Direct comparison of bacterial communities in soils contaminated with different levels of radioactive cesium from the first Fukushima nuclear power plant accident

Potential applications of microbial genomics in nuclear non-proliferation

As nuclear technology evolves in response to increased demand for diversification and decarbonization of the energy sector, new and innovative approaches are needed to effectively identify and deter the proliferation of nuclear arms, while ensuring safe development of global nuclear energy resources. Preventing the use of nuclear material and technology for unsanctioned development of nuclear weapons has been a long-standing challenge for the International Atomic Energy Agency and signatories of the Treaty on the Non-Proliferation of Nuclear Weapons. Environmental swipe sampling has proven to be an effective technique for characterizing clandestine proliferation activities within and around known locations of nuclear facilities and sites. However, limited tools and techniques exist for detecting nuclear proliferation in unknown locations beyond the boundaries of declared nuclear fuel cycle facilities, representing a critical gap in non-proliferation safeguards. Microbiomes, defined as "characteristic communities of microorganisms" found in specific habitats with distinct physical and chemical properties, can provide valuable information about the conditions and activities occurring in the surrounding environment. Microorganisms are known to inhabit radionuclide-contaminated sites, spent nuclear fuel storage pools, and cooling systems of water-cooled nuclear reactors, where they can cause radionuclide migration and corrosion of critical structures. Microbial transformation of radionuclides is a well-established process that has been documented in numerous field and laboratory studies. These studies helped to identify key bacterial taxa and microbially-mediated processes that directly and indirectly control the transformation, mobility, and fate of radionuclides in the environment. Expanding on this work, other studies have used microbial genomics integrated with machine learning models to successfully monitor and predict the occurrence of heavy metals, radionuclides, and other process wastes in the environment, indicating the potential role of nuclear activities in shaping microbial community structure and function. Results of this previous body of work suggest fundamental geochemical-microbial interactions occurring at nuclear fuel cycle facilities could give rise to microbiomes that are characteristic of nuclear activities. These microbiomes could provide valuable information for monitoring nuclear fuel cycle facilities, planning environmental sampling campaigns, and developing biosensor technology for the detection of undisclosed fuel cycle activities and proliferation concerns.

Microbiome analysis of the restricted bacteria in radioactive element-containing water at the Fukushima Daiichi Nuclear Power Station

A major incident occurred at the Fukushima Daiichi Nuclear Power Station following the tsunami triggered by the Tohoku-Pacific Ocean Earthquake in March 2011, whereby seawater entered the torus room in the basement of the reactor building. Here, we identify and analyze the bacterial communities in the torus room water and several environmental samples. Samples of the torus room water (1 × 109 Bq137Cs/L) were collected by the Tokyo Electric Power Company Holdings from two sampling points between 30 cm and 1 m from the bottom of the room (TW1) and the bottom layer (TW2). A structural analysis of the bacterial communities based on 16S rRNA amplicon sequencing revealed that the predominant bacterial genera in TW1 and TW2 were similar. TW1 primarily contained the genus Limnobacter, a thiosulfate-oxidizing bacterium. γ-Irradiation tests on Limnobacter thiooxidans, the most closely related phylogenetically found in TW1, indicated that its radiation resistance was similar to ordinary bacteria. TW2 predominantly contained the genus Brevirhabdus, a manganese-oxidizing bacterium. Although bacterial diversity in the torus room water was lower than seawater near Fukushima, ~70% of identified genera were associated with metal corrosion. Latent environment allocation-an analytical technique that estimates habitat distributions and co-detection analyses-revealed that the microbial communities in the torus room water originated from a distinct blend of natural marine microbial and artificial bacterial communities typical of biofilms, sludge, and wastewater. Understanding the specific bacteria linked to metal corrosion in damaged plants is important for advancing decommissioning efforts.

IMPORTANCE

In the context of nuclear power station decommissioning, the proliferation of microorganisms within the reactor and piping systems constitutes a formidable challenge. Therefore, the identification of microbial communities in such environments is of paramount importance. In the aftermath of the Fukushima Daiichi Nuclear Power Station accident, microbial community analysis was conducted on environmental samples collected mainly outside the site. However, analyses using samples from on-site areas, including adjacent soil and seawater, were not performed. This study represents the first comprehensive analysis of microbial communities, utilizing meta 16S amplicon sequencing, with a focus on environmental samples collected from the radioactive element-containing water in the torus room, including the surrounding environments. Some of the identified microbial genera are shared with those previously identified in spent nuclear fuel pools in countries such as France and Brazil. Moreover, our discussion in this paper elucidates the correlation of many of these bacteria with metal corrosion.

Taxonomic Diversity and Functional Traits of Soil Bacterial Communities under Radioactive Contamination: A Review

Studies investigating the taxonomic diversity and structure of soil bacteria in areas with enhanced radioactive backgrounds have been ongoing for three decades. An analysis of data published from 1996 to 2024 reveals changes in the taxonomic structure of radioactively contaminated soils compared to the reference, showing that these changes are not exclusively dependent on contamination rates or pollutant compositions. High levels of radioactive exposure from external irradiation and a high radionuclide content lead to a decrease in the alpha diversity of soil bacterial communities, both in laboratory settings and environmental conditions. The effects of low or moderate exposure are not consistently pronounced or unidirectional. Functional differences among taxonomic groups that dominate in contaminated soil indicate a variety of adaptation strategies. Bacteria identified as multiple-stress tolerant; exhibiting tolerance to metals and antibiotics; producing antioxidant enzymes, low-molecular antioxidants, and radioprotectors; participating in redox reactions; and possessing thermophilic characteristics play a significant role. Changes in the taxonomic and functional structure, resulting from increased soil radionuclide content, are influenced by the combined effects of ionizing radiation, the chemical toxicity of radionuclides and co-contaminants, as well as the physical and chemical properties of the soil and the initial bacterial community composition. Currently, the quantification of the differential contributions of these factors based on the existing published studies presents a challenge.

Soil Microbes and Plant-Associated Microbes in Response to Radioactive Pollution May Indirectly Affect Plants and Insect Herbivores: Evidence for Indirect Field Effects from Chernobyl and Fukushima

The biological impacts of the nuclear accidents in Chernobyl (1986) and Fukushima (2011) on wildlife have been studied in many organisms over decades, mainly from dosimetric perspectives based on laboratory experiments using indicator species. However, ecological perspectives are required to understand indirect field-specific effects among species, which are difficult to evaluate under dosimetric laboratory conditions. From the viewpoint that microbes play a fundamental role in ecosystem function as decomposers and symbionts for plants, we reviewed studies on microbes inhabiting soil and plants in Chernobyl and Fukushima in an attempt to find supporting evidence for indirect field-specific effects on plants and insect herbivores. Compositional changes in soil microbes associated with decreases in abundance and species diversity were reported, especially in heavily contaminated areas of both Chernobyl and Fukushima, which may accompany explosions of radioresistant species. In Chernobyl, the population size of soil microbes remained low for at least 20 years after the accident, and the abundance of plant-associated microbes, which are related to the growth and defense systems of plants, possibly decreased. These reported changes in microbes likely affect soil conditions and alter plant physiology. These microbe-mediated effects may then indirectly affect insect herbivores through food-mass-mediated, pollen-mediated, and metabolite-mediated interactions. Metabolite-mediated interactions may be a major pathway for ecological impacts at low pollution levels and could explain the decreases in insect herbivores in Fukushima. The present review highlights the importance of the indirect field effects of long-term low-dose radiation exposure under complex field circumstances.

Root-associated microbial community and diversity in napiergrass across radiocesium-contaminated lands after the Fukushima-Daiichi nuclear disaster in Japan

The microbiome derived from soil associated with plant roots help in plant growth and stress resistance. It exhibits potential benefits for soil remediation and restoration of radioactive-cesium (137Cs)-contaminated soils. However, there is still limited information about the community and diversity of root-associated microbiome in 137Cs-contaminated soil after the Fukushima-Daiichi Nuclear Power Plant (FDNPP) disaster. To address this, a comparative analysis of communities and diversity of root-associated microbiomes was conducted in two field types after the FDNPP disaster. In 2013, we investigated the community and diversity of indigenous root-associated microbiome of napiergrass (Pennisetum purpureum) grown in both grassland and paddy fields of 137Cs-contaminated land-use type within a 30-km radius around the FDNPP. Results showed that the root-associated bacterial communities in napiergrass belonged to 32 phyla, 75 classes, 174 orders, 284 families, and 521 genera, whereas the root-associated fungal communities belonged to 5 phyla, 11 classes, 31 orders, 59 families, and 64 genera. The most frequently observed phylum in both grassland and paddy field was Proteobacteria (47.4% and 55.9%, respectively), followed by Actinobacteriota (23.8% and 27.9%, respectively) and Bacteroidota (10.1% and 11.3%, respectively). The dominant fungal phylum observed in both grassland and paddy field was Basidiomycota (75.9% and 94.2%, respectively), followed by Ascomycota (24.0% and 5.8%, respectively). Land-use type significantly affected the bacterial and fungal communities that colonize the roots of napiergrass. Several 137Cs-tolerant bacterial and fungal taxa were also identified, which may be potentially applied for the phytoremediation of 137Cs-contaminated areas around FDNPP. These findings contribute to a better understanding of the distribution of microbial communities in 137Cs-contaminated lands and their long-term ecosystem benefits for phytoremediation efforts.

Frontier issues in international ocean governance: Japan's discharge of nuclear contaminated water into the sea

This paper aimed at explore international ocean governance issues through the perspective of Japan's nuclear contaminated water discharge to the sea. This paper analyzes the core issue of Japan's plan to discharge nuclear contaminated water into the ocean from the perspectives of Japan's international legal obligation, law enforcement issues, and judicial issues after integrated analyzing academic research paper and cases. Japan has obligations such as timely notification, information disclosure, environmental impact assessment, and avoidance of transboundary harm. Intergovernmental and non-governmental international organizations, such as IAEA, IMO and WHO should play a role in setting up an international group of experts to carry out monitoring and assessment, and whose positions and attitudes are important references for judging Japan's behavior. Cases heard before ICJ, ITLOS, and advisory opinion proceeding could provide reference from the judicial perspective on the issue of transboundary harm and proof of damages. Furthermore, this paper discusses the response strategies that the international community especially the opponents may adopt, including promoting the adoption of relevant treaties, take a combination of requesting advisory opinion and file arbitration, establish effective international monitoring mechanism, and engage in close communication with stakeholders.

Diatom DNA metabarcoding to assess the effect of natural radioactivity in mineral springs on ASV of benthic diatom communities

Little is still known about the low dose effects of radiation on the microbial communities in the environment. Mineral springs are ecosystems than can be affected by natural radioactivity. These extreme environments are, therefore, observatories for studying the influence of chronic radioactivity on the natural biota. In these ecosystems we find diatoms, unicellular microalgae, playing an essential role in the food chain. The present study aimed to investigate, using DNA metabarcoding, the effect of natural radioactivity in two environmental compartments (i.e. spring sediments and water) on the genetic richness, diversity and structure of diatom communities in 16 mineral springs in the Massif Central, France. Diatom biofilms were collected during October 2019, and a 312 bp region of the chloroplast gene rbcL (coding for the Ribulose Bisphosphate Carboxylase) used as a barcode for taxonomic assignation. A total of 565 amplicon sequence variants (ASV) were found. The dominant ASV were associated with Navicula sanctamargaritae, Gedaniella sp., Planothidium frequentissimum, Navicula veneta, Diploneis vacillans, Amphora copulata, Pinnularia brebissonii, Halamphora coffeaeformis, Gomphonema saprophilum, and Nitzschia vitrea, but some of the ASVs could not be assigned at the species level. Pearson correlation failed to show a correlation between ASV' richness and radioactivity parameters. Non-parametric MANOVA analysis based on ASVs occurrence or abundances revealed that geographical location was the main factor influencing ASVs distribution. Interestingly, ²³⁸U was the second factor that explained diatom ASV structure. Among the ASVs in the mineral springs monitored, ASV associated with one of the genetic variants of Planothidium frequentissimum was well represented in the springs and with higher levels of ²³⁸U, suggesting its high tolerance to this particular radionuclide. This diatom species may therefore represent a bio-indicator of high natural levels of uranium.

Impact of ionizing radiation on the environmental microbiomes of Chornobyl wetlands

Radioactive contamination has the potential to cause damage to DNA and other biomolecules. Anthropogenic sources of radioactive contamination include accidents in nuclear power plants, such as the one in Chornobyl in 1986 which caused long-term radioactive pollution. Studies on animals within radioactive zones have provided us with a greater understanding of how wildlife can persevere despite chronic radiation exposure. However, we still know very little about the effects of radiation on the microbial communities in the environment. We examined the impact of ionizing radiation and other environmental factors on the diversity and composition of environmental microbiomes in the wetlands of Chornobyl. We combined detailed field sampling along a gradient of radiation together with 16 S rRNA high-throughput metabarcoding. While radiation did not affect the alpha diversity of the microbiomes in sediment, soil, or water, it had a significant effect on the beta diversity in all environment types, indicating that the microbial composition was affected by ionizing radiation. Specifically, we detected several microbial taxa that were more abundant in areas with high radiation levels within the Chornobyl Exclusion Zone, including bacteria and archaea known to be radioresistant. Our results reveal the existence of rich and diverse microbiomes in Chornobyl wetlands, with multiple taxonomic groups that are able to thrive despite the radioactive contamination. These results, together with additional field and laboratory-based approaches examining how microbes cope with ionizing radiation will help to forecast the functionality and re-naturalization dynamics of radiocontaminated environments.

Effect of Biochar on Rhizosphere Soil Microbial Diversity and Metabolism in Tobacco-Growing Soil

In this study, four different biochar application rates and a control were set up using indoor potted tobacco, to study the effects of biochar on the microbial diversity and metabolism of tobacco-growing soil. The five treatments were as follows: control—0% biochar (w/w) + 26 g fertilizer/pot; biochar treatments—1% biochar (w/w) + 26 g fertilizer/pot, 2% biochar (w/w) + 26 g fertilizer/pot, 3% biochar (w/w) + 26 g fertilizer/pot, and 4% biochar (w/w) + 26 g fertilizer/pot. We found that biochar increases the microbial diversity of soils and simultaneously changes the microbial community structure. Under the influence of biochar, soil urease activity increased by 18%, invertase activity increased by 23.40%, polyphenol oxidase activity increased by 59.50%, and catalase activity increased by 30.92%. Biochar also significantly increased the microbial biomass carbon and nitrogen content of the soil. Soil microbial biomass nitrogen had a positive correlation on bacterial diversity, with the highest coefficient, while soil microbial biomass carbon had a positive correlation on fungal diversity, with the highest coefficient. The microbial diversity and metabolic capacity of soil are improved under the influence of biochar, and soil enzyme activity and microbial biomass carbon and nitrogen have positive impacts on soil microbial diversity.

The second decade of the blue butterfly in Fukushima: Untangling the ecological field effects after the Fukushima nuclear accident

Many field observations of the biological effects of the Fukushima nuclear accident have been reported in the first decade after the accident. A series of observational and experimental studies have demonstrated causal adverse effects on the pale grass blue butterfly even at the low-level radiation exposure in the "field," contrary to the dosimetric view that insects are generally tolerant of radiation exposure. However, it has been demonstrated that the pale grass blue butterfly is tolerant of high oral doses of anthropogenic radioactive cesium (¹³⁷ Cs) under "laboratory" conditions. This field-laboratory paradox can be explained by ecological field effects; for example, radiation stress in the field causes physiological and biochemical changes in the host plant, which then trophically affects butterfly larvae. The second decade of butterfly-based Fukushima research will be devoted to demonstrating how such adverse field effects occur. Changes in the host plant's nutritional contents likely affect butterfly physiology. The host plant may also upregulate secondary metabolites that affect herbivorous insects. The plant may be affected by changes in endophytic soil microbes in radioactively contaminated areas. If demonstrated, these results will reveal that the delicate ecological balances among the butterfly, its host plant, and soil microbes have been affected by radioactive pollution in Fukushima, which has important implications for environmental policies and human health. Integr Environ Assess Manag 2022;18:1539-1550. © SETAC.

Kinetics of low radioactive wastewater imbibition and radionuclides sorption in partially saturated ternary-binder mortar

This study seeks to assess the imbibition kinetics of low radioactive wastewater (from the DayaBay nuclear power plant) into a partially saturated ternary-binder mortar, as well as the sorption kinetics of ⁶⁰Co and ¹³⁷Cs from the water. Mortar samples with the initial saturation degrees of 0, 0.4, 0.6, 0.8 and 1.0 were prepared for the wastewater treatment. Pore structure of the mortar was characterized using water vapor sorption isotherm and mercury intrusion porosimetry tests interpreted by the Guggenheim-Anderson-de Boer isothermal equilibrium, and volume- and energy-based fractal models. Results show that the mortar has consistent fractal pore structure between the models, and the liquid imbibitions follow the fractal imbibition kinetics, in which the parameters are non-linearly impacted by the initial saturation degrees. The sorption rate and retention capacity of ¹³⁷Cs are much lower than those of ⁶⁰Co, and both follow the Brouers-Sotolongo fractional kinetics. The findings uncover the complex liquid imbibition and radionuclides sorption kinetics in cement-based porous materials, and the in-situ data would contribute to the material designs and sorption controls for large scale in-situ treatments of wastewater from nuclear power plant.

Biomineralization by Extremely Halophilic and Metal-Tolerant Community Members from a Sulfate-Dominated Metal-Rich Environment

The adaptation to adverse environmental conditions can lead to adapted microbial communities that may be screened for mechanisms involved in halophily and, in this case, metal tolerance. At a former uranium mining and milling site in Seelingstädt, Germany, microbial communities from surface waters and sediment soils were screened for isolates surviving high salt and metal concentrations. The high salt contents consisted mainly of chloride and sulfate, both in soil and riverbed sediment samples, accompanied by high metal loads with presence of cesium and strontium. The community structure was dominated by Chloroflexi, Proteobacteria and Acidobacteriota, while only at the highest contaminations did Firmicutes and Desulfobacterota reach appreciable percentages in the DNA-based community analysis. The extreme conditions providing high stress were mirrored by low numbers of cultivable strains. Thirty-four extremely halotolerant bacteria (23 Bacillus sp. and another 4 Bacillales, 5 Actinobacteria, and 1 Gamma-Proteobacterium) surviving 25 to 100 mM SrCl₂, CsCl, and Cs₂SO₄ were further analyzed. Mineral formation of strontium- or cesium-struvite could be observed, reducing bioavailability and thereby constituting the dominant metal and salt resistance strategy in this environment.