Soil-to-plant transfer factors for radiocesium and radiostrontium in agricultural systems

Use of random forest algorithm for predictive modelling of transfer factor soil-plant for radiocaesium: A feasibility study

A German dataset with soil-plant transfer factors for radiocaesium including many co-variables was analysed and prepared for the application of the Random Forest (RF) algorithm using the R libraries 'party', and 'caret'. A RF predictive model for soil-plant transfer factor was created based on 10 co-variables. These are, for example, taxonomic plant family, plant part, soil type and the exchangeable potassium concentration in the soil. The RF model results were compared with the results of two (semi-)mechanistic models. Of the more than 3000 entries in the original dataset, only about 1200 could be used, as this was the largest complete dataset with the largest number of co-variables available. The obtained RF predictive model can reproduce the experimental observations better than the two (semi)-mechanistic models, which are based on many assumptions and fixed parameter values. Model performance was quantified using the metrics of Root Mean Square Error (rmse) and Mean Absolute Error (mae). The RF model was able to reproduce the variability of the data by up to 6 orders of magnitude. The categorical co-predictors, especially taxonomic plant family and plant part, have a greater influence than the numerical co-predictors, such as pH and exchangeable soil potassium concentration. This feasibility study shows that RF is a promising tool to obtain predictive models for transfer factors. However, to build a widely applicable predictive model, a dataset is needed that contains at least thousands of entries for transfer factors and for the most important co-variables and considers a large parameter space.

A comparison of different detection techniques for 137Cs measurements of cattle in vivo

Agricultural lands with farm animals (e.g. cattle) can be significantly affected by radioactive contamination following nuclear or radiation accidents. In order to optimise the techniques for measuring 137Cs in contaminated cattle, selected radiation detectors have been tested and calibrated using volumetric radiation sources. In addition, a mathematical phantom of a cow was created within Monte Carlo simulations. The main aim of the research was to propose a method for making rapid measurements of 137Cs in cattle in vivo/in situ and to select the most suitable measurement set-up. Measurements of contaminated cattle in vivo were carried out in Belarus with one selected detector, and were then compared with measurements of meat in a laboratory and with measurements of a control group of cows. The proposed measurement method was also tested on measurements of 137Cs in wild boars in Czechia with higher levels of the 137Cs activity.

Gamma spectroscopy study of soil-plant transfer factor characteristics of 40K, 232Th and 226Ra in some crops cultivated in southwestern region of Nigeria

Soil-plant transfer factor (TF) is one of the vital variables employed in assessing plants uptake of radionuclides and their transfer to food chain for predictive ingestion dose and risk evaluation. To further this goal, the TF characteristics of natural 40K, 232Th and 226Ra were thus investigated in some crops (yam, cassava, rice, maize, groundnut, cowpea, okra, pumpkin leaf, banana and pawpaw) cultivated in southwestern part of Nigeria using HPGe gamma spectroscopy. The obtained results of activity concentration (AC) of the radionuclides across all the cultivated soil samples indicated average values that are less than the global average, whereas in the crops, average values of 226Ra and 232Th, were higher than reference values for different crops group. The overall range of the calculated TF of 40K, 232Th and 226Ra across all the crops was 0.05 (in maize and cowpea) to 15.01 (in banana), 0.01 (in pumpkin leaf and groundnut) to 19.80 (in pawpaw), and 0.04 (in cassava) to 21.30 (in cowpea), respectively. Overall arithmetic mean and geometric mean were estimated as 2.66 and 1.60, 1.11 and 0.43, and 1.10 and 0.54 for 40K, 232Th and 226Ra, respectively. TFs mostly correlated negatively with soil radionuclides, while positive correlation was mostly noticeable in the case of crop. Log normal transform of the TFs data indicated a near normal distribution as against the calculated data. The derived results of this study is here presented as a baseline data suggested for possible radiological risk assessment of food chain of the local population.

Accumulation of 90SR by Betula pendula within the East Ural Radioactive Trace zone

This study was conducted in 2010-2020 at the head of the East Ural Radioactive Trace (EURT), which was formed in 1957 as a result of the Kyshtym accident at the Mayak Production Association. The main contaminant in this zone is the long-lived radionuclide Strontium-90 (90Sr). Secondary forests dominated by silver birch (Betula pendula) occupy 45% of the EURT area. Concentration of 90Sr in birch leaves and small branches was higher than that in the trunks. The 90Sr content in birch sapwood varied slightly in the radial direction and did not depend on tree age. This was due to the dynamic equilibrium of the migration processes responsible for the accumulation and horizontal transfer of 90Sr. The 90Sr concentration increases in false heartwood, which is formed as a result of the secondary metabolism of dying parenchyma in the inner part of sapwood and is characterised by a high content of ash elements. The concentration of radionuclides in the aboveground organs of birch increased and the aggregated transfer factors (Tag) decreased with an increase in the soil contamination density, in accordance with the power function. The reasons for these patterns are also discussed.

DETERMINING THE TRANSFER FACTORS FOR ESTIMATES OF THE RADIATION CONTAMINATION OF AGRICULTURAL CROPS

The study aims to provide a basis for measures reducing the consequences of a nuclear accident in its late phase, when plant contamination occurs mainly through the root system. Samples of the above-ground biomass of crops and soil were taken in 2020 in the vicinity of the Temelín and Dukovany nuclear power plants (Czech Republic). The 137Cs activities were determined using gamma spectrometry, and the 90Sr activities were measured through beta radiation. From the obtained values, the radionuclide transfer factors (TFs) from soil to crop biomass were calculated. The average area activity of 137Cs in the soil around Dukovany and Temelín was 1700 and 2400 Bq m-2, respectively. The average area activity of 90Sr around Dukovany and Temelín was 211 and 184 Bq m-2, respectively. The TF 137Cs ranged from < 6.3 × 10-6 to 7.9 × 10-3, with a mean of 3.5 × 10-4 m2 kg-1, and the TF 90Sr ranged from 2.7 × 10-4 to 6 × 10-2, with a mean of 1.7 × 10-2 m2 kg-1.

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.

Cesium transfer to millet and mustard as a function of Cs availability in soils

¹³⁷Cs is one of the most persistent radioactive contaminants in soil after a nuclear accident. It can be taken up by plants and enter the human food chain generating a potential human health hazard. Although a large amount of literature has highlighted the role of the different processes involved in Cs uptake by plants, there is still no simple way to predict its transfer for a specific plant from a particular soil. Based on the assumption that the concentration ratio (CR) of Cs can be predicted from one plant taxon if the CR of another taxon is known and taken as reference, whatever the supporting soils, a series of plant/soil Cs transfer experiments were performed on Rhizotest during 21 days using three soils with different textures, clay and organic matter contents and two plants (millet and mustard) with potentially contrasting Cs uptake capacity based on their phylogeny. CRs of each plant varied by 2-3 orders of magnitude depending on the soil and contrary to expectations, the CRs of mustard were either higher (for clay soil), equal (for clay-loam soil) or lower (for sandy soil) than the one of millet. Considering Cs availability in soils and defining a new CR based on the amount of Cs available in the soil (CR_avail) decreased the range of variation in CR between the different soil types for a given plant by one order of magnitude. Differences in Cs (and K) translocation to shoots, possibly specific to millet within Poales, could partly explain the relative CRs of millet and mustard as a function of soils.

Influence of potassium-solubilizing bacteria on the growth and radiocesium phyto-transfer of Brassica rapa L. var. perviridis grown in contaminated Fukushima soils

The supply of K, being the chemical analog of Cs, affects the phytotransfer of radiocesium such as ¹³⁷Cs from contaminated soils and its accumulation in plant tissues. Since K and Cs have high affinity to the same clay particle surfaces, the presence of potassium-solubilizing bacteria (KSB) could increase the availability of not only K⁺ in the rhizosphere but also of radiocesium. In this study, we obtained five KSB isolates with the highest solubilization capacities from soybean rhizosphere on modified Aleksandrov medium containing sericite as K source. Based on biochemical and 16S rRNA gene sequence analysis, we identified the bacteria as Bacillus aryabhattai MG774424, Pseudomonas umsongensis MG774425, P. frederiksbergensis MG774426, Burkholderia sabiae MG774427, and P. mandelii MG774428. We evaluated the KSB isolates based on plant growth promotion and ¹³⁷Cs accumulation in komatsuna (Brassica rapa L. var. Perviridis) grown in three soils collected from Miyanoiri, Takanishi, and Ota contaminated by ¹³⁷Cs from the Fukushima accident. Inoculation with KSB showed beneficial effects on plant growth and increased the overall plant biomass production (~40%). On the average, KSB inoculation resulted in the removal of 0.07 ± 0.04% of ¹³⁷Cs from the soil, more than twice the control. But similar to the effect of KSB inoculation on komatsuna biomass production, different KSBs performed variably and exhibited site-specific responses independent of their K-solubilizing capacities, with higher ¹³⁷Cs phyto-transfer in roots than in shoots. In terms of root transfer factor (TF), values were highest in komatsuna plants grown in Miyanoiri and Ota soils inoculated with P. frederiksbergensis and Burkholderia sabiae, while they were highest in Takanishi soils inoculated with Bacillus aryabhattai and P. umsongensis. These TF values were also much higher than previously reported values for komatsuna grown in ¹³⁷Cs-contaminated Fukushima soils inoculated with other rhizobacteria. Thus, KSB inoculation significantly enhance not only the growth of komatsuna but ¹³⁷Cs uptake.

Committed effective dose and lifetime cancer risk due to ingestion of natural radionuclides in grains grown in an area of high background radiation

The current study aimed at estimating committed effective dose and cancer risk due to the intake of K-40, Ra-226, Ra-228 and Th-228 present in grains grown in an HBRA. The highest activity concentrations found were (606.2 ± 25.13), (8.07 ± 6.37), (10.01 ± 1.45), (43.97 ± 5.54) Bq.kg^-1 for K-40, Ra-226, Ra-228 and Th-228, respectively. The committed effective dose estimated was 0.5 mSv.y^-1, and the estimated cancer risk suggested that uninterrupted and unrestricted consumption of beans grown in this HBRA is not desirable.

Detailed study of post-Chernobyl Cs-137 redistribution in the soils of a small agricultural catchment (Tula region, Russia)

A detailed study of ¹³⁷Cs redistribution was conducted within a small agricultural catchment in the highly contaminated Plavsk radioactive hotspot in the Tula region of Central Russia, 32 years after the Chernobyl nuclear power plant (NPP) accident, which occurred on April 26, 1986. Although more than three decades have passed since the Chernobyl NPP incident, ¹³⁷Cs contamination is high. The ¹³⁷Cs inventory varies from 67 to 306 kBq·m^-2, which is 2-6 times higher than the radiation safety standard; however, the soils remain suitable for crop cultivation. The initial ¹³⁷Cs fallout within the Plavsk radioactive hotspot was extremely heterogeneous, with a trend of decreasing ¹³⁷Cs inventories from the NW to the SE directions within the studied territory. Contemporary ¹³⁷Cs inventories are also very heterogeneous in the studied catchment. However, the trend of the initial ¹³⁷Cs fallout does not appear in the contemporary ¹³⁷Cs inventories on the slopes. Two methods of interpolation (expert-visual and automatic) were used to calculate the ¹³⁷Cs budget, revealing high similarity in their ¹³⁷Cs loss estimates; however, a large discrepancy was observed in their ¹³⁷Cs gain estimates. A detailed analysis of ¹³⁷Cs redistribution revealed the importance of hollows and "plow ramparts" (positive topographic forms on the boundaries of cultivated fields) in the transport and deposition of sediments. A quarter of the total ¹³⁷Cs gain was deposited within the arable land, whereas a quarter was deposited within the non-plowing sides of the dry valley; the other half was deposited in the valley bottom. About 7-8 × 10⁶ kBq of the ¹³⁷Cs inventory flowed out of the catchment area, which was only about 2% of the ¹³⁷Cs fallout after the Chernobyl NPP accident. About 89% of the total ¹³⁷Cs reserve is concentrated in the top (0-25 cm) layer of soils, regardless of land use or location within the catchment.

Relationships between air dose rates and radionuclide concentrations in agricultural plants observed in areas affected by the Fukushima Dai-ichi accident

Most of environmental monitoring programs include measurements of the air dose rates and the radionuclides activity concentration in plants. Both these parameters depend on deposition density of radionuclides. Therefore, measurements of one parameter can (with some supplementary information) be used as an indicator for the other parameter. After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, the Emergency Operation Centre (EOC) operated by the Environmental Radioactivity Monitoring centre of Fukushima and Ministry of Agriculture, Forestry and Fisheries (MAFF) of Japan carried out large sampling programme over different distances from the NPP. The sampling programme was focused on the usage of the weed leaves as a proxy for the prediction of radionuclide transfer to some cultivated plants. The MAFF monitoring programme in 2011-2016 was addressed mainly to agricultural crops. In both cases, the air dose rates were measured at the sites of the sampling. The paper addresses the assessments of relationship between radionuclide activities concentrations in plants and ambient dose rates. The time-dependent relationships were quantified based on weed, buckwheat, brown rice and soybean data obtained in 2011-2016. The recommendations on optimizing emergency sampling programmes based on use of the data of ambient dose rates are also presented.

Sr-90 soil to plant transfer factor reduction using calcium and polymer soil amendments

Introducing calcium into soils can inhibit Sr-90 uptake by plants. To test the efficacy of calcium amendments on the inhibition of Sr-90 uptake by edible plants, a number of different calcium applications, including calcium nitrate, calcium thiosulfate and a mixture of both liquid solutions, were used in this study. Pea plants (Pisum sativum 'Sabre') grown in Sr-90 contaminated soil from seeds to maturity were watered with these calcium solutions. Two different polymers, one inert and one nutrient enriched, were incorporated into the contaminated soil where pea seeds were sowed to ascertain a continuous supply of calcium and essential nutrients. Results show that the heterogeneity of Sr-90 distribution in soil translated to disparate Sr-90 contents in plant tissues. However, on average, irrigation with calcium solutions in conjunction with the usage of polymers consistently yielded a reduction in Sr-90 uptake by the plants. The lowest soil-to-plant transfer factor (TF) values were measured in the edible pea part of the plant, followed by the flowers, roots, stems, pea shells and then leaves. TF values for pea shells were between 4.9 and 20.9, and between 0.3 and 2.8 for the peas. Results do not allow the identification of one particular chemical solution that would systematically be the best choice to minimize Sr-90 uptake.

Variations in radioactive cesium accumulation in wheat germplasm from fields affected by the 2011 Fukushima nuclear power plant accident

Decreasing the transfer of radioactive cesium (RCs) from soil to crops has been important since the deposition of RCs in agricultural soil owing to the Fukushima nuclear power plant accident of 2011. We investigated the genotypic variation in RCs accumulation in 234 and 198 hexaploid wheat (Triticum spp.) varieties in an affected field in 2012 and 2013, respectively. The effects of soil exchangeable potassium (ExK) content to RCs accumulation in wheat varieties were also evaluated. A test field showed fourfold differences in soil ExK contents based on location, and the wheat varieties grown in areas with lower soil ExK contents tended to have higher grain RCs concentrations. RCs concentrations of shoots, when corrected by the soil ExK content, were positively significantly correlated between years, and RCs concentrations of shoots were significantly correlated with the grain RCs concentration corrected by the soil ExK content. These results indicated that there were genotypic variations in RCs accumulation. The grain to shoot ratio of RCs also showed significant genotypic variation. Wheat varieties with low RCs accumulations were identified. They could contribute to the research and breeding of low RCs accumulating wheat and to agricultural production in the area affected by RCs deposition.

Fit-for-purpose modelling of radiocaesium soil-to-plant transfer for nuclear emergencies: a review

Numerous radioecological models have been developed to predict radionuclides transfer from contaminated soils to the food chain, which is an essential step in preparing and responding to nuclear emergencies. However, the lessons learned from applying these models to predict radiocaesium (RCs) soil-to-plant transfer following the Fukushima accident in 2011 renewed interest in RCs transfer modelling. To help guide and prioritise further research in relation to modelling RCs transfer in terrestrial environments, we reviewed existing models focussing on transfer to food crops and animal fodders. To facilitate the review process, we categorised existing RCs soil-to-plant transfer models into empirical, semi-mechanistic and mechanistic, though several models cross the boundaries between these categories. The empirical approach predicts RCs transfer to plants based on total RCs concentration in soil and an empirical transfer factor. The semi-mechanistic approach takes into account the influence of soil characteristics such as clay and exchangeable potassium content on RCs transfer. It also uses 'bioavailable' rather than total RCs in soil. The mechanistic approach considers the physical and chemical processes that control RCs distribution and uptake in soil-plant systems including transport in the root zone and root absorption kinetics. Each of these modelling approaches has its advantages and disadvantages. The empirical approach is simple and requires two inputs, but it is often associated with considerably uncertainty due to the large variability in the transfer factor. The semi-mechanistic approach factorises more soil and plant parameters than the empirical approach; therefore, it is applicable to a wider range of environmental conditions. The mechanistic approach is instrumental in understanding RCs mobility and transfer in soil-plant systems; it also helps to identify influential soil and plant parameters. However, the comlexity and the large amount of specific parameters make this approach impractical for nuclear emergency preparedness and response purposes. We propose that the semi-mechanistic approach is sufficiently robust and practical, hence more fit for the purpose of planning and responding to nuclear emergencies compared with the empirical and mechanistic approaches. We recommend further work to extend the applicability of the semi-mechanistic approach to a wide range of plants and soils.

Comparison of 0.1 M Stable CsCl and 1 M NH4NO3 as an Extraction Reagent to Evaluate Cs-137 Mobility in Soils

To evaluate the mobility and bioavailability of ¹³⁷Cs in soils, we compared the extraction of ¹³⁷Cs with stable Cs and ammonium solutions from ¹³⁷Cs-contaminated minerals and soils. The extraction yields of ¹³⁷Cs with stable Cs were significantly lower than those with ammonium for minerals with frayed edge sites, but such differences were not observed for minerals without frayed edge sites. The amount of ¹³⁷Cs extracted with stable Cs from soils was lower than, or equal to, that extracted with ammonium. The above results suggest that stable Cs extracted the ¹³⁷Cs from easily accessible sites. Plant available ¹³⁷Cs was assessed using Kochia (Bassia scoparia) cultivated in pots of contaminated soils, and compared with soil parameters including extractable ¹³⁷Cs and K, and radiocesium intercept potential. The ¹³⁷Cs/K ratio extracted with stable Cs solution was found to be a potential index for evaluation of the easily mobile and bioavailable fraction of ¹³⁷Cs in soil.

Radiocaesium transfer from volcanic soils to Swiss chard, cabbage and sweet corn

The root uptake of radiocaesium by different plant parts of Swiss chard (Beta vulgaris L. var. cicla), cabbage (Brassica oleracea L. var. capitata) and sweet corn (Zea mays L. var. saccharata) and the potential influence of K-fertilising on the transfer behaviour was studied in allophanic volcanic soils (umbric andosol and dystric fluvisol) in Chile under temperate climate and heavy rainfall conditions (∼2660 mm y^-1) over several vegetation periods. The soils were spiked homogeneously to 0.20 m depth with 100 kBq ¹³⁴Cs m^-2 and activity concentrations measured. The transfer factor (TF, on a dry mass basis) to Swiss chard had a clear exponential decrease within each crop year for both soil types, either K-fertilised or unfertilised. The highest values of the TFs to Swiss chard were at the beginning of the harvests, and the half-times of TF decrease ranged between 52 and 137 d for umbric andosol and between 40 and 164 d for dystric fluvisol. Over the five seasons there was no consistent ageing effect based on TF in either soil types for the three studied crops. The effect of ¹³⁴Cs foliar uptake by Swiss chard from resuspended soil was estimated to account for about 70% (external leaves) and 30% (internal leaves) increase in the TF for the K-unfertilised umbric andosol, and showed an ambiguous behaviour for the K-fertilised umbric andosol. Consequently foliar uptake does not explain the 370 and 500% increase of the TF to Swiss chard leaves determined during the third growing period in the umbric andosol without and with K-fertilisation, respectively. Therefore an uncertainty factor of 3-5 is recommended to be taken into account when using this parameter for dose calculations. The TF to Swiss chard was found to be higher than previously reported values. The TF to cabbage and sweet corn plant parts was found to be within the range of previously reported values. Normal K-fertilisation resulted in about 2.4-fold reduction in ¹³⁴Cs TF to Swiss chard, 2.3-fold to sweet corn and 3.0-fold to cabbage.

Determination of cesium transfer factors by instrumental neutron activation analysis

Food-chain models are used to predict radionuclide ingestion after fallout deposition. These models include those transfer processes (soil-to-plant transfer factor(s) [TF], plant-to-animal transfer coefficient(s) [TC] and concentration ratio [CR]) that are likely to be important for radiological assessment. The range of variability for transfer factors for the same plant groups is great, about 4-5 orders of magnitude, which limits their applicability. A better way to determine the best estimate the factors for radiocaesium and other important radionuclides is if the site-specific data are available. Soil, plant and animal samples were collected from a pasture area in Hungary during the vegetation period in 2016. Stable ¹³³Cs concentration was analysed by comparative method with neutron activation analysis (NAA). The comparator and the samples were irradiated in thermal neutron flux 2.55 × 10¹² ncm^-2s^-1 for 2 h (soil) and 6 h (vegetation, animal samples) in the TRIGA Mark II research reactor at the Nuclear Engineering Teaching Laboratory. After an appropriate decay time (12 days) the samples were measured by gamma-spectrometry and analysed. The observed stable caesium TC_pm (0.48-0.53) and CR_pm (0.41-0.45) were very close to ¹³⁷Cs factors in the IAEA 2009 Report of 0.49 and 0.54, respectively. This methodology is particularly suitable for the simultaneous study of natural caesium in ecosystem compartments. Consequently, the transfer of stable caesium in a pasture field may be regarded as a useful analogy in predicting the long-term changes of ¹³⁷Cs affected by site-specific environmental factors.

Effects of litter feeders on the transfer of 137Cs to plants

The effects of the Japanese horned beetle larvae on the transfer of ¹³⁷Cs from a contaminated leaf litter to the leaf vegetable, komatsuna (Brassica rapa var. perviridis) was studied. Feces of the larvae which were fed ¹³⁷Cs-contaminated leaf litter were added to a potting mix in which komatsuna plants were cultivated. The presence of feces increased the harvest yield of komatsuna, suggesting that feces provided nutrients for the plant growth. In addition, the amount of exchangeable ¹³⁷Cs in leaf litter was experimentally confirmed to be enhanced by the presence of feces which were excreted by larvae feeding. However, there was no difference in the soil-to-plant transfer factor of ¹³⁷Cs for the presence and absence of feces. Interactions between clay minerals and exchangeable ¹³⁷Cs in the soil beneath the litter layer may diminish the root uptake of ¹³⁷Cs. From these results, it was concluded that the effect of exchangeable ¹³⁷Cs released from feces was limited for the transfer of ¹³⁷Cs to plants if plant roots were not present in litter layers.

Radionuclides: Accumulation and Transport in Plants

Application of radioactive elements or radionuclides for anthropogenic use is a widespread phenomenon nowadays. Radionuclides undergo radioactive decays releasing ionizing radiation like gamma ray(s) and/or alpha or beta particles that can displace electrons in the living matter (like in DNA) and disturb its function. Radionuclides are highly hazardous pollutants of considerable impact on the environment, food chain and human health. Cleaning up of the contaminated environment through plants is a promising technology where the rhizosphere may play an important role. Plants belonging to the families of Brassicaceae, Papilionaceae, Caryophyllaceae, Poaceae, and Asteraceae are most important in this respect and offer the largest potential for heavy metal phytoremediation. Plants like Lactuca sativa L., Silybum marianum Gaertn., Centaurea cyanus L., Carthamus tinctorius L., Helianthus annuus and H. tuberosus are also important plants for heavy metal phytoremediation. However, transfer factors (TF) of radionuclide from soil/water to plant ([Radionuclide]plant/[Radionuclide]soil) vary widely in different plants. Rhizosphere, rhizobacteria and varied metal transporters like NRAMP, ZIP families CDF, ATPases (HMAs) family like P1B-ATPases, are involved in the radio-phytoremediation processes. This review will discuss recent advancements and potential application of plants for radionuclide removal from the environment.

Transfer of radiocesium from rhizosphere soil to four cruciferous vegetables in association with a Bacillus pumilus strain and root exudation

This study was carried out to assess the effect of Bacillus pumilus on the roots of four cruciferous vegetables with different root structures in regard to enhancement of ¹³⁷Cs bioavailability in contaminated rhizosphere soil. Results revealed that B. pumilus inoculation did not enhance the plant biomass of vegetables, although it increased root volume and root surface areas of all vegetables except turnip. The pH changes due to rhizosphere acidification by B. pumilus inoculation and root exudation did not affect the bioavailability of ¹³⁷Cs. However, concentrations of ¹³⁷Cs in plant tissues and soil-to-plant transfer values increased as a result of the larger root volume and root surface area of vegetables due to inoculation. Moreover, leafy vegetables, which possessed larger root volume and root surface areas, had a higher ¹³⁷Cs transfer value than root vegetables.

Estimated association between dwelling soil contamination and internal radiation contamination levels after the 2011 Fukushima Daiichi nuclear accident in Japan

OBJECTIVES

Measurement of soil contamination levels has been considered a feasible method for dose estimation of internal radiation exposure following the Chernobyl disaster by means of aggregate transfer factors; however, it is still unclear whether the estimation of internal contamination based on soil contamination levels is universally valid or incident specific.

METHODS

To address this issue, we evaluated relationships between in vivo and soil cesium-137 (Cs-137) contamination using data on internal contamination levels among Minamisoma (10-40 km north from the Fukushima Daiichi nuclear power plant), Fukushima residents 2-3 years following the disaster, and constructed three models for statistical analysis based on continuous and categorical (equal intervals and quantiles) soil contamination levels.

RESULTS

A total of 7987 people with a mean age of 55.4 years underwent screening of in vivo Cs-137 whole-body counting. A statistically significant association was noted between internal and continuous Cs-137 soil contamination levels (model 1, p value <0.001), although the association was slight (relative risk (RR): 1.03 per 10 kBq/m(2) increase in soil contamination). Analysis of categorical soil contamination levels showed statistical (but not clinical) significance only in relatively higher soil contamination levels (model 2: Cs-137 levels above 100 kBq/m(2) compared to those <25 kBq/m(2), RR=1.75, p value <0.01; model 3: levels above 63 kBq/m(2) compared to those <11 kBq/m(2), RR=1.45, p value <0.05).

CONCLUSIONS

Low levels of internal and soil contamination were not associated, and only loose/small associations were observed in areas with slightly higher levels of soil contamination in Fukushima, representing a clear difference from the strong associations found in post-disaster Chernobyl. These results indicate that soil contamination levels generally do not contribute to the internal contamination of residents in Fukushima; thus, individual measurements are essential for the precise evaluation of chronic internal radiation contamination.

Growth and (137)Cs uptake and accumulation among 56 Japanese cultivars of Brassica rapa, Brassica juncea and Brassica napus grown in a contaminated field in Fukushima: Effect of inoculation with a Bacillus pumilus strain

Fifty six local Japanese cultivars of Brassica rapa (40 cultivars), Brassica juncea (10 cultivars) and Brassica napus (6 cultivars) were assessed for variability in growth and (137)Cs uptake and accumulation in association with a Bacillus pumilus strain. Field trial was conducted at a contaminated farmland in Nihonmatsu city, in Fukushima prefecture. Inoculation resulted in different responses of the cultivars in terms of growth and radiocesium uptake and accumulation. B. pumilus induced a significant increase in shoot dry weight in 12 cultivars that reached up to 40% in one B. rapa and three B. juncea cultivars. Differences in radiocesium uptake were observed between the cultivars of each Brassica species. Generally, inoculation resulted in a significant increase in (137)Cs uptake in 22 cultivars, while in seven cultivars it was significantly decreased. Regardless of plant cultivar and bacterial inoculation, the transfer of (137)Cs to the plant shoots (TF) varied by a factor of up to 5 and it ranged from to 0.011 to 0.054. Five inoculated cultivars, showed enhanced shoot dry weights and decreased (137)Cs accumulations, among which two B. rapa cultivars named Bitamina and Nozawana had a significantly decreased (137)Cs accumulation in their shoots. Such cultivars could be utilized to minimize the entry of radiocesium into the food chain; however, verifying the consistency of their radiocesium accumulation in other soils is strongly required. Moreover, the variations in growth and radiocesium accumulation, as influenced by Bacillus inoculation, could help selecting well grown inoculated Brassica cultivars with low radiocesium accumulation in their shoots.

Relations of fine-root morphology on (137)Cs uptake by fourteen Brassica species

Fourteen Brassica species consisting of seven leafy vegetables and seven root vegetables were examined for (137)Cs uptake differences in relation to their fine-root morphological characters. A pot experiment was conducted from November 2014 to February 2015 in a Phytroton using a contaminated soil of Fukushima prefecture. Leafy vegetables showed bigger root diameters, larger root surface area and larger root volume. Consequently, leafy vegetables had higher (137)Cs uptake compared to root vegetables. Among the three fine-root parameters, only root surface area was observed as a significant contributing factor to higher (137)Cs uptake in terms of transfer factor (TF, dry weight basis). Kakina exhibited higher (137)Cs TF value (0.20) followed by Chinese cabbage (0.18) and mizuna (0.17). Lower TF values were observed in turnip (0.059), rutabaga (Kitanoshou) (0.062) and radish (Ha daikon) (0.064).

Growth and (137)Cs uptake of four Brassica species influenced by inoculation with a plant growth-promoting rhizobacterium Bacillus pumilus in three contaminated farmlands in Fukushima prefecture, Japan

The effectiveness of the plant growth-promoting rhizobacterium Bacillus pumilus regarding growth promotion and radiocesium ((137)Cs) uptake was evaluated in four Brassica species grown on different (137)Cs contaminated farmlands at Fukushima prefecture in Japan from June to August 2012. B. pumilus inoculation did not enhance growth in any of the plants, although it resulted in a significant increase of (137)Cs concentration and higher (137)Cs transfer from the soil to plants. The Brassica species exhibited different (137)Cs uptake abilities in the order Komatsuna>turnip>mustard>radish. TF values of (137)Cs ranged from 0.018 to 0.069 for all vegetables. Komatsuna possessed the largest root surface area and root volume, and showed a higher (137)Cs concentration in plant tissue and higher (137)Cs TF values (0.060) than the other vegetables. Higher (137)Cs transfer to plants was prominent in soil with a high amount of organic matter and an Al-vermiculite clay mineral type.

Transfer of radiocesium to four cruciferous vegetables as influenced by organic amendment under different field conditions in Fukushima Prefecture

Soil-to-plant transfer of radiocesium ((137)Cs) in four cruciferous vegetables as influenced by cattle manure-based compost amendment was investigated. Komatsuna, mustard, radish and turnip were cultivated in three different (137)Cs-contaminated fields at Nihonmatsu City in Fukushima Prefecture from June to August 2012. Results revealed that organic compost amendments stimulated plant biomass production and tended to induce higher (137)Cs concentration in the cruciferous vegetables in most cases. Among the studied sites, Takanishi soil possessing low exchangeable potassium (0.10 cmolc kg(-1)) was associated with an increased concentration of (137)Cs in plants. Radiocesium transfer factor (TF) values of the vegetables ranged from 0.025 to 0.119. The increase in (137)Cs TFs was dependent on larger plant biomass production, high organic matter content, and high sand content in the studied soils. Average (137)Cs TF values for all study sites and compost treatments were higher in Komatsuna (0.072) and radish (0.059), which exhibited a higher biomass production compared to mustard and turnip. The transferability of (137)Cs to vegetables from soils was in the order Komatsuna > radish > mustard > turnip. The highest (137)Cs TF value (0.071) of all vegetables was recorded for a field where the soil had high organic matter content and a high clay proportion of 470 g kg(-1) consisting of Al-vermiculite clay mineral.

Imaging plant leaves to determine changes in radioactive contamination status in Fukushima, Japan

The chemical composition of plant leaves often reflects environmental contamination. The authors analyzed images of plant leaves to investigate the regional radioactivity ecology resulting from the 2011 accident at the Fukushima No. 1 nuclear power plant, Japan. The present study is not an evaluation of the macro radiation dose per weight, which has been performed previously, but rather an image analysis of the radioactive dose per leaf, allowing the capture of various gradual changes in radioactive contamination as a function of elapsed time. In addition, the leaf analysis method has potential applications in the decontamination of food plants or other materials.

Radium concentration factors in passionfruit (Passiflora foetida) from the Alligator Rivers Region, Northern Territory, Australia

In this study, uptake of Ra from soil into the edible fruit of the wild passionfruit species Passiflora foetida was investigated, using selective extraction from the soil samples. A wide range of environmental exposure conditions were represented by the locations that were sampled, including both natural soils, and soils influenced by past and present uranium mining activities. The bioavailable (226)Ra fraction in soils was found to be a better predictor of (226)Ra fruit activity concentrations than the total soil activity concentration, or any of the other fractions studied. Concentration Factors (CFs) derived using the bioavailable fraction varied by only a factor of 7 between different locations, whereas CFs derived using other fractions and total soil varied by up to two orders of magnitude. CFs were highest for those soils containing the lowest concentrations of Mg, Ca and Ba, and approached a saturation value at higher soil concentrations. This finding suggests that group II elements influence radium uptake, most likely the result of increased pressure on the plant to take up essential nutrient group II elements from soil with the lower concentrations, with Ra being taken up as an analogue element. It is also possible that at higher concentrations of bioavailable Ca and Mg in the soil, these ions will outcompete Ra for adsorption sites in the soil and/or on the root surfaces. The study also shows that (228)Ra can potentially be a significant contributor to ingestion doses and should also be considered when assessing committed effective doses from the ingestion of fruits.

Artificial radioactivity of Finnish vegetables in the 2000s

A survey on long-lived artificial radionuclides (137)Cs and (90)Sr in vegetables produced in Finland was carried out in 2009-2010. The mean (137)Cs concentrations of all the outdoor vegetables were well below 0.5 Bq kg(-1), ranging from <0.01 to 8.15 Bq kg(-1) (fresh weight). The highest (137)Cs contents were found in potato and root vegetables. The uneven distribution of the (137)Cs deposition after the Chernobyl accident in 1986 was still seen in the (137)Cs contents of outdoor vegetables. The (137)Cs contents of greenhouse vegetables varied from <0.01 to 9.3 Bq kg(-1), and the highest concentrations were found in organic lettuce grown in peat pots. The concentrations of (90)Sr in the vegetables varied from 0.0087 to 0.17 Bq kg(-1) fresh weight. The mean effective dose resulting from (137)Cs and (90)Sr in vegetables in 2009-2010 was <0.3 µSv a(-1) and poses no health risk to the consumers.

Radioactive pollution from Fukushima Daiichi nuclear power plant in the terrestrial environment

Major contaminants from venting and hydrogen explosions at the Fukushima Daiichi nuclear reactors between 12 and 15 March 2011 were transported northwestward and deposited on soil and plants via precipitation. Surface soils and plant leaves were sampled at 64 sites in the Fukushima Prefecture. The highest concentrations of (134)Cs (84.4 kBq kg(-1)) and (137)Cs (82.0 kBq kg(-1)) in surface soils were observed at Nagadoro in Iidate village located 32 km northwest from the Fukushima Daiichi nuclear power plant. Furthermore, (131)I, (129)Te, (129 m)Te, (110 m)Ag and (140)La were detected in the same samples. Outer surface of plant leaves, such as bamboo, cabbage and grasses were highly contaminated at the high-dose rate areas of Tsushima and Minami-Tsushima in Namie town. Mugwort leaves that grew after the pollution event had extremely low concentration of radionuclides; however, the plant/soil radiocaesium ratio was 0.023 ± 0.006. It is anticipated that decomposition of fallen leaves will promote recycling of radionuclides in the environment.

Effects of low-level radioactive soil contamination and sterilization on the degradation of radiolabeled wheat straw

After the explosion of reactor 4 in the nuclear power plant near Chernobyl, huge agricultural areas became contaminated with radionuclides. In this study, we want to elucidate whether (137)Cs and (90)Sr affect microorganisms and their community structure and functions in agricultural soil. For this purpose, the mineralization of radiolabeled wheat straw was examined in lab-scale microcosms. Native soils and autoclaved and reinoculated soils were incubated for 70 days at 20 °C. After incubation, the microbial community structure was compared via 16S and 18S rDNA denaturing gradient gel electrophoresis (DGGE). The radioactive contamination with (137)Cs and (90)Sr was found to have little effect on community structure and no effect on the straw mineralization. The autoclaving and reinoculation of soil had a strong influence on the mineralization and the community structure. Additionally we analyzed the effect of soil treatment on mineralization and community composition. It can be concluded that other environmental factors (such as changing content of dissolved organic carbon) are much stronger regulating factors in the mineralization of wheat straw and that low-level radiation only plays a minor role.

Soil to leaf transfer factor for the radionuclides ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr at Kaiga region, India

Transfer factors are the most important parameters required for mathematical modeling used for environmental impact assessment of radioactive contamination in the environment. In this paper soil to leaf transfer factor for the radionuclides ⁴⁰K, ²²⁶Ra, ¹³⁷Cs and ⁹⁰Sr is estimated for Kaiga region in Karnataka state, India. Among the plants in which study is carried out, ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr activity in leaves of herbaceous plants is higher than that of tree leaves. Soil to leaf transfer factor for ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr was found to be in the range of 0.03-0.65, 0.32-8.04, 0.05-3.03 and 0.42-2.67 respectively.

Estimating transfer parameters in the absence of data

The calculation of transfer of radionuclides from the abiotic to the biotic environment is a well-established practice in radiological assessments. Concentration ratios provide simple means to estimate radionuclide activity in biota, from measured (or estimated) radionuclide concentrations in either a food source or an abiotic component such as soil or water. They are typically reported by element, and data compilations may include information such as soil type (e.g., sand, loam, clay) and species. The data may be for multiple species at a single location, single species at multiple locations, or represent compilations from multiple sources. Recently published guidance suggests that estimates are best made using data from the same ecosystem. This paper examines this recent guidance, in the context of using measured data from within a single ecosystem and comparing results to more generic values. Results suggest that generic values may be an adequate substitute for site-specific information. It illustrates how ionic potential may be used as an alternative to group chemical properties in estimating transfer factors. Lastly, limited evidence is found to support the concept of allometric scaling functions for elemental concentrations in plants.

Phylogeny can be used to make useful predictions of soil-to-plant transfer factors for radionuclides

Soil-to-plant transfer of radionuclides can be related to plant evolutionary history (phylogeny). For some species and radionuclides the effect is significant enough to be useful in predicting Transfer Factors (TFs). Here a Residual Maximum Likelihood (REML)-based mixed model and a recent plant phylogeny are used to compile data on soil-to-plant transfer of radionuclides and to show how the phylogeny can be used to fill gaps in TFs. Using published data, generic means for TFs are used to anchor the data from REML modelling and hence predict TFs for important groups of plants. Radionuclides of Cs are used as an example. With a generic soil-to-plant TF of 0.07, TFs of 0.035 and 0.085 are predicted for monocot and eudicot gaps, respectively. Also demonstrated is how the known effects of soil conditions can be predicted across plant groups-predicted Cs TFs for gap-filling across all flowering plants are calculated for sandy loams with and without waterlogging. Predictions of TFs for Sr, Co, Cl and Ru are also given. Overall, the results show that general predictions of TFs based on phylogeny are possible-a significant contribution to gap filling for TFs.

Cesium-137 contamination of oak (Quercus petrae Liebl.) from sub-mediterranean zone in South Bulgaria

This study focuses on the cesium-137 ((137)Cs) contamination in grass and in different compartments of oak trees growing in ecosystems, located in the zone with sub-mediterranean climate in South Bulgaria, characterized with high summer temperatures, low precipitation and often periods of drought. In 2008, three experimental sites - PP1, PP2, PP3 - were sampled in oak ecosystems from Maleshevska Mountain at 900 m above sea level. Samples from grass species and oak tree leaves, branches with different diameter, wood disks and bark were analyzed for (137)Cs activity with gamma-spectrometry. The soil-to-plant transfer factor (TF) values for (137)Cs were estimated differentiating different tree compartments. Our findings showed relatively high activity concentrations of (137)Cs in oak trees even 22 years after the Chernobyl accident. The grass under oak was less contaminated compared with the oak trees. The different organs of oak trees could be distinguished according to the (137)Cs contamination as follows: bark>branches (d<1 cm)>leaves>branches (d>3 cm)>wood. The relatively higher contamination of bark compared with the new-formed biomass suggested that a significant part of (137)Cs was accumulated as a result of direct adsorption at the time of the main contamination event. The TF values obtained and the presence of (137)Cs in the branches, leaves and in the wood formed after 1986 confirmed that 22 years after the contamination, the main mechanism of (137)Cs entrance in tree biomass was the root uptake.

Measurement of natural and artificial radioactivity in powdered milk consumed in Jordan and estimates of the corresponding annual effective dose

The activity concentrations of (40)K, (226)Ra, (228)Ra and (137)Cs were measured for 14 brands of the powdered milk consumed in Jordan, which are imported from various regions around the world. The activity concentrations of (40)K were found not to vary greatly from one brand to the other with an average of 348 +/- 26 Bq kg(-1). However, the activity concentrations of (137)Cs revealed a geographical distribution being: (i) undetected in any of the samples from Argentina, (ii) uniformly distributed in samples from Europe with an average of 0.43 +/- 0.05 Bq kg(-1), and (iii) widely varying in samples from New Zealand (from being not detected (ND) to 1.55 Bq kg(-1)). (226)Ra and (228)Ra were measured above the detection limits in five brands only and displayed relatively low activity concentrations of 0.50-2.14 and 0.78-1.28 Bq kg(-1) for (226)Ra and (228)Ra, respectively. The total average annual effective doses due to intake of (40)K, (226)Ra, (228)Ra and (137)Cs from the ingestion of the powdered milk for infants, children and adults were estimated to be (in microSv): 332, 138 and 43, respectively. These results indicate no significant radiation dose to the public.

Extension of sensitivity and uncertainty analysis for long term dose assessment of high level nuclear waste disposal sites to uncertainties in the human behaviour

Biosphere dose conversion factors are computed for the French high-level geological waste disposal concept and to illustrate the combined probabilistic and deterministic approach. Both (135)Cs and (79)Se are used as examples. Probabilistic analyses of the system considering all parameters, as well as physical and societal parameters independently, allow quantification of their mutual impact on overall uncertainty. As physical parameter uncertainties decreased, for example with the availability of further experimental and field data, the societal uncertainties, which are less easily constrained, particularly for the long term, become more and more significant. One also has to distinguish uncertainties impacting the low dose portion of a distribution from those impacting the high dose range, the latter having logically a greater impact in an assessment situation. The use of cumulative probability curves allows us to quantify probability variations as a function of the dose estimate, with the ratio of the probability variation (slope of the curve) indicative of uncertainties of different radionuclides. In the case of (135)Cs with better constrained physical parameters, the uncertainty in human behaviour is more significant, even in the high dose range, where they increase the probability of higher doses. For both radionuclides, uncertainties impact more strongly in the intermediate than in the high dose range. In an assessment context, the focus will be on probabilities of higher dose values. The probabilistic approach can furthermore be used to construct critical groups based on a predefined probability level and to ensure that critical groups cover the expected range of uncertainty.

Plant uptake of radiocaesium from artificially contaminated soil monoliths covering major European soil types

Uptake of (137)Cs was measured in different agricultural plant species (beans, lettuce, barley and ryegrass) grown in 5 undisturbed soil monoliths covering major European soil types. The first cultivation was made three years after soil contamination and plants were grown during 3 successive years. The plant-soil (137)Cs transfer factors varied maximally 12-fold among soils and 35-fold among species when grown on the same soil. Single correlations between transfer factors and soil properties were found, but they varied widely with plant type and can hardly be used as a predictive tool because of the few soils used. The variation of (137)Cs concentrations in plants among soils was related to differences in soil solution (137)Cs and K concentrations, consistent with previous observations in hydroponics and pot trials. Absolute values of transfer factors could not be predicted based on a model validated for pot trials. The (137)Cs activity concentration in soil solution decreased significantly (11- to 250-fold) for most soils in the 1997-1999 period and is partly explained by decreasing K in soil solution. Transfer factors of lettuce showed both increasing and decreasing trends between 2 consecutive years depending on soil type. The trends could be explained by the variation in (137)Cs and K concentrations in soil solution. It is concluded that differences in (137)Cs transfer factors among soils and trends in transfer factors as a function of time can be explained from soil solution composition, as shown previously for pot trials, although absolute values of transfer factors could not be predicted.

Effect of nitrogen, potassium and humic acid on ( 134 )Cs transfer factors to wheat from tropical soils in Neubauer growth units

A Neubauer plantlet experiment was carried out using Inceptisol (Typic Haplustept) and Vertisol (Typic Chromustert) soils contaminated with 134Cs at 74 kBq kg(-1) soil to study the transfer factor to wheat crop (Triticum aestivum) as influenced by four levels of humic acid (100, 200, 300, 400 mg HA kg(-1) soil), potassium and NH4-N (36.4, 54.5, 72.7 and 90.9 mg K or NH4 kg(-1) soil) under tropical climate. The biomass yield and K uptake by wheat were significantly improved in Vertisol with NH4-N and K application. The potassium application significantly increased the potassium concentration in wheat plants. The increase in the levels of each of the treatments dramatically improved the yield, K content and K uptake parameters, irrespective of the soils. The 134Cs transfer factors, irrespective of the treatments were observed to be higher in Vertisols as compared to Inceptisols. Among the treatments, the effect of HA was significantly greater than that of K and NH4-N application in Inceptisol, however, in Vertisols both HA and NH4-N were observed to be superior as compared to K application. With each increment in the levels of the treatments, a significantly lowered TF value was found, higher in Inceptisols (56.3%) than Vertisols (48.5%). Comparison of treatments indicates that in general higher potassium concentration in plant drastically lowered radiocesium transfer to wheat. Neubauer plant culture study, a rapid laboratory experimental model based on simple soil-plant system was quite clearly brought out the potential effectiveness of N, K and HA on soil-to-wheat transfer of radiocesium. Such screening technique needs to be extended to cover wider crop species, different climatic conditions and factors governing/modifying the mobility of radiocesium in soil and its absorption by crop plants.

Mycorrhizal association of maritime pine, Pinus pinaster, with Rhizopogon roseolus has contrasting effects on the uptake from soil and root-to-shoot transfer of 137Cs, 85Sr and 95mTc

The beneficial role of mycorrhizal association on plant nutrition and water supply is well-known, however, very little information exists with respect to the availability of radionuclides. We have measured the effect of controlled mycorrhizal association on the root uptake from soil and accumulation in leaves of three radionuclides. The radionuclides have contrasting chemical and biological properties: Cs is strongly adsorbed on soil, has no biological role and is a close analogue of potassium; Sr is less strongly adsorbed on soil and behaves very similarly to calcium; and Tc is very mobile in soil as pertechnetate, but immobilised when reduced to Tc(IV), it is also considered to be easily assimilated by biological systems. We found that mycorrhizal association had no effect on root-to-needle transfer of Cs, but increased root uptake and that this increase could not be explained by improved potassium nutrition. In contrast, the symbiotic relation decreased Tc soil-to-needle transfer, but this resulted from complex dynamics of root uptake and rapid immobilisation of Tc in soil. No effect of mycorrhizal association on Sr, like its stable analogue Ca, was observed. The addition of a phytotoxic metal, Cu, inhibited mycorrhizal association, thus eliminating the effects observed for non-contaminated plant-fungus couples, but had no additional effect on radionuclide dynamics.

Factors affecting the transfer of radionuclides from the environment to plants

Much of our food directly or indirectly originates from plant material; thus, detailed studies on plant contamination processes are an essential part of international environmental research. This overview attempts to identify and describe the most important parameters and processes affecting the behaviour of radionuclide transfer to plants. Many parameters influence these processes. These parameters are related to: (1) plant, (2) soil, (3) radionuclide, (4) climate and (5) time. Often there is no boundary between the factors and they are linked to each other. Knowledge of important factors in radionuclide transfer to plants can help to assess and prevent radiological exposure of humans. This knowledge can also help to guide researches and modelling related to transfer of radionuclides to food chain.

Soil-to-plant and soil-to-grain transfer of (137)Cs in field-grown maize hybrids during two contrasting seasons: assessing the phenotypic variability and its genetic component

Field-grown maize hybrids were assessed for variability in (137)Cs accumulation in vegetative parts of young and mature maize shoots and grains during 2 years with contrasting climatic conditions. Trials were carried out at different sites in the Tula region of Russia, which is characterized by a highly homogenous soil classified as Luvic Chernozem according to FAO/UNESCO, and average contamination levels of about 509-564 Bq (137)Cs kg(-1) soil. In the first year, 19 hybrids were tested. The two hybrids with the highest and the two with the lowest (137)Cs concentration ratios (C (r)) were also tested in the second year, together with another 11 hybrids. All samples were additionally assessed for their potassium content. In both investigation periods (137)Cs accumulation in vegetative shoots and grains was found to vary up to more than twofold between hybrids. However, C (r) values of those hybrids that showed a relatively low (137)Cs accumulation in the first year were not necessarily low in the second year, and the ratio between the (137)Cs C (r) of low- and high-accumulating hybrids was much smaller than in the year before. In both vegetative shoots and grains the variance caused by the different years was larger than the genotypic variance, thus indicating the limits of genotype selection for this trait. Significant correlations were determined between the (40)K and (137)Cs C (r) values in the same tissue, but for one hybrid indications for uncoupling of the two traits were found. Average Cs/K ratios in young shoots, mature shoots and grains were 0.06, 0.05 and 0.02, respectively, indicating tissue- and stage-specific regulation of accumulation within each plant. The findings are discussed with respect to new approaches towards a better understanding of (137)Cs accumulation and its potential reduction in plants.

Transfer factors of (134)Cs to crops from Typic Haplustept under tropical region as influenced by potassium application

Under greenhouse condition a pot culture investigation was carried out using Inceptisol soil (Typic Haplustept) contaminating with (134)Cs @ 1microCikg(-1) soil to study the transfer factor to Mustard, Gram, Spinach and Wheat crops as influenced by potassium application (0, 27.3, 54.6 and 81.9mgKkg(-1) soil). Potassium application in general improved the biomass, grain yield and also the potassium concentration in all the crops. Irrespective of the crops, (134)Cs transfer factor to straw and grain was highest in control treatment (no K addition) and found to decrease significantly with increase in K application levels. The (134)Cs uptake was highest in Spinach followed by Mustard, Gram and Wheat crops. The weighted transfer factor values (straw plus grain) to Spinach, Mustard, and Gram were observed to be 5.54, 4.38 and 2.20 times higher as compared to Wheat crop.

Radiostrontium uptake by plants from different soil types in Kazakhstan

The transfer of 90Sr to a range of different plant species grown on a range of different soil types in Kazakhstan, including three from the Semipalatinsk Test Site (STS), has been measured in a lysimeter experiment. 90Sr uptake by Stipa spp was significantly higher than for other vegetation species. The uptake of 90Sr from chernozem was significantly lower than that from the other soil types which is consistent with other literature. There was a significant negative relationship between 90Sr uptake and calcium, humus and CEC concentration in the soil for Agropyrum spp, Artemisia spp but not for Stipa spp or Bromus spp. The transfer to vegetation from soil has been quantified using the aggregated transfer coefficients for each species. Tag values range from 0.6 to 11.9 m2 kg-1x10(-3) over all measurements. The transfer of 90Sr to plants from the Kazakh soils was low compared to previously reported data and to that given from literature reviews.

Predicting the transfer of 137Cs to rice plants by a dynamic compartment model with a consideration of the soil properties

This paper describes the predictions of the transfer of 137Cs to rice plants following soil deposition during a non-growth season of rice by a dynamic compartment model considering the soil properties, and their comparison with experimental results. Major processes considered in the model were percolation, soil mixing by plowing, plant uptake, leaching to deep soil, fixation to clay mineral, and time-dependent growth of a plant. To consider the effects of the soil properties (pH, clay mineral, organic matter content, and exchangeable K) on plant uptake and the leaching rates of 137Cs in a root zone soil, the Absalom model was used for the present model. The 137Cs aggregated transfer factors (TFa, m2kg-1 dry plant) of rice plants for two consecutive cultivation years were obtained as a result of simulated 137Cs soil deposition experiments with 17 paddy soils of different properties, all of which were performed before transplanting of the rice. Observed 137Cs TFa values of the rice plants did not show an evident trend for the pH and clay content of the soil properties, while they increased with an increasing organic matter content and a decreasing exchangeable K concentration. Predicted 137Cs TFa values of the rice plants were found to be comparable with those observed.

Soil-to-grain transfer of fallout 90Sr for 28 winter wheat cultivars

In order to identify wheat cultivars with minimum soil-to-grain transfer of fallout 90Sr, 28 winter wheat cultivars were investigated at three different sites with different soil types in Upper Bavaria. Each cultivar was grown on an area of 10 m2 and harvested in August 1999. Mean soil-to-grain concentration ratios (C(r)) were 0.151 +/- 0.029, 0.205 +/- 0.035 and 0.060 +/- 0.012, respectively. The C(r) values obtained varied by factors of up to 2.6 for the different cultivars at a given site, and by factors of up to 5.0 for the different sites and a given cultivar. Site-averaged normalized concentration ratios (SANC(r)) ranged from 0.666 +/- 0.062 to 1.503 +/- 0.161. The cultivars Convent, Ludwig, and Semper, showed the lowest uptake of (90)Sr compared to the mean of all cultivars at each site. A cultivar that shows both minimum uptake of 90Sr and 137Cs could not be identified. The results suggest that 90Sr rather than 137Cs might be the limiting radionuclide concerning the use of contaminated land for wheat production. Thus, more efforts might be necessary identifying wheat cultivars with minimum 90Sr uptake.

Comparison of the accumulation of (137)Cs and (90)Sr by six spring wheat varieties

The uptake of (137)Cs and (90)Sr by six varieties of spring wheat (Triticum aestivum) was compared in field trials on land contaminated by the Chernobyl accident. All the experimental varieties are officially adopted for agricultural use in Belarus and are used in large-scale production. Under identical conditions of nutrition, the productivity of the varieties varied significantly by a factor of 1.3. The extent of (137)Cs and (90)Sr accumulation by wheat grain, quantified as the concentration ratio, differed between the varieties by as much as a factor of 1.6, for both radionuclides. There was a significant linear positive correlation between the (90)Sr activity concentration in grain and straw, and the calcium concentration. The correlation between (137)Cs and potassium was not significant. The results suggest that certain varieties of spring wheat used in normal agricultural practice accumulate less (137)Cs and (90)Sr into grain than others. Some spring wheat varieties accumulated relatively less (137)Cs, but did not accumulate less (90)Sr. One variety, Quattro, had a significantly lower uptake of both (90)Sr (for grain) and (137)Cs (for both grain and straw) than that of the other varieties tested. The reduction efficiency achieved by the use of these varieties, however, is not as high as that achieved by soil amelioration techniques in the past. Nevertheless, since there are no additional costs or production losses associated with these varieties, their use in the contaminated areas is worth considering as a simple, practical, and effective contribution to reducing the uptake of both (90)Sr and (137)Cs and allowing farmers to produce food-grade grain.

Root uptake of 137Cs by natural and semi-natural grasses as a function of texture and moisture of soils

This work studies the dependence of 137Cs root uptake on the structure of landscape, especially on texture and moisture of soils, under natural conditions, on abandoned radiopolluted lands in Northern Ukraine. Researches were carried out on a wide range of landscape conditions, at various levels of 137Cs contamination (from 20 up to 5000 kBqm(-2)), with different types of soils (approx. 20 soil varieties), which differ in texture, granulometric composition, degrees of gleyization and water regime, and anthropogenic transformation. The results showed that transfer factor (TF) values of 137Cs differ 50 times for the natural grassy coenoses and 8 times for the semi-natural ones. The lowest 137Cs TF values were measured in the herbages of dry meadows at automorphous loamy soils, while the highest were observed in wetland meadows at organic soils. Finally, the correlation between 137Cs TF values and granulometric composition of soil was determined for both automorphic and hydromorphic mineral soils.