights the isotope distributions, including those of relatively long-lived nuclides (²³⁸U/²³⁵U) with abundances that depend on geochemical conditions (e.g., fractionation induced from redox processes), as well as shorter-lived nuclides (²³⁴U/²³⁸U, ²²⁸Ra/²²⁶Ra, ²²⁴Ra/²²⁸Ra, ²¹⁰Pb/²²²Rn, ²¹⁰Po/²¹⁰Pb) that are strongly influenced by physical (recoil), lithological, and geochemical factors. Special attention is paid in evaluating the ability to use these isotope variations to elucidate the sources of these nuclides in groundwater, mechanisms of their mobilization from the rock matrix (e.g., recoil, ion-exchange), and retention into secondary mineral phases and ion-exchange sites.

Elevated radium levels in Nubian Aquifer groundwater of Northeastern Africa

The Nubian Sandstone Aquifer System in Northeast Africa and the Middle East is a huge water resource of inestimable value to the population. However, natural radioactivity impairs groundwater quality throughout the aquifer posing a radiological health risk to millions of people. Here we present measurements of radium isotopes in Nubian Aquifer groundwater from population centers in the Western Desert of Egypt. Groundwater has ²²⁶Ra and ²²⁸Ra activities ranging from 0.01 to 2.11 and 0.03 to 2.31 Bq/L, respectively. Most activities (combined ²²⁶Ra + ²²⁸Ra) exceed U.S. EPA drinking water standards. The estimated annual radiation doses associated with ingestion of water having the highest measured Ra activities are up to 138 and 14 times the WHO-recommended maxima for infants and adults, respectively. Dissolved Ra activities are positively correlated with barium and negatively correlated with sulfate, while barite is approximately saturated. In contrast, Ra is uncorrelated with salinity. These observations indicate the dominant geochemical mechanisms controlling dissolved Ra activity may be barite precipitation and sulfate reduction, along with input from alpha-recoil and dissolution of aquifer minerals and loss by radioactive decay. Radium mitigation measures should be adopted for water quality management where Nubian Aquifer groundwater is produced for agricultural and domestic consumption.

Study of Well Waters from High-Level Natural Radiation Areas in Northern Vietnam

The determination of natural radionuclide concentrations plays an important role for assuring public health and in the estimation of the radiological hazards. This is especially true for high level radiation areas. In this study, ²²⁶Ra, ²²⁸Ra and ²³⁸U concentrations were measured in well waters surrounding eight of the high-level natural radiation areas in northern Vietnam. The ²²⁶Ra, ²²⁸Ra and ²³⁸U activity concentrations vary from <1.2 × 10^-3-2.7 (0.46), <2.6 × 10^-3-0.43 (0.07) and <38 × 10^-3-5.32 Bq/L (0.50 of median), respectively. ²²⁶Ra and ²³⁸U isotopes in most areas are in equilibrium, except for the DT-Thai Nguyen area. The calculated radiological hazard indices are generally higher than WHO (World Health Organization) recommendations. Average annual effective dose and excess lifetime cancer risk values due to drinking well water range from to 130 to 540 μSv/year and 7.4 × 10^-6 to 3.1 × 10^-5, respectively.

The Potential Use of Zeolite, Montmorillonite, and Biochar for the Removal of Radium-226 from Aqueous Solutions and Contaminated Groundwater

The present work investigated the potential of using zeolite (clinoptilolite), montmorillonite (Swy2), and Conocarpus biochar as adsorbents to remove 226Ra from aqueous solution. The effect of the initial 226Ra concentrations on sorbents’ equilibrium activity concentrations and sorbents’ radium removal efficiency were investigated. The results showed that zeolite has a higher removal efficiency for 226Ra in comparison with the efficiencies of montmorillonite and biochar. In addition to the linear isotherm model, the Freundlich model, followed by Temkin’s model, provided a better description of the adsorption process than the Langmuir model. Kinetic studies indicated that a pseudo-second-order kinetic model could be the best fit for the adsorption of 226Ra onto the three investigated sorbents, which suggests that the mechanism of adsorption of 226Ra by sorbents was chemisorption. The intraparticle diffusion model indicated that adsorption of 226Ra onto the sorbents involves a multistep process: (i) boundary layer diffusion and (ii) intraparticle diffusion. Moreover, the remediation of groundwater samples polluted with 226Ra was assessed using the investigated sorbents; the results showed that zeolite also has the highest removal efficiency among other sorbents. Thus, the low cost, availability, and the high adsorption efficiency of zeolite can be a promising sorbent on 226Ra removal from aqueous solutions and groundwater remediation.

Assessment of radioactivity and chemical contaminants in domestic water at supply stations in Long Phu District, Vietnam, to prevent public health risks

This paper presents information on the concentration of radioactivity and chemicals at 12 water stations that used groundwater as their raw water supply source. The groundwater's radioactivity was higher than the treated, tap, and surface water, but lower than the national and international recommendations. At five stations (41.7%), the gross alpha contents were higher than the levels advised by Vietnam's regulations, but met the WHO and IAEA's recommendations. The mean activity (Bq L^-1) gross alpha, gross beta, Ra-224, Ra-226, and Ra-228 were 0.093 ± 0.012, 0.221 ± 0.020, 0.031 ± 0.004, 0.028 ± 0.004, and 0.035 ± 0.001, respectively. The contribution of Ra-226 to the gross alpha was in a range of 23%-60% (r = 0.91, p value <0.001), and the ratio of Ra-226/Ra-228 ranged from 0.49-1.06. For the treated and tap water, each age groups' annual committed effective dose was lower than the international regulations. The concentration of the total dissolved solids, sulfate, chloride, sodium, barium, and manganese met the national regulations. However, during the rainy season, the surface water in the area was affected by saltwater intrusion, with salinity up to 4.1‰. Discriminant analysis was applied to study the differences among the water groups. As a result, the treated and tap water were separated from the others.