Radiocesium Activity Research Articles

Quantitative risk assessment of radiocesium associated with Japanese foods imported into the United Kingdom.

Damage to a nuclear power station resulted in radioactive contamination of certain areas of Japan in 2011. Legislation was put in place in Europe to establish controls on the import of certain types of food and feed, including a limit of 100 radioactive decays (becquerel, Bq) per second of radiocesium per kg. This legislation was retained in the United Kingdom after leaving the EU and then reviewed in 2021. A quantitative risk assessment was developed to estimate the radiological risk to public health from consuming Japanese food imported into the United Kingdom should the maximum level on radiocesium be removed. Although Japanese monitoring data indicated occurrences when products exceeded the 100Bq per kg limit, these were found to be rare; a total of 1485 occurrences (0.0013%) of all measured foodstuff samples (>1 million) within the scope of this assessment had radiocesium activity concentrations that exceeded 100Bq per kg. Using the recorded occurrence and level of radiocesium measured, and the current pattern and volume of food imported from Japan, there was an estimated excess risk of fatal cancer of around one in a million per year, categorized as negligible compared to the baseline 2018-2020 UK cancer fatality rate of around 1 in 4. On the basis of the described assessment and the estimated small additional risk, Great Britain lifted import controls related to radioactivity present in food from Japan. A number of recommendations to address data gaps and approaches in this assessment are made, particularly how we can improve modeling UK dietary habits for specialist foods.

Long-Range Consequences of Emergency Underground Nuclear Explosions in Yakutia: Incidence of Malignant Neoplasms

The paper evaluates the possibility of interrelation of emergency underground nuclear explosions with an increased incidence of cancer among the population of areas bordering the area of emergency underground nuclear explosions, for example, in Suntarsky and Nyurbinsky districts, in which the incidence of malignant neoplasms, mortality from malignant neoplasms is higher than the average in the Republic of Sakha (Yakutia). For this purpose, the radiation situation of the sites of underground nuclear explosions “Kraton-3” and “Kristall” was investigated: the radionuclide composition of soil and vegetation was studied by semiconductor gamma-ray spectrometry and a water sample by liquid scintillation spectrometry; dosimetric measurements were carried out: the power of exposure doses. Based on the results of water analysis, it is possible to determine the possibility of migration of tritium from the cavities of emergency underground nuclear explosions. The results of the study of vegetation and soil showed the presence of artificial radionuclides 137Cs, 241Am and traces of 60Co. High values of the specific activity of radiocesium are observed in several samples taken near the area “Kraton-3”. Also in this area, the results of dosimetric measurements showed a slight decrease in the gamma background level, but which still remains elevated and exceeds the safe level by 2.5 times. It is possible that the increased incidence rate in the districts of the republic bordering the area of emergency underground nuclear explosions can be considered as their long-term consequences due to additional dose loads, for example, from caesium during the entire time after the explosions, since the half-life of caesium is approximately 30 years. The results of this study can be considered as a basis for the development of recommendations, possible regulations that can be applied in the implementation of compliance with radiation safety standards during future similar tests and during mining, during which there may be emissions of natural radionuclides to the earth's surface.

Spatial distribution of 137Cs; 40K, 226Ra, 232Th in soils of Monchegorsk city (Murmansk region)

The purpose of the study was to establish the patterns of spatial distribution of radioactivity of technogenic 137Cs and natural radionuclides 232Th, 226Ra, 40K in urban soils of Monchegorsk. Location and time of the study. Soil samples, were collected in summer 2018 in the Monchegorsk city, Murmansk region, Russia. To study the specific activity of radiocesium and natural radionuclides, soil samples were taken from topsoil (0-5 cm) at 82 sites, including 68 sites within the city territory (urban soils) and 14 sites beyond the city limits in the subtorch areas strongly affected by the Severonickel factory. Similar studies of urban soils in Monchegorsk had not been carried out previously. Methods. During expeditionary work and laboratory research, soil, radiological, and mathematical and statistical methods were used. When carrying out gamma spectrometric measurements, radionuclides 137Cs, 226Ra, 232Th and 40K were determined on a low-background semiconductor gamma spectrometer ORTEC (USA) based on a high-purity coaxial germanium detector GEM10P4–70 (HPGe) with a SBS-75 pulse signal processor and Gamma-software. The resolution of the gamma spectrometer along the 1.33 MeV line (60Co) was 1.75 keV, and the relative efficiency was 15%. Calibration and quality control of gamma spectrometric measurements was carried out using volumetric activity measurements with 1-L Marinelli vessels of different densities (RITVERZ, Russia-Germany). Main results. The values of specific activity of radionuclides in soil samples were as following: in the technogenic 137Cs up to 31.3 Bq/kg and in the subtorch soils up to 63.4 Bq/kg. Specific activity of natural radionuclides in urban soils reached to 14.2 Bq/kg for 226Ra, whereas in the subtorch soils it reached 21.6 Bq/kg. The specific activity of 232Th in urban soils reached 18.3 Bq/kg, with 17 Bq/kg registered for the subtorch soils. As for 40K, its specific activity reached 498 Bq/kg in the urban soils and 317 Bq/kg. Conclusion. The gamma survey of the Monchegorsk territory did not reveal any anomaly in radiation. The dose rate of gamma radiation in the city does not exceed 0.074 μSv/hour, which is less than the values elsewhere in Russia, ranging from 0.04 to 0.20 μSv/hour. The obtained data about specific activity of technogenic 137Cs and natural radionuclides 232Th, 226Ra, 40K in the Monchegorsk soils are typical for the Murmansk region.

Accumulation of <sup>137</sup>Cs by ecological groups of coastal-aquatic vegetation of floodplain meadows of the Sozh river

The purpose of the study is to identify differences in the content of 137Cs in the phytomass of coastal aquatic vegetation of the Vetka and Chechersk districts of the Gomel region for the period 2012–2022. The description and identification of ecological groups of coastal aquatic vegetation and the sampling of soil and plants to determine the content of radiocesium in the growing seasons of 2012 and 2022 were carried out according to generally accepted methods. It was found that the content of 137Cs in water samples from the objects of Vetka district did not exceed the normative value for drinking water (10 Bq/kg). The average specific activity of radiocesium in the soil for the studied objects was 807±125 and 586±84 Bq/kg in 2012 and 2022, respectively; and for soil was 549±85 and 395±46 Bq/kg respectively. Over time, there was a decrease in the amount of radiocesium in soil and in ground by 1.3–1.4 times. The average content of the isotope in the plants in 2012 and 2022 was 93–917 and 59–578 Bq/kg, respectively. The amplitude of variation in the average values of accumulation coefficient in the soil-plant system was 1.03 and 0.11 Bq/kg:Bq/kg in 2012 and 2022, respectively. In the ground-plant system it was 3.08 and 0.01 Bq/kg:Bq/kg, respectively. The specific activity of 137Cs in the water of objects in the Chechersk region did not exceed 3 Bq/l. The average content of 137Cs in the ground was 316 and 231 Bq/kg in 2012 and 2022, respectively. The same parameters for the soil were within the limits of 471 and 340 Bq/kg, respectively. The average content of 137Cs in phytomass varied from 149 to 483 Bq/kg in 2012. After 10 years, the amount of radionuclide was 115–288 Bq/kg. The average values of accumulation coefficient in the soil-plant system in 2012 and 2022 were 1.44 and 1.01 Bq/kg:Bq/kg, and in the soil-plant system were 1.70 and 1.10 Bq/kg:Bq/kg, respectively. As a result of the study, similar dominant groups of coastal aquatic plants were not identified in terms of the accumulation of radiocesium in the objects of the Vetka and Chechersk regions.

Variability in radiocesium activity concentration in growing hardwood shoots in Fukushima, Japan

The radiocesium contamination caused by the Fukushima Daiichi Nuclear Power Plant accident has made it difficult to use coppice woods as bed logs for mushroom cultivation. Evaluating the variability in the radiocesium activity concentration of logs is necessary in order to predict how many coppice woodlands are available for producing mushroom bed logs. To clarify the variability in radiocesium activity concentrations and to estimate the sample size required to estimate these concentrations with sufficient accuracy, we modeled the log-transformed radiocesium activity concentrations in growing shoots of hardwoods. We designed two models: (1) a model with mean concentrations that varied among stands with a standard deviation that was the same among stands, and (2) a model with varying means and standard deviations. We fit the data pertaining to only Quercus serrata to both models and calculated the widely applicable information criterion values. Consequently, we adopted the simpler model (1). Applying the selected model to data for all species, we examined the relationship between the number of measurement individuals and the predictive distribution of the expected concentration. Based on previous recommendations and measurement costs, we proposed that five individuals would be appropriate for estimating radiocesium activity concentration in a stand.

RADIOACTIVE CONTAMINATION OF WILD MUSHROOMS IN CHERNIHIV POLESIE

Purpose. We continue our retrospective investigations of radioactive contamination of wild mushrooms from Ukrainian Polesie. The aim of the current study is an assessment of radioactive contamination of wild mushrooms from some locations of Chernihiv Polesie in 1991-2021. Methodology. A study of radiocaesium activity in 66 wild mushroom species (edible, inedible, conditionally edible, poisonous) (from 2 to 25 fruitbodies per sample) and soils (0-5 cm of upper mineral layer, taken by the envelope method) from 14 locations of Chernihiv Polesie was carried out with γ-spectrometry (Ge-detector Canberra GLX 4019, USA). In some mushrooms, 90Sr activity was determined radiochemically on the basis of 90Y accumulation according to the standard method. Scientific novelty. The results of γ-spectrometric studies of the activity of radiocaesium in 66 species of wild mushrooms from the localities of Chernihiv Polesie over a 30-year period are given, the coefficients reflecting the bioaccumulation activity of each species counted, the hyperaccumulator species of radiocaesium are determined, and the potential annual equivalent doses for adults are calculated under the conditions of consumption of some valuable culinary-medicinal mushrooms (B. edulis, C. cibarius, I. badia, Suillus spp, T. equestre). Conclusions. Activity levels of 137Cs in wild mushrooms of Chernihiv Polesie varied over the years 1991-2021 depending on the mushroom species, its ecological affiliation, radioecological situation at the sampling sites, showing a certain tendency to decrease over time. Hyper-accumulative properties in relation to 137Cs are demonstrated by Cortinarius, Sarcodon, Paralepista, Tricholoma, Lactarius, Suillus spp. Widely distributed on the territory of Ukrainian Polesie - I. badia, P. involutus and L. rufus, remain representative bioindicators of radiocaesium contamination. A potential calculated annual effective doses due to the mushrooms consumption by adults, considering only the effect of the 137Cs, reached a high values in Suillus spp., T. equestre, and I. badia – 0.041, 0.035 and 0.025 mSv, respectively, which indicates a relatively insignificant dose load when consuming mushrooms in these localities compared to other localities of Ukrainian Polesie that have higher levels of soil contamination with radionuclides. However, radiation monitoring can still be recommended during mushroom procurement and mass collections.

Effect of plant growth regulators on accumulation of radiocaesium in potato tubers

An important place among the problems of modern agriculture is occupied by the problems of rational use and protection of land and the ecologically dangerous state of the environment. The Zhytomyr region is one of the most affected by the accident at the Chernobyl nuclear power plant. A significant part of agricultural land has a density of contamination with cesium-137 up to 5 Ki/km2, which is 75 % of all contaminated land in the districts, about 20 % of agricultural land has a density of contamination from 5 to 15 Ki/km2, 5 % – above 15 Ki/km2. On lands with a higher density of pollution, it is necessary to apply a complex of agrochemical, agrotechnical and organizational measures to reduce the transfer of radionuclides from the soil to plants. Solving problems related to farming in radioactively contaminated territories occupies one of the leading places in the complex of measures to mitigate the consequences of the Chernobyl accident. The purpose of the research was to establish the effect of different doses and types of plant growth regulators on the productivity of potatoes, the level of radioactive contamination in the agro-ecological conditions of Polissia. Our research was carried out in the agro-ecological conditions of Polіssia LLC. Councilors of Ovrutsky district of Zhytomyr region. The transition of the radioactive isotope cesium-137 from the soil to the plants depends on the content of exchangeable potassium in the soil, the saturation of the soil-absorbing complex with bases, the reaction of the soil solution, the bonification of the soil, and the content of humus. When the agrochemical parameters of the soil improved, in particular when the content of exchangeable potassium in the soil increased from 2.3 mg/100 g of soil to 14.8 mg/100 g of soil, the specific activity of radiocesium in plants de-creased by 3.4 times. The results of our research show that the foliar treatment of potato plants with Biosil and Poteitin contributed to a decrease in the specific activity of tubers from 29.2 to 6.4–2.1 Bq/kg. It was established that foliar spraying of potato plants with Biosil and Poteitin contributed to the reduction of the coefficient of 137Cs transition to 0.03 and 0.01.

On the shapes of deep slopes of radiocesium vertical profiles in lake sediments

The shapes of the deep slope (below the maximum values) of the vertical profiles of radiocesium activity concentrations in the sediment samples taken in 2003–2012 in the Lakes Juodis, Tapeliai and Red lake were studied. The Gaussian shape of the deep slope indicates the migration of radiocesium into the depths of the sediments, and this process is significantly enhanced in some places due to bioturbation caused by tench preparing for hibernation. The exponential shape of the deep slope is typical for sediments in which in winter, in the presence of an ice cover on the lake, thermodynamic mixing occurs in the surface layer caused by the effects of pore water buoyancy. In these sediments, radiocesium dissolved in the pore fluid migrates upwards into the near-bottom water, becoming a source of secondary pollution of the water column. In winter, the presence of such a process is easily determined by the emergence of a layered structure of the water column in the lake and the temperatures of the near-bottom waters exceeding 4 °C. In this case, each layer is characterized by constant standard water parameters (temperature, conductivity, concentrations of oxygen, and trace elements). Complex forms of the deep slope of the vertical profile of radiocesium activity concentrations, combining elements of the exponential and Gaussian forms, indicate the episodic presence of both migration mechanisms.A method is proposed for identifying sediments that are a source of secondary pollution of lake waters by estimating the differences between the normalized logarithms of the radiocesium activity concentrations of the deep slopes (below the maximum concentrations) of its vertical profiles in the sediments of the studied samples and the sample of the carbonate barrier sediments, which were discovered in the shallow part of Lake Juodis in 2003.

Flow filtration/adsorption and simultaneous monitoring technologies of radiocesium 137Cs in river water

This study develops a method that combines a radiation-grafting fibrous Cs-adsorbent filter of ammonium molybdophosphate (AMP) and a Ce:Gd3Al2Ga3O12 scintillator-based γ-ray detector for in situ measurements of the activity concentrations of 137Cs in a continuous water flow. To ensure adequate performance, the study locations were set along an upper tributary stream of the Ukedo River and a nearby spring-fed stream, approximately 30 km northwest of the Fukushima Daiichi Nuclear Power Plant. In the tributary stream, the activity concentrations of 137Cs slowly decreased from 19 to 1.7 mBq/L between 2018 and 2020 until reaching equilibrium with a few millibecquerels in 10 years after the accident. This equilibrium value is significantly below the admissible radiocesium activity (10 Bq/L) for drinking water. The spring-fed stream rarely included 137Cs. The monitoring results support previous views about the environmental fate of 137Cs in a forest ecosystem at the Abukuma granitic catchments. The major advantage of this method is that utilizing fibrous Cs adsorbents with AMP-loaded graft chains enables the effective accumulation of 137Cs through a large amount of stream water. Therefore, 137Cs γ-rays can be detected simultaneously, and combining these strategies provide a unique monitoring platform for on-site and real-time detection of 137Cs at the trace level.

Trophic food chain transfer of radiocaesium from reindeer meat to the blowfly Calliphora vicina and the parasitoid wasp Nasonia vitripennis

The role of insects in the transfer of radionuclides has received little attention, despite their key role in nutrient cycling within ecosystems. In this study, we investigated the trophic food chain transfer of radiocaesium (137Cs) from reindeer meat to the blowfly Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) and further from blowfly pupae to the parasitoid wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae). Radiocaesium was transferred to blowfly larvae during their feeding stage, with the highest whole-organism to food source concentration ratios (CRwo-fs) being found in actively feeding third instar blowfly larvae, with CRwo-fs in the range of 0.68–0.90. CRwo-fs in blowfly larvae at later developmental stages (i.e., post-feeding stage, prepupal stage, pupal stage, and adult stage) were significantly lower, with CRwo-fs in adult flies in the range of 0.07–0.10. Modelling of the data indicated that >70 % of the radiocaesium present in third instar feeding stage larvae was removed exponentially with excreta prior to pupariation. Furthermore, on average 49 % of the radiocaesium activity concentration assimilated in the metamorphing blowfly pupa was retained in the pupal case after the adult blowfly had emerged. When blowfly pupae were parasitised by parasitoid wasps, a greater proportion of radiocaesium was retained in the parasitised pupal case, with only 2–3 % of the activity concentration in the meat being found in the wasps, providing further evidence to support that radiocaesium is biodiluted in insect food chains. Our results indicate that carcass decomposition driven by insects directly affects the fate of radiocaesium retained in vertebrate carcasses and we discuss these findings in connection to radiocaesium cycling and dispersion in terrestrial ecosystems.

Testing mosses exposed in bags as biointerceptors of airborne radiocaesium after the Fukushima Dai-ichi Nuclear Power Station accident

Eight years after the Fukushima nuclear accident, mosses exposed in bags were used to investigate their ability to accumulate radiocaesium and therefore to act as biointerceptors of 134Cs and 137Cs in the evacuated area of the Fukushima territory. Bags were filled with 3 widely studied moss species (Sphagnum palustre, Hypnum cupressiforme, and Hypnum plumaeforme) and exposed for 3, 6 or 9 weeks at 5 former residential sites within the Fukushima area and, for comparison, at three background sites located 700 km away. The radiocaesium activity concentrations found in moss bags were evaluated as function of exposure time, site conditions and moss species. In the Fukushima area, the moss bags accumulated 137Cs at all exposure sites and in all exposure periods, with S. palustre having the highest 137Cs accumulation ability. The 137Cs activity concentrations (from 28 to 4700 Bq kg−1) measured in moss bags increased with the exposure time and were consistent with the decontamination status of each exposure site, highlighting the big potential of moss bags to discriminate among exposure sites. Time dependency of 137Cs activity concentrations measured in mosses allowed the calculation of location-specific and species-specific factors, which can be used to predict radiocaesium accumulation trends in future biomonitoring surveys performed in the same area with the same experimental design. Autoradiography and electron microscopy analyses of the moss surfaces revealed a prevalence of soil-derived particulate form of radiocaesium, suggesting the use of moss bags as warning sensors of resuspended particles potentially harmful for local residents.

Sequential scavenging and measurement of seawater radiocesium concentrations and plutonium isotopic ratios offshore Fukushima

The scientific interest in radiocesium and plutonium found in the oceans and seas has increased enormously in the past years as a consequence of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident and is expected to be ongoing due to many unresolved questions. Hence, continuous development of new and verification of old analytical methods should be at the top of the list of the community, working on the topic. In this study, we processed and analyzed several seawater samples, collected in different time frames (2011–2015) from the North Pacific Ocean offshore Fukushima, to determine their radiocesium activities, 134Cs/137Cs activity ratios and 240Pu/239Pu isotopic ratios using the sequential scavenging method, gamma spectrometry and accelerator mass spectrometry (AMS). The observed radiocesium levels in seawater (0.07–0.042 Bq L−1) clearly indicated that the investigated region remained impacted by releases from the damaged power plant even after four years after the accident. Regarding plutonium, its successful separation from large volume seawater samples was confirmed by detection of 240Pu by AMS. However, several problems emerged during the analyzes, which we tried to address with the use of additional methods (e.g., measurements of uranium by ICPMS). The efficiencies of the applied methods and other issues are also discussed.

Redistribution of the soil 137Cs inventory through litter and sediment transport on a hillslope covered by deciduous forest in Fukushima, Japan

AbstractThe long‐term behaviour of radiocaesium (137Cs) activity concentrations in forest ecosystems and their downstream impacts remain important issues in the deciduous broadleaf forests of Fukushima, Japan following the Fukushima Daiichi Nuclear Power Plant accident. To predict 137Cs cycling and discharge in the forest ecosystem, it is important to understand the spatial dynamics of the 137Cs inventory and transport along hillslopes. Therefore, we observed the spatial distribution of the 137Cs inventory and 137Cs transport via sediment and litter of a deciduous forest hillslope in Fukushima, Japan in 2016 and 2017 and examined how the spatial distribution of 137Cs inventory was formed using a mass balance model. In 2017, the 137Cs activity concentration was significantly greater in the downslope riparian area (455 kBq/m2) than in the upslope ridge area (179 kBq/m2). Annual 137Cs transport within litter and sediment contributed <0.5% to the current 137Cs inventory and cannot explain the current spatial variation of 137Cs inventory on the hillslope. The mass balance model results showed that if the initial 137Cs deposition was distributed uniformly in 2011, the spatial distribution of the hillslope 137Cs inventory was influenced mainly by the movement of leaf litter with a high 137Cs activity concentration.

Study on the Concentration of Radioactive Cesium in the Environment after the Fukushima Daiichi Nuclear Power Plant Accident

The Tohoku-Pacific Ocean Earthquake that occurred on March 11, 2011 and the resulting tsunami caused the loss of many people and extensive damage in a wide area. Among the anthropogenic radionuclides dispersed from the Fukushima Daiichi Nuclear Power Plant, 134Cs and 137Cs have very long half-lives of approximately 2 years and 30 years, respectively, and there are concerns about their uptake into soil and living things. This paper describes a study conducted by the authors' group on radiocesium activity concentrations in the environment.

Radiation-Geochemical Stability of Bottom Sediments in the Ob and Yenisei Estuaries and Adjacent Shoal Area of the Kara Sea

This paper reports the results of investigations on the radioecological state of bottom sediments of the Ob–Yenisei shoal area and Ob and Yenisei estuaries. Materials were obtained in two periods: 1995–2001 and 2014–2019 during seven expeditions on the R/V Akademik Boris Petrov, Professor Shtokman, and Akademik Mstislav Keldysh. Resampling of bottom sediment cores at key-points in areas of increased radiocesium activity and subsequent analysis of the radionuclide distribution made it possible to establish positive trends in the change of the radiation state of the regional ecosystem. The total degradation of the Ob radiocesium overactivity zone and quite significant degradation of the Yenisei zone (primarily the most polluted) were revealed. Comparison of current max-positions of specific activity in the vertical distribution of 137Cs in sediment cores made it possible to determine the sedimentation rate in the distal and proximal facies of the Yenisei estuary: 4.7–5.8 and 3.2–3.7 mm/year, respectively. The established changes that have occurred over ~20 years prove the ability of the Kara Sea ecosystem to self-purify. Pollutant diffusion and assimilation by bottom sediments play a significant role in the self-regeneration of the ecosystem. This is most intense in zone of influence of the river–sea geochemical barrier.

Influence of irrigation water intake on local increase of radiocesium activity concentration in rice plants near a water inlet

To identify the cause of the phenomenon that rice plants close to the water inlet contain relatively higher radiocesium within a paddy field plot, we conducted a field experiment by establishing experimental channel using polypropylene corrugated sheets, and sampling surface water, paddy soil and rice plants according to the distance from the water inlet in 2014 and 2015. It was found that the 137Cs activity concentrations in both dissolved and particulate forms in paddy surface water presented a declining trend from the water inlet towards the outlet. The 137Cs activity concentration in paddy soil in the harvesting season and those of brown rice and rice straws were highest at 1–2 m from the water inlet. Balance calculation suggests that destination of the lost 137Cs from the surface water was likely to be adsorption of the dissolved form and sedimentation of particulate form onto the soil. The concentration of exchangeable potassium ion in paddy soil was below the recommended standard of 250 mg kg−1 (as K2O in dry soil) near the water inlet at the harvesting period both years．These findings suggested that the possible crucial factors to induce rice plant uptake of radiocesium near the water inlet were either (1) direct absorption of dissolved 137Cs in surface water by rice plants, (2) absorption of 137Cs, which was originally retained in particulate matter and released by ion exchange and/or by organic matter decomposition in combination with (3) loss of soil exchangeable potassium caused due partly to transportation of soil particles with exchangeable potassium by the rapid water flow near the water inlet and/or leaching by ion exchange onto the soil of other cations such as calcium ion flowing into the paddy field. These findings will contribute to providing possible measures for producing safe rice in highly contaminated areas in which agricultural production will resume in the near future. We propose providing a non-planting zone for the area closer than about 5 m from the water intake to avoid the occurrence of high 137Cs concentrations in rice crops.

Statistical analysis for 134Cs and 137Cs radioactivity risk levels modeling

After the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) accident, 134Cs and 137Cs were spread widely into the environment. Spatial distribution maps giving radiocesium activities in contaminated soils for post-accident risk modeling were obtained using the Kriging method. We used Generalized extreme-value distribution, Lognormal probability distribution (PDF) and Weibull PDFs for risk assessment of the data. Root mean square error values and coefficient of determination (R2) were calculated for each distribution function. Weibull PDF was found to be more successful in modeling 134Cs and 137Cs activities.

Effects of 137Cs contamination after the TEPCO Fukushima Dai-ichi Nuclear Power Station accident on food and habitat of wild boar in Fukushima Prefecture

After the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Station accident, wild boar was found to have greater radiocesium (137Cs) activity concentrations in their bodies than other wild animals in Japan; however, the reason for this remains unknown. To understand the mechanism of 137Cs transfer from the environment to wild boar, and the factors that affect variation in 137Cs contamination in wild boar, we sampled muscle and stomach contents from wild boar captured in Fukushima Prefecture and analyzed the relationships among 137Cs concentrations in muscle tissue and in the stomach contents, 137Cs ground deposition at capture sites, and wild boar food habits. Significant positive relationships were observed among 137Cs activity concentrations in muscle and stomach contents, as well as 137Cs deposition density at capture sites. These results suggest that 137Cs is transferred from the environment to plant and animal materials consumed by wild boar, and then from these foods to the bodies of wild boar through digestion. However, no correlation was observed between 137Cs concentrations in stomach contents and the presence of any particular food item in stomachs of wild boar, including mushrooms. These findings suggest mushrooms and underground food items, which were found to affect 137Cs concentrations in wild animals in Europe, were not important contributors to high levels of 137Cs contamination in Japanese wild animals.

Seasonal changes in radiocesium and potassium concentrations in current-year shoots of saplings of three tree species in Fukushima, Japan

We studied seasonal changes in radiocesium (137Cs) activity and potassium concentrations in current-year leaves and branches of Pinus densiflora (naturally regenerated saplings), Cryptomeria japonica (planted saplings) and Quercus serrata (planted saplings and coppice shoots) in Fukushima, Japan. We collected current-year shoots from 10 individuals of each species over two growing seasons at intervals of 1–4 months, between June 2016 and December 2017. For the deciduous species Q. serrata, we also collected dead leaves that remained attached to branches in December to investigate reabsorption of 137Cs. All collected shoots were divided into leaves and branches, oven-dried, and ground; dry weights of each sample were recorded. 137Cs activity concentrations were measured using a germanium semiconductor detector. Potassium concentrations were quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). Increases in dry weight were observed in both leaves and branches between May/June and August; growth then slowed considerably and virtually ceased after October. Clear seasonal changes in 137Cs activity concentrations were observed in both 2016 and 2017, regardless of tree species. Concentrations were higher in young leaves and branches during May and June, then decreased and changed relatively little from August to winter. Reduced 137Cs activity concentrations in dead leaves of Q. serrata were observed only in December 2017 (approximately 15% lower than in October). This reduction may indicate reabsorption of 137Cs in leaves prior to shedding. The changes in potassium concentrations were similar to those in 137Cs in both years. Potassium concentrations were higher in young leaves than in mature leaf and branch samples collected later in the year. A reduction of about 50% in the potassium concentrations in dead leaves of Q. serrata was also observed in December. A positive relationship between 137Cs and potassium concentrations in leaves and branches was observed in all species, except for planted Q. serrata. This relationship may indicate that 137Cs moves in tree shoots with potassium. Leaf and branch weight correlated negatively with 137Cs and potassium concentrations. Reduced concentrations may indicate dilution of these elements as a result of biomass increases over the growing season. Our results imply that irrespective of species, 137Cs exhibits seasonal variations resulting from dilution; these variations correspond with trends in potassium, with higher levels in young organs and decreased levels in older organs.

Prussian blue in salt blocks decreases radiocesium activity concentration in milk from dairy cattle fed a diet contaminated by the Fukushima nuclear accident

In Japan, the radiocesium activity concentration in milk must be less than 50 Bq/kg-fresh to meet shipping standards, and the radiocesium concentration of the diet fed to dairy cattle must be less than 500 Bq/kg-dry. After the Fukushima nuclear accident in 2011, we conducted two experiments to investigate whether Prussian blue (PB) could suppress the radiocesium (134Cs + 137Cs) activity concentration in Japanese cattle’ milk. In experiment 1, four cattle were fed a diet with a radiocesium activity concentration of 175 Bq/kg-dry, with or without PB supplementation. The PB intake ranged from 0 to 3.0 g/day, and the average radiocesium intake was 3.42 kBq/day in all treatments. The radiocesium activity concentration in milk decreased from 16.4 to 8.6 Bq/kg-fresh, and the transfer coefficient of radiocesium from diet to milk (Fm) decreased from 4.77 × 10−3 to 2.61 × 10−3 with increased PB intake. In experiment 2, three cattle were fed another diet including a radiocesium activity concentration of 927 Bq/kg-dry of with or without PB supplementation. The PB intake ranged from 0 to 18.9 g/day, and the average radiocesium intake was 15.2 kBq/day in all treatments. The milk's radiocesium activity concentration decreased from 24.3 to 4.2 Bq/kg-fresh, and the Fm decreased from 1.68 × 10−3 to 0.28 × 10−3 with increased PB intake. Our results suggest that both the radiocesium activity concentration in milk and Fm can be reduced by PB, and that Fm is affected by diet. We recommend cattle should be fed absorbents such as PB to minimize the risk of milk radiocesium activity concentration exceeding 50 Bq/kg-fresh even if the diet has a radiocesium activity concentration of less than 500 Bq/kg-dry.