Chemical availability of 137Cs and 90Sr in undisturbed lysimeter soils maintained under controlled and close-to-real conditions

Chemical availability of 137Cs and 90Sr was determined in four undisturbed soils in a lysimeter study three and four years after deposition to the soil surface. The study was part of a larger project on radionuclide soil-plant interactions under well-defined conditions. The soil types were loam, silt loam, sandy loam and loamy sand, and were representatives of important European soil and climatic conditions. The lysimeters were installed in greenhouses with climatic and hydrological control, and were contaminated with 137Cs and 90Sr in an aerosol mixture simulating fallout from a nuclear accident. Soil samples were taken from several depths in each soil in 1997 and 1998 and the samples were sequentially extracted with H2O, NH4Ac, NH2OH.HCl, H2O2 and HNO3. Extractability of 137Cs decreased in the order: HNO3 > R-esidual > or = NH4Ac > H2O2 > or = NH2OH.HCl > or = H2O. More than 80% was found in the acid digestible or residual fractions, and 11-17% in labile fractions. Soil type differences were small. Extractability of 90Sr decreased in the order: NH4Ac > NH2OH.HCl > HNO3 > H2O2 approximately H2O. 31-58% was found in easily available fractions. Differences between soil types were quite small. The results suggest that availability of 137Cs for plant uptake and migration is low, whereas availability of 90Sr is rather high.     

Inventory and vertical migration of 90Sr fallout and 137Cs/90Sr ratio in Spanish mainland soils

In this paper the inventory of ⁹⁰Sr in 34 points distributed along the Spanish peninsular territory is presented. Obtained values range between 173 Bq/m² and 2047 Bq/m². From these data set and those ¹³⁷Cs data obtained in a previous work the ¹³⁷Cs/⁹⁰Sr activity ratio has been established, laying this value between 0.9 and 3.6. Also the migration depth of both radionuclides has been analysed obtaining for ¹³⁷Cs an average value 57% lower than that obtained for ⁹⁰Sr.Additionally, this paper presents the results obtained in 11 sampling points in which the activity vertical profile has been measured. These profiles have been analysed to state the behaviour of strontium in soils and after, by using a convective-diffusive model, the parameters of the model which governs the vertical migration of ⁹⁰Sr in the soil, v (apparent convection velocity) and D (apparent diffusion coefficient) have been evaluated. Mean values obtained are 0.20 cm/year and 3.67 cm²/year, respectively.     

Inventory and vertical migration of ¹³⁷Cs in Spanish mainland soils

In this study the total activity of ¹³⁷Cs deposited per unit area over the Spanish peninsular territory was analysed using a 150 × 150 km² mesh grid, with samples taken from 29 points. The deposited activities ranged between 251 and 6074 Bq/m². A linear relationship was obtained between these values and the mean annual rainfall at each sampling point which allowed a map to be drawn, using GIS software, which shows the distribution of total deposited ¹³⁷Cs activity across the Spanish mainland. At twelve of these sampling points the vertical migration profile of ¹³⁷Cs was obtained. These profiles are separated into two groups with different behaviour, one of which includes clay and loam soils and the other containing sandy soils. For both groups of profiles the parameters of the convective-diffusive model, which describes the vertical migration of ¹³⁷Cs in the soil, v (apparent convection velocity) and D (apparent diffusion coefficient) were calculated.     

Cs and K in fruiting bodies of different fungal species collected in a single forest in southern Poland

Fruiting bodies of fungi belonging to more than 70 species were collected within a few thousand square meter area of one forest during 2006 and 2007. The soil profile was collected to check the cumulative deposition of ¹³⁷Cs, which was relatively high, equal to 64 ± 2 kBq/m² (calculated for October 2006). The majority of this activity was in the first 6 cm. Fruitbodies were analyzed for radiocesium and ⁴⁰K by means of gamma-spectrometry. The highest ¹³⁷Cs activity was 54.1 ± 0.7 kBq/kg (dry weight) for a sample of Lactarius helvus collected in 2006. The results for 2006 were higher than those for 2007. In a few cases the traces of short-lived (T_1/2 = 2.06 a) ¹³⁴Cs were still found in samples. The importance of mycorrhizal fungi for radiocesium accumulation is confirmed. The differences in activity among the species are discussed in relation to observations and predictions from previous studies, where the change in relative accumulation between fruiting bodies of different species was at least partially explained by the differences in the depth of the mycelium localization in a litter/soil system. It is concluded that in some cases, such as Boletus edulis and Xerocomus badius, this prediction is fulfilled and therefore this explanation confirmed.     

Effect of liming on the behaviour of (90)Sr and (137)Cs in a lake ecosystem

Liming of lakes is considered one possible remedial action to reduce the accumulation of radionuclides into fish in the case of a radiological accident. These responses were tested in field conditions in a small acidified lake that was divided into two parts: one limed with CaCO₃ and the other half left as an unlimed control. The transfer of ⁹⁰Sr from water into fish decreased on average by 50% during the first year after liming. However, at the same time the ⁹⁰Sr concentration in water increased, reaching a maximum within 6 months after liming. Approximately 50% more ⁹⁰Sr was detected in water in the limed part of the lake than on control side during the first year. ⁹⁰Sr was most probably released from the sediment as the Ca concentration and pH of the water increased. As a result of these two processes, which counterbalanced each other (increased release of ⁹⁰Sr into water from sediment and decreased transfer of ⁹⁰Sr from water into fish), the ⁹⁰Sr concentration in fish did not notably differ between the limed and control sides of the lake. Liming may only be suitable as a remedial action if carried out immediately after a radiological accident, before significant amounts of radionuclides have been deposited in lake sediments. In the case of ¹³⁷Cs, the effect of liming was less pronounced. ¹³⁷Cs activity concentration in water increased in the first year by 20% and uptake by fish decreased by 20%.     

Determining floodplain sedimentation rates using Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia

Fallout ¹³⁷Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of ¹³⁷Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total ¹³⁷Cs inventories calculated from the detailed profile data. Information on the rates of ¹³⁷Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of ¹³⁷Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for ¹³⁷Cs being known and without having to assume that ¹³⁷Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total ¹³⁷Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, ¹³⁷Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites.     

Cs in a raised bog in central Sweden

The vertical distribution of ¹³⁷Cs activity in peat soil profiles and ¹³⁷Cs activity concentration in plants of various species was studied in samples collected at two sites on a raised bog in central Sweden. One site (open bog) was in an area with no trees and only a few sparsely growing plant species, while the other (low pine) was less than 100 m from the open bog site and had slowly growing Scots pine, a field layer dominated by some ericaceous plants and ground well-covered by plants. The plant samples were collected in 2004–2007 and were compared with samples collected in 1989 from the same open bog and low pine sites. Ground deposition of ¹³⁷Cs in 2005 was similar at both sites, 23?000 Bq m⁻². In the open bog peat profile it seems to be an upward transport of caesium since a clear peak of ¹³⁷Cs activity was found in the uppermost 1–4 cm of Sphagnum layers, whereas at the low pine site ¹³⁷Cs was mainly found in deeper (10–12 cm) layers. The migration rate was 0.57 cm yr⁻¹ at the open bog site and the migration centre of ¹³⁷Cs was at a depth of 10.7, while the rate at the low pine site was 0.78 cm yr⁻¹ and the migration centre was at 14.9 cm. Heather (Calluna vulgaris) was the plant species with the highest ¹³⁷Cs activity concentrations at both sites, 43.5 k Bq⁻¹ DM in 1989 decreasing to 20.4 in 2004–2007 on open bog and 22.3 k Bq kg⁻¹ DM in 1989 decreasing to 11.2 k Bq⁻¹ DM by the period 2004–2007 on the low pine site. ¹³⁷Cs transfer factors in plants varied between 0.88 and 1.35 on the open bog and between 0.48 and 0.69 m² kg⁻¹ DM at the low pine site.     

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.     

Accumulation of Cs in puddle sediments within urban ecosystem

The role of puddle sediments as a final depot of ¹³⁷Cs horizontal migration within the urban landscape is studied using the example of Ekaterinburg city, Russia. Radioactive contamination in the city appeared due to fallout after atmospheric testing of nuclear weapons and nuclear accidents. Contamination density of ¹³⁷Cs in the region was assessed from archive data to be about 5.1 kBq/m², of which the maximum activity concentration (<30 Bq/kg) is associated with the upper 15 cm soil layer. Results of the survey reported here indicate a mean ¹³⁷Cs activity concentration in puddle sediments of 80 Bq/kg, with a maximum value of 540 Bq/kg. It is estimated that horizontal migration has led to about a fourfold concentration of ¹³⁷Cs in puddle sediments.     

Plutonium, 137Cs and 90Sr in selected invertebrates from some areas around Chernobyl nuclear power plant

Results are presented for ¹³⁷Cs, ⁹⁰Sr and plutonium activity concentrations in more than 20 samples of terrestrial invertebrates, including species of beetles, ants, spiders and millipedes, collected in the highly contaminated area of the Chernobyl exclusion zone. The majority of samples were collected in Belarus, with some also collected in the Ukraine. Three other samples were collected in an area of lower contamination. Results show that seven samples exceed an activity concentration of 100 kBq/kg (ash weight - a.w.) for ¹³⁷Cs. The maximum activity concentration for this isotope was 1.52 ± 0.08 MBq/kg (a.w.) determined in ants (Formica cynerea). Seven results for ⁹⁰Sr exceeded 100 kBq/kg (a.w.), mostly for millipedes. Relatively high plutonium activity concentrations were found in some ants and earth-boring dung beetles. Analyses of activity ratios showed differences in transfer of radionuclides between species. To reveal the correlation structure of the multivariate data set, the Partial Least-Squares method (PLS) was used. Results of the PLS model suggest that high radiocesium activity concentrations in animal bodies can be expected mainly for relatively small creatures living on the litter surface. In contrast, high strontium activity concentrations can be expected for creatures which conduct their lives within litter, having mixed trophic habits and a moderate lifespan. No clear conclusions could be made for plutonium.     

Recent Cs deposition in sediments of Admiralty Bay, Antarctica

Cesium-137, radium-226 and lead-210 profiles of a 25 cm sediment core give an indication of recent changes in land-ocean interactions at a polar coastal environment (Admiralty Bay, King George Island, Antarctica). The linear sedimentation accumulation rate at the study site calculated from the unsupported ²¹⁰Pb profile was 6.7 mm/year from 1965 to 2005. A 3.5-fold increase in ¹³⁷Cs concentrations was observed in the top layer of this sediment core. This sharp increase seems to indicate a recent redistribution of fallout radionuclides previously deposited on soil, vegetation and snow. These results imply enhanced land-ocean interactions at this site likely as a result of climate change. Because our results are based on a single core, additional investigations are needed to confirm our observations.     

Concentrations of (137)Cs in summer pasture plants that reindeer feed on in the reindeer management area of Finland

Samples of summer pasture plants that reindeer feed on were collected in order to study ¹³⁷Cs concentrations in different plant species and in species nested in certain site types, and to study the regional distribution of ¹³⁷Cs in the Finnish reindeer management area. Plant species were categorized by the site types of mineral soil forest (xeric heath forest and mesic heath forest) and peatland. A third category called ’other plant species’ included plants with various site types, poorly determined species and species with poor statistics. The ¹³⁷Cs concentrations in different site types differed significantly. The mean ¹³⁷Cs concentrations of the whole reindeer management area in the xeric heath forest plant species was 44 ± 27 Bq/kg dw, in the mesic heath forest plant species 75 ± 59 Bq/kg dw and in the peatland plant species 219 ± 150 Bq/kg dw. The peatland species uptake ¹³⁷Cs more efficiently than plant species of mineral soil forests. A particularly efficient collector of ¹³⁷Cs was Trichophorum sp. It is suggested that Trichophorum sp. could be used as an indicator species for reindeer summer fodder plants. The highest concentrations of ¹³⁷Cs were found in Southern Lapland and the lowest in Northern Lapland. Today, the concentrations of ¹³⁷Cs in summer pasture plants that reindeer feed on in Finland are at such a level that there is no need to avoid any plant species. In the case of future nuclear fallout, reindeer grazing in peatlands would increase concentrations of ¹³⁷Cs in reindeer meat.     

The simulation of long-range transport of ¹³⁷Cs from East Asia to Japan in 2002 and 2006

To evaluate the quantities of ¹³⁷Cs from past nuclear tests being transported to and deposited in Japan by naturally-occurring phenomena, the authors developed long-range transport models for ¹³⁷Cs considering Asian dust. The simulation using these models backed the observed recent increase of ¹³⁷Cs deposition along the coast of the Sea of Japan in early spring. For the sake of public safety, it is vital to ascertain whether an increase of radioactive deposition is caused by natural phenomena or a nuclear accident. The observations in recent years have suggested that dust and soil containing ¹³⁷Cs is transported from the regions around Inner Mongolia to Japan by the wind. In this paper, using observation data from the early spring of 2002 and 2006, the authors have found good agreement between the simulations and the measurements. The simulations reproduced the entrainment of ¹³⁷Cs and subsequent transport to Japan caused by strong winds associated with low pressure areas around the Inner Mongolian grasslands. The most likely cause of high-level ¹³⁷Cs deposition over northern Japan during March 2002 was ¹³⁷Cs associated with particles transported at low-altitude (1 km) and subjected to precipitation on the 22nd to 24th.     

Vertical distributions of (99)Tc and the (99)Tc/(137)Cs activity ratio in the coastal water off Aomori, Japan

Using a sector-field ICP-MS the vertical distributions of the ⁹⁹Tc concentration and ⁹⁹Tc/¹³⁷Cs activity ratio were measured in the coastal waters off Aomori Prefecture, Japan, where a spent-nuclear-fuel reprocessing plant has begun test operation. The ⁹⁹Tc concentrations in surface water ranged from 1.8 to 2.4 mBq/m³, no greater than the estimated background level. Relatively high ⁹⁹Tc/¹³⁷Cs activity ratios (10-12 × 10⁻⁴) would be caused by the inflow of the high-⁹⁹Tc/¹³⁷Cs water mass from the Japan Sea. There is no observable contamination from the reprocessing plant in the investigated area. The ⁹⁹Tc concentration and the ⁹⁹Tc/¹³⁷Cs activity ratio in water column showed gradual decreases with depth. Our results implied that ⁹⁹Tc behaves in a more conservative manner than ¹³⁷Cs in marine environments.     

Radioactivity measurements in moss (Hypnum cupressiforme) and lichen (Cladonia rangiformis) samples collected from Marmara region of Turkey

The present study was conducted to compare the ¹³⁷Cs, ⁴⁰K, ²³²Th, and ²³⁸U activity concentrations in epigeic moss (Hypnum cupressiforme) and lichen (Cladonia rangiformis). The activity levels in 37 moss and 38 lichen samples collected from the Marmara region of Turkey were measured using a gamma spectrometer equipped with a high purity germanium (HPGe) detector. The activity concentrations of ¹³⁷Cs, ⁴⁰K, ²³²Th, and ²³⁸U in the moss samples were found to be in the range of 0.36-8.13, 17.1-181.1, 1.51-6.17, and 0.87-6.70 Bq kg⁻¹ respectively, while these values were below detection limit (BDL)-4.32, 16.6-240.0, 1.32-6.47, and BDL-3.57 Bq kg⁻¹ respectively in lichen. The average moss/lichen activity ratios of ¹³⁷Cs, ⁴⁰K, ²³²Th, and ²³⁸U were found to be 1.32 ± 0.57, 2.79 ± 1.67, 2.11 ± 0.82, and 2.19 ± 1.02, respectively. Very low ¹³⁷Cs concentrations were observed in moss and lichen samples compared to soil samples collected from the same locations in a previous study. Seasonal variations of the measured radionuclide activities were also examined in the three sampling stations.     

Inventories of Pu, Cs, and excess Pb in sediments from freshwater and brackish lakes in Rokkasho, Japan, adjacent to a spent nuclear fuel reprocessing plant

We investigated the vertical profiles of ^239+240Pu, ¹³⁷Cs, and excess ²¹⁰Pb (²¹⁰Pb_ex) in sediment core samples obtained from two freshwater lakes and two brackish lakes situated near the first commercial spent nuclear fuel reprocessing plant in Rokkasho, Japan, before the final test of the plant using actual spent nuclear fuel. The inventory of ^239+240Pu in those lakes was larger than that in soil in Rokkasho, which indicated the inflow of ^239+240Pu from the catchment area in addition to direct deposition on the lake surfaces. The ¹³⁷Cs inventory in sediments of the brackish lakes was lower than that in the soil, which showed that part of the ¹³⁷Cs was removed from the sediments by the brackish water or that it was not deposited into the sediments, because of the high solubility of Cs in brackish water. The ¹³⁷Cs inventory in sediments of the freshwater lakes was higher than that of the brackish lakes, and comparable with that in soil except for one core sample out of four. The ^239+240Pu/¹³⁷Cs ratio in freshwater lake sediments was higher than that in soil, and that indicated that part of the ¹³⁷Cs was lost from the sediments. The low inventory of ¹³⁷Cs may be attributable to competition for absorption sites in sediments with ammonium ions formed in the reducing environment which occurs from summer to fall in the sediments. Those data will be used as background data on the artificial radionuclides in the lakes to assess the effect of released radionuclides on their concentrations.     

Long-term dynamics of radioactive <Superscript>90</Superscript>Sr and <Superscript>137</Superscript>Cs contamination of small mammals in the Chernobyl zone

Between 1986 and 1994, a decrease in nonalimentary ⁹⁰Sr and ¹³⁷Cs intake and changes in the accessibility of radionuclides in the soil-plant link of their cycle resulted in a 10-to 100-fold decrease in their specific activity (SA) in the bodies of small mammals inhabiting the Chernobyl zone, and a similar decrease was observed in the radionuclide transition factor (TF) in the soil-animal chain. Between 1995 and 2005, no consistent increase or decrease in SA or TF could be revealed against the background of a combined effect of different physicochemical and ecological factors. It is suggested that subsequent changes in the level of radioactive contamination of small mammals will generally reflect only the dynamics of physical ⁹⁰Sr and ¹³⁷Cs decay, but, nevertheless, seasonal and local variations in this level will be significant.     

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.     

The Role of Floodplain Soils as a Barrier to Radionuclide Migration: An Example of the Techa–Iset' River System

The contents of ⁹⁰Sr and ¹³⁷Cs and the pattern of their redistribution in the soil and plant cover of floodplain ecosystems have been assessed. It is shown that the radionuclide distribution across the floodplain and along the river flow is determined by the formation of a barrier to their migration near the river channel, at which less mobile ¹³⁷Cs accumulates. The soil and plant cover of the central floodplain are enriched with ⁹⁰Sr. Differences in radionuclide migration in floodplain soils and their input into plants are determined by the relationship between the processes of their immobilization and migration with soil water.     

Cs, Pu concentrations and the Pu/Pu atom ratio in a sediment core from the sub-aqueous delta of Yangtze River estuary

A sediment core collected from the sub-aqueous delta of the Yangtze River estuary was subjected to analyses of ¹³⁷Cs and plutonium (Pu) isotopes. The ¹³⁷Cs was measured using γ-spectrometry at the laboratories at the Nanjing University and Pu isotopes were determined with Accelerator Mass Spectrometry (AMS), measurements made at the Australian National University. The results show considerable structure in the depth concentration profiles of the ¹³⁷Cs and ^239+240Pu. The shape of the vertical ¹³⁷Cs distribution in the sediment core was similar to that of the Pu. The maximum ¹³⁷Cs and ^239+240Pu concentrations were 16.21 ± 0.95 mBq/g and 0.716 ± 0.030 mBq/g, respectively, and appear at same depth. The average ²⁴⁰Pu/²³⁹Pu atom ratio was 0.238 ± 0.007 in the sediment core, slightly higher than the average global fallout value. The changes in the ²⁴⁰Pu/²³⁹Pu atom ratios in the sediment core indicate the presence of at least two different Pu sources, i.e., global fallout and another source, most likely close-in fallout from the Pacific Proving Grounds (PPG) in the Marshall Islands, and suggest the possibility that Pu isotopes are useful as a geochronological tool for coastal sediment studies. The ¹³⁷Cs and ^239+240Pu inventories were estimated to be 7100 ± 1200 Bq/m² and 407 ± 27 Bq/m², respectively. Approximately 40% of the ^239+240Pu inventory originated from the PPG close-in fallout and about 50% has derived from land-origin global fallout transported to the estuary by the river. This study confirms that AMS is a useful tool to measure ²⁴⁰Pu/²³⁹Pu atom ratio and can provide valuable information on sedimentary processes in the coastal environment.