The EDTA Amendment in Phytoextraction of 134Cs From Soil by Indian Mustard (Brassica juncea)

Soil contamination with radiocaesium is a significant problem at any countries when a nuclear accident occurred. Recently, phytoextraction technique is developed to remediate the contaminated environment. However, the application is limited by the availability of the contaminant for root uptake. Therefore, a green house trial experiment of soil amendment with ethylene diamine tetraacetic acid (EDTA) has been conducted to examine ¹³⁴Cs availability for root uptake. Two groups of Indian mustard (Brassica juncea) were cultivated in ¹³⁴Cs contaminated soil. The soil in the first group was treated with EDTA amendment, while the other was not. Plant growth was observed gravimetrically and the ¹³⁴Cs concentration in soil as well as plants were determined using gamma spectrometry. The plant uptake capacity was determined as transfer factor (F_v), and the F_v values of 0.22 ± 0.0786 and 0.12 ± 0.039 were obtained for the soil treated with and without EDTA amendment, respectively. The phytoextraction efficiency of the plant cultivated in ¹³⁴Cs contaminated soil both with and without EDTA amendment was low. The EDTA amendment to the soil seems to enhance the ¹³⁴Cs availability for root uptake of Indian mustard and can still be considered to assist the field phytoremediation of contaminated soil.     

Experimentally determined translocation of 134Cs in potatoes

The results of a greenhouse experiment on the translocation rate of ¹³⁴Cs from potato leaves to tubers were compared with calculations of the radioecological model ECOSYS-87 and other literature values. The ¹³⁴Cs activities applied at three development stages (three pinnate leaves fully developed, onset of flowering, onset of yellowing) to leaves of the plant were taken as starting points for the model to calculate the activity in the tubers at harvest. The default yield in the model was replaced by the experimentally obtained values. The translocation rate measured in the greenhouse experiment was 4 to 14 times higher than the calculations of the model. Some possible reasons for such a high translocation rate, compared with the literature data, are discussed. Based on these comparisons, it is concluded that maximal translocation occurs at the growth stage of flowering of a crop and that the development stage of a crop might be a stronger parameter to describe the time dependency of translocation than the usually applied parameter `days before harvest'.     

137Cs uptake in spring wheat (Triticum aestivum L.cv. Tonic) at varying K supply

Spring wheat (Triticum aestivum L. cv. Tonic) was grown for 16 days in a sandy loam soil which was contaminated with ¹³⁷Cs. The soil was fertilised with K at three rates (0,1 and 2 mmol K per 950 g dry soil) and with NO₃ ^--N at two rates (0 and 2 mmol per 950 g dry soil) in a factorial design. The ¹³⁷Cs Activity Concentration (AC) in the shoot tissue significantly reduced 8.2-fold (nil N treatment, p<0.001) and 9.3-fold (highest N dose, p<0.001) with increasing K supply. In contrast, the K application increased the ¹³⁷Cs AC in soil solution 1.7 fold (nil N treatment) or had no significant effect (highest N dose). At similar K application, the application of N increased the ¹³⁷Cs AC in the shoot compared to the control. This effect is most probably due to the increased NH₄ ⁺ concentration in soil solution which increased the ¹³⁷Cs AC in soil solution. The soil solution composition (¹³⁷Cs and K concentration) in the rhizosphere was estimated from the average soil solution composition at day 16 and solute transport calculations. The ¹³⁷Cs AC in the shoot tissue was predicted from the estimated soil solution composition in the rhizosphere and the relationship between K concentration and ¹³⁷Cs uptake derived from a nutrient solution experiment. The predictions of ¹³⁷Cs AC's in the shoot are qualitatively correct for the fertiliser effects but underestimate the observations between 1.4 and 9.9 fold.     

Production of134Cs thermo-generated aerosols

This paper presents observations made on the behavior of radioactive cesium in laboratory conditions.¹³⁴Cs-loaded aerosols are generated from UO₂ pellets in an electric oven and allowed to deposit on small spruce trees. The transfer of radioactivity to the plants has been studied. In another series of experiments, trees are submitted to artificial rain contaminated by the radioactive aerosols. The two modes of contamination are compared.     

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.     

Potential for phytoextraction of137 Cs from a contaminated soil

Potential for phytoremediation of a soil contaminated with radiocesium was investigated in three phases: (1) hydroponic screening for plant species capable of accumulating elevated levels of cesium in shoots, (2) investigation of several amendments for their potential to increase the bioavailability of ¹³⁷Cs in the contaminated soil, and (3) bioaccumulation of radiocesium in shoots of plants grown in¹³⁷ Cs-contaminated soil.The bioaccumulation ratio for Cs in shoots of hydroponically grown plants ranged between 38 and 165. From solution, dicot species accumulated 2- to 4-fold more cesium in shoots than grasses. In studies investigating the bioavailability of ¹³⁷Cs in aged contaminated soil, ammonium salts were found to be the most effective desorbing agents, releasing approximately 25% of the¹³⁷ Cs. The extent of ¹³⁷Cs desorption from the soil increased with ammonium concentration up to 0.2 M. In a pot study conducted in a greenhouse, there was significant species-dependent variability in the ability to accumulate ¹³⁷Cs in the shoot from contaminated soil. The ability to accumulate ¹³⁷Cs from the soil increased in the order: reed canarygrass (Phalaris arundinacea) < Indian mustard (Brassica juncea) < tepary bean (Phaseolus acutifolius)< cabbage (B. oleracea var. capitata). It was also found that addition of NH₄NO₃ solution to the soil elicited a two- to twelve-fold increase in ¹³⁷Cs accumulation in the shoot. The greatest amount of ¹³⁷Cs (40 Bq g^-1 dw) was removed in shoots of cabbage grown in contaminated soil amended with 80 mmols NH₄NO₃ kg^-1 soil. Bioaccumulation ratios of 2–3 were obtained with the best performing plant species. These values are significantly greater than those previously reported in the literature (usually <0.1) for plants grown on aged contaminated soil. These results indicate that careful species selection along with amendments that increase the bioavailability of¹³⁷ Cs in the soil could greatly enhance the prospects for the use of plants to remediate ¹³⁷Cs-contaminated soils.     

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

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

Transfer of 85Sr and 134Cs from diet to reindeer foetuses and milk

Sr-85 and ¹³⁴Cs in aqueous solution of the chlorides were administered daily to four pregnant reindeer during the last part of gestation. Radionuclide concentrations were determined in calves sacrificed at birth, and secretion of the nuclides was measured in milk. Although the gastrointestinal absorption of ⁸⁵Sr was low, an apparently higher transfer of the absorbed fraction of ⁸⁵Sr than ¹³⁴Cs from the mother to the foetus led to similar accumulation of ⁸⁵Sr and ¹³⁴Cs in foetuses. At birth 1.4–1.6 and 1.5–2.5% of the total administered activities of ⁸⁵Sr and ¹³⁴Cs, respectively, were present in the calves‘ bodies. Transfer coefficients (F _m) for ⁸⁵Sr and ¹³⁴Cs from feed to milk were estimated at 0.0218±0.0026 and 0.185±0.025 day kg⁻¹, respectively, and the observed ratio (OR_milk-diet) for ⁸⁵Sr was 0.124±0.037. Transfer of radiostrontium to reindeer milk was in agreement with previously reported relationships between Ca intake and radiostrontium transfer in ruminants. These relationships suggest that the transfer of radiostrontium to foetuses and milk of free-ranging reindeer can be 3–4 times higher than observed in this experiment (due to lower Ca intake with natural forage), but the transfer to milk will not be as high as that of ionic ¹³⁴Cs. The concentrations of ⁸⁵Sr in milk suggested that the does mobilized skeletal stores of Ca and ⁸⁵Sr for milk production, although the diet appeared to satisfy the Ca requirements. In reindeer with radiostrontium intake during the whole year, radiostrontium concentrations in milk will therefore be higher than indicated by the F _m value observed in our study. No differences in half-times for ⁸⁵Sr and ¹³⁴Cs secretion in milk were detected. Both nuclides were secreted with short- and long-term half-times of 1–2 and 12–19 days, respectively. For ⁸⁵Sr, 80–90% of the activity was excreted with the short half-time, whereas the corresponding value for ¹³⁴Cs was 30–50%.     

Radioactivity in mushrooms,mosses and soil samples of defined biotops in SW Bavaria-two years after “Chernobyl”

Summary Mushrooms, the moos/grass layer and soil samples have been collected in autumn 1987 from two sites in SW-Bavaria in continuation of a former investigation (Elstner et al. 1987). There were still relatively high amounts of ¹³⁷Cs and ¹³⁴Cs in all samples. The ratio ¹³⁷Cs/¹³⁴Cs changed according to the different half-life times of the two radioisotopes, indicating in nearly all cases the Chernobyl accident as source. The distribution of the radioisotopes within the mushroom populations shows considerable variation, even within the same species and location. Besides ¹³⁷Cs, ¹³⁴Cs and ⁴⁰K no other radioisotopes were detected.     

Nutrient acquisition from different soil depths by pedunculate oak

Eight oak trees (Quercus robur L.) received ³²P at a soil depth of 50 cm and ³³P at a soil depth of 15 cm at the end of June 2002 through plastic tubes inserted into the mineral soil. The phosphorus uptake from different soil depths was estimated by analysing the concentration of ³²P and ³³P in the foliage of oak growing in a mixed stand in southern Sweden. ³²P and ³³P were recovered in the leaves/needles after 21 and 39 days. The recovery of labelled P in oak was higher from 15 cm soil depth than from 50 cm, however, more than 4% of the total amount of labelled P was taken up from 50 cm. This indicates that oak can utilize deep soil layers for nutrient uptake. A study on the uptake of Cs (as an analogue to K) and ¹⁵N into the leaves was performed on the same trees and detectable amounts of ¹⁵N and Cs were recovered in leaves and buds. This indicates that ¹⁵N and Cs can be used to study nutrient uptake of mature trees from the mineral soil.     

Natural and Chernobyl-caused radioactivity in mushrooms,mosses and soil-samples of defined biotops in SW Bavaria

Summary Different mushrooms, mosses and corresponding soil samples have been collected mainly from two sites in the alpine region of southwestern Bavaria. At the end of the growthseason, September 1986, gamma spectroscopic analysis showed that the moss-, mould, and needle-layer contained considerably more ¹³⁴Cs and ¹³⁷Cs activity per unit fresh weight than eight different species of mushroom. These two isotopes were carried into the biotop mainly as a consequence of the Chernobyl accident. ¹³¹J could not be found any more in the samples ca. 5–6 months after the catastrophe. The activity of the cesium isotopes decreased with increasing soil depth. In the mushrooms the activity was relatively high in Xerocomus badius and surprisingly low in Boletus edulis; samples of the latter and of Cantharellus cibarius collected in September 1985 (before the accident) and kept deep frozen contained almost identical amounts of ¹³⁷Cs as those collected from August to October 1986. Mushrooms contained considerably more of the natural isotope ⁴⁰K than the needlelayers and the soil samples in the neighbourhood. In all mushrooms except Xerocomus badius the activity of ⁴⁰K was generally higher than the ¹³⁷Cs activity. The results indicate that except Xerocomus badius the analyzed mushrooms do not actively take up Cs from the soil, in contrast to K.     

Nitrate uptake ability by maize roots during and after drought stress

The effects of different intensities and durations of soil drought and re-watering on the nitrate uptake ability of maize roots were studied. Plants were grown in split-root containers with one part of the root system subjected to different intensities and durations of soil drought and re-watering while the other part of the root system was continuously watered to 23% (w/w) soil water content (70% water capacity). Experiments were performed in split-root containers to maintain a high growth rate, thus ensuring high nutrient demand of the shoot irrespective of the soil water regime. To avoid limitation of nitrate uptake by transport processes in the dry soil, and to ensure a uniform ¹⁴N/¹⁵N ratio at the root surface, ¹⁵N was applied to the roots by placing them into an aerated nutrient solution with 0.5 mM Ca(¹⁵NO₃)₂. Shoot elongation and biomass were only slightly affected by drought in one root compartment when the soil in the other root compartment was kept wet. Therefore, the growth-related nutrient demand of the shoot remained at a high level. At moderate levels of soil drought (10% w/w water content) the ability of the roots for N-uptake was not affected even after 10 d of drought. N-uptake ability was reduced to about 20% of the well-watered control only when the soil water content was decreased to 5%. Total soluble sugar content of the roots increased with increasing soil drought, indicating that low N-uptake ability of roots subjected to severe soil drought was not caused by low assimilate supply from the shoot. Nitrate uptake ability of roots maintained in very dry soil (5% soil water content w/w) even for a prolonged period of 8 d, recovered within 3 d following re-watering. Root growth increased one day after re-watering. A short-term experiment with excised roots formerly subjected to severe soil drought showed that nitrate uptake ability recovered in old and young root segments after 2 d of re-watering. Obviously, the increase in N-uptake ability after re-watering was caused not only by new root growth but also by recovery of the uptake ability of formerly stressed roots.     

Identification and expression studies of a catalase and a bifunctional catalase-peroxidase in Frankia strain R43

This study investigated the uptake of ¹³⁴Cs by Lactuca sativaL., Silybum marianumGaertn., Centaurea cyanusL., Carthamus tinctorius L. from the Asteraceae, and Beta vulgaris L. var. `Lutiancai' and Beta vulgaris L. var. `Hongtiancai' from the Chenopodiaceae grown in two widely-distributed soils (a paddy soil and a red soil) in South China. The results showed that the plants growing on the paddy soil had a relatively high yield and low [¹³⁴Cs] while those growing on the red soil showed the opposite trend. The accumulation of ¹³⁴Cs was dependent on plant species and soil types. For the paddy soil, mean values for [¹³⁴Cs] were higher for the species of the Asteraceae (ranging from 165 to 185 Bq g^–1) than for those of the Chenopodiaceae (less than 140 Bq g^–1). For the red soil, S. marianumand C. cyanus of the Asteraceae had high average concentrations of ¹³⁴Cs ranging from 340 to 400 Bq g^–1 but L. sativa and C. tinctorius from the same family had low concentrations of ¹³⁴Cs ranging from 115 to 200 Bq g^–1 on a dry weight basis. B. vulgaris L. var. `Lutiancai' and Beta vulgaris L. var. `Hongtiancai' accumulated from 120 to 231 Bq ¹³⁴Cs g^–1 of plant shoot. The transfer factor values of ¹³⁴Cs for the studied species were in general higher in red soil than in paddy soil except C. tinctorius. All plant species from the Asteraceae family growing on the paddy soil had higher transfer factors than the B. vulgaris species. S. marianum, and C. cyanus growing on the red soil had TFs >1, being much higher than the B. vulgaris species. The results therefore showed that the plant species from the Asteraceae could accumulate higher concentrations of radiocesium than the Beta vulgaristhat has previously been suggested as a candidate for phytoremediation of radiocesium contaminated soils.     

Absorption of radiocaesium by flooded rice: relative importance of roots and shoot base in the transfer of radioactivity

Summary Lowland rice plants were grown in double isolated containers, where shoot base was dipped in Cs¹³⁷ contaminated water and roots in Cs¹³⁴ contaminated nutrient solution andvice versa. The plants were collected after six weeks and plant sample activity determined by γ-spectrometry. Radiocaesium is absorbed by the shoot base and distributed in the different organs of the plant; the transfer coefficient being higher for water-plant than between nutrient solution-plant. Concentration factors obtained and exchangeability of Cs fixed by the plant vary with the radioisotope. Such a behavior may find an explanation in the stable Cs content of the medium. No equilibrium is observed in the plant between two radioisotopes of the same element absorbed by different plant organ. This publication is contribution no. 691 of the EURATOM Biology Division.     

Comparison of <Superscript>233</Superscript>U and <Superscript>33</Superscript>P uptake and translocation by the arbuscular mycorrhizal fungus<Emphasis Type="Italic"> Glomus intraradices</Emphasis> in root organ culture conditions

This study aimed to quantify and compare ²³³U and ³³P uptake and translocation by hyphae of the arbuscular mycorrhizal (AM) fungus Glomus intraradices in root organ culture conditions with transformed carrot (Daucus carota L.) roots as host. Mycorrhizal roots were grown in two-compartment Petri dishes to spatially separate a root compartment (RC) and a hyphal compartment (HC). The HC was labelled with 8.33 Bq ²³³U ml^–1 and 13.33 Bq ³³P ml^–1. After 2 weeks contact between hyphae and the labelled solution, ²³³U and ³³P activities were measured in the RC and in the HC. ²³³U and ³³P were taken up by the extraradical AM mycelium grown in the HC and this uptake represented 4.4% and 16% of the initial isotope supply, respectively. The translocation into roots developing in the RC via hyphae accounted for 5.9% and 72% of the initial isotope supply, respectively. Thus, both uptake and translocation were much higher for ³³P than for ²³³U. This suggests (1) the existence in hyphal tissues of efficient mechanisms limiting the uptake and translocation of non-essential elements such as U, and (2) that the hyphae have a higher sequestration than translocation function for U, and the converse for P.     

137Cs as a tracer of recent sedimentary processes in Lake Michigan

To determine recent sediment movement, we measured the levels of ¹³⁷Cs (an artificial radionuclide produced during nuclear weapons testing) of 118 southern Lake Michigan samples and 27 in Green Bay. These samples, taken from 286 grab samples of the upper 3 cm of sediment, were collected in 1975 as part of a systematic study of Lake Michigan sediment. ¹³⁷Cs levels correlated well with concentrations of organic carbon, lead, and other anthropogenic trace metals in the sediment. ¹³⁷Cs had a higher correlation with silt-sized than with clay-sized sediment (0.55 and 0.46, respectively). Atmospherically derived ¹³⁷Cs and trace metals are being redistributed by sedimentary processes in Lake Michigan after being incorporated in suspended sediment. We determined a distribution pattern of ¹³⁷Cs that represents areas of southern Lake Michigan where sediment deposition is occurring.     

Response of tomatoes (Lycopersicon esculentum) to an unequal distribution of nutrients in the root environment

Tomato (Lycopersicon esculentum Mill.) plants were grown in a split root system. The plants were rooted in two separate cubes of rockwool, which were subsequently irrigated with nutrient solution of equal (control) or different EC values. Besides optimal values, too low and too high values for maximal production were included.The yield was determined by the EC value considered optimal for plant nutrition if present in one of both rockwool cubes. The quality of the fruits was primarily determined by standard EC values available in part of the root environment. Water was preferably taken up from the low EC compartment, nutrients from the high EC compartment. Samples of leaves and fruits were analyzed to get information about uptake and translocation of nutrients in the plant.     

Doses from external irradiation and ingestion of 134Cs, 137Cs and 90Sr of the population of Belarus accumulated over 35 years after the Chernobyl accident

This study considers the exposure of the population of the most contaminated Gomel and Mogilev Oblasts in Belarus to prolonged sources of irradiation resulting from the Chernobyl accident. Dose reconstruction methods were developed and applied in this study to estimate the red bone-marrow doses (RBMs) from (i) external irradiation from gamma-emitting radionuclides deposited on the ground and (ii) ¹³⁴Cs, ¹³⁷Cs and ⁹⁰Sr ingestion with locally produced foodstuffs. The mean population-weighted RBM doses accumulated during 35 years after the Chernobyl accident were 12 and 5.7 mGy for adult residents in Gomel and Mogilev Oblasts, respectively, while doses for youngest age groups were 20–40% lower. The highest mean area-specific RBM doses for adults accumulated in 1986–2021 were 63, 56 and 46 mGy in Narovlya, Vetka and Korma raions in Gomel Oblast, respectively. For most areas, external irradiation was the predominant pathway of exposure (60–70% from the total dose), except for areas with an extremely high aggregated ¹³⁷Cs soil to cow’s milk transfer coefficient (≥?5.0 Bq L^?1 per kBq m^?2), where the contribution of ¹³⁴Cs and ¹³⁷Cs ingestion to the total RBM dose was more than 70%. The contribution of ⁹⁰Sr intake to the total RBM dose did not exceed 4% for adults and 10% for newborns in most raion in Gomel and Mogilev Oblasts. The validity of the doses estimated in this study was assessed by comparison with doses obtained from measurements by thermoluminescence dosimeters and whole-body counters done in 1987–2015. The methodology developed in this study can be used to calculate doses to target organs other than RBM such as thyroid and breast doses. The age-dependent and population-weighted doses estimated in this study are useful for ecological epidemiological studies, for projection of radiation risk, and for justification of analytical epidemiological studies in populations exposed to Chernobyl fallout.

     

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.     

Assessing the Potential of Phytoremediation at a Site in the U.K. Contaminated With 137Cs

Spinacia oleracea L. cv. ‘Bloomsdale’, Beta vulgaris L. cv. ‘Flavescens’, Brassica juncea L. ‘OB825’, and Helianthus annuus L. cv. ‘Oranges and Lemons’ were grown for 8 weeks at a site contaminated with ¹³⁷Cs at Bradwell Nuclear Power Station, UK. The site was a trench approximately 1.5 m deep, 2 m wide, and 100 m long in ‘made ground’ consisting of alluvium with traces of illites, kaolinites, and smectites. ¹³⁷Cs activity concentration was measured in individual plants after 8 weeks growth and the soil in which they grew. The biomass produced and total ¹³⁷Cs removed to shoots differed significantly between species but ¹³⁷Cs activity concentrations and Transfer Factors (TFs) did not. B. vulgaris produced the most biomass and removed the greatest amount of ¹³⁷Cs. For all plants, and within each taxon, plants growing at low soil ¹³⁷Cs activity concentrations had significantly greater TFs than those growing at high soil ¹³⁷Cs activity concentrations. It is concluded that selecting plant taxa suited to a particular site can be an effective way of improving phytoremediation rates, that there is much scope for adjusting harvesting intervals to 8 weeks or less without affecting TFs, and that estimates of time taken for ¹³⁷Cs removal by phytoremediation should consider that TFs may increase as soil concentrations decrease. With refinements in methodology, phytoremediation has the potential to contribute significantly to decontamination of the site at Bradwell.