Accumulation of radiocesium by mushrooms in the environment: a literature review

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.

The elements of life: A biocentric tour of the periodic table

Living systems are built from a small subset of the atomic elements, including the bulk macronutrients (C,H,N,O,P,S) and ions (Mg,K,Na,Ca) together with a small but variable set of trace elements (micronutrients). Here, we provide a global survey of how chemical elements contribute to life. We define five classes of elements: those that are (i) essential for all life, (ii) essential for many organisms in all three domains of life, (iii) essential or beneficial for many organisms in at least one domain, (iv) beneficial to at least some species, and (v) of no known beneficial use. The ability of cells to sustain life when individual elements are absent or limiting relies on complex physiological and evolutionary mechanisms (elemental economy). This survey of elemental use across the tree of life is encapsulated in a web-based, interactive periodic table that summarizes the roles chemical elements in biology and highlights corresponding mechanisms of elemental economy.

Speciation and spatial distribution of Eu(III) in fungal mycelium

Europium, as an easy-to-study analog of the trivalent actinides, is of particular importance for studying the behavior of lanthanides and actinides in the environment. Since different soil organisms can influence the migration behavior of these elements, a detailed knowledge of these interaction mechanisms is important. The aim of this study was to investigate the interaction of mycelia of selected wood-inhabiting (S. commune, P. ostreatus, L. tigrinus) and soil-inhabiting fungi (L. naucinus) with Eu(III). In addition to determining the Eu(III) complexes in the sorption solution, the formed Eu(III) fungal species were characterized using scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, chemical microscopy in combination with the time-resolved laser-induced fluorescence spectroscopy. Our data show that S. commune exhibited significantly higher Eu(III) binding capacity in comparison to the other fungi. Depending on fungal strain, the metal was immobilized on the cell surface, in the cell membranes, and within the membranes of various organelles, or in the cytoplasm in some cases. During the bioassociation process two different Eu(III) fungal species were formed in all investigated fungal strain. The phosphate groups of organic ligands were identified as being important functional groups to bind Eu(III) and thus immobilize the metal in the fungal matrix. The information obtained contributes to a better understanding of the role of fungi in migration, removal or retention mechanisms of rare earth elements and trivalent actinides in the environment.

Developing field-scale, gentle remediation options for nuclear sites contaminated with 137Cs and 90Sr: The role of Nature-Based Solutions

The remediation of contaminated land using plants, bacteria and fungi has been widely examined, especially in laboratory or greenhouse systems where conditions are precisely controlled. However, in real systems at the field scale conditions are much more variable and often produce different outcomes, which must be fully examined if 'gentle remediation options', or GROs, are to be more widely implemented, and their associated benefits (beyond risk-management) realized. These secondary benefits can be significant if GROs are applied correctly, and can include significant biodiversity enhancements. Here, we assess recent developments in the field-scale application of GROs for the remediation of two model contaminants for nuclear site remediation (⁹⁰Sr and ¹³⁷Cs), their risk management efficiency, directions for future application and research, and barriers to their further implementation at scale. We also discuss how wider benefits, such as biodiversity enhancements, water filtration etc. can be maximized at the field-scale by intelligent application of these approaches.

Relationship of 137Cs with Fungal Spore Tracers in the Ambient Aerosols from Fukushima after the 2011 Nuclear Accident, East Japan

Even after 7 years of the nuclear accident that occurred in 2011 at the Fukushima Dai-ichi nuclear power plant (F1NPP), high levels of 137Cs have been detected in ambient aerosols from some polluted areas of Fukushima. Higher levels of radionuclides were often observed in the atmosphere during and after rain events. We presume that biological processes such as fungal activity associated with higher relative humidity may be involved with a possible emission of radioactivity to the atmosphere, which was originally emitted from the F1NPP accident and was deposited over the ground, forest, soil, etc. Here, we report, for the first time, relationships of 137Cs and organic tracers of fungal spores (i.e., arabitol, mannitol and trehalose) in the aerosol samples collected from Fukushima, Japan. Although we found twice-higher concentrations of 137Cs at nighttime than at daytime, fungal spore tracers did not show a consistent trend to 137Cs, that is, organic tracers at nighttime were similar with those at daytime or were even higher in daytime. This study has not clearly demonstrated that fungal spores are the important source of high levels of 137Cs at nighttime. The current unclear relationship is probably associated with the sampling strategy (four consecutive days with a sampling on/off program for day/nighttime samples) taken in this campaign, which may have caused a complicated meteorological situation.

Spatial risk assessment of radiocesium contamination of edible mushrooms - Lessons from a highly frequented recreational area

The radioactive contamination of edible mushrooms increases human health hazards, especially in high mushroom collection intensity areas. Today only coarse-scale data with low spatial resolution are available, which prevents us from predicting human risk. To reduce the risk for human health, we need spatially explicit recommendations at landscape-scale. We used the Bavarian Forest National Park, a famous mushroom hunting location in Europe, as a model system. We aimed to increase the predictability of the contamination of the two most prominent mushroom species, bay boletus (Imleria badia) and ceps (Boletus edulis), and provide an efficient evidence-based risk assessment at landscape-scale. We revealed a high and a low ¹³⁷Cs-activity impact area based on soil samples, which is also reflected by the mushroom species. ¹³⁷Cs-activity of Imleria badia is about five times higher than the contamination of Boletus edulis; with one-third of the Imleria badia samples being over the statutory limit. The difference of contamination between species is more pronounced in the high-impact area. Elevation is a strong predictor in contrast to orientation of slopes. In high-impact areas, mushrooms showed higher ¹³⁷Cs-activities at lower elevations. Soil analysis revealed that the maximum of the ¹³⁷Cs-activity is still in the organic layers, indicating further mushroom contamination. We recommend using only Boletus edulis in the low-impact area for diet. We suggest that Boletus edulis bear a lower health risk than Imleria badia due to lower ¹³⁷Cs-activities. Nevertheless, we need more landscape-scale studies to assess the ¹³⁷Cs contamination risk for humans. Studies are primarily important in high-impact areas, which can be roughly identified by using soil contamination maps. The focus should be on high accumulating mushroom species like Imleria badia. Our study can serve as a blueprint to rapidly assess human health risks caused by radioactive contamination in landscapes intensively used by mushroom collectors.

Parameter Values for Estimation of Internal Doses from Ingestion of Radioactive Fallout from Nuclear Detonations

ABSTRACT

This paper suggests values or probability distributions for a variety of parameters used in estimating internal doses from radioactive fallout due to ingestion of food. Parameters include those needed to assess the interception and initial retention of radionuclides by vegetation, translocation of deposited radionuclides to edible plant parts, root uptake by plants, transfer of radionuclides from vegetation into milk and meat, transfer of radionuclides into non-agricultural plants and wildlife, and transfer from food and drinking water to mother's milk (human breast milk). The paper includes discussions of the weathering half-life for contamination on plant surfaces, biological half-lives of organisms, food processing (culinary factors), and contamination of drinking water. As appropriate, and as information exists, parameter values or distributions are specific for elements, chemical forms, plant types, or other relevant characteristics. Information has been obtained from the open literature and from publications of the International Atomic Energy Agency. These values and probability distributions are intended to be generic; they should be reviewed for applicability to a given location, time period, or season of the year, as appropriate. In particular, agricultural practices and dietary habits may vary considerably both with geography and over time in a given location.

Radiocaesium in Tricholoma spp. from the Northern Hemisphere in 1971-2016

A considerable amount of data has been published on the accumulation of radiocaesium (¹³⁴Cs and particularly, ¹³⁷Cs) in wild fungi since the first anthropogenically influenced releases into the environment due to nuclear weapon testing, usage and subsequently from major accidents at nuclear power plants in Chernobyl (1986) and Fukushima (2011). Wild fungi are particularly susceptible to accumulation of radiocaesium and contamination persists for decades after pollution events. Macromycetes (fruiting bodies, popularly called mushrooms) of the edible fungal species are an important part of the human and forest animal food-webs in many global locations. This review discusses published occurrences of ¹³⁴Cs and ¹³⁷Cs in twenty four species of Tricholoma mushrooms sourced from the Northern Hemisphere over the last five decades, but also includes some recent data from Italy and Poland. Tricholoma are an ectomycorrhizal species and the interval for contamination to permeate to lower soils layers which host their mycelial networks, results in a delayed manifestation of radioactivity. Available data from Poland, over similar periods, may suggest species selective differences in accumulation, with some fruiting bodies, e.g. T. portentosum, showing lower activity levels relative to others, e.g. T. equestre. Species like T. album, T. sulphurescens and T. terreum also show higher accumulation of radiocaesium, but reported observations are few. The uneven spatial distribution of the data combined with a limited number of observations make it difficult to decipher any temporal contamination patterns from the observations in Polish regions. When data from other European sites is included, a similar variability of ¹³⁷Cs activity is apparent but the more recent Ukrainian data appears to show relatively lower activities. ⁴⁰K activity in mushrooms which is associated with essential potassium, remains relatively constant. Further monitoring of ¹³⁷Cs activity in wild mushrooms would help to consolidate these observations.

Aggregated transfer factor of 137Cs in wild edible mushrooms collected in 2016-2020 for long-term internal dose assessment use

Ingestion of edible wild mushrooms collected in areas contaminated with radiocesium released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident may pose a risk of internal dose to their consumers. A species-specific aggregated transfer factor (T_ag), which is calculated using radiocesium concentration in a wild mushroom species (Bq kg^-1 wet mass [WM]) divided by the total concentration in the soil surface area (Bq m^-2), would be a useful tool to estimate the dose from wild mushrooms by ingestion. In this study, we especially focused on the T_ag data collected in 2016-2020 to use these values for a long-term dose assessment. We assumed that ¹³⁷Cs concentrations after that year were almost the same, thus the soil-mushroom system would be in an apparent steady-state condition. In all, we could obtain T_ag values of ¹³⁷Cs in 62 edible wild mushroom species native to Japan. The geometric mean (GM) values were 1.5 × 10^-3 m² kg^-1 WM using GMs of 13 saprobic type species and 5.0 × 10^-3 m² kg^-1 WM using GMs of 21 mycorrhizal type species (N > 2). On average, the GMs of species-specific T_ag values were 1.9 ± 0.9 times higher than those reported in a previous study of wild mushrooms made after the FDNPP accident, probably due to the different approaches for T_ag calculation.

Uranium(VI) bioassociation by different fungi - a comparative study into molecular processes

After the Chernobyl and Fukushima incidents it has become clear that fungi can take up and accumulate large quantities of radionuclides and heavy metals, but the underlying processes are not well understood yet. For this study, the molecular interactions of uranium(VI) with the white-rot fungi, Schizophyllum commune and Pleurotus ostreatus, and the soil-living fungus, Leucoagaricus naucinus, were investigated. First, the uranium concentration in the biomass was determined by time-dependent bioassociation experiments. To characterize the molecular interactions, uranium was localized in the biomass by transmission electron microscopy analysis. Second, the formed uranyl complexes in both biomass and supernatant were determined by fluorescence spectroscopy. Additionally, possible bioligands in the supernatant were identified. The results show that the discernible interactions between metals and fungi are similar, namely biosorption, accumulation, and subsequent crystallization. But at the same time, the underlying biochemical mechanisms are different and specific to the fungal species. In addition, Schizophyllum commune was found to be the only fungus that, under the chosen experimental conditions, released tryptophan and other indole derivatives in the presence of uranium(VI) as determined by nuclear magnetic resonance spectroscopy. These released substances most likely act as messenger molecules rather than serving the direct detoxification of uranium(VI).

Assessment of potentially reusable edible wild plant and mushroom gathering sites in eastern Fukushima based on external radiation dose

Edible wild plant/mushroom gathering, an essential food acquisition and outdoor recreation activity in rural areas, has declined in the area near the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in eastern Japan. The present study first evaluated the spatial distribution of potential gathering sites of various edible wild plant/mushroom species before the accident by administering a face-to-face questionnaire survey to local gatherers as well as utilizing the group analytical hierarchy process (AHP) and geographic information systems (GIS). Then, the damage to and future reusability of previous gathering sites were estimated from the perspective of the external radiation dose by overlaying maps of potential gathering sites and the time-series air dose rate (ADR) up to 2050 incorporating different gathering frequency scenarios. The study area is located in Kawauchi village in the eastern Fukushima prefecture, at 12-30 km southwest of FDNPP. The spatial distributions of gathering sites before the accident differed widely among species at the local scale because of their different environmental preferences. In contrast, the temporal variation in the reusability of the gathering sites was notably small among different species. The external radiation dose in the potential gathering sites declined sharply in the early post-accident years and gradually in the later years through the physical decay of radiocesium, i.e., ¹³⁴Cs and ¹³⁷Cs, with different half-lives. Moreover, the gathering frequency and heterogeneous distribution of radiocesium substantially affected the temporal variation in reusability for the gathering sites. These results indicate that an early resumption of gathering would be possible by reducing the gathering frequency and avoiding higher ADR areas, whereas it will take a much longer period to resume gathering in areas with higher ADR. Further research is required that considers both internal and external radiation doses in the geospatial context for the restoration and safer use of edible wild plants/mushrooms.

Spatial distribution of 137Cs concentrations in mushrooms (Boletus hiratsukae) and their relationship with soil exchangeable cation contents

The activity concentrations of radiocesium (¹³⁷Cs) in wild mushrooms are reported to vary according to species, genus or ecological types. In addition, the concentration fluctuates among the same species collected within the same area. Therefore, we investigated whether the ¹³⁷Cs concentration of wild mushrooms would be (1) spatially biased, or (2) influenced by the ¹³⁷Cs or exchangeable potassium concentrations in the soils below. We set two survey plots 300 m apart in a Himalayan cedar forest in Tsukuba, Japan, where ca. 30 kBq/m² of ¹³⁷Cs was deposited after the Fukushima Nuclear Power Plant accident. From these plots, we collected fruit-bodies (fungal structures for spore production) of co-occurring Boletus hiratsukae, a mycorrhizal species, as well as from the soil below. The mean ¹³⁷Cs concentrations in the fruit-bodies were significantly different between the two plots, but no difference was observed in the soil ¹³⁷Cs concentration between the plots. Significant spatial autocorrelation was observed in the ¹³⁷Cs concentration in the organic layer for both sites, but no significant spatial autocorrelation was observed in the ¹³⁷Cs of fruit-bodies. Therefore, the variation in the ¹³⁷Cs concentrations of co-occurred B. hiratsukae was not explained by spatial bias or radioactivity in the below soil. In contrast, the exchangeable potassium concentration in the soil was negatively correlated with the ¹³⁷Cs in the fruit-bodies. Our results suggest that the ¹³⁷Cs absorption of wild mushrooms would be suppressed by the competitive effect of exchangeable potassium in the surrounding soils.

Rain-induced bioecological resuspension of radiocaesium in a polluted forest in Japan

It is the conventional understanding that rain removes aerosols from the atmosphere. However, the question of whether rain plays a role in releasing aerosols to the atmosphere has recently been posed by several researchers. In the present study, we show additional evidence for rain-induced aerosol emissions in a forest environment: the occurrence of radiocaesium-bearing aerosols in a Japanese forest due to rain. We carried out general radioactive aerosol observations in a typical mountainous village area within the exclusion zone in Fukushima Prefecture to determine the impacts and major drivers of the resuspension of radiocaesium originating from the nuclear accident in March 2011. We also conducted sampling according to the weather (with and without rain conditions) in a forest to clarify the sources of atmospheric radiocaesium in the polluted forest. We found that rain induces an increase in radiocaesium in the air in forests. With further investigations, we confirmed that the fungal spore sources of resuspended radiocaesium seemed to differ between rainy weather and nonrainy weather. Larger fungal particles (possibly macroconidia) are emitted during rainy conditions than during nonrainy weather, suggesting that splash generation by rain droplets is the major mechanism of the suspension of radiocaesium-bearing mould-like fungi. The present findings indicate that radiocaesium could be used as a tracer in such research fields as forest ecology, meteorology, climatology, public health and agriculture, in which fungal spores have significance.

137Cs activity concentration in mushrooms from the Bobrůvka river valley

In the 2017-2018 mushrooming seasons at the (Bohemian-Moravian Highlands near Dolní­ Roží­nka) a total of 505 mushrooms belonging to 9 species were collected, and analyzed by gamma spectrometry for 137Cs activity. The maximum 137Cs activity of 575 Bq.kg-1 was detected in Boletus edulis species, what in native state, is just below the allowed limit. In contrast, in mushroom Imleria badia, which is reported to be associated with the highest cumulative capability from all fungi species, detected activity level was only 316 Bq. kg-1. However, differences in mean contamination values were not significant due to high variability. It was shown, that activity concentration is not dependent on the weight (size) of Imleria badia. Our results also confirmed generally well known lower 137Cs activity in the Russula species representatives belonging to the group of gills or lamella bearing mushrooms.

A long-term study of radionuclide concentrations in mushrooms in the 30-km zone around the Mining-and-Chemical Combine (Russia)

¹³⁷Cs concentrations were measured in mushrooms in an area affected by radioactive discharges of the Mining-and-Chemical Combine (MCC) (Rosatom, Russia) in 2002-2017. The sources of radionuclides in the study sites were global fallouts and waterborne and airborne radioactive discharges of the MCC. The mushroom species Suillus granulatus and S. luteus showed the highest ¹³⁷Cs concentrations (140-7100 Bq kg^-1) for this area. Over the entire monitoring period, no significant change in ¹³⁷Cs concentration was observed in the Suillus spp. samples collected from the sites with the aerial deposition of radionuclides. In the floodplain site with the radionuclide deposition from water and air, a significant decrease in the average ¹³⁷Cs concentration was observed in the period between 2004 and 2017: a three-fold decrease in Suillus spp. and a nine-fold decrease in Lactarius deliciosus. The effective half-lives of ¹³⁷Cs in fruiting bodies of the mushrooms L. deliciosus and Suillus spp. in this site were 3.6 ± 0.6 and 9.2 ± 2.7 years, respectively.

Extensive analysis of radiocesium concentrations in wild mushrooms in eastern Japan affected by the Fukushima nuclear accident: Use of open accessible monitoring data

After the Fukushima Daiichi Nuclear Power Plant accident, there has been an increasing concern regarding the contamination of wild mushrooms with radiocesium (¹³⁴Cs and ¹³⁷Cs) in eastern Japan. In this study, we analyzed the radioactivity monitoring data of 3189 wild edible mushrooms of 107 species collected by the 265 local municipalities in eastern Japan to investigate the radiocesium levels in wild mushrooms. Results of the analysis showed that radiocesium concentrations in mushrooms were normalized with radioactivity deposition data from aircraft monitoring, and then we evaluated the effects of species, sampled location, sampling year and regional deviation between ¹³⁴Cs and ¹³⁷Cs activity of specimens using a hierarchical Bayesian approach considering spatial autocorrelation (an intrinsic CAR model). Normalized activity concentration by species ranged from 1.1×10^-4 to 2.3×10^-2 (m² kg^-1, fresh weight). As reported in previous studies, the mycorrhizal species tended to have higher radiocesium concentrations. Some saprophytic species (e.g. Pholiota lubrica) also had high concentrations. For the mushroom species that were also evaluated in the post-Chernobyl studies, we found that the same species had similar trends of absorption capacities. Our results indicate the extensive analysis of public monitoring data is helpful to understand the situation of mushroom contamination and evaluate the internal dose by ingestion of wild mushrooms according to species and areas.

Fungal spore involvement in the resuspension of radiocaesium in summer

We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012. During the survey periods from 2012 to 2015, the activity concentrations of radiocaesium in air ranged from approximately 10-5 to 10-2 Bq per m3 and were higher in the warm season than in the cold season. Electron microscopy showed that the particles collected on filters in summer were predominantly of biological origin (bioaerosols), with which the observed radiocaesium activity concentration varied. We conducted an additional aerosol analysis based on fluorescent optical microscopic observation and high-throughput DNA sequencing technique to identify bioaerosols at Namie in 2015 summer. The concentrations of bioaerosols fluctuated the order of 106 particles per m3, and the phyla Basidiomycota and Ascomycota (true Fungi) accounted for approximately two-thirds of the bioaerosols. Moreover, the fungal spore concentration in air was positively correlated with the radiocaesium concentration at Namie in summer 2016. The bioaerosol emissions from Japanese mixed forests in the temperate zone predominately included fungal cells, which are known to accumulate radiocaesium, and should be considered an important scientific issue that must be addressed.

Evaluation of abundance of artificial radionuclides in food products in South Korea and sources

Food samples are collected nationwide from January 2016 to February 2017 and their contents of artificial radionuclides are measured to address the growing concerns regarding the radioactive contamination of food products in Korea. Specifically, 900 food samples are collected for this study and their contents of representative artificial radionuclides ¹³⁴Cs, ¹³⁷Cs, ^239,240Pu, and ⁹⁰Sr are analyzed. The analysis shows that the activity concentrations of ¹³⁷Cs in fish range from minimum detectable activity (MDA) to 340 mBq/kg of fresh weight. The concentration factor (CF) determined for ¹³⁷Cs as a measure of its bioavailability is calculated to be ca. 74 and found to be very similar to that (100) recommended by the International Atomic Energy Agency. With an MDA of <0.221 mBq/kg, the results reveal that ^239,240Pu values in fish are below the MDA. The activity concentrations of ¹³⁷Cs and ⁹⁰Sr are lower than the MDA in both shellfish and seaweed, while the activity concentrations of ^239,240Pu in shellfish range from 0.26 to 2.18 mBq/kg, and for seaweed samples range from 2.07 to 3.38 mBq/kg. The atom ratios of ²⁴⁰Pu/²³⁹Pu in shellfish caught at the Korean coast vary from 0.209 to 0.237, with a mean of 0.227. The higher ²⁴⁰Pu/²³⁹Pu atom ratio determined in shellfish is thought to be caused by the plutonium transported from the Pacific Proving Grounds rather than other sources such as the Fukushima nuclear power plant accident. The activity concentrations of ¹³⁷Cs in mushrooms are found to vary from 1.0 to 21.4 Bq/kg, with the highest concentrations observed in the Oak (shiitake) and Sarcodon asparatus. ¹³⁴Cs is detected in three mushroom specimens collected from Jeju Island and about 3-3.6% of ¹³⁷Cs present in the wild mushrooms native to the Jeju Island are introduced as a result of the Fukushima nuclear plant accident. The annual effective doses of ¹³⁷Cs received through consumption of mushrooms and fish are 2.0 × 10^-4 mSv yr^-1 and 3.9 × 10^-5 mSv yr^-1, and those values are negligible compared to the annual effective doses limit of 1 mSv yr^-1.

Artificial 137Cs and natural 40K in mushrooms from the subalpine region of the Minya Konka summit and Yunnan Province in China

A study on ¹³⁷Cs pollution and activity concentrations of ⁴⁰K in mushrooms of the genera Cortinarius, Leccinum, Russula, Tricholoma, Tylopilus, and Xerocomus from two neighboring regions in southwest China in 2010-2013 revealed different patterns of pollution with ¹³⁷Cs, which seemed to be highly dependent on climate conditions. Tricholoma matsutake was collected in Yunnan before and after the Fukushima Dai-ichi nuclear accident and showed similar contamination with ¹³⁷Cs. Mushrooms from the elevation of 2800-3480 m above sea level on the east slope of Minya Konka and forest topsoil showed higher contamination with ¹³⁷Cs than mushrooms from the highlands of Yunnan. In detail, the activity concentration of ¹³⁷Cs in caps of mushrooms from Minya Konka were in the range 62 ± 6-280 ± 150 Bq kg^-1 dry biomass and from Yunnan at < 4.4-83 ± 3 Bq kg^-1 dry biomass. The climate in the region of the Minya Konka is much colder than in Yunnan, which seems to favor deposition of ¹³⁷Cs at higher altitudes from global atmospheric circulation. The activity concentration of ⁴⁰K in mushrooms and soils highly exceeded that of ¹³⁷Cs. The assessed annual effective doses for ¹³⁷Cs in 1 kg of consumed mushrooms of the genera Leccinum and Xerocomus in Yunnan were low, i.e., in the range < 0.0043-0.049 ± 0.004 μSv, while those for ⁴⁰K were 0.26 ± 0.02-0.81 ± 0.09 μSv.

Radionuclides in mushrooms and soil-to-mushroom transfer factors in certain areas of China

Activity concentrations of ²³⁸U, ²²⁶Ra, ²²⁸Ra, ¹³⁷Cs and ⁴⁰K in 64 mushroom samples collected in China from Yunnan, Fujian and Heilongjiang Provinces, were measured. Gamma-ray emissions were determined by using high-purity germanium (HPGe) γ spectrometry. The range of concentrations (Bq kg^-1 dry weight) for ²³⁸U, ²²⁶Ra, ²²⁸Ra, ¹³⁷Cs and ⁴⁰K in all investigated mushroom samples were from 0.12 to 12, 0.05 to 7.5, 0.14 to 14, MDC(<0.01) to 339, and 396 to 1880, respectively. Activity concentrations of ¹³⁷Cs in mushrooms showed some variation between species sampled at the same site. To calculate soil to mushroom transfer factors, levels of radionuclide in 15 paired soil samples and mushrooms were also investigated. The median transfer factors for ²³⁸U, ²²⁶Ra, ²²⁸Ra, ¹³⁷Cs and ⁴⁰K were 8.32 × 10^-2, 3.03 × 10^-2, 6.69 × 10^-2, 0.40 and 1.19, respectively. The results were compared with values of other areas.

Radioactivity in mushrooms from selected locations in the Bohemian Forest, Czech Republic

¹³⁷Cs is one of the most important radionuclides released in the course of atmospheric nuclear weapon tests and during accidents in nuclear power plants such as that in Chernobyl, Ukraine, or Fukushima, Japan. The aim of this study was to compare ¹³⁷Cs and ⁴⁰K concentrations in particular species of mushrooms from selected locations in the Bohemian Forest (Czech: Šumava), Czech Republic, where a considerable contamination from the Chernobyl accident had been measured in 1986. Samples were collected between June and October 2014. Activities of ¹³⁷Cs and ⁴⁰K per dry mass were measured by means of a semiconductor gamma spectrometer. The ¹³⁷Cs values measured range from below detection limit to 4300 ± 20 Bq kg^-1, in the case of ⁴⁰K from 910 ± 80 to 4300 ± 230 Bq kg^-1. Differences were found between individual locations, due to uneven precipitation in the course of the movement of the radioactive cloud after the Chernobyl accident. There are, however, also differences between individual species of mushrooms from identical locations, which inter alia result from different characteristics of the soil and depths of mycelia. The values measured are compared with established limits and exposures from other radiation sources present in the environment. In general, it can be stated that the values measured are relatively low and the effects on the health of the population are negligible compared to other sources of ionizing radiation.

Mycoextraction of radiolabeled cesium and strontium by Pleurotus eryngii mycelia in the presence of alumina nanoparticles: Sorption and accumulation studies

Widespread use of products based on nanomaterials results in the release of nanoparticles into the environment. Nanoparticles can be taken up by organisms, but they can also coexist with other substances such as radionuclides, thus affecting their uptake or toxicity. In contrast, the sorption capacity of nanoparticles is exploited in water purification. The aim of the study was to investigate: (i) bioaccumulation of cesium and strontium by Pleurotus eryngii mycelia in the presence of alumina nanoparticles (Al₂O₃ NPs); and (ii) sorption of radionuclides on the surface of nanoparticles. For the experiments, living and dried mycelia were used to permit distinguishing between active uptake and passive sorption of the NPs by P. eryngii. The results are discussed from the perspective of the use of P. eryngii in the mycoextraction of radionuclides. The sorption capacity of Al₂O₃ NPs and the accumulation by P. eryngii mycelia differ for the applied radioisotopes. The efficiency of Cs and Sr sorption by alumina nanoparticles is 20% and 40%, respectively. Mycelia of P. eryngii have the ability to accumulate 30% of both radioisotopes from the medium. More than 60% of strontium can be removed accumulated from water by P. eryngii mycelia in coexistence with Al₂O₃ NPs, while the efficiency of cesium removal accumulation is negligible. It was found that alumina nanoparticles do not enhance uptake of radionuclides by P. eryngii mycelia; mycoextraction of radionuclides by mycelia and sorption by Al₂O₃ NPs are concurrent processes. There was no difference between live or dried mycelia uptake.

The influence of biotic and abiotic factors on (137)Cs accumulation in higher fungi after the accident at Chernobyl NPP

Levels of soil contamination with (137)Cs, the belonging of fungi to a certain ecological group, the localization depth of the main part of mycelium in soil are the primary factors influencing the value of (137)Cs specific activity in higher fungi after the accident at Chernobyl NPP. It has been found that the value of (137)Cs specific activity in fungi of one species could vary by more than 10 times during a vegetation period. A correlation between the changes of (137)Cs content in fungi during the vegetation period and the amount of precipitates during various periods preceding the collection of samples has not been determined. An assumption has been proposed stating dependence between peculiarities of mycelium growth during the vegetation period and the changes of (137)Cs specific activity in fungi.

Bioaccumulation of the artificial Cs-137 and the natural radionuclides Th-234, Ra-226, and K-40 in the fruit bodies of Basidiomycetes in Greece

The bioaccumulation of artificial Cs-137 and natural radionuclides Th-234, Ra-226, and K-40 by Basidiomycetes of several species is studied and evaluated in relation to their substratum soils. For this reason, 32 fungal samples, representing 30 species of Basidiomycetes, were collected along with their substratum soil samples, from six selected sampling areas in Greece. The fungal fruit bodies and the soil samples were properly treated and the activity concentrations of the studied radionuclides were measured by gamma spectroscopy. The measured radioactivity levels ranged as follows: Cs-137 from <0.1 to 87.2 ± 0.4 Bq kg(-1) fresh weight (F.W.), Th-234 from <0.5 ± 0.9 to 28.3 ± 25.5 Bq kg(-1) F.W., Ra-226 from <0.3 to 1.0 ± 0.5 Bq kg(-1) F.W., and K-40 from 56.4 ± 3.0 to 759.0 ± 28.3 Bq kg(-1) F.W. The analysis of the results supported that the bioaccumulation of the studied natural radionuclides and Cs-137 is dependent on the species and the functional group of the fungi. Fungi were found to accumulate Th-234 and not U-238. What is more, potential bioindicators for each radionuclide among the 32 species studied could be suggested for each habitat, based on their estimated concentration ratios (CRs). The calculation of the CRs' mean values for each radionuclide revealed a rank in decreasing order for all the species studied.

(135)Cs/(137)Cs isotopic composition of environmental samples across Europe: Environmental transport and source term emission applications

(135)Cs/(137)Cs isotopic analyses represent an important tool for studying the fate and transport of radiocesium in the environment; in this work the (135)Cs/(137)Cs isotopic composition in environmental samples taken from across Europe is reported. Surface soil and vegetation samples from western Russia, Ukraine, Austria, and Hungary show consistent aged thermal fission product (135)Cs/(137)Cs isotope ratios of 0.58 ± 0.01 (age corrected to 1/1/15), with the exception of one sample of soil-moss from Hungary which shows an elevated (135)Cs/(137)Cs ratio of 1.78 ± 0.12. With the exception of the outlier sample from Hungary, surface soil/vegetation data are in quantitative agreement with values previously reported for soils within the Chernobyl exclusion zone, suggesting that radiocesium at these locations is primarily composed of homogenous airborne deposition from Chernobyl. Seawater samples taken from the Irish Sea show (135)Cs/(137)Cs isotope ratios of 1.22 ± 0.11 (age corrected to 1/1/15), suggesting aged thermal fission product Cs discharged from Sellafield. The differences in (135)Cs/(137)Cs isotope ratios between Sellafield, Chernobyl, and global nuclear weapons testing fallout indicate that (135)Cs/(137)Cs isotope ratios can be utilized to discriminate between and track radiocesium transport from different nuclear production source terms, including major emission sources in Europe.

Persistence of 137Cs in the litter layers of forest soil horizons of Mount IDA/Kazdagi, Turkey

In 2010-2012, an extensive study was performed in forest sites of Mount IDA (Kazdagi)/Edremit 26 years after the Chernobyl accident. The (137)Cs activity concentrations were determined by gamma-ray spectrometry in the forest soil layers (OL, OF + OH and A horizons) separately. Based on 341 surface soil samples and 118 soil profiles, activity concentrations of (137)Cs in OL horizons varied between 0.25 ± 0.14 and 70 ± 1 Bq kg(-1), while the ranges of (137)Cs activity concentrations in OF + OH and A horizons were 13 ± 1-555 ± 3 Bq kg(-1) and 2 ± 1-253 ± 2 Bq kg(-1), respectively. Cesium-137 deposition in the study area was estimated to be in the range of 1-39 kBq m(-2) and a linear relationship between the deposition of (137)Cs and the altitude was observed. The distributions of (137)Cs activities in OL, OF + OH and A horizons throughout the region were mapped in detail. The highest (137)Cs activities were found in OF + OH horizons, with markedly lower (137)Cs activity in mineral horizons of soil profiles. It is observed that (137)Cs content of humus layer increases with the thickness of the humus layer for coniferous forest sites. The (137)Cs activity concentrations were higher than the recommended screening limits (150 Bq kg(-1)) at some of the investigated areas. The current activity concentration of top soil layers indicates that over many years since the initial deposition, (137)Cs activity is keeping still high in the organic horizons.

Radionuclides in some edible and medicinal macrofungal species from Tara Mountain, Serbia

Edible and medicinal macrofungi used in human diet represent not only important sources of nutritive elements but toxic substances as well (heavy metals and radionuclides). Radioactivity levels of four radionuclides ((40)K, (137)Cs, (226)Ra, (228)Ra) were determined in the basidiomata (fruiting bodies of a Basidiomycetes) of six lignicolous (Fomitopsis pinicola, Ganoderma applanatum, Hericium clathroides, Megacollybia platyphylla, Pluteus cervinus, Trametes gibbosa) and three mycorrhizal (Boletus luridus, Boletus sp. 1, Boletus sp. 2) species as well as their soil (wood) substrates by gamma spectrometry (high-resolution high-purity germanium (HPGe) detector). The aim was to investigate their ability for radionuclide absorption according to transfer factors (from soil and wood), to predict potential bioindicator species as well as species with potential risk for human use. Samples were taken during years 2011 and 2012, at two sites in forest ecosystem of Tara Mountain (Serbia). Observed concentration ranges per dry weight were as follows: 29-3,020 Bq/kg ((40)K), 21.9-735 Bq/kg ((137)Cs), 3-39 Bq/kg ((226)Ra), and 2.0-18 Bq/kg ((228)Ra). Obtained results indicate that the type of basidiome (fleshy/tough), most likely due to a different metabolic rate, has a very important role in radionuclide accumulation. The highest activity concentrations of all analyzed radionuclides were found in species with fleshy basidiomata--P. cervinus, H. clathroides, M. platyphylla, and Boletus species. A species-specific influence on radionuclide uptake was more prominent comparing to habitat differences and the role of fungal trophic mode. No significant variations were observed regarding radionuclide activity among the same fungal species from different sampling sites.

The (137)Cs accumulation by forest-derived products in the Gomel region

This paper reports basic features of the (137)Cs uptake by forest-derived products in the Gomel region. Even with the soil contamination density of 37 kBq m(-2) the radionuclide contents in 20-30% of mushrooms and berries were found to be higher than the admissible levels. The (137)Cs contamination density of soil, site type and meteorological parameters were observed as the major factors which govern the radiocaesium uptake by mushrooms and berries. The (137)Cs contents in forest-derived products were found to increase directly with the soil contamination density. Bilberries (Vaccinium myrtillus) growing on different site types differed significantly in the (137)Cs content. It was also determined that statistically significant differences in the (137)Cs radioactivity of forest foods growing on different natural sites were governed by the factor designated in the current study by "territorial". The differences are to be accounted for both by forms of the Chernobyl fallout and by the natural and climatic conditions determining variations in the availability of radionuclides in the soil. In dry years the (137)Cs concentrations in some mushroom species were higher than in normal years.

Artificial and natural radioactivity in edible mushrooms from Sao Paulo, Brazil

Environmental biomonitoring has demonstrated that organisms such as crustaceans, fish and mushrooms are useful to evaluate and monitor both ecosystem contamination and quality. Particularly, some mushroom species have a high capacity to retain radionuclides and some toxic elements from the soil and the air. The potential of mushrooms to accumulate radionuclides in their fruit-bodies has been well documented. However, there are no studies that determine natural and artificial radionuclide composition in edible mushrooms, in Brazil. Artificial ((137)Cs) and natural radioactivity ((40)K, (22)(6)Ra, (2)(28)Ra) were determined in 17 mushroom samples from 3 commercialized edible mushroom species. The edible mushrooms collected were Agaricus sp., Pleurotus sp. and Lentinula sp. species. The activity measurements were carried out by gamma spectrometry. The levels of (137)Cs varied from 1.45 ± 0.04 to 10.6 ± 0.3 Bq kg(-1), (40)K levels varied from 461 ± 2 to 1535 ± 10 Bq kg(-1), (2)(26)Ra levels varied from 14 ± 3 to 66 ± 12 Bq kg(-1) and (228)Ra levels varied from 6.2 ± 0.2 to 54.2 ± 1.7 Bq kg(-1). (137)Cs levels in Brazilian mushrooms are in accordance with the radioactive fallout in the Southern Hemisphere. The artificial and natural activities determined in this study were found to be below the maximum permissible levels as established by national legislation. Thus, these mushroom species can be normally consumed by the population without any apparent risks to human health.

Influence of alkali and alkaline earth elements on the uptake of radionuclides by Pleurototus eryngii fruit bodies

In the literature, there are many data available on radionuclide contents and their transfer to different species of mushrooms. There are some variables, however, which affect the transfer but are very difficult to observe in collected wild mushrooms. An example is the effect of different concentrations of alkali and alkaline earth elements in the soil. Modification of these concentrations in the soil solution has traditionally been used as a countermeasure to deal with radioactively contaminated areas. In the present work, fruiting bodies of Pleurotus eryngii, a saprophytic mushroom, were grown under controlled laboratory conditions, varying the content of alkali (potassium and cæsium) and alkaline earth (calcium and strontium) elements. The transfer of (134)Cs, (85)Sr, and (60)Co (added to the cultures) and of natural (210)Pb was analysed by increasing the content of each stable element considered. A significant, but nonlinear, enhancement of stable cæsium and (134)Cs was observed with increasing content of stable cæsium in the substrate/mycelium. The transfer of (85)Sr decreased with the addition of each stable cation, whereas the (60)Co and (210)Pb transfers were unaffected.

Inorganic-organic magnetic nanocomposites for use in preventive medicine: a rapid and reliable elimination system for cesium

PURPOSE

To investigate the potential use of Prussian blue-coated magnetic nanoparticles, termed "Prussian blueberry", to bring about the magnetic elimination of cesium.

METHODS

Prussian blueberry were prepared by a layer-by-layer assembly method. The morphology, structure and physical properties of the Prussian blueberry were investigated as was their ability to magnetically eliminate cesium.

RESULTS

We confirmed that Prussian blueberry were composed of a magnetite nanoparticle-core and a Prussian blue-shell. Under a magnetic field, Prussian blueberry (5 mg) reduced the cesium concentration of seawater (3 ml) from 150 ppm to about 50 ppm; but regular Prussian blue could not magnetically eliminate cesium. Moreover, Prussian blueberry removed a similar proportion of cesium from a larger volume of seawater, and from fetal bovine serum and cow's milk.

CONCLUSIONS

Under a magnetic field, Prussian blueberry was able to rapidly eliminate cesium from seawater and from biological matrices such as serum and milk.

137Cs and 40K in fruiting bodies of different fungal species collected in a single forest in southern Poland

Fruiting bodies of fungi belonging to more than 70 species were collected within a few thousand square meter area of one forest during 2006 and 2007. The soil profile was collected to check the cumulative deposition of (137)Cs, which was relatively high, equal to 64 +/- 2 kBq/m(2) (calculated for October 2006). The majority of this activity was in the first 6 cm. Fruitbodies were analyzed for radiocesium and (40)K by means of gamma-spectrometry. The highest (137)Cs activity was 54.1 +/- 0.7 kBq/kg (dry weight) for a sample of Lactarius helvus collected in 2006. The results for 2006 were higher than those for 2007. In a few cases the traces of short-lived (T(1/2) = 2.06 a) (134)Cs were still found in samples. The importance of mycorrhizal fungi for radiocesium accumulation is confirmed. The differences in activity among the species are discussed in relation to observations and predictions from previous studies, where the change in relative accumulation between fruiting bodies of different species was at least partially explained by the differences in the depth of the mycelium localization in a litter/soil system. It is concluded that in some cases, such as Boletus edulis and Xerocomus badius, this prediction is fulfilled and therefore this explanation confirmed.