Foliar and soil uptake of 134Cs and 85Sr by grape vines

Strontium in the environment: Review about reactions of plants towards stable and radioactive strontium isotopes

Radiostrontium is released to the environment from routine and accidental discharge and acts on living organisms either from external sources or after absorption. When incorporated by plants, it enters the food chain and causes primary threat to human health and the environment. Understanding the mechanisms of plants for strontium uptake and retention is therefore essential for decision making concerning agriculture: are uptake rates low enough so that plants can serve as food? Or is radiostrontium accumulated so that plants should not be eaten but could be probably used for extracting strontium from water and soil in hot spots of pollution? The review presents a summary of studies about the origin of stable and radioactive strontium in the environment and effects coming from both internal and external exposure of plants. Mobility and availability of strontium to plant roots in soil are controlled by external factors such as chemical composition of the soil and pH, temperature and agricultural soil cultivation as well as soil biological networks built by microbial communities. Plant surfaces may receive input of strontium from deposition induced by atmospheric pollution or by acquisition from water through the whole immersed surface. Cells have entry mechanisms for strontium such as plasma membrane transporters for calcium and potassium. Part of absorbed strontium can be lost via processes discussed in this review. We give examples on strontium transfer factors for 149 plants to estimate plant absorption capacity for strontium from soil, water and air. Uptake efficiency of terrestrial and aquatic plants is deciding about their remediation potential to either remove radiostrontium by accumulation and rhizofiltration or to retain it in roots or aerial parts. Data of strontium content in soils after fallout and edible plants from long-term monitoring support the evaluation of the potential hazards posed by strontium input to the food chain.

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.

Time series changes in radiocaesium distribution in tea plants (Camellia sinensis (L.)) after the Fukushima Dai-ichi Nuclear Power Plant accident

Radiocaesium ((134)Cs and (137)Cs) release following the accident at the Fukushima Dai-ichi Nuclear Power Plant, belonging to the Tokyo Electric Power Company caused severe contamination of new tea plant (Camellia sinensis (L.)) shoots by radiocaesium in many prefectures in eastern Japan. Because tea plants are perennial crops, there is the fear that the contamination might last for a long time. The objectives of this study were to reveal time series changes in the distribution of radiocaesium in tea plants after radioactive fallout and to evaluate the effect of pruning on reduction of radiocaesium concentrations in new shoots growing next year. The experimental tea field was located in Shizuoka, Japan, approximately 400 km away from the Fukushima Dai-ichi Nuclear Power Plant in a southwest direction. Time series changes in radiocaesium concentrations in unrefined tea, a tea product primarily produced for making Japanese green tea, from May 2011 to June 2013 and distribution of radiocaesium in tea plants from May 2011 to May 2012 were monitored. The radiocaesium concentrations in unrefined tea exponentially decreased; the effective half-lives for (134)Cs and (137)Cs were 0.30 and 0.36 y during the first 2 y after the accident, respectively. With time, the highest concentrations of (137)Cs moved from the upper to the lower parts of plants. Medium pruning 2-3 months after the accident reduced the concentration of (137)Cs in new shoots harvested in the first crop season of the following year by 56% compared with unpruned tea plants; thus, pruning is an effective measure for reducing radiocaesium concentration in tea.

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.

Radiocesium transfer between Medicago truncatula plants via a common mycorrhizal network

Common mycorrhizal networks of arbuscular mycorrhizal fungi have been reported to transfer cesium between plants. However, a direct hyphae-mediated transfer (via cytoplasm/protoplasm) cannot be distinguished from an indirect transfer. Indeed, cesium released by the roots of the donor plant can be taken up by the receiver plant or fungal hyphae. In the present study, Medicago truncatula plants were connected by a common mycorrhizal network and Prussian Blue (ammonium-ferric-hexacyano ferrate) was added in the growth medium to adsorb the released radiocesium. A direct transfer of radiocesium to roots and shoots of the receiver plant was clearly demonstrated for the first time. Even though this transfer was quantitatively low, it suggested that shared mycorrhizal networks could contribute to the redistribution of this radionuclide in the environment, which otherwise would be restricted both in time and space. This finding may also help to understand the behaviour of its chemical analogue, potassium.

Transfer factors of 137Cs and 90Sr from soil to trees in arid regions

Transfer factors of (137)Cs and (90)Sr from contaminated soil (Aridisol) to olive, apricot trees and grape vines were determined under irrigated field conditions for four successive years. The transfer factors (calculated as Bqkg(-1) dry plant material per Bqkg(-1) dry soil) of both radionuclides varied among tree parts and were highest in olive and apricot fruits. However, the values for (90)Sr were much higher than those for (137)Cs in all plant parts. The geometric mean of the transfer factors in olives, apricots and grapes were 0.007, 0.095 and 0.0023 for (137)Cs and 0.093, 0.13 and 0.08 for (90)Sr, respectively, and were negligible in olive oil for both radionuclides. The transfer factors of both radionuclides were similar to, or in the lower limits of, those obtained in other areas of the world. This could be attributed to differences in soil characteristics: higher pH, lower organic matter, high clay content, and higher exchangeable potassium and calcium.

Uptake and transport of radioactive nickel and cadmium into three vegetables after wet aerial contamination

Knowledge of radionuclide or trace element retention and translocation to plants following an aerial contamination event, for example, sprinkling with contaminated water, is necessary for the evaluation of human exposure through consumption of contaminated vegetables. The fate of 63Ni and 109Cd in all plant parts of three different vegetables after wet deposition on leaves or on fruits was studied. Lettuce (Lactuca sativa L.), radish (Raphanus sativus L.), and bean (Phaseolus vulgaris L.) grown under controlled conditions in a growth chamber were contaminated with 63Ni and 109Cd either on leaves, by means of two different contamination methods (a single early contamination and a repetitive one), or on bean husks (third contamination method: a single contamination at a late stage). Spiked and nonspiked organs were harvested at maturity and radionuclide contents were measured. The fraction retained was on average 56% of the initially administered doses of 63Ni and 87% of 109Cd. The leaf-to-other organ translocation factor was considerably higher for 63Ni (on average 43% of retained radioactivity) than for 109Cd (8%). Nickel-63 migrated throughout the whole plant following foliar contamination, and mainly toward young leaves, seeds in formation, and sink organs, whereas 109Cd migrated to a much lesser extent and only to the organs that were closest to the spiked one, and not at all into fruit. After a fruit contamination event, both radionuclides were translocated into the seeds of spiked fruits. Radionuclide retention and translocation were not affected by plant species, but principally by the type of organ contaminated.

Retention and translocation of foliar applied 239,240Pu and 241Am, as compared to 137Cs and 85Sr, into bean plants (Phaseolus vulgaris)

Foliar transfer of 241Am, 239,240Pu, 137Cs and 85Sr was evaluated after contamination of bean plants (Phaseolus vulgaris) at the flowering development stage, by soaking their first two trifoliate leaves into contaminated solutions. Initial retentions of 241Am (27%) and 239,240Pu (37%) were higher than those of 137Cs and 85Sr (10-15%). Mean fraction of retained activity redistributed among bean organs was higher for 137Cs (20.3%) than for 239,240Pu (2.2%), 241Am (1%) or 85Sr (0.1%). Mean leaf-to-pod translocation factors (Bq kg(-1) dry weight pod/Bq kg(-1) dry weight contaminated leaves) were 5.0 x 10(-4) for 241Am, 2.7 x 10(-6) for 239,240Pu, 5.4 x 10(-2) for 137Cs and 3.6 x 10(-4) for 85Sr. Caesium was mainly recovered in pods (12.8%). Americium and strontium were uniformly redistributed among leaves, stems and pods. Plutonium showed preferential redistribution in oldest bean organs, leaves and stems, and very little redistribution in forming pods. Results for americium and plutonium were compared to those of strontium and caesium to evaluate the consistency of the attribution of behaviour of strontium to transuranium elements towards foliar transfer, based on translocation factors, as stated in two radioecological models, ECOSYS-87 and ASTRAL.

Cesium-134 and strontium-85 in strawberry plants following wet aerial deposition

The understanding of the processes that control the behavior of radionuclides in crops can support policymakers to take actions to protect the environment and safeguard human health. Data concerning the behavior of radionuclides in fruits are limited. Strawberry (Fragaria x ananassa Duchesne) plants were contaminated on the aboveground part by sprinkling an aqueous solution of 134Cs and 85Sr at three growing stages: predormancy, anthesis, and beginning of ripening. Intercepted activity was more affected by the posture and physical orientation of leaves rather than by leaf area or biomass. Fruit interception ranges from 0.2 to 1.2% of the sprinkled activity. Translocation coefficients from leaf to fruit are on the order of 10(-4) for 134Cs and 10(-5) for 85Sr. Translocation reaches its highest intensity between anthesis and ripening. If deposition occurs when plants are bearing fruits, the fruit activity will be affected by the activity initially deposited on the fruit surfaces. This is important for 85Sr as it is not translocated in the phloem. The loss of the dead leaves at the resumption of growth causes high plant decontamination, but a fraction of both radionuclides remains in the storage organs, roots, and shoots, which is retranslocated to fruits in the following spring. The values of the environmental half-time, t(w), after deposition at predormancy are 114 d for 134Cs and 109 d for 85Sr. Cesium-134 tends to be allocated to fruits, while 85Sr remains in leaves and crowns. Translocation of radionuclides to roots results in soil contamination.

Post-deposition transport of radionuclides in fruit

This paper considers two main pathways for contamination of fruit by radionuclides: (i) absorption after deposition directly to exposed fruit surfaces, and (ii) absorption after deposition to other exposed plant surfaces followed by translocation to fruit. The aim is to collect the available information on fruit from temperate regions, identify the factors affecting post deposition processes in fruit plant systems, identify gaps in knowledge and give recommendations for future work. The majority of information available on above-ground absorption and further translocation to fruit concerns 134Cs and 85Sr in soluble form in apple, strawberry and grapevine. In general, 85Sr is absorbed and translocated to a lesser extent than is 134Cs. The rate of absorption and translocation depends on the physiological stage and age of the plant, and varies between different plant species and varieties.

Radionuclide transfer from soil to fruit

The available literature on the transfer of radionuclides from soil to fruit has been reviewed with the aim of identifying the main variables and processes affecting the behaviour of radionuclides in fruit plants. Where available, data for transfer of radionuclides from soil to other components of fruit plant have also been collected, to help in understanding the processes of translocation and storage in perennial plants. Soil-to-fruit transfer factors were derived from agricultural ecosystems, both from temperate and subtropical or tropical zones. Aggregated transfer factors have also been collected from natural or semi-natural ecosystems. The data concern numerous fruits and various radionuclides. Soil-to-fruit transfer is nuclide specific. The variability for a given radionuclide is first of all ascribable to the different properties of soils. Fruit plant species are very heterogeneous, varying from woody trees and shrubs to herbaceous plants. In temperate areas the soil-to-fruit transfer is higher in woody trees for caesium and in shrubs for strontium. Significant differences between the values obtained in temperate and subtropical and tropical regions do not necessarily imply that they are ascribable to climate. Transfer factors for caesium are higher in subtropical and tropical fruits, while those for strontium, as well as for plutonium and americium, in the same fruits, are lower; these results can be interpreted taking into account different soil characteristics.

Transfer of radioactivity to fruit: significant radionuclides and speciation

One of the roles of the BIOMASS Theme 3 Fruit Working Group was to identify significant radionuclides to support its work programme. This paper provides a short review of radionuclide emissions to atmosphere together with comments on their relative dosimetric impacts to identify those radionuclides most relevant to the Fruit Working Group. Speciation of the identified radionuclides is also discussed to identify the most likely chemical forms to which fruits might be exposed. It is noted that no information currently exists on radionuclide speciation in regard to the uptake and retention of radionuclides in fruit crops.