Abstract. Twelve years after the nuclear accident that occurred at the Fukushima Dai-ichi Nuclear Power Plant in March 2011, radiocesium contamination (with a large dominance of ¹³⁷Cs, 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, 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 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 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 that were not targeted by remediation, radiocesium is now found in the upper mineral layer of the soil in a quasi-equilibrium state. Nevertheless, ¹³⁷Cs concentrations in forest products (including wood for heating and construction, wild plants, wildlife game, mushrooms) often keep exceeding the threshold values authorized in Japan, which prohibits their exploitation in the area affected by the main plume. Radionuclides from forest were shown to be exported in dissolved and particle-bound forms to downstream river systems and floodplains, although multiple monitoring records showed the continuous decrease in radiocesium concentrations in both river water and sediment across the main plume between 2011–2021. Fish contamination is now generally found below the threshold limits although reputational damage remains a major concern for local fishing communities. The remobilisation of radiocesium from sediment accumulated in reservoirs of the region is also of potential concern as it may lead to secondary contamination of fish or irrigation waters supplied to decontaminated fields. Overall, this synthesis demonstrates the need to continue monitoring post-accidental radiocesium transfers in these environments and to keep sharing data in order to refine our predictive understanding of radiocesium mobility and consolidate the tools available to model contaminant transfers in ecosystems. In forests in particular, novel countermeasures and wood uses remain to be developed and tested. Furthermore, the hydrologic connectivity between ecosystems is of great influence on long term radiocesium transport. The consequences of extreme phenomena (e.g., typhoons, forest fires) that may become more frequent in the future as a result of global change in these contaminated environments should be further anticipated.

中文翻译：

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福岛（日本）难以返回区重新开放后土壤和景观净化后的研究和管理挑战

摘要。2011 年 3 月福岛第一核电站发生核事故 12 年后，放射性铯污染（主要为¹³⁷ Cs，半衰期为 30 年）仍然是东北各城市的主要关注点日本。日本当局在受主要放射性羽流（8953 平方公里）影响的住宅区和耕作区完成了前所未有的去污计划。在划定暴露于对比辐射率的不同区域后，他们实施了一项复杂的修复计划方案，该方案依赖于取决于废物类型、污染程度和来源地区的不同决策规则。中心目标是不让当地居民受到超过 1 mSv yr ^{-1的放射性剂量}除了自然水平。在 2023 年春季难以返回区全面重新开放之际，当前的审查提供了对 2019 年发布的先前综合的更新（Evrard 等人，2019）。尽管这一雄心勃勃的整治和重建计划几近完成，但在 2011 年福岛县的 12 个市镇中，至少有一个街区实施了疏散令，在事故发生前居住在那里的 147,443 名居民中，只有 29.9% 的人曾到 2020 年归还。去污和海啸清理/拆除工作产生的废物计划到 2023 年底全部运到（临时）储存设施。据日本审计委员会估计，2011 年至 2020 年期间进行的所谓“核回收”行动（包括去污）的行动成本为 61223 亿日元（约合 440 亿欧元）。农田净化已被证明会影响土壤肥力，建议施钾以限制残留放射性铯向新作物的转移。在覆盖福岛县 71% 表面积且未作为整治目标的森林中，现在发现放射性铯处于准平衡状态的土壤上层矿物层中。尽管如此，建议施钾以限制残留放射性铯向新作物的转移。在覆盖福岛县 71% 表面积且未作为整治目标的森林中，现在发现放射性铯处于准平衡状态的土壤上层矿物层中。尽管如此，建议施钾以限制残留放射性铯向新作物的转移。在覆盖福岛县 71% 表面积且未作为整治目标的森林中，现在发现放射性铯处于准平衡状态的土壤上层矿物层中。尽管如此，¹³⁷森林产品（包括供暖和建筑用木材、野生植物、野生动物猎物、蘑菇）中的 Cs 浓度经常超过日本规定的阈值，该阈值禁止在受主要羽流影响的地区进行开采。来自森林的放射性核素显示以溶解和颗粒结合的形式输出到下游河流系统和洪泛区，尽管多项监测记录显示 2011-2021 年间主要羽流中的河水和沉积物中的放射性铯浓度持续下降。尽管声誉受损仍然是当地渔业社区的主要关注点，但现在发现鱼类污染通常低于阈值限度。该地区水库中沉积物中放射性铯的再活化也可能引起关注，因为它可能导致鱼类或提供给净化田地的灌溉水受到二次污染。总的来说，这一综合表明需要继续监测这些环境中的事故后放射性铯转移并继续共享数据，以完善我们对放射性铯流动性的预测理解，并整合可用于模拟生态系统中污染物转移的工具。特别是在森林中，新的对策和木材用途仍有待开发和测试。此外，生态系统之间的水文连通性对长期放射性铯运输有很大影响。极端现象（如台风、