Radiocaesium Activity Concentrations Research Articles

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.

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.

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.

Activity Concentrations of Radiocaesium in Self-consumed Crops Collected in Namie, Fukushima from 2019 to 2020 with Associated Internal Radiation Doses to Humans

Activity Concentrations of Radiocaesium in Self-consumed Crops Collected in Namie, Fukushima from 2019 to 2020 with Associated Internal Radiation Doses to Humans

РАДИОНУКЛИДЫ В ВЕРХНЕМ СЛОЕ ПОЧВ ОСОБО ОХРАНЯЕМЫХ ПРИРОДНЫХ ТЕРРИТОРИЙ РОСТОВСКОЙ ОБЛАСТИ

The paper is devoted to the assessment of the features of the distribution of natural radionuclides (226Ra, 232Th, 40K) and artificial 137Cs in the upper soil layer of specially protected areas of the Rostov region. The activity concentration of radionuclides in the soil was measured by the gamma spectrometric method. The distribution of the artificial radionuclide 137Cs in the soils of the Rostov region is uneven. The minimum activity concentration of radiocesium is recorded in the Rostov nature reserve. It is shown that the arithmetic mean, median and modal values of the activity concentration of 137Cs are 21.7, 14.2 and 7.5 Bq/kg, respectively, and the arithmetic mean activity concentration of natural radionuclides in the soils of the protected areas of the Rostov region are 26, 9 Bq/kg for 226Ra, 27.0 Bq/kg for 232Th. These values can be used as background (reference) values in assessing the degree of influence of industry and urbanization on soil radioactivity.

DISTRIBUTION OF RADIOCESIUM CONCENTRATIONS OF SOILS IN THE EIGHT IZU ISLANDS AFTER THE FUKUSHIMA DAIICHI NUCLEAR POWER PLANT ACCIDENT

Large amounts of anthropogenic radionuclides, such as 134Cs and 137Cs(radiocesium), were released into the atmosphere due to the Fukushima Daiichi Nuclear Power Plant (F1-NPP) accident and were transported into various environments. The soil accumulations of diffused radionuclides are marked by large differences in their horizontal distributions, and the vertical air dose rates vary depending on the topography, altitude and other factors. In this study, soil activity concentrations of eight islands in the Izu Islands, ~334-563km south of the F1-NPP, were analyzed from both horizontal and vertical perspectives. Soil samples were collected over a 4-y period from 2012 to 2016, and their activity concentrations of radiocesium were measured. The activity concentrations in the soil were categorized for intervals of a 100-m altitude above sea level, and the relationship between the maximum activity concentration in each category and the distance from the F1-NPP was analyzed. The correlation was good at the lower altitudes.

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.

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.

Minimum detectable activity concentration of radio-cesium by a LaBr3(Ce) detector for in situ measurements on the ground-surface and in boreholes

A 3.81 × 3.81 cm LaBr3(Ce) detector based portable measurement setup has been developed for in situ gamma spectrometric survey of a contaminated site. This system is suitable for above- and below ground surface gamma spectrometric measurements of 137Cs. However, the minimum detectable activity concentration (MDAC), an important parameter of a measurement system, should be estimated for planning purposes of the gamma spectrometric survey. In this study, the MDAC of 137Cs for the measurement setup was investigated. The efficiency of the measurement setups was calculated from Monte Carlo simulations using MCNP code. The numerical model of the different studied set-ups, used in MCNP, performed well for the known cases. The results show that the MDAC varies with the position of the detector with respect to ground surface. A 5–20 min acquisition time, depending on the detector position, can be sufficient to get a MDAC of about 10% of the exemption limit of 137Cs (100 Bq/kg).

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.

Dataset on the 6-year radiocesium transport in rivers near Fukushima Daiichi nuclear power plant

Radiocesium released from the Fukushima Daiichi nuclear power plant (FDNPP) and deposited in the terrestrial environment has been transported to the sea through rivers. To study the long-term effect of riverine transport on the remediation process near the FDNPP, a monitoring project was initiated by the University of Tsukuba. It was commissioned by the Ministry of Education, Culture, Sports, Science, and Technology, and the Nuclear Regulatory Commission in June 2011, and was taken over by the Fukushima Prefectural Centre for Environmental Creation from April 2015. The activity concentration and monthly flux of radiocesium in a suspended form were measured in the project. This provides valuable measurement data to evaluate the impact of the accidentally released radiocesium on residents and the marine environment. It can also be used as verification data in the development and testing of numerical models to predict future impacts.

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.

Soil erosion and radiocesium migration during the snowmelt period in grasslands and forested areas of Miyagi prefecture, Japan.

This study aimed to examine the influence of snowmelt on soil erosion processes in mountainous landscapes in the Miyagi prefecture of Japan. The investigated slopes had different expositions and were covered with grasslands and forests. The snowpack thickness, soil frost depth, volume of surface runoff, physicochemical properties of the soil and sediments, cesium composition of the snow and meltwater, and air dose rate were determined. In mid-February, snow cover reached its maximum thickness (100-179cm). In the forest, the snow depth was always lower by 15-20cm. The soil did not freeze in winter in any of the plots. Surface runoff was observed only in the grassland plots and depended on the slope aspect. The total volume of surface runoff ranged from 31 to 52mm and snowmelt soil losses ranged from 2 to 9kgha-1 DM. Radiocesium concentrations in runoff samples ranged from 0.1 to 8.4BqL-1, below the standard limit for drinking water in Japan (10BqL-1). The average organic matter content of the sampled sediments was 0.4%, higher than that in the surface soil. The silt fraction in sediments became dominant for particle size distribution, and the activity concentration of total radiocesium was, on average, 250Bqkg-1. The air dose rate was always lower than the maximum permissible level (0.2μSvh-1) and varied from 0.02 to 0.09μSvh-1 in winter, and from 0.08 to 0.13μSvh-1 at times of the year without snow.

Spatial distribution of 137Cs concentrations in mushrooms (Boletus hiratsukae) and their relationship with soil exchangeable cation contents

The activity concentrations of radiocesium (137Cs) in wild mushrooms are reported to vary according to species, genus or ecological types. In addition, the concentration fluctuates among the same species collected within the same area. Therefore, we investigated whether the 137Cs concentration of wild mushrooms would be (1) spatially biased, or (2) influenced by the 137Cs or exchangeable potassium concentrations in the soils below. We set two survey plots 300 m apart in a Himalayan cedar forest in Tsukuba, Japan, where ca. 30 kBq/m2 of 137Cs was deposited after the Fukushima Nuclear Power Plant accident. From these plots, we collected fruit-bodies (fungal structures for spore production) of co-occurring Boletus hiratsukae, a mycorrhizal species, as well as from the soil below. The mean 137Cs concentrations in the fruit-bodies were significantly different between the two plots, but no difference was observed in the soil 137Cs concentration between the plots. Significant spatial autocorrelation was observed in the 137Cs concentration in the organic layer for both sites, but no significant spatial autocorrelation was observed in the 137Cs of fruit-bodies. Therefore, the variation in the 137Cs concentrations of co-occurred B. hiratsukae was not explained by spatial bias or radioactivity in the below soil. In contrast, the exchangeable potassium concentration in the soil was negatively correlated with the 137Cs in the fruit-bodies. Our results suggest that the 137Cs absorption of wild mushrooms would be suppressed by the competitive effect of exchangeable potassium in the surrounding soils.

Activity concentration of Fukushima-derived radiocesium in the western subarctic area of the North Pacific Ocean in summer 2017

Vertical profiles of radiocesium (134Cs and 137Cs) were measured in the western subarctic area of the North Pacific in 2017. The highest concentration of 134Cs, which was derived from the accident of the Fukushima Dai-ichi Nuclear Power Plant in 2011, was 0.14 Bq m−3 (or 1.19 Bq m−3 after the decay correction to the accident date). Although the vertical inventory of 134Cs decreased between 2014 and 2017, the inventory in 2017 was larger than that expected. That was probably arose from the return of some portion of the high-concentration water mass along with the anticlockwise subarctic gyre current.

Radiocesium concentrations and GPS-coupled dosimetry in Fukushima snakes

One of the largest releases of radioactive contamination in history occurred at Japan's Fukushima Daiichi Nuclear Power Plant (FDNPP). Although the accident happened in 2011, questions still persist regarding its ecological impacts. For example, relatively little is known about radiocesium accumulation in snakes, despite their high trophic status, limited home range sizes, and close association with soil where many radionuclides accumulate. This study presents one of the most comprehensive radioecological studies of snakes published to date using a combination of whole-body radiocesium analyses, GPS transmitters, and optically stimulated luminescence (OSL) dosimeters. The objectives were to: 1) quantify whole-body radiocesium activity concentrations and internal dose rates among several common species of snakes within and around the Fukushima Exclusion Zone (FEZ), 2) determine effects of species, sex, and body size on radiocesium activity concentrations, 3) measure external dose rates using GPS-coupled dosimeters deployed on free-ranging snakes, 4) compare field-derived empirical dose rates to those generated by computer simulation software (i.e., the ERICA tool), and 5) determine if incorporating snake behavior into computer models improve simulated estimates of external dose. Whole-body radiocesium levels for snakes were highly variable among individuals (16 to 25,000 Bq/kg, FW), but were influenced more by levels of local contamination than species, sex, or size. Doses recorded by OSL dosimeters on snakes, as well as modeling in ERICA, suggest that individual movements and behavior have a substantial influence on dose rates to snakes. However, dose estimates produced with ERICA were comparable to dose received by tracked snakes. The average external plus internal dose rate for snakes captured in the FEZ was 3.6-3.9 μGy/h, with external dose contributing 80% to the total. Further research regarding reptile-specific benchmark dose rates would improve risk assessment for reptiles in radiologically contaminated areas.

137Cs and 40K in Cortinarius caperatus mushrooms (1996–2016) in Poland - Bioconcentration and estimated intake: 137Cs in Cortinarius spp. from the Northern Hemisphere from 1974 to 2016

Cortinarius caperatus grows in the northern regions of Europe, North America and Asia and is widely collected by mushroom foragers across Europe. This study shows that in the last three decades since the Chernobyl nuclear accident, C. caperatus collected across much of Northern Poland exhibited high activity concentrations of radiocaesium (137Cs) - a long-lived radionuclide. The mushroom appears to efficiently bioconcentrate 137Cs from contaminated soil substrata followed by sequestration into its morphological parts such as the cap and stipe which are used as food. The gradual leaching of 137Cs into the lower strata of surface soils in exposed areas are likely to facilitate higher bioavailability to the mycelia of this species which penetrate to relatively greater depths and may account for the continuing high activity levels noticed in Polish samples (e.g. activity within caps in some locations was still at 11,000 Bq kg−1 dw in 2008 relative to a peak of 18,000 in 2002). The associated dietary intake levels of 137Cs have often exceeded the tolerance limits set by the European Union (370 and 600 Bq kg−1 ww for children and adults respectively) during the years 1996–2010. Human dietary exposure to 137Cs is influenced by the method of food preparation and may be mitigated by blanching followed by disposal of the water, rather than direct consumption after stir-frying or stewing. It may be prudent to provide precautionary advice and monitor activity levels, as this mushroom continues to be foraged by casual as well as experienced mushroom hunters.

Radiocesium concentration in indoor air during residential house cleaning in Fukushima Dai-ichi nuclear power plant evacuation areas

After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, outdoor decontamination was conducted by the Japanese Government, whereas indoor contamination was the responsibility of individual residents. However, no data exist regarding 137Cs exposure during indoor cleaning. Therefore, indoor 137Cs radioactivity concentrations in indoor air were determined during cleaning in 60 houses within the evacuation area near the FDNPP, Fukushima Prefecture, Japan. Radiocesium activity concentrations per cubic meter of indoor air during dusting (mean ± SD (median)) was 6.8 ± 7.9 (4.7) and 1.6 ± 2.7 (0.78) Bq/m3 for all aerodynamic diameter of aerosol particle and PM2.5, respectively. Radiocesium activity concentrations in indoor air decreased with decreasing the aerodynamic diameter of aerosol particles (mean: 0.099, 0.22, 0.41, 0.92, 2.2, and 2.9 Bq/m3 for the aerodynamic diameter of <0.25, 0.25–0.5, 0.5–1.0, 1.0–2.5, 2.5–6.6, and >6.6 μm, respectively) and was inversely proportional to the square of the distance from the FDNPP. Indoor 137Cs radioactivity concentrations were significantly higher during dusting than during vacuuming with either a cyclone handy cleaner or a normal vacuum cleaner. The mean deposited activities in tracheobronchial and alveolar regions was estimated to be 1.9 and 2.8 Bq, respectively, during a 2-h dusting period in the studied houses. For values below the detection limit, half of the detection limit was used for calculating the means and SDs.

Fungal spore involvement in the resuspension of radiocaesium in summer

We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012. During the survey periods from 2012 to 2015, the activity concentrations of radiocaesium in air ranged from approximately 10−5 to 10−2 Bq per m3 and were higher in the warm season than in the cold season. Electron microscopy showed that the particles collected on filters in summer were predominantly of biological origin (bioaerosols), with which the observed radiocaesium activity concentration varied. We conducted an additional aerosol analysis based on fluorescent optical microscopic observation and high-throughput DNA sequencing technique to identify bioaerosols at Namie in 2015 summer. The concentrations of bioaerosols fluctuated the order of 106 particles per m3, and the phyla Basidiomycota and Ascomycota (true Fungi) accounted for approximately two-thirds of the bioaerosols. Moreover, the fungal spore concentration in air was positively correlated with the radiocaesium concentration at Namie in summer 2016. The bioaerosol emissions from Japanese mixed forests in the temperate zone predominately included fungal cells, which are known to accumulate radiocaesium, and should be considered an important scientific issue that must be addressed.