Keywords

11.1 Introduction

Prior to the major earthquake in Fukushima Prefecture in 2011, the prefecture had 7177 ha of land under fruit tree cultivation and was the prefecture with the largest area used for fruit trees in Japan (Ministry of Agriculture, Forestry and Fisheries (Japan) 2018). Fukushima Prefecture was ranked second in Japan with respect to the hectarage used for peach cultivation. According to the Special Fruit Production Survey, 2010 (Ministry of Agriculture, Forestry and Fisheries (Japan) 2012), it ranked first among Japanese prefectures for the largest production of dried persimmons, much of which was “anpo-gaki,” a product of especially high value. The sales of anpo-gaki in 2010 by Date Mirai, a former branch of the Japan Agricultural Cooperatives centered around dates, reached ¥1.9 billion (Komatsu 2014a). Although the retail prices of most types of fruit are gradually returning to pre-earthquake levels (Komatsu 2014a, b; Takata 2016), they have still not completely recovered. Nevertheless, Fukushima Prefecture’s position as one of the most important fruit-producing prefectures in Japan has not changed since the Tokyo Electric Power Co.’s Fukushima Daiichi Nuclear Power Plant (FDNPP) 2011 disaster.

The effects of radiocesium from the FDNPP disaster on agricultural products as reference materials for the time of the disaster have been estimated. Numerous studies have reported on the effects of radiocesium on annual crops. These studies include (1) surveys of the effects of radioactive fallout from atmospheric nuclear tests; (2) dynamic surveys after the Chernobyl disaster; and (3) studies in experimental environments such as application-using reagents. Although the transfer coefficient of radiocesium concentration in the soil and perennial fruit crops has been studied (IAEA 2003, 2010), overall, fewer radiocesium-related studies have been conducted on perennial crops than on other crops. One major difference between the FDNPP and Chernobyl disasters was the season in which they occurred; the FDNPP disaster occurred while deciduous fruit trees had no leaves, suggesting that radiocesium fallout would have landed on the tree bodies (i.e., trunks and main branches). With respect to the transfer of radiocesium to inside the fruit-tree bodies, the effects of direct contamination of the trunk and transfer of radiocesium from the soil must be investigated. As fruit trees are long-lived, they have many similarities with timber trees in terms of life cycle and growth. More studies on radiocesium have been reported in forestry than in fruit trees; therefore, forestry studies had to be referred to when clarifying the dynamics of radiocesium in fruit trees. However, in timber plantations, the surface layers of the soil form the litter layer, which contains large quantities of fallen leaves and other organic matter, and this layer plays important roles in root growth and nutrient uptake and cycling. Grass grows on the soil surface in orchards, and, indeed, leaves that fall from trees are often removed by the workers to prevent tree diseases. Considering that orchards are maintained with far more human effort than timber plantations, fruit trees may exhibit vastly different radiocesium dynamics.

In summary, numerous issues related to radiocesium dynamics in orchards were not elucidated before the FDNPP disaster, and there may be numerous differences between perennial crops and timber trees. The reference information available offers starting points to elucidate radiocesium dynamics in fruit trees and develop technologies relevant to this issue.

11.2 FDNPP Disaster and Radioactive Contamination of Orchards

11.2.1 Radiocesium Contamination of Fruit and Leaves in the First Year After the FDNPP Disaster

High concentrations of radiocesium, exceeding the predictions based on coefficients of transfer from the soil at the immature fruit stage (IAEA 2003, 2010), were found in deciduous fruit trees in Fukushima Prefecture after the FDNPP disaster. Radiocesium accumulates readily in immature stages of fruit such as ume (Prunus mume: a small, plum-like fruit, in which the flowers were directly contaminated), and chestnuts (which has edible seeds) (Hamada et al. 2012). However, the FDNPP disaster occurred before budbreak, and radiocesium was detected at above the detection limit in the usual deciduous-tree fruits in Fukushima Prefecture that do not belong to the above groups (Suzuki et al. 2018). Radiocesium was detected in all five of the most common fruit species in Fukushima Prefecture in 2011, that is, peaches, grapes, Japanese pears, apples, and persimmons (Abe et al. 2014; Yuda et al. 2014).

With respect to the effects of tree age on radiocesium concentration in fruit, a study was performed in which peach trees of the “akatsuki” variety, 12- and 18-year old, were compared with peach trees of the “yuzora” variety, 6- and 18-year old, and the radiocesium concentration in mature fruit was found to be substantially higher in the older trees (Abe et al. 2014). In addition, differences were found between radiocesium concentrations in the following seven species of fruit: ume, cherry, peach, grape, pear, apple, and persimmon. The radiocesium concentrations in mature fruit differed according to tree age and species, suggesting that above-ground tree morphological factors, such as the spread of the crown, may have affected fruit radiocesium concentration in the first year after contamination.

11.2.2 Radiocesium Contamination of the Bark and Tree in the First Year After the Disaster

Radiocesium concentrations were compared in (1) soil below peach trees planted in pots, with the soil surface covered before the FDNPP disaster; (2) soil below uncovered trees; and (3) the fruit (Takata et al. 2012a). The radiocesium concentration in covered soil decreased by one-sixth, but, with or without covering, the radiocesium concentration in the roots was below the limit of detection. The radiocesium concentrations in fruit with and without covering were 26.6 and 27.8 Bq kg−1 fresh weight, respectively, the difference between these values being within the range of measurement error. In addition, the radiocesium content was mostly above ground, and there was no difference with and without covering.

In peach trees, the transfer of radiocesium from the above-ground part of the tree to inside the tree has been investigated (Takata et al. 2012b; Takata 2013; duplicated figure: Fig. 11.1). Samples of the trunks were collected in January 2012, and images of the species of radioactive nuclei were prepared using an imaging plate. Figure 11.1 shows a superimposed photograph and the original image, and the black spots are the loci where radioactive nuclei were detected. Photographs were only taken of the outermost layer of the peach tree bark, and no photographs were taken for loci immediately below that. Radiocesium concentrations were measured using germanium semiconductor detectors in the epidermis and directly under the epidermis, and it was found that extremely high concentrations of radiocesium were present in the epidermis. Therefore, the radiocesium deposited on the tree may be heterogeneously distributed in the bark, with a very high concentration in the thin, outermost layer of the bark.

Fig. 11.1
Two sets of photographs of the Akatsuki peach's trunk. Heartwood, annual ring in 2010, and annual ring in 2011 are observed in the wood. Secondary phloem with cambium, cortex, directory under the epidermis, and a superimposed photograph of the epidermis with dark spots indicating radioactive nuclei.

Imaging plate of trunk in ‘Akatsuki’ peach. From Takata (2013)

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11.2.3 Radiocesium Contamination of Soil and Grass in the First Year After the Disaster

In orchards in Fukushima Prefecture, grass is grown using the usual ground management methods. In orchards, unlike other cultivated land, branches are at least 3 m high. Consequently, before radioactive fallout reaches the ground in an orchard, it may be affected by stagnant air, owing to the trees, and radiocesium capture, which may result in differences in the amount of radiocesium deposited on the ground surface. In this context, an investigation of the distribution of mean radiocesium concentrations in the top 5 cm of soil (Sato et al. 2015) revealed that the radiocesium concentration in the 5-cm layer in orchards showed two- to fivefold differences between tree crowns. This difference was greater in higher-density apple orchards than in peach orchards, indicating that horizontal differences in the distribution of radiocesium concentration in soil are affected by planting density.

11.3 Elucidation of Radiocesium Uptake by Tree Bodies and Fruit, and Transfer Routes

11.3.1 Radiocesium Transfer from the Bark to Inside

The route of penetration of the tree through the bark by radiocesium has been hypothesized to involve some mode of transfer from the lenticels on the bark to the phloem and/or xylem (Takata 2013). Lenticels on peach trees are often split, and radiocesium can penetrate the body from these sites. Physical splitting on branches not only occurs at lenticels, and intense images of contamination were also obtained at sites with pruning scars, that is, cavities. Physical irregularities are marked at such sites, and dust containing radiocesium tends to accumulate, such that lenticel tissues are likely to be one of the penetration routes for radiocesium into the trees. The lenticels on the outer bark are continuous with the ray tissue in the inner bark. The ray tissue is composed of parenchyma cells that grow in a radiating pattern and pass through the phloem, cambium, and wood. In addition to having an aeration function for the sapwood (Mio and Matsumoto 1979), in recent years, the ray tissue has been acknowledged to have nutrient storage functions (Islam and Begum 2012). Studies on nutrient and water exchange functions with the wood and phloem are in progress to elucidate these mechanisms (Fromm 2010; Pfautsch et al. 2015; Van Bell 1990). In studies with sugi (Cryptomeria japonica) and konara (Quercus serrata), 133Cs applied to the bark was detected in the wood (Mahara et al. 2017). Visualization assays revealed that 133Cs localized in the ray tissue of sugi, and 133Cs in the bark was transported into the wood via the ray tissue (Aoki et al. 2017). In the FDNPP disaster, it is probable that radiocesium passed through the bark of deciduous trees during the dormant period and was then transferred directly into the body of the fruit trees.

11.3.2 Distribution of Radiocesium in Peach Tree Bodies Five Months After the Disaster

A series of surveys was performed on peach trees to study the distribution of radiocesium in fruit-tree bodies in the first year after the disaster (Takata et al. 2012a, b, c, d). In akatsuki peach trees in orchards that received fallout, at least 20% of the radiocesium, as becquerel equivalents, was in the leaves and fruit (Fig. 11.2). Leaves that fell in November had lower radiocesium concentrations than those that fell in August (Takata 2013), and fresh growth after harvest showed secondary elongation, such that 15–20% of the radiocesium was eliminated from the tree. It has been reported that, in the standard pruning methods for peach trees, 56.6% of the length is removed in the winter pruning season (Takata et al. 2008), but in the first year after the disaster, approximately 30% of the radiocesium in the branches (becquerel equivalents) was eliminated from the tree. By calculating the amount of material collected from the ground (fallen leaves), the amount pruned, and the increase in wood thickness, the amount eliminated from the tree each year can be estimated. The bark of the trunk, which is vertical, has a lower radiocesium concentration than the ground and the main branches, which grow approximately horizontally (Takata et al. 2012b, d). Therefore, when such branches were removed in the winter pruning season, the vigorous renewal of the lateral branches from adventitious buds had a positive effect on tree decontamination. High-pressure washing of the trees to artificially remove radiocesium from the tree bodies in Fukushima Prefecture, from December 2011 to February 2012, considerably reduced the radiocesium concentration.

Fig. 11.2
A stacked column chart plots g D W on the y axis versus dry matter weight and B q or organ. Leaves and fruit exhibit the highest concentration of radiocesium as becquerel equivalents.

Dry matter weight and Cs content for every organ in ‘Akatsuki’ peach tree. From Takata (2013). *Under detection limit. Value means detection limit × dry weight

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In a study performed with the above group the year after the disaster, in which contaminated peach trees were transplanted in uncontaminated soil (Takata et al. 2014; Takata 2016), only approximately 2% of the radiocesium in the tree was transferred to fruit and other newly grown organs, clearly showing there were major differences in radiocesium transfer and distribution between the year of the disaster and subsequent years. This shows that the efficacy of decontamination of the tree is greatest during the first year after the disaster. It is therefore imperative to perform decontamination, such as washing of trees, promptly after a disaster.

Sato et al. (2014) performed a study in which 6-year-old persimmon trees, grown before the FDNPP disaster, were replanted in pots filled with radiocesium-contaminated soil. Of the 137Cs absorbed from the soil after 3 years, 38.9 ± 6.9% (mean ± standard deviation) was above ground, and 61.1 ± 6.9% was below ground, which was approximately the opposite of the distribution of 70.0% above ground and 30.0% below ground for trees cultivated outdoors in the first year after the disaster. In a damage survey performed for 3 years after the disaster in yuzora peach trees planted before the disaster in experimental plots at the National Institute of Fruit Tree Science, distribution to underground parts was <20% (Takata 2019). In a study with 2-year-old Pinot Blanc grapevines in pots, in which contamination was restricted to the soil or leaves (Carini and Lombi 1997), 42% of uptake from the soil only was distributed to underground parts, whereas proportional distribution to underground parts was 10% when uptake was from the leaves only, clearly indicating that the distribution of radiocesium above and below ground reflects the site of origin of the radiocesium. In the case of fruit trees contaminated by the FDNPP disaster, it is highly probable that radiocesium uptake was directly into the tree above ground, and the amount of radiocesium storage in the tree is therefore greater above ground.

11.3.3 Transfer from Soil to Fruit

Comparison of the bodies of peach trees, in which the soil surface was either covered and uncovered at the time of radiocesium fallout, showed that the radiocesium concentration in soil was reduced by one-sixth by covering and the radiocesium concentrations of the roots and the above-ground parts were similar, whether covered or not (Takata et al. 2012a). When peach trees that received radiocesium fallout were replanted, there were no differences in the radiocesium concentration in the fruit, irrespective of whether the soil used was contaminated or uncontaminated with radiocesium. Horii et al. reported that the transfer coefficients over several years after planting uncontaminated unshu mandarin orange (Citrus unshiu), chestnut, and persimmon trees were in the range of 10−4 to 10−3 (2018). On the basis of a previous report (IAEA 2003), and the present results, it is considered that in fruit trees, the contamination of the soil surface layer has little effect on uptake by the roots.

There have been several reports on the transfer of radiocesium from the soil, including one on fig and grape trees, in which the soil concentration was changed locally (Takata et al. 2013b); a second, with blueberry bushes, on the relationship between the exchangeable potassium concentration and radiocesium concentration in fruit (Iwabuchi 2014); and a third on the cation concentration in the soil solution and the suppression of radiocesium uptake (Matsuoka et al. 2019). Radiocesium transfer dynamics within the soil are influenced by the proportions of clay, sand, and organic matter in the soil (Hiraoka et al. 2015), so there is a need for longitudinal studies on the dynamics of radiocesium transfer to the lower layers.

11.4 Development of Techniques to Reduce Radiocesium Content in Trees and Orchards

11.4.1 Time-Course of Radiocesium Content in Mature Peaches Using Fruit Thinning

From the second half of 2011 until 2012, various measures were taken (including high-pressure washing of trees), but many issues could not be clarified until the trees had grown. In a study of cherries contaminated in the Chernobyl disaster, the radiocesium concentration in the fruit was found to have fallen to approximately one-third by the year after the disaster (Antonopoulos-Domis et al. 1996), and it is thought that there was probably a similar tendency after the FDNPP disaster. However, the actual concentrations in fruit were uncertain. The year after the disaster, the provisional regulation value for radiocesium concentration in food was changed from 500 to 100 Bq kg−1, and in connection with that change, there was a demand for establishment of a more precise method for tracking the concentration in fruit. In this context, a study was performed that focused primarily on the changes in concentration in fruit from year to year during the growing season (Takata et al. 2014).

The radiocesium concentration in fruit was generally found to reach a minimum level during the second growing season. The concentration in fruits during the growing season and at harvest was investigated and the variability in the measurement times and the feasibility of moving them forward were predicted (Fig. 11.3). This method was shown to be useful for the removal of contaminated trees. The peach fruit radiocesium concentrations were generally below the specified values in the fruit-producing region of Fukushima Prefecture after the FDNPP disaster, so this prediction system was not needed for peaches, whereas in persimmons (for making anpo-gaki), screening tests were performed to identify orchards where the harvested fruit had high radiocesium concentrations. This prediction method will be useful for radiocesium concentrations in fruit if any more nuclear disasters occur, either in Japan or overseas. In the case of deciduous fruit trees, the trees had no leaves and only the radiocesium fallout could be measured. In future, it will be necessary to elucidate transfer dynamics over a wide range of seasons.

Fig. 11.3
Two line and scatter plots of C s in harvested fruits versus C s in thinning fruits. Both curves and correlation lines are concave-down, increasing in both graphs. The dots are denser and have higher values in the left graph.

Relationship between thinning fruit and harvested fruits in 137Cs (from Takata 2016) left: each tree, n = 70, right: each orchard, n = 24). Dashed line means correlation line. Solid line means Y = X line

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11.4.2 Reducing Fruit Radiocesium Concentrations by Bark Washing

With fruit trees, bark peelability varies between species, with the bark being peeled readily from trees such as pear, grape, persimmon, and apple. By removing the rough bark, at least 80% of the radiocesium is removed (Sato et al. 2015). However, trees in which the seeds are hard stones, such as peaches and ume, have bark that is of low peelability. In this context, Abe et al. (2014) found that high-pressure washing of the bark of akatsuki peach trees, in July 2011, reduced the total radiation level by 55.9%. Washing was, however, not found to be effective for reducing radiocesium concentrations in fruit grown in 2011. This confirmed that most of the radiocesium was transferred internally within 60 days of contamination, suggesting that decontamination in July, approximately 4 months after the disaster, was already too late to restrict transfer of radiocesium into the tree.

In peaches and persimmons, washing the bark from winter 2011 to spring 2012 substantially reduced the radiocesium concentration of fruit harvested in 2012 in comparison with the fruit from unwashed trees (Abe et al. 2014; Sato 2014). This suggests that, in the case of uncontaminated persimmon trees, radiocesium transfer internally from the bark continues the year after contamination. After 3 years of persimmon bark formation, strip-shaped fissures form, and water droplets often collect in the scars left after the fissures, probably leading to the growth of moss and lichen on the bark (Abe et al. 2014). This could influence the radiocesium contamination.

11.4.3 Reducing Transfer to Fruit by Pruning and Cutting the Trunk

In the second year after radioactive contamination, radiocesium inside the fruit tree is the principal source of transfer to fruit (Antonopoulos-Domis et al. 1990), and pruning is considered to be effective for removing radiocesium that has been transferred internally into the tree. The effectiveness of pruning for removing radiocesium inside the tree is suggested to depend on not only the proportional distribution of radiocesium to the part that is removed, but also the amount of fruit collected (Hiraoka et al. 2015; Pröhl et al. 2003). However, in studies performed before the FDNPP disaster, the relationship between pruning and fruit radiocesium concentration had not been investigated.

In order to elucidate the relationship between pruning intensity and radiocesium concentration in chestnuts, Matsuoka et al. (2016) used 7-year-old trees and treatments of no-pruning, standard-pruning, and intense-pruning areas of the orchard in a March 2013 trial. In addition to measurement of the fruit radiocesium concentration over 2 years, in the second year, the trees were cut up, and the proportional radiocesium and radiopotassium distribution in each part was investigated. No significant differences in radiocesium concentration were found in the fruit that grew during the year of treatment, but the level of transfer of radiocesium to all fruit was substantially higher in the nonpruned area. The proportional distribution of radiopotassium to branches and roots that grew during the first to fourth years after the disaster was higher than that of radiocesium, suggesting that the radiocesium in the new growth had not come from the soil.

In March 2014, Kuwana et al. (2017), using persimmon trees of the hachiya variety (the fruit used to make anpo-gaki), included the following treatments: (1) no pruning; (2) standard pruning; (3) intense pruning; and (4) trunk-cutting, with the trunk cut at a height of 60–100 cm above the ground. The radiocesium concentrations were then measured in the fruit collected in each harvest season. The fruit radiocesium concentration decreased with time, except that in the no-pruning area in the fifth year, it was slightly higher than in the fourth year. No significant differences due to treatment mode were found in any of the study years, but the fruit radiocesium concentrations in the three pruned areas tended to show less variability than in the no-pruning areas.

In summary, although intense pruning is not clearly effective in reducing fruit radiocesium concentration, it is effective in restricting the variability of contamination strength in tree bodies and cultivation plots, and, in terms of ensuring yield, pruning operations are considered to be important for safe and stable fruit production.

11.4.4 Soil Radiocesium Elimination and Aerial Radiation Dose Reduction by Topsoil Stripping

Due to the deposition of radiocesium at high concentrations in the soil surface layer in orchards, the aerial radiation dose is higher in orchards than in surrounding areas, and there are concerns about workers suffering external exposure. In orchards, decontamination operations involving topsoil stripping have been performed, but many of the orchards in Fukushima Prefecture are on sloping land because it is a mountainous region, and there are limitations to the use of heavy machinery in such areas. Methods for topsoil stripping that do not involve use of machinery, using revegetation nets and other surface-covering materials, have been investigated (Sato et al. 2019). Approaches that make use of the ecological systems that exist in orchards are considered to be highly practical as orchard radiation decontamination methods.

11.5 Progress Toward Restarting Anpo-Gaki Shipment: Persimmons for Making Anpo-Gaki and Product Control

11.5.1 Restarting Shipments of Persimmons for Anpo-Gaki

In the northern part of Fukushima Prefecture, which is an important area for anpo-gaki production, immature fruit was sampled and tested from all persimmon cultivation plots after the FDNPP disaster. Screening of processed anpo-gaki for transport was performed before shipment. However, several years after the disaster, some products were confirmed to exceed the screening level, albeit only slightly (Table 11.1; Fukushima Prefecture Anpo-gaki Production Area Promotion Association 2018a), but Good Agricultural Practice (GAP) had been introduced in connection with processing (Fukushima Prefecture Anpo-gaki Production Area Promotion Association 2018b), so the adhesion potential to the external fruit during processing was reduced. It is highly likely, therefore, that the cause of the screening level being exceeded lay with the fruit used to make the anpo-gaki. The testing of immature fruit in the cultivation plots was on a sampling basis, so, if certain trees had higher contamination levels, the screening level could be exceeded in the fruit. Therefore, Sekizawa et al. (2019) investigated the intertree differences in fruit 137Cs concentration in the same plots. In the anpo-gaki persimmons with excessive 137Cs concentrations, the trees had high 137Cs concentrations (Table 11.2).

Table 11.1 Results of radioactive substance inspection of Anpo-gaki (sulfur-smoked semi-dry persimmon)
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Table 11.2 Cs-137 concentration of the young persimmon fruit [reorganized the data of Sekizawa et al. (2019)]
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11.5.2 Anpo-Gaki Product Control

To enable stable shipments of anpo-gaki, controls are required in both the production process for the fruit used, and in anpo-gaki processing for concentration variability in the fruit used and fluctuations in radiocesium concentration during processing. The present authors have verified the variability in radiocesium concentration in the fruit used, the proportional changes in radiocesium concentration during processing, and the risk of radiocesium contamination in commercial premises for anpo-gaki to be considered in risk management during anpo-gaki processing. The nondestructive radiation measurement devices used in full-quantity tests of anpo-gaki before shipment were strictly calibrated using model samples with known concentrations of certified reference materials in brown rice.

To clarify the variability in radiocesium concentration in persimmons used for anpo-gaki from the same tree, Sekizawa et al. (2019) performed a follow-up study of the differences in radiocesium concentration between persimmons collected from the same branches of the same trees, in northern Fukushima Prefecture. In 2013, up to 3.6-fold difference in concentration between persimmons from the same main branch was observed, and in 2014, when the radiocesium concentration had halved from the 2013 level, the concentration difference in the same main branch was up to approximately twofold. Both the concentration and concentration difference had decreased in the same main branch over time.

The commercial anpo-gaki processing facilities where persimmons were dried for an extended period with natural air flow were inspected, and radiocesium adhesion to the shelves and floor inside the facilities was confirmed. Although it was shown that the contamination status in the processing facilities had no effect on the anpo-gaki radiocesium concentration, the contamination risk is considered to be higher when persimmons are in direct contact with the floor and/or pipes, and decontamination must therefore be performed every year. For this reason, in 2014, preuse cleaning was included in the Fukushima Prefecture Anpo-gaki Production Area Promotion Association’s “Manual of Good Agricultural Practice for Safe Anpo-gaki Production” (referred to below as the “GAP Manual”).

Screening via nondestructive, full-quantity testing was introduced when anpo-gaki shipments restarted. In the first year after restarting anpo-gaki shipments, tests were performed on the basis of the product packaging as one box containing eight trays, each with six anpo-gaki. Therefore, for the testing device (separate from the calibration source), a reference model sample was prepared in accordance with the preparation method for the brown rice certified reference materials for radiocesium analysis (U-8 containers packed with 81 g of brown rice sample; Hachinohe et al. 2016). These samples were placed in an anpo-gaki tray, with the containers laid on their sides with three next to each other. The mass of each container was approximately twice that of the anpo-gaki; the brown rice samples had a 40K content of 70–100 Bq kg−1, which was approximately 50% that of the edible part of an anpo-gaki (174 Bq kg−1). Using homogeneous brown rice samples with radiocesium concentrations of 0–140 Bq kg−1, reference materials were prepared at five concentrations. These reference materials were introduced in the anpo-gaki full-quantity testing device and were used for verification of screening performance.

In summary, the radiocesium concentration in fruit used for anpo-gaki has a major effect on the concentration in the final product. Therefore, the risk of contamination in the commercial premises should be decreased by predicting the proportional increase in radiocesium concentration due to anpo-gaki processing. Radiocesium testing before and after anpo-gaki processing is effective for managing the risk in the processed product.

11.6 Societal Implementation of Study Results

The radiocesium decontamination measures for orchards are reflected in the fundamental policies for decontamination of agricultural and forestry areas in Fukushima Prefecture and include washing trees, removing rough bark, and pruning. Data and statement methods supporting the effectiveness of such techniques were included in the “Policies for decontamination and technical measures relating to radiocesium in agricultural products” (Fukushima Prefectural Agriculture, Forestry and Fisheries Dept. 2012).

From December 2011 to March 2012, on the basis of the fundamental decontamination policies; in collaboration with prefectural, city, town, and village governments, and the Japan Agricultural Cooperatives, approximately 4300 ha of orchards of peaches, persimmons, apples, pears, and grapes included measures such as high-pressure washing of the trees (Fukushima Prefectural Agriculture, Forestry and Fisheries Dept. 2013). The outcome of these measures was that, since 2012, no restriction of shipment of the principal tree crops produced in Fukushima Prefecture, including peaches, apples, pears, and grapes, has been in effect.

In 2013, the third year of self-imposed control of anpo-gaki shipment, a model area for restarting processing was established, and a plan was established for shipment only of products confirmed to be safe using a nondestructive testing device. To establish this model area, the radiocesium concentration of the persimmons used for anpo-gaki had to meet specified values. Before using the nondestructive testing device, radiocesium reference samples were used in performance tests on the device for calibration.

The results of studies on the prevention of secondary contamination during cultivation and processing are reflected in the GAP Manual (Fukushima Prefecture Anpo-gaki Production Area Promotion Association 2018b), and all producers in the anpo-gaki production process comply with this. Cleaning of commercial premises is performed as a cooperative operation, maintaining a consistent operational level, on the basis of the GAP Manual.

It is expected that replacement of trees that still have fruit radiocesium concentrations exceeding the specified value will be performed after discussing and deciding upon appropriate compensation.

All data obtained in an agriculture, forestry, and fisheries survey, which covers fruit and is performed as emergency monitoring of environmental radiation, is made available on the homepage of the Fukushima Association for Securing Safety of Agricultural Products. In addition, all test data for anpo-gaki obtained using the nondestructive testing device are made available on the homepage of the Fukushima Division of the National Federation of Agricultural Cooperative Associations. In parallel with efforts to ensure safety at production sites, information disclosure and the expansion of public relations activities has ensured that there has been a recovery in demand. The value of prefectural fruit shipment, which in 2011 had fallen to ¥19.7 billion (63% of that in 2010), had recovered to ¥27.1 billion by 2016 (Ministry of Agriculture, Forestry and Fisheries (Japan), 2010, 2011, 2016). In the case of anpo-gaki, the shipments increased yearly since processing was restarted, so that in 2017, shipments were approximately 76% of the 2010 level.

The trade in fruit trees in Fukushima Prefecture is an important industry, and can be reflected in the status of peach trees. Figure 11.4a shows the mean price at the central wholesale market for peaches produced in Fukushima Prefecture. The mean price in the prefecture was ¥438 in 2010, before the disaster, but it decreased to ¥222 in the year of the disaster. Subsequently, as recovery continued, it reached ¥429 in 2015, which was equal to the 4-year predisaster mean. In 2018 and 2019, the mean sale price was approximately ¥500, which was even higher than before the disaster. However, this interpretation may be subjective, and in order to explain this, Fig. Y has been prepared as a follow-up of the national mean sale price shown in Fig. 11.4b. When the mean sale prices of peaches in Fukushima Prefecture and the whole of Japan are compared, the FDNPP disaster caused sales and economic problems. The price of peaches in Fukushima Prefecture before the disaster was ¥20–¥50 below the national mean. This price differential was linked to the production volume and marketing routes in Fukushima Prefecture, although no major fluctuation in that respect is shown here. In contrast to prices only within Fukushima Prefecture, in 2018 and 2019, the mean price of peaches produced in Fukushima Prefecture was nearly ¥100 less than the national mean. Over the past 10 years, Japanese peach production has been supported by the national policy of establishing high prices and high demand, especially in relation to overseas exports, and production can be seen to have increased markedly as a result. In the context of this expansion of the industry itself, production in Fukushima Prefecture has been unable to ride the tide of high-price sales, such that the difference from the national mean has widened as the latter has increased. The period from 2010 to 2020 was one of marked growth in Japanese peach production, but in Fukushima Prefecture, it was a period of recovery from the earthquake-related disaster, and the opportunity to achieve high-price sales was thus missed. This “lost decade” due to the FDNPP disaster means that the earthquake had a major negative impact on fruit production in Fukushima Prefecture.

Fig. 11.4
Two line graphs plot yen per kilogram versus year labeled a and b. Some of the values for a are as follows. (2008, 429), (2012, 222), (2018, 409). Some of the values for b are as follows. Fukushima prefecture (2008, 429), (2012, 222), (2018, 409). National average (2008, 447), (2012, 388), (2018, 534).

(a) Changes in the average unit price of peaches produced in Fukushima Prefecture at the Tokyo Central Wholesale Market (From Ministry of Agriculture, Forestry and Fisheries (Japan) (2021)). (b) Changes in the average unit price of peaches produced in Fukushima Prefecture and national average at the Tokyo Central Wholesale Market (From Ministry of Agriculture, Forestry and Fisheries (Japan) (2021))

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11.7 Conclusions and Future Issues

The radiocesium concentration in fruit in the second year after the disaster was found to be approximately one-third of that during the first year, and by the third year, it had again fallen to a third; this rate of decrease is greater than that due to the half-life predicted by physics (Kusaba et al. 2015a, b; Renaud and Gonze 2014; Takata 2016, 2019; Yuda et al. 2014). These findings were similar to those reported from several studies on fruit trees after the Chernobyl disaster (Antonopoulos-Domis et al. 1990, 1996; Madoz-Escande et al. 2002; Mück 1997; Pröhl et al. 2006). However, there are interspecies differences in the pattern of radiocesium concentration decrease in fruit. In yuzu (a small, sour citrus fruit; Citrus junos) and persimmons, certain trees have especially high concentrations in the same orchards, but the cause of this has not been sufficiently determined (Sekizawa et al. 2019). With respect to long-term changes in radiocesium concentration in fruit trees, there have been few follow-up studies at the same sites (Tagami 2016), and it is uncertain what changes will occur in future. In this respect, it is important not only to perform follow-up studies on concentrations in fruit, but also to ascertain the level of radiocesium, in terms of both concentration and absolute quantity, in the fruit trees from which fruit is taken. In previous studies on fruit trees, it has been shown that radiocesium in the soil makes almost no contribution to radiocesium in the fruit, and the following explanations for this have been put forward: (1) in Japan, even in annual crops, the coefficient of transfer to the fruit is low; (2) uptake of radiocesium deposited directly on fruit trees into the tree via the bark is not complete, and radiocesium in the tree makes a major contribution to the radiocesium concentration in the fruit (Takata et al. 2012c, 2013a); (3) radiocesium in the tree still remains there the following year, so that is the origin of radiocesium in the fruit (Takata et al. 2013a, b); and (4) radiocesium is currently distributed heterogeneously in the upper layers of the soil only; most fruit trees grown in Fukushima Prefecture (excluding blueberries) do not form their main root zones in the top 5 cm of soil, which would be responsible for the uptake of radiocesium (Kusaba et al. 2016; Sato et al. 2019; Takata et al. 2013b). Suggestion (4) is linked to the fact that fertilization with potassium is usually ineffective. It is therefore necessary to perform a follow-up study on the trees that produce radiocesium in the fruit. It is important to note that the accumulation of high levels of radioactive cesium in the upper soil layers of orchards is not only related to the safety of the agricultural products produced, but also to the safety of the growers’ operations. In relation to yuzu trees growing in the lower parts of the slopes, it is suspected that radiocesium was absorbed via the roots due to flooding caused by heavy rain (Sato et al. 2019). It is necessary to perform long-term monitoring of the potential for radiocesium uptake via the roots. Little progress has been made with measures to decontaminate orchards by topsoil-stripping, and there are numerous orchards where the established guidelines (Ministry of the Environment (Japan) 2011) have still not been met (Sato et al. 2019). There is therefore also a need for long-term, continuous measurement of the aerial radiation dose rate.

In Fukushima Prefecture, 8 years after the disaster, some fruit-growing regions are specified as evacuated areas, and measures to restart commercial agriculture in these areas have yet to be established. In areas where almost no radioactive nuclei have been detected, problems in terms of consumption behavior remain. With no direct relationships to radioactive nuclei, this has been linked to the phenomenon of “misinformation.” A major factor involved in this phenomenon is considered to be the delays in updating information for consumers. As a result, even when accurate data is obtained, neither the environment of the sender nor the receiver of that information is satisfactory. In the Tokyo region, which is a major consumption area, opportunities to transmit information about fruit radiocesium concentrations are much fewer than in Fukushima Prefecture. The current situation is disheartening, as straightforward, positive information about areas where cultivation is currently possible and acceptable, which is gradually being accumulated and collated, does not catch people’s attention as much as sensational information about specified safety levels having been exceeded. In addition, in terms of the positioning of fruit in the Japanese market, one difference from other products is the strong perception of fruit being sold as gifts. There are differences between consumption behavior relating to items for gifts and for use in one’s own home. For example, once an alternative avenue for gifts has been identified, it is difficult for the original production site to win those consumers back. Long-term monitoring is as important as the safety survey soon after the disaster. Scientific issues pertaining to this problem must be investigated continuously in 10-year intervals, and the aspect of this being a scientific study must be emphasized. The study must also be accompanied by firm and clear statements that do not misconstrue concealed safety concerns.

The fruit tree industry does not depend solely on production. Making progress with a wide range of research, from studies performed close to the production site with the aim of reducing radiocesium levels to analysis of the consumption psychology of the actual purchasers, should provide a boost that will lead to sales price recovery.