Estimation of soil-to-plant transfer factors of radiocesium in 99 wild plant species grown in arable lands 1 year after the Fukushima 1 Nuclear Power Plant accident

One year after the deposition of radionuclides from the Fukushima 1 Nuclear Power Plant (A formal name is Fukushima Daiichi Nuclear Power Station) in March 2011, radiocesium (¹³⁴Cs, ¹³⁷Cs) concentrations ([Cs]) were comprehensively investigated in the wild plants of 99 species most of which were annual or summer green perennial herbs and started to grow from April 2012 at the heavily contaminated fields of paddy (three study sites) and upland (one study site) in Fukushima Prefecture. The survey was conducted three times (April, July and October) in the year. In each site, soils (soil cores of 5-cm depth) and plants (aerial shoots) were collected for determination of [Cs] on a dry weight basis, and then the transfer factor (TF) of radiocesium from soil to plant ([Cs]_plant/[Cs]_soil) was estimated in each species. The [Cs] values of both soils and plants largely varied. However, some species exhibited relatively high TF values (more than 0.4) (e.g., Athyrium yokoscense, Dryopteris tokyoensis, and Cyperus brevifolius), while others exhibited almost negligible values (less than 0.01) (e.g., Salix miyabeana, Humulus scandens, and Elymus tsukushiensis). In addition, judging from the 11 species grown in both paddy and upland fields, TF values were generally higher in the paddy fields. The estimation of phytoextraction efficiency of soil radiocesium by weed communities in the paddy fields suggests that the weed community is not a practical candidate for phytoremediation technique.     

Difference in cesium accumulation among rice cultivars grown in the paddy field in Fukushima Prefecture in 2011 and 2012

After the accident of the Fukushima 1 Nuclear Power Plant in March 2011, radioactive cesium was released and paddy fields in a wide area including Fukushima Prefecture were contaminated. To estimate the levels of radioactive Cs accumulation in rice produced in Fukushima, it is crucial to obtain the actual data of Cs accumulation levels in rice plants grown in the actual paddy field in Fukushima City. We herein conducted a two-year survey in 2011 and 2012 of radioactive and non-radioactive Cs accumulation in rice using a number of rice cultivars grown in the paddy field in Fukushima City. Our study demonstrated a substantial variation in Cs accumulation levels among the cultivars of rice.     

Concentration of Radiocesium in the Wild Japanese Monkey (Macaca fuscata) over the First 15 Months after the Fukushima Daiichi Nuclear Disaster

Following the massive earthquake that struck eastern Japan on March 11, 2011, a nuclear reactor core meltdown occurred at the Fukushima Daiichi Nuclear Power Plant, operated by Tokyo Electric Power Company, and was followed by the release of large amounts of radioactive materials. The objective of this study was to measure the concentration of radiocesium ¹³⁴Cs and ¹³⁷Cs in the muscle of Japanese monkeys (Macaca fuscata) inhabiting the forest area of Fukushima City and to determine the change in concentration over time as well as the relationship with the level of soil contamination. Cesium concentrations in the muscle of monkeys captured at locations with 100,000–300,000 Bq/m² were 6,000–25,000 Bq/kg in April 2011 and decreased over 3 months to around 1,000 Bq/kg. However, the concentration increased again to 2,000–3,000 Bq/kg in some animals during and after December 2011 before returning to 1,000 Bq/kg in April 2012, after which it remained relatively constant. This pattern of change in muscle radiocesium concentration was similar to that of the change in radiocesium concentration in atmospheric fallout. Moreover, the monkeys feed on winter buds and the cambium layer of tree bark potentially containing higher concentrations of radiocesium than that in the diet during the rest of the year. The muscle radiocesium concentration in the monkeys related significantly with the level of soil contamination at the capture locations.     

Verification of radiocesium decontamination from farmlands by plants in Fukushima

The purpose of this study was to verify radiocesium decontamination from Fukushima farmland by plants and to screen plants useful for phytoremediation. Thirteen species from three families (Asteraceae, Fabaceae, and Poaceae) of crops were grown in shallow and deeply cultivated fields (0–8 and 0–15 cm plowing, respectively). To change plowing depth was expected to make different contacting zone between root system and radiocesium in soil. The radioactivity values of the plants due to the radiocesium ¹³⁴Cs and ¹³⁷Cs were 22–179 and 29–225 Bq kg dry weight^?1, respectively. The ¹³⁴Cs and ¹³⁷Cs transfer factors for plants grown in the shallow field ranged from 0.021 to 0.12 and fro 0.019 to 0.13, respectively, with the geometric means of 0.051 and 0.057, respectively. The ¹³⁴Cs and ¹³⁷Cs transfer factors for plants grown in the deep field ranged from 0.019 to 0.13 and from 0.022 to 0.13, respectively, with the geometric means of 0.045 and 0.063, respectively. Although a reducing ratio was calculated to evaluate the decrease in radiocesium from contaminated soil during cultivation (i.e., phytoremediation ability), no plant species resulted in a remarkable decrease in radiocesium in soil among the tested crops. These results should be followed up for several years and further analyses are required to evaluate whether the phytoremediation technique is applicable to radioactively contaminated farmlands.     

134Cs and 137Cs levels in a grassland, 32 km northwest of the Fukushima 1 Nuclear Power Plant, measured for two seasons after the fallout

We measured the levels of radioactive caesium (RACs; ¹³⁴Cs and ¹³⁷Cs) in plants and soil in a grassland, 32 km northwest of the Fukushima 1 Nuclear Power Plant, from June 2011 to October 2012. In 2011, the highest RACs levels (¹³⁴Cs + ¹³⁷Cs) in plants and in the 0–5 cm soil layer were approximately 80 kBq per kg dry weight (DW). Forage grasses and clovers in this grassland showed similar RACs levels. On a DW basis, the levels of RACs in these plants tended to increase with increasing biomass over both years, but the absolute levels decreased in 2012. The RACs levels in the soil decreased sharply with soil depth; the RACs level in the 5–10 cm soil layer was only 3 % of that in the 0–5 cm layer. The transfer factor (ratio of radioactivity in plant parts on DW basis to that in the 0–10 cm soil layer) was 0.5 and 1.0 for the aboveground and belowground plant parts, respectively, in 2011, and these values decreased by approximately 50 % in 2012. We discuss the possible mechanisms underlying these trends, and strategies to decrease the level of RACs in plants to the permissible level for forage.     

The effect of fertilization on cesium concentration of rice grown in a paddy field in Fukushima Prefecture in 2011 and 2012

After the accident of the Fukushima 1 nuclear power plant in March 2011, radioactive cesium was released and paddy field in a wide area of Fukushima Prefecture was contaminated. To reduce radioactive Cs uptake by rice, it is important to understand factors that affect Cs uptake in rice. Here we describe our study in 2011 and 2012 to investigate Cs concentration in two rice cultivars, Koshihikari and Hitomebore, the top two cultivars in Fukushima prefecture, grown under different fertilizer conditions in the contaminated paddy field. Our study demonstrated that high nitrogen and low potassium conditions increase Cs concentrations both in straw and brown rice.     

Fukushima Nuclear Accident Recorded in Tibetan Plateau Snow Pits

The β radioactivity of snow-pit samples collected in the spring of 2011 on four Tibetan Plateau glaciers demonstrate a remarkable peak in each snow pit profile, with peaks about ten to tens of times higher than background levels. The timing of these peaks suggests that the high radioactivity resulted from the Fukushima nuclear accident that occurred on March 11, 2011 in eastern Japan. Fallout monitoring studies demonstrate that this radioactive material was transported by the westerlies across the middle latitudes of the Northern Hemisphere. The depth of the peak β radioactivity in each snow pit compared with observational precipitation records, suggests that the radioactive fallout reached the Tibetan Plateau and was deposited on glacier surfaces in late March 2011, or approximately 20 days after the nuclear accident. The radioactive fallout existed in the atmosphere over the Tibetan Plateau for about one month.     

Radioactive cesium accumulation in seaweeds by the Fukushima 1 Nuclear Power Plant accident—two years’ monitoring at Iwaki and its vicinity

Accumulations of radionuclides in marine macroalgae (seaweeds) resulting from the Fukushima 1 Nuclear Power Plant (F1NPP) accident in March 2011 have been monitored for two years using high-purity germanium detectors. Algal specimens were collected seasonally by snorkeling at Nagasaki, Iwaki, Fukushima Prefecture (Pref.), Japan, ca. 50 km perimeter from the F1NPP. Additional collections were done at Soma, Hironocho, Hisanohama and Shioyazaki in Fukushima Pref. as well as at Chiba Pref. and Hyogo Pref. as controls. In May 2011, specimens of most macroalgal species showed ¹³⁷Cs levels greater than 3,000 Bq kg^?1 at Shioyazaki and Nagasaki. The highest ¹³⁷Cs level recorded 7371.20 ± 173.95 Bq kg^?1 in Undaria pinnatifida (Harvey) Suringar on 2 May 2011, whereas seawater collected at the same time at Shioyazaki and Nagasaki measured 8.41 ± 3.21 and 9.74 ± 3.43 Bq L^?1, respectively. The concentration factor of marine macroalgae was estimated to be ca. 8–50, depending on taxa and considering a weight ratio of wet/dry samples of ca. 10. ¹³⁷Cs level declined remarkably during the following 5–6 months. In contrast, the ¹³⁷Cs level remained rather stable during the following 12–16 months, and maintained the range of 10–110 Bq kg^?1. Contamination was still detectable in many samples in March 2013, 24 months after the most significant pollution.     

Global searches for microalgae and aquatic plants that can eliminate radioactive cesium, iodine and strontium from the radio-polluted aquatic environment: a bioremediation strategy

The Fukushima 1 Nuclear Power Plant accident in March 2011 released an enormously high level of radionuclides into the environment, a total estimation of 6.3 × 10¹⁷ Bq represented by mainly radioactive Cs, Sr, and I. Because these radionuclides are biophilic, an urgent risk has arisen due to biological intake and subsequent food web contamination in the ecosystem. Thus, urgent elimination of radionuclides from the environment is necessary to prevent substantial radiopollution of organisms. In this study, we selected microalgae and aquatic plants that can efficiently eliminate these radionuclides from the environment. The ability of aquatic plants and algae was assessed by determining the elimination rate of radioactive Cs, Sr and I from culture medium and the accumulation capacity of radionuclides into single cells or whole bodies. Among 188 strains examined from microalgae, aquatic plants and unidentified algal species, we identified six, three and eight strains that can accumulate high levels of radioactive Cs, Sr and I from the medium, respectively. Notably, a novel eustigmatophycean unicellular algal strain, nak 9, showed the highest ability to eliminate radioactive Cs from the medium by cellular accumulation. Our results provide an important strategy for decreasing radiopollution in Fukushima area.     

Predicting radiocaesium root uptake based on potassium uptake parameters. A mechanistic approach

This paper describes the application of a mechanistic model in the study of radionuclide soil–plant transfer and the obtainment of predictive estimates of radionuclide plant contamination. Soil–plant K and ¹³⁴Cs transfer rates were measured and compared with those predicted by the Barber–Cushman model. The experiment was performed on pea plants grown in pots and in two different types of soil (Calcic Luvisol and Fluvisol). For K, model predictions proved valid for all development stages sampled; for ¹³⁴Cs, the quality of the prediction depended on the plant stage. In both, parameter estimates varied depending on plant age and soil type. The model was also run for ¹³⁴Cs using the Michaelis–Menten parameters obtained for K. In this case, the predicted values were significantly correlated with those measured, but about three times higher. Thus, a positive plant discrimination of K versus ¹³⁴Cs in plant absorption is observed for the types of soil studied. As regression proved to be significant, K absorption rates may be used to estimate ¹³⁴Cs absorption in determining radiocaesium plant uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Measurements of gamma (γ)-emitting radionuclides with a high-purity germanium detector: the methods and reliability of our environmental assessments on the Fukushima 1 Nuclear Power Plant accident

The severe accident of Fukushima 1 Nuclear Power Plant due to the Tohoku Region Pacific Coast Earthquake in 11 March 2011 caused wide contamination and pollution by radionuclides in Fukushima and surrounding prefectures. In the current JPR symposium, a group of plant scientists attempted to examine the impact of the radioactive contamination on wild and cultivated plants. Measurements of gamma (γ) radiation from radionuclides in “Fukushima samples”, which we called and collected from natural and agricultural areas in Fukushima prefecture were mostly done with a high-purity Ge detector in the Graduate School of Maritime Sciences, Kobe University. In this technical note, we describe the methods of sample preparation and measurements of radioactivity of the samples and discuss the reliability of our data in regards to the International Atomic Energy Agency (IAEA) Interlaboratory comparisons and proficiency test (IAEA proficiency test).     

Radioecological indexes of fallout measurements from the Fukushima nuclear accident

Fallout from the Fukushima nuclear accident has been monitored for about 1 month in Thessaloniki, Northern Greece. Three different radionuclides, one short-lived, one relatively long-lived and one long-lived fission product were identified in air, grass and milk samples. The ¹³¹I, ¹³⁷Cs and ¹³⁴Cs activity concentrations in air reached 497, 145 and 126 μBq m⁻³, respectively on 4 April, 2011. These radionuclides are of particular concern regarding their transfer from the environment to population through the ingestion pathways for the assessment of the Fukushima accident consequences. Radioecological indexes (eco-indexes) of fallout measurements in the air–grass–cow-milk–man pathway for ¹³¹I were determined, as they are related to radiological impact of the Fukushima derived radionuclides on the public and environment.     

In situ γ-spectrometry several years after deposition of radiocesium

Several years after the deposition of fallout radiocesium, the maximal activity of this radionuclide will not remain at the soil surface but be found rather in deeper layers. In order to estimate the total radiocesium contamination of a large area and the resulting γ-dose rate by in-situ spectrometry, it is necessary to approximate the vertical distribution of this radionuclide by an analytical function. Observations at ten undisturbed grassland soils in Bavaria, Germany, show that the resulting depth distributions can be approximated closely by a three-parameter Lorentz function. This function characterises the observed distributions in all three critical sections, i.e. the surface layer, the distribution around the maximal concentration, and the tail at greater depth. It is also shown that the observed total activity per unit area of the soil due to ¹³⁷Cs agrees very well with the corresponding value obtained from the integrated Lorentz function. The two coefficients of the Lorentz function, which characterise the location (depth) and width of the maximum in the activity distribution, are shown to be correlated. In part II of this study, it will be shown how the parameters of the Lorentz function can also be obtained by in-situ γ-ray spectrometry. As a result, it is possible to use in-situ γ-ray spectrometry to obtain the total ¹³⁷Cs activity per unit area also for sites where the vertical distribution of this radionuclide in the soil is no longer exponential. Received: 7 March 1996 / Accepted in revised form: 20 June 1996     

Disparity in 90Sr and 137Cs uptake in Alpine plants: phylogenetic effect and Ca and K availability

Background and aims

Uptake of ⁹⁰Sr and ¹³⁷Cs in plants varies widely between soil types and between plant species. It is now recognized that the radionuclide uptake in plants is more influenced by site-specific and plant-specific parameters rather than the bulk radionuclide concentration in soil. We hypothesized that the stress which Alpine plants experience because of the short growing season may enhance the phylogenetic effect on the ¹³⁷Cs and ⁹⁰Sr transfer factors as well as the dependency of the uptake by plant to the concentrations of exchangeable Ca and K of soils.

Methods

We carried out a field study on the ⁹⁰Sr and ¹³⁷Cs uptake by 11 species of Alpine plants growing on 6 undisturbed and geochemically different soils in the Alpine valley of Piora, Switzerland.

Results

Results show that a strong correlation exists between the log TF and the log of exchangeable Ca or K of the soils.

Conclusions

Cs uptake by Phleum rhaeticum (Poales) and Alchemilla xanthochlora (Rosales) is more sensitive to the amount of exchangeable K in the soil than the corresponding uptake by other orders. Moreover, the ⁹⁰Sr results indicate a phylogenetic effect between Non-Eudicot and Eudicots: the order Poales (Phleum rhaeticum) concentrating much less ⁹⁰Sr than Eudicots do.     

Genotypic effects in phytoavailability of radiocaesium are pronounced at low K intensities in soil

The differences in radiocaesium uptake between species were analysed in a series of solution culture and pot trials. Since radiocaesium uptake is very sensitive to the solution potassium (K) concentration, it was hypothesised that species depleting K in the rhizosphere to a larger extent, will have a higher radiocaesium uptake. Five species (bean, lettuce, winter barley, ryegrass and bentgrass) were grown for 18–21 days in nutrient solution spiked with ¹³⁷Cs and at 4 K concentrations between 0.025 and 1.0 mM. Shoot ¹³⁷Cs activities all decreased between 17- and 81-fold with increasing K supply. Shoot ¹³⁷Cs activities were 4-fold different between species at the lowest K supply and 3.4-fold different at high K supply. The same five species were grown in two ¹³⁴Cs spiked soils with contrasting exchangeable K but similar clay content. Shoot ¹³⁴Cs activities were up to 19-fold higher in the soil with lowest exchangeable K. Differences in shoot activity concentrations between the species were only 4.5-fold in the high K soil, but were 15-fold in the low K soil. Bulk soil solution ¹³⁴Cs and K concentration data were combined with radiocaesium uptake characteristics measured in solution culture to predict radiocaesium uptake from soil. Predictions were within 1.6-fold of observations in the high K soil but largely underestimated ¹³⁴Cs uptake in lettuce, ryegrass and barley in the low K soil. A solute transport model was used to estimate K and radiocaesium concentrations in the rhizosphere. These calculations confirmed the assumption that higher radiocaesium uptake is found for species that deplete K in the rhizosphere to a larger extent.     

The role of vegetation in the regulation of fluxes of technogenic radionuclides at different stages after radioactive fallout

In the remote period after the radioactive fallout in the Chernobyl accident, the biological cycle of ¹³⁷Cs in pine forests of the northern forest-steppe zone and in those of Bryanskoe Polesye become essentially different. In the cleaner northern zone with dark-gray forest soil, the ¹³⁷Cs flux to the soil with litterfall exceeds its influx to the vegetation by a factor of 5; i.e., the ¹³⁷Cs cycle differs from that of stable K, the descending flux being still dominant. In the more contaminated Bryanskoe Polesye zone with podzolic illuvial-iron sandy soil, the annual ¹³⁷Cs influx to above-ground vegetation via root uptake exceeds its return to the soil with litterfall, i.e., the ¹³⁷Cs cycle approaches the biological cycle of stable K.     

Removal Efficiency of Radioactive Cesium and Iodine Ions by a Flow-Type Apparatus Designed for Electrochemically Reduced Water Production

The Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011 attracted people’s attention, with anxiety over possible radiation hazards. Immediate and long-term concerns are around protection from external and internal exposure by the liberated radionuclides. In particular, residents living in the affected regions are most concerned about ingesting contaminated foodstuffs, including drinking water. Efficient removal of radionuclides from rainwater and drinking water has been reported using several pot-type filtration devices. A currently used flow-type test apparatus is expected to simultaneously provide radionuclide elimination prior to ingestion and protection from internal exposure by accidental ingestion of radionuclides through the use of a micro-carbon carboxymethyl cartridge unit and an electrochemically reduced water production unit, respectively. However, the removability of radionuclides from contaminated tap water has not been tested to date. Thus, the current research was undertaken to assess the capability of the apparatus to remove radionuclides from artificially contaminated tap water. The results presented here demonstrate that the apparatus can reduce radioactivity levels to below the detection limit in applied tap water containing either 300 Bq/kg of ¹³⁷Cs or 150 Bq/kg of ¹²⁵I. The apparatus had a removal efficiency of over 90% for all concentration ranges of radio–cesium and –iodine tested. The results showing efficient radionuclide removability, together with previous studies on molecular hydrogen and platinum nanoparticles as reactive oxygen species scavengers, strongly suggest that the test apparatus has the potential to offer maximum safety against radionuclide-contaminated foodstuffs, including drinking water.     

Association of Chernobyl-derived 239+240Pu, 241Am, 90Sr and 137Cs with different molecular size fractions of organic matter in the soil solution of two grassland soils

Radiocesium is normally bound only rather weakly and unspecifically by humic substances, in contrast to the actinides Pu and Am. Recently, however, it was observed that fallout ¹³⁷Cs in the soil solution from an Of-horizon of a podzol forest soil (slightly decomposed plant material) was associated essentially only with one single size fraction of the humic substances. In deeper soil layers with well humified material (AOh-horizon), radiocesium was associated with all size fractions of the dissolved organic matter (DOM). To examine whether this unexpected behaviour is also observable for DOM isolated from other soils, we determined the association of fallout ¹³⁷Cs,⁹⁰Sr,²³⁸Pu, ^239+240Pu and ²⁴¹Am with various size fractions of DOM from in situ soil solutions isolated from two layers (0–2 cm and 2–5 cm) of two grassland soils (a soddy podzolic soil and a peat soil) within the 10 km zone of the nuclear reactor at Chernobyl (Ukraine). The four size fractions of DOM as obtained by gel filtration of the soil solution were (mean nominal molecular weight in daltons): fraction I: ≥2000, fraction II: 1300; fraction III: 560, fraction IV: inorganic compounds. The results for the well humified DOM (humus accumulation horizon of podzol, deeper layer of peat soil) showed that Pu and Am are essentially associated with the high molecular weight fractions, while Sr is present only in the `inorganic' fraction. Radiocesium is found in all the size fractions separated. A quite similar pattern was also found for Pu, Am, and Sr in the soil solution from only slightly decomposed plant material (0–2 cm of peat soil), but not for radiocesium. This radionuclide was again essentially only observable in one single low molecular weight fraction of DOM. The above results thus support our recent observations in the different horizons of a forest podzol mentioned above, even though no reason for the different binding of radiocesium by well humified soil organic matter and by only slightly decomposed plant material can be given at present. The data demonstrate, however, that information on only the total amount of a radionuclide in the soil solution will not be sufficient to interpret or predict its fate adequately in the soil. Received: 13 February 1998 / Accepted in revised form: 14 July 1998     

Radiocesium distribution in the tissues of Japanese black beef heifers fed fallout-contaminated roughage due to the fukushima daiichi nuclear power station accident

This study examined the accumulation and tissue distribution of radioactive cesium nuclides in Japanese Black beef heifers raised on roughage contaminated with radioactive fallout due to the accident at the Fukushima Daiichi Nuclear Power Station on March 2011. Radiocesium feeding increased both (134)Cs and (137)Cs levels in all tissues tested. The kidney had the highest level and subcutaneous adipose had the lowest of radioactive cesium in the tissues. Different radioactive cesium levels were not found among parts of the muscles. These results indicate that radiocesium accumulated highly in the kidney and homogenously in the skeletal muscles in the heifers.     

The pale grass blue butterfly in ex-evacuation zones 5.5 years after the Fukushima nuclear accident: Contributions of initial high-dose exposure to transgenerational effects

Biological impacts of the Fukushima nuclear accident have been reported in various organisms but have not been evaluated sufficiently. Here, we collected the pale grass blue butterfly, Zizeeria maha, in September 2016, 5.5 years after the accident, from ex-evacuation zones in Fukushima Prefecture to evaluate the remaining biological effects of the accident. Although the morphological abnormality rate was not high, it was significantly positively correlated with the initial ¹³¹I and ¹³⁷Cs deposition levels (as of March 2011). The capture rate was negatively correlated with the initial ¹³⁷Cs deposition level at the borderline of significance. Neither the abnormality rate nor the capture rate was correlated with the ground radiation dose (as of September 2016). Generalized linear model (GLM) analysis also indicated contributions of the initial ¹³¹I and ¹³⁷Cs deposition levels but not the ground radiation dose. These results suggest that the butterflies present in the ex-evacuation zones in 2016 were still affected, although not severely, mainly because of the initial high-dose exposure to radioiodine, radiocesium, and other radionuclides. We conclude that transgenerational effects of radioactive contamination have successively manifested in the 5.5 years since the accident, possibly through genetic mutations, although potential contributions of other modes of damage cannot be ignored.