Radiocesium in muscle tissue of reindeer and pike from northern Sweden before and after the Chernobyl accident. A retrospective study on tissue samples from the Swedish Environmental Specimen Bank.

After the Chernobyl accident in April 1986, considerable deposition of radionuclides occurred regionally in eastern, central and northwestern Sweden. Locally, the fallout of radiocesium exceeded the remainder from atmospheric nuclear weapons tests by several magnitudes. Since the end of the 1960s samples of organs from various plant and animal species, annually collected at different localities, have been preserved in the Swedish Environmental Specimen Bank (ESB). In this work samples from the ESB have been used for retrospective studies of radioactive pollution. The activities of Cs-134 and Cs-137 in muscle tissues from reindeer, Rangifer tarandus, and pike, Esox lucius, preserved in the ESB, were measured. The samples were collected annually; the reindeer at three localities in northern Sweden and the pike at one of them. In material collected prior to the Chernobyl accident, the levels of Cs-137 were 57-180 Bq/kg in reindeer and 14-24 Bq/kg in pike, fresh weight basis. These levels relate to earlier nuclear bomb tests. A significant decrease was found in pike during the pre-Chernobyl period (1971-86). In post-Chernobyl samples the burden of Cs-137 varied from amounts equal to the former levels in the northernmost locality and up to 80 times higher for the maximum values in the southernmost locality. The highest value recorded was 18,425 Bq/kg in reindeer. The geographic variations in reindeer from Chernobyl fallout were in accordance with the pattern of deposition estimated by aircraft surveys performed in May 1986. The ratio between 'new' and 'old' radiocesium burdens in pike, caught in 1987, approached the corresponding ratio for reindeer grazing in the precipitation area of the lake; 33 and 19, respectively.     

Migration of radiocesium in two forest soils as obtained from field and column investigations.

Depth profiles of radiocesium were measured in a podsolic parabrown earth of a spruce stand and in a podsol of a pine stand up to 3 years after the Chernobyl accident. At the same sites undisturbed soil columns of 20 cm diameter and 40 cm length were taken, transferred to the laboratory and irrigated intermittently with synthetic rainwater containing initially a known amount of radiocesium. The resulting migration of radiocesium in the columns under unsaturated conditions was determined as a function of time up to 3 years with a scanner technique. The depth profiles of radiocesium observed in the field and in the columns were evaluated with a compartment model to obtain the residence half-times of this radionuclide in the various soil horizons. The field observations yielded a residence half-time in the organic layer of both soils of approximately 4-6 years for Chernobyl-derived cesium, and of 10-15 years for cesium from the global fallout of weapons testing. In the mineral soil (0-5 cm), under spruce the residence time of Chernobyl-derived cesium was 15 years, that of cesium from the global fallout (present in the soil since approximately 30 years) was 50 years. Under pine, the residence time in the mineral soil was 4 years for Chernobyl-derived cesium and 11 years for global fallout cesium. Obviously, in each layer of both soils cesium becomes less available for migration with time. The residence times of radiocesium evaluated from the column experiments were in good agreement with those obtained from the field observations. Due to the comparatively short duration of the column experiments, however, the long-term increase of the residence time of radiocesium in the soil was not yet unambiguously observable.     

Uptake of radiocesium by mushrooms

After the Chernobyl accident in April 1986 the 134Cs, 137Cs and 40K activity of mushrooms of different genera and their corresponding soils from woods located in the province of Umbria (Italy) was determined. The results indicated: a temporally increasing trend for 137Cs up to a "limit value" depending on local fallout in 1986; different cesium concentrations in various mushroom genera; and uptake of potassium from soil that did not appear to compete with cesium uptake. No reliable correlation can be inferred between the cesium content of the soil and those of 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.     

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].     

Radionuclide contamination of foods imported into Iraq following the Chernobyl nuclear reactor accident

Since early 1986, a monitoring program for radionuclides in imported foods has been carried out by the Iraqi Atomic Energy Commission. After the Chernobyl nuclear reactor accident in the Soviet Union, the program was expanded; our laboratory was officially designated by the Iraqi Government to measure radionuclide activity concentrations in foodstuff imported from countries known to be severely contaminated by Chernobyl radioactive fallout. Gamma-spectrometric analysis was used. Food items such as powdered milk, lamb meat, poultry, cereals and grains imported into Iraq before the Chernobyl accident did not contain any detectable fission products. However, all lamb meat, 81% of the lentil, 44% of the powdered milk and chick-pea, and 17% of the roast beef samples were contaminated with 137Cs or 134Cs and 137Cs. The highest 137Cs contamination levels found were 82, 147, 420, 6 and 4 Bq kg-1, respectively. Contamination by 134Cs was approximately 50% of the values given above.     

Migration of fallout radiocaesium in a grassland soil from 1986 to 2001. Part II: evaluation of the activity-depth profiles by transport models

The vertical migration of (134)Cs, deposited by the Chernobyl fallout (1986), and (137)Cs, deposited by the Chernobyl and the global fallout, in the soil of an undisturbed Bavarian grassland in Germany was investigated from 1986 to 2001. The activity-depth profiles of both isotopes at ten sampling dates were evaluated by the classical convection-dispersion equation and a random walk particle model. In both models, the apparent migration velocity v and the apparent dispersion coefficient D were assumed to be independent of time. However, optimized values of v and D were significantly different for the different locations sampled at different times. If nevertheless constant values of v and D were used, the simulated activity densities per soil layer were out of the range of the spatial variability of the observed activity densities determined in 2001. It is concluded that without further simultaneous investigations e.g. on bioturbation at the study site, migration parameters of radiocaesium determined by classical transport models based on convection and dispersion during the first years after the deposition of the activity cannot be used for predictive purposes.     

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.     

Geochemical landscape strategy in monitoring the areas contaminated by the Chernobyl radionuclides

The Chernobyl accident led to radionuclide contamination of vast areas that now need to be monitored; the development of a regional land use strategy is now needed. Landscape geochemistry enables us to structure, classify and map the environmental factors responsible for the redistribution of radionuclides (i.e. soil-forming rocks and soil properties, vegetation cover, types of ground water migration, and vertical and lateral geochemical barriers). Combined with land use information, regional geochemical landscape maps serve as the basis to map in toposequence conditions of mass migration and accumulation in natural and cultivated landscapes. Such mapping makes it easier to choose representative monitoring sites. This type of mapping is also helpful to interrelate and extrapolate the data already obtained on radionuclides' environmental migration for different groups of geochemical landscapes with similar types of contamination, migration and accumulation patterns. A geochemical landscape approach is demonstrated using the example of part of the Bryansk region (Russia), which is considerably contaminated with ¹³⁴Cs and ¹³⁷Cs.     

Iodine-129 and caesium-137 in Chernobyl contaminated soil and their chemical fractionation

Soil samples from areas in Belarus, Russia and Sweden contaminated by the Chernobyl accident were analysed for (129)I by radiochemical neutron activation analysis, as well as for 137Cs by gamma-spectrometry. The atomic ratio of (129)I/137Cs in the upper layer of the examined soil cores ranged from 0.10 to 0.30, with an average of 0.18, and no correlation between (129)I/137Cs ratio and the distance from Chernobyl reactor to sampling location was observed. It seems feasible to use the (129)I/137Cs ratio to reconstruct the deposition pattern of 131I in these areas. The association of (129)I and 137Cs in the Chernobyl soil and Irish Sea sediment was investigated by a sequential extraction method. Similar speciation of (129)I in the Chernobyl soil and Irish Sea sediment was found. Approximately 70% of (129)I is bound to oxides and organic matter, and 10-20% is in the readily available phase, while most of the 137Cs (73%) in Chernobyl soil remains in the extraction residue.     

Specific cesium activity in freshwater fish and the size effect.

The specific Cs-137 activity of muscle tissue of silver carp (Hypophthalmichthys molitrix) from the cooling pond of the Chernobyl nuclear power plant caught in 1987 and 1988 increased almost linearly with fish weight ("size effect") in contrast to liver tissue, whose specific activity remained independent of weight. A kinetic model for uptake and excretion was developed to describe the size effect in muscle tissue by introducing a weight-dependent Cs biological half-time to fish. Similar size effects of specific Cs-137 activity were also found for other species of fish from the cooling pond, but were primarily attributed to changes in feeding habits with increasing weight of fish rather than to metabolic changes, since the specific Cs-137 activity both of muscle and liver tissue increased with fish weight for those species in contrast to silver carp.     

Iodine-129 in soils from Northern Ukraine and the retrospective dosimetry of the iodine-131 exposure after the Chernobyl accident

Forty-eight soil profiles down to a depth of 40 cm were taken in Russia and Ukraine in 1995 and 1997, respectively, in order to investigate the feasibility of retrospective dosimetry of the 131I exposure after the Chernobyl accident via the long-lived 129I. The sampling sites covered areas almost not affected by fallout from the Chernobyl accident such as Moscow/Russia and the Zhitomir district in Ukraine as well as the highly contaminated Korosten and Narodici districts in Ukraine. 129I was analyzed by radiochemical neutron activation analysis (RNAA) and accelerator mass spectrometry (AMS). 127I was measured for some profiles by RNAA or ion chromatography (IC). The results for 127I demonstrated large differences in the capabilities of the soils to store iodine over long time spans. The depth profiles of 129I and of 137Cs showed large differences in the migration behavior between the two nuclides but also for each nuclide among the different sampling sites. Though it cannot be quantified how much 129I and 137Cs was lost out of the soil columns into deeper depths, the inventories in the columns were taken as proxies for the total inventories. For 129I, these inventories were at least three orders of magnitude higher than a pre-nuclear value of 0.084+/-0.017 mBq m(-2) derived from a soil profile taken in 1939 in Lutovinovo/Russia. From the samples from Moscow and Zhitomir, a pre-Chernobyl 129I inventory of (44+/-24) mBq m(-2) was determined, limiting the feasibility of 129I retrospective dosimetry to areas where the 129I inventories exceed 100 mBq m(-2). Higher average 129I inventories in the Korosten and Narodici districts of 130 and 848 mBq m(-2), respectively, allowed determination of the 129I fallout due to the Chernobyl accident. Based on the total 129I inventories and on literature data for the atomic ratio of 129I/131I=13.6+/-2.8 for the Chernobyl emissions and on aggregated dose coefficients for 131I, the thyroid exposure due to 131I after the Chernobyl accident was estimated for the inhabitants of four villages in the Korosten and of three villages in the Narodici districts. The limitations and uncertainties of the 129I retrospective dosimetry are discussed.     

Long-term decline of 137Cs concentration in honey in the second decade after the Chernobyl accident

In the years 2001-2004 the (137)Cs activity was investigated in a total of 336 samples of different varieties of honey harvested in the Liguria Region of Northern Italy. Our purpose was to define (a) residual radioactive contamination following the Chernobyl accident and (137)Cs long-term decline, (b) correlation between (137)Cs activity and different honey varieties, and (c) correlation between (137)Cs activity and the prevailing geomorphological configuration in the collection areas. The mean (137)Cs specific activity was 4.33+/-5.04 S.D. Bq/kg. Chestnut honey showed higher levels of radioactive contamination, which were ascribed to the extensive, superficial and deep, root apparatus of the tree. Honey samples from acidic argillite soils, which withhold radionuclides after deposition and slowly release them to plants, also showed higher (137)Cs activity. Long-term decline was calculated at 456 days, a value lower than those published from different food sources in the years following the accident. The rate of long-term decline decreases with time.     

Chernobyl fallout in the uppermost (0-3 cm) humus layer of forest soil in Finland, North East Russia and the Baltic countries in 2000--2003

The situation resulting from the Chernobyl fallout in 1987 was compared to that in 2000--2001 in Finland and NW Russia and that in 2003 in the Baltic countries. 786 humus (0-3 cm layer) samples were collected during 2000--2001 in the Barents Ecogeochemistry Project, and 177 samples in the Baltic countries in 2003. Nuclides emitting gamma-radiation in the 0-3 cm humus layer were measured by the Radiation and Nuclear Safety Authority-STUK in Finland. In 1987 the project area was classified by the European Commission into four different fallout classes. 137Cs inventory Bg/m2 levels measured in 2000--2003 were compared to the EU's class ranges. Fitting over the whole project area was implemented by generalizing the results for samples from the Baltic countries, for which Bq/m2 inventories could be calculated. A rough estimation was made by comparing the mass of organic matter and humus with 137Cs concentrations in these two areas. Changes in 137Cs concentration levels are illustrated in both thematic maps and tables. Radionuclide 137Cs concentrations (Bq/kg d.w.) were detected in the humus layer at all the 988 sampling sites. 134Cs was still present in 198 sites 15 years after the nuclear accident in Chernobyl. No other anthropogenic nuclides emitting gamma-radiation were detected, but low levels of 60Co, 125Sb and 154Eu isotopes were found in 14 sites. Fifteen years after the Chernobyl accident, the radioactive nuclide 137Cs was and still is the most significant fallout radionuclide in the environment and in food chains. The results show that the fallout can still be detected in the uppermost humus layer in North East Europe.     

137Cs availability for soil to understory transfer in different types of forest ecosystems

A quantitative analysis of 137Cs bioavailability in forest soils in the long term after the Chernobyl NPP accident based on a 3-year (1996-1998) investigation is presented. Five forest sites with different trees, composition and properties of soil were studied to identify factors determining radiocaesium transfer to different understory species. The following parameters were investigated: 137Cs activity concentrations and its speciation in various horizons of forest soil, accumulation of this radionuclide by different species of understory vegetation and distribution of root biomass in the soil profile. It has been shown that one decade after the deposition maximum 137Cs activity in soil of the experimental sites considered is located in different soil layers dependent on moisture regime, characteristics of litter and soil properties. A linear dependence between aggregated transfer factors for different species and groups of species of understory vegetation and exchangeable and available fractions of radiocaesium in soil was found. The vertical distribution of 137Cs activity, percentage of exchangeable radiocaesium in each horizon of litter and soil, as well as distribution of root systems (mycelia) over the soil profile are key factors governing variations in the availability of 137Cs for transfer to all forest understory components.     

Transfer of 137Cs from Chernobyl debris and nuclear weapons fallout to different Swedish population groups

Data from measurements on the body burden of ¹³⁴Cs, ¹³⁷Cs and ⁴⁰K in various Swedish populations between 1959 and 2001 has been compiled into a national database. The compilation is a co-operation between the Departments of Radiation Physics in Malmö and Göteborg, the National Radiation Protection Authority (SSI) and the Swedish Defense Research Agency (FOI). In a previous study the effective ecological half time and the associated effective dose to various Swedish populations due to internal contamination of ¹³⁴Cs and ¹³⁷Cs have been assessed using the database. In this study values of human body burden have been combined with data on the local and regional ground deposition of fallout from nuclear weapons tests (only ¹³⁷Cs) and Chernobyl debris (both ¹³⁴Cs and ¹³⁷Cs), which have enabled estimates of the radioecological transfer in the studied populations.The assessment of the database shows that the transfer of radiocesium from Chernobyl fallout to humans varies considerably between various populations in Sweden. In terms of committed effective dose over a 70 y period from internal contamination per unit activity deposition, the general (predominantly urban) Swedish population obtains 20-30 μSv/kBq m^− 2. Four categories of populations exhibit higher radioecological transfer than the general population; i.) reindeer herders (∼700 μSv/kBq m^− 2), ii.) hunters in the counties dominated by forest vegetation (∼100 μSv/kBq m^− 2), iii.) rural non-farming populations living in sub-arctic areas (40-150 μSv/kBq m^− 2), and iv.) farmers (∼50 μSv/kBq m^− 2). Two important factors determine the aggregate transfer from ground deposition to man; i.) dietary habits (intakes of foodstuff originating from natural and semi-natural ecosystems), and ii.) inclination to follow the recommended food restriction by the authorities. The transfer to the general population is considerably lower (∼a factor of 3) for the Chernobyl fallout than during the 1960s and 70s, which is partly explained by a higher awareness of the pathways of radiocaesium to man both by the public and by the regulating authorities, and by the time-pattern of the nuclear weapons fallout during the growth season in Sweden.     

Environmental radioactivity monitoring program in Iraq: outlook and results

Environmental monitoring studies have been started in Iraq during the 1970's as part of research projects carried out by the Health Physics Department. Nuclear Research Center, IAEC. These studies were concerned mainly with the determination of global fallout in rain water and the activity concentration of radionuclides in environmental samples. No fission products could be detected in rain water. However, soil and vegetation samples contained ¹³⁴Cs and ¹³⁷Cs. The activity concentration of those radionuclides were very low (10 Bq kg^‐1).

In 1981, the radioactivity monitoring program was enlarged due to the construction of two French made reactors: Tammuz 1 and Tammuz 2. An extensive radioactivity monitoring program around Tuwaitha site was instituted. It included exposure rate measurements as well as the determination of activity concentration of radionuclides in environmental samples such as: soil, grass, milk, vegetables and river water. Thus the radiological background was established before the commissioning of the two reactors. The results obtained had indicated that the average exposure rate was 7.0–0.8 μ R h,^‐1 and only few Bq kg^‐1 of ¹³⁷Cs were detected in some soil and vegetation samples.

At the beginning of 1986 a radioactivity in imported food monitoring program was established. This program proved to be very useful on the national level, since our laboratories were officially designated by the Iraqi government following the Chernobyl accident to measure the activity concentration of radionuclides in imported foods, where thousands of samples had been analyzed. The contamination levels in the vast majority of the samples were below the Iraqi derived intervention level of 370 Bq kg^‐1.

The Chernobyl accident had the greatest impact on the environmental radioactivity monitoring programs in Iraq. Almost all areas in Iraq were monitored for possible fallout debris contamination. It was found that the exposure rates had increased substantially, in some points up to eight times the background levels, and high activity concentrations of ¹³¹I,¹³⁴Cs and ¹³⁷Cs were detected in many environmental samples such as: soil, milk, meat, grass and grains, with lower concentrations of ⁹⁵Zr, ⁹⁵Nb, ¹⁰³Ru, ¹²⁵Sb, ¹⁴¹Ce and ¹⁴⁴Ce.     

Transport of fallout radiocesium in the soil by bioturbation: a random walk model and application to a forest soil with a high abundance of earthworms

It is well known that bioturbation can contribute significantly to the vertical transport of fallout radionuclides in grassland soils. To examine this effect also for a forest soil, activity-depth profiles of Chernobyl-derived 134Cs from a limed plot (soil, hapludalf under spruce) with a high abundance of earthworms (Lumbricus rubellus) in the Olu horizon (thickness=3.5 cm) were evaluated and compared with the corresponding depth profiles from an adjacent control plot. For this purpose, a random-walk based transport model was developed, which considers (i) the presence of an initial activity-depth distribution, (ii) the deposition history of radiocesium at the soil surface, (iii) individual diffusion/dispersion coefficients and convection rates for the different soil horizons, and (iv) mixing by bioturbation within one soil horizon. With this model, the observed 134Cs-depth distribution at the control site (no bioturbation) and at the limed site could be simulated quite satisfactorily. It is shown that the observed, substantial long-term enrichment of 134Cs in the bioturbation horizon can be modeled by an exceptionally effective diffusion process, combined with a partial reflection of the randomly moving particles at the two borders of the bioturbation zone. The present model predicts significantly longer residence times of radiocesium in the organic soil layer of the forest soil than obtained from a first-order compartment model, which does not consider bioturbation explicitly.     

Mobility of radiocesium in three distinct forest floors

The degree of mixing of organic matter with minerals in organic and hemi-organic horizons of forest soils largely differs between humus types. As clay minerals might control the mobility of radiocesium in these forest floor horizons, plant contamination could greatly vary with the kind of humus. We measured the mobility of radiocesium in the upper O, OAh and Ah horizons of three acid forest soils with three distinct humus types: eumoder, dysmoder and fibrimor. We used two different approaches: a physico-chemical test quantifying the radiocesium interception potential (RIP) and a biological assay simulating an experimental rhizosphere. The results show that the (137)Cs horizon-to-plant transfer is directly governed by RIP, and thus by frayed edge sites born by weathered micaceous minerals. The inverse relationship between RIP and organic matter content indicates that in the three sites investigated the mixing of organic residues with Cs-fixing minerals is a key process in 137Cs mobility. These Cs-fixing clay minerals indeed decrease in the sequence eumoder > dysmoder > fibrimor because they are more diluted in forest floor with less bioturbation. Our results suggest that humus type might be an important parameter in classifying forest soils with respect to their ability to transfer radiocesium to the above standing vegetation.     

Influence of soil acidification in southern Norway on the Cs exposure of moose?

The mean ¹³⁷Cs activity concentration in 278 liver samples of moose (Alces alces) from 16 municipalities located in different parts of Norway varied within the range 43-752 Bq kg^− 1 among the municipalities. In general the geographical variation corresponded to the fallout pattern produced by the Chernobyl accident. In three communities in the southernmost part of the country however the transfer factor, defined as the activity in moose liver divided by the corresponding level in surface soil, was 6.5 times higher on average than elsewhere in Norway. Possible reasons for this highly significant difference are discussed, and it is hypothesized that the apparently much higher plant uptake in the south may be related to extensive soil acidification in this area from transboundary pollution.