Radioactivity of the atmospheric aerosols detected by CTBTO stations in Africa following the accident at the Fukushima Daiichi nuclear power plant

Radionuclides from the reactor accident Fukushima Daiichi nuclear power plant were observed in the airborne aerosols at CTBT International Monitoring System (IMS) stations (MRP43, CMP13) in Africa. The maximum activity concentrations in the air measured in Mauritania were 186.44 10-6 Bq.m-3, 264.16 10-6 Bq.m-3 and 1269.94 10-6 Bq.m-3 for 134Cs, 137Cs and 131I respectively, and in Cameroon 16.42 10-6 Bq.m-3, 25.53 10-6 and 37.58 10-6 Bq.m-3 respectively for 134Cs, 137Cs and 131I. The activity ratio of 134Cs/137Cs is almost constant throughout the period of time relevant to this study due to their long half-lives of 30.2 years for 137Cs and 2.06 years for 134Cs. Whereas the 131I/137Cs activity ratio varies in time according to the radioactive decay with a half-live of 8.06 days for 131I and different removal rates of both radionuclides from the atmosphere during transport. The EMAC atmospheric chemistry-general circulation was used to simulate the emission and transport of the isotope 137Cs and map the deposition of the 137Cs deposition over Africa.

Ultrastructural Analysis of Large Japanese Field Mouse (Apodemus speciosus) Testes Exposed to Low-Dose-Rate (LDR) Radiation after the Fukushima Nuclear Power Plant Accident

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, great attention has been paid to the impact of chronic low-dose-rate (LDR) radiation exposure on biological systems. The reproductive system is sensitive to radiation, with implications connected to infertility. We investigated the testis ultrastructure of the wild large Japanese field mouse (Apodemus speciosus) from three areas contaminated after the FDNPP accident, with different levels of LDR radiation (0.29 µSv/h, 5.11 µSv/h, and 11.80 µSv/h). Results showed good preservation of the seminiferous tubules, comparable to the unexposed animals (controls), except for some ultrastructural modifications. Increases in the numerical density of lipid droplet clusters in spermatogenic cells were found at high levels of LDR radiation, indicating an antioxidant activity rising due to radiation recovery. In all groups, wide intercellular spaces were found between spermatogenic cells, and cytoplasmic vacuolization increased at intermediate and high levels and vacuolated mitochondria at the high-level. However, these findings were also related to the physiological dynamics of spermatogenesis. In conclusion, the testes of A. speciosus exposed to LDR radiation associated with the FDNPP accident showed a normal spermatogenesis, with some ultrastructural changes. These outcomes may add information on the reproductive potential of mammals chronically exposed to LDR radiation.

Dataset on Cs-137 in waters surrounding Taiwan

The Fukushima accident released short-lived Cs-134 and longer-lived Cs-137 to the ocean. The amount, although substantial, is much less than that produced during the atomic bomb tests 60 yrs ago. Cs-134 and Cs-137 are anthropogenic radionuclides and soluble in seawater; hence, the radioactivity can be used as a tracer for special events or currents. Samples of Cs-134 and Cs-137 in seawater were collected around Taiwan, including the Kuroshio, the northern South China Sea, the Taiwan Strait, and the southern East China Sea from 2018 to 2021. The average surface Cs-137 activity was 1.18±0.25 Bq m - 3, and the activities of Cs-134 samples were all under the detection limit. Complete data are archived, including sampling date, location, water depth, temperature, salinity, and Cs-137 activity; the total sample amount is 577.

Twelve years on: An evaluation of mental health status in Tomioka Town, located within 20 km of the Fukushima Daiichi Nuclear Power Station

We investigated the rate of depression among Tomioka residents using the Kessler 6-item Psychological Distress scale, finding that the distribution of scores indicating depression among Tomioka residents was substantially worse than for the general population. The results of our study indicated poor mental health among those wishing to return and those undecided regarding their intention to return, and a potential mismatch between perceived health risks and reality.

External Doses Available for Epidemiological Studies Related to the Fukushima Health Management Survey: First 4-month Individual Doses and Municipality-average Doses for the First Year

BACKGROUND

One of the components of the Fukushima Health Management Survey (FHMS) is the Basic Survey, which estimates individual external doses for the first 4 months after the 2011 nuclear power plant accident. However, external exposure continues long-term. According to estimations by international organizations, the external dose during the first year accounts for a significant part of the long-term dose. Thus, the present study was intended to estimate the first-year doses by extrapolating the Basic Survey results.

METHODS

For most municipalities of non-evacuated areas, ambient dose rate had been continuously measured for at least one designated point in each municipality after the accident. In the present study, a municipality-average dose received by residents for a period was assumed to be proportional to the ambient dose measured at the designated point of that municipality during the same period. Based on this assumption, 4-month municipality-average doses calculated from the Basic Survey results were extrapolated to obtain first-year doses.

RESULTS

The extrapolated first-year doses for 49 municipalities in the non-evacuated areas had a good correlation with those estimated by UNSCEAR, although the extrapolated doses were generally higher (slope of the regression line: 1.23). The extrapolated municipality-average doses were in reasonable agreement (within 30%) with personal dosimeter measurements, suggesting that the extrapolation was reasonable.

CONCLUSION

The present paper reports the first 4-month average doses for all 59 municipalities of Fukushima Prefecture and the extrapolated first-year doses for 49 municipalities. The extrapolated doses will be the basis for future epidemiological studies related to the FHMS.

Ten years of investigations of Fukushima radionuclides in the environment: A review on process studies in environmental compartments

In March 2011, severe nuclear accident happened at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the gigantic earthquake and following huge tsunami wave. A lot of investigations to assess environmental and radiological impacts of released radionuclides have been conducted by domestic and international organizations. Environmental radioactivity research related to the FDNPP accident has spread widely over different scientific fields due to specific features of the accident, and specifically its impact on the marine environment. The present paper summarizes major lessons learned from the environmental investigations of the FDNPP accident. Environmental radioactivity studies have typical interdisciplinary character; especially physics and chemistry are fundamental as a base of process studies in the environment. In this sight, we review chemical aspects regarding FDNPP-derived radiocesium transfer within and between compartments (atmosphere, ocean and land). We also discuss future trends in investigations of behavior of anthropogenic radionuclides in the environment, important not only for a better understanding of impacts of the FDNPP accident on the environment, but also for improving our general knowledge of the total environment in the Anthropocene era and its protection for the future.

Late phase radiocesium dynamics in Fukushima forests post deposition

The long term dynamics of radiocesium in typical forest ecosystems was studied in the radioactive contaminated areas in Fukushima Prefecture. Six observations sites located in Yamakiya Village (Kawamata Town; since 2014), Tsushima Village (Namie Town, since 2015), and Tomioka Town (since 2017) were monitored. The forests consisted of artificial plantations of Japanese cedar (Cryptomeria japonica) at Yamakiya Village, Tsushima Village, and Tomioka Town. Tsushima Village also had a natural mixed forest dominated by Japanese red pine (Pinus densiflora), and Tomioka Town had a young and a mature artificial plantation of Japanese cypress (Chamaecyparis obtuse). Concentrations of ¹³⁷Cs were monitored in the samples collected from the main aboveground biomass compartments, fresh litterfall, forest litter, and soil. Concentrations of exchangeable forms of ¹³⁷Cs and stable K were measured in soil samples. During the observation period, the litter radiocesium inventories at all sites decreased significantly to approximately 1% or less of the total ground deposition. Approximately 80% of the total radiocesium inventory is localized in the upper 5-cm layer of soil and there is little downward migration of radiocesium. At the sites with the longest monitoring series (Yamakiya and Tsushima), the radiocesium expectation depths and expectation mass depths were relatively constant at 2-3 cm and 5-6 kg m^-2, respectively. Aboveground biomass compartments showed similar decreasing trends in radiocesium aggregated transfer factors, T_ag, in the compartments that were exposed to atmospheric fallout in March 2011 (old foliage, small branches, and outer bark). The mean T_ag in cedar stand compartments currently are in the range of 10^-3-10^-2 m² kg^-1 dw. However, the mean T_ag and their dynamic trend significantly differed in the wood compartments of the cedar stands, which may indicate root uptake differences of orders of magnitude between observation sites. The difference in radiocesium concentration in wood between the sites becomes less pronounced when normalized by the ratio of exchangeable ¹³⁷Cs/K in the soils.

The Kuroshio radiocesium stream

The Fukushima accident released short-lived Cs-134 and longer-lived Cs-137 to the ocean. The amount, although substantial, is much less than that produced during the atomic bomb tests 60 years ago. But, the latter has received little attention. Here we found only Cs-137 in waters near the origin of the Kuroshio. The speed of the Kuroshio current generally decreases with water depth, yet, the Cs-137 activity increases with depth to reach a subsurface maximum of 2.4 Bq m^-3. As a result, a core of high Cs-137 flux, or a radiocesium stream, exists at approximately 200-400 m in depth. In total, the Kuroshio transports about 1 PBq year^-1 Cs-137 northward between 121 and 123°E, 1000 times more than the 0.73-1.0 TBq year^-1 discharged to the ocean at Fukushima in 2016-2018.

A modeling approach to estimate 3H discharge from rivers: Comparison of discharge from the Fukushima Dai-ichi and inventory in seawater in the Fukushima coastal region

Estimation of ³H discharge from river catchments is important to evaluate the effect of Fukushima Dai-ichi discharge and future planned ³H release to the ocean on the coastal environment. Using a previously developed model based on the tank model and observed ³H concentration in river water, the ³H discharge from the Abukuma River and 13 other rivers in the Fukushima coastal region were estimated from June 2013 to March 2020. The ³H discharge from catchments of the Abukuma River and 13 other rivers in the Fukushima coastal region during 2014-2019 were estimated to be 1.2-4.0 TBq/y. These values were approximately 2-22 times larger than the annual ³H discharge from the Fukushima Dai-ichi after 2016, indicating the significance of ³H discharge from the catchments through the rivers. This estimation is expected to be useful to evaluate and predict ³H concentrations and inventories in the Fukushima coastal region for consideration of planned ³H release to the ocean.

Effects of Ionizing Radiation on Flora Ten Years after the Fukushima Dai-ichi Disaster

The aim of this work is to analyze the effects of ionizing radiation and radionuclides (like 137Cs) in several higher plants located around the Fukushima Dai-ichi Nuclear Power Plant (FNPP), evaluating both their adaptive processes and evolution. After the FNPP accident in March 2011 much attention was focused to the biological consequences of ionizing radiation and radionuclides released in the area surrounding the nuclear plant. This unexpected mishap led to the emission of radionuclides in aerosol and gaseous forms from the power plant, which contaminated a large area, including wild forest, cities, farmlands, mountains, and the sea, causing serious problems. Large quantities of 131I, 137Cs, and 134Cs were detected in the fallout. People were evacuated but the flora continued to be affected by the radiation exposure and by the radioactive dusts' fallout. The response of biota to FNPP irradiation was a complex interaction among radiation dose, dose rate, temporal and spatial variation, varying radiation sensitivities of the different plants' species, and indirect effects from other events. The repeated ionizing radiations, acute or chronic, guarantee an adaptation of the plant species, demonstrating a radio-resistance. Consequently, ionizing radiation affects the genetic structure, especially during chronic irradiation, reducing genetic variability. This reduction is associated with the different susceptibility of plant species to chronic stress. This would confirm the adaptive theory associated with this phenomenon. The effects that ionizing radiation has on different life forms are examined in this review using the FNPP disaster as a case study focusing the attention ten years after the accident.

Ten-year radiocesium fluvial discharge patterns from watersheds contaminated by the Fukushima nuclear power plant accident

After the Fukushima Dai-ichi nuclear power plant accident in March 2011, the fluvial discharge of ¹³⁷Cs from watersheds to rivers was analyzed between 2011 and 2021. The concentrations of dissolved and particulate ¹³⁷Cs were measured in river water samples collected from two rivers (the Hiso and Wariki rivers, mainly draining farmlands and forests, respectively) draining approximately 4-7 km² watersheds in a montane area (the areal deposition of ^134+137Cs; 1-3 MBq·m^-2 in March 2011) of Iitate Village, Fukushima. Over the 10 yr analysis, the particulate ¹³⁷Cs concentrations in the Hiso and Wariki rivers decreased by 70 and 50 times, respectively, and that of the dissolved form decreased by 150 and 130 times, respectively. Moreover, the apparent K_d (distribution coefficient) of ¹³⁷Cs for water samples from both rivers have increased gradually over these periods. In 2011, the ¹³⁷Cs discharge rates through the Hiso and Wariki rivers were 0.63% and 0.46% per year of the total amount of ¹³⁷Cs deposited in their catchments, respectively; however, by 2021, these rates had decreased to 0.09% and 0.03% per year. The cumulative ¹³⁷Cs discharge rates over 10 yr in the farmland- and forest-dominated rivers were 1.95% and 1.33%, respectively. These rates of the farmland-dominated river were ∼1.4-fold greater than those of the forest-dominated river. Moreover, ∼90% of the of the discharge occurred in particulate form while the remaining ∼10% was in the dissolved form. Thus, ¹³⁷Cs deposited within these watersheds due to the accident was gradually discharged by the rivers over the 10-yr period; however, the majority remains stored in soils and litters etc. of the catchment area. These results indicate that ¹³⁷Cs outflow from land-to-ocean will be limited in the future, as the river export of ¹³⁷Cs is expected to continue decreasing.

Dynamics of radiocaesium within forests in Fukushima-results and analysis of a model inter-comparison

Forests cover approximately 70% of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident in 2011. Following this severe contamination event, radiocaesium (¹³⁷Cs) is anticipated to circulate within these forest ecosystems for several decades. Since the accident, a number of models have been constructed to evaluate the past and future dynamics of ¹³⁷Cs in these forests. To explore the performance and uncertainties of these models we conducted a model inter-comparison exercise using Fukushima data. The main scenario addressed an evergreen needleleaf forest (cedar/cypress), which is the most common and commercially important forest type in Japan. We also tested the models with two forest management scenarios (decontamination by removal of soil surface litter and forest regeneration) and, furthermore, a deciduous broadleaf forest (konara oak) scenario as a preliminary modelling study of this type of forest. After appropriate calibration, the models reproduced the observed data reliably and the ranges of calculated trajectories were narrow in the early phase after the fallout. Successful model performances in the early phase were probably attributable to the availability of comprehensive data characterizing radiocaesium partitioning in the early phase. However, the envelope of the calculated model end points enlarged in long-term simulations over 50 years after the fallout. It is essential to continue repetitive verification/validation processes using decadal data for various forest types to improve the models and to update the forecasting capacity of the models.

Radiation dose rate to Japanese cedar and plants collected from Okuma, Fukushima Prefecture

After the 2011 Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident, wild populations of animals and plants living in the evacuation zone received additional ionizing radiation of both internal and external radiation doses. Morphological abnormalities of pine and fir trees near the FDNPS were reported. In order to evaluate dose-effect relationships, it is necessary to quantify the radiation doses to trees and plants. In this study, the internal and external dose rates to Japanese cedar and plants collected at three sites in Okuma, approximately 4 km southwest of FDNPS were estimated applying the ERICA Assessment Tool. The activity concentrations of ¹³⁴Cs and ¹³⁷Cs in soils, cedar trunks, and plants were determined. The total dose rates to cedar ranged from 2.2 ± 1.2 to 6.1 ± 2.2 μGy h^-1. These rates were within the derived consideration reference levels (DCRLs) reported by ICRP 108 as 4-40 μGy h^-1 for pine trees. The highest estimate for plants was 7.1 ± 2.7 μGy h^-1, much smaller than the DCRLs reported for grasses and herbs (40-400 μGy h^-1). On average, the internal radiation dose rates to cedars at the two sites accounted for 5% and 29% of the external dose rates, respectively, while the value in another site was only 0.4% for cedar. This was attributed to differences in the crown area between the three sites. The trunk diameter of cedars shows a positive correlation with the ratio of internal to external radiation dose rates. It indicates that the total dose rate to cedars is easily estimated with the soil radiocaesium inventory and trunk diameter. The internal radiation dose rate to the plant varied depending on the plant species. This variation was considerably large in plants due to the presence of two species, including Solidago altissima and Artemisia indica var. maximowiczii.

Comparison of thyroid doses to the public from radioiodine following the Chernobyl and Fukushima accidents

Estimates of thyroid doses to the public from radioiodine intake following the accidents at Chernobyl and Fukushima Daiichi nuclear power plants are compared. The basis for thyroid dose estimates after the Chernobyl accident was a large set of measurements of ¹³¹I thyroidal content for approximately 400,000 residents in Belarus, Ukraine, and Russia. Due to a lack of direct thyroid measurements after the Fukushima accident (just over 1000 residents were measured), thyroid doses were estimated based on ecological models and are therefore associated with much higher uncertainty than those based on direct thyroid measurements. Thyroid dose estimates for evacuees were up to 50,000 mGy for Chernobyl and up to approximately 100 mGy for Fukushima. This large difference in thyroid dose to the public is mainly due to the different dominant pathways of radioiodine intake: ingestion of fresh, locally produced cows' milk (Chernobyl) and inhalation of contaminated air (Fukushima).

Development of an application tool to support returnees in Fukushima

To promote radiation protection and health promotion among returning residents (returnees) in coastal areas of Fukushima, eHealth principles were used to develop a new application tool (app) that can record radiation exposure and health status while providing comprehensive support to returnees. Intended users are returnees and health and welfare workers. After assessing their needs, a flowchart and prototype for operational logic were created using commercially available software tools. Professional developers will focus on improving the user interface and ensuring data security. The finished app will be compatible with mobile telephones and tablets. Utility and ease of use are paramount to serve returnees of all ages effectively.

Needs Survey for Health Support Application Development Project for Residents Returning from Evacuation After the Fukushima Nuclear Accident

The purpose of this study was to identify the needs of stakeholders in developing a mobile application (MP) to be used by returning residents and providers of healthcare and medical/social services. The needs assessment of the residents revealed that among the elderly, ownership of smartphones and tablets was low and they were less likely to use the applications themselves.

Multifaceted effects of chronic radiation exposure in Japanese red pines from Fukushima prefecture

Despite many studies carried out to date, the long-term effects of chronic exposure on plants and animals inhabiting the territories affected by the Fukushima Dai-Ichi NPP accident remain the subject of scientific discussions. Our investigations were performed on Japanese red pine, the native tree species that is widely spread in the radioactive contaminated areas. Earlier observations revealed the radiation-induced cancellation of the apical dominance in young trees of this species. To understand the mechanism of such transformation, we evaluated the morphometric parameters of needles, the frequency of cytogenetic abnormalities, and the concentrations of the major classes of phytohormones in several natural populations of young red pine trees growing under different exposure conditions in Fukushima prefecture. No significant relationships between the morphometric parameters of needles and dose rates at the experimental sites were revealed. The frequencies of aberrant cells in the needle's intercalary meristem and the frequencies of cancellation of the apical dominance in the young pine populations in the radioactive contaminated areas were significantly higher than in the reference population. However, only cytogenetic abnormalities increased with the dose rate. We have not found the relation between the frequency of cytogenetic abnormalities in needles and cancellation of the apical dominance in the individual trees. In this paper, for the first time, it is shown that chronic radiation exposure changes the concentration ratio of the major classes of phytohormones in the needles of Japanese red pine. Given the complete lack of information about the most important regulatory system of plants in chronically irradiated populations, this study fills a substantial gap in our knowledge. Finally, our findings indicated that the most probable causes of the cancellation of apical dominance observed in chronically exposed Japanese red pines are radiation damage to the apical meristems of the trees and changes in their phytohormonal balance.

Total Diet Study to Assess Radioactive Cs and 40K Levels in the Japanese Population before and after the Fukushima Daiichi Nuclear Power Plant Accident

We conducted a total diet study (TDS) of ¹³⁷Cs, ¹³⁴Cs, and ⁴⁰K to assess their average dietary exposure levels in a Japanese adult population before and after the Fukushima Daiichi nuclear power plant (FDNPP) accident. Nineteen market baskets were evaluated in 2006–2011. In each basket, a TDS sample comprising tap water and 160–170 food items, which were combined into 13 groups, were collected for analysis by gamma-ray spectrometry. From 2006 to 2010, the ¹³⁷Cs activity concentration in the “fish and shellfish” group was 0.099 Bq/kg, representing the highest value obtained, whereas the total committed effective dose (CED) of radiocesium isotopes (¹³⁷Cs + ¹³⁴Cs) was 0.69 μSv. In 2011, “milk and dairy products” from Sendai City had a Cs activity concentration of 12 Bq/kg, representing the highest values among all food groups studied. However, the annual CED of radioactive Cs in Fukushima City was 17 μSv after the FDNPP accident, which is 60-fold lower than the maximum permissible dose of 1 mSv/year. The mean CED obtained for ⁴⁰K was 180 μSv, which is comparable to the global average. Our results reveal the average dietary exposure of ¹³⁷Cs, ¹³⁴Cs, and ⁴⁰K, which can aid in estimating the radiological safety of foods.

129I in a sediment core offshore Fukushima: Distribution, source and its implication

¹²⁹I released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has been observed in the atmospheric, terrestrial and oceanic environments, and it also entered the marine sediments via dispersion by sea water movement and deposition around Japan. However, there have been few studies of marine sediment cores in contrast to the large number of studies on seawater. In this work, a sediment core collected near FDNPP was analyzed for ¹²⁹I. It is observed that the ¹²⁹I/¹²⁷I atomic ratios in this sediment core are comparable to those in the seawater and sediments collected from offshore Fukushima after the accident, but 2 orders of magnitude higher than those in seawater in this region before the accident, suggesting the significant amount of ¹²⁹I has been transferred and incorporated to the offshore shallow sediments. The difference in environmental behavior between ¹²⁹I and ¹³⁷Cs is discussed based on their depth distributions in the sediment core in comparison with the grain size distribution of sediments. The peak concentrations of iodine isotopes were found in a relatively deeper layer than radiocesium. Radiocesium follows the distribution of fine grains in the sediment core, implying its high association to fine grains.

Mass balance and latest fluxes of radiocesium derived from the fukushima accident in the western North Pacific Ocean and coastal regions of Japan

This article summarizes and discusses mass balance calculations of the activities of Fukushima-derived ¹³⁷Cs released to the atmosphere and ocean prior to 2018 as well as the ¹³⁷Cs inventories on land and in the ocean, biota, and sediment. We propose that the consensus value of the total amount of ¹³⁷Cs released to the atmosphere was 15-21 PBq; atmospheric deposition of ¹³⁷Cs on land was 3-6 PBq; atmospheric deposition of ¹³⁷Cs on the North Pacific was 12-15 PBq; and direct discharge of ¹³⁷Cs to the ocean was 3-6 PBq. We also evaluated the movement of ¹³⁷Cs from one domain to another for several years after the accident. We calculated that the amount of ¹³⁷Cs transported by rivers might be 40 TBq. The annual deposition of ¹³⁷Cs due to resuspension at Okuma during the period 2014-2018 was 4-10 TBq year^-1. The ¹³⁷Cs discharged to the ocean was 0.73-1.0 TBq year^-1 in 2016-2018. The integrated amount of FNPP1-derived ¹³⁷Cs that entered the Sea of Japan from the Pacific Ocean from 2011 until 2017 was 270 ± 20 TBq, 6.4% of the estimated amount of FNPP1-derived ¹³⁷Cs in Subtropical Mode Water in the North Pacific. The integrated amount of FNPP1-derived ¹³⁷Cs that returned to the North Pacific Ocean through the Tsugaru Strait from the Sea of Japan was 110 ± 10 TBq. Decontamination efforts removed 134 TBq of ¹³⁷Cs from surface soil prior to February 2019, an amount that corresponded to 4% of the¹³⁷Cs deposited on land in Japan.

Distribution of 239,240Pu in marine products from the seas around the Korean Peninsula after the Fukushima nuclear power plant accident

In March 2011, an earthquake caused the shutdown of the active reactors at the Fukushima Daiichi Nuclear Power Plant (NPP), with the succeeding tsunami resulting in the release of radioactively contaminated water into the adjacent Japanese coastal waters. Marine biota selected from various trophic levels were collected in Korean coastal waters throughout 2014 and 2015 and their plutonium levels were measured to evaluate the radioactive contamination levels in the marine organisms that constitute the primary seafood diet in the Republic of Korea (ROK). The results showed that the activity concentrations of ^239,240Pu in plankton, macroalgae, mollusks, crustaceans, and cephalopods ranged from 13 to 58, 0.64 to 0.80, 0.94 to 5.40, 0.06 to 0.50, and 0.26 mBq kg^-1 of wet weight (w.w.), respectively. The activity concentrations of ^239,240Pu measured in the muscles of fish varied from 0.09 to 0.30 mBq kg^-1 (w.w.), relatively low values compared to those in other groups regardless of fish species, size, and sampling area. The concentration characteristics of ^239,240Pu in the various organs in the respective marine products revealed that the internal organs showed higher concentrations than the muscle or skin (or exoskeleton). The highest concentration of ^239,240Pu was measured in the viscera of an abalone, which had an activity concentration of 6.31 mBq kg^-1 (w.w.). The concentration factors (CFs) in the >300-μm fraction of plankton and in anchovy, shrimp, and mackerel ranged 67-84% of the International Atomic Energy Agency (IAEA)-recommended values, although the CF in macroalgae was much lower at approximately 5% of IAEA values, suggesting a wide range of ^239,240Pu CF in macroalgae. The mean transfer factor (TF) between macroalgae (0.6-0.8 mBq kg^-1) and abalone (5.4 mBq kg^-1) was estimated to be 7.5, implying that effective Pu transfer occurred between the two species. These figures equate to annual effective doses of ^239,240Pu to Koreans through consumption of macroalgae, shellfish, and fish of 1.8 × 10^-6, 1.4 × 10^-6, and 7.1 × 10^-7 mSv yr^-1, respectively, and a total dose of 3.9 × 10^-6 mSv yr^-1, values that are negligible compared to the annual effective dose limit of 1 mSv yr^-1.

The detection of Fukushima-derived radiocesium in the Bering Sea and Arctic Ocean six years after the nuclear accident

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, radionuclides released by this event were observed in the Pacific Ocean. Models predicted that these radionuclides would be transported to the Bering Sea; however, limited evidence currently reveals the transportation of these radionuclides to the Arctic Ocean. Here, we provide the first direct observation showing that FDNPP-derived ¹³⁴Cs and ¹³⁷Cs were present in subarctic regions and the Arctic Ocean (Chukchi Sea) in 2017. Furthermore, we conclude that these radionuclides were transported from the Pacific Ocean into the Bering and Chukchi Seas by ocean currents. Additionally, the ¹³⁷Cs activity concentrations in the Bering Sea exceed those in all previous reports. Due to the continuous leaking of radionuclides from the FDNPP, we hypothesize that FDNPP-derived radionuclides will be continuously transported to the Arctic Ocean in the next several years. Our results suggest that though far away from Fukushima, the accident-derived anthropogenic radionuclides also influenced the Arctic Ocean by ocean currents.

Simulation study of the effects of buildings, trees and paved surfaces on ambient dose equivalent rates outdoors at three suburban sites near Fukushima Dai-ichi

The influence of buildings, trees and paved surfaces on outdoor ambient dose equivalent rates (H˙^∗(10)) in suburban areas near to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) was investigated with Monte Carlo simulations. Simulation models of three un-decontaminated sites in Okuma and Tomioka were created with representations of individual buildings, trees and roads created using geographic information system (GIS) data. The ¹³⁴Cs and ¹³⁷Cs radioactivity distribution within each model was set using in-situ gamma spectroscopy measurements from December 2014 and literature values for the relative radioactive cesium concentration on paved surfaces, unpaved land, building outer surfaces, forest litter and soil layers, and different tree compartments. Reasonable correlation was obtained between the simulations and measurements for H˙^∗(10) across the sites taken in January 2015. The effect of buildings and trees on H˙^∗(10) was investigated by performing simulations removing these objects, and their associated ¹³⁴Cs and ¹³⁷Cs inventory, from the models. H˙^∗(10) were on average 5.0% higher in the simulations without buildings and trees, even though the total ¹³⁴Cs and ¹³⁷Cs inventory within each model was slightly lower. The simulations without buildings and trees were then modified to include ¹³⁴Cs and ¹³⁷Cs in the ground beneath locations where buildings exist in reality, and the inventory of paved surfaces modelled as if they had high retention of ¹³⁴Cs and ¹³⁷Cs fallout like soil areas. H˙^∗(10) increased more markedly in these cases than when considering the shielding effect of buildings and trees alone. These results help clarify the magnitude of the effect of buildings, trees and paved surfaces on H˙^∗(10) at the un-decontaminated sites within Fukushima Prefecture.

The deposition densities of radiocesium and the air dose rates in undisturbed fields around the Fukushima Dai-ichi nuclear power plant; their temporal changes for five years after the accident

The deposition densities of radiocesium and the air dose rates were repeatedly measured in a large number of undisturbed fields within the 80 km zone that surrounds the Fukushima Dai-ichi Nuclear Power Plant site between 2011 and 2016, and features of their temporal changes were clarified. The average air dose rate excluding background radiation in this zone decreased to about 20% of the initial value during the period from June 2011 to August 2016, which was essentially a result of the radioactive decay of ¹³⁴Cs with a half-life of 2.06 y. The air dose rate reduction was faster than that expected from the decay of radiocesium by a factor of about two, with most of this reduction being attributed to the penetration of radiocesium into the soil. The average deposition densities of ¹³⁴Cs and ¹³⁷Cs in fields that were not decontaminated were found to have decreased nearly according to their expected radioactive decay, which indicated that the movement of radiocesium in the horizontal direction was relatively small. The effect of decontamination was apparently observed in the measurements of air dose rates and deposition densities. Nominally, the average air dose rates in the measurement locations were reduced by about 20% by decontamination and other human activities, of which accurate quantitative analysis is and continue to be a challenge. In this paper, new original data obtained during 2013-2016 were added to the previously reported data collected up to 2012, and it is discussed throughout.

137Cs and 90Sr in surface waters of the Sea of Japan: Variations and the Fukushima Dai-ichi Nuclear Power Plant accident impact

⁹⁰Sr and ¹³⁷Cs activity concentrations in surface waters of the Sea of Japan (SOJ) decreased during the period of 1993-2010 with effective half-lives of 18 and 15 y, respectively. The longer effective half-life of ⁹⁰Sr in the SOJ may suggest a surplus of ⁹⁰Sr to SOJ surface waters, however, no clear evidence of possible ⁹⁰Sr source has been found. After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, temporal variations of ¹³⁷Cs in the surface water of the SOJ have changed, while ⁹⁰Sr variations followed the pre-accident trends. The ⁹⁰Sr/¹³⁷Cs ratios reveal that increases of ¹³⁷Cs due to the FDNPP accident continued in surface waters of the SOJ until 2016.

Pu isotopes in the seawater off Fukushima Daiichi Nuclear Power Plant site within two months after the severe nuclear accident

The marine environment is complex, and it is desirable to have measurements for seawater samples collected at the early stage after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident to determine the impact of Fukushima-derived radionuclides on this environment. Here Pu isotopes in seawater collected 33-163 km from the FDNPP site at the very early stage after the accident were determined (May 2011, within two months after the accident). The distribution and temporal variation of ²³⁹Pu and ²⁴⁰Pu were studied. The results indicated that both ^239+240Pu activity concentrations (from 0.81 ± 0.16 to 11.18 ± 1.28 mBq/m³) and ²⁴⁰Pu/²³⁹Pu atom ratios (from 0.216 ± 0.032 to 0.308 ± 0.036) in these seawater samples were within the corresponding background ranges before the accident, and this suggested that Fukushima-derived Pu isotopes, if any, were in too limited amount to be distinguished from the background level in the seawater. The analysis of Pu isotopic composition indicated that the major sources of Pu in the seawater after the accident were still global fallout and the Pacific Proving Ground close-in fallout. The contribution analysis showed that the contributions of the Pacific Proving Ground close-in fallout in the water column of the study area ranged from 26% to 77% with the average being 48%.

Radiocesium and 40K distribution of river sediments and floodplain deposits in the Fukushima exclusion zone

In this study, radiocesium and ⁴⁰K analysis were accomplished for samples of riverbed sediments and floodplain deposits collected from five rivers in the vicinity (<20 km) of the damaged Fukushima Daiichi Nuclear Power Plant after seven years of the accident. Sediment particle size distribution and major oxide content were determined also for six selected samples to understand the retention and migration process of radiocesium in river environments. The radiocesium activity concentration varied from 103 ± 6 Bq·kg^-1 to 22,000 ± 500 Bq·kg^-1 in riverbed sediments and from 92 ± 5 Bq·kg^-1 to 117,000 ± 2000 Bq·kg^-1 in floodplain deposits. The ¹³⁴Cs/¹³⁷Cs ratio (decay corrected to 15 March 2011) was 1.02 in the both samples. Compared to monitoring results in 2011, it was proved that the radiocesium distribution pattern had been changed remarkably during seven years. The radiocesium was primarily attached to fine clay particles but its sorption on sand and coarse sand particles was also considerable. The sorption process of radiocesium was not affected by the presence of water and moreover, after seven years of the Fukushima accident, a significant radiocesium migration cannot be expected without particle migration. Consequently, radiocesium will remain for a long time in the river environments and its redistribution is mainly affected by the erosion process of the sediments. The average ⁴⁰K activity concentration of riverbed sediment and floodplain deposit samples was 640 ± 152 Bq·kg^-1 changing from 319 ± 18 Bq·kg^-1 to 916 ± 41 Bq·kg^-1. In the river estuary zones, significant activity concentration decrements were observed for both radionuclides. This suggests that seawater intrusion has a decreasing effect on both natural and artificial radionuclides via wash-out of particulate radiocesium and ⁴⁰K, and desorption of these radionuclides, but to reveal the detail of this process further investigations are required. The analysis of ⁴⁰K can help in a simple and easy way to reveal the mineral composition differences of sediment samples.

Long-range transport of radiocaesium derived from global fallout and the Fukushima accident in the Pacific Ocean since 1953 through 2017-Part I: Source term and surface transport

Long range transport of radiocaesium derived from local fallout occurred early 1950s, global fallout which occurred mainly late 1950s and early 1960s and the Fukushima accident occurred in 2011 were investigated and presented for ocean surface in the Pacific Ocean. HAM database and its update were used in this study to present whole history of radioccaesium transport in surface layer in the interested region. Since both the main local/global fallout regions and injection of radiocaesium by Fukushima accident occurred in the western North Pacific and constrain of surface current systems which governed surface transport processes were subtropical gyre and subarctic gyre, radiocaesium transport in surface water in the mid latitude was characterized as rapid eastward transport along Kuroshio and Kuroshio extension. Behaviors were similar and repeated for local/global fallout and Fukushima derived radiocaesium. A part of radiocaesium transported/deposited/injected in the mid latitude subducted into ocean interior and the radiocaesium activity concentrations were kept higher rather than those in surface water.

Similarities and differences of 137Cs distributions in the marine environments of the Baltic and Black seas and off the Fukushima Dai-ichi nuclear power plant in model assessments

The compartment model POSEIDON-R with an embedded food web model was used to assess ¹³⁷Cs distributions in the Baltic and Black seas and off the Pacific coast of Japan during 1945-2020 due to the weapon testing and accidents at the Chernobyl and Fukushima Dai-ichi nuclear power plants. The results of simulations conducted with generic parameters agreed well with measurements of ¹³⁷Cs concentrations in the water, bottom sediments, and in fish. In the Black and Baltic seas, salinity variations affected the transfer of ¹³⁷Cs through the food web. The contamination of pelagic fish followed the water contamination with some delay, whereas demersal fish depuration was found to be related to decreasing ¹³⁷Cs concentrations in the upper sediment layer. On the Pacific shelf off Japan, intensive currents and eddies caused the simulated depuration rates in fish to be one-two orders of magnitude larger than those in the semi-enclosed Black and Baltic seas.

2018 38 1253-68)

This article presents errata on a published article.

Radiocesium concentrations in soil and leaf after decontamination practices in a forest plantation highly polluted by the Fukushima accident

Owing to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident a vast amount of radiocesium was released polluting the land. Afterwards, a variety of decontamination practices has been done, reducing the ambient dose rates. In this study we evaluated the effectiveness of eight forest decontamination practices by means of monitoring the radiocesium (¹³⁷Cs) concentration in soil and leaf samples, and the daily discharge rates in ten plots during 27 months (May 2013-July 2015). A forest plantation located 16 km southwest to the FDNPP and within the exclusion area was selected. Radiocesium concentrations were analysed using a germanium gamma ray detector. The differences in radiocesium activities between the different plots were statistically significant (p < 0.05) and four homogeneous groups were distinguished. Tree thinning and litter removal greatly reduced the radioactivity and the two plots devoted to these practices presented the highest discharge rates of ¹³⁷Cs (Th + LR; 350-380 Bq/m² day), followed by the two Th plots (163-174 Bq/m² day). The clearcutting with LR and the LR plots (104 and 92 Bq/m² day) also had higher rates than those rates in the control plots (51 Bq/m² day). We only observed low rates in the two plots with matting (19-25 Bq/m² day). The temporal variability was explained by (i) the different rainfall depths registered during the measurement intervals (accumulated precipitation from 14 to 361 mm); and (ii) the fluctuations of the total surface coverage. The decrease trend in radiocesium concentration was high in 2013, moderate in 2014 and low in 2015 owing to the vegetation recovery after the countermeasures, thus reducing the possibility of the second pollution of the neighbouring areas. The average proportions of contribution of ¹³⁷Cs discharge by soil and leaf fraction were 96.6% and 3.4%.

Radioactive and stable cesium isotope distributions and dynamics in Japanese cedar forests

Dynamics of the Fukushima-derived radiocesium and distribution of the natural stable isotope ¹³³Cs in Japanese cedar (Cryptomeria japonica D. Don) forest ecosystems were studied during 2014-2016. For the experimental site in Yamakiya, Fukushima Prefecture, we present the redistribution of radiocesium among ecosystem compartments during the entire observation period, while the results obtained at another two experimental site were used to demonstrate similarity of the main trends in the Japanese forest ecosystems. Our observations at the Yamakiya site revealed significant redistribution of radiocesium between the ecosystem compartments during 2014-2016. During this same period radionuclide inventories in the aboveground tree biomass were relatively stable, however, radiocesium in forest litter decreased from 20 ± 11% of the total deposition in 2014 to 4.6 ± 2.7% in 2016. Radiocesium in the soil profile accumulated in the 5-cm topsoil layers. In 2016, more than 80% of the total radionuclide deposition in the ecosystem resided in the 5-cm topsoil layer. The radiocesium distribution between the aboveground biomass compartments at Yamakiya during 2014-2016 was gradually approaching a quasi-equilibrium distribution with stable cesium. Strong correlations of radioactive and stable cesium isotope concentrations in all compartments of the ecosystem have not been reached yet. However, in some compartments the correlation is already strong. An increase of radiocesium concentrations in young foliage in 2016, compared to 2015, and an increase in 2015-2016 of the ¹³⁷Cs/¹³³Cs concentration ratio in the biomass compartments with strong correlations indicate an increase in root uptake of radiocesium from the soil profile. Mass balance of the radionuclide inventories, and accounting for radiocesium fluxes in litterfall, throughfall and stemflow, enabled a rough estimate of the annual radiocesium root uptake flux as 2 ± 1% of the total inventory in the ecosystem.

Use of Iodine-131 to Tellurium-132 Ratios for Assessing the Relationships between Human Inhaled Radioactivity and Environmental Monitoring after the Accident in Fukushima

Significant differences in findings were seen between the intake amounts of iodine-131 that were derived from direct measurements and the estimated intake from environmental monitoring data at the Fukushima accident. To clarify these discrepancies, we have investigated the iodine-131 and tellurium-132 body burdens of five human subjects, who after being exposed to a radioactive plume, underwent 21.5 h whole body counter measurements at Fukui Prefectural Hospital, so clear intake scenario and thyroid counter measurement data were available. To determine the iodine-131 and tellurium-132 body burdens, we introduced a new method of whole body counter calibration composed of a self-consistent approach with the time-dependent correction efficiency factors concept. The ratios of iodine-131 to tellurium-132, ranging from 0.96 ± 0.05 to 2.29 ± 0.38, were consistent with results of the environmental measurements. The 24 h iodine uptake values ranging from 12.1–16.0% were within euthyroid range in Japanese people. These results suggest, even if the relatively low thyroid iodine uptake in the Japanese population was taken into consideration, that there is no doubt about the consistency between direct measurements and environmental monitoring data. Adequate intake scenario is suggested to be principally important to estimate the inhaled radioactivity in areas in or around nuclear accidents.

An assessment on the environmental contamination caused by the Fukushima accident

The radiological releases from the damaged fuel to the atmosphere and into the cooling water in the Fukushima Daiich Nuclear Power Plant (FDNPP) accident are investigated. Atmospheric releases to the land and ocean mostly occurred during the first week after the accident whereas continuous release from the damaged fuel into the cooling water resulted in an accumulation of contaminated water in the plant during last six years. An evaluation of measurement data and analytical model for the release of radionuclides indicated that atmospheric releases were mainly governed by the volatility of the radionuclides. Using the measurement data on the contaminated water, the mechanism for the release of long-lived radionuclides into the cooling water was analyzed. It was found that the radioactivity concentrations of ⁹⁰Sr in the contaminated water in the Primary Containment Vessel (PCV) of unit 2 and unit 3 were consistently higher than that of ¹³⁷Cs and the radioactivity concentration of ⁹⁰Sr in the turbine building of unit 1 in year 2015 was higher than that in year 2011. It was also observed that the radioactivity concentration of long-lived radionuclides in the contaminated water in the FDNPP is still high even in year 2015. The activity ratio of ²³⁸Pu/^239+240Pu for the contaminated water was in the range of 1.7-5.4, which was significantly different from the ratios from the soil samples representing the atmospheric releases of FDNPP. It is concluded that the release mechanisms into the atmosphere and cooling water are clearly different and there has been significant amount of long-lived radionuclides released into the contaminated water.

Effects of bark washing and epiphytic moss on 137Cs activity concentration in bark and stemflow in Japanese persimmon (Diospyros kaki Thunb.)

The effects of bark washing, and of epiphytic moss growing on the bark surfaces, on the ¹³⁷Cs activity concentrations in bark and stemflow samples were evaluated at two Japanese persimmon orchards located in Fukushima City and Date City, both approximately 60-65 km northwest of the Fukushima Dai-ichi nuclear power plant. The means of ¹³⁷Cs in stemflow captured by 1 g of sphagnum placed on the main trunks of washed and unwashed trees, and on sites with moss and with no moss growing on bark of the non-washed trees in Date City, were 0.37 Bq, 1.08Bq, 0.77 Bq and 0.52 Bq respectively. The ¹³⁷Cs was significantly lower in the washed bark and in the absence of moss at p = 0.00031 and p = 0.0443 by t-test respectively. The ¹³⁷Cs in directly-collected stemflow on the main trunks was significantly higher for the unwashed tree at 6.0 Bq L^-1 compared with the washed tree at 1.1 Bq L^-1 (p = 0.017 by Tukey's test). The extraction rate of dissolved ¹³⁷Cs with deionized water was 7.3% even after stirring for 40 h. These results indicate that the moss acts as reservoir of ¹³⁷Cs, and that bark-washing decontamination can reduce the additional ¹³⁷Cs supply from moss in subsequent years following the radioactive fallout.

Radiocesium distribution and fluxes in the typical Cryptomeria japonica forest at the late stage after the accident at Fukushima Dai-Ichi Nuclear Power Plant

The Fukushima-derived radiocesium distribution in the typical Japanese cedar (Cryptomeria japonica D. Don) forest ecosystem was determined. In four years after the Fukushima accident, about 74% of the total radiocesium inventory was localized in soil, 20% was in the litter, and only 6% was associated with the aboveground biomass. Most of the radiocesium that was initially intercepted by the tree canopies has been already transported to the ground surface. The importance of the processes for removal of radiocesium from the tree canopies decreased in the order litterfall > throughfall >> stemflow. Within the tree compartments, the largest radiocesium activity fraction, about 46%, was observed in old foliage, which indicates that the process of removal of the initial deposit from the tree crowns has not yet completed. The aggregate soil-to-wood transfer factor was 1.1⋅10^-3 m² kg^-1 d.w., which is close to the geometric means of transfer factors recommended by IAEA for other coniferous tree species. Further studies in Fukushima forest are necessary to assess the variation of this parameter under various soil-landscape conditions. Presence of the residues of the initial deposits does not allow to obtain the accurate values of the annual radiocesium fluxes in the ecosystem. Based on the conservative assumptions, the ranges of the fluxes were estimated. Analysis of the flux structures shows that up to percents of the total radiocesium activity in the ecosystem may be involved into biogenic cycling.

Measurements of air dose rates in and around houses in the Fukushima Prefecture in Japan after the Fukushima accident

Measurements of air dose rates for 192 houses in a less contaminated area (<0.5 μSv h^-1) of the Fukushima Prefecture in Japan were conducted in both living rooms and/or bedrooms using optically stimulated luminescence (OSL) dosimeters and around the houses via a man-borne survey at intervals of several meters. The relation of the two air dose rates (inside and outside) for each house, including the background from natural radionuclides, was divided into several categories, determined by construction materials (light and heavy) and floor number, with the dose reduction factors being expressed as the ratio of the dose inside to that outside the house. For wooden and lightweight steel houses (classed as light), the dose rates inside and outside the houses showed a positive correlation and linear regression with a slope-intercept form due to the natural background, although the degree of correlation was not very high. The regression coefficient, i.e., the average dose reduction factor, was 0.38 on the first floor and 0.49 on the second floor. It was found that the contribution of natural radiation cannot be neglected when we consider dose reduction factors in less contaminated areas. The reductions in indoor dose rates are observed because a patch of ground under each house is not contaminated (this is the so-called uncontaminated effect) since the shielding capability of light construction materials is typically low. For reinforced steel-framed concrete houses (classed as heavy), the dose rates inside the houses did not show a correlation with those outside the houses due to the substantial shielding capability of these materials. The average indoor dose rates were slightly higher than the arithmetic mean value of the outdoor dose rates from the natural background because concrete acts as a source of natural radionuclides. The characteristics of the uncontaminated effect were clarified through Monte Carlo simulations. It was found that there is a great variation in air dose rates even within one house, depending on the height of the area and its closeness to the outside boundary. Measurements of outdoor dose rates required consideration of local variations depending on the environment surrounding each house. The representative value was obtained from detailed distributions of air dose rates around the house, as measured by a man-borne survey. Therefore, it is imperative to recognize that dose reduction factors fluctuate in response to various factors such as the size and shape of a house, construction materials acting as a shield and as sources, position (including height) within a room, floor number, total number of floors, and surrounding environment.

Long-term variations of radionuclides in the Bratislava air

Variations of aerosol radionuclides (2001-2015) in the ground-level air in Bratislava (Slovakia) showed ⁷Be maxima in spring/early summer and minima in winter, however, an inverse trend was observed for ²¹⁰Pb, ¹³⁷Cs and ⁴⁰K. A decreasing amplitude and splitting of summer maxima for ⁷Be in the last years has been found. A temporal behavior of the ⁷Be/²¹⁰Pb activity ratio showed higher levels during warm seasons due to vertical convection of air masses from higher altitudes. The ¹³⁷Cs activity concentration in the surface air between 2003 and 2010 was decreasing with an effective half-life of 1.9 ± 0.3 years. The yearly average ¹³⁷Cs concentrations during 2009-2014 were almost constant, disturbed only by the Fukushima accident in 2011. The increased atmospheric ¹³⁷Cs and ⁴⁰K levels observed during the autumn-winter season may be due to surface soil resuspension, biomass burning and radionuclide transport by winds. Seasonal variations of ²²²Rn activity concentrations were found with maxima at the end of autumn and in winter, and minima in spring. The variability of the average annual course of ²²²Rn has been larger than that of ²¹⁰Pb. The ²¹⁰Pb/²²²Rn activity ratio was highest at the end of winter and in the spring, while from June to December remained nearly constant. More intensive atmospheric mixing in spring months caused a decrease in the ²²²Rn activity concentration, while the aerosol component of the atmosphere has been affected mainly during the autumn and winter seasons. The mean residence time of aerosols in the atmosphere was calculated using the ²¹⁰Pb/²²²Rn method to be 4.5 ± 0.9 days.

Impact of the Fukushima accident on tritium, radiocarbon and radiocesium levels in seawater of the western North Pacific Ocean: A comparison with pre-Fukushima situation

Tritium, radiocarbon and radiocesium concentrations in water column samples in coastal waters offshore Fukushima and in the western North Pacific Ocean collected in 2011-2012 during the Ka'imikai-o-Kanaloa (KoK) cruise are compared with other published results. The highest levels in surface seawater were observed for ¹³⁴Cs and ¹³⁷Cs in seawater samples collected offshore Fukushima (up to 1.1 Bq L^-1), which represent an increase by about three orders of magnitude when compared with the pre-Fukushima concentration. Tritium levels were much lower (up to 0.15 Bq L^-1), representing an increase by about a factor of 6. The impact on the radiocarbon distribution was measurable, but the observed levels were only by about 9% above the global fallout background. The ¹³⁷Cs (and similarly ¹³⁴Cs) inventory in the water column of the investigated western North Pacific region was (2.7 ± 0.4) PBq, while for ³H it was only (0.3 ± 0.2) PBq. Direct releases of highly contaminated water from the damaged Fukushima NPP, as well as dry and wet depositions of these radionuclides over the western North Pacific considerably changed their distribution patterns in seawater. Presently we can distinguish Fukushima labeled waters from global fallout background thanks to short-lived ¹³⁴Cs. However, in the long-term perspective when ¹³⁴Cs will decay, new distribution patterns of ³H, ¹⁴C and ¹³⁷Cs in the Pacific Ocean should be established for future oceanographic and climate change studies in the Pacific Ocean.

Morphological abnormalities in Japanese red pine (Pinus densiflora) at the territories contaminated as a result of the accident at Fukushima Dai-Ichi Nuclear Power Plant

Our research, carried out in 2014-2016 at eight sites in the radioactive contaminated territories of Fukushima Prefecture, showed that the young trees of Japanese red pine (Pinus densiflora) are sensitive to radiation. Irradiation induced cancellation of the apical dominance in this species. The effect is similar to that observed in young trees of Scots pine growing in the Chernobyl zone. At the same time, we did not observed any morphological abnormalities in mature trees of Japanese red pine. The probability of cancelling the apical dominance in Japanese red pine increased to 0.11 and 0.14 in the two less irradiated populations, and to 0.5 and 0.9 at sites were the absorbed dose rates were approximately 14 and 25 μGy h^-1, respectively. Most of the observed abnormalities appeared in the second whorl after the beginning of exposure. No new abnormalities were observed in the fifth whorl. This temporal pattern is similar to those reported for Scots pine in Chernobyl and for Japanese fir in Fukushima. Additional detailed studies are necessary for interpretation of the observed temporal pattern and, in general, for explanation of the mechanism of formation of the morphological abnormalities.

Risk Communication Strategies: Lessons Learned from Previous Disasters with a Focus on the Fukushima Radiation Accident

PURPOSE OF THE REVIEW

It has been difficult to both mitigate the health consequences and effectively provide health risk information to the public affected by the Fukushima radiological disaster. Often, there are contrasting public health ethics within these activities which complicate risk communication. Although no risk communication strategy is perfect in such disasters, the ethical principles of risk communication provide good practical guidance.

FINDINGS

These discussions will be made in the context of similar lessons learned after radiation exposures in Goiania, Brazil, in 1987; the Chernobyl nuclear power plant accident, Ukraine, in 1986; and the attack at the World Trade Center, New York, USA, in 2001. Neither of the two strategies is perfect nor fatally flawed. Yet, this discussion and lessons from prior events should assist decision makers with navigating difficult risk communication strategies in similar environmental health disasters.

Radiostrontium monitoring of bivalves from the Pacific coast of eastern Japan

In early April 2011, radiostrontium was accidentally released from the Fukushima Daiichi Nuclear Power Plant to the Pacific coast of eastern Japan. We developed a simple procedure to analyze radiostrontium levels in marine mussels (Septifer virgatus) and seawater using crown ether (Sr Resin; Eichrom). Then, we used our method to describe the spatial and temporal distribution of radiostrontium in mussels and seawater on the Pacific coast of eastern Japan from 2011 to 2013 and for 2015. Activity of (90)Sr in mussels and seawater decreased with distance from the Fukushima Daiichi Nuclear Power Plant and between 2011 and 2013 tended to be higher in areas south of the Fukushima Daiichi Nuclear Power Plant than to the north of it. Activity in mussels and seawater also tended to decrease from 2011 to 2013 and by 2015 had reached levels experienced prior to the Fukushima accident. Our results suggest that radiostrontium discharged from the Fukushima Daiichi Nuclear Power Plant was dispersed by coastal currents in a southerly direction along the Pacific coast of eastern Japan from 2011 to 2013, following which its activity decreased to background levels by 2015.

Indication of the radioactive fallout in Riyadh, Saudi Arabia following the Fukushima nuclear accident

On March 2011, a severe damage has occurred to Fukushima Di-iachi nuclear reactor complex in Japan following the huge earthquake and the resulting Tsunami. Consequently, vast amounts of radioactive fallout were released into the atmosphere and contaminated the environment in Japan. Soon after the accident, traces of anthropogenic radionuclides were detected in environmental samples collected in many parts in the northern hemisphere even very far away from Japan creating a global concern. There is no information about radioactive contamination in the Arabian Peninsula caused by the Japanese Fukushima nuclear accident. The first evidence of Fukushima radioactive fallout in Riyadh (24° 43' N, 46° 38' E), Saudi Arabia has been confirmed in April 8, 2011. The airborne fission products (131)I, (134)Cs and (137)Cs were measured in air samples. The radionuclide concentrations were determined by identifying their characteristic gamma rays using a germanium detector. Their activity concentrations were studied as a function of time over a period of 20 days at the end of which they had mostly fallen below our limit of detection. The maximum activity concentration of (131)I, (134)Cs and (137)Cs in air of, respectively, 323.7 ± 18.5, 17.2 ± 1.0 and 26.0 ± 1.8 μBq m(-3) were observed on April 10-11, 2011. The (131)I/(137)Cs and (134)Cs/(137)Cs activity ratio values in air were presented and discussed. Finally, the effective doses to the public of Riyadh city from inhalation of (131)I, (134)Cs and (137)Cs due to contribution from Fukushima incident was found far below levels of concern.

Pre- and post-accident (129)I and (137)Cs levels, and (129)I/(137)Cs ratios in soil near the Fukushima Dai-ichi Nuclear Power Plant, Japan

To evaluate the deposition density and extent of subsurface infiltration of (129)I and (137)Cs in the restricted area that was highly contaminated by the accident of Fukushima Dai-ichi Nuclear Power Plant, cumulative inventories of (129)I and (137)Cs, concentrations of (129)I and (137)Cs, and (129)I/(137)Cs ratio in 30-cm-long soil columns were compared with pre-accident levels from the same area. The cores were collected before and after the accident from locations of S-1 (4 km west of FDNPP) and S-2 (8 km west of FDNPP). Deposition densities of (129)I and (137)Cs in the soil following the accident were 0.90-2.33 Bq m(-2) and 0.80-4.04 MBq m(-2), respectively, which were 14-39 and 320-510 times larger than the pre-accident levels of (129)I (59.3-63.3 mBq m(-2)) and (137)Cs (2.51-7.88 kBq m(-2)), respectively. Approximately 90% of accident-derived (129)I and (137)Cs deposited in the 30-cm soil cores was concentrated in the surface layer from 0 to 44-95 kg m(-2) of mass depth (0-4.3-6.2 cm depth) and from 0 to 16-25 kg m(-2) of mass depth (0-1.0-3.1 cm depth), respectively. The relaxation mass depths (h0) of 10.8-11.2 kg m(-2) for (129)I estimated in the previous study were larger than those of 8.1-10.6 kg m(-2) for (137)Cs at both sites, owing to the larger infiltration depth of radioiodine mainly by the gravitational water penetration in the surface soil in our study sites. Approximately 7-9% of the accident-derived (129)I was present in the lower layer from 44 to 100 kg m(-2) (4.3-8.6 cm depth) at S-1, and from 95 to 160 kg m(-2) (6.2-10.2 cm depth) at S-2. Approximately 1% of (137)Cs seems to infiltrate deeper than (129)I in the lower layer at each site in contrast to the surface layer.

Comparison of the accident process, radioactivity release and ground contamination between Chernobyl and Fukushima-1

In this report, we have reviewed the basic features of the accident processes and radioactivity releases that occurred in the Chernobyl accident (1986) and in the Fukushima-1 accident (2011). The Chernobyl accident was a power-surge accident that was caused by a failure of control of a fission chain reaction, which instantaneously destroyed the reactor and building, whereas the Fukushima-1 accident was a loss-of-coolant accident in which the reactor cores of three units were melted by decay heat after losing the electricity supply. Although the quantity of radioactive noble gases released from Fukushima-1 exceeded the amount released from Chernobyl, the size of land area severely contaminated by (137)Cesium ((137)Cs) was 10 times smaller around Fukushima-1 compared with around Chernobyl. The differences in the accident process are reflected in the composition of the discharged radioactivity as well as in the composition of the ground contamination. Volatile radionuclides (such as (132)Te-(132)I, (131)I, (134)Cs and (137)Cs) contributed to the gamma-ray exposure from the ground contamination around Fukishima-1, whereas a greater variety of radionuclides contributed significantly around Chernobyl. When radioactivity deposition occurred, the radiation exposure rate near Chernobyl is estimated to have been 770 μGy h(-1) per initial (137)Cs deposition of 1000 kBq m(-2), whereas it was 100 μGy h(-1) around Fukushima-1. Estimates of the cumulative exposure for 30 years are 970 and 570 mGy per initial deposition of 1000 kBq m(-2) for Chernobyl and Fukusima-1, respectively. Of these exposures, 49 and 98% were contributed by radiocesiums ((134)Cs + (137)Cs) around Chernobyl and Fukushima-1, respectively.

Modeling of long range transport pathways for radionuclides to Korea during the Fukushima Dai-ichi nuclear accident and their association with meteorological circulations

The Lagrangian FLEXible PARTicle (FLEXPART) dispersion model and National Centers for Environmental Prediction/Global Forecast System (NCEP/GFS) meteorological data were used to simulate the long range transport pathways of three artificial radionuclides: (131)I, (137)Cs, and (133)Xe, coming into Korean Peninsula during the Fukushima Dai-ichi nuclear accident. Using emission rates of these radionuclides estimated from previous studies, three distinctive transport routes of these radionuclides toward the Korean Peninsula for a period from 10 March to 20 April 2011 were exploited by three spatial scales: 1) intercontinental scale - plume released since mid-March 2011 and transported to the North to arrive Korea on 23 March 2011, 2) global (hemispherical) scale - plume traveling over the whole northern hemisphere passing through the Pacific Ocean/Europe to reach the Korean Peninsula with relatively low concentrations in late March 2011 and, 3) regional scale - plume released on early April 2011 arrived at the Korean Peninsula via southwest sea of Japan influenced directly by veering mesoscale wind circulations. Our identification of these transport routes at three different scales of meteorological circulations suggests the feasibility of a multi-scale approach for more accurate prediction of radionuclide transport in the study area. In light of the fact that the observed arrival/duration time of peaks were explained well by the FLEXPART model coupled with NCEP/GFS input data, our approach can be used meaningfully as a decision support model for radiation emergency situations.

Radiocesium monitoring in Indonesian waters of the Indian Ocean after the Fukushima nuclear accident

As data on anthropogenic radionuclide concentrations (i.e., (134)Cs and (137)Cs) in Indonesian marine environments including the Indian Ocean are scarce, offshore monitoring has been performed in the West Sumatra and South Java Seas. The activity concentration of (137)Cs ranges from below minimum detectable activity (MDA) to 0.13Bqm(-3) in the surface seawater of the South Java Sea and from lower than MDA to 0.28Bqm(-3) in the surface seawater of the West Sumatra Sea. The concentrations of (137)Cs in the surface seawater of the West Sumatra and South Java Seas are lower than the estimation of (137)Cs concentration in the subsurface waters owing to the input of the North Pacific Ocean via the Indonesian Throughflow (ITF). The concentrations of (134)Cs in the sampling locations were lower than MDA. These results have indicated that these Indonesian marine waters have not yet been influenced by the Fukushima radioactive release.

Radiation protection issues on preparedness and response for a severe nuclear accident: experiences of the Fukushima accident

Radiation protection issues on preparedness and response for a severe nuclear accident are discussed in this paper based on the experiences following the accident at Fukushima Daiichi nuclear power plant. The criteria for use in nuclear emergencies in the Japanese emergency preparedness guide were based on the recommendations of International Commission of Radiological Protection (ICRP) Publications 60 and 63. Although the decision-making process for implementing protective actions relied heavily on computer-based predictive models prior to the accident, urgent protective actions, such as evacuation and sheltering, were implemented effectively based on the plant conditions. As there were no recommendations and criteria for long-term protective actions in the emergency preparedness guide, the recommendations of ICRP Publications 103, 109, and 111 were taken into consideration in determining the temporary relocation of inhabitants of heavily contaminated areas. These recommendations were very useful in deciding the emergency protective actions to take in the early stages of the Fukushima accident. However, some suggestions have been made for improving emergency preparedness and response in the early stages of a severe nuclear accident.

Trans-oceanic transport of 137Cs from the Fukushima nuclear accident and impact of hypothetical Fukushima-like events of future nuclear plants in Southern China

A Lagrangian model was adopted to assess the potential impact of (137)Cs released from hypothetical Fukushima-like accidents occurring on three potential nuclear power plant sites in Southern China in the near future (planned within 10 years) in four different seasons. The maximum surface (0-500 m) (137)Cs air concentrations would be reached 10 Bq m(-3) near the source, comparable to the Fukushima case. In January, Southeast Asian countries would be mostly affected by the radioactive plume due to the effects of winter monsoon. In April, the impact would be mainly on Southern and Northern China. Debris of radioactive plume (~1 mBq m(-3)) would carry out long-range transport to North America. The area of influence would be the smallest in July due to the frequent and intense wet removal events by trough of low pressure and tropical cyclone. The maximum worst-case areas of influence were 2382000, 2327000, 517000 and 1395000 km(2) in January, April, July and October, respectively. Prior to the above calculations, the model was employed to simulate the trans-oceanic transport of (137)Cs from the Fukushima nuclear accident. Observed and modeled (137)Cs concentrations were comparable. Sensitivity runs were performed to optimize the wet scavenging parameterization. The adoption of higher-resolution (1° × 1°) meteorological fields improved the prediction. The computed large-scale plume transport pattern over the Pacific Ocean was compared with that reported in the literature.

A dynamic model to estimate the activity concentration and whole body dose rate of marine biota as consequences of a nuclear accident

This paper describes a dynamic compartment model (K-BIOTA-DYN-M) to assess the activity concentration and whole body dose rate of marine biota as a result of a nuclear accident. The model considers the transport of radioactivity between the marine biota through the food chain, and applies the first order kinetic model for the sedimentation of radionuclides from seawater onto sediment. A set of ordinary differential equations representing the model are simultaneously solved to calculate the activity concentration of the biota and the sediment, and subsequently the dose rates, given the seawater activity concentration. The model was applied to investigate the long-term effect of the Fukushima nuclear accident on the marine biota using (131)I, (134)Cs, and, (137)Cs activity concentrations of seawater measured for up to about 2.5 years after the accident at two locations in the port of the Fukushima Daiichi Nuclear Power Station (FDNPS) which was the most highly contaminated area. The predicted results showed that the accumulated dose for 3 months after the accident was about 4-4.5Gy, indicating the possibility of occurrence of an acute radiation effect in the early phase after the Fukushima accident; however, the total dose rate for most organisms studied was usually below the UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation)'s bench mark level for chronic exposure except for the initial phase of the accident, suggesting a very limited radiological effect on the marine biota at the population level. The predicted Cs sediment activity by the first-order kinetic model for the sedimentation was in a good agreement with the measured activity concentration. By varying the ecological parameter values, the present model was able to predict the very scattered (137)Cs activity concentrations of fishes measured in the port of FDNPS. Conclusively, the present dynamic model can be usefully applied to estimate the activity concentration and whole body dose rate of the marine biota as the consequence of a nuclear accident.