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

Root-associated microbial community and diversity in napiergrass across radiocesium-contaminated lands after the Fukushima-Daiichi nuclear disaster in Japan

The microbiome derived from soil associated with plant roots help in plant growth and stress resistance. It exhibits potential benefits for soil remediation and restoration of radioactive-cesium (137Cs)-contaminated soils. However, there is still limited information about the community and diversity of root-associated microbiome in 137Cs-contaminated soil after the Fukushima-Daiichi Nuclear Power Plant (FDNPP) disaster. To address this, a comparative analysis of communities and diversity of root-associated microbiomes was conducted in two field types after the FDNPP disaster. In 2013, we investigated the community and diversity of indigenous root-associated microbiome of napiergrass (Pennisetum purpureum) grown in both grassland and paddy fields of 137Cs-contaminated land-use type within a 30-km radius around the FDNPP. Results showed that the root-associated bacterial communities in napiergrass belonged to 32 phyla, 75 classes, 174 orders, 284 families, and 521 genera, whereas the root-associated fungal communities belonged to 5 phyla, 11 classes, 31 orders, 59 families, and 64 genera. The most frequently observed phylum in both grassland and paddy field was Proteobacteria (47.4% and 55.9%, respectively), followed by Actinobacteriota (23.8% and 27.9%, respectively) and Bacteroidota (10.1% and 11.3%, respectively). The dominant fungal phylum observed in both grassland and paddy field was Basidiomycota (75.9% and 94.2%, respectively), followed by Ascomycota (24.0% and 5.8%, respectively). Land-use type significantly affected the bacterial and fungal communities that colonize the roots of napiergrass. Several 137Cs-tolerant bacterial and fungal taxa were also identified, which may be potentially applied for the phytoremediation of 137Cs-contaminated areas around FDNPP. These findings contribute to a better understanding of the distribution of microbial communities in 137Cs-contaminated lands and their long-term ecosystem benefits for phytoremediation efforts.

Uptake and Translocation of Cesium in Lettuce (Lactuca sativa L.) under Hydroponic Conditions

The uptake of radiocesium (RCs) by plants is key to the assessment of its environmental risk. However, the transfer process of RCs in the water-vegetable system still remains unclear. In this work, the uptake and accumulation processes of Cs+ (0-10 mM) in lettuce were explored under different conditions by using hydroponics. The results showed that the higher exposure concentration of Cs+ could lead to a faster uptake rate and would be beneficial to the uptake and accumulation of Cs+. The uptake of K+ by roots and leaves was inhibited significantly when Cs+ concentration increased, but unapparent for Ca2+ and Mg2+. It was found that the higher K+ and Ca2+ concentration was, the higher inhibition was found for the uptake of Cs+ in root. The uptake of Cs+ leads the decrease of chlorophyll content and brought a negative effect on plant photosynthesis, consequently, a negative effect on lettuce morphology and obvious decrease of biomass and root length. The contents of glutathione (GSH), malondialdehyde (MDA), and root vitality were increasing during the growth following stress of high concentrations of Cs+, which caused stresses on the antioxidant system of lettuce. The enrichment coefficient for Cs+ in leaves was in the range of 8-217. Moreover, the transfer factor was in the range of 0.114-0.828, which suggested that the high Cs+ concentration could enhance the transfer of Cs+ from lettuce root to leaf. This study provides more information on the transfer of RCs from water to food chain, promoting the understanding of the potential risk of RCs.

Response of Amaranthus tricolor to cesium stress in hydroponic system: Growth, photosynthesis and cesium accumulation

Remediation of the cesium-contaminated environment is of paramount importance, and phytoremediation is a cost-effective and green technique. In this paper, the response of Amaranthus tricolor to cesium ions in hydroponic solution was investigated at various cesium concentration (0, 0.05, 0.2, 0.4 and 0.6 mM), in terms of the growth weight, height and photosynthesis. The maximal Cs content in stems and leaves of A. tricolor was 13.05 mg/g dry wt under spiked Cs level of 0.4 mM in solution. The maximal transfer factor (TF) and bioconcentration factor (BCF) were 1.87 and 181.25 respectively, when the corresponding Cs content in roots and shoots was 7.04 mg/g and 13.05 mg/g dry wt respectively. TFs are higher than 1 in the conditions of normal plant growth. The growth of A. tricolor was enhanced after the treatment of Cs at low concentrations (0.05 and 0.2 mM), while it was inhibited at 0.4 and 0.6 mM. The leaf number and dry weight of stem, leaf parts and root parts were maximum at the spiked cesium level of 0.2 mM, which significantly increased by 19.19%, 47.56% and 94.56% respectively, compared with the control samples. Under 0.6 mM cesium stress, curl and withering of the leaves occurred, and the plant growth and cesium accumulation dropped to the minimum. Cs at the spiked level of 0.6 mM in solution inhibited the performance of PSII, especially in terms of blockage in electron transfer process beyond Q_A and restraint of P700 reduction. On contrast, the performance of PSII was enhanced by the spiked Cs at level of 0.2 mM, leading to the growing density of reaction centers per excited cross-section and increasing electron transfer process beyond Q_A. In summary, A. tricolor has potential for remediating the Cs-contaminated environment.

Efficacious bioremediation of heavy metals and radionuclides from wastewater employing aquatic macro- and microphytes

Cytotoxic, mutagenic, and carcinogenic contaminants, such as heavy metals and radionuclides, have become an alarming environmental concern globally, especially for developed and developing nations. Moreover, inefficient prevalent wastewater treatment technologies combined with increased industrial activity and modernization has led to increase in the concentration of toxic metals and radioactive components in the natural water bodies. However, for the improvement of ecosystem of rivers, lakes, and other water sources different physicochemical methods such as membrane filtration, reverse osmosis, activated carbon adsorption, electrocoagulation, and other electrochemical treatment are employed, which are uneconomical and insufficient for the complete abatement of these emerging pollutants. Therefore, the application of bioremediation employing aquatic macrophytes and microphytes have gained considerable importance owing to the benefits of cost-effectiveness, eco-friendly, and higher energy efficiency. Thus, the present review aims to enlighten the readers on the potential application of algae, cyanobacteria, plant, and other aquatic micro- and macrophytes for the elimination of carcinogenic metals and radioactive isotopes from wastewater. Additionally, the use of transgenic plants, genetically modified species, algal-bacterial symbiosis for the enhancement of removal efficiency of mutagenic contaminants are also highlighted. Furthermore, species selection based on robustness, mechanism of different pathways for heavy metal and radionuclide detoxification are elucidated in this review article.

Effects of environmental conditions, low-level potassium, ethylenediaminetetraacetic acid, or combination treatment on radiocesium-137 decontamination in Napier grass

Phytoextraction is widely used to remove environmental pollutants such as heavy metals or radionuclides from soil. It is important to understand how to enhance the accumulation of contaminants by plants. Previously, we found that Napier grass (Pennisetum purpureum Schum.) has the potential to effectively remove Cs (¹³³Cs and ¹³⁷Cs). In order to enhance the remediation efficiency of Napier grass, we evaluated the effects of low-level K (K), ethylenediaminetetraacetic acid (EDTA), or the combination of low-level K and EDTA (K+EDTA). We also examined the differences in ¹³⁷Cs decontamination between two cropping years (2018 and 2019). Overall, there were no prominent effects from the K, EDTA, or K+EDTA treatments on plant growth (plant height, tiller number), aboveground biomass, ¹³⁷Cs concentration, and ¹³⁷Cs removal ratio (CR) in 2 years. However, the aboveground biomass (P < 0.001), ¹³⁷Cs concentration (P < 0.001 in 2019 only), and CR (P < 0.001) in plants grown in the first growing period were significantly higher than in plants grown in the second growing period in both years. The mean ¹³⁷Cs concentration (P < 0.001) and total CR (P < 0.001) per year was significantly greater in 2019 than in 2018. The precipitation amount during the cultivation period in 2019 (1197 mm) was 1.8-fold higher than in 2018 (655 mm). In this study, the K, EDTA, and K+EDTA treatments had less effect plant growth than the natural environmental conditions. To enhance remediation efficiency, soil moisture is one important factor to produce more aboveground biomass to achieve high CR in Napier grass.

Biometric traits of onion (Allium cepa L.) exposed to 137Cs and 243Am under hydroponic cultivation

To elucidate the features of bioaccumulation and phytotoxic effects of long-lived artificial radionuclides, a hydroponic experiment was carried out with the cultivation of onion (Allium cepa L.) in low-mineralized solutions spiked with ¹³⁷Cs (250 kBq L^-1) or ²⁴³Am (9 kBq L^-1). After the 27-day growth period, ≈70% of ¹³⁷Cs and ≈14% of ²⁴³Am were transferred from the solutions to onion biomass with transfer factor values ≈ 400 and ≈ 80, respectively. Since the bioaccumulation of both radionuclides mainly took place in the roots of onion (77% ¹³⁷Cs and 93% ²⁴³Am of the total amount in biomass), edible organs - bulbs and leaves - were protected to some extent from radioactive contamination. At the same time, the incorporation of the radionuclides into the root tissues caused certain changes in their biometric (geometric and mass) traits, which were more pronounced under the ²⁴³Am-treatment of onion. Exposure to ²⁴³Am significantly reduced the number, length, and total surface area of onion roots by 1.3-2.6 times. Under the influence of ¹³⁷Cs, the dry-matter content in roots decreased by 1.3 times with a corresponding increase in the degree of hydration of the root tissues. On the whole, the data obtained revealed the specific features of ¹³⁷Cs and ²⁴³Am behaviour in "hydroponic solution - plant" system and suggested that biometric traits of onion roots could be appropriate indicators of phyto(radio)toxicity.

Natural and anthropogenic radionuclides in water and wastewater: Sources, treatments and recoveries

Water-energy nexus in the context of changing climate amplifies the importance of comprehending the transport, fate and recovery of radioisotope. While countries have been more interested for zero/low greenhouse gas emission technologies, energy production from nuclear power plant (NPP) can be a prominent solution. Moreover, radioisotopes are also used for other benefits such as in medical science, industrial activities and many more. These radionuclides are blended accidently or intentionally with water or wastewater because of inefficacious management of the nuclear waste; and therefore, it is an imperative task to manage nuclear waste so that the harmful consequences of the waste on environment, ecology and human health can be dispelled. Due to generation of significant amount of waste throughout its utilization, a noticeable number of physical, chemical and biological processes has been introduced as remediation processes although mechanisms of optimum removal process are still under investigation. Removal mechanisms and influencing factors for radionuclide removal are elucidated in this review so that, further, operation and process development can be promoted. Again, resource recovery, opportunities and challenges are also discussed for elevating the removal rates and minimizing the knowledge gaps existing in development and applications of novel decontamination processes.

Uptake of 133Cs and 134Cs by Ceratophyllum demersum L. under field and greenhouse conditions

The phytoremediation abilities of Hornwort (Ceratophyllum demersum L.) were tested under greenhouse and field conditions. Plants were exposed for 8, 16, and 24 days (greenhouse with stable isotope ¹³³Cs), 8 days (field with ¹³³Cs), and 8 days (climabox with radioactive isotope ¹³⁴Cs). The plants were exposed to different concentration of stable Cs provided as CsCl (0.008, 0.033, 0.133, 0.267, 0.533, 0.800, 1.067, and 1.333 mM) and different activities of ¹³⁴Cs (4.46, 4.46, 4.74, 4.64, 2.23 and 2.26 kBq). The results of the experiment revealed a significant effect (p < 0.001) of exposure time on Cs uptake. The results showed highest average ¹³³Cs removal rates of 11%, 17% and 19% for 8, 16, and 24 days, respectively, in the greenhouse, 10% for the ¹³⁴Cs experiment, and 27% for the field experiment with ¹³³Cs. The results indicated that increasing the length of exposure lowered the uptake ability, hence indicating that the plant has limited capacity for Cs removal. The accumulated amount of Cs by plants is significantly dependent (p < 0.001) on the concentration of treatment and complies to a sigmoid curve. Comparison of experiments revealed the greenhouse experiment with ¹³³Cs and the experiment with ¹³⁴Cs did not differ significantly in their removal rate. However, the field experiment was significantly different from the previous two (p < 0.001), providing a higher removal rate. C. demersum was also able to resist phytotoxic effects of Cs in the greenhouse experiment for 16 days without significant effects (p > 0.05) on health. Even after 24 days of exposure, the plant resisted up to 0.267 mM treatment concentration with no significant tissue lesion (p > 0.05). These results indicate that C. demersum has potential for remediating aquatic habitats, especially in the case of acute events, where a short duration of phytoremediation may take place.

Response of Arabidopsis halleri to cesium and strontium in hydroponics: Extraction potential and effects on morphology and physiology

Stable isotopes of cesium (Cs) and strontium (Sr) as well as their radioactive isotopes are of serious environmental concern. The pollution of the biosphere, particularly soil and water has received considerable attention for removal of these contaminants in recent years. Arabidopsis halleri (A. halleri) is a hyperaccumulator plant species able to take up large amounts of several metals into its above ground organs without showing significant signs of toxicity. Therefore, we investigated responses, metal accumulation and element distribution in roots and leaves of A. halleri after treatment with stable Cs and Sr. Plants were hydroponically grown in different concentrations of cesium sulfate (between 0.002 and 20 mM) and strontium nitrate (between 0.001 and 100 mM). Uptake of Cs and Sr into leaves was analyzed from extracts by inductively coupled plasma mass spectrometry (ICP-MS). Although internal concentration of Cs and Sr increased with rising external concentrations, the amount of accumulated metal in relation to available metal decreased. Therefore, the potential of the plant to effectively transfer metals from growth medium to leaves occurred at low and moderate concentrations, whereas after that when the concentration of metal increased further the transfer factors were decreased. A. halleri accumulated Sr more efficiently than Cs. The transfer factors were higher for Sr (up to 184) than for Cs (up to 16). The results indicate positive correlation of Cs and Sr accumulation to K and Ca transport to leaves. The toxicity of Cs and Sr was assessed by measuring photosynthetic efficiency and growth parameters. In leaves, Cs and Sr affected the chlorophyll fluorescence at their low and high concentrations. Significant reduction of plant growth (dry weight of roots and leaves) was observed at Sr concentrations >0.01 mM. Cs-treated plants exhibited only decreased length of leaves at concentrations>0.02 mM. The distribution of the elements within the different tissues of leaves and roots was investigated by using Energy Dispersive X-Ray microanalysis (EDX) with a scanning electron microscope (SEM). EDX revealed that Cs and Sr were accumulated differently in root and leaf tissues. The hydroponic experiment showed a potential for A. halleri to treat hotspots with radioactive Cs and Sr.

Response of Plantago major to cesium and strontium in hydroponics: Absorption and effects on morphology, physiology and photosynthesis

Human activities lead to increasing concentration of the stable elements cesium (Cs) and strontium (Sr) and their radioactive isotopes in the food chain, where plants play an important part. Here we investigated Plantago major under the influence of long-term exposure to stable Cs and Sr. The plants were cultivated hydroponically in different concentrations of cesium sulfate (between 0.002 and 20 mM) and strontium nitrate (between 0.001 and 100 mM). Uptake of Cs and Sr into leaves was analyzed from extracts by inductively coupled plasma mass spectrometry (ICP-MS). It was increased with increasing external Cs and Sr concentrations. However, the efficiency of Cs and Sr transfer from solution to plants was higher for low external concentrations. Highest transfer factors were 6.78 for Cs and 71.13 for Sr. Accumulation of Sr was accompanied by a slight decrease of potassium (K) and calcium (Ca) in leaves, whereas the presence of Cs in the medium affected only uptake of K. The toxic effects of Cs and Sr were estimated from photosynthetic reactions and plant growth. In leaves, Cs and Sr affected the chlorophyll fluorescence even at their low concentrations. Low and high concentrations of both ions reduced dry weight and length of roots and leaves. The distribution of the elements between the different tissues of leaves and roots was investigated using Energy Dispersive X-Ray microanalysis (EDX) with scanning electron microscope (SEM). Overall, observations suggested differential patterns in accumulating Cs and Sr within the roots and leaves. When present in higher concentrations the amount of Cs and Sr transferred from environment to plants was sufficient to affect some physiological processes. The experimental model showed a potential for P. major to study the influence of radioactive contaminants and their removal from hotspots.

Uptake, accumulation and phytoextraction efficiency of cesium in Gypsophila paniculata

To evaluate the phytoextraction efficiency of Gypsophila paniculata from Cs-contaminated soils and analyze the mechanism of Cs accumulation in G. paniculata, we analyzed the characteristics of Cs bioaccumulation and subcellular distribution, in addition to its chemical forms in the plant under hydroponic conditions. The results showed that total Cs content in the aboveground parts and the entire plant were as high as 6137.32 mg·kg^-1dry weight and 7338.49 mg·kg^-1dry weight, respectively, after 17 days in the 50 mg·L^-1 Cs treatment. The BCF was between 2.35 and 3.38. The TF was between 1.00 and 2.46 in G. paniculata. Subcellular distribution of Cs in the plant was as follows: soluble fraction > cell wall > organelles. Inorganic Cs (F-ethanol) and water-soluble Cs (F-dH2O) were the main types of Cs in G. paniculata. Further studies show that the phytoextraction efficiency can reach 10.30-11.91% planting a season of G. paniculata under potted conditions. The results suggested that G. paniculata, a perennial, drought-tolerant herb, was a high-accumulator of Cs, which may have potential uses in phytoremediation of Cs-contaminated soil.

First report of community dynamics of arbuscular mycorrhizal fungi in radiocesium degradation lands after the Fukushima-Daiichi Nuclear disaster in Japan

Arbuscular mycorrhizal fungi (AMF) can be beneficial for improving restoration of radioactive-cesium (¹³⁷Cs)-contaminated soils through soil remediation. However, there has been no information on species diversity and the composition of AMF communities in ¹³⁷Cs-contaminated soil after the Fukushima-Daiichi Nuclear Power Plant (NPP) disaster. We examined the community dynamics of indigenous AMF colonizing roots of napiergrass (Pennisetum purpureum) in two different ¹³⁷Cs-contaminated land-use fields (grassland and paddy field) by an Illumina MiSeq sequencing investigation within a 30-km radius around the Fukushima-Daiichi NPP in 2013 (sampling year 1) and 2014 (sampling year 2). We found nine AMF families, including Glomeraceae, Gigasporaceae, Paraglomeraceae, Claroideoglomeraceae, Acaulosporaceae, Archeosporaceae, Ambisporaceae, Diversisporaceae and uncultured Glomeromycotina in roots. Glomeraceae was the most abundant in both grassland and paddy field, followed by Paraglomeraceae. The diversity of AMF in grassland and paddy field was higher in 2014 than in 2013. Furthermore, the AMF community structure was impacted by sampling year and land-use type. The AMF community structures colonizing napiergrass roots were also significantly impacted by land-use type and year throughout the 2-year investigation. To our knowledge, our results are the first report to reveal the community dynamics of indigenous AMF in the ¹³⁷Cs-contaminated fields around NPP.

Evaluation of the potential for caesium transfer from contaminated soil to the food chain as a consequence of uptake by edible vegetables

This paper analyzes the effect of caesium (Cs) concentration on seed germination, seedling growth, root uptake, and leaf uptake of Lactuca sativa to understand the potential transfer of the metal from contaminated soil to humans through the food chain. The results of germination experiments show that seed germination and seedling growth strongly depend on increasing Cs concentration, with a decrease in the number of germinated seeds compared to the control up to 13.6% and a reduction in seedling growth up to 10.3% at the highest Cs tested concentration (15 mM). Uptake experiments indicate a low transfer of Cs from soil to leaves and roots of the plants, ranging between 0.06% and 2.2%. The transfer is found to be a not-monotone function of soil potassium (K) content, with highest values corresponding to 1-2 mM K₂SO₄. Increasing concentrations of K lead to lower translocation of Cs from roots to leaves. Values above the average amount applied (20 and 40 mM K₂SO₄) almost stop the translocation, suggesting the use of a high amount of K₂SO₄ protects the food chain from Cs contamination.

Enhanced irreversible fixation of cesium by wetting and drying cycles in soil

The retention of radioactive cesium (Cs) in soil is significantly related to the types of clay minerals, while the weathering process affects the irreversible adsorption sites in clay minerals. In this study, the effect of weathering (exposure duration of Cs and repeated wetting and drying cycles) on fractionation of Cs in soils was investigated using fractionation analysis by the sequential extraction. The residual fraction of Cs increased slowly with exposure time but increased rapidly by repeated wetting and drying cycles. XRD analysis shows that a 1.43 nm of interlayer size for vermiculite is shortened to 1.00 nm, i.e., similar to that of illite. The change implies the potential that the structure of expandable clay minerals is transformed to the non-expandable structure by weathering process after Cs retention. Based on the result, the residual fraction of Cs, most stable form of Cs in the soil, reached relatively rapidly to a maximum. However, the process is much slower kinetically in the field because the bench-scale weathering process used in this study is more aggressive. This study implies that Cs fractionations in the soil are converted into a more stable fraction by weathering processes in the soil. Therefore, Cs removal should be conducted as soon as possible after accidental release of Cs in an environmental side.

Influence of potassium concentration gradient on stable caesium uptake by Calla palustris

The effect of potassium (K) concentration gradient on stable caesium (Cs) uptake by Calla palustris was studied under hydroponic conditions after eight-day exposure in a greenhouse experiment. The plants were exposed to two different concentrations of Cs (provided as 0.5 and 1 mM CsCl) and five different concentrations of K (provided as K₂SO₄ in 0.5, 1, 2, 5, and 10 mM). The results indicate negative dependence of Cs uptake on K concentrations for both Cs treatments. The application of K reduced the transfer of stable Cs from water to plant by about 44-72% for 0.5 mM CsCl and 56-74% for 1 mM CsCl. The highest efficiency of Cs removal from water was observed for plants in K⁺ deficient solutions (plants starving), with an efficiency 8.0% for plants cultivated in 0.5 mM CsCl and 9.4% for plants in 1 mM CsCl. An increasing concentration of K also supported translocation of Cs from roots to leaves. Higher translocation was observed for the treatments with lower level of Cs, where the concentration of Cs in leaves became higher than that in roots. The Cs uptake and translocations were affected not only by the external concentration of K, but also the external concentration of stable Cs. A high concentration of K in the environment protects the food chain from Cs uptake by plants, but lowers the efficiency of phytoremediation techniques.

Effects of cesium accumulation on chlorophyll content and fluorescence of Brassica juncea L

The aim of our study was to investigate the toxicological mechanism of cesium on Indian mustard (Brassica juncea L.). The impact of cesium toxicity to plants was evaluated using phytophysiology and genetic methods. In this study, Brassica juncea was grown on Cs-contaminated Hoagland's nutrient solution, and chlorophyll content, chlorophyll fluorescence, and Cs bioaccumulation were measured. Transcriptome data was used to perform an in-depth analysis of the molecular mechanisms underlying the effects of Cs accumulation. The results showed that Cs accumulated up to 3586.70 mg kg^-1 in B. juncea treated with 100 mg L^-1 Cs. The chlorophyll content and several chlorophyll fluorescence parameters (F_v/F₀, F_v/F_m, ΦPS II, qP, and NPQ) significantly decreased under Cs exposure. The starting process of PSII was also inhibited under higher Cs conditions. These results indicate that excessive Cs can damage PS II in leaves, decreasing photochemical activity and the energy conversion rate. Further analysis revealed that Cs interfered with the expression of chloroplastic metabolic genes (25 up and 36 down) and inhibited the expression of PsaB, psbC, PetF, LHCA1, and LHCB5. The results indicate that stable Cs leads to abnormal expression of genes related to photosynthesis pathway, blocking the electron transport process from plastoquinone-QA to plastoquinone-QB, resulting in abnormal photosynthesis, which leads to abnormal growth of B. juncea.

Stable and radioactive cesium: A review about distribution in the environment, uptake and translocation in plants, plant reactions and plants' potential for bioremediation

Radiocesium in water, soil, and air represents a severe threat to human health and the environment. It either acts directly on living organisms from external sources, or it becomes incorporated through the food chain, or both. Plants are at the base of the food chain; it is therefore essential to understand the mechanisms of plants for cesium retention and uptake. In this review we summarize investigations about sources of stable and radioactive cesium in the environment and harmful effects caused by internal and external exposure of plants to radiocesium. Uptake of cesium into cells occurs through molecular mechanisms such as potassium and calcium transporters in the plasma membrane. In soil, bioavailability of cesium depends on the chemical composition of the soil and physical factors such as pH, temperature and tilling as well as on environmental factors such as soil microorganisms. Uptake of cesium occurs also from air through interception and absorption on leaves and from water through the whole submerged surface. We reviewed information about reducing cesium in the vegetation by loss processes, and we extracted transfer factors from the available literature and give an overview over the uptake capacities of 72 plants for cesium from the substratum to the biomass. Plants with high uptake potential could be used to remediate soil and water from radiocesium by accumulation and rhizofiltration. Inside plants, cesium distributes fast between the different plant organs and cells, but cesium in soil is extremely stable and remains for decades in the rhizosphere. Monitoring of contaminated soil therefore has to continue for many decades, and edible plants grown on such soil must continuously be monitored.

Stable cesium (133Cs) uptake by Calla palustris from different substrates

The uptake of stable cesium (¹³³Cs) by Calla palustris was evaluated from four different substrates: water, soil, keramzit (a clay granule) and water with the addition of a potassium compound, after an eight days exposure to a solution of 0.5mM cesium chloride. Stable cesium was used because it is commonly supposed that its uptake by plants is the same of that of radiocesium (¹³⁷Cs). The plants were differentiated in their parts (roots, healthy leaves, dead leaves and flowers) and analyzed with ICP-MS. The lowest average concentration of absorbed Cs was found in plants exposed in soil (0.7mg/kg, S.D.=96.8), while the highest in plants exposed in water (147mg/kg, S.D.=51.7). During the experiment the water planted plants removed 31.6% of provided Cs while those planted in soil removed only 0.06%. The addition of potassium to water was tested because of the competition effect that arises between these two elements: this effect was confirmed with the result that the average uptake in the presence of potassium was lower (41mg/kg in exposed plants, S.D.=76.1). The uptake was also lower in the solid-based substrates (soil and keramzit), because of the known tendency of Cs to bind with soil particles, thus becoming less available to plants. There was no evidence that the different parts of the plant showed different uptake effectiveness, or that the health of the plant (evaluated with a qualitative method) had any effect on the uptake of Cs.

Cs phytoremediation by Sorghum bicolor cultivated in soil and in hydroponic system

Cs accumulation characteristics by Sorghum bicolor were investigated in hydroponic system (Cs level at 50-1000 μmol/L) and in soil (Cs-spiked concentration was 100 and 400 mg/kg soil). Two varieties of S. bicolor Cowly and Nengsi 2# grown on pot soil during the entire growth period (100 days) did not show significant differences on the height, dry weight (DW), and Cs accumulation. S. bicolor showed the potential phytoextraction ability for Cs-contaminated soil with the bioaccumulation factor (BCF) and the translocation factor (TF) values usually higher than 1 in soil system and in hydroponic system. The aerial parts of S. bicolor contributed to 86-92% of the total removed amounts of Cs from soil. Cs level in solution at 100 μmol/L gave the highest BCF and TF values of S. bicolor. Cs at low level tended to transfer to the aerial parts, whereas Cs at high level decreased the transfer ratio from root to shoot. In soil, the plant grew well when Cs spiked level was 100 mg/kg soil, but was inhibited by Cs at 400 mg/kg soil with Cs content in sorghum reaching 1147 mg/kg (roots), 2473 mg/kg (stems), and 2939 mg/kg (leaves). In hydroponic system, average Cs level in sorghum reached 5270 mg/kg (roots) and 4513 mg/kg (aerial parts), without significant damages to its biomass at 30 days after starting Cs treatment. Cs accumulation in sorghum tissues was positively correlated with the metal concentration in medium.

Uptake and translocation of sulfamethazine by alfalfa grown under hydroponic conditions

Antibiotics are routinely used in intensive animal agriculture operations collectively known as Concentrated Animal Feed Operations (CAFO) which include dairy, poultry and swine farms. Wastewater generated by CAFOs often contains low levels of antibiotics and is typically managed in an anaerobic lagoon. The objective of this research is to investigate the uptake and fate of aqueous sulfamethazine (SMN) antibiotic by alfalfa (Medicago sativa) grass grown under hydroponic conditions. Uptake studies were conducted using hydroponically grown alfalfa in a commercially available nutrient solution supplemented with 10mg/L of SMN antibiotic. Analysis of alfalfa sap, root zone, middle one-third, and top portion of the foliage showed varying uptake rate and translocation of SMN. The highest average amount of SMN (8.58μg/kg) was detected in the root zone, followed by the top portion (1.89μg/kg), middle one-third (1.30μg/kg), and sap (0.38μg/kg) samples, indicating a clear distribution of SMN within the sampled regions. The ultraviolet (UV) spectra of parent SMN and translocated SMN identified in different parts of the plant present the possibility of metabolization during the uptake process. Uptake of SMN using alfalfa grown under hydroponic conditions has potential as a promising remediation technology for removal of similar antibiotics from wastewater lagoons.

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.

Analysis of the accumulation and redistribution patterns of cesium in Vicia faba grown on contaminated soils

The aim of this study was to investigate the relationship between cesium (Cs) contamination and plant growing stages in crops or vegetables grown on Cs-contaminated soils. Vicia faba was grown on Cs-contaminated soils under pot-culture conditions, and Cs uptake and bioaccumulation at various growing stages were then measured. The results showed that Cs uptake by V. faba was significantly greater on soils with a higher Cs content. As shown by the bioaccumulation factor (BCF), the highest transfer coefficient occurred when V. faba reached the maturation stage. Cs was easily transferred to young organs, especially seeds, with an average percentage of 9.60% in seeds during the maturation stage. This implies that Cs can be transferred to the human food chain at all growth stages of the plant, especially the last stages. Uptake rates of Cs remained stable during the generative growth phase of V. faba. This implies that the cultivation of varieties with short generative growth periods can reduce Cs accumulation in the edible parts of plants.

The chemical toxicity of cesium in Indian mustard (Brassica juncea L.) seedlings

To distinguish between the radiological and chemical effects of radiocesium, we study the chemical toxicity of cesium in the seedlings of Indian mustard (Brassica juncea L.). In this study, the experiment was designed in two factors and five levels random block design to investigate the interaction effects of Cs and K. Results showed that excessive Cs was one of the main factors influence the growth of Brassica juncea seedlings. And the toxicity of Cs in Brassica juncea is likely to be caused by Cs interacts with K-binding sites in essential K-dependent protein, either competes with K for essential biochemical functions, causing intracellular metabolic disturbance. To test the hypothesis that the toxicity of Cs might cause intracellular metabolic disturbance, next-generation sequencing (NGS)-based Illumina paired-end Solexa sequencing platform was employed to analysis the changes in gene expression, and understand the key genes in B. juncea seedlings responding to the toxicity of Cs. Based on the assembled de novo transcriptome, 2032 DEGs that play significant roles in the response to the toxicity of Cs were identified. Further analysis showed that excessive Cs is disturbance the auxin signal transduction pathway, and inhibited the indoleacetic acid-induced protein (AUX/IAA) genes expression eventually lead the seedlings growth and development be inhibited. The results suggest that disturbances to tryptophan metabolism might be linked to changes in growth.

Characterizations of bio-accumulations, subcellular distribution and chemical forms of cesium in Brassica juncea, and Vicia faba

We aim to investigate the tolerance and enrichment mechanism of cesium (Cs) in hyperaccumulation plants. In this study, Brassica juncea and Vicia faba were subjected to varying doses of Cs for 21 days to investigate the differences in bio-accumulations, subcellular distribution and chemical forms of Cs in two cultivars by differential centrifugation, and extraction of Cs in different chemical forms, respectively. The results showed that 49.87%-61.08% of the Cs were in the leaf of B. juncea, while in V. faba, 1.58%-79.29% of the Cs was in the root. The translocation factor (TF) arrived 2.79 to 3.71 in B. juncea, while it only reached 0.26 to 0.62 in V. faba. Cs subcellular distribution of the two plants was in sequence as follows: soluble fraction > cell wall >> organelles. Cs was more easily distributed to metal-sensitive fractions of V. faba. The inorganic Cs (F-ethanol), and water-soluble Cs (F-dH2O) are the main existing types of Cs in the two plants. In B. juncea, the relative content of inorganic Cs, and organic acids/CsH2PO4 (F-dH2O) were higher than that of V. faba in the stem. This suggests that Cs may induce related transporter gene expression (such as phosphate transporter, organic cation, high affinity nitrate transporter, amino acid permease, etc.) to help the transport of Cs between root to shoot.

Uranium and cesium accumulation in bean (Phaseolus vulgaris L. var. vulgaris) and its potential for uranium rhizofiltration

Laboratory scale rhizofiltration experiments were performed to investigate uranium and cesium accumulation in bean (Phaseolus vulgaris L. var. vulgaris) and its potential for treatment of uranium contaminated groundwater. During 72 h of rhizofiltration, the roots of the bean accumulated uranium and cesium to concentrations 317-1019 times above the initial concentrations, which ranged from 100 to 700 μg l(-1) in artificially contaminated solutions. When the pH of the solution was adjusted to 3, the ability to accumulate uranium was 1.6 times higher than it was for solutions of pH 7 and pH 9. With an initial uranium concentration of 240 μg l(-1) in genuine groundwater at pH 5, the bean reduced the uranium concentration by 90.2% (to 23.6 μg l(-1)) within 12 h and by 98.9% (to 2.8 μg l(-1)) within 72 h. A laboratory scale continuous clean-up system reduced uranium concentrations from 240 μg l(-1) to below 10 μg l(-1) in 56 h; the whole uranium concentration in the bean roots during system operation was more than 2600 μg g(-1) on a dry weight basis. Using SEM and EDS analyses, the uranium removal in solution at pH 7 was determined based on adsorption and precipitation on the root surface in the form of insoluble uranium compounds. The present results demonstrate that the rhizofiltration technique using beans efficiently removes uranium and cesium from groundwater as an eco-friendly and cost-effective method.

Stable cesium uptake and accumulation capacities of five plant species as influenced by bacterial inoculation and cesium distribution in the soil

The effects of inoculation with Bacillus and Azospirillum strains on growth and cesium accumulation of five plant species, Komatsuna, Amaranth, sorghum, common millet and buckwheat, grown on cesium-spiked soil were assessed for potential use in cesium remediation. Pot experiments were performed using "artificially" Cs-contaminated soil. Three treatments were applied based on Cs location in the soil. For a soil height of 15 cm in the pots, Cs was added as follows: in the top five cm to imitate no ploughing condition; in the bottom five cm simulating inverted ploughing; and uniformly distributed Cs reproducing normal plowing. Generally, inoculation of Cs-exposed plants significantly enhanced growth and tolerance to this element. Transfer factor (ratio of Cs concentration in the plant tissues to that in surrounding soil) was strongly influenced by Cs distribution, with higher values in the top-Cs treatment. Within this treatment, inoculation of Komatsuna with Bacillus and Azospirillum strains resulted in the greatest transfer factors of 6.55 and 6.68, respectively. Cesium content in the shoots was high in the Azospirillum-inoculated Komatsuna, Amaranth, and buckwheat, i.e., 1,830, 1,220, and 1,030 µg per pot, respectively (five plants were grown in each pot). Therefore, inoculation of Komatsuna and Amaranth with the strains tested here could be effective in enhancing Cs accumulation. The decrease of Cs transfer under uniform- and bottom-Cs treatments would suggest that countermeasures aiming at decreasing the transfer of Cs could rely on ploughing practices.

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.