Derivation of 137Cs deposition density from measurements of 137Cs inventories in undisturbed soils

The 137Cs inventories in undisturbed soils were measured for 292 locations across the territory of Vietnam. The logarithmic inventory values were regressed against characteristics of sampling sites, such as geographical coordinates, annual rainfall and physico-chemical parameters of soil. The regression model containing latitude and annual rainfall as determinants could explain 76% of the variations in logarithmic inventory values across the territory. The model part was interpreted as the logarithmic 137Cs deposition density. At the 95% confidence level, 137Cs deposition density could be predicted by the model within +/- 7% relative uncertainty. The latitude mean 137Cs deposition density increases northward from 237 Bq m(-2) to 1097 Bq m(-2), while the corresponding values derived from the UNSCEAR (1969) global pattern are 300 Bq m(-2) and 600 Bq m(-2). High 137Cs inputs were found in high-rainfall areas in northern and central parts of the territory.     

Preliminary evaluation of (135)Cs/(137)Cs as a forensic tool for identifying source of radioactive contamination

Ratios of the fission products (135)Cs and (137)Cs were determined in soil and sediment samples contaminated from three different sources, to assess the use of (135)Cs/(137)Cs as an indicator of source of radioactive contamination. Soil samples from the Chernobyl exclusion zone were found to have to be heavily depleted in (135)Cs ((135)Cs/(137)Cs approximately 0.45), indicative of a high thermal neutron flux at the source. Sludge samples from a nuclear waste treatment pond were found to have a (135)Cs/(137)Cs ratio of approximately 1, whereas sediment collected downstream from a nuclear reactor was highly variable in both (137)Cs activity and (135)Cs/(137)Cs ratio. Comparison of these preliminary results of variability in radiocaesium isotope ratios with reports of Pu isotope ratios suggests (135)Cs/(137)Cs similarly varies with fuel and reactor conditions, and may be used to corroborate other methods of characterizing radioactive contamination.     

Behavior of 137Cs in soils of transitional bogs

Specific features of ¹³⁷Cs accumulation, transformation, and migration in humus-peaty and peaty-gley soils of transitional bogs are discussed with reference to the southwestern part of the Russian Federation, which was most heavily contaminated after the Chernobyl accident. The influence of physicochemical soil properties and concentrations of typomorphic elements on these processes is characterized. It is concluded that bog soils accumulate ¹³⁷Cs in the form of hardly movable compounds and, as a consequence, transitional bogs are transformed into critical ecosystems.     

Frequency distributions of 137Cs in fish and mammal populations

We collected fish and mammals in several radioactively contaminated locations in the Chornobyl Exclusion Zone and analyzed them for 137Cs content. Frequency distributions were built for populations of channel catfish, yellow-necked mice and bank voles. We combined our data with similar data from several other studies to demonstrate the relationship between the standard deviations and means of 137Cs of fish and mammal populations. The frequency distributions of 137Cs in populations of fish and mammals are not normal, as indicated by the strong relationship between standard deviation and mean. Distributions for mammals are more skewed than those for fish. Fish and mammals probably use their environments in fundamentally different ways. The highest concentrations and thus greatest risks are therefore confined to relatively few individuals in each population.     

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.     

Ecological half-life of 137Cs in lichens in an alpine region

About 17 years after the Chernobyl accident, lichen samples were collected in an alpine region in Austria (Bad Gastein), which was heavily contaminated by the Chernobyl fallout. Measured 137Cs activity concentrations in selected lichens (Cetraria islandica, Cetraria cucullata, and Cladonia arbuscula) ranged from 100 to 1100 Bq kg(-1) dry weight, depending on lichen species and sampling site. Ecological half-lives for 137Cs in different lichen samples, obtained by comparison with earlier measurements of the same lichen species at the same site, ranged from 2 to 6 years, with average values between 3 and 4 years. Comparison with earlier studies indicated that ecological half-lives hardly changed during the last 10 years, suggesting that ecological clearance mechanisms (e.g. washout or soil transfer) did not vary substantially at the selected sampling area.     

Precipitation scavenging of 7Be and 137Cs radionuclides in air

Atmospheric depositional fluxes of the naturally occurring 7Be of cosmogenic origin and 137Cs from fallout of the Chernobyl accident were measured over a 6-year period (January 1987-December 1992) at Thessaloniki, Greece (40 degrees 38'N, 22 degrees 58'E). Total precipitation accumulation during 1987-1992 varied between 33.7 cm and 65.2 cm, reflecting a relatively dry (precipitation-free) climate. The activity concentrations of 7Be and 137Cs in rainwater depended on the precipitation rate, being higher for low precipitation rates and lesser for high precipitation rates. 137Cs was removed by rain and snow more efficiently than 7Be. Snowfall was more efficient than rainfall in removing the radionuclides from the atmosphere. The annual bulk depositional fluxes of 7Be varied between 477 and 1133 Bq m(-2) y(-1) and this variability was attributed to the amount of precipitation and the variations of the atmospheric concentrations of 7Be. The annual bulk depositional fluxes of 137Cs showed a significant decrease over time from 1987 to 1992, resulting in a removal half-life of 1.33 years. The presence of 137Cs in air, and therefore in rainwater and snow, long after the Chernobyl accident (26 April 1986) was mainly due to the resuspension process. The normalized depositional fluxes of both radionuclides showed maximal values during the spring season where the maximum amount of precipitation occurred. The relatively high positive correlation between 7Be and 137Cs normalized depositional fluxes indicates that the scavenging process of local precipitation controlled the fluxes of both radionuclides. The dry depositional flux of 7Be was less than 9.37% of total (wet and dry) depositional flux. The fraction of dry-to-total depositional flux of 137Cs was much higher than that of 7Be, due to the resuspended soil.     

137Cs in marine samples from the Brazilian southeastern coastal region

The present work presents the results of ¹³⁷Cs concentration in seawater, fish and sediments samples collect in 11 sampling points, crossing the Brazilian Southeastern coastal region, from Vitória (ES) to Santos (SP), on a routine basis from 1997 to 2002. This monitoring program was carried out by the Instituto de Radioproteção e Dosimetria (IRD/CNEN/MCT), in cooperation with the Instituto de Estudos do Mar Almirante Paulo Moreira (IEAPM/Brazilian Navy), aiming at determining artificial radionuclides in marine samples. Additionally to the ¹³⁷Cs results, ⁹⁰Sr concentrations in fish samples from 1998 to 2002 are also reported.The ¹³⁷Cs in seawater follows a lognormal distribution, with a geometric mean of 1.8 Bq m^-3 and a geometric standard deviation of 1.4 (n=54), decay corrected to June/2002. For ¹³⁷Cs levels in fish samples a geometric mean of 0.19 Bq kg⁻¹ and a geometric standard deviation of 2.9 (n=39), decay corrected to June/2002, with a range of 0.03 to 1.7 Bq kg⁻¹, were obtained. Based on the ¹³⁷Cs mean concentration in fish as well as in seawater, a transfer factor of 1 × 10² was calculated, which is quite in agreement with the recommended value found in the Safety Report Serie 19.     

Accumulation of Chernobyl-derived 137Cs in bottom sediments of some Finnish lakes

The amount and vertical distribution of Chernobyl-derived 137Cs in the bottom sediments of some Finnish lakes were studied. Sediment and surface water samples were taken in 2000 and 2003 from 12 stations in nine lakes and the results were compared with those obtained in corresponding surveys carried out in 1969, 1978, 1988 and 1990. Each of the five deposition categories of Chernobyl fallout in Finland were represented. The depth profiles of 137Cs in the sediments showed considerable variety in the lakes studied. The peak values varied between 1.5 and 46 kBq kg(-1) dry wt. The size and shape of the peak did not always correlate with the amount of deposition in the area, but on the other hand, reflected differences in sedimentation processes in different lakes. In some of the lakes the peak still occurred in the uppermost (0-2 cm) sediment layer, but in an extreme case the peak occurred at a depth of 22-23 cm corresponding to a sedimentation rate of 16 mm year(-1) during the 14 years after the Chernobyl accident. The total amounts of 137Cs in sediments varied from 15 to 170 kBq m(-2) at the sampling stations studied. Since 1990, the amounts have continued to increase slightly in two lakes, but started to decrease in the other lakes. In most of the lakes, the total amounts of 137Cs in sediments were about 1.5-2 times higher than in local deposition. In two lakes, the ratio was below 1, but in one case 3.2. Compared with the total amounts of 137Cs at the same stations in the late 1960s and 1970s, the values were now at their highest, at about 60-fold. The most important factors affecting 137Cs values in sediments were the local amount of deposition and the type of the lake and the sediment, but in addition, there were a number of other factors to be considered.     

137Cs contamination in tea and yerba mate in South America

Gamma-ray spectra from more than 50 samples of food products available in stores of Buenos Aires city were measured using a germanium detector. Activity concentrations of 137Cs up to 10 Bq/kg were found in tea and yerba mate manufactured in Apóstoles, Argentina. Further measurements of tea leaves, yerba mate leaves and soils, all coming from a cultivated area in that region, also show the presence of 137Cs contamination. The results suggest that the area was fertilized with a product that originated in a region affected by the fallout from the Chernobyl nuclear plant accident.     

Mapping 137Cs deposition: data validation methods and data interpretation

The "Atlas of caesium deposition on Europe after the Chernobyl accident" was prepared within the framework of the Joint Study Project 6 (JSP6) of the collaborative programme on the consequences of the Chernobyl accident between the European Commission and the Ministries responsible for Chernobyl affairs in Belarus, Russia and Ukraine. The radiological data provided by scientific institutes and competent authorities of more than 30 European countries were integrated into an information platform. Data validation and intercomparison were therefore essential before the interpretation of the deposition with the help of isoline maps prepared with a geographic information system (GIS) could be done. The data validation was a two-step procedure: after performing a primary logical consistency check, other techniques based on spatial statistics were used to outline uncertain data. The purpose of this paper is to present these validation methods and to discuss the advantages and constraints of these techniques. Rather than trying to improve the techniques of spatial data analysis, suggestions are made on how an adaptation of the sampling information could improve the final result.     

Root uptake of 137Cs by natural and semi-natural grasses as a function of texture and moisture of soils

This work studies the dependence of 137Cs root uptake on the structure of landscape, especially on texture and moisture of soils, under natural conditions, on abandoned radiopolluted lands in Northern Ukraine. Researches were carried out on a wide range of landscape conditions, at various levels of 137Cs contamination (from 20 up to 5000 kBqm(-2)), with different types of soils (approx. 20 soil varieties), which differ in texture, granulometric composition, degrees of gleyization and water regime, and anthropogenic transformation. The results showed that transfer factor (TF) values of 137Cs differ 50 times for the natural grassy coenoses and 8 times for the semi-natural ones. The lowest 137Cs TF values were measured in the herbages of dry meadows at automorphous loamy soils, while the highest were observed in wetland meadows at organic soils. Finally, the correlation between 137Cs TF values and granulometric composition of soil was determined for both automorphic and hydromorphic mineral soils.     

The transfer of 137Cs and 90Sr from feed to rabbits

Radiological assessment of the impact of nuclear weapons testing on the local population in the Semipalatinsk Test Site (STS) requires comprehensive site-specific information on radionuclide behaviour in the environment. However, information on radionuclide behaviour in the conditions of the STS is rather sparse and, in particular, there are no data in the literature on parameters of radionuclide transfer from feed to rabbit products which have been identified as contributors to internal dose to the inhabitants. The transfer of (137)Cs and (90)Sr to rabbit meat was studied under laboratory conditions in a controlled experiment with 32 locally bred rabbits maintained in the Kazakh Agricultural Research Institute. The equilibrium transfer coefficients for (137)Cs and (90)Sr from feed to rabbit meat were estimated to be 0.4 d kg(-1) and 0.15 d kg(-1), respectively. The biological half-lives were estimated to be 0.1 d for (137)Cs and 0.14 d for (90)Sr. Whereas for (137)Cs the distribution in the body is relatively homogeneous, there are large differences between the organs and tissues for (90)Sr for which, as expected, the highest concentrations were found in bone.     

Ecological half-life of 137Cs in plants associated with a contaminated stream

Ecological half-life (Te) is a useful measure for studying the long-term decline of contaminants, such as radionuclides, in natural systems. The current investigation determined levels of radiocesium (137Cs) in two aquatic (Polygonum punctatum, Sagittaria latifolia) and three terrestrial (Alnus serrulata, Myrica cerifera, Salix nigra) plant species from a contaminated stream and floodplain on the U.S. Department of Energy's Savannah River Site. Current 137Cs levels in plants were used in conjunction with historical data to determine Te of 137Cs in each species. Median concentrations of 137Cs were highest in S. latifolia (0.84 Bq g(-1)) and lowest in M. cerifera (0.10 Bq g(-1)). Te's ranged from 4.85 yr in M. cerifera to 8.35 yr in S. nigra, both terrestrial species. Te's for all aquatic (6.30 yr) and all terrestrial (5.87) species combined were very similar. The Te's of the two aquatic primary producers (P. punctatum and S. latifolia) in the Steel Creek ecosystem were somewhat longer than Te values previously reported for some consumers from this ecosystem.     

Reconstruction of 137Cs signal in Cuba using 7Be as tracer of vertical transport processes in the atmosphere

Levels of 137Cs and 7Be in aerosols have been measured in the region of Cienfuegos (Cuba) during the period 1994-1998. 137Cs showed the same seasonal trend as 7Be and the monthly regimes of precipitation seemed to be responsible for the observed pattern. The 137Cs/7Be ratio obtained in Cienfuegos and Miami (FL) in this period was used to calibrate the long-term database of 137Cs concentrations recorded in Miami (250 km from Cienfuegos). The database was then employed to reconstruct the 137Cs monthly concentrations in Cienfuegos since 1957.     

Comparison of Pu and (137)Cs as tracers of soil and sediment transport in a terrestrial environment

Following atmospheric nuclear weapons testing in the 1950s and 1960s significant quantities of (137)Cs and (239+240)Pu were deposited worldwide. In recent decades, (137)Cs has been commonly used as a tracer of soil erosion and sedimentation, particularly in the Northern Hemisphere where atomic deposition was three times as great as in the Southern Hemisphere. The relatively short 30-year half-life of this isotope means that its sensitivity as a tracer is rapidly decreasing. In contrast, with half-lives of 24,110 and 6561 years, the sensitivity of the two plutonium isotopes remains essentially the same as when it was deposited. Here we use the technique of Accelerator Mass Spectrometry to demonstrate the potential of anthropogenic Pu as an alternative to (137)Cs as a tracer of soil transport in Australia. We measure an average (137)Cs/(239+240)Pu activity ratio of 27.3+/-1.5 and an average (240)Pu/(239)Pu atom ratio of 0.149+/-0.003, both slightly lower than the global average.     

Levels of 137Cs in muddy sediments on the seabed in the Bay of Cadiz (Spain). Part II. Model of vertical migration of (137)Cs

This second part of the study reports the development of a model to describe the vertical migration of the artificial radioisotope (137)Cs in the sediment column on the seabed of the Bay of Cadiz. The application of the model provides an overall picture of the process of sedimentation in the Inner Bay of Cadiz. The spatial distribution of the rate of sedimentation enables us to study the sources of sediments and the means by which the sediments have been transported. A method has been derived from the rate of sedimentation to perform the dating of the layers of sediment. The model describes the behaviour of (137)Cs in the area under study, taking into account the time of residence in the zones that are the source of accumulation, the origin of the sedimentary material, together with the diffusion of the radionuclide in the sediment of the seabed.     

A theoretical description of diffusion and migration of 137Cs in soil.

Careful measurements of activity concentrations of 137Cs in soil samples taken layer by layer in autumn of 1999 in Slovenia are confronted with a prediction based on the diffusion-convection equation with a boundary condition which--unlike the boundary conditions applied in the literature so far--conserves the deposited activity over time, except for the natural decay. It is shown that it is essential to consider the deposits from atmospheric nuclear weapons tests and the Chernobyl accident to arrive at a good fit to the measured data. The corresponding Green's function as well as the diffusion constant and migration speed based on the analysis are given.     

A comparison of three models of 137Cs transfer in forest ecosystems.

The predictions of three models of 137Cs transfer in forest ecosystems (FOA, LOGNAT and FORESTLAND) were compared. The scenario for the model-model comparison consisted of an acute dry deposition of 137Cs over a coniferous forest. The model predictions were subsequently compared (model-data comparison) with values derived from experimental data measured in forests of the Bryansk region in Russia that were contaminated by the Chernobyl accident and that have similar characteristics to the forests described in the scenario. The predictions of radiocaesium levels in the litter-soil layer, berries, needles, wood, whole tree and moose made with the models were in relatively good agreement with each other (within a factor of 1.4-2.9). The best agreement was observed for berries and moose and the worst for wood. There was also good agreement between the model predictions for the same variables and the experimental data (within a factor of 1.2 3.2). In this case, the best agreement was observed for the litter-soil layer and the worst for wood and the whole tree. Overall, at least for the studied scenario and for the first 10 years after deposition, any of the models can be used if the final aim is to estimate average concentrations in different forest components. The agreement between the model predictions worsens with time and there were differences in the form of the time dependencies predicted by the models, especially for wood. This may lead to larger differences between the model predictions and the experimental data for times beyond the period for which data were available for comparison (10 years after the deposition).