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.     

Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth > 2000 m) and analysed for ^239,240Pu and ¹³⁷Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity — depth profiles of ²¹⁰Pb, together with ¹⁴C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess ²¹⁰Pb inventory was used to normalize ^239,240Pu and ¹³⁷Cs inventories for variable sediment fluxes. The ^239,240Pu/²¹⁰Pb_xs ratio was uniform across the entire sea, with a mean value of 1.24 × 10^− 3, indicating homogeneous fallout of ^239,240Pu. The ¹³⁷Cs/²¹⁰Pb_xs ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of ^239,240Pu/¹³⁷Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of ^239,240Pu in the water column and major sedimentation of ¹³⁷Cs in the eastern basin. Although areas with water depths of > 2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the ^239,240Pu and 0.95% of the ¹³⁷Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments.     

Specific activity and activity ratios of radionuclides in soil collected about 20 km from the Fukushima Daiichi Nuclear Power Plant: Radionuclide release to the south and southwest

Soil samples at different depths (0-2, 5-7 and 10-12 cm) were collected from J Village, about 20 km south of Fukushima Daiichi Nuclear Power Plant (FNPP) to determine their radionuclide specific activities and activity ratios. The concentrations and activity ratios of ¹³¹I, ^{134, 136, 137}Cs and ^129mTe were obtained, but only trace amounts of ⁹⁵Nb, ^110mAg and ¹⁴⁰La were detected which were too low to provide accurate concentrations. Radionuclides such as ⁹⁵Zr, ^{103, 106}Ru and ¹⁴⁰Ba that were found in Chernobyl fallout, were not found in these soil samples. This suggests that noble gasses and volatile radionuclides predominated in the releases from FNPP to the terrestrial environment. The average activity ratios of ¹³¹I/¹³⁷Cs, ¹³⁴Cs/¹³⁷Cs, ¹³⁶Cs/¹³⁷Cs and ^129mTe/¹³⁷Cs were 55, 0.90, 0.22 and 4.0 (corrected to March 11, 2011) in the 0-2 cm soil samples of April 20 and 28, 2011.     

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].     

The distribution and transport of Sellafield derived 137 Cs and 241 Am to western Irish Sea sediments

Sellafield derived (137)Cs and (241)Am were analysed in surficial sediments at 23 sites in the western Irish Sea. Concentrations varied between 3-175 Bq (137)Cs/kg and 1-147 Bq (241)Am/kg. There are two distinct basins in the western Irish Sea separated by an area of restricted depth and this bathymetry is reflected in the radionuclide concentrations. Highest concentrations were found in the northerly samples and substantially lower concentrations further south. This pattern of distribution can be explained by the predominantly northerly residual flow and the existence of seasonal stratification in this area of weak tides. (137)Cs/(241)Am ratios were also highest in the northern basin, and it is suggested that this is caused by differences in the mechanisms of transport of the two elements. The direct physical migration of contaminated particles from the eastern Irish Sea is the dominant transport mechanism in the north of the study area, whereas transport in the dissolved phase is most important to the southern region. Concentrations of both elements were best correlated with the percentage <15 microm particulate fraction suggesting that particles within this range are most important for direct transport and scavenging from the soluble phase.     

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.     

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.     

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.     

GIS supported calculations of (137)Cs deposition in Sweden based on precipitation data

It is of interest to know the spatial variation and the amount of (137)Cs e.g. in case of an accident with a radioactive discharge. In this study, the spatial distribution of the quarterly (137)Cs deposition over Sweden due to nuclear weapons fallout (NWF) during the period 1962-1966 was determined by relating the measured deposition density at a reference site to the amount of precipitation. Measured quarterly values of (137)Cs deposition density per unit precipitation at three reference sites and quarterly precipitation at 62 weather stations distributed over Sweden were used in the calculations. The reference sites were assumed to represent areas with different quarterly mean precipitation. The extent of these areas was determined from the distribution of the mean measured precipitation between 1961 and 1990 and varied according to seasonal variations in the mean precipitation pattern. Deposition maps were created by interpolation within a geographical information system (GIS). Both integrated (total) and cumulative (decay corrected) deposition densities were calculated. The lowest levels of NWF (137)Cs deposition density were noted in north-eastern and eastern parts of Sweden and the highest levels in the western parts of Sweden. Furthermore the deposition density of (137)Cs, resulting from the Chernobyl accident was determined for an area in western Sweden based on precipitation data. The highest levels of Chernobyl (137)Cs in western Sweden were found in the western parts of the area along the coast and the lowest in the east. The sum of the deposition densities from NWF and Chernobyl in western Sweden was then compared to the total activity measured in soil samples at 27 locations. Comparisons between the predicted values of this study show a good agreement with measured values and other studies.     

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.     

Reconstructing historical radionuclide concentrations along the east coast of Ireland using a compartmental model

A mathematical model is presented that simulates the annually averaged transport of radionuclides, originating from the BNFL reprocessing plant at Sellafield, throughout the Irish Sea. The model, CUMBRIA77, represents the processes of radionuclide transport and dispersion in the marine environment and allows predictions of radionuclide concentration in various environmental media, including biota, to be made throughout the whole of the Irish Sea. In this paper we describe the use of the model to reconstruct the historical activity concentrations of 137Cs and 239+240Pu in a variety of environmental media in the western Irish Sea and along the Irish east coast back to 1950. This reconstruction exercise is of interest because only limited measurements of 137Cs and 239+240Pu activity are available prior to the 1980s. The predictions were compared to the available measured data to validate their accuracy. The results of the reconstruction indicate that activity concentrations of 137Cs in the western Irish Sea follow a similar, though slightly delayed and smoothed, profile to the discharges from the Sellafield site, with concentrations at the time of peak discharge (the mid-1970s) being around an order of magnitude higher than those measured in the 1980s and 1990s. By contrast, the concentrations of 239+240Pu at the time of peak discharges were similar to those presently measured. These differences reflect the distinct marine chemistries of the two nuclides, in particular the higher propensity of plutonium to bind to sediments leading to extended transport times. Despite these differences in behaviour the doses to Irish seafood consumers from 137Cs remain significantly higher than those from 239+240Pu.     

Levels and trends of radioactive contaminants in the Greenland environment

Levels of radioactive contaminants in various Greenland environments have been assessed during 1999-2001. The source of 137Cs, 90Sr and (239,240)Pu in terrestrial and fresh water environments is mainly global fallout. In addition, the Chernobyl accident gave a small contribution of 137Cs. Reindeer and lamb contain the largest observed 137Cs concentrations in the terrestrial environment--up to 80 Bq kg(-1) fresh weight have been observed in reindeer. Due to special environmental conditions, 137Cs is transferred to landlocked Arctic char with extremely high efficiency in South Greenland leading to concentrations up to 100 Bq kg(-1) fresh weight. In these cases very long ecological half-lives are seen. Concentrations of 99Tc, 137Cs and 90Sr in seawater and in marine biota decrease in the order North-East Greenland and the coastal East Greenland current > South-West Greenland > Central West Greenland and North-West Greenland > Irmiger Sea-Faroe Islands. The general large-scale oceanic circulation combined with European coastal discharges and previous contamination of the Arctic Ocean causes this. As the same tendency is seen for the persistent organic pollutants (POPs) DDT and PCB in marine biota, it is suggested that long-distance oceanic transport by coastal currents is a significant pathway also for POPs in the Greenland marine environment. The peak 99Tc discharge from Sellafield 1994-1995 has only been slightly visible in the present survey year 2000. The concentrations are expected to increase in the future, especially in East Greenland. The Bylot Sound at the Thule Airbase (Pituffik) in North-West Greenland was contaminated with plutonium and enriched uranium in a weapons accident in 1968. Biological activity has mixed accident plutonium efficiently into the new sediments resulting in continued high surface sediment concentrations three decades after the accident. Transfer of plutonium to benthic biota is low--and lower than observed in the Irish Sea. This is supposed to be caused by the physico-chemical form of the accident plutonium. A recent study indicates that 'hot particles' hold considerably more plutonium than previously anticipated and that the Bylot Sound sediments may account for the major part of the un-recovered plutonium after the accident, i.e. approximately 3 kg.     

The radioecological consequences for lowland pastures used to fatten upland sheep contaminated with radiocaesium

Current farming practice in upland areas of Cumbria, England, affected by Chernobyl fallout is to remove lambs to lowland pastures for fattening prior to slaughter. The radiocaesium (137Cs and 134Cs) burden of lambs is rapidly lost via excreta deposited on the pasture. This may increase the radiocaesium activities in vegetation of these pastures. Studies were performed to assess the radioecological consequences of this practice. Results obtained from experiments were used to calibrate a soil/vegetation model which was used to predict long-term radiocaesium behavior.     

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.     

Application of potassium chloride to a Chernobyl-contaminated lake: modelling the dynamics of radiocaesium in an aquatic ecosystem and decontamination of fish

This study tests a whole-lake experiment to reduce the bioaccumulation of radiocaesium (137Cs) in fish in lakes contaminated by the Chernobyl accident. In many lakes in the Chernobyl contaminated areas, radiocaesium activity concentrations in fish are still significantly higher (up to 100 times in some species) than acceptable limits for human consumption. Estimates of the long-term rate of decline of 137Cs in fish in these regions, in the absence of countermeasures, show that radioactivity in fish in some lakes may remain above acceptable consumption limits for a further 50-100 years from the present date. In February 1998 we applied 15 t of potassium chloride to Lake Svyatoe, Kostiukovichy. The addition of potassium chloride fertilizer to the lake resulted in a decrease in activity concentration of 137Cs to approximately 40% of pre-countermeasure values in a number of different fish species. In contrast to Lake Svyatoe, 137Cs activity concentrations in fish from four control lakes showed no systematic decrease over the study period. Simplified models for transfers of 137Cs in lakes successfully 'blind' predicted the changes in 137Cs in water and fish resulting from this major alteration of the potassium concentration of the lake. The experiment represents the first test of a predictive model for the dynamics of radiocaesium in response to a major perturbation in potassium (its major competitor ion) in a whole lake ecosystem.     

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.     

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.     

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.     

Retrospective determination of 137Cs specific activity distribution in spruce bark and bark aggregated transfer factor in forests on the scale of the Czech Republic ten years after the Chernobyl accident

The ¹³⁷Cs specific activities (mean 32 Bq kg⁻¹) were determined in spruce bark samples that had been collected at 192 sampling plots throughout the Czech Republic in 1995, and were related to the sampling year. The ¹³⁷Cs specific activities in spruce bark correlated significantly with the ¹³⁷Cs depositions in areas affected by different precipitation sums operating at the time of the Chernobyl fallout in 1986. The ratio of the ¹³⁷Cs specific activities in bark and of the ¹³⁷Cs deposition levels yielded bark aggregated transfer factor T_ag about 10.5 × 10⁻³ m⁻² kg⁻¹. Taking into account the residual specific activities of ¹³⁷Cs in bark 20 Bq kg⁻¹ and the available pre-Chernobyl data on the ¹³⁷Cs deposition loads on the soil surface in the Czech Republic, the real aggregated transfer factor after and before the Chernobyl fallout proved to be T*_ag = 3.3 × 10⁻³ m⁻² kg⁻¹ and T**_ag = 4.0 × 10⁻³ m⁻² kg⁻¹, respectively. The aggregated transfer factors T*_ag for ¹³⁷Cs and spruce bark did not differ significantly in areas unequally affected by the ¹³⁷Cs fallout in the Czech Republic in 1986, and the figures for these aggregated transfer factors were very similar to the mean bark T_ag values published from the extensively affected areas near Chernobyl. The magnitude of the ¹³⁷Cs aggregated transfer factors for spruce bark for the pre-Chernobyl and post-Chernobyl period in the Czech Republic was also very similar. The variability in spruce bark acidity caused by the operation of local anthropogenic air pollution sources did not significantly influence the accumulation and retention of ¹³⁷Cs in spruce bark. Increasing elevation of the bark sampling plots had a significant effect on raising the remaining ¹³⁷Cs specific activities in bark in areas affected by precipitation at the time when the plumes crossed, because the sums of this precipitation increased with elevation (covariable).     

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.