Behavior Of Radiocesium Research Articles

Influence of cations and low molecular weight organic acids on Cs(I) adsorption on montmorillonite and vermiculite

To predict the mobility of radiocesium (RCs) in the environment, it is essential to understand the adsorption and desorption processes. In this study, we focused on the effects of certain environmental factors, including typical cations (K+, Na+, and NH4+) and low molecular weight organic acids (LMWOAs) such as acetic acid, malic acid, and citric acid on the behavior of RCs on montmorillonite and vermiculite. The results showed that montmorillonite possesses the strongest adsorption capacity for Cs+ than that of vermiculite. Since K+ and NH4+ exhibit similar physicochemical properties to Cs+, there is a significant inhibition of Cs+ adsorption on montmorillonite and vermiculite during the competitive interaction with K+ and NH4+. Compared to NH4Cl, the desorption ratios of Cs+ on montmorillonite and vermiculite are higher in the presence of KCl as the background solution. Low molecular weight organic acids can cover the surfaces of montmorillonite and vermiculite to different extents, which effectively blocks the adsorption sites for Cs+, and leads to an obvious decrease in the adsorption and desorption of Cs+. Due to the high expandable performance, Cs+ is primarily reversibly adsorbed by montmorillonite. Nevertheless, the adsorption of Cs+ on vermiculite exhibits typical irreversible characteristics due to the interlayer collapse. After the adsorption of LMWOAs on montmorillonite and vermiculite, the irreversible adsorption of Cs+ is increased obviously, mainly due to the blocking effect of organic matters on the adsorption sites with high affinity to Cs+.

Dispersant-enhanced migration of radiocesium among soil size fractions: A novel strategy for volume reduction of radioactively contaminated soil

In the aftermath of the Fukushima Daiichi Nuclear Power Plant accident, a pioneering large-scale decontamination project was initiated, aiming to enable the return of evacuees. This project, the first of its kind in human history, involved the transportation of soils collected during decontamination to interim storage facilities. Before recycling or disposal, these soils undergo processes like volume reduction. However, there's a need for innovative methods to reduce volume effectively and treat secondary wastes more efficiently. The current study explores the impact of a dispersant, sodium hexametaphosphate (SHMP), on the behavior of radiocesium (r-Cs: 137Cs) dynamics in different size fractions of radioactively contaminated soils from Fukushima. The solid-phase speciation analysis of Fukushima soils validated that at least 50% of the 137Cs or other minerals are associated with difficult-to-extract soil phases. Nonetheless, the low 137Cs/133Cs ratio in corresponding soil phases implies a slower r-Cs fixation mechanism. The wet-sieving of r-Cs contaminated soil fraction, < 2 mm, with SHMP, resulted in different soil subfractions (2000–212, 212–53, and < 53 μm). Following SHMP treatment, dispersion of > 92% of 137Cs associated with < 212 μm soil size fractions was observed. The migration of 137Cs towards smaller soil size fractions can be attributed to either SHMP-induced cation exchange or the formation of polyvalent complexes involving SHMP and soil minerals. The condensation of 137Cs in < 212 μm, as induced by SHMP, enabled the subsequent reuse of the larger soil fraction (> 212 μm), which was less contaminated. This study provides a new perspective on the effects of dispersants and contributes to a better understanding of the complex interactions among organic carbon, 137Cs, monovalent and polyvalent cations, and soil functional groups concerning the volume reduction of soils contaminated with r-Cs.

Behavior of Radiocesium (137Cs) on the Coastal Seafloor near the Fukushima Daiichi Nuclear Power Plant Inferred from Radiocesium Distributions in Long Cores

Behavior of Radiocesium (137Cs) on the Coastal Seafloor near the Fukushima Daiichi Nuclear Power Plant Inferred from Radiocesium Distributions in Long Cores

Gravitational separation of 137Cs contaminated soil in Fukushima environment: Density dependence of 137Cs activity and application to volume reduction

Behavior of radiocesium in Fukushima after its deposition is mainly controlled by mobility of soil components, of which the density is one of the parameters governing the mobility; however, little information is available on the density of soil components associated with radiocesium in environment. Furthermore, the reduction of the volume of radiocesium-contaminated soil in the interim storage is highly demanded. In this study, we developed a gravitational separation method using a sodium polytungstate (SPT) solution combined with size fractionation to understand the relation between 137Cs activity and the density of surface soil components and evaluate the feasibility of the method for the volume reduction of the contaminated soil. In all soil samples examined, 137Cs concentration of the small size (<0.063 mm) and high-density (2.4–2.8 g cm−3) fraction was the highest among the separated fractions, whereas most of the radiocesium-rich micro-particles were distributed in the small size (<0.063 mm) and low density (<2.4 g cm−3) fraction. Although ultrasonication improved the size separation efficiency, a single-step gravitational separation method using an SPT solution with a density of 2.4 g cm−3 without size separation and ultrasonication revealed that the 137Cs concentration on 50°C-dry weight basis in the dense (>2.4 g cm−3) fraction was 25.6–82.7% lower than that of the bulk sample for all soil samples. In particular, for the samples with a bulk 137Cs concentration of 29.6 Bq g−1 50°C-dry weight, the 137Cs concentration in the fraction was below the safety treatment requirement (i.e., 8 Bq g−1). Therefore, single-step gravitational separation may be used for the volume reduction of contaminated soils.

Visualization of radiocesium distribution in surface layer of seafloor around Fukushima Daiichi Nuclear Power Plant

Large quantities of volatile radionuclides were released into the atmosphere and the hydrosphere following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March, 2011. Monitoring of radiocesium in sediment is important for evaluating the behavior of radiocesium in the environment and its effect on aquatic organisms. In this study, the radiocesium distribution in the surface sediment around the FDNPP was visualized as a radiocesium concentration map using periodical survey data from a towed gamma-ray detection system. The uncertainty of the radiocesium map was evaluated via comparison with a large amount of sediment core sample data. The characteristics of the radiocesium distribution were examined considering the seafloor topography and a geological map, which were obtained via acoustic wave survey. The characteristics of the formation of 137Cs anomaly at the estuaries were analyzed using a contour map of 137Cs concentration combined with water depth. Validation of the created map showed that it was comparable with actual sediment core samples. The map generated using the towed radiation survey depicted the 137Cs concentration distribution as the position resolution of a 1 km mesh. Finally, the 137Cs concentration decreased with time in consideration of such uncertainty.

Behavior of Radiocesium in Sediments in Fukushima Coastal Waters: Verification of Desorption Potential through Pore Water.

Concentrations of 137Cs in seawater, seabed sediment, and pore water collected from the area around Fukushima were investigated from 2015 to 2018, and the potential of coastal sediments to supply radiocesium to the bottom environment was evaluated. The 137Cs concentration in the pore water ranged from 33 to 1934 mBq L-1 and was 10-40 times higher than that in the overlying water (seawater overlying within 30 cm on the seabed). At most stations, the 137Cs concentrations in the overlying water and the pore water were approximately proportional to those in the sediment. The conditional partition coefficient between pore water and sediment was [0.9-14] × 102 L kg-1, independent of the year of sampling. These results indicated that an equilibrium of 137Cs between pore water and sediment has been established in a relatively short period, and 137Cs in the pore water is gradually exported to seawater near the seabed. A simple box model estimation based on these results showed that 137Cs in the sediment decreased by about 6% per year by desorption/diffusion of 137Cs from the seabed.

Reduction in the Radiocesium in Meats of the Sika Deer and Wild Boar by Cooking

The behavior of radiocesium in wild animal meats upon cooking was investigated. The ratio of the concentration change (processing factor, Pf), remaining ratio (food processing retention factor, Fr), and removal ratio of radiocesium in the meats by grilling, boiling, and steaming were determined. Differences in cooking methods, rather than differences in meat parts or animal species, clearly influenced the Pf, Fr, and removal ratios. The mean Fr values were 0.9 (range, 0.7 to 1.0) for grilling, 0.6 (range, 0.4 to 0.7) for boiling, and 0.5 (range, 0.4 to 0.7) for steaming. The removal effect of grilling (11%) was lower than that of boiling (41%) or steaming (47%). The mean value of Pf was 1.2 (range, 1.1 to 1.6) for grilling, 0.8 (range, 0.6 to 0.9) for boiling, and 0.8 (range, 0.7 to 1.0) for steaming. The radiocesium concentration in the meats increased only upon grilling, but not by boiling or steaming. This difference is due to the lower removal effect of grilling than that of boiling and steaming. Therefore, boiling and steaming were more effective than grilling for removing radiocesium and reducing its concentration in wild animal meats. Furthermore, the ratio of water content fluctuations due to boiling was negatively correlated with Pf and Fr. It was evident that greater reductions in water content resulted in lower concentrations and improved radiocesium removal in the meats. These results suggest that some of the radiocesium naturally present in the meats is soluble in water and that the radiocesium dissolved in water can be removed from the meat with the release of water from the tissue.

Behavior of radiocesium in decontaminated paddy fields in Fukushima Prefecture, Japan

The 2011 Great East Japan earthquake and tsunami led to dispersal of radionuclides into the surrounding area from the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant. Before agricultural activities can safely resume after this accident, it is necessary to evaluate the dynamics of radiocesium in irrigation water in the area. We measured the concentrations of total and dissolved radiocesium in irrigation water and analyzed radiocesium concentrations in rice and soil samples, the soil to brown rice transfer factor (TF) in two decontaminated paddy fields located within the zone where paddy rice culture was prohibited, and radiocesium/water balance in a paddy field in 2014. Our key findings were as follows: (1) about 85% of the radiocesium in the irrigation water did not drain away but accumulated in the paddy field; (2) in comparison with the amount of the radiocesium deposited in the fields, the amount of radiocesium that accumulated during irrigation was approximately 0.076%; (3) the outflow of total radiocesium from paddy field was 13.0% of the inflow to a paddy field (irrigation water and fallout); (4) the soil to brown rice TF was 0.0015–0.0068 in the decontaminated paddy fields where soil improvement was performed to increase the content of exchangeable potassium to 200 (mg K)/kg soil before the conventional application; and (5) the concentration of radiocesium in brown rice was about 2% of the standard limit in Japan (100 Bq/kg), and the impact on brown rice from radiocesium in the irrigation water was limited.

Radioactive contamination in the Tokyo metropolitan area in the early stage of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident and its fluctuation over five years.

Radioactive contamination in the Tokyo metropolitan area in the immediate aftermath of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident was analyzed via surface soil sampled during a two-month period after the accident. 131I, 134Cs, and 137Cs were detected in these soil samples. The activity and inventory of radioactive material in the eastern part of Tokyo tended to be high. The 134Cs/137Cs activity ratio in soil was 0.978 ± 0.053. The 131I/137Cs ratio fluctuated widely, and was 19.7 ± 9.0 (weighted average 18.71 ± 0.13, n = 14) in the Tokyo metropolitan area. The radioactive plume with high 131I activity spread into the Tokyo metropolitan area and was higher than the weighted average of 6.07 ± 0.04 (n = 26) in other areas. The radiocesium activity and inventory surveyed in soil from a garden in Chiyoda Ward in the center of Tokyo, fell approximately 85% in the four months after the accident, and subsequently tended to rise slightly while fluctuating widely. It is possible that migration and redistribution of radiocesium occurred. The behavior of radiocesium in Tokyo was analyzed via monitoring of radiocesium in sludge incineration ash. The radiocesium activity in the incineration ash was high at wastewater treatment centers that had catchment areas in eastern Tokyo and low at those with catchment areas in western Tokyo. Similar to the case of the garden soil, even in incineration ash, the radiocesium activity dropped rapidly immediately after the accident. The radiocesium activity in the incineration ash fell steadily from the tenth month after the accident until December 2016, and its half-life was about 500 days. According to frequency analysis, in central Tokyo, the cycles of fluctuation of radiocesium activity in incineration ash and rainfall conformed, clearly showing that radiocesium deposited in urban areas was resuspended and transported by rainfall run-off.

Behavior of radioactive cesium during incineration of radioactively contaminated wastes from decontamination activities in Fukushima

Large volumes of decontamination wastes (DW) generated by off-site decontamination activities in Fukushima Prefecture have been incinerated since 2015. The behavior of radioactive cesium during incineration of DW was investigated at a working incineration plant. The incineration discharged bottom ash (BA) and fly ash (FA) with similar levels of radiocesium, and the leachability of the radiocesium from both types of ash was very low (<1%). These results are significantly different from those obtained for the incineration of contaminated municipal solid waste (CMSW) reported in earlier studies. The source of radiocesium in DW-FA is chiefly small particles derived from DW and DW-BA blown into the flue gas, not the deposition of gaseous synthesized radiocesium compounds on the surfaces of ash particles in the flue gas as observed in CMSW incineration. This source difference causes the behavior of radiocesium during waste incineration to differ between DW and CMSW.

Content and Behavior of Radiocesium in Undisturbed Bulgarian Soils

Content and Behavior of Radiocesium in Undisturbed Bulgarian Soils

Fate of radiocesium in freshwater aquatic plants and algae in the vicinity of the Fukushima Daiichi nuclear power plant

The behavior of radiocesium (137Cs) in aquatic plants (five species) and algae (three genera) grown in either a river (one sampling point) or pond (four sampling points) in the vicinity of the Fukushima Daiichi nuclear power plant was investigated. The 137Cs concentration of <0.45-μm fractions of water taken from the river and ponds was between 5.01 × 10−1 and 2.98 Bq/L, while that of sediment was between 4.85 × 103 and 5.72 × 104 Bq/kg dry weight. The ratio of 137Cs concentration of sediment/water in ponds was ~104. The sediment-to-plant transfer factor (TF) [(137Cs concentration Bq/kg dry weightplant) × (137Cs concentration Bq/kg dry weightsediment)−1] was also measured. For aquatic plants, the highest value was 5.55 for Potamogeton crispus from the river, while the lowest was 3.34 × 10−2 for P. distinctus from a pond. There were significant differences in values between aquatic plants belonging to the same genus. The water-to-plant TF [(137Cs concentration Bq/kg dry weightplant) × (137Cs concentration Bq/Lwater)−1] of filamentous algae (Spirogyra sp.) and cyanobacteria (coexisting Anabaena sp. and Microcystis sp.) were 2.39 × 103 and 1.26 × 103, respectively. The 137Cs concentration of cyanobacteria in pond water was 4.87 × 10−1 Bq/L, which was the same order of magnitude as the 137Cs concentration of pond water. Enrichment of 137Cs in cyanobacteria was not observed.

The transfer of radiocesium from the bark to the stemflow of chestnut trees (Castanea crenata) contaminated by radionuclides from the Fukushima Dai-ichi nuclear power plant accident

We report on the behavior of radiocesium in tree bark and its transfer into the stemflows of chestnut trees in a forest in the Fukushima Prefecture, Japan. In stems that were present at the time of the accident, the radiocesium concentration of the bark was found to be approximately 10 times that of the wood. The average 137Cs concentration of the dissolved fraction (<0.45 μm) in the stemflow was measured to be around 10 Bq/L. The 137Cs concentration ratio [present at the time of the accident (Bq/kg) in the bark/the dissolved fraction in the stemflow (Bq/L)] was approximately 103. A strong positive correlation was observed between the radiocesium concentration and the electrical conductivity of the dissolved fraction of the stemflow; this result suggests that radiocesium and electrolytes have the same elution mechanism from the tree. The size fractionation analysis of the <0.45 μm fraction through ultrafiltration revealed that the radiocesium was present as an almost dissolved species. Some of the particles in the particulate fraction (>0.45 μm) of the stemflow were strongly adsorbed radiocesium.

Characteristics of initial deposition and behavior of radiocesium in forest ecosystems of different locations and species affected by the Fukushima Daiichi Nuclear Power Plant accident

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, information about stand-level spatial patterns of radiocesium initially deposited in the surrounding forests was essential for predicting the future dynamics of radiocesium and suggesting a management plan for contaminated forests. In the first summer (approximately 6 months after the accident), we separately estimated the amounts of radiocesium (134Cs and 137Cs; Bq m−2) in the major components (trees, organic layers, and soils) in forests of three sites with different contamination levels. For a Japanese cedar (Cryptomeria japonica) forest studied at each of the three sites, the radiocesium concentration greatly differed among the components, with the needle and organic layer having the highest concentrations. For these cedar forests, the proportion of the 137Cs stock in the aboveground tree biomass varied from 22% to 44% of the total 137Cs stock; it was 44% in highly contaminated sites (7.0 × 105 Bq m−2) but reduced to 22% in less contaminated sites (1.1 × 104 Bq m−2). In the intermediate contaminated site (5.0–5.8 × 104 Bq m−2), 34% of radiocesium was observed in the aboveground tree biomass of the Japanese cedar stand. However, this proportion was considerably smaller (18–19%) in the nearby mixed forests of the Japanese red pine (Pinus densiflora) and deciduous broad-leaved trees. Non-negligible amounts of 134Cs and 137Cs were detected in both the sapwood and heartwood of all the studied tree species. This finding suggested that the uptake or translocation of radiocesium had already started within 6 months after the accident. The belowground compartments were mostly present in the organic layer and the uppermost (0–5 cm deep) mineral soil layer at all the study sites. We discussed the initial transfer process of radiocesium deposited in the forest and inferred that the type of initial deposition (i.e., dry versus wet radiocesium deposition), the amount of rainfall after the accident, and the leaf biomass by the tree species may influence differences in the spatial pattern of radiocesium by study plots. The results of the present study and further studies of the spatial pattern of radiocesium are important for modeling future radiocesium distribution in contaminated forest ecosystems.

土壌汚染の新知見

土壌汚染の新知見

Behavior of radiocesium in atmospheric arerosol and fallout in Prague

Radiocesium in ground layer atmospheric aerosol and fallout in Prague has been examined. After a decline in 1986–1988, controlled by a sum of two negative exponentials,137Cs aerosol concentration reached a constant level based on an equilibrium between its deposition and resuspension. Deposition velocity was compared to that of7Be and226Ra. It confirmed the supposed source of137Cs as resuspension from the ground. Resuspension factor of the order of magnitude of 10−9 was determined, reminding similar values found earlier in Prague as well as those found in Munich. It also agrees well with the USAEC resuspension model. Solubility of137Cs was measured in combined wet and dry fallout. The average undissolved fraction of137Cs was found to be about 70% which can be explained by the conditions of the137Cs aerosol formation in Chernobyl.

Transfer of Radiocesium to Ruminants in Natural and Semi-natural Ecosystems and Appropriate Countermeasures

A review of studies conducted before and after the Chernobyl accident is presented, showing that both the duration and the extent of radiocesium contamination of ruminants will be more severe in unimproved ecosystems compared with agricultural areas. Although such unimproved ecosystems provide comparatively small quantities of food for human consumption, the integrated dose from these areas to the human population can be large. Ecological characteristics that make unimproved ecosystems particularly vulnerable to this form of pollution include the presence of (1) soils that do not immobilize radiocesium and therefore allow its uptake into vegetation; (2) vegetation species with high uptake rates of radiocesium; (3) the predominant utilization by small ruminants which attain higher muscle radiocesium levels than cattle. Unimproved ecosystems, which often are located at high altitudes, are predisposed to receiving higher fallout because of high precipitation rates which enhance the likelihood of deposition. Countermeasures have been developed and used successfully to reduce radiocesium levels in ruminants grazing in unimproved ecosystems. Apart from decontamination by altering farming practices and providing uncontaminated feeds, sustained reductions of 50% to 80% in the radiocesium concentrations of both milk and meat have been achieved in many ruminant species when AFCF is given via a sodium chloride lick or as a sustained-release bolus. Food production in unimproved ecosystems must be evaluated separately from that of ordinary agricultural systems. In addition to detailed studies on the behavior of radiocesium, consideration should be given to the collection of aggregated transfer coefficients from various ecosystems which were affected by Chernobyl fallout. By combining bioavailability estimates and aggregated transfer coefficients, based on Chernobyl and nuclear weapons test fallout data, it may in the future be possible to make a rapid assessment of both the immediate and the long-term impact of a future nuclear accident on food production in unimproved ecosystems.

Association of cesium with ferric components in altered flood basalt

Cesium content in eleven positions of a continental basalt with a columnar joint was determined by means of neutron activation analysis. Concentration of cesium is about four times higher at the altered portions of the fracture than at the unaltered. Water and Fe3+ content determined by gravimetry, Mossbauer spectroscopy, and inductively coupled plasma optical emission spectroscopy were also correlated with cesium concentration, suggesting accumulation of cesium with ferric components. Such processes may be important for estimating the behavior of radiocesium in the environment.