Transfer and behaviour of 137Cs in two Finnish lakes and their catchments

The long-term behaviour of 137Cs was studied in two freshwater ecosystems in southern Finland in an area most loaded by the Chernobyl fallout in 1986. Samples were taken from water, sediments, aquatic plants and fish in the lakes and from soil, mushrooms and seed plants in the catchments. The activity concentrations of 137Cs in fish have remained at a relatively high level and decreased much more slowly in these two lakes than in other lakes studied by us. One reason for the continuously high concentrations in fish is evidently the prolonged stay of caesium at a relatively high level in the water of these lakes, which is associated with a slow sedimentation rate. The hydrographical properties of the lakes, i.e. the oligotrophic character associated with a deficiency of potassium in water and a low pH are other reasons for the effective uptake and long retention time of 137Cs in fish. The effect of humic substances on the uptake and delay of caesium in fish could not be proved clearly in this study. The swampy soil type of the catchment associated with a more oligotrophic status and lower pH of the water in Lake Siikaj?rvi explain at least partly the difference in activity concentrations and transfer of 137Cs between the two lakes studied. This refers to the higher transfer from the catchment to the lake and the higher uptake of 137Cs by fish and other biota in Lake Siikaj?rvi than in Lake Vehkaj?rvi. Perch and pike were more efficient accumulators of caesium than the best indicators among the aquatic plants. In the terrestrial environment, caesium was most effectively accumulated by mushrooms.     

Long-term trends in the uptake of radiocesium in Rozites caperatus

Measurements of (134)Cs and (137)Cs in Rozites caperatus from 1991 to 2001 showed differences in the uptake pattern of Chernobyl and fallout derived radiocesium over time. The effective half-life of Chernobyl derived (137)Cs was determined to 12.4 years, whereas fallout derived (137)Cs had an effective half-life of 9.8 years. However, the trend for Chernobyl derived (137)Cs was clearly not linear. An effective average half-life of 3.1 years was determined for Chernobyl derived (137)Cs in the period from 1991 to 1994. The corresponding ecological half-life was 3.4 years. In the period from 1994 to 2001 it is possible that the effective half-life was longer than the physical, which indicates that more Chernobyl cesium becomes available than disappears through radioactive decay. The difference may be due to depth distribution of radiocesium, i.e. fallout derived cesium have penetrated deeper than Chernobyl. The changes in the half-lives of Chernobyl derived radiocesium over time together with the half-life of the older fallout derived radiocesium may be valuable in predictions of future radiocesium concentrations in mushrooms and thereby of food chain transfer to man.     

Accumulation of radiocesium in wild mushrooms collected from a Japanese forest and cesium uptake by microorganisms isolated from the mushroom-growing soils

Mushrooms and soils samples collected from a sub-alpine forest of Mt. Fuji in Japan were measured for 137Cs and stable Cs. The ranges of 137Cs specific activities and stable Cs concentrations in the mushrooms were 291-7950 Bq kg(-1) dry weight and 4.69-58.1 mg kg(-1) dry weight, respectively. Both 137Cs specific activities and stable Cs concentrations in the mushrooms were higher than those in common agricultural plants. The 137Cs specific activities and stable Cs concentrations in the soils were 3.18-149 Bq kg(-1) dry weight and 0.618-2.18 mg kg(-1) dry weight, respectively. The appearance frequencies of filamentous actinomycetes and planktonic bacteria from the soils decreased according to increasing Cs contents in the medium. No relationship was observed between the appearance frequencies of those and the stable Cs concentrations in the soils. The filamentous actinomycetes from any soil sample could not grow in the presence of 25 mM Cs, although the planktonic bacteria from the soil samples could grow with up to 50 mM Cs in YM agar. In addition, the planktonic bacteria from approximately 70% of the soil samples could grow even in the presence of 100 mM Cs. Filamentous actinomycetes were more sensitive to Cs than planktonic bacteria. In in vitro experiments, Cs uptake by these strains of filamentous actinomycetes and planktonic bacteria was high in the presence of 5 mM CsCl and the strains accumulated Cs, the same as in mushrooms. Our results indicate that filamentous actinomycetes in the soils have higher sensitivity to Cs than planktonic bacteria, and several strains of filamentous actinomycetes have a high Cs accumulation in the presence of 5 mM Cs.     

Migration of fallout radiocaesium in a grassland soil from 1986 to 2001. Part I: activity-depth profiles of (134)Cs and (137)Cs

The temporal changes of the vertical distribution of (134)Cs (deposited by the Chernobyl fallout in 1986) and (137)Cs (deposited by the Chernobyl and the global fallout) in the soil were investigated at an undisturbed Bavarian grassland site in Germany. At ten sampling dates between 1986 and 2001, the activity density of (134)Cs and (137)Cs was determined in various soil layers down to 80 cm depth. In 2001, the small-scale spatial variability of the radiocaesium activity was determined by sampling five plots within 10 m(2) (coefficient of variation about 20% for the upper soil layers). Between 1987 and 1990, substantial changes of the activity-depth profiles were observed. The percentage depth distributions of (134)Cs and (137)Cs were rather similar. The 50%-depth of the accumulated activity increased from 2.4 cm in 1988 to 5.3 cm in 2001 for (134)Cs and from 2.7 to 5.8 cm for (137)Cs. This indicates that at the study site the migration data of Chernobyl-derived (137)Cs can be estimated by those of total (137)Cs. In the second part of this study, the activity-depth profiles will be evaluated by the convection-dispersion model [Schimmack, W, Feria Márquez, F. Migration of fallout radiocaesium in a grassland soil from 1986 to 2001. Part II: Evaluation of the activity-depth profiles by transport models. Sci Total Environ 2006-this issue].     

137Cs and relationships with major and trace elements in edible mushrooms from Mexico

137Cs and 40K specific activity together with major and trace elements were determined in soil samples and in different edible wild mushroom species collected from a seminatural temperate forest ecosystem located in the central part of the Mexican Volcanic Belt. The activity measurements were made using a gamma-ray spectrometer system with a high purity germanium (HpGe) detector. The major and trace elements were determined using emission spectrography and mass spectrometry, respectively. The aggregated transfer factors for 137Cs were estimated in 30 local mushroom species collected from 1993 to 1999. Differences as large as three orders of magnitude were observed. The contribution of mushrooms for the total 137Cs dietary intake by the local population was estimated to be 37%. Mushrooms also showed to be good accumulators for Rb, Cu, Cs and Se.     

Radiocaesium and natural gamma emitters in mushrooms collected in Spain

Mushrooms can accumulate heavy metals in general, including radionuclides found in the nature. However, little attention has been paid to the radioactive content of mushrooms collected in Spain and the dose for the population due to their ingestion. To address this, we analysed the contents of 137Cs, 40K, 226Ra and 7Be present in different species of mushrooms, according to their genus and nutritional mechanism. We observed that mycorrhizal mushrooms accumulate 137Cs more than saprophytes, and vice versa for 7Be. 40K and 226Ra are accumulated to the same degree by the two groups of mushrooms. We estimated the dose due to ingestion of mushrooms in Spain to be 2 microSv/year, and the contribution of 40K and 226Ra to be generally greater than that of 137Cs. The contribution of 137Cs to the dose was calculated by taking into account the results of an experiment carried out under the controlled laboratory conditions, which showed that approximately 98% of 134Cs was associated with the readily digestible fraction of the mushrooms.     

Arbuscular mycorrhizal fungi mediated uptake of 137Cs in leek and ryegrass

In a first experiment of soil contaminated with 137Cs, inoculation with a mixture of arbuscular mycorrhizae enhanced the uptake of 137Cs by leek under greenhouse conditions, while no effect on the uptake by ryegrass was observed. The mycorrhizal infection frequency in leek was independent of whether the 137Cs-contaminated soil was inoculated with mycorrhizal spores or not. The lack of mycorrhizae-mediated uptake of 137Cs in ryegrass could be due to the high root density, which was about four times that of leek, or due to a less well functioning mycorrhizal symbiosis than of leek. In a second experiment, ryegrass was grown for a period of four cuts. Additions of fungi enhanced 137Cs uptake of all harvests, improved dry weight production in the first cut, and also improved the mycorrhizal infection frequencies in the roots. No differences were obtained between the two fungal inoculums investigated with respect to biomass production or 137Cs uptake, but root colonization differed. We conclude that, under certain circumstances, mycorrhizae affect plant uptake of 137Cs. There may be a potential for selecting fungal strains that stimulate 137Cs accumulation in crops. The use of ryegrass seems to be rather ineffective for remediation of 137Cs-contaminated soil.     

Effect of industrial pollution on the distribution of 137Cs in soil and the soil-to-plant transfer in a pine forest in SW Finland

The objective of this study was to evaluate the effect of industrial pollution on the distribution of radiocaesium in soil and on its transfer from soil to plants. The study was started in September 2000 in four Scots pine stands located at distances of 0.5, 2, 4 and 8 km along a transect running SE from the Cu-Ni smelter at Harjavalta in SW Finland. Annual emissions from the smelter in 1990 were 80 t of Cu, 31 t of Ni and 9000 t of SO(2), and in 1999 these were 5.9, 0.8 and 3400 t, respectively. At each site, soil profiles were sampled with a corer, and samples were separated into litter (L), organic soil layer (O) and mineral soil layers (B, E). Mushrooms, lichens (Cladina spp. and Cetraria islandica), lingonberry (Vaccinium vitis-idaea) and crowberry (Empetrum nigrum) plants were collected at each site, except at a distance of 0.5 km, where only mushrooms were available. In the organic soil layer, 137Cs activity decreased from 8000 Bq/m(2) at a distance of 8 km from the smelter to 1500 Bq/m(2) at a distance of 0.5 km; in litter, 137Cs concentration increased from 6300 Bq/m(2) at 8 km to 14000 Bq/m(2) at 0.5 km. 137Cs activity concentration decreased significantly in plants, mushrooms and lichens as the pollution load increased. In lichens, 137Cs activity decreased from 910 Bq/kg at 8 km to 170 Bq/kg at 2 km, while in lingonberry it decreased from 1470 to 20 Bq/kg and in crowberry from 310 to 20 Bq/kg. Aggregated transfer factors for 137Cs decreased in a similar way in lingonberry from 7.6x10(-2) m(2)/kg at 8 km to 7.7x10(-4) m(2)/kg at 2 km and in crowberry from 1.6x10(-2) to 7.9x10(-4) m(2)/kg.     

The fate of 137Cs in coniferous forests following the application of wood-ash.

In the future, it may become common practice in Swedish forestry to recycle wood-ash, a waste product of the combustion of bio-fuel. As a consequence of the Chernobyl radioactive fallout in 1986, large areas of central Sweden were contaminated. Application of recycled wood-ash, originating from contaminated areas, to a previously uncontaminated forest, risks an increase in the concentration of radioactive 137Cs. We measured 137Cs radioactivity in different parts of coniferous forests in seven field experiments. Measurements of radioactivity were made 5-8 years after an application of wood-ash equivalent to 3000 kg ha(-1). The sites, in a north-south transect across Sweden, have a background radioactivity ranging from 0 to 40 kBq m(-2), the higher levels are mainly a result of the Chernobyl fall-out. Depending on its origin, the radioactivity of the applied wood-ash ranged from 0.0 to 4.8 kBq kg(-1), corresponding to 0.0-1.44 kBq m(-2). In autumn 1999, samples were taken from the soil, field vegetation, needles and twigs and the levels of 137Cs determined. In addition, soil samples were analysed for extractable K. The highest 137Cs concentration was found in the soil. At six of the seven sites there were no statistically significant effects of wood-ash application on 137Cs activity. This was despite the fact that the wood-ash had, in one case, added the same amount of radioactivity as the background. However, at one site with intermediate 137Cs deposition (10-20 kBq m(-2)), there was a statistically significant decrease in 137Cs radioactivity in the soil, needles and twigs from the plots treated with wood-ash. The decrease in radioactivity was partly due to the fact that one of the main constituents of wood-ash is K, which is antagonistic to 137Cs. Based on our results, it appears that application of wood-ash containing 137Cs does not necessarily increase the 137Cs radioactivity in plants and soil. However, some of the observed effects could be a result of the low number of replicates used in this study.     

Fractionation of caesium (Cs) in coniferous forest soil in central Sweden

Sequential extraction procedure (SEP) was applied for fractionation of Chernobyl fallout ¹³⁷Cs bound onto soils of a coniferous forest ecosystem located in central Sweden. Results of sequentially extracted ¹³⁷Cs fractions demonstrated that 8% (mean value) of the total deposited ¹³⁷Cs was water soluble (F1) and 13% was NH₄OAc extractable (F2). Oxidation of F2 residuals by H₂O₂ led to a release of 15% of soil-bound ¹³⁷Cs (F3). Acid digestion of F3 residuals showed a possibility of releasing an extra amount of soil-bound ¹³⁷Cs, 22% of the total soil ¹³⁷Cs inventory (F4). These two fractions (F3 and F4) include strongly bound ¹³⁷Cs that seems to require longer biodegradation processes by soil microflora and microfauna before becoming available for uptake by plants and fungi. More than 37% of the total soil ¹³⁷Cs inventory was bound onto soil residuals in a non-extractable form that includes slowly degradable organic matter and other soil residual compartments. The distribution coefficient (K_d) was rather low and shows an inverse relation with the increase of percentage of soil organic matter, which indicates a week binding of ¹³⁷Cs onto forest soil. In contrast, chemical fractionation of soil bound ¹³⁷Cs showed a substantial fraction of ¹³⁷Cs was strongly bound onto soil as organically bound ¹³⁷Cs. Apparently, the binding processes of radiocaesium onto forest soil seems to be time dependent.     

Accumulation of potassium, rubidium and caesium (Cs and Cs) in various fractions of soil and fungi in a Swedish forest

Radiocaesium (¹³⁷Cs) was widely deposited over large areas of forest in Sweden as a result of the Chernobyl accident in 1986 and many people in Sweden eat wild fungi and game obtained from these contaminated forests. In terms of radioisotope accumulation in the food chain, it is well known that fungal sporocarps efficiently accumulate radiocaesium (¹³⁷Cs), as well as the alkali metals potassium (K), rubidium (Rb) and caesium (Cs). The fungi then enhance uptake of these elements into host plants. This study compared the accumulation of these three alkali metals in bulk soil, rhizosphere, soil-root interface, fungal mycelium and sporocarps of mycorrhizal fungi in a Swedish forest. The soil-root interface was found to be distinctly enriched in K and Rb compared with the bulk soil. Potassium concentrations increased in the order: bulk soil < rhizosphere < fungal mycelium < soil-root interface < fungal sporocarps; and Rb concentration in the order: bulk soil < rhizosphere < soil-root interface < fungal mycelium < fungal sporocarps. Caesium was more or less evenly distributed within the bulk soil, rhizosphere and soil-root interface fractions, but was actively accumulated by fungi. Fungi showed a greater preference for Rb and K than Cs, so the uptake of ¹³⁷Cs could be prevented by providing additional Rb or K at contaminated sites. The levels of K, Rb, and Cs found in sporocarps were at least one order of magnitude higher than those in fungal mycelium. These results provide new insights into the use of transfer factors or concentration ratios. The final step, the transfer of alkali metals from fungal mycelium to sporocarps, raised some specific questions about possible mechanisms.     

Caesium-137 migration in Hungarian soils

Distribution of 137Cs activity concentration has been measured in soils from 19 Hungarian counties. The levels of soil contamination in Hungary after the Chernobyl fallout are sufficient to study the vertical distribution of the 137Cs under natural conditions. Samples were taken layer by layer on plain, grassy and uncultivated fields down to a depth of 20 cm. The results show that radiocaesium migrates very slowly in the soils investigated. The 137Cs concentration peaks in almost all of the soils remain in the top 5 cm layer, but the distribution patterns are different. Variations in diffusion, sorption-desorption, and complexing processes, plant uptake and plant- and animal-originated mechanical changes result in the formation of site-specific radionuclide distribution profiles. On the basis of the experimental data a model has been developed for the long-term prediction of the 137Cs migration. By application of an applied diffusion-convection model the results can be well fitted, the initial deposition can be calculated and the data can be used for the long-term prediction of the 137Cs distribution profile.     

Upward mobilization of 137Cs in surface soils of Chamaecyparis obtusa Sieb. et Zucc. (hinoki) plantation in Japan

The use of 137Cs has recently been adopted to estimate erosion in hinoki plantations in Japan. However, there have been several reports of the upward mobilization of 137Cs in forest humus layers. In this study, the vertical distribution of 137Cs within the soil profile was measured in a hinoki plantation. In order to confirm the upward migration of 137Cs from mineral soil to fresh surface litter and to identify mechanisms of the transfer, changes in 137Cs specific activity in the contents of litterbags were examined in a hinoki plantation. A controlled laboratory experiment was also conducted to assess the effect of microbial activity on the upward migration of 137Cs. As a result, the higher 137Cs activities in the surface organic layer of a hinoki plantation than in fresh litter and the increasing 137Cs total content of litterbags with time demonstrated the upward mobilization of 137Cs from mineral soil to the surface organic layer. Physical movement of soil particles by raindrop splash was considered an important process in 137Cs upward migration. The results of our laboratory experiment indicate an influence from soil microbial activity on the upward mobilization of 137Cs. Thus, upward migration of 137Cs and constant litter removal by runoff may induce 137Cs loss from steep forested catchments and underestimation of the 137Cs inventory leading to the overestimation of soil redistribution rates.     

Dynamic behaviour of 137Cs contamination in trees of the Briansk region, Russia

Seven trees were felled in the Briansk region in 1997. The trees were sectioned for sampling, both at different heights and according to year rings, and samples were analysed for content of 137Cs. In general, the specific activity of 137Cs was much higher in the fresh parts of the three (needles, leaves and twigs) than in the core wood. The year ring study showed that 137Cs had penetrated deeply in to the trunk, and no peak was detectable in the year ring corresponding to the Chernobyl accident in 1986. The specific activity in the trunk wood had a maximum at the height corresponding to the growth years at approximately 1986. Neutron activation analysis was used to analyse for stable Cs. The results showed that the relationship between concentrations of 137Cs and stable caesium is much higher in the newer parts of growing trees than in the older parts. Together with a tendency of inward migration this leads to a preliminary conclusion that the 137Cs activity will continue to accumulate in the core wood.     

Measurements of long-term external and internal radiation exposure of inhabitants of some villages of the Bryansk region of Russia after the Chernobyl accident

A Nordic-Soviet programme was initiated in 1990 to evaluate the external and internal radiation exposure of the inhabitants of several villages in the Bryansk region of Russia. This area was one of the number of areas particularly affected by the nuclear accident at the Chernobyl Nuclear Power Plant in 1986. Measurements were carried out yearly until 1998 and after that more irregularly; in 2000, 2006 and 2008 respectively. The effective dose estimates were based on individual thermoluminescent dosemeters and on in vivo measurements of the whole body content of ¹³⁷Cs (and ¹³⁴Cs during the first years of the programme). The decrease in total effective dose during the almost 2 decade follow-up was due to a continuous decrease in the dominating external exposure and a less decreasing but highly variable exposure from internal irradiation. In 2008, the observed average effective dose (i.e. the sum of external and internal exposure) from Chernobyl ¹³⁷Cs to the residents was estimated to be 0.3 mSv y⁻¹. This corresponds to 8% of the estimated annual dose in 1990 and to 1% of the estimated annual dose in 1986. As a mean for the population group and for the period of the present study (2006-2008), the average yearly effective dose from Chernobyl cesium was comparable to the absorbed dose obtained annually from external exposure to cosmic radiation plus internal exposure to naturally occurring radionuclides in the human body. Our data indicate that the effective dose from internal exposure is becoming increasingly important as the body burdens of Chernobyl ¹³⁷Cs are decreasing more slowly than the external exposure. However, over the years there have been large individual variations in both the external and internal effective doses, as well as differences between the villages investigated. These variations and differences are presented and discussed in this paper.     

Removal of radioactive iodine and cesium in water purification processes after an explosion at a nuclear power plant due to the Great East Japan Earthquake

The presence of radionuclides at five water purification plants was investigated after an explosion at a nuclear power plant hit by the Great East Japan Earthquake on 11 March 2011. Radioactive iodine (¹³¹I) and cesium (¹³⁴Cs and ¹³⁷Cs) were detected in raw water in Fukushima and neighboring prefectures. ¹³¹I was not removed by coagulation-flocculation-sedimentation. ¹³¹I was removed by granular activated carbon (GAC) and powdered activated carbon (PAC) at a level of about 30%-40%, although ¹³¹I was not removed in some cases. This was also confirmed by laboratory-scale experiments using PAC. The removal percentages of ¹³¹I in river and pond waters by 25 mg dry/L of PAC increased from 36% to 59% and from 41% to 48%, respectively, with chlorine dosing before PAC. ¹³⁴Cs and ¹³⁷Cs were effectively removed by coagulation at both a water purification plant and in laboratory-scale experiments when turbidity was relatively high. In contrast, ¹³⁴Cs and ¹³⁷Cs in pond water with low turbidity were not removed by coagulation. This was because ¹³⁴Cs and ¹³⁷Cs in river water were present mainly in particulate form, while in pond water they were present mainly as cesium ions (¹³⁴Cs⁺ and ¹³⁷Cs⁺). However, the removal of ¹³⁴Cs and ¹³⁷Cs in pond water by coagulation increased markedly when ¹³⁴Cs and ¹³⁷Cs were mixed with sediment 24 h before coagulation.     

137Cs loss via soil erosion from a mountainous headwater catchment in central Japan

Eroded sediment and coarse organic material were sampled for a year at the outlet of the study catchment in central Japan to investigate characteristics of 137Cs loss and to quantify erosional 137Cs loss in a forested headwater catchment. Results showed that loss of both eroded sediment and 137Cs varied markedly according to the magnitude of rainfall events. About 90% of the total sediment delivery and the total 137Cs loss was associated with only two storm rainfall events. The significant contribution of high-magnitude-low-frequency storm events to 137Cs loss from the catchment was emphasized. To quantify the contribution of erosional 137Cs loss to 137Cs cycling, the current mean 137Cs inventory of the study catchment was estimated from direct measurements of 137Cs in soil cores collected from 27 points. The input of 137Cs through litterfall to the soil was estimated from monitoring the annual litterfall of the study catchment. The present 137Cs fallout input was estimated from published 137Cs fallout data. Consequently, the loss of 137Cs associated with eroded sediment was estimated to represent 0.013% of the 137Cs inventory of the study catchment, which is comparable to the input through litterfall. The equivalent value for 137Cs runoff with coarse organic material was estimated as 0.0003%. Therefore, the effect of 137Cs loss in association with coarse organic material on estimates of erosion rate obtained by measuring 137Cs inventories in soil core samples was inferred to be negligible in Japanese cypress plantations. Results confirm the applicability of 137Cs measurements to estimate erosion rates in other relatively stable forested areas.     

Transfer of 137Cs and stable Cs from soil to potato in agricultural fields.

The concentrations of 137Cs, stable Cs and K were measured in soils and potatoes collected from 26 agricultural fields in Aomori, Japan and soil-to-potato transfer factors of 137Cs and stable Cs were determined. The concentrations of 137Cs derived from fallout deposition and stable Cs in soils were 1-37 Bq kg-1 and 1-11 mg kg-1, respectively. The isotopes, 137Cs and stable Cs, were homogeneously mixed in the rooting zone in the upper 20 cm of soil in agricultural fields. The concentrations of 137Cs and stable Cs in potatoes were 50-2000 mBq kg-1 dry wt. and 0.004-0.13 mg kg-1 dry wt., respectively. The soil-to-potato transfer factor of 137Cs was in the range of 0.0037-0.16, which was higher than that of stable Cs of 0.00052-0.080. The transfer factors of 137Cs and stable Cs were correlated and the geometric mean of 137Cs was 0.030, which was four times higher than that of stable Cs at 0.0075. This implied that artificially added 137Cs is more mobile and more easily absorbed by plants than stable Cs in the soil. The concentration of K in potatoes showed a relatively constant value, independent of that in the soil. The transfer factors of both 137Cs and stable Cs decreased with increasing K concentration in the soil, which was mainly supplied as fertilizers to the fields. This suggests that the transfer of both 137Cs and stable Cs from soil to potato was affected by the presence of K in the soil. However, the transfer factors of 137Cs and stable Cs were independent of the amount of organic materials in soils.     

Mapping of 137Cs deposition over eastern France 16 years after the Chernobyl accident

We observed the relationship between present-day 137Cs surface activity and the rainfall in May 1986 to establish a relevant map of 137Cs deposition over eastern France. This study was performed in an area of the lower Rh?ne valley where clayey soils are assumed to trap caesium efficiently. Based on the rainwater/airborne activity ratio deduced from this relationship, we verified that present-day activities, measured in clayey soils of this type, are relatively representative of the initial depositions. The interlocked contaminated areas of the resulting map can be related to rainfall occurrences, as is the case for all countries affected by the Chernobyl fallout. This map can be reasonably compared with those obtained for countries bordering France in terms of both activity levels and extent of homogeneous activity areas. Lastly, we demonstrate that it would not be possible to produce a coherent map of initial fallout by extending the campaign over the whole of the eastern territory based on present-day soil activity measurements alone. Hence, only the relationship between 137Cs deposition and the rainfall of the first week of May 1986 can be used to construct a map depicting the Chernobyl fallout over eastern France.