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The movement of radioactive Cs emitted from the Fukushima Nuclear accident has been studied by the academic staff of the Graduate School of Agricultural and Life Sciences, The University of Tokyo. The targeted items for research ranged widely, including soils, plants, animals, fish, mountains, water, etc. The relevant feature, with regard to the fallout, is that the radioactive Cs has remained at the initial contact sites and has hardly moved since. However, in the case of living individuals, such as animals, the amount of radioactivity has decreased with time at a much faster rate than the physiological half-life because of their metabolic activities. The biological half-life in animals was estimated to be within a period of 100 days. Soil plays a major role in fixing fallout. When fallout nuclides are adsorbed into the soil, plants growing there can absorb little of the radioactive Cs. In the mountains, radioactive Cs was gradually transferred from litter to soil and moved little even when washed with heavy rains. The method of contamination by radioactive nuclides is completely different from that of heavy metals.

We summarize the inspections of radiocesium concentration levels in agricultural, livestock, forest and fishery produced in Fukushima Prefecture, Japan, for 3 years from the nuclear accident in 2011. The ratio in which radiocesium concentration exceeded the 100 Bq/kg from March 2011 to June 2011 was 18 % in agricultural products (excluding rice), 3 % in livestock productions, 49 % in forest productions, and 52 % in fishery produced. After June 2011, radiocesium concentration reduced drastically. Radiocesium concentration in agricultural and livestock products hardly exceeded the 100 Bq/kg. On the other hand radiocesium concentrations of forest and fishery products have been falling every year, but there were a little high concentration samples. Soybean is one of the agricultural products, and the radiocesium concentration is higher than the other agricultural products. We analyzed the absorption process in soybean in contaminated areas. The radiocesium concentration of the above-ground part was lateral root > leaf≒petiole≒pod > stem≒main root. There was a difference in concentration ratio of radiocesium: potassium among parts of the plant. Comparing 10 soybean varieties, radiocesium concentration of wild soya bean showed more than twice as high as other varieties. And the radiocesium inside the soybean grain was distributed generally uniformly throughout the entire grain.

We summarize the inspections of radiocesium concentration levels in rice produced in Fukushima Prefecture, Japan, for 3 years from the nuclear accident in 2011. In 2011, three types of verifications, preliminary survey, main inspection, and emergency survey, revealed that rice with radiocesium concentration levels over 500 Bq/kg (the provisional regulation level until March 2012 in Japan) was identified in the areas north and west of the Fukushima nuclear power plant. The internal exposure of an average adult eating rice grown in the area north of the nuclear plant was estimated as 0.05 mSv/year. In 2012, Fukushima Prefecture authorities decided to investigate the radiocesium concentration levels in all rice using custom-made belt conveyor testers. Notably, rice with radiocesium concentration levels over 100 Bq/kg (the new standard since April 2012 in Japan) were detected in only 71, 28 and 2 bags out of the total 10,338,000 in 2012, 11,001,000 in 2013 and 10,988,824 in 2014, respectively. We considered that there were almost no rice exceeding 100 Bq/kg produced in Fukushima Prefecture after 3 years from the nuclear accident, and the safety of Fukushima’s rice were ensured because of the investigation of all rice.

After the accident at the Fukushima Daiichi Nuclear Power Plant, radioactive cesium (Cs) was released and the agricultural fields in Fukushima were contaminated. It became important to obtain data for radioactive Cs accumulation in rice grown in contaminated fields. We conducted a 3-year investigation in a Fukushima paddy field of radioactive Cs concentrations in various rice cultivars, and in two commercial rice cultivars grown under four different nutrient conditions. Our studies demonstrated substantial variation in radioactive Cs concentrations among the rice cultivars, and an increase in radioactive Cs concentrations in straw and brown rice under high nitrogen and low potassium conditions. Our 3-year investigations of radioactive Cs-contaminated rice in Fukushima paddy field shows that the rice grown in Fukushima is now well-monitored and contains much less than the allowed levels of radiation (100 Bq kg).

To achieve the reduction of the radiocesium content in rice grain, the application of potassium (K) fertilizer to the paddy field is currently recommended. However, physiological basis of the effect of the K addition on the radiocesium accumulation in rice has not been enough provided. Here, the uptake and the distribution of cesium (Cs) in rice plant grown in either K-deficient or K-sufficient hydroponic medium containing Cs are presented aiming to describe the exact impact of K fertilization on the Cs behavior within the plant. In the K-deficient plant, the amount of Cs accumulated in the rice grain was 10 times as much as the K-sufficient rice. The determination of Cs content as well as other cationic ions in each part of the rice showed the intensive transport of Cs to the ear part composed of brown rice, husk and culm, in which K was also accumulated. It could supposed that Cs transport is regulated basically similarly to the K transport within the plant body. Then, K fertilization is suggested to reduce the Cs content in rice grain efficiently through the reduction of Cs uptake in the roots and Cs accumulation to the ear part.

We performed consecutive field trials of rice cultivation to reduce radiocesium (Cs and Cs) absorption by rice in a partially decontaminated paddy soil in the Iitate Village in Fukushima prefecture, Japan. People had evacuated this area because of the high levels of radioactive contamination caused by the nuclear disaster in 2011 at the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power. The radiocesium concentrations were measured for paddy soil and for lowland rice grown on variously decontaminated paddy soil in 2012 and 2013. The results show that the radiocesium concentration in the brown rice cultured in the fields of Sasu and Maeda with 2000–6000 Bq/kg dry weight (0–15 cm average soil depth) was below 40 Bq/kg, which is below the Japanese new standard for food (100 Bq/kg). In addition, the radiocesium concentration in the brown rice depended on the decontamination level of the paddy soil. In addition, the radiocesium concentration in the rice was reduced depending on the exchangeable K content of the soil, which plateaued around 20 mg KO per 100 g dry soil. However, in 2013, in a test field of Komiya where the radiocesium concentrations were higher than 8000 Bq/kg dry weight, brown rice with more than 100 Bq/kg was harvested, indicating the need for further decontamination. Overall, our results show that decontamination and additional K fertilization can reduce the radiocesium concentration in rice to less than the new standard, and that we could resume rice cultivation in the Iitate village by rather practical way.

Contamination of food and animal products by radioactive cesium represents an important potential route of exposure in the human food chain. Therefore, following the Fukushima Daiichi nuclear power plant accident, the development of solutions for radiocesium contamination is a serious social issue in Japan. Most farm animals are kept in closed barns in Japan; this reduced the initial contamination of animal products by radioactive nuclides in the early phase of the accident. Furthermore, pigs and chickens were given imported feed that was not contaminated. However, more than 10 million tons of grass feed were needed for herbivorous livestock in Japan. We report the effects of “clean feeding” management on livestock products contaminated with radioactive cesium due to the nuclear accident. The present results concerning products from herbivores (horses, sheep, and cattle) revealed that radiocesium levels were undetectable in the meat or milk of herbivores that fed on non-contaminated feed after an initial period of consuming radiocesium-contaminated feed. Thus, we conclude that “clean feeding” management can play a crucial role in solving the social problem of food contamination.

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.

In the present chapter, I present the distribution of radiocesium in wild boars as well as the official monitoring data of wild boars from Fukushima. After the nuclear accident in 2011, the radiocesium contamination levels in wild boars from most places in Fukushima Prefecture exceeded 100 Bq/kg. The most contaminated wild boars were observed in Soso district where the radiocesium concentration in the soil was the highest in the entire Fukushima Prefecture. To understand radiocesium contamination in wild boars in more detail, we measured radiocesium concentrations in different organs and tissues of wild boars inhabiting Iitate Village in Soso district in 2012 and 2013. After capturing the wild boars, we collected 24 organs and tissues and put them into vials. Using an NaI(Tl) scintillation counter, we determined the concentrations of radiocesium (Cs and Cs) and found that the levels were highest in the muscles (approximately 15,000 Bq/kg) and lowest in the ovaries (approximately 600 Bq/kg) in 2012, indicating a large variation between the organs and tissues. The trends were similar in 2012 and 2013. Observations of the contamination levels in wild boars could reveal the radiocesium availability in the forest and village ecosystem.

Wildlife, mainly 69 bird (Aves) species, has been observed in Abukuma Mountains, northeastern Fukushima Prefecture, which is the most radioactively contaminated area, over the seasons since July 2011. However, it is still unclear whether the changes in the bird community have been caused by the radioactive contamination and/or by changes in human activity, adding to the natural dynamics. The aerial dose rate at the survey area was initially estimated to be more than 100 μSv/h (mainly Cs, Cs, and I), which decreased in the summer of 2014 to 0.1–20 μSv/h (mainly Cs and Cs). Radioactivity in wild habitats is heterogeneous among the microhabitats and is dynamic through time and seasonal conditions. Microhabitat radio-heterogeneity was clearly indicated by the 2-month-long measurement with 200 dosimeter badges in this study. The ecological factors related to free living (in-situ) wildlife in the highly contaminated area of Fukushima are discussed.