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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.