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Agricultural Implications of the Fukushima Nuclear Accident (III): After 7 Years

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An Overview of Our Research

Tomoko M. Nakanishi

Immediately after the Fukushima nuclear plant accident (FNPA), 40–50 researchers at the Graduate School of Agricultural and Life Sciences, the University of Tokyo, analyzed the behavior of the radioactive materials in the environment, including agricultural farmland, forests, rivers, etc., because more than 80% of the contaminated land was related to agriculture. Since then, a large number of samples collected from the field were measured for radiation levels at our faculty. A feature of the fallout was that it has hardly moved from the original point contaminated. The fallout was found as scattered spots on all surfaces exposed to the air at the time of the accident. The adsorption onto clay particles, for example, has become firm with time so that it is now difficult to be removed or absorbed by plants. Cs was found to bind strongly to fine clay particles, weathered biotite, and to organic matter in the soil, therefore, Cs has not mobilized from mountainous regions, even after heavy rainfall. In the case of farmland, the quantity of Cs in the soil absorbed by crop plants was small, and this has been confirmed by the real-time imaging experiments in the laboratory. The downward migration of Cs in soil is now estimated at 1–2 mm/year. The intake of Cs by trees occurred via the bark, not from the roots since the active part of the roots is generally deep within the soil where no radioactive materials exist. The distribution profile of Cs within trees was different among species. The overall findings of our research is briefly summarized here.

Pp. 1-8

Transfer of Radiocesium to Rice in Contaminated Paddy Fields

Keisuke Nemoto; Naoto Nihei

Rice contaminated with high concentrations of radiocesium was found in some local areas after the nuclear accident in Fukushima Prefecture in 2011. Here we discuss the issues of cultivating rice in contaminated areas through our field experiments. The transfer of radiocesium to commercial rice has been artificially down-regulated by potassium fertilizer in radiocesium-contaminated areas in Fukushima. Since 2012, we have continued to cultivate rice experimentally in paddy fields under conventional fertilizer to trace the annual change of radiocesium uptake. The radiocesium concentration in rice cultivated under conventional fertilizer has seen almost no change since 2013. One of the reasons for this is that radiocesium fixation in soil has hardly progressed in these paddy fields.

Pp. 9-14

Cesium Translocation in Rice

Keitaro Tanoi; Tatsuya Nobori; Shuto Shiomi; Takumi Saito; Natsuko I. Kobayashi; Nathalie Leonhardt; Tomoko M. Nakanishi

To breed a low Cs rice variety, it is important to clarify the mechanism of Cs transport in a plant. In the present report, we found a difference in Cs distribution in rice cultivars using a Cs tracer experiment. In addition, the difference was also found in Cs distribution of each leaf position among the same rice cultivars. There has been no report clarifying the molecular mechanism of Cs translocation, nor those of other cations, in plants. Using the rice cultivars, Akihikari and Milyang23, to find the Cs translocation mechanism can contribute to developing crops that contain lower levels of Cs when cultivated in radiocesium contaminated land.

Pp. 15-25

Absorption of Radioceasium in Soybean

Naoto Nihei; Shoichiro Hamamoto

Radioactive materials, primarily radiocesium (Cs + Cs), were released into the environment by the Fukushima Daiichi Nuclear Power Plant accident in March 2011. The percentage of soybean plants that had a concentration of radiocesium over 100 Bq/kg was higher than that of other crops. To examine the reason why the concentration of radiocesium in soybeans was high, its concentration and distribution in seeds were analyzed and compared to rice.

Potassium fertilization is one of the most effective countermeasures to reduce the radiocesium uptake by soybean and nitrogen fertilizer promotes soybean growth. To use potassium and nitrogen fertilizers safely and efficiently, applied potassium behavior in soil and the effect of nitrogen fertilizer on radiocesium absorption in soybean were studied.

Pp. 27-33

An Observational Study of Pigs Exposed to Radiation

Junyou Li; Chunxiang Piao; Hirohiko Iitsuka; Masanori Ikeda; Tomotsugu Takahashi; Natsuko Kobayashi; Atsushi Hirose; Keitaro Tanoi; Tomoko Nakanishi; Masayoshi Kuwahara

On June 28, 2011, 26 pigs were rescued from the alert area, 17 km northwest of the , where radiation levels were approximately 1.9–3.8 μSv/h. The pigs were transferred outside of the radiation alert area to the Animal Resource Science Center (ARSC), The University of Tokyo. It was confirmed by the farm owner that the pigs were never fed radiation-contaminated concentrate and they had access to uncontaminated groundwater () while living inside the radiation alert area; however, radiocesium was detected in the rescued pigs’ organs, testis/ovary, spleen, liver, kidney, psoas major, urine, and blood, within nine months after the nuclear disaster. Radiocesium levels in samples collected in early January 2012 were significantly lower than those collected in either early or late September 2011, indicating a continuing decrease in radiation levels over that duration. Radiocesium was not detected in organs collected in August 2012. In September 2011, the authors of the present study visited a local farm to collect samples from pigs who remained inside the radiation alert area. Radiocesium concentration in these pigs was nearly ten times higher than from the rescued pigs.

Seven of the 16 sows rescued were able to reproduce. The present study showed that the age of sow significantly affected their ability to reproduce. These 7 sows had 15 parturition events and birthed 166 piglets, including two malformed piglets. However, the present study confirmed that body weight did not affect reproductive performance. The average body weight of reproductive and non-reproductive sows was 226.3 versus 230.6 kg, respectively.

Hematology analysis showed that red blood cells (RBC) were lower in rescued pigs than in the non-exposed pigs. The level of HGB, HCT, MCV, and MCH, which are all related to RBC counts, were consistent with the changes in RBC between the two groups. The plasma biochemical indexes that relate to liver and kidney functions also showed differences between the two groups of pigs.

The present study was not scientifically designed and did not contain proper control groups for all tests. As a result, we are not able to conclude the exact effects of the radiation exposure to the pigs’ health.

Pp. 35-50

A Composting System to Decompose Radiocesium Contaminated Baled Grass Silage

Takahiro Yoshii; Tairo Oshima; Saburo Matsui; Noboru Manabe

Due to the Fukushima Daiichi nuclear power plant accident, a tremendous amount of organic waste (e.g., baled grass silage) contaminated with radioactivity was generated in Tohoku region, northeastern Japan. To establish a safe and efficient way to treat cesium contaminated silage, we investigated the use of aerobic, high temperature composting. Radiocesium (Cs and Cs) contaminated silage (2000 kg, approximately 2700 Bq/kg), water (4000 kg) and matured compost soil (as inoculum, 16,000 kg) were mixed by a wheel loader, and then the mixture was piled up. Air was supplied from the bottom of a compost pile continuously, and the fermentation continued for 7 weeks. The temperature at 100 cm below the surface reached approximately 100 °C. The water content decreased to less than 30% after 7 weeks. The level of radioactive cesium in the final product (18,000 kg) was 265 Bq/kg, which was below the tolerance value for fertilizer (400 Bq/kg) suggested by the Japanese government. The radioactive cesium within silage remained in the final products. We cultivated tomato (fruit), soybean (seed), carrot (root), Italian ryegrass (leaf feed for livestock), Swiss chard (leaf), cosmos (flower) and field mustard (seed) in an experimental farm fertilized with the matured compost made from the radiocesium contaminated silage, for 3 months. Radiocesium levels of edible parts and non-edible parts of each crop were lower than 20 Bq/kg, which was less than one-fifth of the Japanese government value for food (100 Bq/kg). This research demonstrated that the final product can be used safely as an organic fertilizer.

Pp. 51-58

Weathered Biotite: A Key Material of Radioactive Contamination in Fukushima

Toshihiro Kogure; Hiroki Mukai; Ryosuke Kikuchi

The eastern area of Fukushima Prefecture, where the Fukushima Daiichi nuclear power plant is located, is covered mainly with weathered granitic soil originated from the geology of this area. Weathered biotite (WB), or partially to almost vermiculitized biotite, is abundant in the soil. WB has frequently been found as radioactive soil particles sorbing radiocesium and has been identified as “bright spots” by autoradiography. Laboratory experiments using the Cs radioisotope indicated that WB collected from Fukushima sorbed Cs far more efficiently than other clay minerals from Cs solutions whose concentration was comparable to that expected for the radioactive contamination in Fukushima. This supports the abundance of radioactive WB particles in the actual contaminated soil. The Cs-desorption property of WB was also different from those of other minerals. If the period of immersion in the Cs solution was more than a few weeks, the sorbed Cs in the WB were hardly desorbed by ion-exchange with any electrolyte solutions. These results imply that decontamination of the radioactive soils is difficult if using “mild” chemical treatments and that most radioactive Cs are now fixed stably (dare one say “safely”) by WB in the soil of the Fukushima area.

Pp. 59-75

Radiocesium Accumulation in Koshiabura () and Other Wild Vegetables in Fukushima Prefecture

Naoto Nihei; Keisuke Nemoto

Wild vegetables naturally grow in the mountains, and their new buds and leaves are routinely eaten by local residents. In Fukushima, wild vegetables are more contaminated than agricultural products because most forests have not been decontaminated and radiocesium still remains in the forest soil. Radiocesium concentrations in wild vegetables can vary depending on the species, and in the case of koshiabura (), it was found to have the highest concentration among wild vegetables. To acquire basic knowledge about radiocesium accumulation in koshiabura, we collected young trees which had been grown in the forest of Date City, Fukushima and investigated the radiocesium concentration in each part and its seasonal transition.

Pp. 77-83

The Transition of Radiocesium in Peach Trees After the Fukushima Nuclear Accident

Daisuke Takata

In this chapter, we introduce the effects of radiocesium released by the Fukushima Daiichi nuclear accident on fruit trees, especially the change of radiocesium in fruit during the past 6 years. We investigated radiocesium and K in peach during the maturity of its fruit chronologically for 6 years. In the investigation during one crop period, the concentration of radiocesium in young fruit 15 days after the full bloom was the highest, and this result was common in all the investigated years. After that, the concentration of radiocesium decreased as the fruit became bigger; the decrease until 60 days after the full bloom was considerable. This tendency was also common among all investigations conducted until 2016. Though the concentration of K during the same period also decreased in the same way as radiocesium, the rate of the decrease from 15 to 30 days after the full bloom was different. When looking at the chronological transition, the concentration of radiocesium in harvested fruit decreased by one third every year from 2011 to 2013. However, such decrease could not be seen from 2014 to 2016. While the concentration in the harvested fruit tended to stop decreasing, the concentration in fruit 15 days after the full bloom tended to decrease over the years from 2012 to 2016. During the past 6 years, there was no year-over-year decrease in the concentration of K in fruit. The reason why the transition of radiocesium in fruit varied according to their stage of maturity was because the difference in timing to use the tree’s nutrient reserves.

To understand the year-over-year transition of radiocesium in peach, the amount of Cs in every part of the tree was measured. When comparing the distribution of Cs and K in the peach trees, it was found that Cs was existing in the body of the tree, which was contaminated by fallout, while K was distributed more in the leaves and fruit. Also, while the weight of the trees and the amount of K in the tree body increased with time, the amount of Cs decreased over the years. It is considered that radiocesium stored in the mature woody parts such as stem and branches had been transferred to fruit, leaves, or young branches.

Pp. 85-94

Application of the Artificial Annual Environmental Cycle and Dormancy-Induced Suppression of Cesium Uptake in Poplar

Yusaku Noda; Tsutomu Aohara; Shinobu Satoh; Jun Furukawa

In perennial woody plants, dormancy-induced alteration of potassium (K) localization is assumed one of the mechanisms for adapting and surviving the severe winter environment. To establish if radio-cesium (Cs) localization is also affected by dormancy initiation, the artificial annual environmental cycle was applied to the model tree poplar. Under the short day-length condition, the amount of Cs in shoots absorbed through the roots was drastically suppressed, but the amount of K was unchanged. Potassium uptake from the rhizosphere is mainly mediated by KUP/HAK/KT and CNGC transporters. However, in poplar, these genes were constantly expressed under the short-day condition and there were no up- or down-regulation. These results indicated the suppression of Cs uptake was triggered by the short-day length, however, the key transporter and the mechanism remains unclear. We hypothesized that Cs and K transport systems are separately regulated in poplar.

Pp. 95-105

Radiocesium Contamination in Forests and the Current Situation of Growing Oak Trees for Mushroom Logs

Natsuko I. Kobayashi; Ryosuke Ito; Masaya Masumori

The radiocesium contamination in mushrooms and in mushroom logs is a matter of concern for the forestry industry. To know the contamination situation precisely and the future for mushroom log production, the Cs distribution in six fields cultivating oak trees in Tamura city, Fukushima, was investigated in 2015. The Cs concentration in new branches was found to correlate with that in the wood. This result suggests that the Cs concentration in tree trunks could be estimated without felling based on the Cs concentration in new branches. In addition, trees grown in one of the six fields was found to have very low Cs concentration even though the concentration of Cs in the soil was high. The impact of the nutritional conditions on the Cs absorption in the oak seedlings grown hydroponically was also investigated by a radiotracer experiment.

Pp. 107-122

Radiocesium Dynamics in Wild Mushrooms During the First Five Years After the Fukushima Accident

Toshihiro Yamada

Dynamics of radiocesium in wild mushrooms, especially in mycorrhizal fungi, in forest ecosystems were investigated for 5 years after the Fukushima nuclear accident, in relation to substrates such as litter, soil and wood debris. Some mushroom species contained a high level of radiocesium in the first or second year, and then the radiocesium content decreased. Changes in radiocesium activities were ambiguous for many other mushrooms. Radiocesium accumulation with time was not common contrary to expectations. Reduction of radiocesium activities in litter and increase in mushrooms and soils, i.e. transfer of radiocesium from litter to mushrooms and soils, was recognized in the first and second year, but it was not obvious in subsequent years. Radiocesium accumulated in several mushroom species, especially in mycorrhizal fungi, while radiocesium in the other mushrooms did not exceed those in the neighboring forest litter. Similar differences in radiocesium level among mushroom species were observed in relation to K levels, though Cs/K ratio in mushrooms was lower than in O horizon, but at the same level of the A horizon in general. These facts suggested differences in the mechanisms of cesium accumulation. Residual Cs due to nuclear weapons tests or the Chernobyl accident still remained in mushrooms and soils. From the ratio of the past residual Cs, it was suggested that the residual Cs was tightly retained in the material cycles of forest mushroom ecosystem, whereas Cs emitted from the Fukushima accident was still fluid.

Pp. 123-139

The Spatial Distribution of Radiocesium Over a Four-Year Period in a Forest Ecosystem in North Fukushima After the Nuclear Power Station Accident

Masashi Murakami; Takahiro Miyata; Natsuko Kobayashi; Keitaro Tanoi; Nobuyoshi Ishii; Nobuhito Ohte

We have investigated the redistribution dynamics of radiocesium deposited after the nuclear power station accident in March 2011 in a forested catchment located in North Fukushima over a four-year period (2012–2015). At the catchment scale, Cs accumulation decreased drastically by 50% of the estimated initial accumulation during the first 2 years. Cs-137 accumulation in the forest floor occurred in the litter layers and the surface part of mineral soils and have accounted for about 90% of the total catchment scale accumulation. The internal Cs cycle among the soil-plant system was also identified as a retention mechanism and was biologically dynamic. Monitoring the decreasing and retaining mechanisms of radioactivity at the ecosystem scale will be required for effective forest and water resource management.

Pp. 141-152

Parallel Measurement of Ambient and Individual External Radiation in Iitate Village, Fukushima

Yoichi Tao; Muneo Kanno; Soji Obara; Shunichiro Kuriyama; Takaaki Sano; Katsuhiko Ninomiya

This report is based on a survey we conducted in March–June 2017 to measure radiation levels in Iitate Village after the 2011 Fukushima Daiichi nuclear power plant accident. Six NPO members including two evacuees who returned after the evacuation order was lifted in April 2017 took part in the study. Each participant worked in the area each day, carrying an ambient radiation measuring device, two personal radiation measuring devices, and a GPS receiver to record their movement and compare ambient and individual external doses. No matter where they were, results showed that for those taking the same daily route for the same amount of time, the individual dose was about 11~30% lower than that of the ambient dose; the ratio of ambient to individual external dose was 100 to 70–89. Further measurement and additional data are needed to protect the health of villagers, and to identify areas that require further decontamination.

Pp. 153-163

Mobility of Fallout Radiocesium Depending on the Land Use in Kasumigaura Basin

Shuichiro Yoshida; Sho Shiozawa; Naoto Nihei; Kazuhiro Nishida

Although Lake Kasumigaura stores twice as much radiocesium compared to the direct fallout onto the lake surface, the additional source of radiocesium has not been determined. The present study examined the major source of radiocesium deposited in the lake based on surveys of the dry beds of the rivers flowing into the lake. The basin of four rivers, two of which flow through an urbanized region and the other two through a rural region to Lake Kasumigaura, were selected. The radioactivity per unit area of the dry river bed and the top of the river bank was measured. On the dry river beds of the rivers flowing from the urbanized area, the deposition of radiocesium per unit area was found to be much higher than the direct fallout per unit area, revealing a considerable amount of radiocesium had been discharged from the urbanized upstream of the rivers by flooding events. On the other hand, rivers flowing from the rural area stored almost the same amount of radiocesium as the direct fallout. These observations revealed that the urbanized areas located upstream to Kasumigaura Lake were a major additional source of radiocesium contamination in the lake.

Pp. 165-176

Challenges of Agricultural Land Remediation and Renewal of Agriculture in Iitate Village by a Collaboration Between Researchers and a Non-profit Organization

Masaru Mizoguchi

We have tested several ways to revitalize agriculture in Fukushima by developing farmland decontamination methods that farmers can undertake by themselves. As a result, the rice harvested in a test field passed the official inspection of Fukushima Prefecture in 2014. Despite the efforts of local people, we have not yet succeeded to dispel the anxieties in the general public who believe that Fukushima’s agricultural crops might contain radioactive cesium. Such “harmful rumors” are hampering the recovery of local agriculture in Fukushima. In this chapter, we review the challenges of agricultural land remediation and renewal of agriculture from a collaboration between researchers and a non-profit organization (NPO) and propose the scenario for the recovery of local agriculture and village life.

Pp. 177-190

Radiocesium Contamination on a University Campus and in Forests in Kashiwa City, Chiba Prefecture, a Suburb of Metropolitan Tokyo

Kenji Fukuda

Kashiwa, a city in Chiba Prefecture, became the most contaminated suburb of Metropolitan Tokyo after the Fukushima Daiichi nuclear accident. The Kashiwa Campus of the University of Tokyo and nearby urban forests were surveyed to examine the distribution of radiocesium in the aboveground parts of trees, turf grass, and soil. The air dose rate 1 m aboveground in the summer of 2011 was 0.3–0.6 μSv/h and more than 90% of the radiocesium was in the surface soil. A nursery lawn was effectively decontaminated by removing the turf and surface soil using a sod cutter. In the forests, the radiocesium concentration was higher in the leaves of evergreen trees and outer bark of trees, while the total amount of radiocesium in the aboveground parts of trees was less than 10% of the amount in the surface soil. Therefore, decontamination by cutting trees would not be effective. The decrease in the radiocesium concentration in the surface soil could be explained by natural decay, while the effects of cesium movement to deeper soil were not prominent.

Pp. 191-209

The State of Fisheries and Marine Species in Fukushima: Six Years After the 2011 Disaster

Nobuyuki Yagi

The recovery of Fukushima fisheries remains sluggish 6 years after the disaster. The Fukushima Fisheries Cooperative Association (FCA) decided to allow limited fishing in June 2012 (known as the trial operation). Total landing value of fish and fishery products from the trial operation has been gradually increasing due to the increased number of catchable target species and increased fishing areas. But the landing value in 2016 was only 5% of the value recorded in the pre-disaster years. Safety of the products has been demonstrated by various surveys conducted by the government authorities and independent researchers. Several studies indicated that the population of key fish species in Fukushima waters showed a tangible increase after the 2011 disaster reflecting low fishing pressures in this period. Weak consumer confidence would have contributed to the extremely slow recovery of Fukushima fisheries. In addition to the consumers’ attitudes, fish distributors’ risk-averse attitudes could have brought additional adverse effects against the recovery of Fukushima fisheries. This situation could continue for several more years. Continued support for fishers in Fukushima is needed for the foreseeable future to sustain the livelihood of small fishing households as well as maintain societies, traditional knowledge, and other human or social capital in the region.

Pp. 211-220

Visualization of Ion Transport in Plants

Ryohei Sugita; Natsuko I. Kobayashi; Atsushi Hirose; Keitaro Tanoi; Tomoko M. Nakanishi

We have developed a real-time radioisotope imaging system (RRIS) to visualize ion transport in plants, and to measure radioactivity in living plants. To know the mechanisms of ion transport in plants, the use of living plants allows us to visualize ion movement in real time. In addition, the RRIS can analyze how a change to the plant environment affects ion transport. In this chapter, we will introduce some of the applications of the RRIS. We analyzed the effect of light on cesium, potassium, magnesium, phosphate, and calcium transport in plants using the RRIS. The results show that magnesium, potassium, and calcium transport in plants were not influenced by light. On the other hand, the amount of cesium and phosphate absorption in roots decreased after light-off. Moreover, the amount of phosphate transport from root to shoot also decreased after light-off.

Pp. 221-231

Sr Analysis Using Inductively Coupled Plasma Mass Spectrometry with Split-Flow Injection and Online Solid-Phase Extraction for Multiple Concentration and Separation Steps

Makoto Furukawa; Yoshitaka Takagai

We aimed to develop a rapid and sensitive method to analyze the radioactivity of Sr by combining multiple techniques, including online solid-phase extraction (SPE) and inductively coupled plasma mass spectrometry (ICP-MS). An automatic analytical system was designed to execute the proposed process from sample injection to measurement. The analysis time is approximately 20 min and the limit of detection is 0.3 Bq/L (equivalent to 0.06 pg/L) with 50 mL of the sample. Although several challenges were encountered with the ICP-MS measurements of Sr, several techniques were leveraged to overcome them. Online solid-phase extraction (SPE) was used to concentrate the sample automatically; the interference from polyatomic ions and isobars was removed by an oxidation, and the extraction and recovery ratio of solid phase were measured by split-flow injection with internal standard correction during the transient signal measurement. These improvements were shown to allow measurements of Sr in various kinds of samples to be conducted more quickly than by alternative conventional radiometric methods.

Pp. 233-248

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Tipo: libros

ISBN impreso

978-981-13-3217-3

ISBN electrónico

978-981-13-3218-0

Editor responsable

Springer Nature

País de edición

Reino Unido

Fecha de publicación