Research and management challenges following soil and landscape decontamination at the onset of the reopening of the Difficult-To-Return Zone, Fukushima (Japan)

. Twelve years after the nuclear accident that occurred at the Fukushima Dai-ichi Nuclear Power 15 Plant in March 2011, radiocesium contamination (with a large dominance of 137 Cs, with a 30-years half-life) remains a major concern in various municipalities of Northeastern Japan. The Japanese authorities completed an unprecedented decontamination programme in residential and cultivated areas affected by the main radioactive plume (8953 km²). They implemented a complex remediation programme scheme relying on different decision rules depending on the waste type, its contamination level and its region of origin, 20 after delineating different zones exposed to contrasted radiation rates. The central objective was not to expose local inhabitants to radioactive doses exceeding 1 mSv yr -1 in addition to the natural levels. At the onset of the full reopening of the Difficult-to-Return Zone in Spring 2023, the current review provides an update of a previous synthesis published in 2019 (Evrard et al., 2019). Although this ambitious remediation and reconstruction programme is almost completed, in the 12 municipalities of Fukushima Prefecture in 25 which an evacuation order was imposed in at least one neighbourhood in 2011, from the 147,443 inhabitants who lived there before the accident, only 29.9% of them had returned by 2020. Waste generated by decontamination and tsunami cleaning/demolition work is planned to have been fully transported to (interim) storage facilities by the end of 2023. The cost of the operations conducted between 2011–2020 for the so-called ‘nuclear recovery’ operations (including decontamination) was estimated by the Audit Board 30 of Japan in 2023 to 6122.3 billion yen (~44 billion euro). Decontamination of cropland was shown to have impacted soil fertility, and potassium fertilization is recommended to limit the transfer of residual radiocesium to new crops. In forests that cover 71% of the surface area of the Fukushima Prefecture and


Introduction
The Fukushima Dai-ichi Nuclear Power Plant accident (FDNPP) that occurred in March 2011 resulted in the emissions of large quantities of radionuclides into the environment (Morino et al., 2013).Among these radionuclides, more than 10 years after the accident, radiocesium is the most problematic substance (mainly for its longer-lived 137 Cs isotope (T 1/2 = 30 years) as less than 10% of the shorter-lived 134 Cs isotope (T 1/2 = 2 years) emitted initially in similar quantities as 137 Cs was still found in the environment by 2022).The fraction of other isotopes such as those of plutonium that was supplied by FDNPP accident and that were detected shortly after March 2011 in environmental samples (2011)(2012)(2013) were no longer detected during the last years (Diacre et al., 2023).As the main radioisotope being found in the vicinity of FDNP twelve years after the accident, 137 Cs is a gamma emitter that is quickly bound to clay minerals (mainly micas such as illite and vermiculite), which show frayed-edge sites with high selectivity for Cs + cations (Cremers et al., 1988;Okumura et al., 2018).Accordingly, 137 Cs may therefore persist in soils and contaminate them for several decades, which may prevent them to fulfil their functions and provide the expected ecosystem services (Keesstra et al., 2016).Possible exposure of organisms to radiations emitted by radiocesium found in soils and other environmental compartments together with the food chain contamination justified the evacuation and/or the decontamination of those zones exposed to radiation dose rates exceeding a given thresholdi.e., typically 20 mSv yr -1 in emergency conditions and 1 mSv yr -1 in 'normal' conditions as recommended by ICRP (2020) - (Lyons et al., 2020).Although the impact of high radiation doses is debated in Fukushima, a recent study showed the natural rewilding of the Fukushima landscape following human abandonment, and suggested that if any effects of radiological exposure in mid-to large-sized mammals in the Fukushima Exclusion Zone existed, they occurred at individual or molecular scales, and did not appear to manifest (or have not yet manifested) in population-level responses (Lyons et al., 2020).
Another potential issue associated with 137 Cs is related to the fact that different types of microparticles bearing this radioisotope were found in the environment and that their inhalation may lead to specific health risks (Hagiwara et al., 2021;Okumura et al., 2019;Miura et al., 2018).Contrary to the situation observed after the Chernobyl accident where a large (i.e., 30 km-radius zone) contaminated area remained evacuated and abandoned for several decades, resulting in a large scale rewilding of the area (Fesenko et al., 2022), the Japanese authorities decided to conduct ambitious decontamination works in residential and cultivated areas affected by the main radioactive plume (Yasutaka and Naito, 2016).Different zones were delineated to organise decontamination works depending on the initial radioactive contamination levels found in these zones and the resulting exposition of inhabitants and workers to radiation dose rates.The long-term goal was to keep individual exposure doses below 1 mSv yr -1 or 0.23 µSv h -1 (reference level of exposure dose in normal times as recommended by the International Commission on Radiological Protection -ICRP).In immediate post-accidental conditions (so-called "emergency exposure situations"), higher dose exposure levels have been allowed (the 20 mSv yr -1 level was set in Japan for residence, which corresponds to a level 3.8 µSv h -1 as it takes into account the fact that people spent max.8 hours day -1 outdoors and 16 hours day -1 indoors, with indoor dose exposures being 40% of those outdoors).A level of 5 mSv yr -1 or 2.5 µSv h -1 has also been defined to enforce the individual dose control for workers (e.g.decontamination works, working in forests) in exposed areas of Japan.
As a result of the progressive radioactive decay and the associated decrease in air dose rates with time, evacuation orders have been gradually lifted in some areas, while they were maintained in the areas exposed to the highest radiation dose rates (i.e., Difficult-to-Return Zone -DTRZ or 帰還困難区域 in Japanese; Figure 1).
The 20-mSv yr -1 threshold remained the main guide to delineate these zones, as the so-called DTRZ corresponds to the area where exposure dose was expected to exceed this value even 5 years after the accident (i.e. by 2016).
To allow reopening these SDZ and DTRZ zones, decontamination was conducted across wide areas of Fukushima and neighbouring Prefectures in Japan, starting with the less contaminated areas (i.e., Intensive Contamination Survey Areas -ICAs; 汚染状況重点調査地域 in Japanese) followed by the Special Decontamination Zone -SDZ (除染特別地域) (Evrard et al., 2019) and, finally, parts of the DTRZ (Figure 1).Decontamination has been completed between 2017-2019 in the ICAs and in the SDZ, with the progressive transfer of remediation waste to interim storage facilities built in Okuma and Futaba Towns (Figure 2).After a partial reopening in 2022, several additional portions of the DTRZ will be reopened from 2023 onwards without obligatory decontamination except in "Special Reconstruction and Revitalization Zones" (特定復興再生拠点区 域) (Figure 2).Nevertheless, residential and cultivated zones of the DTRZ located outside of these Specific Reconstruction and Revitalization Zones may be decontaminated as well, in response to the local residents' willingness to see their property remediated.According to the definition given by the Japanese Ministry of Environment, a "Specific Reconstruction and Revitalisation Zone" is an area within the DTRZ where environmental rehabilitation projects, such as decontamination and house demolition, are being promoted together with infrastructure development in order to lift the evacuation order.These zones, made possible following Amendments made to the Fukushima Act on Special Measures for Reconstruction and Revitalisation (Act No. 25 of March 31, 2012) (Cabinet Order, 2012), are set up by the Mayor of the municipality, and a plan is prepared and needs approval from the Prime Minister.
The plan is being undertaken and completed within five years after approval, and its completion will allow to lift the evacuation order.
In this unique transition context, it is timely to provide an updated synthesis and feedback after an initial review article published in 2019 (Evrard et al., 2019) regarding the completion of this unique remediation programme.
The goal is to make the latest information available to the international community and to identify the main challenges for ongoing and future research at the time when the Fukushima DTRZ will be reopened (i.e.Spring 2023).Although the current article will mainly focus on the resumption of forestry and agricultural activities in the main plume, it will also address the impacts of decontamination on transfers of radionuclides in different terrestrial environments.Of note, the general transfers of radionuclides in Fukushima environments were also covered by recent comprehensive synthesis articles (Table 1), although not with a focus on the impact of decontamination.In contrast, the current article will not address the fate of radioactive contamination in coastal and marine waters, which can be found elsewhere (Table 1).
Table 1.Selection of other review articles and reports dealing with specific radionuclide transfer processes or remediation techniques along with their social impacts in different environmental conditions.

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The privileged option is rather to identify the lessons of that unprecedented soil decontamination programme, as well as the gaps and needs in remediation actions.After summarizing the calendar for reopening, data on people having returned and the costs of the remediation works, the challenges for restarting soil cultivation in the remediated cropland will be discussed.Then, focus will be laid on decontamination tests and methods in forests, as these areas covering ca.75% of the fallout-impact region have not been remediated at this stage (with the exception of 20m-wide buffer strips around houses and roads), and radionuclide cycling remains active in these zones.Furthermore, the potential export of radionuclides stored in soils under forests will also be addressed, as this may provide a long-lasting source of contamination to downstreamremediatedor non-decontaminated environments.The situation in ponds and reservoirs where 137 Cs may be remobilized from sediment will also be examined.Finally, the main challenges for ongoing and future research will be synthesized.(where only a small part was located within the DTRZ).

Progress and cost of remediation works
Updated information related to decontamination is regularly provided in Japanese language on a specific website of the Japanese Ministry of Environment (http://josen.env.go.jp/), although much less information is regularly communicated in English.For the aggregated costs, information was made available from the above-mentioned extensive report of the Board of Audit of Japan published in February 2023 (Board of Audit of Japan, 2023).
The management of radioactive waste (i.e., containing at least 8000 Bq kg -1 of radionuclides) depends first on the nature of the material, i.e. whether it consists of soil/vegetation resulting from decontamination works (referred to as category 1) or whether it consists of debris related to the tsunami or to the demolition operations in residential settlements (referred to as category 2; Figure 3).For the second category of waste, a threshold of 100,000 Bq kg -1 of 137 Cs has been set to determine the disposal location of this material.
Wastes from the area where countermeasures were implemented (so-called 'specified waste') outside of the DTRZ and with a 137 Cs content lower than 100,000 Bq kg -1 are being stored in a specific disposal site open in Tomioka Town on 17 November 2017 (Figure 2).For the waste originating from the DTRZ, it is being disposed at the Clean Centre (クリーンセンター) in Futaba Town as decided on 5 August 2022 (Figure 2) (Japanese Ministry of the Environment, 2023a) along with the domestic waste produced in the 8 municipalities of the Futaba County (including Hirono Town, Naraha Town, Tomioka Town, Kawauchi Town, Okuma Town, Futaba Town, Namie Town and Katsurao Village and covering a surface area of 866 km²).
Regarding the waste resulting from decontamination (soil and vegetation; category 1), as of 7 March 2023 (Japanese Ministry of the Environment, 2023a), the progress of these operations has exceeded 90%, with the latest work being completed in the special reconstruction and revitalization zones of the DTRZ.
Out of a total of 1,372 temporary storage sites scattered across the landscapes in the Fukushima Prefecture, by February 2023, 31 sites were still storing soil to be removed, 1,341 had seen their waste being completely removed, and 1,070 temporary storage sites had been restored to their original state.13.43 million m 3 of this waste had been transported to interim storage facilities.The soil removed from these sites was sorted and processed, and as late February in 2023, approximately 11.54 million m 3 of this waste was stored at the interim storage facilities.Furthermore, 17,382 steel rectangular containers filled with ash dust mainly resulting from biomass combustion was stored at the same facilities by February 2023.At the end of January 2023, approximately 1.42 million tonnes of waste had been treated at each at the temporary incineration facilities operated by national authorities.Wood crushers are being used to limit the volume of waste from forests (with corresponding volume reduction rates between 45-63%) and combustible waste (i.e.fallen leaves and branches) is being incinerated at these temporary facilities with a very high volume reduction (96-99%) and a very low transfer of 137 Cs to exhaust air (≤0.3 Bq m -3 ) (Hashimoto et al., 2022a).Special attention is nevertheless being required for the subsequent management of combustion ash with high 137 Cs concentrations (> 2,000,000 Bq kg -
In accordance with the Act on Special Measures Concerning the Handling of Contamination by Radioactive Substances, the specified waste containing more than 100,000 Bq kg -1 of 137 Cs is also being stored at these interim storage facilities in Okuma and Futaba towns that became operational in October 2017.These facilities covered a total area of 1285 ha acquired from 1853 land owners by late February in 2023 (orange surface areas on Figure 2).According to the Japanese law, this material is supposed to be transported to final disposition sites located outside of the Fukushima Prefecture at locations that remain to be selected by 2047 (i.e., 30 years after the interim storage facilities became operational).
The costs of the recovery and reconstruction operations conducted by the Japanese authorities following the Great East Japan Earthquake and the associated nuclear accident at FDNPP during the period comprised between 2011 and 2020 were recently synthesized by the Board of Audit of Japan in February 2023 (Board of Audit of Japan, 2023).A conversion rate of 1 EUR = 140 yen (as of January 1 st , 2023) was used in the current text.They estimated that the total of these costs reached 38,171.1 billion yen (~273 billion euro), with a provisioned and remaining budget of 6144 billion yen (~44 billion euro).Among these costs, 20% of the budget (7745.6 billion yen; ~55 billion euro) was devoted to reconstruction/public works and 16% of the budget (6122.3 billion yen; ~44 billion euro) was spent for the 'nuclear recovery policy' including decontamination.Most of the provisioned and unused budget by 2020 is expected to be spent on reconstruction/publics works (34% of residual budget; 2094 billion yen; ~14 billion euro) and nuclear recovery (22%; 1343.9 billion yen; ~9.6 billion euro).For the period between 2011-2020, as the annual budget of the State of Japan varied from ~90,000 to ~100,000 billion yen /year (~700 to 800 billion euro), this demonstrates that the budget spent on the reconstruction following the Great East Japan Earthquake and the associated nuclear accident at FDNPP was far from negligible.

Recultivation of cropland
In the least contaminated cropland fields (with typical 137 Cs activities < 5000 Bq kg -1 ), tillage and topsoil/subsoil interchange provided a common countermeasure (Evrard et al., 2019).A study conducted at an experimental site of the ICA zone (Ibaraki Prefecture) between 2011-2017 confirmed that 137 Cs concentrations in both soils and crops (i.e., soybean) decreased exponentially with time elapsed since the accident as a result of tillage operations (Li et al., 2019).In contrast, in paddy fields and other cropland with 137 Cs levels exceeding 5000 Bq kg -1 (covering a surface area of ~827 km² in Fukushima Prefecture) (Nakanishi, 2018), a major countermeasure for soil decontamination has generally consisted in the removal of the 5-cm upper layer concentrating radiocesium.
In the SDZ and DTRZ, the soil removal was compensated by the addition of crushed granite and/or saprolite extracted locally and its mixing with the residual initial soil profile (Evrard et al., 2019).In the official reports and guideline books, this practice is justified by the need to supply "fresh", "clean" or "new" soil "in order to ensure the conditions that enable resumption of agricultural production are restored"(Japanese Ministry of Environment, 2013).However, this decontamination process may have led to a decrease in fertility of these soils and enhanced erosion, with strong heterogeneities within the fields (Inoue et al., 2020).Technical developments are currently under progress to contribute to the rapid assessment of soil fertility in this context based on hyperspectral reflectance measurements (400-2500 nm) of soil samples, and the subsequent calculation of spectral index algorithms (Inoue et al., 2020).
Another commonly applied countermeasure is the application of potassium (K) fertilizers in order to promote the K-Cs (as an analogue) competition at the soil solution-root interface and reduce the root uptake of radiocesium by crops (Zhu and Smolders, 2000).The positive effect of potassium fertilizer on radiocesium transfer to vegetation has been widely studied in post-Chernobyl studies; that countermeasure is most effective in soils with naturally low levels of exchangeable potassium.As a remedial action in contaminated soils of Fukushima Prefecture, increasing exchangeable potassium up to 25 mg K2O 100 g −1 in soil was recommended for agricultural soils where the concentration of exchangeable potassium was inferior to that level (Japanese Ministry of Agriculture, 2013).Furthermore, recent research based on field experiments demonstrated that a complementary soil property (i.e. the non-exchangeable K) and a level < 50 mg K2O 100 g −1 could be used as another threshold for use along with that of exchangeable K (<25 mg K2O 100 g −1 ) to identify soils that would need additional K fertilization (Kurokawa et al., 2020).Another field of research is devoted to the optimization of agricultural practices for the K budget.For example, Nishikiori et al. (2020) investigated the plant-available K budget at the field scale, by comparing two fields with different soil textures and drainage conditions.The major inputs of K to the fields were shown to be fertilization, straw return and irrigation, while the major outputs were plant harvesting, surface runoff and water percolation.Nevertheless, most K harvested with the plants (85%) was brought back to the soil by straw return.In contrast, water percolation and surface runoff were the dominant output pathways, with most of K being discharged from the fields before mid-summer drainage, contributing significantly to the general negative K balance comprised from -20 to -289 kg ha -1 ).A careful irrigation adapted to the soil conditions is thus recommended to reach a more appropriate K budget in soils in order to limit the radiocesium transfer to the plants.
The potential transfers of radiocesium via irrigation water in paddy fields also remain a matter of concern.The monitoring of total and dissolved radiocesium in irrigation water, rice and soil from two decontaminated paddy fields showed that 85% of radiocesium in irrigation water was not exported and remained in the field (Shin et al., 2019).However, the quantity of additional radiocesium supplied by irrigation water was negligible (~0.08% of the initial inventory) compared to the initial supply by radioactive fallout in 2011.This resulted in very low soil to brown rice transfer factors of radiocesium (0.0015-0.0068).
In parallel to these studies investigating the transfer of radionuclides in cultivated land, strict controls were implemented by Japanese authorities to monitor radiocesium concentrations in food products.Accordingly, between 2012 and 2021, more than 2.5 million samples of food products were analysed for radiocesium (Nakamura et al., 2022).The Japanese radiocesium permitted levels (i.e. 100 Bq kg -1 for general foodstuff and 10 Bq kg -1 for drinking water) were not exceeded in more than 99% of the samples analysed, and they were never exceeded in recent years.Despite these low levels of contamination detected in foodstuff, Japanese food shipping restrictions remained imposed by many countries (including the European Union following Regulation 2016/6, China and South Korea), by 2023, despite the U.S. Food and Drug Administration (FDA) deactivated its import alert in September 2021 (US FDA, 2023).

Radionuclide cycling in forests and contamination of forest products
The situation in forests should receive a particular attention, as they cover 71% of the surface of Fukushima Prefecture (ca.970,000 ha) (Hashimoto et al., 2022c).Evergreen coniferous trees (Japanese cedar -Cryptomeria japonica, Japanese cypress -Chamaecyparis obtusa, red pine -Pinus densiflora) used for construction timber account for about 40% and deciduous trees (konara oak -Quercus serrata)mainly for papermaking materials and mushroom cultivationfor about 60% (Hashimoto et al., 2022d).Before FDNPP accident, the Abukuma Highlands were actively used for cultivating trees (mainly konara oak) for producing mushroom logs.
The FDNPP accident atmospheric fallout was at the origin of the contamination of 2600 km² of forests with radiocesium levels exceeding 100 kBq m -2 , which should be compared to the 360-km² surface area of cropland affected by those levels (Onda et al., 2020).Overall, 60-90% of radiocesium that fell on cedar and cypress forests was first intercepted by the canopy (leaves and branches) and partially absorbed by the foliage.In contrast, the leaves of deciduous trees had not burst yet, and the level of fallout trapping was therefore lower in broadleaf forests (Hashimoto et al., 2022b;Kato et al., 2019b).Then, radiocesium was rapidly transferred by water (throughfall and stemflow) and defoliation (litterfall) towards the forest floor and the underlying mineral soil, which represented the most important pools of radiocesium a few years after the accident.Vertical redistribution of radiocesium between forest floor and mineral layers was established within 1-2 years after the fallout and changed slowly thereafter.The rapid accumulation in topsoil layers is likely related to the relatively wet climate, which promoted the early vertical migration of radiocesium in numerous Japanese forests.In the mineral soil layer, radiocesium is firmly retained on mineral soil particles and its content peaks at shallow depths (typically < 5 cm) (Hashimoto et al., 2022b).However, despite the current low migration with depth, bioturbation by organisms may also contribute to further soil and associated radiocesium transfer across the soil profile.
In contaminated forests, both the forest floor and the topsoil layers now represent significant reservoirs of radiocesium available for root uptake by trees and understory species.That phenomenon is the predominant cause of the long-term radiocesium recycling associated with the biomass turnover and that of a possible longlasting contamination of forest products (Goor and Thiry, 2004).Variability in stemwood contamination (i.e., the trunk excluding the bark) is expected to depend on various factors: time after fallout, tree species and age, position in the stand, radiocesium and K contents in the soil, etc. (Ohashi et al., 2020).Initial vertical and radial movement of radiocesium within the stemwood and its redistribution between sapwood and heartwood has been variable depending mainly on tree species (Ota and Koarashi, 2022).Radiocesium content and distribution in stemwood of both coniferous and deciduous trees is now approaching the equilibrium state, although a higher 137 Cs concentrations in heartwood of cedars compared to oaks remains under investigation (Hashimoto et al., 2022b).An aggregated transfer factor for different major tree species has been proposed to calculate the tree organs contamination in radiocesium taking into account the total surface contamination levels estimated by airborne surveys (Hashimoto et al., 2020c).However, the proportion of radiocesium remaining in the forest floor of different forests remains quite variable (Imamura et al., 2020), which may induce uncertainty in further recycling by trees as radiocesium found in the organic layer (devoid of clay minerals) is usually much more bioavailable for root uptake (Thiry et al., 2000).A field monitoring of radiocesium bioavailability in soils was conducted at two neighboured forest sites (one with Japanese cedar, the other with konara oak) of Kawauchi Village between 2011-2017 (Manaka et al., 2019).An exponential decrease in the proportion of exchangeable 137 Cs was observed in organic and mineral soil layer samples at both sites.The proportion significantly decreased within 2-4 years after the accident, becoming almost constant thereafter (2-4%).These results support the interpretation that contaminated forests have entered a steady-state phase of 137 Cs cycling.Several articles on tree contamination with time have been published in recent years and they all confirm similar findings, which increases our confidence in these results (Gonze et al., 2021;Yoschenko et al., 2022).
The fate of radiocesium cycling in forests can also be anticipated with numerical modelling.Recent simulations showed that initial foliar absorption by coniferous trees and subsequent internal transfers promotes the radiocesium persistence in trees and thus have a strong possible impact on the early phasing of tree contamination (Thiry et al., 2020;Thiry et al., 2018).The simulated contribution of foliage and root uptake to the tree contamination were equivalent 10-15 years after the atmospheric deposits, but the further root uptake was too low to compensate the activity decline in the tree with time.In a model inter-comparison for Japanese forests (Hashimoto et al. (2020a), convergent simulations confirmed that an equilibrium state in tree wood contamination is reached ca. 10 years after the initial fallout, even in konara oaks, and that they then decline slowly.The highest uncertainty in the simulations of wood contamination remains for newly planted trees, where root uptake is the only pathway.These results indicated that the parametrization of long term net root uptake remains uncertain without additional field monitoring.
Although there is no restriction on the use of wood as a building material, wood contamination in particular represents a problem for log production for mushroom cultivation and fuel chips production, not only in Fukushima Prefecture but also in neighbouring Prefectures of Japan (due to the lower 137 Cs limits -40 or 50 Bq kg -1 max.allowed for these uses of wood) (see Table 2).Debarking of trunks can lower 137 Cs concentrations to allow the use of the wood for biofuel production, although care will have to be taken to manage the resulting ashes (Hashimoto et al., 2022a).A technology for methane fermentation of contaminated wood biomass has also been tested (Hashimoto et al., 2022b), with the methane gas produced devoid of radiocesium, which was recovered instead in the fermentation digestate.However, decontaminating digestate before its use as a common fertilizer remains problematic (Kobayashi et al., 2020).New challenges may involve the management of abandoned contaminated fields and certain waste substrates using new forests or short rotation coppice dedicated to bio-fuel production.That implies the in situ radiological control of radiocesium cycling on long timescales through appropriate and sustainable methods of biomass cultivation adapted to the Japanese ecological conditions and its conversion into energy as it was tested in post-Chernobyl studies (Vandenhove et al., 2001;Thiry et al., 2001) and, more recently, in post-Fukushima experiments (Kobayashi et al., 2013).Tree logs soaking and/or further wood chips/sawdust washing in presence of a suitable radiocesium absorbent (e.g.Neda (2013) represent other potential countermeasures, which still need to be tested or improved for the Fukushima conditions.For Chernobyl contaminated forests, the study of Shaw et al. (2001) revealed that a cost-effective management strategy would also require novel alternative uses of forest products, which could provide added value to the standing crop in return for small increase in public and worker doses.In that context, Dubourg (1996) recommended a radiological clean-up approach involving both the incineration of the most contaminated parts of the tree and the branches, and the transformation into paper pulp of the less contaminated part of the trunk.Another idea that emerged after the Chernobyl accident but that was never tested (personal communication: Y. Thiry) and that remains debated would imply a shift in the local use of wood products through e.g. the production of wood shingles after a special treatment of standing coniferous trees through debarking.As practiced in Scandinavia from the early medieval period, the debarking provokes the decline of the tree together with the resination of the stemwood.After several years of tree decline, the natural impregnation of the timber is supposed to be associated with a loss of potassium in stemwood and by analogy with a removal of radiocesium.Shingling (itabuki -板葺) using cedar wood was widely used in forest areas of Japan and even in urban areas until the end of the Edo period (1603-1867)(Japanese Architecture and Art Net Users Systems, 2001).Hopefully, by promoting a natural decontamination of wood, such a practice, once adapted, could also provide a source of added-value and revitalization for the local wood industry in contaminated forest areas.with nature and collect edible food from forests (including plantsreferred to as sansai or 山 菜and mushrooms).Because of the high contamination found in forests and its static character, the absence of decontamination and the ability of these organisms to absorb radiocesium efficiently, they represent the vast majority of food products exceeding the standard limit of 100 Bq kg -1 (Hori et al., 2018), with the dominance of wild plants in Spring and that of mushrooms in Autumn (Hashimoto et al., 2022a).As of Nov. 2020, shipping restrictions on mushrooms had been imposed by 117 municipalities in 11 Prefectures (Figure 4).
It is impossible to provide a comprehensive list of species to avoid collecting, as there are 4000 -5000 species of wild mushrooms in Japan.Nevertheless, a study showed that although 76% of the mushrooms collected between 2016-2019 in Kawauchi Village located nearby the DTRZ exceeded the maximum allowed threshold of 100 Bq kg -1 in 137 Cs, the committed effective dose due to consuming mushrooms was lower than 1 mSv per year (Cui et al., 2020). 137Cs concentrations in mushrooms were found to be related to the soil contamination, and normalized concentrations allow comparisons between regions/species.In general, as observed in Chernobyl-contaminated forests, mycorrhizal fungi living in symbiosis with trees have higher 137 Cs concentrations than saprotrophic fungi, obtaining their nutrients from decomposing dead wood and leaves (Komatsu et al., 2019).However, this general result was counterbalanced by the fact that some species showed a different behaviour, which justifies the general prohibition of all mushrooms in a wide area across Northeastern Japan as a matter of precaution.In a similar way as for wild mushrooms, 137 Cs concentrations were found to be strongly variable in wild plants, with some plants showing noticeably higher contamination levels, e.g.koshiabura (Eleutherococcus sciadophylloides) and some cooking techniques were found to be effective to decrease 137 Cs levels in wild plants, e.g.

Hashimoto et al. (2022a
).There has also been a large impact in recreational activities, with a large decrease in the number of climbers and fishers visiting the Fukushima Prefecture, along with a similar decrease of urban visitors.
In addition to wild mushroom picking, mushroom cultivation is very popular in Japan and it represented 80% of the non-wood forestry production in 2017 (i.e. the non-wood forestry production excluding timber, which accounted for 43% of the total forestry production in Japan).Two techniques are being used, i.e. bed-log cultivation (mainly used for shiitake production) or sawdust medium cultivation, with the second technique becoming increasingly dominant in recent decades in Japan (as it is less man-power consuming and given the increasing preference of the Japanese population for mushrooms other than shiitake).Of note, wood-log standards are more stringent than those associated with sawdust, and the concentration of sawdust can then be adjusted to meet the standards.The increase in sawdust cultivation was further accentuated after the FDNPP accident, with the restriction of the production and shipment of shiitake mushrooms across a wide area in Japan.
The problem is that wood (mainly of konara oak -Quercus serrata) from the Fukushima Prefecture (e.g. Abukuma Mountains) was not only used for the local production of shiitake but also to provide the mushroom logs used for the production carried out in other Japanese Prefectures.This production had to be stopped because of the very high levels of 137 Cs (up to more than 10 times the index value) recorded in the production region (Hashimoto et al., 2022a).Interestingly, as observed for cultivated soils, a strong negative correlation was observed between radiocesium concentrations in the most recent branches of konara oak and exchangeable K in the soil surface (0-5 cm depth) layer (Kanasashi et al., 2020).Since mushroom log production requires a 20-year cycle, a long term monitoring may open the way to a better use of konara oaks grown on soils with high concentrations of exchangeable K to produce less or even uncontaminated wood.

Decontamination of forests
Forest decontamination methods can be subdivided into two groups: (i) the measures actually implemented in Fukushima-impact zones and (ii) those evaluated for research or practical issues.As of (i), only the area located within 20 m of the forest edges (bordering residential areas, roads and other living areas) were treated.In this buffer zone, the vegetation and contaminated organic layer (litter and humus) is gathered and transported out of forests.Among the potential methods investigated although not implemented widely (ii), the removal of the forest floor litter layer had soon been considered as a potential method for reduction of tree contamination in experimental studies.Removal of forest floor was likely to be more useful when operated after the peak of transfer of radiocesium from the above ground parts of trees to the organic layer (Thiry et al., 2018).That peak typically occurs around 3-5 years after the initial deposition, although the time period varies with tree species and soil organic layer characteristics (IAEA-TECDOC-1927, 2020).Koarashi et al. (2020) tested the impact of litter removal conducted in a broadleaf forest in July 2014 (i.e., more than 3 years after the accident).They observed no effect on tree contamination and a decrease of litter 137 Cs contamination in the 1 st year following remediation and suggested that this method should be applied even more rapidly (within 1-2 years) after the accident, before the significant transfer of 137 Cs from litter to the underlying mineral soil.For coniferous stands, Thiry et al. (2018) indicated a low response of tree contamination to litter removal even in the long term, because the initial 137 Cs foliar absorption is more influential than the root pathway for a long time.
In addition, clear-cutting (i.e.cutting all trees) and thinning (i.e.partial cutting) can be implemented, however, their additional contribution to decrease air dose rates could not be demonstrated.Potassium fertilization can therefore be used to limit the absorption of radiocesium by the plants, as demonstrated for konara oaks (Kobayashi et al., 2019).
In parallel to these decontamination issues, it should be stressed that the absence of forest management in manmade forests can lead to other problems, such as the spread of insects and diseases.Forest maintenance includes planting, clearing, thinning and maintenance of forest roads, which are crucial to avoid a degradation of different forest functions (e.g.carbon sequestration, wood production, landslide control).Moreover, thinning and other particular silviculture treatments remain important for reducing fuel load and fire hazard, or just for implementing strategic fuel breaksi.e. through converting one strip of land from one vegetation type to another for firefighting purposes, as experimented in Chernobyl forests (Ager et al., 2019).Still, the forest area which has been maintained in the Fukushima Prefecture has decreased by ca.50% from 2011 onwards as a result of the access restrictions due to high dose rates (Hashimoto et al., 2022a).Restrictions have also been imposed on the shipping of wildlife meat (i.e.wild board, Asian black bear, Sika deer, Spot-billed duck, green pheasant, copper pheasant) in the Fukushima Prefecture and/or in nearby Prefectures because of their excessive muscle contamination in 137 Cs.These shipping restrictions along with a decrease of the hunter numbers and of the capture pressure (i.e., number of captures per hunter) observed all across Japan led to wildlife population expansion.Wild boar proliferation, in particular, leads to extensive damage to houses and crops in the main 137 Cs-fallout-impacted area (Hashimoto et al., 2022a).A recent study analysed 137 Cs concentrations in wild boar muscle samples (n=221) collected from the DTRZ and surrounding areas between 2016 and 2020.This research outlined higher activity concentrations observed in the DTRZ compared to the surrounding areas, and an overall decrease of 137 Cs values with time (Saito et al., 2022).Seasonal variations in 137 Cs muscle concentrations were also observed, and these may be related to changing food habits and the fractions of available 137 Cs in the material ingested by wild boars (Saito et al., 2020).Nevertheless, these seasonal variations were shown to be less pronounced than in wild board contaminated in Germany following the Chernobyl accident, and this observation may be due to their more diverse food sources for wild boards in Japan (Berendes and Steinhauser, 2022).
Overall, as the 137 Cs contamination in wildlife muscles decreases with the distance from FDNPP, the strategy may be two-fold.First, in the areas farther from FDNPP where muscle contamination is likely to remain below the standard limit of 100 Bq kg -1 for meat consumption, shipping of the meat may be authorized after inspections of all slaughtered individuals conducted at special facilities specifically designed to this end in Tochigi and Ibaraki Prefectures.Second, in the areas close to FDNPP where this threshold is expected to be exceeded for a long time and where wildlife population expands, active extermination (by hunting or capturation) and the subsequent incineration of the bodies should be considered (Hashimoto et al., 2022a).

Export of radionuclides from forest to riverine ecosystems
Forests that remain contaminated with 137 Cs may supply contamination to lower landscape areas.A study showed that dissolved 137 Cs concentrations measured in a stream draining a forested headwater catchment was mainly derived from soil water with high dissolved 137 Cs concentrations originating from litter leachate.When storms occur, with the expansion of soil saturated zones, an increase in dissolved 137 Cs concentrations coinciding with the release of water stored in shallow soil layers is observed (Iwagami et al., 2019).This additional supply of dissolved 137 Cs from forest litter has been confirmed by leaching tests conducted on broadleaf litter in an area affected by saturation overland flow during storm events (Sakakibara et al., 2021).
Different pathways of radiocesium transfer from forests to river systems can be found, i.e. via litter fall into rivers, lateral inflow from the forest litter layer, and lateral transfer from the underlying forest soil.In a modelling exercise, Kurikami et al. (2019) showed that the decreasing trend of 137 Cs in river water and freshwater fish was due to a combination of the decreasing contamination trend in the forest leaves/needles and litter compartments, and the increasing contamination trend in soil.
When clearcutting is conducted, suspended sediment exports were found to increase two-fold, with a much more limited increase in 137 Cs export due to the very high sediment contribution of areas with low 137 Cs concentrations, e.g.channel bank erosion (Nishikiori et al., 2019).
Another approach relied on the use of a mass balance model to map the spatial distribution of 137 Cs inventories and quantify 137 Cs transport via sediment and litter in 2016-2017 along a deciduous forested hillslope of Date, in the Fukushima Prefecture (Oda et al., 2022).They showed that 137 Cs inventories were significantly higher in downslope riparian areas (455 kBq m -2 ) than in the upslope ridge area (179 kBq m -2 ).Annual 137 Cs transport with litter and sediment corresponded to less than 0.5% of the 137 Cs hillslope inventory, and transport of litter with high 137 Cs activity concentrations was found to provide the main pathway of 137 Cs transfer at that scale.
Nevertheless, these transfers of 137 Cs in forest environments, although significant in terms of export of contaminated material, were not shown to have an impact on radiation dose rates in forests, as shown by the monitoring of radiation levels along a hiking trail across forests in Tomioka Town in 2019, which remained stable despite the occurrence of Super Typhoon Hagibis in October 2019 (Taira et al., 2020).

Impacts of decontamination in radionuclide activities in riverine systems
Multiple recent publications confirmed that 137 Cs concentrations in river water and in sediment transported in rivers draining the main radioactive pollution plume strongly decreased between 2011 and 2020, and some of these datasets are available in open access (Taniguchi et al., 2020;Evrard et al., 2021).A database compiling 137 Cs activities measured in sediment (n=782) collected from 27 to 71 locations during 16 fieldwork campaigns conducted between November 2011 and November 2020 across catchments (6450 km²) draining the main radioactive pollution plume of the Fukushima Prefecture demonstrated that the radiocesium levels in sediment transiting these rivers decreased by more than 90% between 2011-2020 (Evrard et al., 2021).
Interestingly, very similar results were obtained based on continuous and more detailed monitoring in local upper catchments of the region.Fluvial discharge of 137 Cs was monitored between 2011 and 2021 from two small rivers including the Hiso River draining mainly farmland (4 km²), and the Wariki River, draining mainly forests (7 km²), in Iitate Village (Ueda et al., 2021).Both particulate and dissolved 137 Cs concentrationsparticulate fluxes representing 90% of the total 137 Cs exportwere shown to have decreased very strongly by more than 90% over a 10-year period (with higher decreases observed in the catchment dominated by farmland than in that dominated by forests).
In the main river of the region (i.e.Abukuma River, draining ca.5300 km² of land characterised by heterogeneous initial 137 Cs deposition levels), Taniguchi et al. (2019) found that the high 137 Cs concentrations observed in suspended sediment just after the accident in 2011 showed a steep exponential decline that lasted for about one year and that was dominated by the supply of 137 Cs from paddy fields, other farmland and urban areas.
This initial phase was followed by a more gradual secondary decline, with a higher contribution of 137  (2022) showed the occurrence of two phases, with a first stage of increase of erosion (+237%) during decontamination (2013-2016)when soils were left bare to remove the topsoil surface layer concentrating 137 Cs followed by a decrease during the subsequent revegetation stage (2016).Despite this higher sediment supply, they showed that the material delivered to river systems contained reduced 137 Cs levels compared to the predecontamination period and that this stage of higher sediment supply and transfer was only temporary due to the rapid vegetation recovery after the completion of remediation works.
Typhoon Hagibis that made landfall in Japan on October 12, 2019 (Irasawa et al., 2020) was the first extreme rainfall event that occurred in the region after the completion of decontamination in the Special Decontamination Areas early in 2019.Its impact on sediment sources and sediment 137 Cs contamination was investigated through the analysis of flood sediment deposits collected in the Mano and Niida River catchments and to the comparison of their geochemical and colour properties with those analysed in potential sources (e.g., cropland, forests, and subsurface material originating from landslides and channel bank erosion) (Evrard et al., 2020).The results showed that cropland and forests provided the main supply of sediment, and that these sources had reduced 137 Cs concentrations, which may be explained by the effective decontamination of cropland and the dominance of rill and gully erosion under forestsmobilising deeper soil layers depleted in 137 Csafter such an intense event.
A potential concern was that sediment from forestswith high 137 Cs concentrations as these zones have not been remediatedthat may be supplied to river systems during heavy rainfall events and deposited in nearby cropland that has been remediateddue to river overflow during intense hydrological eventsmay lead to a recontamination of these areas.To investigate this potential issue, sediment that had deposited after the flood generated by the 2019 Hagibis typhoon was collected along two rivers in Iitate Village to determine the total and exchangeable 137 Cs, and acid-extractable potassium (K) contents (Asano et al., 2022).These parameters were compared to those measured in nearby decontaminated soils (where no flood sediment deposition had occurred).
Although sediment deposited by the flood showed 4 times higher 137 Cs concentrations than decontaminated soils, it showed a 3-times lower 137 Cs exchangeable content.Furthermore, acid-extractable K referred to as nonexchangeable K was found to be sufficiently high to restrict 137 Cs transfer from soil to crops that may be planted to these fields afterwards.
Another issue may be related to the intermittent storage of 137 Cs contaminated sediment in the river floodplain that may be remobilized in the future during extreme flooding events, although their residence times remain currently uncertain (Golosov et al., 2022).This will depend on the floodplain morphology, vegetation characteristics and on the planning of management operations (as river channels may be dredged and cleaned by the authorities).Overall, another study (2015)(2016)(2017)(2018)(2019) conducted to determine changes in radioactive air dose rates in two riverside parks (along the Mizunashi River) of Minamisoma City showed a general decrease in these rates.They attributed 35% of the reduction to the physical decay of radiocesium, 14% to the vertical migration of radiocesium into the soil, and 51% to the combined effect of typhoons and remediation works between 2015-2019.They outlined in addition the great attenuation of air dose rates due to the strongest typhoon Hagibis in 2019, which generated a significant flush of contaminated sediment stored in the plain towards the Pacific Ocean (Yamasaki et al., 2023).
As fishing was a major recreational activity in the region (which is allowed after purchasing a fishing ticket from a cooperative), the emergency monitoring of wild and cultured freshwater products by the Fukushima Prefecture was implemented as soon as on March 30, 2011, with the exception of the designated evacuation zone (now referred to as the Difficult-to-Return Zone), which had not been targeted by monitoring inspections because of the expected high 137 Cs activities in freshwater products (Wada et al., 2022).For cultured fish in ponds (mainly common carp, salmon and char), very few samples exceeded the Japanese regulatory limit of 100 Bq kg -1 of 137 Cs in 2011-2012, and these concentrations were found to be below the detection limits of 137 Cs (~7 Bq kg -1 ) in all samples from 2015 onwards.This may be explained by the fact that radiocesium uptake from food was controlled (using non-contaminated pellets and setting an intake screen from preventing contaminated wild prey to enter from outside into the ponds).In contrast, several freshwater fishes were contaminated (containing more than 500 Bq kg -1 of radiocesium and up to 18,700 Bq kg -1 in 2011-2012), and the 100-Bq kg -1 regulatory limit was no longer exceeded in freshwater fish by 2020 onwards (with the exception of the Difficult-to-Return Zone as it was not covered by the monitoring inspections).This justified the prohibition of shipment of eight species (ayu, common carp, crucian carp, Japanese dace, masu salmon, white-spotted charr, Japanese eel, Japanese mitten crab) from some areas of the Fukushima and four neighbouring Prefectures as of April 2021 and the ongoing prohibition of fishing in the Difficult-to-Return Zone (where salmon and char fishes showing contamination levels of up to 25,006 Bq kg -1 were analysed in 2016) (Wada et al., 2019).Although fishing has been allowed again in the Abukuma River for most species as of April 2021, reputational damage remains problematic for the carp aquaculture industry in particular.For wild species, one of the main issues in the contamination of salmonids eating preys that feed themselves on litter and fungi from contaminated forests, thereby demonstrating radiocesium accumulation along the food web (Wada et al., 2019).Dam reservoirs were shown to act as a sink for radionuclides where they have been accumulating for more than one decade since the FDNPP accident (Sakai et al., 2021).In addition to the problems associated with the accumulation of contaminated sediment in these reservoirs, concerns were raised regarding the possible remobilisation of radionuclides from sediment to the water column under anaerobic conditions.Dissolved 137 Cs concentrations found in sediment-pore water from two highly contaminated reservoirs (i.e., Ogaki Dam and Yokokawa Dam) of the Fukushima-impacted area (3-66 Bq L −1 ) were one to two orders of magnitude higher than in reservoir water, showing evidence of the remobilisation of bioavailable 137 Cs from sediment (Funaki et al., 2021).Furthermore, these authors identified a competitive ion exchange process between 137 Cs and NH4 + via a highly selective interaction with the frayed edge sites of phyllosilicate minerals, leading to a very high variability of solid-liquid partition coefficient (Kd) values of sediment-pore water.The continuous supply of 137 Cs -contaminated sediment from the upper catchment prevailed over the diffusive flux of 137 Cs from sediment to overlying water.

Remobilisation of radionuclides from reservoir and pond sediment
Accordingly, reservoirs used for irrigation were shown to provide a perennial source of 137 Cs both in particlebound and dissolved forms, in response to resuspension and desorption processes.Furthermore, a control was identified between reservoir outflow water temperature and dissolved 137 Cs activities in water.This further demonstrated that desorption of 137 Cs from sediment is due to the exchange with cations such as NH4 + generated by biological activities.Furthermore, dissolved 137 Cs concentrations in the outflow water exhibited seasonal variations with an increasing trend in summer (Kubota et al., 2022).(2014)(2015)(2016)(2017)(2018)(2019), and they demonstrated that dissolved 137 Cs concentrations were significantly higher in outflow than in inflow water.They also calculated the mass balance of 137 Cs in the reservoir and showed that dissolved 137 Cs outputs were significantly higher than the inputs, and they estimated that 32%-40% of the dissolved 137 Cs in the output water was produced in the reservoir.It therefore represents a source of bioavailable dissolved 137 Cs, with 0.04-0.09% of the 137 Cs accumulated in the reservoir sediment being eluted to the overlaying water each year.Similar results have been obtained from another reservoir (i.e.Matsugabou Dam) of the Fukushima Prefecture (Hayashi and Tsuji, 2020).
Furthermore, in the ponds of Okuma Town from 2015 to 2019 (Konoplev et al., 2021;Wakiyama et al., 2019), a decline in both particulate and dissolved 137 Cs activity concentrations was revealed.The decline rate constants for the particulate 137 Cs activity concentration were found to be higher than for the dissolved 137 Cs activity concentration.In terms of seasonality, the dissolved 137 Cs concentrations were higher from June to October, depending on the specific pond and year, most likely due to temperature dependence of 137 Cs desorption from frayed edge sites of micaceous clay minerals.The apparent Kd ( 137 Cs) in the suspended sediment water system was observed to decrease over time.It was hypothesized that this trend was associated with the decomposition of glassy hot particles.
This outlines questions regarding the interest of removing contaminated sediment accumulated in reservoirs in order to limit 137 Cs desorption and allow the safe resumption of agricultural water use.Another problem is related to the contamination of fish found in these ponds, as 137 Cs levels found in fish collected in 2015-2016 in four ponds in the DTRZ nearby FDNPP were found to be higher than in forest rivers of the zone and they systematically exceeded by one to three orders of magnitude (up to 15,700 Bq kg -1 ) Japanese regulatory limit (100 Bq kg -1 ).This further demonstrates radiocesium bioaccumulation through the food web around bottom sediment in the ponds (Wada et al., 2019).This biomagnification process was observed in lakes and not in rivers (Ishii et al., 2020a).Even outside of the DTRZ and 5 years later, by 2020, despite remaining below the 100 Bq kg -1 value, 137 Cs continued to exceed the detection limits of ca.7 Bq kg -1 in 92.7% of fish samples collected from lakes and ponds of the Fukushima Prefecture where radiocesium has accumulated and may be progressively eluted from sediment (Wada et al., 2022).A peak in 137 Cs activities in lake fish was observed in Summer, which may reflect the preferential remobilisation of 137 Cs from sediment during this season due to the higher concentrations of NH4 + observed in bottom waters, although it may also be attributed to the higher feeding rates of fish observed during this part of the year (Matsuzaki et al., 2021).

Conclusions
Twelve years after the FDNPP accident, unprecedented soil decontamination works were completed across a wide area in Japan and their effectiveness could be demonstrated through continuous research and monitoring efforts implemented by numerous Japanese research groups and their foreign counterparts.Nevertheless, it remains important to continue environmental monitoring activities initiated after the accident using optimized spatio-temporal approaches and novel indicators if necessary.Of note, data collection started earlier after the FDNPP accident compared to the situation in Chernobyl, and data was more comprehensive and shared in a more open way in Japan (Hashimoto et al., 2022d;Ishii et al., 2020b;Hashimoto et al., 2020b) although further improvements remain possible.
Based on this post-accidental experience, feedback can be provided to a wide range of communities, to improve our preparedness in potentially affected regions (e.g., those located in the vicinity of nuclear power plants or those that may be affected by contaminant deposition following other industrial accidents) in the future (Hashimoto et al., 2022d).For instance, to be effective, the removal of the organic matter layer in deciduous forests should be conducted rapidly after the accident, which is now too late in the case of Fukushima.As the forest cover is too large to be fully decontaminated, in addition to the 20-m buffer zones along the forest edges, priority could be given to the decontamination of the so-called satoyama zones (Hashimoto et al., 2022d).In all cases, providing added value to the contaminated forest biomass is a real issue and it still requires the further development and consolidation of various economic and technological approaches.
Runoff and river systems were shown to provide significant pathways of radiocesium redistribution.
Accordingly, the expected increased frequency of typhoons may be of concern, as these events may lead to widespread flooding and significant forest disturbance (i.e., tree fall and associated landslides) (Morimoto et al., 2021) and the associated 137 Cs transfers.The potential impact of forest fires that may occur more frequently in the Fukushima region in response to increasing fuel load and global change should also be investigated, as they may lead to the release of 137 Cs into the local atmosphere as investigated in the Chernobyl-affected region (Evangeliou et al., 2014).Finally, the spatial pattern of deposition and the subsequent redistribution of microparticles containing radiocesium that were found in different environmental compartments including soils and that may lead to specific health risks if they are inhaled should also be further investigated (Fueda et al., 2023).

Figure 1 .
Figure 1.(A) Map of the 137 Cs deposition on soils across Northeastern Japan following FDNPP after Kato et al. (2019a); (B) -(C) delineation of the areas where decontamination works have been conducted following FDNPP accident in Japan including Intensive Contamination Survey Areas -ICAs (40 municipalities; 7836 km²), Special Decontamination Zone -SDZ (parts of 11 municipalities; 1117 km²) and DTRZ -Difficult to Return Zone (parts of 8 municipalities; 335 km²) (Source: Japanese Ministry of Environment).The corresponding shapefiles can be freely downloaded from Evrard et al. (2023).

Figure 2 .
Figure 2. Detailed map of the reconstructed initial 137 Cs fallout decay-corrected to July 2011 (Kato et al., 2019a), the municipalities of the Difficult-to-Return Zone, the "Specific Reconstruction and Revitalization Zones", and the radioactive waste management and storage facilities (see the inset map for a zoomed view on the location of these facilities).The corresponding shapefiles can be freely downloaded from Evrard et al. (2023).

Figure 3 .
Figure 3. Procedures for the treatment of waste containing radioactive materials from Fukushima Prefecture, after information shared by Reprun Fukushima -(Japanese Ministry of the Environment, 2023b)

Figure 4 .
Figure 4. Map of the Japanese municipalities with mushroom shipping restrictions as of November 2022 after Hashimoto et al. (2022a).The corresponding shapefiles can be freely downloaded from Evrard et al. (2023).
Cs from forests.Overall, the particulate form of 137 Cs represented 96.5% of the exports investigated in this study between June 2011 and August 2015.Decontamination works conducted in farmland and residential areas took place from 2013 to 2018 in the Special Decontamination Areas, including in those areas located nearby the Niida River flowing across Iitate Village and Minamisoma Town.A study combining river monitoring with governmental decontamination data and highresolution satellite images provided a comprehensive impact assessment of these remediation works.Feng et al.

Figure 5 .
Figure 5. Main dam reservoirs in the radioactive pollution plume of Fukushima Prefecture.

Funaki
et al. (2020) investigated 137 Cs concentrations in input and output water from Ogaki Dam Reservoir