Absorption Of Radionuclides Research Articles

Phase field-volumetric lattice Boltzmann model of ion uptake in porous nuclear waste form materials under continuous flow

The flow field within the mesopores of sorbent particles plays a crucial role in radionuclide diffusion and ion uptake kinetics, thus, impacting the overall performance of porous nuclear waste form materials. To fundamentally understand the influence of microstructures and material properties on the radionuclide absorption and retention processes requires a coupled multi-physics model that considers the advection and diffusion within the flow field, the reaction at liquid-solid interfaces, and finally, the solid-state diffusion within a complex nanoporous medium. This study employs the volumetric lattice Boltzmann method (VLBM) to accurately and efficiently calculate the steady state velocity field inside the mesopores of sorbent particles. The obtained velocity field is then utilized to calculate the advection of ions in the steady flow. A phase field (PF) model of ion uptake is used to describe the reaction occurring at the solid-liquid interface and diffusion inside the porous medium. The integrated PF-VLBM model is verified in terms of the mass conservation and numerical efficiency and validated qualitatively with experimental observation data. Then, it is applied to study the influence of thermodynamic and kinetic properties, as well as flow field conditions on the ion uptake kinetics. The numerical results demonstrate that the ion uptake kinetics in porous particles has three distinct stages, which is in agreement with the observations in continuous flow experiments. In the first stage, the kinetics is predominantly controlled by the flow field and ion diffusivity in the liquid phase. The kinetics in the second stage is primarily governed by ion diffusivity in the solid phase. In the third stage the system reaches a dynamic equilibrium with a net zero uptake flux at the interface. It is also found that porous structures significantly affect the efficiency and capacity of ion uptake. The simulation results can help to understand the physics behind the observed ion uptake kinetics in experiments and to facilitate the development of constitutive equations that can account for heterogeneous microstructures in engineering performance codes.

Syndrome of lymphovenous insufficiency in diseases of the lower limb veins. View from the position of a lymphologist

Purpose of the study: to assess the state of the lymphatic bed and develop methods of lymphatic influence to improve the results of treatment of diseases of the veins of the lower extremities.Material and methods. 692 patients with diseases of the veins of the lower extremities were examined, in whom special methods for studying phlebo- and lymphodynamics, microcirculation and regional immunity were carried out. Of these, 153 patients with acute superficial thrombosis; 154 - with deep vein thrombosis; 385 - with chronic venous insufficiency. The main group - 405 patients, using lymphological methods of treatment, the control group - 287 patients, using traditional treatment, according to clinical recommendations.Results. Radionuclide lymphoscintigraphy revealed that with thrombosis of the veins of the lower extremities at the onset of the disease, the rate of lymph flow increased by 1.2 times (p < 0.005), and the intensity of radionuclide absorption increased by 9.3% (p < 0.05) relative to healthy people. From 12-15 days of the disease, the rate of lymph flow decreased by 1.4 times (p < 0.05), and the intensity of radiopharmaceutical excretion decreased by 25% (p < 0.005). Chronic venous insufficiency is accompanied by impaired lymph flow of varying severity. The disorders increased as the degree of venous insufficiency increased. Against the background of the use of lymphological approaches in patients with lymphovenous insufficiency syndrome, at the level of statistically significant differences, the rate of lymph flow increased, microcirculation and regional immunity were restored, which contributed to a significant improvement in both immediate and long-term results of treatment. In patients with trophic ulcers, there was an acceleration in the timing of clearance, granulation and epithelialization compared with conventional treatment (p < 0.05).Conclusion. Diseases of the veins of the lower extremities, accompanied by phlebohypertension, already at the earliest stages of the disease lead to significant changes in the lymphatic system, with characteristic manifestations. The use of methods of conservative and surgical lymphogenous correction improves the results of treatment of the pathology in question.

Influence of soil chemical composition on U, 226Ra and 210Pb uptake in leaves and fruits of Quercus ilex L.

To determine their transfer factors, activity concentrations of natural radionuclides were measured in the leaves and acorns of holm oak (Quercus ilex L.) trees collected from seven locations with different soil properties and radionuclide activity concentrations. The chemical and mineralogical compositions of the soils were also analysed to investigate the effect these had on radionuclide absorption by the trees. Soil chemistry showed significant effects on radionuclide incorporation into Quercus ilex L. tissues. A significant relationship was established between activity concentrations and soil content of Ca and P with 238U and 226Ra in the leaves and acorns of Quercus ilex L. Differentiated transfer was found for 40K, which showed greater transfer to the leaves than the other radionuclides. The activity concentration of U and 226Ra was higher in the fruits than in the leaves, with the opposite effect being observed for 40K. The risk of U and 226Ra transfer into the food chain through acorn consumption by livestock is predicted to increase in soils poor in Ca and rich in P.

Hybrid Composite Materials for Immobilization of Radionuclides in Liquid Radioactive Waste

The biphasic hybrid composite materials for immobilization and fixation of radionuclides of the Liquid Radioactive Waste (LRW) of the research water-water reactor KIR WWR-K have been studied. It was found that the hybrid compositions have a high synergistic effect regard to the sorption of radionuclides, especially 137Cs+ and 134Cs+ . The distribution coefficient of cesium radionuclides in the composite materials are 2 times higher in comparison with the those sorption activity in the mineral matrix. It has been established that the sorption of radionuclides by two-phase hybrid compositions is carried out by a combination of three mechanisms. Firstly, due to the electrostatic binding reaction between the functional groups of sorbents and metal ions stabilized by the system of coordination bonds with electron-donating nitrogen and oxygen atoms of the amino and carbonyl groups of the polymer matrix. Secondly, as a result of ion exchange between counterions of the mineral matrix and radionuclides ions in the environmental solution. Finally, due to the superequimolar absorption of radionuclides as a result of deformation of the crystal lattice of mineral fillers of the polymer matrix of bentonite and copper ferrocyanide, which increases their pore size. It has been shown that biphasic hybrid composite materials have an increased mechanical and radiation resistance while retaining elasticity even at high doses of electron irradiation, at which in despite on a noticeable decrease the value of deformation there is no significant decline in their compressive strength. The obtained information on the mechanism of binding of biphasic hybrid composite materials with various metal ions makes it possible to synthesize new classes of materials for selective sorption of certain types of radionuclides in the body of mineral and polymer matrices. This will allow us to use these materials as a highly effective sorption materials with a synergetic effect for the detection, identification, immobilization and fixation of LRW radionuclides.

Подходы к геомиграционному моделированию при оценке безопасности пункта захоронения РАО в расчетном комплексе GeRa

The study focuses on the safety assessment of near-surface radioactive waste disposal facilities (NSDF) based on the numerical simulation of radionuclide transport in the near field via groundwater flow and mass transport processes using the GeRa software. It also evaluates the methods that may provide near and far field model coupling seeking to arrange a sound safety assessment process. The study specifically focuses on the degradation of the underlying concrete safety barrier indicated through a reduced radionuclide absorption capacity. The study provides calculations for those radionuclides that are typically found in the radioactive waste subject to disposal in deep disposal facilities. The findings evidence some fundamental difference in the activity-yield curves associated with the sorption properties, changes in the barrier properties and the half-lifes of the modelled radionuclides.

Effect of charge and anisotropic diffusivity on ion exchange kinetics in nuclear waste form materials

Motifs of radionuclide absorption particles (absorbers or fillers) for the nuclear waste treatment usually have crystal structures with nano-sized tunnels for fast ion diffusion. On the other hand, the accumulation of ions generates an electric field which affects the ion diffusion. Therefore, the strong anisotropic kinetic properties and the electric field affect ion exchange kinetics, especially in an assembly of these particles which may block the fast diffusion tunnels for each other. In this work, we developed a mesoscale model to describe the effect of anisotropic kinetic properties and electric field on ion exchange kinetics. With the model we simulated the effect of anisotropic diffusivity, electrochemical potential, particle morphology, size and aggregation on ion exchange kinetics during batch experiments. It is found that (1) ion exchange results in charge accumulation inside the particle because different ions have different diffusivities and different diffusion driving forces. The electric neutrality is not preserved; (2) the electric field speeds up the slower diffusion ions (either uptake or release) and slows down the faster diffusion ions to reduce charge accumulation and maintains charge neutrality; (3) the ion exchange becomes very slow at the later stages because (a) diffusion driving force (electrochemical gradient, Cs+ concentration in the solution and Na+ inside the particle) continuously decreases, as observed in batch experiments; and (b) the diffusivity decreases due to the Cs+ concentration dependence of ion diffusivity. This can explain the observed experimental phenomena that the radionuclide capacity usually cannot be reached; (4) for needle-like particle and their clusters, both surface area and diffusion distance along the direction with the fastest diffusivities have significant impact on the ion exchange kinetics.

A Methodology for Calculation of Internal Dose Following Exposure to Radioactive Fallout from the Detonation of a Nuclear Fission Device.

The purpose of this paper is to provide a methodology for the calculation of internal doses of radiation following exposure to radioactive fallout from the detonation of a nuclear fission device. Reliance is on methodology previously published in the open literature or in reports not readily available, though some new analysis is also included. Herein, we present two methodologic variations: one simpler to implement, the other more difficult but more flexible. The intention is to provide in one place a comprehensive methodology. Pathways considered are (1) the ingestion of vegetables and fruits contaminated by fallout directly, (2) the ingestion of vegetables and fruits contaminated by continuing deposition by rain- or irrigation-splash and resuspension, (3) the ingestion of vegetables and fruits contaminated by absorption of radionuclides by roots after tillage of soil, (4) the non-equilibrium transfer of short-lived radionuclides through the cow-milk and goat-milk food chains, (5) the equilibrium transfer of long lived radionuclides through milk and meat food chains, and (6) inhalation of descending fallout. Uncertainty in calculated results is considered. This is one of six companion papers that describe a comprehensive methodology for assessing both external and internal dose following exposures to fallout from a nuclear detonation. Input required to implement the dose-estimation model for any particular location consists of an estimate of the post-detonation external gamma-exposure rate and an estimate of the time of arrival of the fallout cloud. The additional data required to make such calculations are included in the six companion papers.

Environmental evaluation of nuclide pollution rate of podzolized chernozem after long land use

At present, the development of agriculture is impossible without the use of fertilizers which provide increased soil fertility and yields as well as improve the quality of agricultural products. However, it can lead to signifcant changes in the composition, properties and formation of arable soil regimes. First of all, the negative influence of fertilizer materials on the environment is related to their chemical composition and presence of ballast substances. The maximum permissible concentrations of chemical elements in the soil must be taken into account under applying fertilizer materials for each crop. The research was conducted under the conditions of a long stationary feld experiment using different levels of mineral fertilizers of N 45P45K45, N90P90K90 and N135P135K135. . The research results reveal that different doses of mineral fertilizers have an effect on the change of the specifc activity of radioactive isotopes in the soil (226Ra, 232Th, 40K, 137Cs, 90Sr) in their long-running application (50 years). The specifc activity of radionuclides in podzolized chernozem and in winter wheat grain was established. Winter wheat plants accumulated 232Th most of all but the use of fertilizers reduced it due to biological dilution in larger mass of the crop. The absorption of radioactive nuclides by winter wheat grain after cultivation after peas and silage corn depended on fertilization varied similar to that of the clover predecessor. According to the specifc activity of radioactive nuclides in the soil and winter wheat grain, the coefcient of their biological absorption is calculated. Absorption of radionuclides by soil prevents them from moving through the profle and further penetration into groundwater. Thus, their specifc activity was two times lower at the depth of 40–60 cm than in the soil layer of 0–20 cm. This indicates that radioisotopes are fxed in the upper layers of the soil which in turn increases their entry into crop production. Key words: radioactive isotopes, radium, thorium, potassium, cesium, strontium, specifc activity of radioactive nuclides.

ENVIRONMENTAL CONSEQUENCES OF URANIUM MINING BY UNDERGROUND LEACHING AND ASSESSMENT OF THE ENVIRONMENTAL INFLUENCE

The article considers the study of the radiation safety of uranium mining enterprises, since in the process of mining and processing of uranium ores a significant amount of radionuclides enter the environment, as well as methods for the absorption of radionuclides using sorbents (bentonites).

Sorption–Diffusion Model of 137Cs Absorption by Bottom Deposits of Lakes in the Reconstruction of 137Cs Fallout to Water Basins

For 6 drainless lakes with average depths of ≤12 m, the fallout of 137Cs to water basins is reconstructed by using in calculation the sorption-diffusion model off radionuclide absorption by the bottom and the data of later (in years) monitoring of 137Cs. The model was used to calculate the concentration of 137Cs in water by the date of lake contamination, with the subsequent determination of the amount of 137Cs in the bulk of lake water. The manifold difference in the 137Cs fallout density to water basins (18–700 kBq/m2), time of 137Cs exposure, and dissimilar natural properties of lakes had no effect on the correction of estimating the 137Cs fallout: the calculated results agreed with the data on the content of 137Cs in coastal soils of water basins. By the dates of 137Cs monitoring in lake water (7, 16, 35 years after the contamination of a water basin) its amount in the water bulk did not exceed 0.18–6.6% of the amount fallen on the lake surface. The parameters of the 137Cs migration in the water–bottom system, the distribution (Kd) and diffusion (D) coefficient were 2000–4000 L/kg and 1.0–0.2 × 10–7 cm2/s, respectively. Silts as the main examples of the sorption properties of the water basin bottom determined for many years the contamination odd rainless lakes with 137Cs.

Simulation of the shielding properties of environmental components against the external radioactive radiation from the Ordovician Dictyonema shale

This paper presents the results of simulating the conditions of absorption of natural radionuclides (uranium-238, thorium-232, potassium-40) in different environment media (water and quartz sand) to assess the effect of the shielding properties of environmental components on the intensity of external radiation exposure to the benthic biota. The source of radiation was the lower Tremadocian Dictyonema shale, which formed the bottom of the Baltic Paleobasin. Water and quartz sand, which was gradually deposited on the roof of the Dictyonema shale, were used in the simulation as media (materials) absorbing the primary radiation. The manuscript shows an experiment conducted in full-scale conditions considering a single exposure of a section of Ordovician rocks that includes highly radioactive Dictyonema shale. This is a small area, but the simulation results are also valid for larger areas as the Baltic Paleobasin. During the late Tremadocian — Floian, along with transgression, benthic biota began to emerge. The experiment shows quantitatively what dosage this biota could have experienced over tens and hundreds of thousands of years, until the Dictyonema shale was covered with a sufficiently thick layer of water-flooded sediments. Experimental data show that the presence of a 10 cm thick layer of water reaches absorption of 40 % of the integral flux of all gamma lines of natural radionuclides (NRN), and in a moist quartz sand layer of the same thickness the absorption value does not exceed 50 %. Thus, despite the screening effect of the environment, the benthic biota of Baltoscandia in the Early Ordovician could have been under significant radiation exposure for millennia. The main value of the experiment is that it was performed in situ, and exclusively natural media were used as modelling elements.

Adsorption of Radioactive Materials by Green Microalgae Dunaliella salina from Aqueous Solution

Introduction: Nuclear accidents release large quantities of radioactive materials into the environment. Iodine-131 and cesium-137 are two radionuclides released during nuclear accident, which can pose the greatest cancer risks. These radionuclides can be moved to other areas through rain and wind. The aim of this study was to develop efficient and economical biological methods for the absorption of water-soluble radionuclides released after a nuclear accident. Material and Methods: The exposure of the algae to an aqueous solution of I-131 radionuclide was performed for 1, 2, and 3 h. The concentration activities of the samples were 27 μCi/ml and 270 μCi/ml. After the removal of the alga by centrifuging, the activities of the sample solutions were measured using a calibrated dose calibrator. The measured activities at the mentioned periods of time were statistically significant for both groups (P<0.05). Results: The obtained results of the current study revealed that the activity of radioiodine-131 decreased 1, 2, and 3 h after adding algae, compared to the control group at the same time (21.8, 32.33, 39.84 for 27 μCi/ml and 15.38, 21.53, and 30 for 270 μCi/ml, respectively). Furthermore, radioactive iodine is absorbed very well with this type of algae. Conclusion: It can be concluded that Dunaliella salina can be used for the decontamination of radioiodine. This method can play a significant role in the decontamination of hazardous radioiodine after nuclear accidents. © 2019, Mashhad University of Medical Sciences.

Establishment of Criteria for Skin Decontamination in a Radiation Emergency.

In the event of a radiological or nuclear emergency, internal or external contamination (or both) by radionuclides can occur. In such cases, removal of the radionuclides from the injured skin is important because such surface contamination may induce skin damage such as deterministic effects at very high skin doses (2 to 3 Gy). In addition, internal contamination will occur due to radionuclide absorption through the injured skin. Previous studies have suggested various decontamination criteria. However, those criteria are impractical in the case of large-scale population monitoring. Here, to identify practical decontamination criteria, the VARSKIN 4.0 software code is used to assess skin doses originating from surface contamination by Co, I, and Cs. In addition, Integrated Modules for Bioassay Assessment dosimetry software is used to assess the effective doses following radionuclide intake through external contamination for the same three radionuclides. The effective dose dependence on the soluble material type is also assessed. In particular, the effective dose due to radionuclide absorption is found to be greater than the skin dose rate due to surface contamination for the same radioactivity levels. Based on the calculation results, decontamination criteria and actions that depend on the effective dose and surface contamination level (Bq cm) for alpha and beta or gamma radiation are suggested. Actions for contaminated injured persons are classified as no action, optional, recommended, or required.

Allometric relationship in the bioaccumulation of radionuclides (134Cs &241Am) and delineation of contamination pathways (food and seawater) in bloody cockle Anadara senilis using radiotracer techniques

The uptake and depuration kinetics of 134Cs and 241Am were investigated in the bloody cockle Anadara senilis exposed via seawater and food in controlled conditions, using animals of different weight groups in order to assess how their bioaccumulation is affected by allometry and, hence, the individual's age. This study is one of the few experiments investigating bioaccumulation capacities of radionuclides in a West-African bivalve. Results showed that allometric relationships were mainly dependent on the exposure pathway considered. Significant relationships with body weight of bloody cockles were found during the uptake from dissolved phase for both radionuclides; they followed inverse power functions: smaller cockles concentrated both radionuclides more than larger ones. In contrast, radionuclide absorption and assimilation efficiencies from water and food, respectively, did not show any significant relationship with weight: only slight variation was observed between small and large organisms for the retention of 241Am accumulated from food. A bioaccumulation model was used to assess the contribution of each pathway of exposure (food vs. water) in organisms grouped in small and large individuals. We found that, regardless of the size, 134Cs was mainly bioaccumulated through the dietary pathway. In the case of 241Am, the relative contribution of each pathway is weight-dependent: major contribution of dissolved pathway in smaller organisms and the major dietary contribution in larger organisms.

Fingerprinting Sediment Transport in River‐Dominated Margins Using Combined Mineral Magnetic and Radionuclide Methods

AbstractBoth magnetic properties and radionuclides are widely used to trace sediment transport in aquatic environments; however, these methods have not been used in combination. In this study, the East China Sea (ECS), a typical river‐dominated margin, was chosen to demonstrate the advantages of combining these two methods to track sediment movements on a seasonal to annual timescale. The ratios between saturation isothermal remnant magnetization and anhysteretic remnant magnetization (χARM/SIRM) and 7Be/210Pbex activity ratios as well as mass balance of 7Be provide information on the seasonal transport of sediment from the Changjiang Estuary to the neighboring shelf. Both 210Pb budget and SIRM distribution in the inner shelf of the ECS show that a small fraction (at most 14% of annual Changjiang sediment discharge) of particles could be transported offshore. Most of 7Be activities in inner shelf sediments of the ECS were below detection limit due to relatively lower residence times and dilution by the older sediment. The observation that radionuclide activities exhibit a better correlation with χARM/SIRM ratios than with grain size suggests that iron oxides are the primary carriers of 7Be, 210Pb, and 234Th. The absorption of radionuclides onto magnetic minerals further reinforces the reliability of this combined approach in tracing sediment transport. Our study indicates that radionuclides, with different half‐lives, can be utilized for quantifying sediment dynamics, whereas magnetic properties can yield more detailed information on sediment transport directions. The combined analysis of magnetic parameters and radionuclides offers a better understanding of sediment transport in river‐dominated areas.

Rapid breakthrough of 131I in an in vitro human epidermis model

Skin contamination with radionuclides may cause local radiation damage, but also systemic distribution if the nuclides penetrate the epidermal membrane. Detailed information of the skin absorption of radionuclides is of importance for e.g. dose estimations and development of decontamination strategies. In the present study, penetration of 131I through human epidermis was studied using an in vitro flow through diffusion chamber. Epidermis was exposed to a Na131I-solution, used in nuclear medicine, and the potential concentration-dependency of skin penetration was examined by including two concentrations of non-radioactive NaI. Penetration of 131I occurred after a few minutes of exposure and steady state penetration rate was obtained after about 50–70min independently of the iodine concentration and receptor solution used. The two receptor solutions evaluated; phosphate buffered saline solution and an ethanol and water-mixture (1:1), resulted in significantly higher penetration rate of 131I using the ethanol and water-mixture. The penetration of iodine was calculated to be concentration-dependent independently of the receptor solution utilized. In addition, radioactive iodine did not accumulate in epidermis in the in vitro-model used.In conclusion, the present study provides detailed information on the rapid iodine penetration at the early phase of radionuclide exposure, defined as the first 30min of the experiment, and is clearly suitable for decontamination studies. In addition, methodological aspects, e.g. impact of the receptor solution, should carefully be considered in studies of radionuclide skin penetration using in vitro-techniques.

Preliminary assessment of uranium mining legacy and environmental radioactivity levels in Sabugal region, Portugal

An environmental radioactivity survey carried out in the Sabugal region, Portugal, showed enhanced radioactivity levels in surface water streams related to water discharges from old uranium mines. Water from irrigation wells in this region displayed variable radionuclide levels due to natural occurrence of radionuclides and to contamination by mine water drainage. Horticulture products grown near the uranium mine sites contained elevated radium (226Ra) concentrations, but lower concentrations of uranium and other radionuclides. Despite the relatively high radioactivity in irrigation water, the absorption and accumulation of radionuclides in agriculture products were limited. Nevertheless, taking into consideration the volume of uranium waste piles, it is considered as necessary to improving the management of mine wastes and mine drainage to prevent further increase of environmental radioactivity in the area. The assessment of environmental impact and radiation issues lasting from the past uranium mining shall be used as lessons to improving future mining activities.

Influence of copper, cobalt and iodine microelements on the exchange of 137Cs in the cows organisms at different physiological states

Aim. To estimate the impact of additions of different doses of copper, cobalt and iodine salts to the diet of dry and lactating cows on the absorption and removal of 137 Сs from the organism. Methods. Four groups of black and white breed cows –– were selected for the study on the farm in Narodychi district of Zhytomyr region following the traditional methods. The animals were fed salts of microelements with concentrated feedstuffs. Specifi c radioactivity of feedstuffs, feces, urine, milk was defi ned by the gamma-spectrometry method using AMA-OZF analyzer. Results. During the dry period the content of 137 Сs in nutrition of cows of experimental groups was almost the same, whereas its removal from the organism of animals was different depending on the impact of microelements on the degree of radionuclide absorption. The exceeding of the norms of copper and cobalt by 30 % and iodine – by 70 % promotes the decrease of “visible” absorption of cesium and enhances its removal due to the radionuclide, accumulated in the tissues. The radioactivity of the diet of animals dur- ing lactation increased considerably (22–26-fold) and amounted to 17–22 kBq per day; at the same time high bioavailability of the radionuclide was revealed. The increase in 137 Cs content in the diet of cows during the grazing period is related to the use of contaminated fi elds. In May specifi c radioactivity of cow milk was the lowest; its insignifi cant increase (50–65 Bq/l) was observed in June, July and August. The radioactivity of cow milk in September and October increased considerably (150–184 Bq/l). The fortifi cation of the diet of animals of the 3 rd experimental group with copper, cobalt, and iodine promoted the decrease in the radioactivity of cow milk comparing the cow milk of the 1 st experimental group and the milk of the 4 th experimental group. During the lactation period the least absorption of the radionuclide was revealed for the normative consumption of all the microelements, and the highest – for the increased consumption of cobalt only. Conclusions. The vegeta- tive feedstuffs of dairy cattle in Polissia provides the requirement of cobalt for 30–35 %, iodine – for 25–30 %, copper – for 70 % in winter, and during the grazing period in summer – for 25, 35, and 60 % respectively. The fortifi cation of the diet of cows with microelements promotes the decrease in the absorption of 137 Сs in the gastrointestinal tract and its reduced transfer into cow milk.

Molecular level characterization of diatom‐associated biopolymers that bind 234Th, 233Pa, 210Pb, and 7Be in seawater: A case study with Phaeodactylum tricornutum

AbstractIn order to investigate the importance of biogenic silica associated biopolymers on the scavenging of radionuclides, the diatom Phaeodactylum tricornutum was incubated together with the radionuclides 234Th, 233Pa, 210Pb, and 7Be during their growth phase. Normalized affinity coefficients were determined for the radionuclides bound with different organic compound classes (i.e., proteins, total carbohydrates, uronic acids) in extracellular (nonattached and attached exopolymeric substances), intracellular (ethylene diamine tetraacetic acid and sodium dodecyl sulfate extractable), and frustule embedded biopolymeric fractions (BF). Results indicated that radionuclides were mostly concentrated in frustule BF. Among three measured organic components, Uronic acids showed the strongest affinities to all tested radionuclides. Confirmed by spectrophotometry and two‐dimensional heteronuclear single quantum coherence‐nuclear magnetic resonance analyses, the frustule BF were mainly composed of carboxyl‐rich, aliphatic‐phosphoproteins, which were likely responsible for the strong binding of many of the radionuclides. Results from this study provide evidence for selective absorption of radionuclides with different kinds of diatom‐associated biopolymers acting in concert rather than as a single compound. This clearly indicates the importance of these diatom‐related biopolymers, especially frustule biopolymers, in the scavenging and fractionation of radionuclides used as particle tracers in the ocean.

Safety of Food Produced in Japan: Past and Present Status of Radioactive Contamination

In 2011, the radionuclide released from the nuclear power plant in Fukushima contaminated 3.4% of agricultural and marine products to a level exceeding the standard. After measures were introduced to inhibit radionuclide absorption and to decontaminate farmland, contamination exceeding regulatory limits fell to 0.002% in 2014. The 0.002% of contamination remaining involves fungi and wild edible plants from forested regions and some fish caught in rivers where decontamination has not been done. Restrictions were placed on shipments of food exceeding regulatory limits, so such food was never distributed. The allowable dose, which is the basis of regulatory limits of radionuclide concentrations in food in Japan is 1 mSv per year based on the guideline set by the Codex Alimentarius Commission which is responsible for establishing international standards for food. The issue of radioactive food contamination was thus resolved in a short time. According to a survey conducted 2014, the estimated radiation dose a person would consume over 1 year from radioactive cesium contained in food distributed for consumption ranged from 0.0007 to 0.0022 mSv a year. This amounts to less than 1% of the yearly permissible dose of 1 mSv.