Transfer of radionuclides through ecological systems: Lessons learned from 10 years of research within CERAD CoE.

Norway's Centre of Excellence for Environmental Radioactivity (CERAD) research programme included studies on transfer of radionuclides in various ecosystems within the context of environmental risk assessment. This article provides highlights from 10 years of research within this topic and summarises lessons learnt from the process. The scope has been extensive, involving laboratory-based experiments, field studies and the implementation of transfer models quantifying radionuclide uptake directly from the surrounding environment and via food chains. Field studies have had a global span and have, inter alia, covered sites contaminated with radionuclides associated with particles, ranging from nanoparticles to fragments, due to nuclear accidents (e.g., Chornobyl and Fukushima accidents) along with sites having enhanced levels of naturally occurring radioactive materials (e.g., Fen Complex in Norway and Taboshar in Tajikistan). Focus has been put on speciation and kinetics in determining radionuclide behavior and fate as well as on the influence of environmental factors that are potentially critical for the transfer of radionuclides. In particular, seasonal factors have been shown to greatly affect the dynamics of 137Cs and 90Sr bioaccumulation and loss in freshwater fish. The work has led to the collation of organism-specific (i) parameters important for kinetic models, i.e., uptake and depuration rates, and (ii) steady-state concentration ratios, CRs, where the use of stable analogue CRs as proxies for radionuclides has been brought into question. Dynamic models have been developed and applied for radiocaesium transfer to reindeer, radionuclide transfer in Arctic marine systems, transfer to fish via water and feed and commonly used agricultural food-chain transfer models applied in the context of nuclear emergency preparedness. The CERAD programme should contribute substantially to the scientific community's understanding of radionuclide transfer in environmental systems.

Recent trends in the phytoremediation of radionuclide contamination of soil by cesium and strontium: Sources, mechanisms and methods: A comprehensive review.

This comprehensive review examines recent trends in phytoremediation strategies to address soil radionuclide contamination by cesium (Cs) and strontium (Sr). Radionuclide contamination, resulting from natural processes and nuclear-related activities such as accidents and the operation of nuclear facilities, poses significant risks to the environment and human health. Cs and Sr, prominent radionuclides involved in nuclear accidents, exhibit chemical properties that contribute to their toxicity, including easy uptake, high solubility, and long half-lives. Phytoremediation is emerging as a promising and environmentally friendly approach to mitigate radionuclide contamination by exploiting the ability of plants to extract toxic elements from soil and water. This review focuses specifically on the removal of 90Sr and 137Cs, addressing their health risks and environmental implications. Understanding the mechanisms governing plant uptake of radionuclides is critical and is influenced by factors such as plant species, soil texture, and physicochemical properties. Phytoremediation not only addresses immediate contamination challenges but also provides long-term benefits for ecosystem restoration and sustainable development. By improving soil health, biodiversity, and ecosystem resilience, phytoremediation is in line with global sustainability goals and environmental protection initiatives. This review aims to provide insights into effective strategies for mitigating environmental hazards associated with radionuclide contamination and to highlight the importance of phytoremediation in environmental remediation efforts.

Uptake from water and depuration of 137Cs and 90Sr by silver Prussian carp (Carassius gibelio).

To follow up field observations in the Chornobyl Exclusion Zone (ChEZ), a series of controlled model aquarium experiments were conducted to determine the uptake and depuration rates of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) in fresh water, varying in temperature from 5 to 27 °C, with daily feeding rates of 0-1.5 % fish weight day-1. In the present study, the 137Cs uptake rates in muscle tissues directly from water, 0.05-0.09 day-1 at temperatures of 5-27 °C, were significantly lower than previously reported for fish fed under natural conditions in contaminated lakes within the ChEZ. The rate of 90Sr uptake in bone tissues of silver Prussian carp varied from 0.055 day-1 at a water temperature of 5 °C and feeding rates ≤0.15 % fish weight day-1 to 1.5 ± 0.2 day-1 at a temperature of 27 ± 1 °Ð¡ and at the highest tested feeding rate of 1.5 % day-1. The rate of decrease of 137Cs concentration in muscle tissues was kb = 0.0028 ± 0.0004 day-1 (T1/2 = 248 ± 35 days) at the lowest water temperature tested (5 °Ð¡). At water temperatures between 13 and 26 °Ð¡ and a feeding rate of 0.15 % day-1, the rate increased to kb = 0.0071-0.0092 day-1 (T1/2 = 75-99 days). The rates of decrease of 90Sr activity concentration in bone tissues at water temperatures between 22 and 25 °Ð¡ and a feeding rate of 0.5 % day-1 were kb=0.004-0.0014 day-1, and the associated biological half-life T1/2 ranged 50-160 days, respectively. The present work supported conclusions related to the main pathways of 137Cs and 90Sr uptake by silver Prussian carp, and demonstrated the usefulness of combining field and laboratory uptake and depuration experiments.

Effects of environmental low-dose irradiation on functional-metabolic organ responses in a natural mouse population (Apodemus agrarius Pallas, 1771) within the East Urals Radioactive Trace (EURT) area, Russia.

HYPOTHESIS: The level of radiation-induced functional metabolic reactivity can differ among organs (spleen, liver and myocardium) and reproductive-sexual groups (breeding and non-breeding under-yearlings: females and males). MATERIALS AND METHODS: We analyzed Apodemus agrarius individuals captured in the zone of the East Urals Radioactive Trace (EURT, Russia). In this area, concentrations are 90Sr and 137Cs at 10,000 and 1000 Bq/kg, respectively, in a layer of soil not deeper than 10 cm. Comparative analysis was based on six biochemical parameters including the glycolysis level, peroxidation of lipids, H2O2-oxidoreductase status and concentrations of protein, DNA and RNA in tissues. RESULTS: External and internal doses of 137Cs and 90Sr for A. agrarius varied by an order of magnitude, from 0.013 to 0.177 mGy/d. The level of radiation exposure was found to not differ among females but it differed between the two male reproductive groups (breeding < non-breeding under-yearlings). Sexually mature males received a significantly lower dose than females. An increase in the dose rate correlated with an increase in all biochemical indicators, thus indicating high level of tissue metabolic functions. The reproductive status of females did not affect their radiation-induced organ response rate, whereas the response to radiation of breeding males was more than 1.5-fold higher than that of non-breeding males and 2-fold higher than that of females. CONCLUSIONS: We believe that the variation of the dose load is due to migration processes: breeding males are more likely to migrate than females and therefore have less contact with radionuclides. The higher the response to radiation of breeding males can be explained by a hormonal factor: testosterone causes radiosensitivity. The reactivity of the tissues examined (myocardium < liver < spleen) develops apparently in accordance with the degree of their 'staticity' in accordance with the law of radiosensitivity of Bergonié and Tribondeau.

Designing yeast as plant-like hyperaccumulators for heavy metals.

Hyperaccumulators typically refer to plants that absorb and tolerate elevated amounts of heavy metals. Due to their unique metal trafficking abilities, hyperaccumulators are promising candidates for bioremediation applications. However, compared to bacteria-based bioremediation systems, plant life cycle is long and growing conditions are difficult to maintain hindering their adoption. Herein, we combine the robust growth and engineerability of bacteria with the unique waste management mechanisms of plants by using a more tractable platform-the common baker's yeast-to create plant-like hyperaccumulators. Through overexpression of metal transporters and engineering metal trafficking pathways, engineered yeast strains are able to sequester metals at concentrations 10-100 times more than established hyperaccumulator thresholds for chromium, arsenic, and cadmium. Strains are further engineered to be selective for either cadmium or strontium removal, specifically for radioactive Sr90. Overall, this work presents a systematic approach for transforming yeast into metal hyperaccumulators that are as effective as their plant counterparts.

Structural-functional modifications of the liver to chronic radioactive exposure in pygmy wood mouse (Apodemus uralensis) within the East-Urals Radioactive Trace.

The hepatic parameters (contents of glycogen, total lipids, nuclear and cytoplasmic proteins, DNA and RNA, fructose-6-phosphate, water, lipid peroxidation products, as well as activities of succinate dehydrogenase and glucose phosphate isomerase), radiometric data, and the relative population abundance of the pygmy wood mouse (Apodemus uralensis Pall., 1811) inhabiting natural (Middle Urals, Southern Urals, and Trans-Urals) areas and radioactivity territory (the EURT zone after of the Kyshtym accident in the South Urals in 1957) were analysed. Structural-functional modifications of the liver in A. uralensis from the EURT area are presented, taking into account irradiation power by dose-forming radionuclides (external and internal exposure to 137Cs and 90Sr), population size, and reproductive status (sexually immature and sexually mature yearlings, representing different ontogenetic patterns). The sexually immature mice from the EURT area can be considered to be the more sensitive (reactive) intrapopulation group to synergistic factors, such as radiation burden and population overabundance. The extent of structural-functional hepatic modification under current conditions of radionuclide exposure, in addition to the 60 year long effect of radioactive contamination in the EURT, can exceed the level of natural (geographic) variation observed in this species in the Urals region, which points to a long term evolutionary-ecological process.

Heterogeneity of soil contamination by 90Sr and its absorption by herbaceous plants in the East Ural Radioactive Trace area.

A nuclear accident occurred at the production association Mayak in the Urals in 1957. Approximately 74 PBq of radioactive substances were released into the environment, which resulted in the contamination of a vast area, named the East Ural Radioactive Trace (EURT). We have studied the current levels of contamination of soils and plants by 90Sr in the head part of the EURT. The heterogeneity of soil contamination (concentrations and contamination densities) in the EURT zone was considered at three scales. 1) At the macro-level, the soil contamination by 90Sr decreased by three orders of magnitude in the cross section of the zone. 2) At the meso-level, the variability of the soil contamination was estimated within several sectors, selected by the results of macro-scale mapping. 3) At the micro-level, differences in soil contamination between individual samples (0.01 m2) selected at the site (1000 m2) exceeded the one order of magnitude. The similarity of geometric mean (GM) values of the soil contamination was shown, based on the measurements of 3, 25 and 30 soil samples at the micro-level. In 57% of cases, the value of the GM obtained by 3 measurements differed by no >20% from the GM value by 25 measurements. In the most of cases, the differences in GM obtained by these two methods did not exceed 40%. Thus, in small sites it is possible to take only three soil samples to assess the level of soil contamination. We evaluated the absorption variability of 90Sr for six species of herbaceous plants (Rumex confertus, Leonurus quinquelobatus, Arctium tomentosum, Urtica dioica, Lathyrus pratensis, Bromopsis inermis). The range of concentration ratios (CRwo-soil) for 90Sr was 0.003-0.49, and the diapason of aggregated transfer factors (Tag) was 0.56-7.3. The 'plant species' factor determined about 55% of the total variability of CRwo-soil and Tag.

Radiostrontium transport in plants and phytoremediation.

Radiostrontium is a common product of nuclear fission and was emitted into the environment in the course of nuclear weapon tests as well as from nuclear reactor accidents. The release of 90Sr and 89Sr into the environment can pose health threats due to their characteristics such as high specific activities and easy access in human body due to its chemical analogy to calcium. Radiostrontium enters the human food chain by the consumption of plants grown on sites comprising fission-derived radionuclides. For humans, Sr is not an essential element, but, due to solubility in water and homology with calcium, once interred in the body, it gets deposited in bones and in teeth. This concern has drawn the attention of researchers throughout the globe to develop sustainable treatment processes to remediate soil and water resources. Nowadays, phytoremediation has become a promising approach for the remediation of large extents of toxic heavy metals. Some of the plants have been reported to accumulate Sr inside their biomass but detailed mechanisms at genetic level are still to be uncovered. However, there is inadequate information offered to assess the possibility of this remediation approach. This review highlights phytoremediation approach for Sr and explains in detail the uptake mechanism inside plants.

A Novel Adaptation Mechanism Underpinning Algal Colonization of a Nuclear Fuel Storage Pond.

Geochemical analyses alongside molecular techniques were used to characterize the microbial ecology and biogeochemistry of an outdoor spent nuclear fuel storage pond at Sellafield, United Kingdom, that is susceptible to seasonal algal blooms that cause plant downtime. 18S rRNA gene profiling of the filtered biomass samples showed the increasing dominance of a species closely related to the alga Haematococcus pluvialis, alongside 16S rRNA genes affiliated with a diversity of freshwater bacteria, including Proteobacteria and Cyanobacteria High retention of 137Cs and 90Sr on pond water filters coincided with high levels of microbial biomass in the pond, suggesting that microbial colonization may have an important control on radionuclide fate in the pond. To interpret the unexpected dominance of Haematococcus species during bloom events in this extreme environment, the physiological response of H. pluvialis to environmentally relevant ionizing radiation doses was assessed. Irradiated laboratory cultures produced significant quantities of the antioxidant astaxanthin, consistent with pigmentation observed in pond samples. Fourier transform infrared (FT-IR) spectroscopy suggested that radiation did not have a widespread impact on the metabolic fingerprint of H. pluvialis in laboratory experiments, despite the 80-Gy dose. This study suggests that the production of astaxanthin-rich encysted cells may be related to the preservation of the Haematococcus phenotype, potentially allowing it to survive oxidative stress arising from radiation doses associated with the spent nuclear fuel. The oligotrophic and radiologically extreme conditions in this environment do not prevent extensive colonization by microbial communities, which play a defining role in controlling the biogeochemical fate of major radioactive species present.IMPORTANCE Spent nuclear fuel is stored underwater in large ponds prior to processing and disposal. Such environments are intensively radioactive but can be colonized by microorganisms. Colonization of such inhospitable radioactive ponds is surprising, and the survival mechanisms that microbes use is of fundamental interest. It is also important to study these unusual ecosystems, as microbes growing in the pond waters may accumulate radionuclides present in the waters (for bioremediation applications), while high cell loads can hamper management of the ponds due to poor visibility. In this study, an outdoor pond at the U.K. Sellafield facility was colonized by a seasonal bloom of microorganisms, able to accumulate high levels of 137Cs and 90Sr and dominated by the alga Haematococcus This organism is not normally associated with deep water bodies, but it can adapt to radioactive environments via the production of the pigment astaxanthin, which protects the cells from radiation damage.

Complexes of myo-inositol-hexakisphosphate (InsP6) with zinc or lanthanum to enhance excretion of radioactive strontium from the body.

90Sr, which was released into the atmosphere and the ocean following the Chernobyl and Fukushima Daiichi nuclear power plant disasters, is an important nuclear fission element. Compounds that inhibit the absorption of 90Sr into the bloodstream and enhance its elimination can be beneficial in decreasing the absorbed radiation dose in people exposed to 90Sr. Recently, we prepared complexes of myo-inositol-hexakisphosphate (InsP6) with zinc or lanthanum as decorporation agents. These complexes, called Zn-InsP6 and La-InsP6 respectively, are insoluble in water and can potentially chelate additional metal cations. Hypothesizing that these complexes can assist the excretion of 90Sr from the body, we evaluated them using 85Sr instead of 90Sr. In in vitro binding experiments, Zn-InsP6 showed higher strontium adsorption capacity than La-InsP6. We then performed in vivo biodistribution experiments of Zn-InsP6 in mice after oral administration of 85SrCl2. Mice treated with Zn-InsP6 showed significantly lower bone accumulation of radioactivity than mice in a non-treatment control group. Zn-InsP6 adsorbed radiostrontium in the gastrointestinal tract, inhibited this ion's absorption into the bloodstream, and enhanced its excretion in the feces. Therefore, Zn-InsP6 appears to be a promising 90Sr "decorporation" agent.

Radionuclide uptake and dose assessment of 14 herbaceous species from the east-Ural radioactive trace area using the ERICA Tool.

The evaluation of radiation exposure in 14 species of herbaceous plants from the East-Ural Radioactive Trace (EURT) zone was performed, using the ERICA Tool, v. 1.2. Recent (up to 2015) levels of radionuclide activity concentration were measured in soil and vegetative plant mass. 239,240Pu content was used for the first time to estimate external dose rates for herbaceous plant species along the pollution gradient. In addition, a new approach to assessing the geometry of objects was adopted, including not only aboveground but also underground plant organs. This improved approach to the evaluation of radiation exposure confirms previous findings that herbaceous plant populations currently exist under low-level chronic exposure in the EURT area. This reassessment based on new data suggests a 48-977-fold increase in the total dose rate per plant organism at the most polluted site compared to background areas. The highest capacity for the transfer of 90Sr and 137Cs was observed in Taraxacum officinale and Plantago major. In these species, the total dose rate per plant exceeded 150 µGy h-1 due to 90Sr + 137Cs + 239,240Pu radionuclide anthropogenic pollution in the EURT zone. All estimated total dose rates per plant were below the dose rate screening value of 400 µGy h-1.

A synergetic biomineralization strategy for immobilizing strontium during calcification of the coccolithophore Emiliania huxleyi.

The coccolithophore species Emiliania huxleyi has one of the most global distributions in the modern oceans. They are characteristically covered with calcite scales called coccoliths. In this study, stable strontium immobilization during the calcification process was investigated to indirectly assess a proposed bioremediation approach for removing Sr2+ contamination from marine environments. Results indicate that E. huxleyi has high Sr2+ tolerance and removal efficiency in response to Sr2+ stress ranging from 5.6 to 105.6 ppm. Sr2+ immobilization during E. huxleyi calcification indicates a concentration-dependent synergistic mechanism. At lower concentrations of Sr2+ (25.6 ppm), Sr2+ is incorporated into coccoliths through competitive supply between Sr2+ and Ca2+. In addition, calcite productivity decreases with increased Sr2+ removal efficiency due to crystallographic transformation of coccoliths from hydrated calcite into aragonite at 55.6 ppm Sr2+. Further formation of strontianite at 105.6 ppm Sr2+ is due to precipitation of Sr2+ on the edge of the rims and radial arrays of the coccoliths. Our study implies that coccolithophores are capable of significant removal of Sr2+ from the marine environment.

Removal of Soluble Strontium via Incorporation into Biogenic Carbonate Minerals by Halophilic Bacterium Bacillus sp. Strain TK2d in a Highly Saline Solution.

Radioactive strontium (90Sr) leaked into saline environments, including the ocean, from the Fukushima Daiichi Nuclear Power Plant after a nuclear accident. Since the removal of 90Sr using general adsorbents (e.g., zeolite) is not efficient at high salinity, a suitable alternative immobilization method is necessary. Therefore, we incorporated soluble Sr into biogenic carbonate minerals generated by urease-producing microorganisms from a saline solution. An isolate, Bacillus sp. strain TK2d, from marine sediment removed >99% of Sr after contact for 4 days in a saline solution (1.0 × 10-3 mol liter-1 of Sr, 10% marine broth, and 3% [wt/vol] NaCl). Transmission electron microscopy and energy-dispersive X-ray spectroscopy showed that Sr and Ca accumulated as phosphate minerals inside the cells and adsorbed at the cell surface at 2 days of cultivation, and then carbonate minerals containing Sr and Ca developed outside the cells after 2 days. Energy-dispersive spectroscopy revealed that Sr, but not Mg, was present in the carbonate minerals even after 8 days. X-ray absorption fine-structure analyses showed that a portion of the soluble Sr changed its chemical state to strontianite (SrCO3) in biogenic carbonate minerals. These results indicated that soluble Sr was selectively solidified into biogenic carbonate minerals by the TK2d strain in highly saline environments.IMPORTANCE Radioactive nuclides (134Cs, 137Cs, and 90Sr) leaked into saline environments, including the ocean, from the Fukushima Daiichi Nuclear Power Plant accident. Since the removal of 90Sr using general adsorbents, such as zeolite, is not efficient at high salinity, a suitable alternative immobilization method is necessary. Utilizing the known concept that radioactive 90Sr is incorporated into bones by biomineralization, we got the idea of removing 90Sr via incorporation into biominerals. In this study, we revealed the ability of the isolated ureolytic bacterium to remove Sr under high-salinity conditions and the mechanism of Sr incorporation into biogenic calcium carbonate over a longer duration. These findings indicated the mechanism of the biomineralization by the urease-producing bacterium and the possibility of the biomineralization application for a new purification method for 90Sr in highly saline environments.

Forage grasses with lower uptake of caesium and strontium could provide 'safer' crops for radiologically contaminated areas.

Substitution of a species or cultivar with higher uptake of an element by one with lower uptake has been proposed as a remediation strategy following accidental releases of radioactivity. However, despite the importance of pasture systems for radiological dose, species/cultivar substitution has not been thoroughly investigated for forage grasses. 397 cultivars from four forage grass species; hybrid ryegrass (Lolium perenne L. x Lolium multiflorum Lam.), perennial ryegrass (Lolium perenne L.), Italian ryegrass (Lolium multiflorum Lam.) and tall fescue (Festuca arundinacea Shreb.); were sampled from 19 field-based breeding experiments in Aberystwyth and Edinburgh (UK) in spring 2013 and analysed for caesium (Cs) and strontium (Sr) concentrations. In order to calculate concentration ratios (CRs; the concentration of an element in a plant in relation to the concentration in the soil), soils from the experiments were also analysed to calculate extractable concentrations of Cs and Sr. To test if cultivars have consistently low Cs and Sr concentration ratios, 17 hybrid ryegrass cultivars were sampled from both sites again in summer 2013 and spring and summer 2014. Tall fescue cultivars had lower Cs and Sr CRs than the other species. Three of the selected 17 hybrid ryegrass cultivars had consistently low Cs CRs, two had consistently low Sr CRs and one had consistently low Cs and Sr CRs. Cultivar substitution could reduce Cs CRs by up to 14-fold and Sr CRs by 4-fold in hybrid ryegrass. The identification of species and cultivars with consistently low CRs suggests that species or cultivar substitution could be an effective remediation strategy for contaminated areas.

Reconstruction of radionuclide intakes for the residents of East Urals Radioactive Trace (1957-2011).

The East Urals Radioactive Trace (EURT) was formed after a chemical explosion in the radioactive waste-storage facility of the Mayak Production Association in 1957 (Southern Urals, Russia) and resulted in an activity dispersion of 7.4 × 1016 Bq into the atmosphere. Internal exposure due to ingestion of radionuclides with local foodstuffs was the main factor of public exposure at the EURT. The EURT cohort, combining residents of most contaminated settlements, was formed for epidemiological study at the Urals Research Center for Radiation Medicine, Russia (URCRM). For the purpose of improvement of radionuclide intake estimates for cohort members, the following data sets collected in URCRM were used: (1) Total ß-activity and radiochemical measurements of 90Sr in local foodstuffs over all of the period of interest (1958-2011; n = 2200), which were used for relative 90Sr intake estimations. (2) 90Sr measurements in human bones and whole body (n = 338); these data were used for average 90Sr intake derivations using an age- and gender-dependent Sr-biokinetic model. Non-strontium radionuclide intakes were evaluated on the basis of 90Sr intake data and the radionuclide composition of contaminated foodstuffs. Validation of radionuclide intakes during the first years after the accident was first carried out using measurements of the feces ß-activity of EURT residents (n = 148). The comparison of experimental and reconstructed values of feces ß-activity shows good agreement. 90Sr intakes for residents of settlements evacuated 7-14 days after the accident were also obtained from 90Sr measurements in human bone and whole body. The results of radionuclide intake reconstruction will be used to estimate the internal doses for the members of the EURT cohort.

No effect of digestate amendment on Cs-137 and Sr-90 translocation in lysimeter experiments.

The soil-plant transfer of Cs-137 and Sr-90 in different crops was determined with respect to the present-day amendment practice of using digestate from biogas fermenters. The studies were performed using large lysimeters filled with undisturbed luvisol monoliths. In contrast to the conservative tracer, Br-, neither of the studied radionuclides showed a significant vertical translocation nor effect of the applied digestate amendment compared to a non-amended control was found. Furthermore, no significant plant uptake was measured for both nuclides in wheat or oat as indicated by the low transfer factors between soil-shoot for Cs-137 (TF 0.001-0.010) and for Sr-90 (0.10-0.51). The transfer into nutritionally relevant plant parts was even lower with transfer factors for soil-grain for Cs-137 (TF 0.000-0.001) and for Sr-90 (0.01-0.06). Hence, the amendment with biogas digestate is unfortunately not an option to further reduce plant uptake of these radionuclides in agricultural crops, but it does not increase plant uptake either.

137Cs and 90Sr IN lizards of Semipalatinsk test site.

The paper provides research results of 137Cs and 90Sr radionuclides concentrations in bodies of Lacertidae family lizards, inhabiting different parts of Semipalatinsk Test Site, and the parameters of these radionuclides' transfer into lizards' bodies. It shows that high activity concentration of radionuclides in lizards' bodies can be noticed if they live directly at locally contaminated areas. Since the distance from contaminated spots exceeds home range of the studied animals, no increased values of radionuclides' activity were found in the animal bodies. At some individual radioactively contaminated spots, very high activity concentrations of 90Sr radionuclide up to 7.8 × 105 Bq kg-1 were found in lizards. So under certain conditions, lizards can significantly contribute to radionuclides redistribution in the natural environment. Mean concentration ratios (CR) of radionuclides were as follows: 137Cs-6.2 × 10-3, 90Sr-1.1 × 10-2.

Highly stable and magnetically separable alginate/Fe3O4 composite for the removal of strontium (Sr) from seawater.

In this study, a highly stable alginate/Fe3O4 composite was synthesized, and systematically investigated for the practical application of strontium (Sr) removal in complex media, such as seawater and radioactive wastewater. To overcome the drawbacks of the use of alginate microspheres, high contents of alginic acid and Fe3O4 were used to provide a more rigid structure with little swelling and facile separation, respectively. The synthesized composite was optimized for particle sizes of <400 µm and 1% content of Fe3O4. The alginate/Fe3O4 composite showed excellent Sr uptake (≈400.0 mg/g) and exhibited outstanding selectivity for Sr among various cations (Na, Mg, Ca and K). However, in diluted Sr condition (50 mg/L), Ca significantly affected Sr adsorption, resulting in a decrease of Kd value from 3.7 to 2.4 at the 0.01 M Ca. The alginate/Fe3O4 composite could be completely regenerated using 0.1 M HCl and CaCl2. In real seawater spiked with 50 mg/L of Sr, the alginate/Fe3O4 composite showed 12.5 mg/g of Sr uptake, despite the highly concentrated ions in seawater. The adsorption experiment for radio-active 90Sr revealed a removal efficiency of 67% in real seawater, demonstrating the reliability of the alginate/Fe3O4 composite.

Mycoextraction of radiolabeled cesium and strontium by Pleurotus eryngii mycelia in the presence of alumina nanoparticles: Sorption and accumulation studies.

Widespread use of products based on nanomaterials results in the release of nanoparticles into the environment. Nanoparticles can be taken up by organisms, but they can also coexist with other substances such as radionuclides, thus affecting their uptake or toxicity. In contrast, the sorption capacity of nanoparticles is exploited in water purification. The aim of the study was to investigate: (i) bioaccumulation of cesium and strontium by Pleurotus eryngii mycelia in the presence of alumina nanoparticles (Al2O3 NPs); and (ii) sorption of radionuclides on the surface of nanoparticles. For the experiments, living and dried mycelia were used to permit distinguishing between active uptake and passive sorption of the NPs by P. eryngii. The results are discussed from the perspective of the use of P. eryngii in the mycoextraction of radionuclides. The sorption capacity of Al2O3 NPs and the accumulation by P. eryngii mycelia differ for the applied radioisotopes. The efficiency of Cs and Sr sorption by alumina nanoparticles is 20% and 40%, respectively. Mycelia of P. eryngii have the ability to accumulate 30% of both radioisotopes from the medium. More than 60% of strontium can be removed accumulated from water by P. eryngii mycelia in coexistence with Al2O3 NPs, while the efficiency of cesium removal accumulation is negligible. It was found that alumina nanoparticles do not enhance uptake of radionuclides by P. eryngii mycelia; mycoextraction of radionuclides by mycelia and sorption by Al2O3 NPs are concurrent processes. There was no difference between live or dried mycelia uptake.

Ageing impact on the transfer factor of 137Cs and 90Sr to lettuce and winter wheat.

The study focuses on long-term (extending from 1 to 10 years) lysimeter experiments of the transfer factor of 137Cs and 90Sr to lettuce and winter wheat crops. Transfer factors (Fvs) were the ratio of the activity concentrations of the radionuclides in crops to those in soil, both as dry weight (Bq kg-1). Fvs of 137Cs to lettuce decreased significantly with ageing; geometric means for the 1st, 2nd and 10th year contaminated soil were 0.114, 0.030 and 0.013, respectively. However, a significant decline of Fvs for 137Cs was only seen between the 1st and 2nd year for both wheat compartments (straw and grains) which disappeared thereafter. The dynamic of 137Cs Fvs may be explained according to the distribution coefficient experiment (Kd) which had a value of 3600 L kg-1 showing a high affinity of the clay minerals for caesium. Desorption data revealed that Cs fixation enhanced with ageing. The mechanism involved may be an initial sorption of caesium species to the surface soil particles followed by progressive irreversible fixation to the interlayer of the porous clay minerals. Fvs of 90Sr were high and showed trivial variation for both crops for the time course studied. Sorption of Sr2+ species to the clay mineral may be the governing process, which was supported by high desorption percentage (ranged 77%) with low Kd, i.e. 10 L kg-1. In general, higher Fvs of 137Cs and 90Sr for lettuce was observed in comparison to winter wheat. The diversity of plant species and root systems would play essential roles for such behaviours.