137Cs Deposition Density Research Articles

Time dependence of 137Cs contamination in wild Japanese monkeys after the Fukushima Daiichi nuclear accident

Over the 10 years immediately after the Fukushima Daiichi nuclear accident, we measured the changes in the muscle 137Cs concentration (Bq/kg) of wild Japanese monkeys living in Fukushima City, which is located approximately 70 km from the Fukushima Daiichi Nuclear Power Plant. The muscle137Csconcentration, which was observed at a maximum of 13,500 Bq/kg immediately after the accident, had decreased to several hundred Bq/kg 10 years later. The muscle 137Cs concentration was significantly related to the soil contamination levels (10,000–30,000, 30,000–60,000, 60,000–100,000, and 100,000–300,000 Bq/m2), sex, age class (immature, mature), body weight (> 5000 g, 5000–10,000 g, < 10,000 g), and seasons (the cold period from December to April, the warm period from May to November).The value of muscle 137Cs concentration and the aggregated transfer factor (Tag: calculated by dividing muscle 137Cs concentration [Bq/kg] by soil 137Cs deposition density at the capture site [Bq/m2]) apparently decreased with time for several years. However, post hoc pairwise comparisons showed no difference from 2017 to 2020, and the accumulation of 137Cs in muscle may continue for some time.

Reconstruction of radio-ecological model parameters based on the results of monitoring the radiation situation in Mazovia after the Chernobyl accident (based on the «Warsaw» scenario of the IAEA EMRAS project)

The paper analyzes the consistency of the input data of the radioecological model: the results of measurements of 137Cs and 131I concentrations in the atmosphere after the Chernobyl accident in Warsaw, the meteo-data on precipitation during the main radioactive fallout, the values of minimum 137Cs deposition densities on the territories of two dairy areas of Warsaw Area and Ostroleka Area in the central part of Mazovia. According to meteorological data in Warsaw Area during the period of radioactive fallout there were local rains. In Ostroleka Area, according to all weather stations, there was no rainfall during this period. In Warsaw Area, a minimum 137Cs deposition density of 1.3 kBq/m 2 with an error of less than 10% was found to be consistent with the “dry” deposition density of 137Cs (1.2 kBq/m 2 ) reconstructed by a simulated agroclimatic model based on atmospheric 137Cs measurements. This agreement, taking into account the amount of precipitation recorded at weather stations during the period of radioactive fallout and the significant, more than 10 times, dispersion of 137Cs fallout densities across the Warsaw Area, suggests that a homogeneous cloud-uniform fallout model is preferable for this region in radio-ecological modeling. For the Ostroleka Area, the variation in deposition densities of 137Cs was relatively small, at 3.2, and the estimated dry deposition density of 137Cs was 2.0-2.7 times lower than the measured minimum deposition densities in districts and settlements. This discrepancy, given the absence of precipitation recorded by all weather stations during the deposition period, led to the assumption that the 137Cs and 131I atmospheric concentrations in Ostroleka Area were 2-2.7 times higher than those in Warsaw Area. The adjustment of the 137Cs and 131I atmospheric concentrations in the Ostroleka Area for this region will be verified by measuring the 131I specific activity in milk under the Warsaw scenario.

Impact of soil erosion potential uncertainties on numerical simulations of the environmental fate of radiocesium in the Abukuma River basin

The Fukushima Dai-ichi Nuclear Power Plant accident in March 2011 resulted in the deposition of significant quantities of radionuclides, including radiocesium (137Cs), over a wide area. Most of the deposited 137Cs is strongly adsorbed on fine soil particles such as clay and silt near the ground surface. Therefore, to estimate the environmental fate of 137Cs, it is necessary to predict its transport with eroded sediment in rainfall-runoff processes. In this study, a distributed radiocesium prediction model was applied to simulations of 137Cs transport associated with hydrological processes in the Abukuma River Basin, the largest river system in Fukushima, over the period of 2011–2012. The soil erosion potential, which is a key input to the distributed radiocesium prediction model, was estimated using the Universal Soil Loss Equation (USLE). This study focused on the uncertainty in estimating the environmental fate of 137Cs associated with the USLE factors. The USLE has five physically meaningful factors: the rainfall and runoff factor (R), soil erodibility factor (K), topographic factor (LS), cover and management factor (C), and support practice factor (P). Because the USLE factors were determined using various methods, R, LS, and the product of C and P (C×P) were divided into two, three, and five cases, respectively, based on previous studies. Therefore, we conducted 30 different simulations. The average total 137Cs outflow during the computational period in the simulation cases using the same USLE factors was 13.3 and 11.7 TBq for R (two cases), 12.6, 13.9 and 10.9 TBq for LS (three cases), and 26.5, 8.64, 0.47, 22.8 and 4.03 TBq for C×P (five cases). For the total outflow, C and P had the highest uncertainty of all the USLE factors. The outflow rates of the average total 137Cs in the simulation cases using the same C and P from the croplands and forest areas and from the undisturbed croplands and paddy fields were 62–91% and 18–34%, respectively. These results were due to the high erodibility of the croplands, the large forest areas in grids with high 137Cs deposition density, and the high concentration of 137Cs in the soil of the undisturbed croplands and paddy fields. This study indicates that land use, especially forest areas, croplands, and undisturbed paddy fields, has a significant impact on the environmental fate of 137Cs.

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.

Prompt Mapping of Radioactively Contaminated Areas

The paper presents a methodology for prompt mapping of radioactively contaminated areas. The efficiency of obtaining cartographic information is achieved by using correlation dependences between the characteristics of radioactive contamination obtained during various radiological surveys of contaminated areas. The method of spatial interpolation based on regression-kriging is used to formalize the data on radioactive contamination. This method allows combining the information resulting from direct measurements of density of territory contamination by radionuclides we are interested in with the information contained in other characteristics of radioactive contamination received at the surveyed area (for example, ER). Such an approach allows more accurate mapping of 137Cs deposition density and concentration of its activity in the root layer of soil, as well as significant reduction of the time and cost to survey the mapped area (sampling, sample preparation and measurement of samples). This, in turn, accelerates and reduces the cost for mapping of radioactively contaminated territories (fields, lands, sites). The methodology has been tested on the fields contaminated by radionuclides resulting from the Chornobyl accident in the Narodychi, Polissia and Ivanivka Districts and has proved its performance and efficiency. Comparison and analysis of the obtained maps of radioactive contamination of the territory show that in the conditions of limited amount of data on direct measurements and time limit, the use of correlation dependences between the characteristics of radioactive contamination of soil is often the only possible way to increase the information content and accuracy of the obtained cartographic information.

Radiocesium contamination of the moss Hypnum plumaeforme caused by the Fukushima Dai-ichi Nuclear Power Plant accident

We investigated 134Cs and 137Cs activity concentrations in the common Japanese moss species Hypnum plumaeforme collected from 32 sites within ca. 100 km radius of the Fukushima Dai-ichi Nuclear Power Plant. A total of 32 samples of H. plumaeforme were collected during the field surveys from November 2013 to September 2014. The maximum radiocesium activity concentrations in H. plumaeforme were 60.9 ± 1.8 kBq kg−1 for 134Cs and 123 ± 2.3 kBq kg−1 for 137Cs. The mean value for the 134Cs/137Cs was 1.17 ± 0.05, and the mean Tag value was 0.09 ± 0.13. Positive correlations were obtained between total 134Cs + 137Cs activity concentrations in H. plumaeforme and the air dose rate with a correlation coefficient (r) of 0.55 (P = 0.001), and between 137Cs activity concentration in H. plumaeforme and 137Cs deposition density on soil with r of 0.55 (P = 0.001). These results suggest that the perennial moss species H. plumaeforme could be more suitable and useful as a qualitative indicator for the radiocesium pollution compared to vascular plants spreading over the lowlands including human habitation in Fukushima Prefecture.

Determining the initial Fukushima reactor accident-derived cesium-137 fallout in forested areas of municipalities in Fukushima Prefecture

ABSTRACT This study determined the initial distribution of Fukushima reactor-derived radiocesium fallout in forest areas of Fukushima Prefecture based on analysis of airborne monitoring surveys by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT). The results of the fifth airborne monitoring surveys were compared with the third airborne survey data in order to correct for variation of deposition density due to multiple factors such as weathering processes and measurement uncertainties between two surveys. Finally, the results of the third and the corrected fifth airborne surveys were combined to reconstruct the initial radiocesium fallout map over the whole Fukushima Prefecture area following the Fukushima reactor accident. Our calculation results showed that forest areas accumulated 72% of the total atmospheric input of 137Cs to the land of Fukushima Prefecture. The deposition density in forest areas showed significant variability among municipalities. Nevertheless, forest areas accumulated a large percentage of atmospherically deposited radiocesium in many municipalities. Statistical analysis of the variability in 137Cs deposition density indicated that deposition density varied significantly, even within a municipality. Furthermore, the inconsistency in the probability distributions of measured deposition density among municipalities makes it difficult to obtain a representative initial radiocesium fallout input following the accident. To reduce uncertainty in environmental parameters related to radiocesium transfer in forest environments, we strongly recommend that the deposition density of initial 137Cs fallout at each location is determined by in-situ sampling survey and using the reconstructed 137Cs fallout map presented in this study.

Vertical distribution and temporal dynamics of dissolved 137Cs concentrations in soil water after the Fukushima Dai-ichi Nuclear Power Plant accident

Radiocesium (137Cs) migration from headwater forested areas to downstream rivers has been investigated in many studies since the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, which was triggered by a catastrophic earthquake and tsunami on 11 March 2011. The accident resulted in the release of a huge amount of radioactivity and its subsequent deposition in the environment. A large part of the radiocesium released has been shown to remain in the forest. The dissolved 137Cs concentration and its temporal dynamics in river water, stream water, and groundwater have been reported, but reports of dissolved 137Cs concentration in soil water remain sparse.In this study, soil water was sampled, and the dissolved 137Cs concentrations were measured at five locations with different land-use types (mature/young cedar forest, broadleaf forest, meadow land, and pasture land) in Yamakiya District, located 35 km northwest of FDNPP from July 2011 to October 2012. Soil water samples were collected by suction lysimeters installed at three different depths at each site. Dissolved 137Cs concentrations were analyzed using a germanium gamma ray detector. The dissolved 137Cs concentrations in soil water were high, with a maximum value of 2.5 Bq/L in July 2011, and declined to less than 0.32 Bq/L by 2012. The declining trend of dissolved 137Cs concentrations in soil water was fitted to a two-component exponential model. The rate of decline in dissolved 137Cs concentrations in soil water (k1) showed a good correlation with the radiocesium interception potential (RIP) of topsoil (0–5 cm) at the same site. Accounting for the difference of 137Cs deposition density, we found that normalized dissolved 137Cs concentrations of soil water in forest (mature/young cedar forest and broadleaf forest) were higher than those in grassland (meadow land and pasture land).

Radiocaesium activity concentrations in parmelioid lichens within a 60 km radius of the Fukushima Dai-ichi Nuclear Power Plant

Radiocaesium activity concentrations (134Cs and 137Cs) were measured in parmelioid lichens collected within the Fukushima Prefecture approximately 2 y after the Fukushima Dai-ichi Nuclear Power Plant accident. A total of 44 samples consisting of nine species were collected at 16 points within a 60 km radius of the Fukushima Dai-ichi Nuclear Power Plant. The activity concentration of 134Cs ranged from 4.6 to 1000 kBq kg−1 and for 137Cs ranged from 7.6 to 1740 kBq kg−1. A significant positive correlation was found between the 137Cs activity concentration in lichens and the 137Cs deposition density on soil (n = 44), based on the calculated Spearman's rank correlation coefficients as r = 0.90 (P < 0.01). The two dominant species, Flavoparmelia caperata (n = 12) and Parmotrema clavuliferum (n = 11), showed strong positive correlations, for which the r values were calculated as 0.92 (P < 0.01) and 0.90 (P < 0.01) respectively. Therefore, Flavoparmelia caperata and Parmotrema clavuliferum are suggested as biomonitoring species for levels of radiocaesium fallout within the Fukushima Prefecture.

Measurement of Internal Radiation Exposure among Decontamination Workers in Villages near the Crippled Fukushima Daiichi Nuclear Power Plant

Decontamination workers may face a high risk of exposure to internal irradiation through inhalation during decontamination activities; there is, however, little previous research on the levels of internal contamination during decontamination procedures. The authors reviewed the medical records, including whole body counter measurements, of decontamination workers in villages near the crippled Fukushima Daiichi Nuclear Power Plant to assess their levels of internal radiation exposure. In total, 83 decontamination workers were enrolled in this study. They were regularly engaged in decontamination activities in highly contaminated areas where surface 137Cs deposition density was over 100 kBq m-2. The present study showed low levels of internal exposure among the decontamination workers near the Fukushima Daiichi nuclear plant. The cesium burdens of all the decontamination workers were below detection limits. They had reported no acute health problems. The resuspension of radioactive materials may cause minimal internal contamination during decontamination activities.

Accumulation of 137Cs in Brazilian soils and its transfer to plants under different climatic conditions

The spatial distribution and behaviour of the global fallout 137Cs in the tropical, subtropical and equatorial soil–plant systems were investigated at several upland sites in Brazil selected according to their climate characteristics, and to the agricultural importance. To determine the 137Cs deposition density, undisturbed soil profiles were taken from 23 environments situated between the latitudes of 02°N and 30°S. Sampling sites located along to the equator exhibited 137Cs deposition densities with an average value of 219 Bq m −2. Extremely low deposition densities of 1.3 Bq m −2 were found in the Amazon region. In contrast, the southern part of Brazil, located between latitudes of 20°S and 34°S, exhibited considerably higher deposition densities ranging from 140 Bq m −2 to 1620 Bq m −2. To examine the 137Cs soil-to-plant transfer in the Brazilian agricultural products, 29 mainly tropical plant species, and corresponding soil samples were collected at 43 sampling locations in nine federal states of Brazil. Values of the 137Cs concentration factor plant/soil exhibited a large range from 0.020 (beans) to 6.2 (cassava). Samples of some plant species originated from different collecting areas showed different concentration factors. The 137Cs content of some plants collected was not measurable due to a very low 137Cs concentration level found in the upper layers of the incremental soils. Globally, the soil-to-plant transfer of 137Cs can be described by a logarithmic normal distribution with a geometric mean of 0.3 and a geometric standard deviation of 3.9.

137Cs in the western South Pacific Ocean

The 137Cs activities were determined for seawater samples from the East Caroline, Coral Sea, New Hebrides, South Fiji and Tasman Sea (two stations) Basins of the western South Pacific Ocean by gamma spectrometry using a low background Ge detector. The 137Cs activities ranged from 1.4 to 2.3 Bq m(-3) over the depth interval 0-250 m and decreased exponentially from the subsurface to 1000 m depth. The distribution profiles of 137Cs activity at these six western South Pacific Ocean stations did not differ from each other significantly. There was a remarkable difference for the vertical profiles of 137Cs activity between the East Caroline Basin station in this study and the GEOSECS (Geochemical Ocean Sections Study) station at the same latitude in the Equatorial Pacific Ocean; the 137Cs inventory over the depth interval 100-1000 m increased from 400+/-30 Bq m(-2) to 560+/-30 Bq m(-2) during the period from 1973 to 1992. The total 137Cs inventories in the western South Pacific Ocean ranged from 850+/-70 Bq m(-2) in the Coral Sea Basin to 1270+/-90 Bq m(-2) in the South Fiji Basin. Higher 137Cs inventories were observed at middle latitude stations in the subtropical gyre than at low latitude stations. The 137Cs inventories were 1.9-4.5 times (2.9+/-0.7 on average) and 1.7-4.3 times (3.1+/-0.7 on average) higher than that of the expected deposition density of atmospheric global fallout at the same latitude and that of the estimated 137Cs deposition density in 10 degrees latitude by 10 degrees longitude grid data obtained by Aoyama et al. [Aoyama M, Hirose K, Igarashi Y. Re-construction and updating our understanding on the global weapons tests 137Cs fallout. J Environ Monit 2006;8:431-438], respectively. The possible processes for higher 137Cs inventories in the western South Pacific Ocean than that of the expected deposition density of atmospheric global fallout may be attributable to the inter-hemisphere dispersion of the atmospheric nuclear weapons testing 137Cs from the northern stratosphere to the southern one and its subsequent deposition, and water-bearing transport of 137Cs from the North Pacific Ocean to the western South Pacific.

GIS supported calculations of 137Cs deposition in Sweden based on precipitation data

It is of interest to know the spatial variation and the amount of 137Cs e.g. in case of an accident with a radioactive discharge. In this study, the spatial distribution of the quarterly 137Cs deposition over Sweden due to nuclear weapons fallout (NWF) during the period 1962–1966 was determined by relating the measured deposition density at a reference site to the amount of precipitation. Measured quarterly values of 137Cs deposition density per unit precipitation at three reference sites and quarterly precipitation at 62 weather stations distributed over Sweden were used in the calculations. The reference sites were assumed to represent areas with different quarterly mean precipitation. The extent of these areas was determined from the distribution of the mean measured precipitation between 1961 and 1990 and varied according to seasonal variations in the mean precipitation pattern. Deposition maps were created by interpolation within a geographical information system (GIS). Both integrated (total) and cumulative (decay corrected) deposition densities were calculated. The lowest levels of NWF 137Cs deposition density were noted in north-eastern and eastern parts of Sweden and the highest levels in the western parts of Sweden. Furthermore the deposition density of 137Cs, resulting from the Chernobyl accident was determined for an area in western Sweden based on precipitation data. The highest levels of Chernobyl 137Cs in western Sweden were found in the western parts of the area along the coast and the lowest in the east. The sum of the deposition densities from NWF and Chernobyl in western Sweden was then compared to the total activity measured in soil samples at 27 locations. Comparisons between the predicted values of this study show a good agreement with measured values and other studies.

Using total beta-activity measurements in milk to derive thyroid doses from Chernobyl fallout

Following the Chernobyl accident, more than 200 childhood thyroid cancer cases have been observed in Brest Oblast of Belarus in territories slightly contaminated with 137Cs, but with suspected relatively high 131I fallout. The most helpful measurements available that can be used to estimate thyroid doses for the population of Brest Oblast are the total beta-activity measurements in cow's milk performed using DP-100 device within a few weeks after the accident. The 131I concentrations in milk were derived from the total beta-activity measurements on the basis of (1) a radioecological model used to estimate the variation with time of the radionuclide composition in milk and (2) the determination of the calibration factors of the DP-100 device for the most important radionuclides present in milk. As a result, 131I concentrations in milk were reconstructed for territories with different levels of 137Cs deposition. A non-linear dependence of the 131I concentration in milk on the 137Cs deposition density was obtained; it was used to estimate the thyroid doses from the consumption of 131I-contaminated cow's milk by the population of Brest Oblast. The average individual thyroid doses have been estimated to be 0.15, 0.18, 0.12, 0.06, 0.04 and 0.03 Gy for newborn, children aged 1, 5, 10 and 15 y and adults, respectively. The collective thyroid dose for the entire population of Brest Oblast is estimated to be 64,500 man Gy, the contribution from the adult population being about one half of the total. The methodology that is described could be applied in the framework of epidemiological studies of the relationship between radiation exposure to the thyroid gland and thyroid cancer in areas where numerous total beta-activity measurements in cow's milk were performed within a few weeks after the accident.

Concentrations of 137Cs in lynx ( Lynx lynx) in relation to prey choice

Concentrations of 137Cs were determined in 747 lynxes killed in Norway during the period 1986–2001. Highly variable 137Cs concentrations and aggregated transfer coefficient values were observed, probably caused by variable 137Cs concentrations in prey and the lynx's extensive home ranges and roaming distances. Adult lynxes had higher 137Cs concentrations than sub-adults, and lynxes killed in regions with extensive reindeer grazing areas were more contaminated than others. A model with 137Cs deposition density, the year lynxes were killed, age, and extent of reindeer grazing area accounted for 50% of the variability in observed 137Cs concentrations. The analyses were equivocal regarding the influence of stomach content on 137Cs concentrations in lynx muscle, i.e., on the lynx's specialization in prey species. Gender was not significant. Information on caesium retention in lynx and better estimates of deposition densities in lynxes' home ranges are important for further elucidation of factors influencing 137Cs contamination in lynxes.

Derivation of 137Cs deposition density from measurements of 137Cs inventories in undisturbed soils

The 137Cs inventories in undisturbed soils were measured for 292 locations across the territory of Vietnam. The logarithmic inventory values were regressed against characteristics of sampling sites, such as geographical coordinates, annual rainfall and physico-chemical parameters of soil. The regression model containing latitude and annual rainfall as determinants could explain 76% of the variations in logarithmic inventory values across the territory. The model part was interpreted as the logarithmic 137Cs deposition density. At the 95% confidence level, 137Cs deposition density could be predicted by the model within ± 7% relative uncertainty. The latitude mean 137Cs deposition density increases northward from 237 Bq m –2 to 1097 Bq m –2, while the corresponding values derived from the UNSCEAR (1969) global pattern are 300 Bq m –2 and 600 Bq m –2. High 137Cs inputs were found in high-rainfall areas in northern and central parts of the territory.