放射性セシウムで汚染した木質チップの再利用に係わる線量評価

Large quantities of radioactive material were released into the ocean as a result of the Fukushima Daiichi Nuclear Power Plant disaster. Because of the movement of the highly radioactive water mass, coastal seawater, seabed sediments, and many marine organisms were contaminated by radioactive material. Although radioactive concentrations in many species decreased over time, concentrations in some fish species decreased very slowly (e.g., Japanese rockfish and skate). In this study, the changes in radioactive cesium (Cs) concentrations in marine organisms are reported over the 4 years since the accident and possible reasons for the slower decrease in radioactive concentrations observed in some fish species are discussed. Marine organisms and seawater and seabed sediment samples were collected from May 2012 to May 2014. Radioactive Cs concentrations in the collected organisms and samples were measured using a germanium semiconductor detector. An ultrasonic pinger was inserted into the bodies of some fish, and fish movements were recorded by biotelemetry for 1 year. Japanese rockfish were cultured in a large water tank for 1 year, and the biological half-life of radioactive Cs was estimated in the fish. Radioactive Cs concentrations in benthic and omnivorous fish, such as Japanese rockfish (367 days) and a skate species (560 days), had relatively long ecological half-lives. Japanese rockfish remained within the same rocky area (within a radius of 200 m) in open sea areas throughout the year. The ecological half-life of radioactive Cs was approximately 270 days longer in rockfish than that in other marine fish. These results suggest that relatively high radioactive Cs concentrations remained in coastal benthic fish owing to slow Cs excretion rates.

Radioactive cesium dynamics derived from hydrographic observations in the Abukuma River Estuary, Japan

The accident caused at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant by the Great East Japan Earthquake of 11 March 2011 resulted in radioactive fallout over a wide area of eastern Japan. Production of bioenergy crops and their conversion to energy may be one way to resume agricultural production at an early date and to put renewable energy to practical use. We examined yearly changes in radioactive cesium concentrations in the harvested parts of six perennial Gramineae candidate bioenergy crops and the distribution of the cesium in plant organs and rhizosphere soil layers under no‐till conditions in an experimental field 112 km from the nuclear power plant. Average radioactivity of the sum of cesium‐134 and cesium‐137 in the harvested parts (foliage) of the six bioenergy crops on the day of harvest declined considerably from 193.3 Bq kg−1 in 2011 to 31.6% of the 2011 level in 2012, 28.8% in 2013 and 28.7% in 2014. Radioactivity was higher in the underground plant parts (subterranean stem and root) than in the aboveground parts (foliage and stubble). In 2014, radioactivity in the untilled rhizosphere soil was higher in the shallow layer (0–5 cm from the soil surface) than in the deeper layers, indicating that rainfall and perennial bioenergy crop cultivation for more than 3 years had a limited effect on the soil distribution of the fallout. These results provide unique and specific information on radioactive cesium transfer to bioenergy crops and could help in the planning of feedstock supplies in radiation‐polluted areas.

Radioactive cesium concentrations in coastal suspended matter after the Fukushima nuclear accident

Of all things relevant to the Great East Japan Earthquake, what drew the highest degree of attention from not only Japan but elsewhere around the world was the Fukushima Daiichi (No.1) Nuclear Power Plant’s nuclear power accidents that bears comparison with Chernobyl’s. During the subsequent four months, though this nuclear plant has not gone critical again, the leakage of radioactive materials from within the plant’s compounds continues. The possibility of another major accident happening, e.g. hydrogen explosion, breaking of containment vessel, in which radioactive materials would once again be strewed over the peripheral districts is not totally eradicated, albeit not so high. Given such a situation, the JDR Editorial staff has decided to examine the developments since the outbreak of the Great East Japan Earthquake and furnish the readers with updated information about developments leading to the outbreak of the accidents at the Fukushima Daiichi Nuclear Power Plant and on debates that have since evolved in Japan. Thus, this presentation here could be termed a summarization of articles that have been carried in Japanese newspapers and magazines. It admittedly includes such information whose authenticity was not fully confirmed. The judgments and views expressed in this article represent the common ground shared by vernacular newspapers and magazines. As was the case with the previous issue of this journal, the judgments and views that represent the majority opinion in Japan are carried in this issue without modification. (K.J., July 11, 2011)

BackgroundThe Great East Japan Earthquake on 11th March 2011 and the subsequent Fukushima Dai-ichi nuclear power plant disaster caused radioactive contamination in the surrounding environment. In the immediate aftermath of the accident the Government of Japan placed strict measures on radio-contamination of food, and enhanced radio-contamination monitoring activities. Japan is a pilot country in the WHO Foodborne Disease Burden Epidemiology Reference Group (FERG), and through this initiative has an opportunity to report on policy affecting chemicals and toxins in the food distribution network. Nuclear accidents are extremely rare, and a policy situation analysis of the Japanese government’s response to the Fukushima Dai-ichi nuclear accident is a responsibility of Japanese scientists. This study aims to assess Japan government policies to reduce radio-contamination risk and to identify strategies to strengthen food policies to ensure the best possible response to possible future radiation accidents.Methods and FindingsWe conducted a hand search of all publicly available policy documents issued by the Cabinet Office, the Food Safety Commission, the Ministry of Health, Labor and Welfare (MHLW), the Ministry of Agriculture, Forestry and Fishery (MAFF) and prefectural governments concerning food safety standards and changes to radiation and contamination standards since March 11th, 2011. We extracted information on food shipment and sales restrictions, allowable radio-contamination limits, monitoring activities and monitoring results. The standard for allowable radioactive cesium (Cs-134 and Cs-137) of 100 Bq/Kg in general food, 50 Bq/Kg in infant formula and all milk products, and 10 Bq/Kg in drinking water was enforced from April 2012 under the Food Sanitation Law, although a provisional standard on radio-contamination had been applied since the nuclear accident. Restrictions on the commercial sale and distribution of specific meat, vegetable and fish products were released for areas at risk of radioactive contamination. Monitoring of radioactive materials in food products in the prefectures has been mainly conducted before shipment to restrict the distribution of radio-contaminated foods. Between March 2011 and March 2012, 133,832 tests of non-commercial and commercial products were conducted, and 1,204 tests (0.9%) were found to violate the provisional standards. Since April 2012, 278,275 tests were conducted, and 2,372 tests (0.9%) were found to violate the revised standards. MHLW assessment of representative market baskets of foodstuffs at 15 locations throughout Japan between February and March 2014 found very low estimated dietary intake of radioactive cesium (0.0007–0.019 mSv/year), as did assessments of the contents of an average day’s food. Monitoring of fisheries products in coastal areas affected by the nuclear accident found very limited and declining radio-contamination of live fish outside of Fukushima prefecture. Fisheries monitoring is of limited geographical scope and covers only certain fishes.ConclusionsArea-specific bans on production and distribution have been effective in preventing radioactive contamination in the Japanese food market. Currently there is no major concern about radioactive cesium concentrations in retail foodstuffs in Japan, and very low levels of contamination at the production and wholesale stage. However, because the residue limits and food safety policies were revised on an ad hoc, emergency basis after the nuclear accident, the monitoring procedure needs to be reviewed based on objective and scientifically rational criteria. A transparent and objective scientific framework is needed for prioritizing foodstuffs for inspection and revising Prefecture-specific restrictions. Monitoring of fishes and other seafood products in the wild should be regularized and the information made more publicly accessible, and monitoring activities expanded to identify foodstuffs that are no longer a food safety risk. Consultation with producers and consumers should be more formalized to ensure their concerns are incorporated into regular policy reviews in an appropriate and transparent manner. However, despite the limited available knowledge on best practice in food control and enforcement of provisional radio-contamination limits after the accident, current Japanese policy is sufficient to protect the Japanese public from major risk of radio-contamination from the commercial food market.

Radioactive cesium and potassium levels in human placenta: After the Fukushima nuclear power plant accident

It is extremely important to understand the mechanisms underlying the effect of radiation on animals including humans. Radiation potentially induces alterations of the immune system, which may cause serious diseases. The Fukushima Daiichi Nuclear Power Plant (FNPP) accident occurred in 2011, in which radioactive contaminants were released over a wide area. After farmers evacuated from the ex-evacuation zone set within 20-km radius from FNPP, pigs were left behind and unleashed in the zone (abandoned pigs). Their small intestine was considered to have been affected by the dietary intake of radioactive contaminants. The present study thus aimed to clarify the effect of radiation by investigating whether there is any alteration in the expression of genes encoding immune-related molecules and in morphology of the intestine of abandoned pigs. Microarray analysis revealed changes of the expression of various genes involved in inflammation and oxidative stress including IFN-γ, which is an important inflammatory cytokine, was highly elevated in abandoned pigs, and its expression level was correlated with radioactive cesium concentration in skeletal muscle. On the other hand, there were no morphological changes in the intestine. At the sampling stage of this study, only 1 year passed since the FNPP accident occurred, it would be premature to conclude that the identified alteration of gene expression was caused only by artificial radionuclides attributed to the FNPP accident. We need to continue monitoring the effect of long-term radiation exposure in living organisms in the ex-evacuation zone.

The 2011 earthquake severely damaged the Fukushima Daiichi Nuclear Power Plant (FNPP), resulting in the release of large quantities of radioactive material into the environment. The deposition of these radionuclides in rice straw as livestock feed led to the circulation of contaminated beef in the market. Based on the safety concern of the consumers, a reliable method for estimating concentrations of radioactive cesium in muscle tissue is needed. In this study, we analyzed the concentrations of radioactive cesium in the blood and skeletal muscle of 88 cattle, and detected a linear correlation between them. We then developed software that can be used to estimate radioactive cesium concentrations in muscle tissue from blood samples. Distribution of this software to the livestock production field would allow us to easily identify high-risk cattle, which would be beyond the safety regulation, before shipping out to the market. This software is planned to be released as freeware. This software would contribute to food safety, and aid the recovery of the livestock industry from the damage creacted by the 2011 Tohoku earthquake and tsunami.

Strontium‐90 (90Sr) was released together with radioactive cesium (Cs) from the Fukushima Dai‐ichi Nuclear Power Plant (FNPP) accident. Although the total amount of 90Sr released into the marine environment from the FNPP was estimated to be a factor of 100 lower than that of 137Cs, the public have been concerned about the safety of commercial species because of the tendency of accumulation in bones of organisms, its long physical half‐life and less information about 90Sr concentrations in commercial species. In this study, we investigated the concentrations of 90Sr in marine fishes off Japan before and after the FNPP accident. Except for within a 20‐km radius from the FNPP, 90Sr concentrations higher than the background level (<0.046 Bq kg−1 wet) were only detected in 4 of 26 specimens collected off Fukushima. Furthermore, 90Sr concentrations in all samples collected outside of Fukushima were under the detection limit (<0.040 Bq kg−1 wet). Also, the concentrations of 90Sr in marine fishes were notably lower than those of 137Cs, and thus the activity ratios of 137Cs to 90Sr in the whole body of teleost fishes were 5–190 times higher than that of before the accident. The activity ratio tended to decrease owing to a decrease in the 137Cs concentration in marine fish. Our result together with ananalysis of other data sets indicated that the influence of the FNPP accident on 90Sr in marine fishes was limited to the area near the FNPP and outside of the FNPP harbor area can be considered as negligible.

Effect of particle granularity on smoldering fire in wood chips made from wood waste: An experimental study

The Fukushima Daiichi Nuclear Power Plant accident led to contamination with radioactive cesium in an extensive environment in Japan in 2011. We evaluated the concentration of radioactive cesium in the skeletal muscles of 22 wild boars and the expression of IFN-γ, TLR3, and CyclinG1 in the small intestine and compared them with those of wild boar samples collected from Hyogo prefecture. The average 137Cs radioactivity concentration in wild boars in the ex-evacuation zone was 470 Bq/kg. Most of samples still showed radioactivity concentration that exceeded the regulatory limit for foods, but the dose remarkably decreased compared with samples just after the accident. IFN-γ expression was significantly higher in wild boars in the ex-evacuation zone than in samples from Hyogo prefecture. TLR3 expression was also upregulated. CyclinG1 expression also tended to be high. Hence, wild boars might have received some effects of low-dose radiation, and immune cells were activated to some extent. However, pathological examination revealed no inflammatory cell infiltration or pathological damage in the small intestine of wild boars in the ex-evacuation area. Long-term monitoring would be necessary, but we consider that the living body responds appropriately to a stimulus from a contaminated environment.

Following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the forests in the Fukushima area were highly contaminated with radiocesium (137Cs and 134Cs). Therefore, there is a need to develop strategies for remediation of the contaminated forests. We assessed changes in radioactive cesium (134Cs and 137Cs) contamination and nutrient status in composts derived from wood chip, bamboo leaf and bamboo powder using rice bran and wheat meal as sub-materials. Changes in soil properties and Komatsuna (Brassica rapa var. perviridis) growth were also investigated due the application of composts and initial materials at 0, 2.5, 5 and 10 kg·m−2 input levels. Mixing of sub-materials significantly reduced the concentration of radioactive Cs and improved compost quality. The effectiveness of three composts on soil quality improvement varied depending on their types and rates of applications. Amendments of bamboo leaf composts at 10 kg·m−2 resulted in the significantly highest soil inorganic N, available P and exchangeable K contents. Amendments of final composts also enhanced Komatsuna growth. Furthermore, radioactive Cs contaminations of the Komatsuna plants grown in these composts were below 0.1 Bq·kg−1. This study may help to remediate the forests contaminated with radiocesium in the Fukushima area while improving the soil organic matter content to enhance soil sustainability.

Radioactive caesium concentrations in pigs fed brown rice contaminated by the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant

Appropriate treatment is urgently needed for farm and ranch waste that has been contaminated with radioactive cesium from the Fukushima Daiichi nuclear power plant accident. We previously developed an aerobic ultra-high temperature fermentation (more than 115 °C) method to inhibit intestinal infectious diseases. Fermented waste (compost), in which pathogens were sterilized, was useful as a fertilizer to grow crops. In the present study, we examined the kinetics of radioactive cesium in farming fields to promote sustainable circular agriculture including livestock in farms and pasture fields in wide areas of Tohoku and Kanto, in an approximately 200 km radius from the nuclear power plant. The compost produced at the experimental ranch of the Animal Resource Science Center, the University of Tokyo, was contaminated with radioactive cesium (approximately 900 Bq/kg). Some crops (soybean, sweet corn, eggplant, bitter gourd, potato, cabbage, and ginger) were cultivated in cubic holes (approximately 1 × 1 × 1 m) that were filled with contaminated compost in the field of the experimental ranch. Each crop was planted in a hole and cultivated in an appropriate manner for a suitable time period. Radiocesium levels in the roots, stems, leaves, and fruits of each crop at harvest were lower than 20 Bq/kg, which was below the new reference/regulation value (100 Bq/kg) for food. In conclusion, when crops were planted using compost contaminated with radioactive cesium (900 Bq/kg; more than twice the new tolerance value of 400 Bq/kg for fertilizer and compost), the radiocesium levels in the crops were as low as one-fifth of the new reference/regulation value.