226Ra Uptake Research Articles

Model of U and 226Ra uptake by Spergularia rubra (L.) J. Presl & C. Presl in an area affected by Cu ore mining

Spergularia rubra (L.) J. Presl & C. Presl has a mycorrhizal resistance that leads to increased uranium uptake. The results show that 35% of the 238U is retained in the carbonate fraction and 59% in the residual or non-reactive fraction. 226Ra shows a different pattern with an average association of 19% in the organic matter fraction, 10% in the carbonate compounds and the remaining 71% in the residual fraction. The relationships between the activity concentrations of 238U and 226Ra in the soil fractions and in Spergularia were found to be statistically representative of the carbonate and organic matter fractions, respectively.

Adsorption of Ba and 226Ra on illite: A comparative experimental and modelling study

Illite, smectite and illite/smectite mixed layers are major phases in various argillaceous rock formations foreseen as potential host rocks for the deep geological disposal of high-level radioactive waste and are important sorbents for cationic radionuclides potentially released in the repository. 226Ra is a critical radionuclide in the safety analysis and an important source of radioactivity in technically enhanced naturally occurring radioactive materials. A comprehensive study was carried out on the adsorption of Ba and Ra on purified homoionic Na-illite (Illite du Puy) over a wide range of experimental conditions (pH, concentration, ionic strength) allowing for the development of a quasi-mechanistic Ba/Ra adsorption model for illite. Ba adsorption isotherms obtained at fixed ionic strength and pH exhibit a non-linear behaviour in the Ba equilibrium concentration range between ∼10−7 and ∼10−2 M. The pH dependent adsorption of trace 226Ra and Ba was investigated at different ionic strengths and evidenced a more pronounced adsorption of 226Ra than Ba on illite. Finally, a competition experiment of trace 226Ra in the presence of increasing Ba concentrations showed an unexpected 226Ra adsorption behaviour which was not observed for montmorillonite in earlier studies. This large set of experimental data could be successfully modelled by Ba/226Ra exchange reactions against Na, together with selectivity coefficients, on two different site types, namely planar sites and high affinity sites. The modelling of the pH dependent adsorption of Ba and 226Ra at high ionic strength and high pH required an additional surface complexation reaction. Two additional exchange sites had to be introduced to quantitatively describe the 226Ra uptake on illite in the 226Ra/Ba competition experiment. The nature of these sites, however, remains unclear. The implementation of the 226Ra adsorption model into predictive transport modelling codes is of key importance for the safety analysis of deep geological disposal of radioactive waste.

Biodistribution of naturally occurring radionuclides and radiocesium in wild European perch (Perca fluviatilis)

Wild European perch (Perca fluviatilis) is one of the most important freshwater fish species, in Sweden, due to its widespread and his value for recreational fishing. Little it is known regarding the biodistribution of naturally occurring radionuclides such as 238U, 234U, 226Ra, 210Po in perch. Therefore, in this study, perches from five lakes located in different counties in Sweden were collected to investigate the biodistribution of 238U, 234U, 226Ra, 210Po and 137Cs in organs and tissues of perch as well as their radiological impact. The results showed that uranium radionuclides ranged between 0.1 and 6 Bq/kg with an average value of 1.1 ± 1.5 Bq/kg. 226Ra varied from 0.4 to 8 Bq/kg with a mean concentration of 1.7 ± 1.9 Bq/kg. The ranged of 210Po was 0.5 – 250 Bq/kg, with an average value of 24 ± 52 Bq/kg. On the other hand, the highest activity concentration of 137Cs, 151 ± 1 Bq/kg, was detected in muscle samples of perch from Redsjösjön lake. For uranium radionuclides and 226Ra uptake from water is the main source whereas for 210Po and 137Cs the uptake is controlled by the perch diet. Regarding naturally occurring radionuclides, the perch tended to accumulated uranium radionuclides in fins, gills, and skin; 226Ra in bones, fins and skin and 210Po in the organs linked to digestive system. Finally, in case of consumption, it is advised the consumption of skinned fillets of perch due to the higher bioaccumulation of the radionuclides investigated in the skin and scales.

Substratum influences uptake of radium-226 by plants

Radium-226, an alpha emitter with half-life 1600 years, is ubiquitous in natural environments. Present in rocks and soils, it is also absorbed by vegetation. The efficiency of 226Ra uptake by plants from the soil is important to assess for the study of heavy metals uptake by plants, monitoring of radioactive pollution, and the biogeochemical cycle of radium in the Critical Zone. Using a thoroughly validated measurement method of effective 226Ra concentration (ECRa) in the laboratory, we compare ECRa values of the plant to that of the closest soil, and we infer the 226Ra soil-to-plant transfer ratio, RSP, for a total of 108 plant samples collected in various locations in France. ECRa values of plants range over five orders of magnitude with mean (min–max) of 1.66 ± 0.03 (0.020–113) Bq kg−1. Inferred RSP values range over four orders of magnitude with mean (min–max) of 0.0188 ± 0.0004 (0.00069–0.37). The mean RSP value of plants in granitic and metamorphic context (0.073 ± 0.002; n = 50) is significantly higher (12 ± 1 times) than that of plants in calcareous and sedimentary context (0.0058 ± 0.0002; n = 58). This difference, which cannot be attributed to a systematic difference in emanation coefficient, is likely due to the competition between calcium and radium. In a given substratum context, the compartments of a given plant species show coherent and decreasing RSP values in the following order (acropetal gradient): roots > bark > branches and stems ≈ leaves. Oak trees (Quercus genus) concentrate 226Ra more than other trees and plants in this set. While this study clearly demonstrates the influence of substratum on the 226Ra uptake by plants in non-contaminated areas, our measurement method appears as a promising practical tool to use for (phyto)remediation and its monitoring in uranium- and radium-contaminated areas.

Recrystallization and Uptake of 226Ra into Ba-Rich (Ba,Sr)SO4 Solid Solutions

226Ra is an important contributor to naturally occurring radioactive materials (NORM) and also considered in safety cases related to the disposal of spent nuclear fuel in a deep geological repository. Recrystallization and solid solution formation with sulfates is regarded as an important retention mechanism for 226Ra. In natural systems sulfates often occur as (Ba,Sr)SO4. Therefore, we have chosen this solid solution at the Ba-rich end for investigations of the 226Ra uptake. The resulting 226Ra-solubility in aqueous solution was assessed in comparison with a thermodynamic model of the solid solution-aqueous solution system (Ba,Sr,Ra)SO4 + H2O. The temperature and composition of the initial (Ba,Sr)SO4 solid solution were varied. Measurements of the solution composition were combined with microscopic observations of the solid and thermodynamic modeling. A complex recrystallization behavior of the solid was observed, including the dissolution of significant amounts of the solid and formation of metastable phases. The re-equilibration of Ba-rich (Ba,Sr)SO4 to (Ba,Sr,Ra)SO4 leads to a major reconstruction of the solid. Already trace amounts of Sr in the solid solution can have a significant impact on the 226Ra solubility, depending on the temperature. The experimental findings confirm the thermodynamic model, although not all solids reached equilibrium with respect to all cations.

Sequestration of Radionuclides Radium-226 and Strontium-90 by Cyanobacteria Forming Intracellular Calcium Carbonates.

226Ra is a naturally occurring radionuclide with a half-life of 1600 years. In contrast, 90Sr is a radionuclide of sole anthropogenic origin, produced by nuclear fission reactions and has a half-life of 29 years; each of these radionuclides poses potential threats to human and ecosystem health. Here, the cyanobacterium Gloeomargarita lithophora, capable of forming intracellular amorphous calcium carbonate inclusions, was investigated for its ability to uptake 226Ra and 90Sr. In BG-11 medium, G. lithophora accumulated 3.9 μg g-1 of 226Ra within 144 h and 47.9 ng g-1 of 90Sr within 1 h, corresponding to ∼99% removal of trace radionuclides. The presence of high-concentration Ca2+ in the background media solution did not inhibit 90Sr and 226Ra uptake by G. lithophora. In contrast, dead biomass of G. lithophora accumulated 0.8 μg g-1 of 226Ra and 8.87 ng g-1 of 90Sr. Moreover, Synechocystis, a nonbiomineralizing cyanobacteria, removed only 14 and 25% of 226Ra and 90Sr, respectively. This suggested that sequestration of 90Sr and 226Ra was not intrinsic to all cyanobacteria but was likely a specific biological trait of G. lithophora related to the formation of intracellular amorphous Ca-carbonates. The unique ability of G. lithophora to uptake 90Sr and 226Ra at high rates makes it an attractive candidate for further studies involving bioremediation of these radionuclides.

A Study of 226Ra Concentration Ratios for Leafy Vegetables

The aim of this work was to study the factors that influence the 226Ra uptake by two types of leafy vegetables collected from different farms in Al Sharqiya region in Saudi Arabia with their corresponding soils and irrigation waters. Quality assurance and validation of the radioanalyses for the different samples matrices were carried out. It was a reasonable approach to determine the 226Ra concentration ratios on the basis of both the exchangeable and total 226Ra content in the soils. It was found that the activity concentration of 226Ra in soils is independent on its corresponding activities in irrigation water but correlates well with the soil content of clay and silt. No significant dependency of the 226Ra concentration ratios for the studied vegetables on the radium total activities in soils. Good negative correlations were found between the organic matter content of soils and the concentration ratios of 226Ra in cabbage and lettuce. Some variations of the 226Ra uptake were found through the two leafy vegetables which may be explained by other factors related to the metabolic characteristics of the plant species. The 226Ra concentration ratios based on the exchangeable radium leached from soil for cabbage and lettuce were found to be higher than those determined on the basis of its total activity in soil. The exchangeable 226Ra may contribute for a better understanding of its uptake by leafy vegetables in these farms.

Barite recrystallization in the presence of 226Ra and 133Ba

Despite the long history of studies on (Ba,Ra)SO4, various recent investigations aimed at improving our understanding of its formation processes and thermodynamics. Accumulation of natural Ra isotopes (mainly 226Ra and 228Ra) in (Ba,Ra)SO4 plays an important role in many geotechnical applications and water desalination facilities. In the near field of a nuclear waste repository, barite formation may be expected e.g. as a consequence of contact of spent nuclear fuel or vitrified high level waste with sulfate containing ground water, and may control the potential release of Ra from waste forms upon leakage.Here, we present results of long term batch-type barite recrystallization experiments conducted in the simultaneous presence of 226Ra and 133Ba as a function of initial Ra2+ concentration and pH with the same type and charge of barite powder as used in previous studies (Curti et al., 2010; Klinkenberg et al., 2014; Brandt et al., 2015). Due to the simultaneous measurement of 133Ba and 226Ra our data allow for a direct relation of 226Ra uptake with barite recrystallization, which leads to more accurate partition coefficients compared to previous studies. During a reaction period of five years, barite is continuously recrystallizing. Within the investigated radium concentration range (Ba(1−X)RaXSO4 with X < 0.0006), we measure a partition coefficient of D = 2.1 ± 0.5. The partition coefficient is constant within uncertainty during almost five years (1793 days) of experimental duration. This value is in line with a description of (Ba,Ra)SO4 as an ideal solid solution based on the solubility products (KSP) of the endmembers barite (log10(KSP(barite)) = −9.97) and radium sulfate (log10(KSP(RaSO4)) = −10.26; dimensionless Guggenheim parameter, a0 = 0.0 ± 0.3). Apparent discrepancies to previous theoretical results (a0 = 1.0 ± 0.4) may be resolved when the uncertainties related to the solubility of RaSO4 are considered.Compared to results of previous publications, recrystallization is extremely slow in the experiments presented here. While previous authors suggested complete equilibration of bulk microcrystalline barite within less than three years, a recrystallization of less than 7% of the barite mass is observed within five years. We describe the progress of recrystallization with a new modified homogeneous recrystallization model. Observed recrystallization rates are in the range 0.11–1.5 nmol/(m2 s) and increase with decreasing pH. According to this modified homogeneous recrystallization model, complete bulk barite equilibration is expected in about 1400–16,900 years.The strongly decreased recrystallization kinetics in our experiments is likely related to a strongly prolonged pre-equilibration time (0.8 years), which according to XRD investigations, leads to a higher crystallinity (higher crystal domain size and lower Debye-Waller parameters) of the barite powder.

Water hardness determines 226Ra uptake in the tropical freshwater mussel

Chemical data for freshwater mussels (Velesunio spp.) and water from 15 sampling sites in the Alligator Rivers Region and Rum Jungle uranium provinces in tropical Northern Australia were analysed to develop a predictive model of radium-226 (226Ra) bioaccumulation for variable water calcium (Ca) and magnesium (Mg) concentrations. Application of the model as a 226Ra screening approach for freshwater mussels in tropical waterbodies potentially impacted by operational or remediated uranium mine sites is discussed in relation to Mudginberri Billabong, located approximately 12 km downstream of Ranger uranium mine in the Alligator Rivers Region.

Vegetation composition and 226Ra uptake by native plant species at a uranium mill tailings impoundment in South China

A field investigation was conducted for the vegetation composition and 226Ra uptake by native plant species at a uranium mill tailings impoundment in South China. 80 species belonging to 67 genera in 32 families were recorded in the sampling sites. The Poaceae and Asteraceae were the dominant families colonizing the impoundment. The number of the plant species and vegetation community composition in the sampling sites seemed most closely related to the activities of 226Ra and the pH value of the uranium tailings. The plant species in the sampling sites with relatively low activities of 226Ra and relatively high pH value formed a relatively stable vegetation community. The plant species in the sampling sites with medium activities of 226Ra and medium pH value formed the transitional vegetation community. The plant species in the sampling sites with relatively high activities of 226Ra and relatively low pH value formed a simple unstable vegetation community that was similar to that on the unused grassland. The activities of 226Ra and transfer factors (TFs) varied greatly with the plant species. The high activities of 226Ra and TFs were found in the leaves of Pteris multifida (150.6 Bq/g of AW; 9.131), Pteridium aquilinum (122.2 Bq/g of AW; 7.409), and Dryopteris scottii (105.7 Bq/g of AW; 6.408). They satisfied the criteria for a hyperaccumulator for 226Ra. They may be the candidates for phytoremediation of 226Ra in the uranium mill tailings impoundment areas and the contaminated soils around.

Sorption of 226Ra from oil effluents onto synthetic cation exchangers

Increasing environmental awareness is being urged for the safe disposal of 226Ra-contaminated production water generated in the oil industry. Birnessite, antimony silicate and their cationic derivatives were studied for the take-up of 226Ra using the batch-type method under experimentally determined parameters, viz. contact time, solution-solid ratio and 226Ra concentration. Data was expressed in terms of distribution coefficients. Sorption experiments were performed in different concentrations of nitric acid in order to speculate the mechanism of 226Ra uptake. Variation in the magnitude of sorption efficiency of the materials in the presence of the major components of waste streams, i.e. Na+, K+ and Ca2+, revealed that K+ was the greatest competitor and Na+ the least. The application of the materials to sorb 226Ra from actual oil co-production water samples, collected from Der Ezzor and Al Fourat petroleum companies (DEZPC and AFPC), was interpreted in terms of the exchange properties of the materials and water characterisation. Of the parameters studied, the selectivity of materials was shown to be greatly dependent on the pH of wastewater to be treated.

Radium Uptake by Recrystallized Gypsum: An Incorporation Study

Batch experiments of 226Ra uptake by recrystallized gypsum CaSO4.2H2O(s), monitored over 200 days, have shown that the published value for the distribution coefficient of 226Ra between gypsum and an aqueous phase, 0.03 (Gnanapragasam and Lewis, 1995), is an upper limit. This suggests that this value needs to be confirmed. A solid solution between gypsum and radium sulfate (Ca,Ra)SO4.2H2O(s) cannot be considered per se, which is not surprising considering gypsum's high solubility product (lg Ks = -4.58) and the ionic radius of VIIIRa (1.48Å), when compared to that of VIIICa (1.12Å).

INGESTION OF 226Ra FROM ACTIVATED PAINTS ON MILITARY EQUIPMENT: TRANSFER FACTORS AND DOSES

The use of 226Ra-activated markings was specific for military equipment some decades ago and the extent of possible internal exposure of former military personnel due to ingestion of 226Ra is an issue of discussion. Whole- or partial-body counts are not sensitive enough to trace an overexposure due to a possible 226Ra uptake four decades ago. Thus retrospective workplace assessments are needed. These are done by wiping tests with linen and skin pads on 226Ra markings on decommissioned military equipment. The contamination investigations are performed in wipe-activity measuring cycles with exponentially increasing numbers of wipes. The activity wiped off does not increase with the number of wipes but levels off instead. Wipes with linen pads are more effective than wipes with skin. The skin-skin activity transfer is investigated by respective wipes too. The maximum committed dose in a typical scenario is calculated under worst case assumptions. For the typical work of 1 y an effective dose of about 70 μSv, and for the bone surface a dose of about 3 mSv, is obtained.

Industrial radioactive barite scale: suppression of radium uptake by introduction of competing ions

Incorporation of radioactive isotopes during the formation of barite mineral scale is a widespread phenomenon occurring within the oil, mining and process industries. In a series of experiments radioactive barite/celestite solid solutions (SS Barite–Celestite) have been synthesized under controlled conditions by the counter diffusion of 226Ra, Ba 2+, Sr 2+ and SO 4 2− ions through a porous medium (silica gel), to investigate inhibiting effects in Ra uptake associated with the introduction of a competing ion (Sr 2+). From characterization studies, the particle size and the morphology of the crystals appear to be related to the initial [Sr]/[Ba] molar ratio of the starting solution. Typically, systems richer in Sr produce smaller sized crystals and clusters characterized by a lower degree of order. The activity introduced to the system is mainly incorporated in the crystals generated from the barite/celestite solid solution as suggested by the activity profiles of the hydrogel columns analysed by γ-spectrometry. There is a relationship between the initial [Sr]/[Ba] molar ratio of the starting solution and the activity exhibited by the synthesized crystals. An effective inhibition of the 226Ra uptake during formation of the crystals (SS Barite–Celestite) was obtained through the introduction of a competing ion (Sr 2+): the higher the initial [Sr]/[Ba] molar ratio of the starting solution, the lower the intensity of the activity peak in the crystals.

Biosorption of226Ra in high level natural radiation areas of Ramsar, Iran

Bacterial strains isolated from hot springs and soil of high level natural radiation areas of Ramsar, a northern coastal city of Iran, have been studied for their 226Ra sorption ability from aqueous solutions. Gamma-spectrometry showed that the uptake values of strains A-C, T-A, A-E and CH-G at a radioactivity level of 4.3±0.2 Bq·mlℒ1 were 202±53, 171±49, 123±11 and 53±6 Bq·gℒ1, respectively. Biosorption was the major mechanism involved in 226Ra uptake and was not affected by 2,4-dinitrophenol (DNP) or incubation at 4°C. There was an inverse relationship between the rapid radium uptake value and biomass weight in the strains A-C and A-E. Strain A-C was identified as Citrobacter freundii and strains T-A, A-E and CH-G belonged to the genera Corynebacterium, Chromobacterium and Chryseobacterium, respectively.

Evaluation of the variation of 226Ra and Ca uptake by plant and their relationship

The transfer of 226Ra from soil to plant has been studied for wild trees and grasses to identify the site- and the plant-specific variability in relation to the transfer of Ca. Twelve species of plants and soils were sampled from three different forests and one flood plain in Okayama, Japan. The concentrations of 226Ra in plant varied about 60 times by species and sites, while those in soil were not different significantly among sites. The transfer factors defined as the concentration ratio of 226Ra between plant and soil were linearly correlated with that of Ca, implying that the ability of Ca uptake by plant reflect the ability of 226Ra uptake. The Ca concentrations in plant showed species-specific value and varied 22 times. The range of transfer factor (plant/soil) for Ca increased by the variability of the Ca concentration in soil among sites. These results suggest that the wide variability of 226Ra concentration in plant can be ascribed to both the differences in plant and soil factors of Ca concentration.

226Ra bioavailability to plants at the Urgeiriça uranium mill tailings site

Large amounts of solid wastes (tailings) resulting from the exploitation and treatment of uranium ore at the Urgeiriça mine (north of Portugal) have been accumulated in dams (tailing ponds). To reduce the dispersion of natural radionuclides into the environment, some dams were revegetated with eucalyptus ( Eucalyptus globolus) and pines ( Pinus pinea). Besides these plants, some shrubs ( Cytisus spp .) are growing in some of the dams. The objective of this study is to determine the 226Ra bioavailability from uranium mill tailings by quantifying the total and available fraction of radium in the tailings and to estimate its transfer to plants growing on the tailing piles. Plant and tailing samples were randomly collected and the activity concentration of 226Ra in plants (aerial part and roots) and tailings was measured by gamma-spectrometry. The exchangeable fraction of radium in tailings was quantified using one single step extraction with 1 mol dm −3 ammonium acetate (pH=7) or 1 mol dm −3 calcium chloride solutions. The results obtained for 226Ra uptake by plants show that 226Ra concentration ratios for eucalyptus and pines decrease at low 226Ra concentrations in the tailings and appear relatively constant at higher radium concentrations. For shrubs, the concentration ratios increase at higher 226Ra solid waste concentrations approaching a saturation value. Percentage values of 16.0±8.3 and 12.9±8.9, for the fraction of radium extracted from the tailings, using 1 mol dm −3 ammonium acetate or calcium chloride solutions, respectively, were obtained. The 226Ra concentration ratios determined on the basis of exchangeable radium are one order of magnitude higher than those based on total radium. It can be concluded that, at a 95% confidence level, more consistent 226Ra concentration ratios were obtained when calculated on the basis of available radium than when total radium was considered, for all the dams.

Methane and nitrous oxide evolution and 15N and 226Ra uptake as affected by application of gypsum and phosphogypsum to Louisiana rice

A field study was conducted to determine the effects of gypsum and phosphogypsum on methane and nitrous oxide evolution and on 15N and 226Ra uptake by Oryza sativa L. (rice). Gypsum and phosphogypsum at 2.5, 5.0 and 10.0 tons ha −1 and 15N labelled urea (150 kg N ha −1) were applied pre-flood to experimental plots drill-seeded with `cypress', a semi-dwarf long-grain rice cultivar. Methane and nitrous oxide were measured twice a week over the main cropping season. Plant samples were collected at harvest and 15N uptake and 226Ra activity measured. Three rates of gypsum reduced methane evolution 49, 52 and 66%, respectively, compared with control plots. Phosphogypsum (2.5, 5.0 and 10.0 tons ha −1) decreased emissions of methane 47, 46 and 51%, respectively, over the 84-day study. Nitrous oxide fluxes were low (10–29 g ha −1 day −1) and only detected from control plots on two sampling dates. The assimilation of applied 15N in grain collected from gypsum plots was significantly higher compared with control and phosphogypsum treatments. The measured grain 226Ra activities were low and averaged 0.518 Bq kg −1 for phosphogypsum compared with a control plot activity of 0.222 Bq kg −1.

Soil to plant transfer of Radium-226

A study of the uptake of 226Ra by vegetables was carried out in zones contaminated by wastes from an abandoned radium salts factory and from uranium mines and in uncontaminated regions of purely natural radioactivity. Radium-226 uptake depends on its concentration in the soil, the logarithm of its concentration in the vegetables being a linear function of the logarithm of the concentration in the soil. Concentration factors for 226Ra uptake by cabbage leaves range from 0·007 to 0·11; for herbage, they range from 0·09 to 0·5.

226Ra uptake by sagebrush from uniform and non-uniform soil amendments

A two-group plant uptake experiment was conducted in which sagebrush seedlings ( Artemisia tridentata) were grown in pots containing soil spiked with 226Ra. The objective was to determine the effect of soil tracer amendment configuration on the uptake of 226Ra as determined by the concentration in leaves. The soil in all pots was spiked to contain the same total radioactivity. In one group, the radioactivity was distributed uniformly in the soil. In the other group, the activity was injected into the soil along a narrow vertical line, the site of injection being chosen randomly. The mean 226Ra leaf concentration from each group was 0.8 kBq/kg; however, the coefficient of variation of the leaf concentration from uniformly contaminated soil was 30% as compared to 84% for uptake from injected soil. It was concluded from statistical hypothesis testing that the mean leaf concentration was indistinguishable for the two groups.