Plant uptake of radiocaesium: a review of mechanisms, regulation and application

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.

Effects of accompanying anions on cesium retention and translocation via droplets on soybean leaves

Plant foliar uptake and translocation is an important pathway for the migration of radiocesium to the human diet. This study reports the effects of accompanying anions ( [Formula: see text] , [Formula: see text] , [Formula: see text] , and I(-)) on cesium retention and translocation. An experiment to simulate cesium retention and translocation was conducted in a greenhouse by applying droplets of stable cesium solutions to the upper surface of four soybean [Glycine max (L.) Merr.] trifoliate leaves. The average percentages of cesium retention with the accompanying anions [Formula: see text] , [Formula: see text] , [Formula: see text] , and I(-) on the leaves were 7.2, 21.5, 49.3, and 10.2%, respectively. Retention values of the four treatments were stable during the 3-day exposure period, indicating that cesium could be absorbed and penetrate the cuticle quickly once it was dissolved. Scanning electron microscopy coupled with energy dispersive X-ray microanalysis showed that particles containing cesium remained on the leaf surfaces after washing. Also, nano-sized particles containing cesium were observed inside the leaf tissues. Cesium concentrations in the uncontaminated leaves, pods, stems, and roots increased during the study period indicating cesium redistribution from the contaminated leaves.

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.

Studies on soil to grass transfer factor (Fv) and grass to milk transfer coefficient (Fm) for cesium in Kaiga region

Detailed studies were carried out to establish site-specific soil to grass transfer factors (Fv) and grass to cow milk transfer coefficients (Fm) for radioactive cesium ((137)Cs) and stable cesium (Cs) for Kaiga region, where a nuclear power station has been in operation for more than 10 years. The study included adopted cows, cows of local farmers, and cows from the dairy farm. A grass field was developed specifically for the study and 2 local breed cows were adopted and allowed to graze in this grass field. The soil and grass samples were collected regularly from this field and analyzed for the concentrations of (137)Cs and stable Cs to evaluate the soil to grass Fv values. The milk samples from the adopted cows were analyzed for the (137)Cs and stable Cs concentrations to evaluate Fm values. For comparison, studies were also carried out in dominant grazing areas in different villages around the nuclear power plant and the cows of local farmers which graze in these areas were identified and milk samples were collected and analyzed regularly. The geometric mean values of Fv were found to be 1.1 × 10(-1) and 1.8 × 10(-1) for (137)Cs and stable Cs, respectively. The Fm of (137)Cs had geometric mean values of 1.9 × 10(-2) d L(-1) and 4.6 × 10(-2) d L(-1), respectively, for adopted Cows 1 and 2; 1.7 × 10(-2) d L(-1) for the cows of local farmers, and 4.0 × 10(-3) d L(-1) for the dairy farm cows. The geometric mean values of Fm for stable Cs were similar to those of (137)Cs. The Fm value for the dairy farm cows was an order of magnitude lower than those for local breed cows. The Fm values observed for the local breed cows were also an order of magnitude higher when compared to the many values reported in the literature and in the IAEA publication. Possible reasons for this higher Fm values were identified. The correlation between Fv and Fm values for (137)Cs and stable Cs and their dependence on the potassium content ((40)K and stable K) in the soil and grass were also studied. In order to estimate the ingestion dose accurate data of the dietary habits of the population was necessary and this data was collected through a well planned demographic survey. The internal doses to a child due to the ingestion of (137)Cs along with the milk of the local cows and from the dairy farm were found to be 0.29 μSv y(-1) and 0.04 μSv y(-1),while that to an adult were 0.39 μSv y(-1) and 0.05 μSv y(-1), respectively.

Methodological approaches for using synchrotron X-ray fluorescence (SXRF) imaging as a tool in ionomics: examples from Arabidopsis thaliana

Here we present approaches for using multi-elemental imaging (specifically synchrotron X-ray fluorescence microscopy, SXRF) in ionomics, with examples using the model plant Arabidopsis thaliana. The complexity of each approach depends on the amount of a priori information available for the gene and/or phenotype being studied. Three approaches are outlined, which apply to experimental situations where a gene of interest has been identified but has an unknown phenotype (phenotyping), an unidentified gene is associated with a known phenotype (gene cloning) and finally, a screening approach, where both gene and phenotype are unknown. These approaches make use of open-access, online databases with which plant molecular genetics researchers working in the model plant Arabidopsis will be familiar, in particular the Ionomics Hub and online transcriptomic databases such as the Arabidopsis eFP browser. The approaches and examples we describe are based on the assumption that altering the expression of ion transporters can result in changes in elemental distribution. We provide methodological details on using elemental imaging to aid or accelerate gene functional characterization by narrowing down the search for candidate genes to the tissues in which elemental distributions are altered. We use synchrotron X-ray microprobes as a technique of choice, which can now be used to image all parts of an Arabidopsis plant in a hydrated state. We present elemental images of leaves, stem, root, siliques and germinating hypocotyls.

Soil to rice transfer factors for (226)Ra, (228)Ra, (210)Pb, (40)K and (137)Cs: a study on rice grown in India

India is the second largest producer of rice (Oryza sativa L.) in the world and rice is an essential component of the diet for a majority of the population in India. However, detailed studies aimed at the evaluation of radionuclide transfer factors (F(v)) for the rice grown in India are almost non-existent. This paper presents the soil to rice transfer factors for natural ((226)Ra, (228)Ra, (40)K, and (210)Pb) and artificial ((137)Cs) radionuclides for rice grown in natural field conditions on the West Coast of India. A rice field was developed very close to the Kaiga nuclear power plant and the water required for this field was drawn from the cooling water discharge canal of the power plant. For a comparative study of the radionuclide transfer factors, rice samples were also collected from the rice fields of nearby villages. The study showed that the (226)Ra and (228)Ra activity concentrations were below detection levels in different organs of the rice plant. The soil to un-hulled rice grain (40)K transfer factor varied in the range of 6.5 × 10(-1) to 2.9 with a mean of 0.15 × 10(1), and of (210)Pb varied in the range of <1.2 × 10(-2) to 8.1 × 10(-1) with a mean of 1.4 × 10(-1), and of (137)Cs varied in the range of 6.6 × 10(-2) to 3.4 × 10(-1) with a mean of 2.1 × 10(-1). The mean values of un-hulled grain to white rice processing retention factors (F(r)) were 0.12 for (40)K, 0.03 for (210)Pb, and 0.14 for (137)Cs. Using these processing retention factors, the soil to white rice transfer factors were estimated and these were found to have mean values of 1.8 × 10(-1), 4.2 × 10(-3), and 3.0 × 10(-2) for (40)K, (210)Pb, and (137)Cs, respectively. The study has shown that the transfer of (40)K was higher for above the ground organs than for the root, but (210)Pb and (137)Cs were retained in the root and their transfer to above the ground organs of the rice plant is significantly lower.

Temporal and seasonal variations of radiocaesium content in some plants from the western part of Ukrainian Polesye

We present measurements of (137)Cs contamination for some of the berry plants and medicinal herbs growing in the western part of Ukrainian Polesye during 1996-2009. Basing on the calculations of the aggregated transfer factors, we classified the medicinal herbs into five groups according to their ability for accumulation of (137)Cs: very weak (T(ag) < 10(-3)), weak (10(-3) < T(ag) < 10(-2)), moderate (10(-2) < T(ag) < 5 × 10(-2)), strong (5 × 10(-2) < T(ag) < 10(-1)) and very strong (T(ag) > 10(-1)). The (137)Cs concentrations in the berry plants significantly decreased during the time of our monitoring and the rate of this decrease was much higher than that typical of the corresponding soils. This is because with time the (137)Cs in the soil was becoming less accessible for uptake by plant roots due to its fixation on micaceous clay minerals. The seasonal variations of the (137)Cs concentrations in the vegetative and generative organs of the plants revealed a good interdependence between the seasonal peculiarities of (137)Cs accumulation by the organs and the features of their vegetation period.

Temporal evolution of ¹³⁷Cs⁺, K⁺ and Na⁺ in fruits of South American tropical species

Concentrations of (137)Cs, K and Na in fruits of lemon (Citrus limon B.) and of K and Na in fruits of coconut (Cocos nucifera L.) trees were measured by both gamma spectrometry and neutron activation analysis, with the aim to understand the behaviour of monovalent inorganic cations in tropical plants as well as the plant ability to store these elements. Similar amounts of K(+) were incorporated by lemon and coconut trees during the growth and ripening processes of its fruits. The K concentration decreased exponentially during the growth of lemons and coconuts, ranging from 13 to 25 g kg(-1) dry weight. The incorporation of Na(+) differed considerably between the plant species studied. The Na concentration increased linearly during the lemon growth period (0.04 to 0.70 g kg(-1) d.w.) and decreased exponentially during the coconut growth period (1.4 to 0.5 g kg(-1) d.w.). Even though radiocaesium is not an essential element to plants, our results have shown that (137)Cs incorporation to vegetable tissues is positively correlated to K distribution within the studied tropical plant species, suggesting that the two elements might be assimilated in a similar way, going through the biological cycle together. A mathematical model was developed from the experimental data allowing simulating the incorporation process of monovalent inorganic cations by the fruits of such tropical species. The agreement between the theoretical approach and the experimental values is satisfactory along fruit development.

Radionuclide activity concentrations in forest surface fuels at the Savannah River Site

BACKGROUND/OBJECTIVE

A study was undertaken at the United States Department of Energy's Savannah River Site (SRS), Aiken, South Carolina to investigate radionuclide activity concentrations in litter and duff from select areas at SRS. Litter (i.e. vegetative debris) and duff (i.e. highly decomposed vegetative debris) can often be the major fuels consumed during prescribed burns and have potential to release radiological contaminants into the environment.

METHODS

Repeated samples from 97 locations were collected systematically across SRS and analyzed for radionuclide activity. Radionuclide activity concentrations found in litter and duff were compared. As spatial trends were of interest, spatial distributions of radionuclide activity concentrations found in litter and duff and spatial dependency amongst the data were explored.

RESULTS

(7)Be, (40)K, and (137)Cs showed statistically significant proportional differences between litter and duff samples. Duff sample concentrations for (137)Cs (p < 0.0001) and (40)K (p = 0.0015) were statistically higher compared to litter samples. (7)Be activity concentrations were statistically higher in litter as compared to duff (p < 0.0001). For (40)K litter and duff samples, spatial correlation tests were not significant at p = 0.05 and the maps did not indicate any apparent high concentrations centered near possible radionuclide sources (i.e. SRS facilities). For (7)Be litter samples, significant spatial correlation was calculated (p = 0.0085). No spatial correlation was evident in the (7)Be duff samples (p = 1.0000) probably due to small sample size (n = 7). (137)Cs litter and duff samples showed significant spatial correlations (p < 0.0001 and p < 0.0001, respectively).

CONCLUSIONS

To date, few studies characterize radionuclide activity concentrations in litter and duff, and to our knowledge none present spatial analysis. Key findings show that across SRS, (137)Cs is the primary radionuclide of concern, with the highest number of samples reported above MDC in litter (51.4%) and duff samples (83.2%). However, (137)Cs litter and duff spatial trends in the maps generated from the kriging parameters do not appear to directly link the areas with higher activity concentrations with SRS facilities. The results found herein provide valuable baseline monitoring data for future studies of forest surface fuels and can be used to evaluate changes in radioactivity in surface fuels in the southeast region of the U.S.

Seasonal variation of the ¹³⁷Cs level and its relationship with potassium and carbon levels in conifer needles

Seasonal variations in foliar ¹³⁷Cs levels were examined in Norway spruce (Picea abies (L.) Karst.), and Scots pine (Pinus sylvestris L.) in western Finland. Our aim was to test the occurrence of seasonal variation in contents and concentrations of ¹³⁷Cs, potassium and carbon in needles. The study focused on analysing levels of total ¹³⁷Cs in the three youngest needle age classes and comparing them to the levels of potassium and carbon. Spruce and pine needles were collected from 50- and 65-year-old stands on 18 sampling occasions between April 1996 and February 1997. Phases of intensive growth, needle elongation and dormancy were apparent in the time series for the needle contents and activity concentration of ¹³⁷Cs, both of which varied according to needle age class and tree species. The sequence of phases with a temporal fluctuation of needle contents, activity concentrations of ¹³⁷Cs and concentrations of K and carbon varied occasionally, and the efficiency of their translocation revealed some differences in the dynamics of ¹³⁷Cs, K and carbon in spruce and pine. The data clearly showed that the needles' K contents responded strongly to changes in K demand from other parts of the tree due to seasonal changes and that these responses were stronger than the associated retranslocations of ¹³⁷Cs, particularly in Scots pine. During intensive growth, K was less mobile than ¹³⁷Cs in the needles. The uptake of ¹³⁷Cs by current-year needles is simultaneously affected by uptake from the soil via the roots and retranslocation from other internal sources, and both of these processes affect the observed transfer rates during the growth period. Our results provided information on the transfer rates and revealed differentiation of root uptake and retranslocation of ¹³⁷Cs in needles. The study can support dynamic modelling of atmospheric ¹³⁷Cs contamination in forests.

Ionome of soybean seed affected by previous cropping with mycorrhizal plant and manure application

Two field experiments were conducted to investigate the effects of previous cultivation of an arbuscular mycorrhizal (AM) host plant and manure application on the concentration of 19 mineral elements in soybean ( Glycine max L. Merr. cv. Tsurumusume) seeds. Each experiment ran for two years (experiment 1 took place in 2007-2008, and experiment 2 took place in 2008-2009) with a split plot design. Soybeans were cultivated after growing either an AM host plant (maize, Zea mays L. cv. New dental) or a non-AM host plant (buckwheat, Fagopyrum esculentum Moench. cv. Kitawase-soba) in the first year in the main plots, with manure application (0 and 20 t/ha) during the soybean season in split plots from both main plots. On the basis of the two experiments, manure application significantly increased the available potassium (K) and decreased the available iron (Fe) and cesium (Cs) in the soil. However, higher concentrations of cadmium (Cd) and barium (Ba) and lower concentrations of Cs in the seed were induced by the application of manure. Cd levels in the seed were decreased by prior cultivation with the AM host plant. The present study showed that the identity of the prior crop and manure application changed the mineral contents of the soybean seed and suggests a connection between environmental factors and food safety.

Uptake and translocation of cesium-133 in napiergrass (Pennisetum purpureum Schum.) under hydroponic conditions

The present study reports the potential remediation of cesium (Cs) using napiergrass, which produces the largest biomass among the herbaceous plants in hydroponic culture containing stable Cs (Cs-133) at concentrations of 50, 150, 300, 1000, and 3,000 μM using cesium chloride (CsCl), with 0 μM Cs as a control concentration. Plant height was significantly decreased in higher Cs-treated conditions (300, 1000, and 3000 μM Cs) at 7 weeks after treatment (WAT), but tiller numbers tended to increase compared with the control plant. No significant difference was observed in the aboveground dry matter weight in all Cs treatments throughout the study period. Cs content in the roots, leaf blades, and leaf sheaths clearly increased with increasing Cs concentration in the solutions. Cs content in the aboveground parts (leaf blades and leaf sheaths) was consistently higher than in the roots at concentration of 3,000 μM. Total Cs contents in the aboveground parts were 6305 and 26,365 mg kg(-1) at 7WAT in 1000- and 3000-μM Cs treatments, respectively. Mean values of transfer factors (TFs) in the aboveground parts were 50 μM=0.78, 150 μM=1.02, 300 μM=0.86, 1,000 μM=0.68, and 3,000 μM=0.94, respectively at 7WAT. Due to its high Cs content and high TF in the aboveground parts, napiergrass may be a candidate plant with high potential for phytoremediation of Cs from Cs-137-contaminated soil.

The uptake of Cs and Sr from soil to radish (Raphanus sativus L.)- potential for phytoextraction and remediation of contaminated soils

The (133)Cs and (88)Sr uptake by plant Raphanus sativus L. was studied during cultivation in outdoor potted-soil. The distribution, accumulation of (133)Cs, (88)Sr and the antioxidant responses in plants were measured after 30 and 60 days of cultivation. The results showed that the uptake capacity of radish for (88)Sr was far higher than that for (133)Cs when the concentration of (88)Sr was as the same as that of (133)Cs in the soil (The concentration of (88)Sr or (133)Cs in the soil was from 2.5 mg kg(-1) to 40 mg kg(-1)). The highest (88)Sr accumulation was 239.18 μg g(-1) dw, otherwise, the highest (133)Cs accumulation was 151.74 μg g(-1) dw (The concentration of (88)Sr in the soil was 40 mg kg(-1)), and the lowest (88)Sr accumulation was 131.03 μg g(-1) dw, otherwise, the lowest (133)Cs accumulation was 12.85 μg g(-1) dw (The concentration of (88)Sr in the soil is 5 mg kg(-1)). The (88)Sr and (133)Cs TF values were 1.16-1.72 and 0.24-0.60, respectively. There was little influence of high concentration of (88)Sr on the total biomass of plants, so the radish is one of the ideal phytoremediation plant for Sr polluted soils. The important physiological reasons that radish had good tolerance to (88)Sr stress were that the MDA content was higher under the (88)Sr stress than that under the (133)Cs stress, and the activities of POD and CAT were lower under the (88)Sr stress than that under (133)Cs stress.

Isolation and purification of an axenic diazotrophic drought-tolerant cyanobacterium, Nostoc commune, from natural cyanobacterial crusts and its utilization for field research on soils polluted with radioisotopes

Nitrogen fixation and drought tolerance confer the ability to grow on dry land, and some terrestrial cyanobacteria exhibit these properties. These cyanobacteria were isolated in an axenic form from Nostoc commune clusters and other sources by modifying the method used to isolate the nitrogen-fixing and drought-tolerant cyanobacterium Nostoc sp. HK-01. Of these cyanobacteria, N. commune, which is difficult to isolate and purify, uses polysaccharides to maintain water, nitrogen fertilizers for nitrogen fixation, and can live in extreme environments because of desiccation tolerance. In this study, we examined the use of N. commune as biosoil for space agriculture and possible absorption of radioisotopes ((134)Cs, (137)Cs). This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

134Cs transfer factors to green gram and soybean as influenced by waste mica

Greenhouse pot culture experiment was carried out to study the (134)Cs transfer factors from soils to green gram and soybean as influenced by waste mica application (@ 0, 10, 20, 40 g mica kg(-1) soil) and compared with muriate of potash (MOP) application (0.17 g kg(-1) soil). For the study, the soils were contaminated with (134)Cs radionuclide @ 37 kBq kg(-1) soil. The shoot biomass and K uptake by crops were significantly improved with waste mica application (@ 40 g kg(-1) soil). Compared to control, waste mica and MOP application significantly improved the yield, K content in plant and its uptake. Amongst the soils, crops grown in vertisol recorded higher shoot biomass compared to inceptisol and ultisol. Irrespective of the treatments, higher (134)Cs transfer factors were seen in ultisol (0.30) as compared to inceptisol (0.16) and vertisol (0.13). It was observed that higher the K concentration in soil and plant, lowered (134)Cs transfer to green gram and soybean. The study recommended that waste mica @ 20 g kg(-1) would be useful for checking the (134)Cs transfer factors from soils to green gram and soybean.

Variability of 137Cs and 40K soil-to-fruit transfer factor in tropical lemon trees during the fruit development period

In this investigation we evaluate the soil uptake of (137)Cs and (40)K by tropical plants and their consequent translocation to fruits, by calculating the soil-to-fruit transfer factors defined as F(v) = [concentration of radionuclide in fruit (Bq kg(-1) dry mass)/concentration of radionuclide in soil (Bq kg(-1) dry mass in upper 20 cm)]. In order to obtain F(v) values, the accumulation of these radionuclides in fruits of lemon trees (Citrus limon B.) during the fruit growth was measured. A mathematical model was calibrated from the experimental data allowing simulating the incorporation process of these radionuclides by fruits. Although the fruit incorporates a lot more potassium than cesium, both radionuclides present similar absorption patterns during the entire growth period. F(v) ranged from 0.54 to 1.02 for (40)K and from 0.02 to 0.06 for (137)Cs. Maximum F(v) values are reached at the initial time of fruit growth and decrease as the fruit develops, being lowest at the maturation period. As a result of applying the model a decreasing exponential function is derived for F(v) as time increases. The agreement between the theoretical approach and the experimental values is satisfactory.

Functional HAK/KUP/KT-like potassium transporter encoded by chlorella viruses

Chlorella viruses are a source of interesting membrane transport proteins. Here we examine a putative K(+) transporter encoded by virus FR483 and related chlorella viruses. The protein shares sequence and structural features with HAK/KUP/KT-like K(+) transporters from plants, bacteria and fungi. Yeast complementation assays and Rb(+) uptake experiments show that the viral protein, termed HAKCV (high-affinity K(+) transporter of chlorella virus), is functional, with transport characteristics that are similar to those of known K(+) transporters. Expression studies revealed that the protein is expressed as an early gene during viral replication, and proteomics data indicate that it is not packaged in the virion. The function of HAKCV is unclear, but the data refute the hypothesis that the transporter acts as a substitute for viral-encoded K(+) channels during virus infection.

Potential of Calendula alata for phytoremediation of stable cesium and lead from solutions

Calendula alata plants were tested for their potential to remove stable cesium and lead from solutions in a 15-day period. The plants were grown hydroponically and placed in solutions containing CsCl and Pb(C₂H₃O₂)₂ at different concentrations (0.6, 2 and 5 mg l⁻¹). When plants were incubated in CsCl solutions 46.84 ± 2.12%, 41.35 ± 1.59%, and 52.06 ± 1.02% cesium was found to be remediated after 15 days. Moreover, more than 99% lead was removed from the Pb(C₂H₃O₂)₂ solution in all three concentrations after 15 days during the same period. When both CsCl and Pb(C₂H₃O₂)₂ were supplemented together in the solution, 9.92 ± 1.22%, 45.56 ± 3.52%, and 46.16 ± 1.48% cesium and 95.30 ± 0.72%, 96.64 ± 0.30%, and 99.02 ± 0.04% lead were removed after 15 days. The present study suggests that hydroponically grown C. alata could be used as a potential candidate plant for phytoremediation of cesium and lead from solutions; however, plants were found to be more efficient for the remediation of lead than cesium.

Soil vulnerability for cesium transfer

The recent events at the Fukushima Daiichi nuclear power plant in Japan have raised questions about the accumulation of radionuclides in soils and the possible impacts on agriculture surrounding nuclear power plants. This article summarizes the knowledge gained after the nuclear power plant accident in Chernobyl, Ukraine, on how soil parameters influence soil vulnerability for radiocesium bioavailability, discusses some potential agrochemical countermeasures, and presents some predictions of radiocesium crop concentrations for areas affected by the Fukushima accident.

Characteristics of cesium accumulation in the filamentous soil bacterium Streptomyces sp. K202

A filamentous soil bacterium, strain K202, was isolated from soil where an edible mushroom (Boletopsis leucomelas) was growing and identified as belonging to the genus Streptomyces on the basis of its morphological characteristics and the presence of LL-2, 6-diaminopimelic acid. We studied the existence states of Cs and its migration from extracellular to intracellular fluid in the mycelia of Streptomyces sp. K202. The results indicated that Cs accumulated in the cells through at least 2 steps: in the first step, Cs(+) was immediately and non-specifically adsorbed on the negatively charged cell surface, and in the second step, this adsorbed Cs(+) was taken up into the cytoplasm, and a part of the Cs entering the cytoplasm was taken up by an energy-dependent transport system(s). Further, we confirmed that a part of the Cs(+) was taken up into the mycelia competitively with K(+), because K(+) uptake into the intact mycelia of the strain was significantly inhibited by the presence of Cs(+) in the culture media. This suggested that part of the Cs is transported by the potassium transport system. Moreover, (133)Cs-NMR spectra and SEM-EDX spectra of the mycelia that accumulated Cs showed the presence of at least 2 intracellular Cs states: Cs(+) trapped by intercellular materials such as polyphosphate and Cs(+) present in a cytoplasmic pool.

Natural radioactivity in winter wheat from organic and conventional agricultural systems

The distribution of natural radionuclides was studied in winter wheat plants collected from three sites in Belgium during 2004-2007. Activity concentrations of (40)K, (226)Ra, (228)Ra and (228)Th in organically and conventionally grown wheat, and in the corresponding soil samples, were determined using ultra low-level gamma-ray spectrometry. The observed soil-to-wheat concentration ratios were calculated for the different parts of the wheat plant (root, stem and grain) in the two agricultural systems (organic and conventional). There were large variations in radionuclide activity concentrations between the sites and fields, but no significant difference between conventionally and organically grown wheat plants was observed.

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.

Natural and artificial radioactivity determination of some medicinal plants

Several medicinal plants used in Italy were analysed to determine natural and artificial radioactivity in those parts (leaves, fruits, seeds, roots, peduncles, flowers, barks, berries, thallus) used generally as remedies. The radionuclides were determined by alpha ((238)U, (210)Po) and gamma ((214)Pb-Bi, (210)Pb, (40)K and (137)Cs) spectrometry. (238)U ranged between <0.1 and 7.32 Bq kg(dry)(-1); (210)Po between <0.1 and 30.3 Bq kg(dry)(-1); (214)Pb-(214)Bi between <0.3 and 16.6 Bq kg(dry)(-1); (210)Pb between <3 and 58.3 Bq kg(dry)(-1); (40)K between 66.2 and 3582.0 Bq kg(dry)(-1); (137)Cs between <0.3 and 10.7 Bq kg(dry)(-1). The percentage of (210)Po extraction in infusion and decoction was also determined; the arithmetical mean value of percentage of (210)Po extraction resulted 20.7+/-7.5.

Caesium and strontium accumulation in shoots of Arabidopsis thaliana: genetic and physiological aspects

Due to the physico-chemical similarities of caesium (Cs(+)) to potassium (K(+)) on the one hand and strontium (Sr(2+)) to calcium (Ca(2+)) on the other hand, both elements can easily be taken up by plants and thus enter the food chain. This could be detrimental when radionuclides such as (137)Cs and (90)Sr are involved. In this study, both genetic and physiological aspects of Cs(+) and Sr(2+) accumulation in Arabidopsis thaliana were investigated using 86 Arabidopsis accessions and a segregating F(2) population of the low Cs(+) accumulating Sq-1 (Ascot, UK) crossed with the high uptaking Sorbo (Khurmatov, Tajikistan). Hydroponically grown plants were exposed to subtoxic levels of Cs(+) and Sr(2+) using radioactive isotopes as tracers. In the natural accessions shoot concentration of Cs(+) as well as Sr(2+) varied about 2-fold, whereas its heritability ranged for both ions between 0.60 and 0.73. Shoot accumulation of Cs(+) and Sr(2+) could be compromised by increasing concentrations of their essential analogues K(+) and Ca(2+), respectively, causing a reduction of up to 80%. In the case of the segregating F(2)/F(3) population Sq-1×Sorbo, this study identified several QTL for the trait Cs(+) and Sr(2+) accumulation, with main QTL on chromosomes 1 and 5. According to the correlation and discrimination surveys combined with QTL-analysis Cs(+) and Sr(2+) uptake seemed to be mediated mostly via non-selective cation channels. A polymorphism, affecting amino acids close to the K(+)-pore of one candidate, CYCLIC-NUCLEOTIDE-GATED CHANNEL 1 (CNGC1), was identified in Sorbo and associated with high Cs(+) concentrating accessions.

Arbuscular mycorrhizal fungi decrease radiocesium accumulation in Medicago truncatula

The role of arbuscular mycorrhizal fungi (AMF) in plant radiocesium uptake and accumulation remains ambiguous. This is probably due to the presence of other soil microorganisms, the variability of soil characteristics and plant nutritional status or the availability of its chemical analogue, potassium (K). Here, we used an in vitro culture system to study the impact of increased concentration of K on radiocesium accumulation in non K-starved mycorrhizal and non-mycorrhizal Medicago truncatula plants. In the presence of AMF radiocesium uptake decreased regardless of the concentration of K, and its translocation from root to shoot was also significantly lower. Potassium also reduced the accumulation of radiocesium in plants but to a lesser extent than mycorrhization, and without any effect on translocation. These results suggest that AMF in combination with K can play a key role in reducing radiocesium uptake and its subsequent translocation to plant shoots, thereby representing good potential for improved phytomanagement of contaminated areas.

Effect of potassium and phosphorus on the transport of radiocesium by arbuscular mycorrhizal fungi

Potassium, a chemical analogue of cesium, and phosphorus, an essential macronutrient transported by arbuscular mycorrhizal fungi (AMF), have been suggested to influence the transport of radiocesium by AMF. However, no study investigated the effects of increasing concentrations of both elements on the importance of this transport. Here, the arbuscular mycorrhizal-plant (AM-P) in vitro culture system associating Medicago truncatula plantlets with Glomus intraradices was used to evaluate this effect. Using three concentrations of K (0, 1, 10 mM) and two concentrations of P (30 and 3000 microM) added to a compartment only accessible to the AMF, we demonstrated that K and P individually and in combination significantly influenced radiocesium transport by AMF. Whilst increased concentration of K decreased the amount of radiocesium transported, the opposite was observed for P. Although the exact mechanisms involved need to be assessed, both elements were identified as important factors influencing the transport of radiocesium by AMF.

Influence of fertilizing on the (137)Cs soil-plant transfer in a spruce forest of Southern Germany

Fertilization with 2.5t/ha limestone: (83% CaCO(3), 8% MgO, 6% K(2)O, 3% P(2)O(5)) reduces the (137)Cs transfer from spruce forest soil into plants like fern (Dryopteris carthusiana) and blackberry (Rubus fruticosus) by a factor of 2-5 during at least 11 years as measured by the aggregated transfer factor T(ag). In 1997 and 2006 these results were confirmed by additional measurements of the (137)Cs transfer factor TF, related to the root zone (O(h) horizon), which were explained by the selective sorption of (137)Cs in the root zone by measurements of the Radiocaesium Interception Potential (RIP) in fertilized (RIP>179meq/kg) and non-fertilized soils (RIP<74meq/kg).

Migration and bioavailability of (137)Cs in forest soil of southern Germany

To give a quantitative description of the radiocaesium soil-plant transfer for fern (Dryopteris carthusiana) and blackberry (Rubus fruticosus), physical and chemical properties of soils in spruce and mixed forest stands were investigated. Of special interest was the selective sorption of radiocaesium, which was determined by measuring the Radiocaesium Interception Potential (RIP). Forest soil and plants were taken at 10 locations of the Altdorfer Wald (5 sites in spruce forest and 5 sites in mixed forest). It was found that the bioavailability of radiocaesium in spruce forest was on average seven times higher than in mixed forest. It was shown that important factors determining the bioavailability of radiocaesium in forest soil were its exchangeability and the radiocaesium interception potential (RIP) of the soil. Low potassium concentration in soil solution of forest soils favors radiocaesium soil-plant transfer. Ammonium in forest soils plays an even more important role than potassium as a mobilizer of radiocaesium. The availability factor - a function of RIP, exchangeability and cationic composition of soil solution - characterized reliably the soil-plant transfer in both spruce and mixed forest. For highly organic soils in coniferous forest, radiocaesium sorption at regular exchange sites should be taken into account when its bioavailability is considered.

Desorption of 137cs from Cetraria islandica (L.) Ach. using solutions of acids and their salts mixtures

The desorption of 137Cs from Cetraria islandica (L.) Ach. lichen was investigated using the solutions: A) H2SO4-HNO3-K2SO4, B) H2SO4-HNO3- -Na2SO4 and C) H2SO4-HNO3-(NH4)2SO4-(NH)4NO3 at pH 2.00, 2.58, 2.87, 3.28 and 3.75, similar to acid rain. After five consecutive desorptions using solutions A, B and C, from 44.0 % (solution B, pH 3.75) to 68.8 % (solution C, pH 3.28) of 137Cs had been desorbed from the lichen. In all cases, the most successful 137Cs desorption was the first one. In the presence of K+ (solution A) the total amount of desorbed 137Cs did not depend on the pH of the solution and this was confirmed by the analogous reactions of Cs+ and K+, due to their similar ionic radii. The dependencies of the non-desorbed content of 137Cs on the number of desorptions gave curves indicating that at least two types of sorption occur. One of them can be dominant if suitable desorbants are used. The results indicate lichens as secondary sources of environment pollution with 137Cs.

40K/137Cs discrimination ratios to the aboveground organs of tropical plants

In the present work, the accumulation of caesium and potassium in aboveground plant parts was studied in order to improve the understanding on the behaviour of monovalent cations in several compartments of tropical plants. We present the results for activity concentrations of (137)Cs and (40)K, measured by gamma spectrometry, from five tropical plant species: guava (Psidium guajava), mango (Mangifera indica), papaya (Carica papaya), banana (Musa paradisíaca), and manioc (Manihot esculenta). Caesium and potassium have shown a high level of mobility within the plants, exhibiting the highest values of concentration in the growing parts (fruits, leaves, twigs, and barks) of the woody fruit and large herbaceous shrub (such as manioc) species. In contrast, the banana and papaya plants exhibited the lowest levels of (137)Cs and (40)K in their growing parts. However, a significant correlation between activity concentrations of (137)Cs and (40)K was observed in these tropical plants. The (40)K/(137)Cs discrimination ratios were approximately equal to unity in different compartments of each individual plant, suggesting the possibility of using caesium to predict the behaviour of potassium in several tropical species.

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.

Role and influence of mycorrhizal fungi on radiocesium accumulation by plants

This review summarizes current knowledge on the contribution of mycorrhizal fungi to radiocesium immobilization and plant accumulation. These root symbionts develop extended hyphae in soils and readily contribute to the soil-to-plant transfer of some nutrients. Available data show that ecto-mycorrhizal (ECM) fungi can accumulate high concentration of radiocesium in their extraradical phase while radiocesium uptake and accumulation by arbuscular mycorrhizal (AM) fungi is limited. Yet, both ECM and AM fungi can transport radiocesium to their host plants, but this transport is low. In addition, mycorrhizal fungi could thus either store radiocesium in their intraradical phase or limit its root-to-shoot translocation. The review discusses the impact of soil characteristics, and fungal and plant transporters on radiocesium uptake and accumulation in plants, as well as the potential role of mycorrhizal fungi in phytoremediation strategies.

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.

Phytoremediation of 137cesium and 90strontium from solutions and low-level nuclear waste by Vetiveria zizanoides

Vetiver grass (Vetiveria zizanoides) L. Nash plantlets when tested for their potential to remove (90)Sr and (137)Cs (5 x 10(3) k Bq l(-1)) from solutions spiked with individual radionuclide showed that 94% of (90)Sr and 61% of (137)Cs could be removed from solutions after 168 h. When both (90)Sr and (137)Cs were supplemented together to the solution, 91% of (90)Sr and 59% of (137)Cs were removed at the end of 168 h. In case of (137)Cs, accumulation occurred more in roots than shoots, while (90)Sr accumulated more in shoots than roots. When experiments were performed to study the effect of analogous elements, K(+) ions reduced the uptake of (137)Cs, while (90)Sr accumulation was found to decrease in the presence of Ca(2+) ions. Plants of V. zizanoides could also effectively remove radioactive elements from low-level nuclear waste and the level of radioactivity was reduced below detection limit at the end of 15 days of exposure. The results of the present study indicate that V. zizanoides may be a potential candidate plant for phytoremediation of (90)Sr and (137)Cs.

The high affinity K+ transporter AtHAK5 plays a physiological role in planta at very low K+ concentrations and provides a caesium uptake pathway in Arabidopsis

Caesium (Cs(+)) is a potentially toxic mineral element that is released into the environment and taken up by plants. Although Cs(+) is chemically similar to potassium (K(+)), and much is known about K(+) transport mechanisms, it is not clear through which K(+) transport mechanisms Cs(+) is taken up by plant roots. In this study, the role of AtHAK5 in high affinity K(+) and Cs(+) uptake was characterized. It is demonstrated that AtHAK5 is localized to the plasma membrane under conditions of K(+) deprivation, when it is expressed. Growth analysis showed that AtHAK5 plays a role during severe K(+) deprivation. Under K(+)-deficient conditions in the presence of Cs(+), Arabidopsis seedlings lacking AtHAK5 had increased inhibition of root growth and lower Cs(+) accumulation, and significantly higher leaf chlorophyll concentrations than wild type. These data indicate that, in addition to transporting K(+) in planta, AtHAK5 also transports Cs(+). Further experiments showed that AtHAK5 mediated Cs(+) uptake into yeast cells and that, although the K(+) deficiency-induced expression of AtHAK5 was inhibited by low concentrations of NH(4)(+) in planta, Cs(+) uptake by yeast was stimulated by low concentrations of NH(4)(+). Interestingly, the growth of the Arabidopsis atakt1-1 mutant was more sensitive to Cs(+) than the wild type. This may be explained, in part, by increased expression of AtHAK5 in the atakt1-1 mutant. It is concluded that AtHAK5 is a root plasma membrane uptake mechanism for K(+) and Cs(+) under conditions of low K(+) availability.

Quantitative determination of cesium binding to ferric hexacyanoferrate: Prussian blue

Ferric hexacyanoferrate (Fe4III[FeII(CN)6]3), also known as insoluble Prussian blue (PB) is the active pharmaceutical ingredient (API) of the drug product, Radiogardase. Radiogardase is the first FDA approved medical countermeasure for the treatment of internal contamination with radioactive cesium (Cs) or thallium in the event of a major radiological incident such as a "dirty bomb". A number of pre-clinical and clinical studies have evaluated the use of PB as an investigational decorporation agent to enhance the excretion of metal cations. There are few sources of published in vitro data that detail the binding capacity of cesium to insoluble PB under various chemical and physical conditions. The study objective was to determine the in vitro binding capacity of PB APIs and drug products by evaluating certain chemical and physical factors such as medium pH, particle size, and storage conditions (temperature). In vitro experimental conditions ranged from pH 1 to 9, to cover the range of pH levels that PB may encounter in the gastrointestinal (GI) tract in humans. Measurements of cesium binding were made between 1 and 24h, to cover gastric and intestinal tract residence time using a validated atomic emission spectroscopy (AES) method. The results indicated that pH, exposure time, storage temperature (affecting moisture content) and particle size play significant roles in the cesium binding to both the PB API and the drug product. The lowest cesium binding was observed at gastric pH of 1 and 2, whereas the highest cesium binding was observed at physiological pH of 7.5. It was observed that dry storage conditions resulted in a loss of moisture from PB, which had a significant negative effect on the PB cesium binding capacity at time intervals consistent with gastric residence. Differences were also observed in the binding capacity of PB with different particle sizes. Significant batch to batch differences were also observed in the binding capacity of some PB API and drug products. Our results suggest that certain physiochemical properties affect the initial binding capacity and the overall binding capacity of PB APIs and drug products during conditions that simulated gastric and GI residence time. These physiochemical properties can be utilized as quality attributes to monitor and predict drug product quality under certain manufacturing and storage conditions and may be utilized to enhance the clinical efficacy of PB.

Potassium transport systems in the moss Physcomitrella patens: pphak1 plants reveal the complexity of potassium uptake

Potassium uptake is one of the most basic processes of plant physiology. However, a comprehensive description is lacking. At a cellular level fungi have provided a helpful but imperfect plant model, which we aim to improve using Physcomitrella patens. Blast searches in expressed sequence tag databases demonstrated that Physcomitrella expresses the same families of K(+) and Na(+) transport systems as flowering plants. We cloned two inward rectifier channels, PpAKT1-2, and four HAK-type transporters (PpHAK1-4). In both types of transport system, phylogenetic analyses revealed that despite their high sequence conservation they could not be included in Arabidopsis or rice (Oryza sativa) clusters. Both inward rectifier channels and one HAK transporter (PpHAK1) were expressed in yeast. PpAKT1 and activated mutants of PpAKT2 and PpHAK1 showed clear functions that were similar to those of homologous systems of flowering plants. A pphak1 null mutant line of Physcomitrella failed to deplete K(+) below 10 mum. Moreover, in a non-K(+)-limiting medium in which wild-type plants grew only as protonema, pphak1-1 plants produced leafy gametophores and contained 60% more K(+). We found that Physcomitrella takes up K(+) through several systems. PpHAK1 is the dominant system in plants that underwent K(+) starvation for long periods but an as-yet unidentified system, which is non-selective for K(+), Rb(+), and Cs(+), dominates in many other conditions. Finally, we discuss that, similar to PpHAK1, one of the functions of AtHAK5 may be to control cellular K(+) content and that a non-selective as-yet unidentified system also exists in Arabidopsis.

Biosorption of cesium-137 and strontium-90 by mucilaginous seeds of Ocimum basilicum

Mucilaginous seeds of Ocimum basilicum were used in uptake studies with cesium-137 and strontium-90. Results showed that uptake was dependent on the structural integrity of the mucilage fibrils. Water imbibed seeds showed higher adsorption of both 137Cs and 90Sr in comparison to seeds pretreated with NaOH, HCl and Na-periodate solution. The uptake was pH dependent and while some divalent metal ions had no or little detrimental effect, the alkali metal ions Li+, Na+ and K+ decreased the uptake. The maximum adsorption capacity was 160 mg cesium g(-1) and 247 mg strontium g(-1) seed dry weight.