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 (CR_wo-soil) for ⁹⁰Sr was 0.003-0.49, and the diapason of aggregated transfer factors (T_ag) was 0.56-7.3. The 'plant species' factor determined about 55% of the total variability of CR_wo-soil and T_ag.

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 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.

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.

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.

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.

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 β-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 β-activity of EURT residents (n = 148). The comparison of experimental and reconstructed values of feces β-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.

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 K_d 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.

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.

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.

Evaluation of factors influencing accumulation of stable Sr and Cs in lake and coastal fish

As a result of nuclear accidents and weapons tests, the radionuclides Cs-137 and Sr-90 are common contaminants in aquatic ecosystems. Concentration ratios (CR) based on concentrations of stable Cs and Sr in biota and media are used for the estimation of transfer of their radioisotopes for radiation dose calculations in environmental and human safety assessments. Available element-specific CRs vary by over an order of magnitude for similar organisms, thus affecting the dose estimates proportionally. The variation could be reduced if they were based on a better understanding of the influence of the underlying data and how that affects accumulation and potential biomagnification of stable Cs and Sr in aquatic organisms. For fish, relationships have been identified between water concentrations of K and CR of Cs-137, and between water concentrations of Ca and CR of Sr-90. This has not been confirmed for stable Cs and Sr in European waters. In this study, we analysed an existing dataset for stable Cs and Sr, as well as K and Ca, in four Swedish lakes and three Baltic Sea coastal areas, in order to understand the behaviour of these elements and their radioisotopes in these ecosystems. We found significant seasonal variations in the water concentrations of Cs, Sr, K and Ca, and in electrical conductivity (EC), especially in the lakes. CR values based on measurements taken at single or few time points may, therefore, be inaccurate or introduce unnecessarily large variation into risk assessments. Instead, we recommend incorporating information about the underlying variation in water concentrations into the CR calculations, for example by using the variation of the mean. The inverse relationships between fish CR(Cs)-[K]water and fish CR(Sr)-[Ca]water, confirmed that stable Cs and Sr follow the same trends as their radioisotopes. Thus, they can be used as proxies when radioisotope data are lacking. EC was also strongly correlated with K and Ca concentrations in the water and could potentially be used as a quick and cost-effective method to estimate water chemistry to obtain less variable CR. We also recommend some simple improvements to data collection that would greatly enhance our ability to understand Cs and Sr uptake by fish.

Long-term behavior of (90)Sr and (137)Cs in the environment: Case studies in Switzerland

We present long-term records of the (137)Cs and (90)Sr activity concentrations in soil, grass and milk from two lowland and two alpine pastures of Switzerland. The data is used for better understanding the long-term behavior of these radionuclides in the environment. Transfer factors between compartments are used as qualitative indicators of the magnitude of transfer and as a way to compare different elements (e.g. Cs and Sr) in similar conditions. The long-term behavior was quantified by means of the effective half-life which integrates all processes that cause a decrease of activity in a given medium such as leaching, fixation, erosion and radioactive decay. Our study shows that (90)Sr is more likely transferred from alpine soil to grass than (137)Cs. This is explained by a stronger fixation of Cs in the soils. We observed higher transfers of (90)Sr to grass in soils with lower Ca concentrations, and vice versa. In contrast, the transfer of (137)Cs to grass was not affected by the variations of the K content in the soil. We provide evidence that shows that (137)Cs, after intake by dairy cattle, is more likely transferred to milk than (90)Sr. However, as the (90)Sr and Ca transfers to milk are influenced by parameters/processes that were not taken into account in our study, our result cannot be entirely validated. The effective half-lives of (137)Cs and (90)Sr in soil, grass and milk corresponded with previous estimates in alpine soils. We have found that processes other than radioactive decay are responsible for a major decrease of the (90)Sr activity in soil. For (137)Cs, on the other hand, radioactive decay is among the most relevant process. Our data shows to be of interest in studying the trends of behavior of radionuclides in alpine regions.

The transfer of (137)Cs, Pu isotopes and (90)Sr to bird, bat and ground-dwelling small mammal species within the Chernobyl exclusion zone

Protected species are the focus of many radiological environmental assessments. However, the lack of radioecological data for many protected species presents a significant international challenge. Furthermore, there are legislative restrictions on destructive sampling of protected species to obtain such data. Where data are not available, extrapolations are often made from 'similar' species but there has been little attempt to validate this approach. In this paper we present what, to our knowledge, is the first study purposefully designed to test the hypothesis that radioecological data for unprotected species can be used to estimate conservative radioecolgical parameters for protected species; conservatism being necessary to ensure that there is no significant impact. The study was conducted in the Chernobyl Exclusion Zone. Consequently, we are able to present data for Pu isotopes in terrestrial wildlife. There has been limited research on Pu transfer to terrestrial wildlife which contrasts with the need to assess radiation exposure of wildlife to Pu isotopes around many nuclear facilities internationally. Our results provide overall support for the hypothesis that data for unprotected species can be used to adequately assess the impacts for ionising radiation on protected species. This is demonstrated for a range of mammalian and avian species. However, we identify one case, the shrew, for which data from other ground-dwelling small mammals would not lead to an appropriately conservative assessment of radiation impact. This indicates the need to further test our hypothesis across a range of species and ecosystems, and/or ensure adequate conservatism within assessments. The data presented are of value to those trying to more accurately estimate the radiation dose to wildlife in the Chernobyl Exclusion Zone, helping to reduce the considerable uncertainty in studies reporting dose-effect relationships for wildlife. A video abstract for this paper is available from: http://bit.ly/1JesKPc.

Inter-comparison of dynamic models for radionuclide transfer to marine biota in a Fukushima accident scenario

We report an inter-comparison of eight models designed to predict the radiological exposure of radionuclides in marine biota. The models were required to simulate dynamically the uptake and turnover of radionuclides by marine organisms. Model predictions of radionuclide uptake and turnover using kinetic calculations based on biological half-life (TB1/2) and/or more complex metabolic modelling approaches were used to predict activity concentrations and, consequently, dose rates of (90)Sr, (131)I and (137)Cs to fish, crustaceans, macroalgae and molluscs under circumstances where the water concentrations are changing with time. For comparison, the ERICA Tool, a model commonly used in environmental assessment, and which uses equilibrium concentration ratios, was also used. As input to the models we used hydrodynamic forecasts of water and sediment activity concentrations using a simulated scenario reflecting the Fukushima accident releases. Although model variability is important, the intercomparison gives logical results, in that the dynamic models predict consistently a pattern of delayed rise of activity concentration in biota and slow decline instead of the instantaneous equilibrium with the activity concentration in seawater predicted by the ERICA Tool. The differences between ERICA and the dynamic models increase the shorter the TB1/2 becomes; however, there is significant variability between models, underpinned by parameter and methodological differences between them. The need to validate the dynamic models used in this intercomparison has been highlighted, particularly in regards to optimisation of the model biokinetic parameters.

Dynamic modelling of radionuclide uptake by marine biota: application to the Fukushima nuclear power plant accident

The dynamic model D-DAT was developed to study the dynamics of radionuclide uptake and turnover in biota and sediments in the immediate aftermath of the Fukushima accident. This dynamics is determined by the interplay between the residence time of radionuclides in seawater/sediments and the biological half-lives of elimination by the biota. The model calculates time-variable activity concentration of (131)I, (134)Cs, (137)Cs and (90)Sr in seabed sediment, fish, crustaceans, molluscs and macroalgae from surrounding activity concentrations in seawater, with which to derive internal and external dose rates. A central element of the model is the inclusion of dynamic transfer of radionuclides to/from sediments by factorising the depletion of radionuclides adsorbed onto suspended particulates, molecular diffusion, pore water mixing and bioturbation, represented by a simple set of differential equations coupled with the biological uptake/turnover processes. In this way, the model is capable of reproducing activity concentration in sediment more realistically. The model was used to assess the radiological impact of the Fukushima accident on marine biota in the acute phase of the accident. Sediment and biota activity concentrations are within the wide range of actual monitoring data. Activity concentrations in marine biota are thus shown to be better calculated by a dynamic model than with the simpler equilibrium approach based on concentration factors, which tends to overestimate for the acute accident period. Modelled dose rates from external exposure from sediment are also significantly below equilibrium predictions. The model calculations confirm previous studies showing that radioactivity levels in marine biota have been generally below the levels necessary to cause a measurable effect on populations. The model was used in mass-balance mode to calculate total integrated releases of 103, 30 and 3 PBq for (131)I, (137)Cs and (90)Sr, reasonably in line with previous estimates.

Transfer factor of (90)Sr and (137)Cs to lettuce and winter wheat at different growth stage applications

The effect of clay soil contamination time on the transfer factors (Fvs) of (137)Cs and (90)Sr was investigated in four different growth stages of winter wheat and lettuce crops. The experiment was performed in an open field using lysimeters. The Fvs were the ratio of the activity concentrations of the radionuclides in crops to those in soil, both as dry weight (Bq kg(-1)). Significant difference of log-Fvs was evaluated using one-way Analysis of Variance (ANOVA). Basically, Fvs of (90)Sr were higher than those of (137)Cs, despite of the application stage or crop' variety. Higher Fvs for both radionuclides were observed for lettuce in comparison to winter wheat. Fvs of (90)Sr showed comparable trends for both crops with enhanced Fvs obtained when contamination occurred in early stages, i.e. 1.20 for lettuce and 0.88 and 0.02 for winter wheat, straw and grains, respectively. Despite the fluctuation noted in the pattern of Fvs for (137)Cs, soil contaminated at the second stage gave the highest Fvs for lettuce and grains, with geometric means of 0.21 and 0.01, respectively. However, wheat-straw showed remarkable increase in Fv for the latest contamination (ripening stage), about 0.06. It could be concluded that soil contamination at early growth stages would represent high radiological risk for the scenarios studied with an exception to (137)Cs in winter wheat-straw which reflected greater hazard at the latest application.

Long-term monitoring of radioactivity in fish from New York waters

As part of an environmental surveillance program operated by the New York State (NYS) Department of Health, measurements of various radionuclides in aquatic life (primarily fish) collected from waterways in NYS have occurred for decades. An investigation was undertaken to gain a better understanding of the occurrence, activity levels, and extent of radionuclide variations in aquatic life obtained from local waterways in relation to concentrations reported in fish from sites outside NYS (e.g., Pacific Ocean tuna). The man-made isotopes (137)Cs and (90)Sr were detectable at activities below 1 Bq/kg in the edible portions of fish from most NYS waterways, with the exception of greater activities in fish collected downstream of Brookhaven National Laboratory. Calculated effective doses resulting from eating the fish, estimated as 11-390 nSv/yr for (137)Cs and 0.3-7.9 nSv/yr for (90)Sr, are considered extremely low.

Highly effective biosorption of Sr(II) from low level radioactive wastewater

Bacillus subtilis was first used to remove Sr(II) from low-level radioactive wastewater. Influence parameters, biosorption kinetics and biosorption equilibrium were investigated. The results showed that the maximum adsorption capacity of Sr(II) at over 2,000 mg g(-1) by Bacillus subtilis was higher than for other biosorbents. At pH 6.3, Sr(II) concentration of 15 mg L(-1), biomass dosage of 0.3 g L(-1) and temperature of 20 °C, the maximum removal efficiency was as high as 96.3% at 1,440 minutes. The biosorption kinetics and the equilibrium isotherm data can be described by the pseudo-second-order equation and Freundlich isotherm equation, respectively. The negative values of ΔG and the positive values of ΔH implied that Sr(II) biosorption on Bacillus subtilis was a spontaneous and endothermic process. Fourier transform infrared spectroscopy indicated that the functional groups, hydroxyl, carboxylate and amide groups, might participate in the interaction between Sr(II) and Bacillus subtilis.

Photosynthetic biomineralization of radioactive Sr via microalgal CO2 absorption

Water-soluble radiostrontium ((90)Sr) was efficiently removed as a carbonate form through microalgal photosynthetic process. The immobilization of soluble (90)Sr radionuclide and production of highly-precipitable radio-strontianite ((90)SrCO3) biomineral are achieved by using Chlorella vulgaris, and the biologically induced mineralization drastically decreased the (90)Sr radioactivity in water to make the highest (90)Sr removal ever reported. The high-resolution microscopy revealed that the short-term removal of soluble (90)Sr by C. vulgaris was attributable to the rapid and selective carbonation of (90)Sr together with the consumption of dissolved CO2 during photosynthesis. A small amount of carbonate in water could act as Sr(2+) sinks through the particular ability of the microalga to make the carbonate mineral of Sr stabilized firmly at the surface site.

Dispersion and fate of ⁹⁰Sr in the Northwestern Pacific and adjacent seas: global fallout and the Fukushima Dai-ichi accident

The 3D compartment model POSEIDON-R was applied to the Northwestern Pacific and adjacent seas to simulate the transport and fate of (90)Sr in the period 1945-2010 and to perform a radiological assessment on the releases of (90)Sr due to the Fukushima Dai-ichi nuclear accident for the period 2011-2040. The contamination due to runoff of (90)Sr from terrestrial surfaces was taken into account using a generic predictive model. A dynamical food-chain model describes the transfer of (90)Sr to phytoplankton, zooplankton, molluscs, crustaceans, piscivorous and non-piscivorous fishes. Results of the simulations were compared with observation data on (90)Sr for the period 1955-2010 and the budget of (90)Sr activity was estimated. It was found that in the East China Sea and Yellow Sea the riverine influx was 1.5% of the ocean influx and it was important only locally. Calculated concentrations of (90)Sr in water, bottom sediment and marine organisms before and after the Fukushima Dai-ichi accident are in good agreement with available experimental measurements. The concentration of (90)Sr in seawater would return to the background levels within one year after leakages were stopped. The model predicts that the concentration of (90)Sr in fish after the Fukushima Dai-ichi accident shall return to the background concentrations only 2 years later due to the delay of the transfer throughout the food web and specific accumulation of (90)Sr. The contribution of (90)Sr to the maximal dose rate due to the FDNPP accident was three orders of magnitude less than that due to (137)Cs, and thus well below the maximum effective dose limits for the public.

Determination of the (137)Cs and (90)Sr radioisotope activity concentrations found in digestive organs of sheep fed with different feeds

In this study, 12 weanling lambs were fed for 6 months at the Vetenary Control and Research Institute of Elazığ in Turkey. Sheep were divided into two groups according to feeding type. Each group of sheep was fed a different amount of feed. The activity concentrations of (137)Cs and (90)Sr were determined in rumen, small intestine and large intestine tissue samples of sheep fed various feeds and quantities. Transfer coefficients and concentration ratios were estimated. The highest average (137)Cs and (90)Sr activity concentrations were 82 ± 22 Bq kg(-1) fw in the straw group small intestine sample and 74 ± 9.0 Bq kg(-1) fw in the fresh lucerne group rumen sample, respectively. Radioactivity levels for (137)Cs and (90)Sr are under the maximum permitted radioactive pollution level for all the samples. The transfer coefficient of (137)Cs and (90)Sr in the samples of sheep ranged from 1.0 × 10(-1) to 2.1 × 10(0) d kg(-1) and 1.7 × 10(-1) to 2.3 × 10(0) d kg(-1), respectively. Calculated transfer coefficients of (90)Sr and (137)Cs in the samples of sheep were higher than the expected values. Geometric means of Ff and CR for (137)Cs were maximum in the fresh lucerne group large intestine sample. Geometric means of Ff and CR for (90)Sr were maximum in the fresh lucerne group small intestine sample.

Increase in accumulation of strontium-90 in the maternal skeleton during pregnancy and lactation: analysis of the Techa River data

The unique contamination of the Techa River (Southern Urals, Russia) in the 1950s by long-lived (90)Sr allows investigation of the accumulation of bone-seeking elements in humans. This study is based on information compiled at the Urals Research Center for Radiation Medicine (Chelyabinsk, Russia) over a long period of time. It includes the results of in vivo measurements of (90)Sr-body burden with a whole body counter (WBC), data on personal medical examinations and residence and family histories. Data on 185 women from two Techa riverside villages Muslyumovo and Brodokalmak were selected. The settlements differ in terms of (90)Sr diet intake (higher in Muslyumovo than in Brodokalmak) and ethnicity (residents were mainly Slavs in Brodokalmak and Turkic in Muslyumovo). Results of a total of 555 WBC measurements performed in 1974-1997 were available for the women studied; maximum measured values reached 40 kBq/body. The women from each settlement were subdivided into three groups according to their childbearing history: pregnancy and lactation occurred (1) during the period of maximal (90)Sr intake (1950-1951); (2) after the period of maximal intake and (3) before this period or women who were childless. An increase was found in accumulation of (90)Sr in maternal skeleton during pregnancy and lactation (group 1) by a factor of 1.5-2 in comparison with non-pregnant, non-lactating women. This result was found in both Muslyumovo and Brodokalmak samples. An increase in accumulation of toxic elements in pregnant/lactating women is associated with increased radiation/toxic doses and risk for the women's health.

Concentrations of 90Sr in the tooth tissues 60 years after intake: results of TL measurements and applications for Techa River dosimetry

This article focuses on the study of (90)Sr in the tooth tissues of Techa riverside residents 60 years after intake. The Techa River was contaminated by radioactive wastes in the 1950s. Contamination of the river system, including water, bottom sediment, floodplain soil, and grass, depended on the distance from the source of releases. Therefore, the average (90)Sr intake was different in different settlements located downstream the river. An additional factor influencing (90)Sr accumulation in the teeth is the rate of tissue mineralization at the time of intake which depended on the donor's age at the time of releases. Measurements of (90)Sr concentration in various dental tissues (enamel, crown, and root dentin) of 166 teeth were performed about 60 years after the main intake using the method of thermoluminescence passive beta detection. The paper presents the current levels of tooth tissue contamination, and the tooth-to-tooth variability of (90)Sr concentration in tooth tissues was assessed for the tissues which were matured at the time of massive liquid radioactive waste releases into the Techa River. A model describing the expected levels of (90)Sr in matured dental tissues depending on age and intake has been elaborated for the population under study. The results obtained will be used for calculation of internal dose in enamel and for interpretation of tooth doses measured by means of the electron paramagnetic resonance method, among the population of the Techa River region.

Global searches for microalgae and aquatic plants that can eliminate radioactive cesium, iodine and strontium from the radio-polluted aquatic environment: a bioremediation strategy

The Fukushima 1 Nuclear Power Plant accident in March 2011 released an enormously high level of radionuclides into the environment, a total estimation of 6.3 × 10¹⁷ Bq represented by mainly radioactive Cs, Sr, and I. Because these radionuclides are biophilic, an urgent risk has arisen due to biological intake and subsequent food web contamination in the ecosystem. Thus, urgent elimination of radionuclides from the environment is necessary to prevent substantial radiopollution of organisms. In this study, we selected microalgae and aquatic plants that can efficiently eliminate these radionuclides from the environment. The ability of aquatic plants and algae was assessed by determining the elimination rate of radioactive Cs, Sr and I from culture medium and the accumulation capacity of radionuclides into single cells or whole bodies. Among 188 strains examined from microalgae, aquatic plants and unidentified algal species, we identified six, three and eight strains that can accumulate high levels of radioactive Cs, Sr and I from the medium, respectively. Notably, a novel eustigmatophycean unicellular algal strain, nak 9, showed the highest ability to eliminate radioactive Cs from the medium by cellular accumulation. Our results provide an important strategy for decreasing radiopollution in Fukushima area.

Increased sex ratio in Russia and Cuba after Chernobyl: a radiological hypothesis

BACKGROUND

The ratio of male to female offspring at birth may be a simple and non-invasive way to monitor the reproductive health of a population. Except in societies where selective abortion skews the sex ratio, approximately 105 boys are born for every 100 girls. Generally, the human sex ratio at birth is remarkably constant in large populations. After the Chernobyl nuclear power plant accident in April 1986, a long lasting significant elevation in the sex ratio has been found in Russia, i.e. more boys or fewer girls compared to expectation were born. Recently, also for Cuba an escalated sex ratio from 1987 onward has been documented and discussed in the scientific literature.

PRESENTATION OF THE HYPOTHESIS

By the end of the eighties of the last century in Cuba as much as about 60% of the food imports were provided by the former Soviet Union. Due to its difficult economic situation, Cuba had neither the necessary insight nor the political strength to circumvent the detrimental genetic effects of imported radioactively contaminated foodstuffs after Chernobyl. We propose that the long term stable sex ratio increase in Cuba is essentially due to ionizing radiation.

TESTING OF THE HYPOTHESIS

A synoptic trend analysis of Russian and Cuban annual sex ratios discloses upward jumps in 1987. The estimated jump height from 1986 to 1987 in Russia measures 0.51% with a 95% confidence interval (0.28, 0.75), p value < 0.0001. In Cuba the estimated jump height measures 2.99% (2.39, 3.60), p value < 0.0001. The hypothesis may be tested by reconstruction of imports from the world markets to Cuba and by radiological analyses of remains in Cuba for Cs-137 and Sr-90.

IMPLICATIONS OF THE HYPOTHESIS

If the evidence for the hypothesis is strengthened, there is potential to learn about genetic radiation risks and to prevent similar effects in present and future exposure situations.

Accumulation and transfer of 137Cs and 90Sr in the plants of the forest ecosystem near the Ignalina Nuclear Power Plant

The radioecological state of the forest ecosystem in the vicinity of the Ignalina Power Plant prior to decommissioning was analysed with specific emphasis on (137)Cs and (90)Sr activity concentrations in plant species growing in two reference sampling sites (Tilze and Grikiniskes). In the period of 1996-2008 the mean contamination of plants with (137)Cs was from 45 to 119 Bq/kg and with (90)Sr - from 3 to 42 Bq/kg. Measured (137)Cs TF values for soil-root transfer mainly ranged between 1.0-1.4, except for Calamagrostis arundinacea which had a TF value of 0.1. On average, the (137)Cs TF value from root to shoot was 1.7 fold higher than for soil to root transfer. (90)Sr TF values (soil-root) were in the range of 1.2-1.8 but for Calluna vulgaris it was 0.2. The mean root to shoot TF value for (90)Sr was 7.7 fold higher. These results indicate the higher (90)Sr bioavailability than that of (137)Cs in the forested area. The Grikiniskes reference site is located nearby the Ignalina NPP, specifically the heated water outlet channel, which results in altered microclimatic conditions. These specific microclimatic conditions result in relationships between (137)Cs TF (soil-root) values and pH, moisture and organic matter content in the soil at Grikiniskes which appear to be different to those at the Tilze reference sampling site.

[Interpopulation defferences in parameters of hemocyte DNA-comets of snail Lymnaea stagnalis from regions with the different environmental load]

The research of hemocytes of snail Lymnaea stagnalis from regions with different environmental load has been carried out by means of DNA-comet assay. Significant interpopulation distinctions in parameters of hemocytes DNA comets, and also significant differences of sensitivity of hemocyte genetic matherial in snails form different ecological zones to the influence of external damaging factors (in particular, heavy metals) have been revealed by means of the software analysis of hemocyte DNA-comet images. Since the two populations of mollusks are characterized by high genetic identity, the different levels of proliferative processes in hemocytes of snail Lymnaea stagnalis from different ecological zones (that we revealed using the comet assay) may act as an indicator of the intensity of damaging effects and environmental quality.

Research into the factors affecting the uptake of 90Sr and 137Cs by plants from radioactively contaminated soils of the southern Urals

The objective of this work was to study the factors affecting the intake of 90Sr and 137Cs by plants from soils exposed to radioactive contamination resulting from operations of the Mayak Industrial Association. Specific activities of 90Sr and 137Cs in the samples were determined by the radiochemical method. The most severe contamination by 90Sr and 137Cs of natural soils was found in forest soil cover and in the 0-5 cm soil layer. The contamination density of the area is mainly determined by activity in the soil layer 0-20 cm that contains 3-97% of 90Sr and 60-92% of 137Cs. Portions of radionuclides contained in soil (89-96% of 90Sr and 18-73% of 137Cs) can be converted into cationic use. An insignificant share of water-soluble radionuclides goes from soil to agricultural produce.

Transport behavior and rice uptake of radiostrontium and radiocesium in flooded paddy soils contaminated in two contrasting ways

In order to investigate the transport behavior and rice uptake of radiostrontium and radiocesium in flooded rice fields, lysimeter experiments with two paddy soils were performed in a greenhouse. A solution containing (85)Sr and (137)Cs was applied in two different ways - being mixed with the top soil 27 d before transplanting or being dropped to the surface water 1d after transplanting. Rice uptake was quantified with two kinds of transfer factor - TF(m) (dimensionless) and TF(a) (m(2)kg(-1)-dry) for the pre- and post-transplanting depositions, respectively. For brown rice, the TF(m) values of (85)Sr and (137)Cs differed between the soils by factors of 2 (1.6×10(-2) and 2.5×10(-2)) and 7 (2.2×10(-2) and 1.5×10(-1)), respectively. Corresponding factors by the TF(a) values were 2 (2.5×10(-4) and 4.4×10(-4)) for (85)Sr and 3 (1.1×10(-3) and 2.9×10(-3)) for (137)Cs. Straws had several times higher TF(m) and TF(a) values of (85)Sr than of (137)Cs. The surface-water concentrations were substantially higher for the TF(a) than for the TF(m), indicating the possibility of a much higher plant-base uptake for the TF(a). In the TF(a) soils, (137)Cs and, to a lesser degree, (85)Sr were severely localized towards the soil surface, probably leading to an increased root uptake. The activity loss due to plant uptake and water percolation was generally inconsiderable. Time-dependent K(d) values of (85)Sr measured in a parallel experiment ranged from 20 to 170, whereas (137)Cs had much higher K(d) values. The use of TF(a) values instead of TF(m) values turned out to be a reasonable approach to the evaluation of a vegetation-period deposition.

Radiation dose assessment for the biota of terrestrial ecosystems in the shoreline zone of the Chernobyl nuclear power plant cooling pond

Radiation exposure of the biota in the shoreline area of the Chernobyl Nuclear Power Plant Cooling Pond was assessed to evaluate radiological consequences from the decommissioning of the Cooling Pond. This paper addresses studies of radioactive contamination of the terrestrial faunal complex and radionuclide concentration ratios in bodies of small birds, small mammals, amphibians, and reptiles living in the area. The data were used to calculate doses to biota using the ERICA Tool software. Doses from 90Sr and 137Cs were calculated using the default parameters of the ERICA Tool and were shown to be consistent with biota doses calculated from the field data. However, the ERICA dose calculations for plutonium isotopes were much higher (2-5 times for small mammals and 10-14 times for birds) than the doses calculated using the experimental data. Currently, the total doses for the terrestrial biota do not exceed maximum recommended levels. However, if the Cooling Pond is allowed to draw down naturally and the contaminants of the bottom sediments are exposed and enter the biological cycle, the calculated doses to biota may exceed the maximum recommended values. The study is important in establishing the current exposure conditions such that a baseline exists from which changes can be documented following the lowering of the reservoir water. Additionally, the study provided useful radioecological data on biota concentration ratios for some species that are poorly represented in the literature.

Frequency distributions of 90Sr and 137Cs concentrations in an ecosystem of the "Red Forest" area in the Chernobyl exclusion zone

In the most highly contaminated region of the Chernobyl Exclusion Zone, the "Red Forest" site, the accumulation of the major dose-affecting radionuclides (90Sr and 137Cs) within the components of an ecological system encompassing 3,000 m(2) was characterized. The sampled components included soils (top 0-10 cm depth), Molina caerulea (blue moor grass), Camponotus vagus (carpenter ants), and Pelobates fuscus (spade-footed toad). In a comparison among the components of this ecosystem, the 90Sr and 137Cs concentrations measured in 40 separate grids exhibited significant differences, while the frequency distribution of the values was close to a logarithmically-normal leptokurtic distribution with a significant right-side skew. While it is important to identify localized areas of high contamination or "hot spots," including these values in the arithmetic mean may overestimate the exposure risk. In component sample sets that exhibited logarithmically normal distribution, the geometric mean more accurately characterizes a site. Ideally, risk assessment is most confidently achieved when the arithmetic and geometric means are most similar, meaning the distribution approaches normal. Through bioaccumulation, the highest concentrations of 90Sr and 137Cs were measured in the blue moor grass and spade-footed toad. These components also possessed distribution parameters that shifted toward a normal distribution.

Method for simultaneous 90Sr and 137Cs in-vivo measurements of small animals and other environmental media developed for the conditions of the Chernobyl exclusion zone

To perform in vivo simultaneous measurements of the 90Sr and 137Cs content in the bodies of animals living in the Chernobyl Exclusion Zone (ChEZ), an appropriate method and equipment were developed and installed in a mobile gamma beta spectrometry laboratory. This technique was designed for animals of relatively small sizes (up to 50 g). The 90Sr content is measured by a beta spectrometer with a 0.1-mm-thick scintillation plastic detector. The spectrum processing takes into account the fact that the measured object is "thick-layered" and contains a comparable quantity of 137Cs, which is a characteristic condition of the ChEZ. The 137Cs content is measured by a NaI scintillation detector that is part of the combined gamma beta spectrometry system. For environmental research performed in the ChEZ, the advantages of this method and equipment (rapid measurements, capability to measure live animals directly in their habitat, and the capability of simultaneous 90Sr and 137Cs measurements) far outweigh the existing limitations (considerations must be made for background radiation and the animal size, skeletal shape, and body mass). The accuracy of these in vivo measurements is shown to be consistent with standard spectrometric and radiochemical methods. Apart from the in vivo measurements, the proposed methodology, after a very simple upgrade that is also described in this paper, works even more accurately with samples of other media, such as soil and plants.

Biological removal of cationic fission products from nuclear wastewater

Nuclear energy is becoming a preferred energy source amidst rising concerns over the impacts of fossil fuel based energy on global warming and climate change. However, the radioactive waste generated during nuclear power generation contains harmful long-lived fission products such as strontium (Sr). In this study, cationic strontium uptake from solution by microbial cultures obtained from mine wastewater is evaluated. A high strontium removal capacity (q(max)) with maximum loading of 444 mg/g biomass was achieved by a mixed sulphate reducing bacteria (SRB) culture. Sr removal in SRB was facilitated by cell surface based electrostatic interactions with the formation of weak ionic bonds, as 68% of the adsorbed Sr(2+) was easily desorbed from the biomass in an ion exchange reaction with MgCl₂. To a lesser extent, precipitation reactions were also found to account for the removal of Sr from aqueous solution as about 3% of the sorbed Sr was precipitated due to the presence of chemical ligands while the remainder occurred as an immobile fraction. Further analysis of the Sr-loaded SRB biomass by scanning electron microscopy (SEM) coupled to energy dispersive X-ray (EDX) confirmed extracellular Sr(2+) precipitation as a result of chemical interaction. In summary, the obtained results demonstrate the prospects of using biological technologies for the remediation of industrial wastewaters contaminated by fission products.

Concentrations of 137Cs, 90Sr, 108m Ag, 239+240 Pu and atom ratio of 240Pu/239Pu in tanner crabs, Chionoecetes japonicus and Chionoecetes opilio collected around Japan

The anthropogenic radionuclides, (137)Cs, (90)Sr, (108m)Ag, (239+240)Pu, were measured in two Chionoecetes species, red queen crab (Chionoecetes japonicus) and snow crab (Chionoecetes opilio) collected around Japan during 1996-2007. There was no increase in the concentrations of these radionuclides and no large variation of the atom ratio of (240)Pu/(239)Pu during this research period. These results indicated that the source of the radionuclides was not the radioactive wastes dumped by the former USSR and Russia and originated from past nuclear weapon tests. The higher atom ratio in the crab species than that from global fallout would be contributed by the Pacific Proving Grounds close-in fallout. The variability of the concentration of radionuclides in the crab species would result from the variability of the composition and quantity in the diet. However, the decrease in the concentration of radionuclides with sampling depth would depend on the concentration in the seawater and diet.

Evaluating the potential of native ureolytic microbes to remediate a 90Sr contaminated environment

This study was a preliminary evaluation of ureolytically driven calcite precipitation and strontium coprecipitation for remediating (90)Sr contamination at the Hanford 100-N Area in Washington; in particular the approach is suitable for treating sorbed (90)Sr that could otherwise be a long-term source for groundwater contamination. Geochemical conditions at the site are compatible with long-term calcite stability, and therefore groundwater and sediment samples were examined to assess the ureolytic capabilities of the native microbiota. Quantitative assays detected up to 2 × 10(4) putative ureC gene copies mL(-1) in water and up to 9 × 10(5) copies g(-1) in sediment. The ureC assays and laboratory-based estimates of ureolytic activity indicated that the distribution of in situ ureolytic potential was very heterogeneous with depth and also that the ureolytic activity was predominantly associated with attached organisms. A mixed kinetic-equilibrium model was developed for the 100-N site to simulate urea treatment and predict strontium removal. Together, the microbial characterization data and modeling suggest that the site has the requisite biogeochemical characteristics for application of the calcite precipitation remediation approach for (90)Sr.

Biomaterials for the decorporation of (85)Sr in the rat

Although four stable isotopes of strontium occur naturally, Sr is produced by nuclear fission and is present in surface soil around the world as a result of fallout from atmospheric nuclear weapons tests. It can easily transfer to humans in the event of a nuclear/radiological emergency or through the plant-animal-human food chain causing long-term exposures. Strontium is chemically and biologically similar to calcium, and is incorporated primarily into bone following internal deposition. Alginic acid (alginate) obtained from seaweed (kelp) extract selectively binds ingested strontium in the gastrointestinal tract blocking its systemic uptake and reducing distribution to bone in rats, while other natural polysaccharides including chitosan and hyaluronic acid had little in vivo affinity for strontium. Alginate exhibits the unique ability to discriminate between strontium and calcium and has been previously shown to reduce intestinal absorption and skeletal retention of strontium without changing calcium metabolism. In our studies, the effect of commercially available alginate on intestinal absorption of strontium was examined. One problem associated with alginate treatment is its limited solubility and gel formation in water. The aqueous solubility of sodium alginate was improved in a sodium chloride/sodium bicarbonate electrolyte solution containing low molecular weight polyethylene glycol (PEG). Furthermore, oral administration of the combined alginate/electrolyte/PEG solution accelerated removal of internal strontium in rats when compared to treatment with individual sodium alginate/electrolyte or electrolyte/PEG solutions. Importantly, both alginate and PEG are nontoxic, readily available materials that can be easily administered orally in case of a national emergency when potentially large numbers of the population may require medical treatment for internal depositions. Our results suggest further studies to optimize in vivo decorporation performance of engineered alginate material via modification of its chemical and physicochemical properties are warranted.

Caesium and strontium accumulation in shoots of Arabidopsis thaliana: genetic and physiological aspects

Due to the physico-chemical similarities of caesium (Cs(+)) to potassium (K(+)) on the one hand and strontium (Sr(2+)) to calcium (Ca(2+)) on the other hand, both elements can easily be taken up by plants and thus enter the food chain. This could be detrimental when radionuclides such as (137)Cs and (90)Sr are involved. In this study, both genetic and physiological aspects of Cs(+) and Sr(2+) accumulation in Arabidopsis thaliana were investigated using 86 Arabidopsis accessions and a segregating F(2) population of the low Cs(+) accumulating Sq-1 (Ascot, UK) crossed with the high uptaking Sorbo (Khurmatov, Tajikistan). Hydroponically grown plants were exposed to subtoxic levels of Cs(+) and Sr(2+) using radioactive isotopes as tracers. In the natural accessions shoot concentration of Cs(+) as well as Sr(2+) varied about 2-fold, whereas its heritability ranged for both ions between 0.60 and 0.73. Shoot accumulation of Cs(+) and Sr(2+) could be compromised by increasing concentrations of their essential analogues K(+) and Ca(2+), respectively, causing a reduction of up to 80%. In the case of the segregating F(2)/F(3) population Sq-1×Sorbo, this study identified several QTL for the trait Cs(+) and Sr(2+) accumulation, with main QTL on chromosomes 1 and 5. According to the correlation and discrimination surveys combined with QTL-analysis Cs(+) and Sr(2+) uptake seemed to be mediated mostly via non-selective cation channels. A polymorphism, affecting amino acids close to the K(+)-pore of one candidate, CYCLIC-NUCLEOTIDE-GATED CHANNEL 1 (CNGC1), was identified in Sorbo and associated with high Cs(+) concentrating accessions.

[Regulation of acidity of arable lands contaminated by Sr-90: analysis of cost of the averted doses of irradiation of population of Belarus]

Results of researches on study of efficiency of soil acidity optimization on decrease of a collective doze from 90Sr to the population of Belarus are presented. On the basis of the "cost--benefit" analysis it is shown, that the savings for averted collective doze due to optimization of soil acidity of arable lands on cereals amount to 21-170 thousand US dollars per 1 man.-Sv depending on density of 90Sr soil contamination of districts of Belarus. It is established, that high effect on averting of collective doze 90Sr at cultivation of cereals can be expected at liming of sod-podsolic loamy sand soils with contamination density of 90Sr more than 12 kBq/m2, sand soils more than 16 kBq/m2, light loam soils more than 17 kBq/m2, at present time share of these lands in Belarus is about half from the area of the arable lands contaminated with radiostrontium - 86 thousand hectares.

[Underlying examination in the imaging of 89Sr bremsstrahlung radiation]

The radiopharmaceutical strontium chloride ((89)Sr) has been released as a new means of pain relief for painful bone metastasis in cancer patients. Because (89)Sr is a pure beta-emitting nuclide, it was considered difficult to know its distribution in the body from outside. Imaging with a gamma camera using bremsstrahlung radiation has been reported as one method, but there has been little detailed basic examination. We examined the optimal energy window and collimator when imaging with a gamma camera using bremsstrahlung radiation produced from (89)Sr beta rays. The results showed that setting the energy window at 75 keV, which is the peak formed by the characteristic X-ray of lead that is produced by the interaction of bremsstrahlung radiation and lead, is optimal for imaging. Also important are the material of the collimator and the use of an MELP collimator.

Retention half times in the skeleton of plutonium and 90Sr from above-ground nuclear tests: a retrospective study of the Swiss population

Plutonium and (90)Sr are considered to be among the most radiotoxic nuclides produced by the nuclear fission process. In spite of numerous studies on mammals and humans there is still no general agreement on the retention half time of both radionuclides in the skeleton in the general population. Here we determined plutonium and (90)Sr in human vertebrae in individuals deceased between 1960 and 2004 in Switzerland. Plutonium was measured by sensitive SF-ICP-MS techniques and (90)Sr by radiometric methods. We compared our results to the ones obtained for other environmental compartments to reveal the retention half time of NBT fallout (239)Pu and (90)Sr in trabecular bones of the Swiss population. Results show that plutonium has a retention half time of 40+/-14 years. In contrast (90)Sr has a shorter retention half time of 13.5+/-1.0 years. Moreover (90)Sr retention half time in vertebrae is shown to be linked to the retention half time in food and other environmental compartments. These findings demonstrate that the renewal of the vertebrae through calcium homeostatic control is faster for (90)Sr excretion than for plutonium excretion. The precise determination of the retention half time of plutonium in the skeleton will improve the biokinetic model of plutonium metabolism in humans.

Plutonium, 137Cs and 90Sr in selected invertebrates from some areas around Chernobyl nuclear power plant

Results are presented for (137)Cs, (90)Sr and plutonium activity concentrations in more than 20 samples of terrestrial invertebrates, including species of beetles, ants, spiders and millipedes, collected in the highly contaminated area of the Chernobyl exclusion zone. The majority of samples were collected in Belarus, with some also collected in the Ukraine. Three other samples were collected in an area of lower contamination. Results show that seven samples exceed an activity concentration of 100 kBq/kg (ash weight--a.w.) for (137)Cs. The maximum activity concentration for this isotope was 1.52+/-0.08 MBq/kg (a.w.) determined in ants (Formica cynerea). Seven results for (90)Sr exceeded 100 kBq/kg (a.w.), mostly for millipedes. Relatively high plutonium activity concentrations were found in some ants and earth-boring dung beetles. Analyses of activity ratios showed differences in transfer of radionuclides between species. To reveal the correlation structure of the multivariate data set, the Partial Least-Squares method (PLS) was used. Results of the PLS model suggest that high radiocesium activity concentrations in animal bodies can be expected mainly for relatively small creatures living on the litter surface. In contrast, high strontium activity concentrations can be expected for creatures which conduct their lives within litter, having mixed trophic habits and a moderate lifespan. No clear conclusions could be made for plutonium.

A review and test of predictive models for the bioaccumulation of radiostrontium in fish

Empirical relations between the (90)Sr concentration factor (CF) and the calcium concentration in freshwater aquatic systems have previously been determined in studies based on data obtained prior to the Chernobyl accident. The purpose of the present research is to review and compare these models, and to test them against a database of post-Chernobyl measurements from rivers and lakes in Ukraine, Russia, Belarus and Finland. It was found that two independently developed models, based on pre-Chernobyl empirical data, are in close agreement with each other, and with empirical data. Testing of both models against new data obtained after the Chernobyl accident confirms the models' predictive ability. An investigation of the influence of fish size on (90)Sr accumulation showed no significant relationship, though the data set was somewhat limited.

[Radioecological studies of freshwater mollusks in the Chernobyl accident exclusion zone]

Species-specificity and dynamics of 90Sr, 137Cs and some transuranic elements accumulation in bivalve and gastropod freshwater molluscs of the Chernobyl exclusion zone during 1997-2008 was analyzed. The results of radiation dose and chromosome aberration rate estimation and the analysis of hemolymph composition of freshwater snail (Lymnaea stagnalis L.) was produced. The absorbed dose rate was registered in the range of 0.3-85.0 microGy/h. In closed water bodies the heightened chromosome aberration rate (up to 27%) in embryo tissues, and also the change of haematological indexes for the adult individuals of snails was registered.

Foliar transfer into the biosphere: review of translocation factors to cereal grains

A review of the published literature about foliar transfer radionuclides to cereal grains was carried out with a special interest for translocation factors. Translocation describes the distribution of radionuclides within the plant after foliar deposition and radionuclide absorption onto the surface of leaves. It mainly depends on elements and the plant growth stage. The collected data were derived from both in-field and greenhouse experiments. They were analysed in order to select those coming from a contamination simulating a sprinkling irrigation or a rain. The data set contains 307 values. For each radionuclide the translocation factor values were sorted according to 5 characteristic stages of the cereal vegetative cycle: leaf development-tillering, stem elongation, earing-flowering, grain growth and ripening. Wheat, barley and rye have been treated together, independently of rice. For mobile elements such as cesium, the translocation factor is maximum when the contamination occurred at the earing-flowering stage. For less mobile elements such as strontium this maximum occurred for a foliar contamination at the grain growth stage. This review enabled us to propose the most probable value as well as the range of variation of translocation factors for some radionuclides according to the cereal vegetative cycle. Moreover, from these results, a radionuclide classification is proposed according to three mobility groups.

Root uptake of radionuclides following their acute soil depositions during the growth of selected food crops

Greenhouse experiments were performed to investigate the root uptake of radionuclides following their acute soil deposition during the growth of several food crops. For this purpose, the soil under the standing plants was contaminated without any direct contamination of their stems or leaves. The intention of this design was to differentiate foilar uptake and root uptake subsequent to a radionuclide deposition during the vegetation period. Soil-to-plant transfer of a radionuclide was quantified with its aggregated transfer factors specified for the time periods from deposition until harvest (T(ag)(a), m(2)kg(-1)). Deposition time-dependent T(ag)(a) values of Mn, Co, Sr and Cs for selected crop species were measured in an acid sandy soil. For rice and Chinese cabbage, HTO experiments were also carried out using this soil. Particularly for rice, experiments with various paddy soils were also performed for (90)Sr and (137)Cs. The obtained T(ag)(a) values varied considerably with the radionuclides, plant species, and times of deposition. Recommendations about, and limitations in, the use of the T(ag)(a) values were discussed.

[On the effect of partial flooding on 137Cs and 90Sr in forest biogeocenosis]

The analysis was made on 137Cs and 90Sr distribution oak, pine and hornbeam plantations depending on different under soil water levels. Intensity of 137Cs and of 90Sr migration along the vertical layers of soils is determined by under soil water level at a specific sampling site. The closer under soil water to the surface of the soil, the lowest radionuclide contamination is in the upper soil levels and the highest radionuclide contamination is in the deeper layers. The "fast" and "slow" quasi diffusion coefficients for 137Cs and for 90Sr and their contribution to the total migration of radionuclide through vertical soil levels were determined. A decrease in 137Cs and increase in 90Sr transfer factors to the elements of overground phytomass as a result of under soil water level lowering was established.

[Unsolved radioecological problems of Chernobyl NPP Exclusion Zone at late phase of the accident]

Some scientific and scientific-industrial radioecological problems of Chernobyl NPP Exclusion Zone are considered. These problems are demanding its solution or development of already obtaining results for adequate understanding and planning of conducted researches as well as for decision support of activities directed to minimization of the accident consequences. Following problems are discussed: an estimation of radiological significance of natural and technogenic objects of the Zone, long-term dynamics of radioecological processes, autorehabilitation processes of the Zone ecosystems, complex estimation of the influence of the Zone technogenic objects to radioecological state of ecosystems, radioecology of urban ecosystems (by the example of former town Pripyat) and problems of rehabilitation of abandoned areas.