Uptake of 40K and 137Cs in native plants of the Marshall Islands

Uptake of 137Cs and 40K was studied in seven native plant species of the Marshall Islands. Plant and soil samples were obtained across a broad range of soil 137Cs concentrations (0.08-3900 Bq/kg) and a narrower range of 40K soil concentrations (2.3-55 Bq/kg), but with no systematic variation of 40K relative to 137Cs. Potassium-40 concentrations in plants varied little within the range of 40K soil concentrations observed. Unlike the case for 40K, 137Cs concentrations increased in plants with increasing 137Cs soil concentrations though not precisely in a proportionate manner. The best-fit relationship between soil and plant concentrations was P = aSb where a and b are regression coefficients and P and S are plant and soil concentrations, respectively. The exponent b for 40K was zero, implying plant concentrations were a single value, while b for 137Cs varied between 0.51 and 0.82, depending on the species. For both 40K and 137Cs, we observed a decreasing concentration ratio (where concentration ratio=plant concentration/soil concentration) with increasing soil concentrations. For the CR values, the best-fit relationship was of the form CR = aSb/S = aSb(-1). For the 40K CR functions, the exponent b - 1 was close to - 1 for all species. For the 137Cs CR functions, the exponent b - 1 varied from -0.19 to -0.48. The findings presented here, aswell as those by other investigators, collectively argue against the usefulness of simplistic ratio models to accurately predict uptake of either 40K or 137Cs in plants over wide ranges of soil concentration.     

Concentration of caesium-137, cobalt-60 and potassium-40 in some wild and edible plants around the nuclear power plant in Bulgaria

The activities of 137Cs, 60Co and 40K were determined in samples of wild (Taraxacum officinale, Plantago lanceolata and Populus nigra 'Italica') and edible (vegetable, corn, fruit) plants as well as soil collected from the 30 km safety zone of the Bulgarian NPP "Kozloduy" and comparisons with earlier measurements and analyses of samples from other regions and with literature values were performed. The derived transfer factors for 137Cs and 40K from soil to plants ranged between 0.002 and 0.009 for 137Cs, and between 0.09 and 0.35 for 40K. The individual effective dose (calculated from the present results and data on the activity of other foodstuffs and from information about dietary habits) comprises 4.5% of the annual dose limit.     

Equilibrium of radiocesium with stable cesium within the biological cycle of contaminated forest ecosystems

Concentrations of (137)Cs and stable Cs were determined in plant, mushroom, lichen and soil samples collected at two forest sites with different contamination levels in Belarus in 1998. The concentration of (137)Cs in soil was the highest in near-surface organic layers (Of and Oh horizons) and decreased with depth in the mineral layers, whereas the concentrations of stable Cs were almost constant in the soil profile. The levels of (137)Cs and stable Cs in biological samples varied depending both on the species and the plant part sampled. Even though different species and parts of the same species were included, the concentration ratios of (137)Cs to stable Cs were fairly constant for samples collected at the same forest site, and were in the same order of magnitude as the (137)Cs to stable Cs ratios for the organic soil layers. This finding suggests that (137)Cs, mainly deposited on the forest ecosystems from the Chernobyl accident in 1986, was well mixed with stable Cs within the biological cycle in the forest ecosystems by 1998. The transfer factor for each biological sample of (137)Cs was almost the same as that of stable Cs, if they were calculated based on the concentrations in the Of + Oh layer. This suggests that the stable-Cs-based transfer factor could be used as equilibrium transfer factor of (137)Cs for different types of biological samples in the forest.     

Foliar and root uptake of 134Cs, 85Sr and 65Zn in processing tomato plants (Lycopersicon esculentum Mill.)

Rice is a staple food in Japan and other Asian countries, and the soil-to-plant transfer factor of 137Cs released into the environment is an important parameter for estimating the internal radiation dose from food ingestion. Soil and rice grain samples were collected from 20 paddy fields throughout Aomori Prefecture, Japan in 1996 and 1997, and soil-to-polished rice transfer factors were determined. The concentrations of 137Cs, derived from fallout depositions, stable Cs and K in paddy soils were 2.5-21 Bq kg(-1), 1.2-5.3 and 5000-13000 mg kg(-1), respectively. The ranges of 137Cs, stable Cs and K concentration in polished rice were 2.5-85 mBq kg(-1) dry wt., 0.0005-0.0065 and 580-910 mg kg(-1) dry wt., respectively. The geometric mean of soil-to-polished rice transfer factor of 137Cs was 0.0016, and its 95% confidence interval was 0.00021-0.012. The transfer factor of 137Cs was approximately 3 times higher than that of stable Cs at 0.00056, and they were well correlated. This implied that fallout 137Cs, mostly deposited up to the 1980s, is more mobile and more easily absorbed by plants than stable Cs in the soil, although the soil-to-plant transfer of stable Cs can be used for predicting the long-term transfer of 137Cs. The transfer factors of both 137Cs and stable Cs decreased with increasing K concentration in the soil. This suggests that K in the soil was a competitive factor for the transfers of both 137Cs and stable Cs from soil-to-polished rice. However, the transfer factors of 137Cs and stable Cs were independent of the amount of organic materials in soils.     

Comparative analysis of (239)Pu, (137)Cs, (210)Pb and (40)K spatial distributions in the top soil layer at the Baltic coast

This paper presents the results of an investigation into the spatial distribution of radionuclides of artificial ((239,240)Pu, (137)Cs) and natural ((210)Pb, (40)K) origins in the upper (0-5 cm) soil layers on the Baltic coastline of Lithuania ( approximately 5 km(2) area). The samples were analysed by gamma ray spectrometry and combined radiochemical procedures. The highest (210)Pb, (239,240)Pu and (137)Cs activity concentrations were determined in the forest samples, whereas (40)K activity was rather homogeneous across the study area. Relatively high (239,240)Pu and (40)K activity concentrations were determined along the surf zone. The (210)Pb and (137)Cs activity concentrations showed a gradual increase from the surf zone to the forest. The average activity concentrations of (239,240)Pu, (137)Cs, (210)Pb and (40)K in the beach and forest samples, respectively, were as follows: 0.32+/-0.08 and 0.74+/-0.14; 50+/-4 and 1190+/-50; 4.7+/-2.0 and 48+/-6; 186+/-15 and 216+/-17 Bq/kg.     

Radiocaesium contamination of meadow vegetation--time-dependent variability and influence of soil characteristics at grassland sites in Austria

Long-term trends of 137Cs and 40K concentrations in meadow grass and soil-plant transfer data at eight different sites in Upper Austria are presented. Geometric means of 137Cs TF-data and Tagg values vary between 0.03-1.06 and 0.0005-0.0184 depending on site, respectively. 40K results are less variable with TF values covering a range of 0.31-2.01. Only at one site was a significant decrease of 137Cs concentration (decay-corrected) in meadow vegetation observed during the observation period 1992-1999. Seasonal trends of 40K and 137Cs were investigated at one site in 1996. Both elements show decreasing concentrations in plants from beginning of May-July, followed by a peak in September. Although this pattern was not very pronounced, there are some hints that it may explain deviations of long-term trends in 137CS levels in grass caused by unusual weather conditions as indicated by phenological climate data (beginning of sweet cherry and black elder blossoming). Finally, TF values were correlated with soil characteristics, revealing a negative correlation of radiocaesium soil-plant transfer with soil pH, exchangeable and extractable fractions of Mg, Ca and Na as well as a positive correlation with exchangeable Al.     

Long-term effects of single potassium fertilization on 137Cs levels in plants and fungi in a boreal forest ecosystem

We examined the long-term effects of a single application of potassium (K) fertilizer (100 kg K ha⁻¹) in 1992 on ¹³⁷Cs uptake in a forest ecosystem in central Sweden. ¹³⁷Cs activity concentrations were determined in three low-growing perennial shrubs, heather (Calluna vulgaris), lingonberry (Vaccinium vitis-idaea) and bilberry (Vaccinium myrtillus), and in four wild fungal species (Cortinarius semisanguineus, Lactarius rufus, Rozites caperata and Suillus variegatus). Uptake of ¹³⁷Cs by plants and fungi growing on K-fertilized plots 17 years after application of the K fertilizer was significantly lower than in corresponding species growing in a non-fertilized control area. The ¹³⁷Cs activity concentration was 21-58% lower in fungal sporocarps and 40-61% lower in plants in the K-fertilized area compared with the control. Over the study period, this decrease in ¹³⁷Cs activity concentration was more consistent in plants than in fungi, although the effect was statistically significant and strongly pronounced in all species. The effect of K fertilization in reducing ¹³⁷Cs activity concentration in fungi and plants decreased over time but was still significant in 2009, 17 years after fertilization. This suggests that application of K fertilizer to forests is an appropriate and effective long-term measure to decrease radiocaesium accumulation in plants and fungi.     

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.     

Uptake and distribution of 137Cs and 90Sr in salix viminalis plants

Agricultural areas in middle and northern parts of Sweden were contaminated with radionuclides after the Chernobyl accident in 1986. Alternative crops in these areas are biomass plantations with fast-growing Salix clones for energy purposes. The uptake and internal distribution of 137Cs and 90Sr in Salix viminalis were studied. Plants were grown in microplots under field conditions. The soils in the experimental site had been contaminated in 1961 with 35.7 and 13.4 MBq m(-2) of 137Cs and 90Sr, respectively. The experiment was carried out during three years. The plots were fertilised with 60 kg N ha(-1) and three treatments of K, consisting of 0, 80 and 240 kg K ha(-1) during the first two years. The activity concentration of 137Cs in the different plant parts varied between 140 and 20,000 Bq kg(-1) and was ranked in the following order: lowest in stems < cuttings < leaves < roots. The fine roots (0-1 mm) had the highest 137Cs activity concentration. One-year-old stems had higher 137Cs activity concentrations than two-year-old stems. The activity concentration of 137Cs in the plants was significantly affected by K-supply and was higher in the 0 kg K treatment than in the 80 or 240kg K treatment. Leaves contained more 90Sr than stems and cuttings.     

The presence of some artificial and natural radionuclides in a Eucalyptus forest in the south of Spain

Long-lived artificial radionuclides (137Cs, 90Sr) were studied in a Eucalyptus plantation located in the south-west of Spain. Radionuclide concentrations were determined in different types of samples corresponding to specific forest components (soil, trees, herbs and litter). Depth profile distributions were obtained in two selected core soils. Two layers were separately measured in three other cores. The concentration factor, defined as the ratio between the mean activity concentration in a component and the mean activity concentration in the soil, was calculated for each component. The biomass of different components was estimated in order to evaluate the total density concentration (Bq/ha) of the artificial radionuclides (137Cs, 90Sr) in the Eucalyptus plantation. The transfer of the radionuclides between the different forest components can be inferred from the results. Additionally, other naturally occurring radionuclides (40K, 226Ra, 228Ra, 228Ac) were determined for comparison. Transport of radionuclides from forest to a nearby pulp mill is also discussed.     

Modelling 137Cs uptake in plants from undisturbed soil monoliths

A model predicting 137Cs uptake in plants was applied on data from artificially contaminated lysimeters. The lysimeter data involve three different crops (beans, ryegrass and lettuce) grown on five different soils between 3 and 5 years after contamination and where soil solution composition was monitored. The mechanistic model predicts plant uptake of 137Cs from soil solution composition. Predicted K concentrations in the rhizosphere were up to 50-fold below that in the bulk soil solution whereas corresponding 137Cs concentration gradients were always less pronounced. Predictions of crop 137Cs content based on rhizosphere soil solution compositions were generally closer to observations than those based on bulk soil solution composition. The model explained 17% (beans) to 91% (lettuce) of the variation in 137Cs activity concentrations in the plants. The model failed to predict the 137Cs activity concentration in ryegrass where uptake of the 5-year-old 137Cs from 3 soils was about 40-fold larger than predicted. The model generally underpredicted crop 137Cs concentrations at soil solution K concentration below about 1.0 mM. It is concluded that 137Cs uptake can be predicted from the soil solution composition at adequate K nutrition but that significant uncertainties remain when soil solution K is below 1 mM.     

Radioactivity concentrations of 40K, 134Cs, 137Cs, 90Sr, 241Am, 238Pu and 239+240Pu radionuclides in Jordanian soil samples

In November 2000, surface and core soil samples were collected from different regions of Jordan. The samples were analyzed by direct gamma spectrometry and combined radiochemical separation procedure to quantify (40)K, (134)Cs, (137)Cs, (90)Sr, (241)Am, (238)Pu and (239+240)Pu radioactivity. Concentrations (Bq.kg(-1) dry weight) have been observed to vary in the range 1.5-2.6 for (134)Cs, 2.8-11.4 for (90)Sr, and 0.13-0.48 for (241)Am, 0.016-0.062 for (238)Pu, 0.28-1.01 for (239+240)Pu and 155-543 for (40)K. The typical concentration of (137)Cs found in topsoils (0-2 cm) ranged in 7.5-576 Bq.kg(-1), dry weight. These values were greater than those observed in samples taken at greater depths (up to 32 cm). Activity ratios of (134)Cs/(137)Cs, (90)Sr/(137)Cs, (239+240)Pu/(137)Cs, (238)Pu/(137)Cs, (241)Am/(137)Cs, (239+240)Pu/(238)Pu and (241)Am /(238)Pu have mean values of 0.0049 (R=1), 0.29 (R=0.76), 0.41 (R=0.90), 0.39 (R=0.85), 0.41 (R=0.88), 7.72 (R=0.97) and 16.66 (R=0.98), respectively. The underlying concentrations were correlated and relatively higher than those reported in neighboring countries. One moss sample, as a biomonitor indicator, was measured and evaluated along with the soil samples. Its data showed higher concentrations of all measured radionuclides due to accumulations over years. The depth distribution of the fission product (137)Cs and the total deposition (Bq.m(-2)) were also studied in selected samples. Estimations of the annual effective dose equivalent due to (137)Cs-soil contamination showed values up to more than 200 microSv.     

Contamination of the southern Baltic Sea with 137Cs and 90Sr over the period 2000-2004

Changes of the (137)Cs activity concentrations in the southern Baltic Sea waters were investigated over the period 2000-2004 and distribution of the (90)Sr concentrations was determined in 2004. In the discriminated period further decrease of (137)Cs concentrations was observed. The average activity concentration of (137)Cs declined from 59.4Bq/m(3) in 2000 to 45.1Bq/m(3) in 2004. The greatest changes of (137)Cs activities occurred in 2003 as a consequence of the medium-size inflow of a saline waters from the North Sea. This inflow affected (137)Cs activities as well as its distribution in the Baltic Sea. Changes in (90)Sr activity concentrations proceeded at much slower rate. The average activity concentration of (90)Sr was equal to 8.7Bq/m(3) in 2004. The annual fluvial (137)Cs fluxes from the Vistula river were also estimated. In 2000, the (137)Cs load from Vistula was of an order of 0.15TBq/year, and in 2004 0.05TBq/year.     

Distribution and ratios of Cs and K in control and K-treated coconut trees at Bikini Island where nuclear test fallout occurred: effects and implications

Coconut trees growing on atolls of the Bikini Islands are on the margin of K deficiency because the concentration of exchangeable K in coral soil is very low, ranging from only 20 to 80 mg kg⁻¹. When provided with additional K, coconut trees absorb large quantities of K and this uptake of K significantly alters the patterns of distribution of ¹³⁷Cs within the plant. Following a single K fertilization event, mean total K in trunks of K-treated trees is 5.6 times greater than in trunks of control trees. In contrast, ¹³⁷Cs concentration in trunks of K-treated and control trees is statistically the same while ¹³⁷Cs is significantly lower in edible fruits of K-treated trees. Within one year after fertilization (one rainy season), K concentration in soil is back to naturally low concentrations. However, the tissue concentrations of K in treated trees stays very high internally in the trees for years while ¹³⁷Cs concentration in treated trees remains very low in all tree compartments except for the trunk. Potassium fertilization did not change soil Cs availability.     

Radioactivity in fungi in Slovenia,Yugoslavia, following the Chernobyl accident

Caesium (¹³⁷Cs and ¹³⁴Cs) concentrations in higher fungi (Basidiomycetes) from Slovenia, north-west Yugoslavia, are reported following the Chernobyl accident. Special attention was paid to the Cortinariaceae, already known as Cs accumulators. The highest levels were found in Cortinarius armillatus, C. traganus (both inedible species) and Rozites caperata. The median concentration of ^137,134Cs in R. caperata from over 40 sampling sites was about 22 kBq/kg dry weight. High levels were also found in Xerocomus badius and Laccaria amethystina.From the ¹³⁷Cs/¹³⁴Cs ratios, which reflect the depth of the mycelium and the excess ¹³⁷Cs from historic pre-Chernobyl fallout, it may be surmised that radiocaesium levels in certain species will probably increase further next year and subsequently as Cs migrates down the soil profile.In addition, ^110mAg was found at concentrations up to 500 Bq/kg dry weight in certain species known to be Ag accumulators, particularly Agaricaceae and Lycoperdaceae.     

Time-dependence of the radiocaesium contamination of roe deer: measurement and modelling

In spruce forest and peat bog, the migration of 137Cs from soil to plants, fungi, roe deer and consumers has been surveyed. In spruce forest the 137Cs activity concentration in roe deer decreases slowly with time and has superimposed periodic maxima in autumn which are correlated with the mushroom season. The decrease with time can be described by an effective half-life of 3.5 yr caused by a fraction of the 137Cs in the soil becoming unavailable for green grazing plants with time. The additional transfer of 137Cs into roe deer meat during the mushroom season depends on precipitation in July, August and September which also determines the yield of fungi in autumn. Our model confirms the assumption that fungi also have access to a fraction of the 137Cs in the soil which is unavailable for green plants. On peat bog the 137Cs activity concentration in roe deer is higher than in spruce forest and its effective half-life is about 17 yr, due to reversible binding of 137Cs to organic matter in the peat bog.     

Concentrations of 137Cs in lynx (Lynx lynx) in relation to prey choice

Concentrations of (137)Cs were determined in 747 lynxes killed in Norway during the period 1986-2001. Highly variable (137)Cs concentrations and aggregated transfer coefficient values were observed, probably caused by variable (137)Cs concentrations in prey and the lynx's extensive home ranges and roaming distances. Adult lynxes had higher (137)Cs concentrations than sub-adults, and lynxes killed in regions with extensive reindeer grazing areas were more contaminated than others. A model with (137)Cs deposition density, the year lynxes were killed, age, and extent of reindeer grazing area accounted for 50% of the variability in observed (137)Cs concentrations. The analyses were equivocal regarding the influence of stomach content on (137)Cs concentrations in lynx muscle, i.e., on the lynx's specialization in prey species. Gender was not significant. Information on caesium retention in lynx and better estimates of deposition densities in lynxes' home ranges are important for further elucidation of factors influencing (137)Cs contamination in lynxes.     

Correlations between potassium, rubidium and cesium ((133)Cs and (137)Cs) in sporocarps of Suillus variegatus in a Swedish boreal forest

An analysis of sporocarps of ectomycorrhizal fungi Suillus variegatus assessed whether cesium (¹³³Cs and ¹³⁷Cs) uptake was correlated with potassium (K) or rubidium (Rb) uptake. The question was whether intraspecific correlations of Rb, K and ¹³³Cs mass concentrations with ¹³⁷Cs activity concentrations in sporocarps were higher within, rather than among, different fungal species, and if genotypic origin of sporocarps within a population affected uptake and correlation. Sporocarps (n = 51) from a Swedish forest population affected by the fallout after the Chernobyl accident were studied. The concentrations were 31.9 ± 6.79 g kg⁻¹ for K (mean ± SD, dwt), 0.40 ± 0.09 g kg⁻¹ for Rb, 8.7 ± 4.36 mg kg⁻¹ for ¹³³Cs and 63.7 ± 24.2 kBq kg⁻¹ for ¹³⁷Cs. The mass concentrations of ¹³³Cs correlated with ¹³⁷Cs activity concentrations (r = 0.61). There was correlation between both ¹³³Cs concentrations (r = 0.75) and ¹³⁷Cs activity concentrations (r = 0.44) and Rb, but the ¹³⁷Cs/¹³³Cs isotopic ratio negatively correlated with Rb concentration. Concentrations of K and Rb were weakly correlated (r = 0.51). The ¹³³Cs mass concentrations, ¹³⁷Cs activity concentrations and ¹³⁷Cs/¹³³Cs isotopic ratios did not correlate with K concentrations. No differences between, within or, among genotypes in S. variegatus were found. This suggested the relationships between K, Rb, ¹³³Cs and ¹³⁷Cs in sporocarps of S. variegatus is similar to other fungal species.     

Soil-fungi transfer coefficients: Importance of the location of mycelium in soil and of the differential availability of radionuclides in soil fractions

Soil-fungus transfer coefficients are usually defined as the ratio between the content of the fruiting bodies and that of the soil. Since, however, the methodology of how to determine the soil content is not firmly established, there exist a variety of definitions in the literature. We analyzed the 137Cs, 90Sr, 40K, and 226Ra content of mushroom and soil samples from two pine-wood ecosystems in Spain. The location of the mycelium in the soil profiles of these ecosystems was determined by means of the ergosterol concentration. The results showed the mycelium to generally be localized in the surface layer of soil (0-5 cm). We also carried out a speciation procedure for this layer of soil to determine the different degrees of association of the radionuclides in the soil. The results led us to propose some variations to the traditional definition used in quantifying radionuclide transfer. With these modifications, we were able to analyze Cs-K competition in several species of mycorrhizal and saprophytic fungi.     

Radiocesium contamination behavior and its effect on potassium absorption in tropical or subtropical plants

The accumulation and long-term decline of radiocesium contamination in tropical plant species was studied through measurements of gamma-ray spectra from pomegranate (Punica granatum) and chili pepper (Capsicum fructescens) trees. The plants were originally grown at a (137)Cs contaminated site (where a radiological accident occurred in the city of Goiania, Brazil, in 1987), and transplanted to uncontaminated soil, so that the main source of contamination of the new leaves and fruits would be the fraction of the available radiocesium in the body of the plants. Measurements of (137)Cs and (40)K concentrations along the roots, main trunk, twigs, leaves and fruits before and after the transplant process of both plant species indicated a direct competition between Cs and K ions, suggesting that these elements could have a common accumulation mechanism. Cesium transfer factors from soil to pomegranate, green and red chili pepper fruits were evaluated as 0.4 +/- 0.1, 0.06 +/- 0.01 and 0.05 +/- 0.01, respectively. Biological half-life values due to (137)Cs translocation from the tree reservoir (BHL(T)) were calculated as 0.30 years for pomegranate, 0.12 years and 0.07 years for red and green peppers, respectively.