Biofilm-mediated interactions between plastics and radiocesium in coastal environments.

A ubiquitous distribution of plastic debris has been reported in aquatic and terrestrial environments; however, the interactions between plastics and radionuclides and the radioactivity of environmental plastics remain largely unknown. Here, we characterize biofilms developing on the surface of plastic debris to explore the role of plastic-associated biofilms as an interaction medium between plastics and radiocesium (137Cs) in the environment. Biofilm samples were extracted from plastics (1-50 mm in size) collected from two contrasting coastal areas in Japan. The radioactivity of plastics was estimated based on the 137Cs activity concentration of the biofilms and compared seasonally with surrounding environmental samples (i.e., sediment and sand). 137Cs traces were detected in biofilms with activity concentrations of 21-1300 Bq·kg-1 biofilm (dry weight), corresponding to 0.04-4.5 Bq·kg-1 plastic (dry weight). Our results reveal the interaction between 137Cs and plastics and provide evidence that organic and mineral components in biofilms are essential in 137Cs retention in environmental plastics. Given the ubiquitous distribution of plastic debris in the environment, more attention should be directed to bioaccumulation and the radioecological impacts of plastic-associated radionuclides on ecosystems.

Distinct food-web transfers of 137Cs to fish in river and lake ecosystems: A case study focusing on masu salmon in the Fukushima evacuation zone.

This study was conducted to elucidate the spatial and size variations, and food-web transfer of 137Cs in freshwater fish in the upper reaches of the Ukedo River system, a highly contaminated river system flowing through the Fukushima evacuation zone. Fish collection and environmental surveys were conducted in the summer of 2020 at five forest rivers and at the Ogaki Dam reservoir (an artificial lake) with different air dose rates (mean 0.20-3.32 µSv/h). From the river sites, two salmonid species (masu salmon and white-spotted charr) were sampled, with masu salmon generally exhibiting higher 137Cs concentrations, ranging widely (10.6 Bq/kg-wet to 13.0 kBq/kg-wet) depending on the fish size (size effect) and site. The 137Cs concentrations in masu salmon were explained by the air dose rates, 137Cs concentrations in water, sediments (excluding the lake site), and primary producers, with site-specific variations. In the rivers, masu salmon (fluvial type with parr marks) mainly fed on terrestrial insects with higher 137Cs concentrations compared with those of aquatic insects, indicating that 137Cs was transferred mainly to fish through the allochthonous forest food-web during summer. In the lake, masu salmon (lake-run type with larger size and silvery body coloration) mainly preyed on smaller fish with lower 137Cs concentrations, demonstrating that 137Cs is transferred to fish through the autochthonous lake food-web with biomagnification. Differences in 137Cs concentrations among masu salmon (mean 441 Bq/kg-wet) and other fish species (mean 74.8 Bq/kg-wet to 2.35 kBq/kg-wet) were also found in the lake. The distinct 137Cs transfers to river and lake fish were supported by stable isotope analysis: δ15N and δ13C values enriched stepwisely through the food-webs were, respectively, higher and lower in the lake. Our results obtained using multiple approaches clearly revealed the distinct food-web transfer of 137Cs in river and lake ecosystems. These findings can contribute to prediction of radioactive contamination in freshwater fish in the Fukushima evacuation zone.

Impacts of farmland decontamination on 137Cs transfers in rivers after Fukushima nuclear accident: Evidence from a retrospective sediment core study.

Following the Fukushima Daiichi Nuclear Power Plant disaster in March 2011, the Japanese government initiated an unprecedented decontamination programme to remediate 137Cs-contaminated soils and allow population return. This programme involved the removal of topsoil under farmland and residential land, and its replacement with "fresh soil" composed of granitic saprolite. However, decontamination was limited to these two land uses, without remediating forests, which cover 70 % of the surface area in the affected region. In this unprecedented context, the specific impact of this unique decontamination programme on 137Cs transfers in river systems remains to be quantified at the catchment scale. In this study, based on the analysis of a sediment core collected in June 2021 in the Mano Dam reservoir draining a decontaminated catchment, the effects of soil decontamination on particle-bound 137Cs dynamics and sediment source contributions in response to a succession of extreme precipitation events were retrospectively assessed. The sequence of sediment layer deposition and its chronology were reconstructed through the analysis of several diagnostic properties (organic matter, elemental geochemistry, visible colourimetry, granulometry) and contextual information. During abandonment (2011-2016), cropland contribution decreased (31 %). Concurrently, 137Cs activity and deposition flux decreased (19 and 29%year-1, respectively). Following decontamination (2017), sediment transfer increased (270 %) in response to increased contributions from decontaminated cropland and "fresh soil" (625 % and 180 % respectively). Meanwhile, forest contributions remained stable. In contrast, 137Cs activity dropped (65 %), although 137Cs deposition flux remained constant. Forests acted as a stable source of 137Cs. Accordingly, 137Cs deposition flux after decontamination (2016-2021) was similar to that observed during the 5-years period of land abandonment (2011-2016), as a result of the regrowth of spontaneous vegetation over farmland, protecting soil against erosion. Future research should further investigate the impact of longer land abandonment that prevailed in some regions decontaminated lately on the 137Cs fluxes in the rivers.

The surface of small glaciers as radioactive hotspots: Concentration of radioisotopes during predicted intensive melting in the Alps.

Glaciers are considered secondary sources of pollutants, including radioisotopes such as Cesium or Plutonium, with heightened concentrations compared to other ecosystems. The predicted melting of glaciers poses a substantial risk of releasing stored radioisotopes, yet understanding the glacier-specific factors influencing their concentration remains limited. This study investigates the relationship between glacier altitude, surface area, organic matter content in dark supraglacial sediment (cryoconite), precipitation, and activity concentrations of natural (210Pb) and anthropogenic radionuclides (137Cs and 241Am) across 19 Alpine glaciers. Results indicate that radioisotope concentrations depend on organic matter content in the cryoconite, highlighting the role of biotic-abiotic interactions in pollutant accumulation on glaciers. Moreover, 210Pb activity concentration decreases with glacier altitude, likely due to atmospheric variations in 222Rn. Water precipitation events, such as during peaks in 137Cs deposition and after the Chernobyl Nuclear Power Plant disaster, do not impact current activity concentrations. Importantly, radioisotope concentrations in cryoconite are higher on smaller glaciers. This directly supports the hypothesis that the cryoconite retains a significant share of radioisotopes stored in the ice during intensive melting. Since many small glaciers in the Alps are predicted to disappear within the next 50 years, we anticipate release of radioisotopes to mountain ecosystems might be higher than previously forecasted.

Downward migration of 137Cs promotes self-cleaning of forest ecosystem by reducing root uptake of Japanese cedar in Fukushima.

Approximately 70 % of the area highly 137Cs-contaminated by the Fukushima Daiichi Nuclear Power Plant accident is forested. Decontamination works in most of these forests have not progressed, and the forestry industry remains stagnant. Although the long-term dynamics of 137Cs in the forest ecosystem will be controlled by the amount of 137Cs absorbed by roots in the future, temporal changes in 137Cs of tree roots have rarely been reported. In the present study, we monitored the depth distribution of 137Cs in the soil and absorptive very fine (VF) roots of 0.5 mm or less in a Japanese cedar forest from 2011 to 2023. As a result, the 137Cs inventory in the mineral soil increased over time due to the migration from the forest canopy and litter layers, whereas that in the VF roots tended to decrease since 2020, although there was a large variation. Temporal decrease in the exchangeable 137Cs fraction with fixation and temporal increase in VF root biomass with their growth were not clearly observed, the 137Cs concentration in the VF roots at 0-2 cm decreased with the decrease in 137Cs concentration in the litter layers. Although the 137Cs concentration in the VF roots below 2 cm tended to increase with increasing 137Cs concentration in the soil at the same depth, the downward migration of 137Cs within the soil can reduce the amount of 137Cs absorbed by roots because the VF root biomass decreases exponentially with depth. In other words, 137Cs can be removed from the long-term active cycles of forest ecosystems as they migrate deeper into the soil. This natural migration process can be regarded as a "self-cleaning" of the forest ecosystem, the green and sustainable remediation using such self-cleaning should be actively adopted for the future forest management.

All-in-one treatment: Capture and immobilization of 137Cs by ultra-stable inorganic solid acid materials HMMoO6·nH2O (M = Ta, Nb).

Capture and immobilization of 137Cs is urgent for radioactive contamination remediation and spent fuel treatment. Herein, an effective all-in-one treatment method to simultaneously adsorb and immobilize Cs+ without high-temperature treatment is proposed. According to the strategy of incorporating high-valency metal ions into molybdates to increase the material stability and affinity towards radionuclides, layered HMMoO6·nH2O (M = Ta (1), Nb (2)) are prepared. Both materials exhibit excellent acid resistance (even 15 mol/L HNO3). They maintain remarkable adsorption capacity for Cs+ in 1 mol/L HNO3 solutions and can selectively capture Cs+ under excessive competitive ions. Furthermore, they show successful cleanup for actual 137Cs-liquid-wastes generated during industrial production. In particular, adsorbed Cs+ can be firmly immobilized in interlayer spaces of materials due to the highly stable anionic framework. The removal mechanism is attributed to ion exchange between Cs+ and interlayer H+ by multiple characterizations. Study of the structure-function relationship shows that the occurrence of Cs+ ion exchange is closely related to plate-like layered structure. This work develops an efficient all-in-one treatment method for capturing and immobilizing radiocesium by ultra-stable inorganic solid acid materials with low energy consumption and high safety for radionuclide remediation.

Public Attitudes toward the Final Disposal of Radioactively Contaminated Soil Resulting from the Fukushima Daiichi Nuclear Power Station Accident.

Radioactively contaminated soil from the Fukushima Daiichi nuclear power station accident in 2011 is required by law to be finally disposed of outside Fukushima Prefecture by 2045. To gain public acceptance of this policy, it is essential to promote understanding and nationwide discussion. We conducted a web-based survey of 2000 people in Japan to examine public attitudes toward final disposal of the contaminated soil outside Fukushima Prefecture. Results show that policy approval was negatively correlated with perceived risk of a final disposal site, sense of inequity associated with building a final disposal site near residential areas, and values that are absolutely non-negotiable or protected from trade-offs with other values (protected values). Policy approval was positively correlated with high levels of interest in the Fukushima accident and subjective knowledge of decontamination and the policy. Respondents' comments and opinions about the policy indicated that respondents who approved of the policy accepted burden sharing, while those who disapproved were unconvinced by the rationale behind disposal outside Fukushima Prefecture and were dissatisfied by the lack of information disclosure and transparency. While the government's efforts to disseminate information about the current status and future of Fukushima have been effective to a certain extent, they are insufficient to achieve widespread public understanding of the policy. Our results indicate that attention needs to be paid to procedural fairness and explanations of risks.

Dispersant-enhanced migration of radiocesium among soil size fractions: A novel strategy for volume reduction of radioactively contaminated soil.

In the aftermath of the Fukushima Daiichi Nuclear Power Plant accident, a pioneering large-scale decontamination project was initiated, aiming to enable the return of evacuees. This project, the first of its kind in human history, involved the transportation of soils collected during decontamination to interim storage facilities. Before recycling or disposal, these soils undergo processes like volume reduction. However, there's a need for innovative methods to reduce volume effectively and treat secondary wastes more efficiently. The current study explores the impact of a dispersant, sodium hexametaphosphate (SHMP), on the behavior of radiocesium (r-Cs: 137Cs) dynamics in different size fractions of radioactively contaminated soils from Fukushima. The solid-phase speciation analysis of Fukushima soils validated that at least 50% of the 137Cs or other minerals are associated with difficult-to-extract soil phases. Nonetheless, the low 137Cs/133Cs ratio in corresponding soil phases implies a slower r-Cs fixation mechanism. The wet-sieving of r-Cs contaminated soil fraction, < 2 mm, with SHMP, resulted in different soil subfractions (2000-212, 212-53, and < 53 µm). Following SHMP treatment, dispersion of > 92% of 137Cs associated with < 212 µm soil size fractions was observed. The migration of 137Cs towards smaller soil size fractions can be attributed to either SHMP-induced cation exchange or the formation of polyvalent complexes involving SHMP and soil minerals. The condensation of 137Cs in < 212 µm, as induced by SHMP, enabled the subsequent reuse of the larger soil fraction (> 212 µm), which was less contaminated. This study provides a new perspective on the effects of dispersants and contributes to a better understanding of the complex interactions among organic carbon, 137Cs, monovalent and polyvalent cations, and soil functional groups concerning the volume reduction of soils contaminated with r-Cs.

Study on the relationship between the dispersal of wild boar (Sus scrofa) and the associated variability of Cesium-137 concentrations in its muscle Post-Fukushima Daiichi Nuclear Power Plant accident.

After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011, the wild boar (Sus scrofa) population within the Fukushima Evacuation Zone (FEZ) increased substantially in size and distribution. This growing population and their potential dispersal from the FEZ, where they are exposed to high levels of radionuclides, into the surrounding landscape underscores the need to better understand boar movement patterns in order to establish policies for managing shipping restrictions for boar meat and develop management strategies. In this study, we quantified the genetic population structure of boar in and around Fukushima prefecture using sequence data of the mitochondrial DNA control region and MIG-seq analysis using 348 boar samples to clarify boar dispersal patterns. Among boar samples, seven Asian haplotypes and one European haplotype were detected. The European haplotype originated from hybridization between domestic pigs and native boar in the evacuation zone after the accident and was detected in 15 samples across a broad geographic area. Our MIG-seq analysis revealed genetic structure of boar was significantly different between boar inhabiting the eastern (including FEZ. i.e., East clade) and western (i.e., West clade) regions in Fukushima prefecture. In addition, we investigated the relationships between boar dispersal and Cesium (Cs)-137 activity concentrations in boar muscle using MIG-seq genetic data in Nihonmatsu city, located in the central-northern region of Fukushima. High Cs-137 activity concentrations, exceeding 1000 Bq/kg, in boar muscle had a significantly high probability of belonging to the East clade within localized regions. Thus, our results provide evidence of the spatial scale of dispersal of individuals or offspring of boar from the FEZ. Results of this research also indicate that dispersal of individuals between areas with different Cs-137 contamination levels is one of the biggest factors contributing to variation in Cs-137 activity concentration in boar muscle within localized regions.

Unique transport paths of 137Cs from the Indian to Southern Oceans.

To assess ocean-scale transport systems, we examined the latitudinal cross-sectional distribution of 137Cs activity concentrations in the Indian and Southern Oceans between December 2019 and January 2020 using low-background γ-spectrometry. At 0°-20°S, 137Cs concentrations exhibited a gradual decrease below the mixing layer (1-0.1 mBq/L). However, the concentrations steeply decreased toward the Southern Ocean along a transect of 30°-60°S (from 0.8 to 0.02 mBq/L) with minor vertical variation at each site. For the 137Cs inventories (0-800 m depth) from 15 to 600 Bq/m2, a maximum value was recorded at 30°S, indicating the downwelling of 137Cs as a reservoir for the Subantarctic Mode Water. The significantly low concentrations (0.02 mBq/L) at 60°S suggest minimal transport of 137Cs to the Southern Ocean. These findings assist in understanding 137Cs circulation patterns and provide valuable insights into the transport pathways of soluble contaminants.

Conceptualization of the comprehensive phyto-radiotoxicity incurred by radiocesium and strategies to expunge the metal using biotechnological and phytoremediative approaches.

Agricultural pollution with 137Cs is an ecological threat due to its sustained half-life and radioactivity. Release of radiocesium isotopes after major nuclear power plant accidents like the Fukushima Dai-ichi and the Chernobyl nuclear power plant disasters have severely affected the surrounding growth of agricultural crops and vegetables cultivated across extensive areas. Even years after the nuclear accidents, biosafety in these agricultural fields is still questionable. Due to similarity in charge and ionic radius between radiocesium and K+, the radionuclides are promiscuously uptaken via K+ channels expressed in plants. Bioaccumulation of radiocesium reportedly promotes physiological and anatomical anomalies in crops due to radiation and also affects the rhizospheric architecture. Due to radiation hazard, the ecological balance and quality are compromised and ingestion of such contaminated food results in irreversible health hazards. Recently, strategies like exogenous supplementation of K+ or genetic engineering of K+ channels were able to reduce radiocesium bioaccumulation in plants taking the advantage of competition between radiocesium and K+ translocation. Furthermore, bioremediation strategies like phycoremediation, mycoremediation, phytoremediation and rhizofiltration have also showed promising results for removing radiocesium from polluted sites. It has been proposed that these eco-friendly ways can be adopted to de-pollute the contaminated sites prior to subsequent cultivation of crops and vegetables. Hence it is essential to: 1) understand the basic radiotoxic effects of radiocesium on agricultural crops and surrounding vegetation and, 2) design sustainable ameliorative strategies to promote radiocesium tolerance for ensuring food and social security of the affected population.

Particulate matter from water moss of a large Siberian river: Morphometric, mineral, elemental and radionuclide composition.

Particulate matter trapped by tufts of water moss Fontinalis antipyretica inhabiting fast flowing waters of the Yenisei River (Siberia, Russia) contaminated with artificial radionuclides has been studied as a potential monitor of radioactive releases to the river. Particulate matter, which was removed from wet tufts of water moss of the Yenisei by rinsing them in water, constituted at least 38% of bulk dry weight of the moss biomass sample and was similar in the contents of chemical elements, minerals, organic matter, and artificial radionuclides to bottom sediments of the Yenisei. Considerable bulk percentages of artificial radionuclides in the sample of water moss, 77% of 137Cs, 44% of 60Co, 41% of 152Eu, 55% of 154Eu, 66% of 241Am, and 34-36% of plutonium were associated with extracellular particles. The comparative study and correlation analysis suggested that 137Cs was mainly associated with mineral particles trapped by moss and that organic matter was responsible for binding plutonium in samples of water moss. Consequently, analysis of extracellular particles of water moss can provide data on contents and speciation of radionuclides transported by water current. Although a considerably high proportion of particulate matter had been washed out from tufts of water moss, some extracellular mineral particulate material and a large number of epiphytic diatoms remained attached to leaves of water moss. Our study proves that particulate matter trapped by water moss can be used as an informative monitor to trace radioactive pollutants transported by water current in running waters deficient in bottom sediments and potential biomonitors.

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.

Oscillatory Cs-137 Distribution Pattern in Scotch Pine Bark.

The vertical distribution of the anthropogenic radionuclide Cs-137 in the Scots pine (Pinus sylvestris L.) bark was studied in two model trees in the radioactive contamination zone of the Bryansk region. Each tree was divided into 10-cm bars from the trunk base to a length of 17 m, and the bark with the bast was separated from each bar to obtain a separate sample. In addition to Cs-137, the natural radionuclide K-40 was measured in the bark of model tree 2 from the trunk base to a 6.5-m length. Specific activities of Cs-137 and K-40 were measured by γ-ray spectrometry. The vertical distribution of Cs-137 in the bark was for the first time observed to have a wave-like pattern with a period of approximately 1 m. The K-40 distribution showed a similar oscillatory pattern, consistent with a similar mechanism responsible for potassium and cesium behavior in woody plants. The correlation coefficient between specific activities of Cs-137 in model trees 1 and 2 was 0.80; the correlation coefficient between Cs-137 and K-40 activities in model tree 2 was 0.45. Cs-137 was assumed to provide a radiotracer to assess the intake and distribution of chemical elements in Scotch pine tissues. The oscillatory pattern observed for the vertical distributions of cesium and potassium in the pine bark has not been described in the available literature before.

Bioaccumulation of contaminants in Scarabaeidae and Silphidae beetles at sites polluted by coal combustion residuals and radiocesium.

Anthropogenic contamination from coal-fired power plants and nuclear reactors is a pervasive issue impacting ecosystems across the globe. As a result, it is critical that studies continue to assess the accumulation and effects of trace elements and radionuclides in a diversity of biota. In particular, bioindicator species are a powerful tool for risk assessment of chemically contaminated habitats. Using inductively coupled plasma mass spectrometry (ICP-MS) and auto-gamma counting, we analyzed trace element and radiocesium contaminant concentrations in Scarabaeidae and Silphidae beetles (Order: Coleoptera), important taxa in decomposition and nutrient cycling, at contaminated and reference sites on the Savannah River Site, South Carolina, U.S. Our results revealed variability in trace element concentrations between Scarabaeidae and Silphidae beetles at uncontaminated and contaminated sites. Compared to Scarabaeidae, Silphidae had higher levels of chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), and zinc (Zn). Unexpectedly, concentrations of Cr, Cu, and Ni were higher in both taxa at the uncontaminated sites. Scarabaeidae and Silphidae beetles at the coal combustion waste site consistently had high concentrations of arsenic (As), and Scarabaeidae had high concentrations of selenium (Se). Of the 50 beetles analyzed for radiocesium levels, two had elevated radioactivity concentrations, both of which were from a site contaminated with radionuclides. Our results suggest carrion beetles may be particularly sensitive to bioaccumulation of contaminants due to their trophic position and role in decomposition, and thus are useful sentinels of trace element and radionuclide contamination.

Radioactivity of anthropogenic and natural radionuclides in marine sediments of the Chaun Bay, East Siberian Sea.

Natural radioactive isotopes serve as a useful proxy of geological and geochemical processes in marine environment, while radiocesium serves as an indicator of man-made contamination. Monitoring of natural and anthropogenic radioactivity under conditions of the climate changes in the Arctic region is of high importance in investigations of this natural system. For the first time, we report the data on spatial distribution of natural (232Th, 226Ra, 40K) and anthropogenic (137Cs) radionuclide activities in the marine sediments from Chaun Bay (East Siberian Sea). The measured activity concentrations varied in the range 23.7-77.9 (mean 39.2) Bq kg-1 for 232Th, 16.5-39.3 (mean 26.6) Bq kg-1 for 226Ra, 535-991 (mean 726) Bq kg-1 for 40K, and 0.5-4.7 (mean 2.0) Bq kg-1 for 137Cs. The radiocesium level in the sediments showed no local sources of anthropogenic pollution in the Chaun Bay, while the average activity concentration of 40K was 1.8 times higher than worldwide.

Effect of soil organic matter on the fate of 137Cs vertical distribution in forest soils.

Understanding the fate of the vertical distribution of radiocesium (137Cs) in Japanese forest soils is key to assessing the radioecological consequences of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The 137Cs behavior in mineral soil is known to be primarily governed by interaction with clay minerals; however, some observations suggest the role of soil organic matter (SOM) in enhancing the mobility of 137Cs. Here we hypothesized that soil organic carbon (SOC) concentration profile determines the ultimate vertical pattern of 137Cs distribution in Japanese forest soils. In testing this hypothesis, we obtained soil samples that were collected before the FDNPP accident at four forest sites with varying SOC concentration profiles and quantified the detailed vertical profile of 137Cs inventory in the soils roughly half a century after global fallout in the early 1960 s. Results showed that the higher the SOC concentration in the soil profile, the deeper the 137Cs downward penetration. On the basis of the data for surface soils (0-10 cm), the 137Cs retention ratio for each of the 2-cm thick layers was evaluated as the ratio of 137Cs inventory in the target soil layer to the total 137Cs inventory in and below the soil layer. A negative correlation was found between the ratio and SOC concentration of the layer across all soils and depths. This indicates that the ultimate fate of 137Cs vertical distribution can be predicted as a function of SOC concentration for Japanese forest soils, and provides further evidence for SOM effects on the mobility and bioavailability of 137Cs in soils.

Visualization of the initial radiocesium dynamics after penetration in living apple trees with bark removal using a positron-emitting 127Cs tracer.

Following the Fukushima nuclear accident in March 2011, radiocesium (rCs) contamination in deciduous trees remains over 10 years later even though the trees were leafless at the time of the accident. This phenomenon is considered to be the result of repeated retranslocation of rCs that initially penetrated the bark into the internal tissues. To implement effective measures after a possible accident in the future, it is necessary to clarify how rCs is translocated in the tree after penetration. In this study, rCs translocation was dynamically visualized using a positron-emitting tracer imaging system (PETIS) and autoradiography after the bark of apple branches was removed. The PETIS results showed the translocation of 127Cs from the branch to young shoots and the main stem in apple trees under controlled spring growing conditions. The transport velocity of rCs in the branch was faster than that in the main stem. The transport of rCs, which was either acropetal or basipetal, in the main stem through the branch junction favored basipetal movement. Autoradiography of transverse sections of the main stem indicated that basipetal translocation was due to transport in the phloem. This study demonstrated the initial translocation responses of rCs similar to previous field research, which indicates that rCs transport to the young shoots tends to be higher under controlled conditions. Our laboratory-based experimental system may be useful to gain an improved understanding of rCs dynamics in deciduous trees.

Biodistribution of naturally occurring radionuclides and radiocesium in wild European perch (Perca fluviatilis).

Wild European perch (Perca fluviatilis) is one of the most important freshwater fish species, in Sweden, due to its widespread and his value for recreational fishing. Little it is known regarding the biodistribution of naturally occurring radionuclides such as 238U, 234U, 226Ra, 210Po in perch. Therefore, in this study, perches from five lakes located in different counties in Sweden were collected to investigate the biodistribution of 238U, 234U, 226Ra, 210Po and 137Cs in organs and tissues of perch as well as their radiological impact. The results showed that uranium radionuclides ranged between 0.1 and 6 Bq/kg with an average value of 1.1 ± 1.5 Bq/kg. 226Ra varied from 0.4 to 8 Bq/kg with a mean concentration of 1.7 ± 1.9 Bq/kg. The ranged of 210Po was 0.5 - 250 Bq/kg, with an average value of 24 ± 52 Bq/kg. On the other hand, the highest activity concentration of 137Cs, 151 ± 1 Bq/kg, was detected in muscle samples of perch from Redsjösjön lake. For uranium radionuclides and 226Ra uptake from water is the main source whereas for 210Po and 137Cs the uptake is controlled by the perch diet. Regarding naturally occurring radionuclides, the perch tended to accumulated uranium radionuclides in fins, gills, and skin; 226Ra in bones, fins and skin and 210Po in the organs linked to digestive system. Finally, in case of consumption, it is advised the consumption of skinned fillets of perch due to the higher bioaccumulation of the radionuclides investigated in the skin and scales.

Soil dust and bioaerosols as potential sources for resuspended 137Cs occurring near the Fukushima Dai-ichi nuclear power plant.

One of the current pathways to radiation exposure, caused by the radionuclides discharged during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, is the inhalation of resuspended 137Cs present in the air. Although wind-induced soil particle resuspension is recognized as a primary resuspension mechanism, studies regarding the aftermath of the FDNPP accident have suggested that bioaerosols can also be a potential source of atmospheric 137Cs in rural areas, although the quantitative impact on the atmospheric 137Cs concentration is still largely unknown. We propose a model for simulating the 137Cs resuspension as soil particles and bioaerosols in the form of fungal spores, which are regarded as a potential candidate for the source of 137Cs-bearing bioaerosol emission into the air. We apply the model to the difficult-to-return zone (DRZ) near the FDNPP to characterize the relative importance of the two resuspension mechanisms. Our model calculations show that soil particle resuspension is responsible for the surface-air 137Cs observed during winter-spring but could not account for the higher 137Cs concentrations observed in summer-autumn. Higher 137Cs concentrations are reproduced by the emission of 137Cs-bearing bioaerosols (fungal spores) that replenishes the low-level soil particle resuspension in summer-autumn. Our model results show that the accumulation of 137Cs in fungal spores and large emissions of spores characteristic of the rural environment are likely responsible for the presence of biogenic 137Cs in the air, although the former must be experimentally validated. These findings provide vital information for the assessment of the atmospheric 137Cs concentration in the DRZ, as applying the resuspension factor (m-1) from urban areas, where soil particle resuspension would dominate, can lead to a biased estimate of the surface-air 137Cs concentration. Moreover, the influence of bioaerosol 137Cs on the atmospheric 137Cs concentration would last longer, because undecontaminated forests commonly exist within the DRZ.