Radiocaesium contamination of meadow vegetation--time-dependent variability and influence of soil characteristics at grassland sites in Austria

Long-term trends of 137Cs and 40K concentrations in meadow grass and soil-plant transfer data at eight different sites in Upper Austria are presented. Geometric means of 137Cs TF-data and Tagg values vary between 0.03-1.06 and 0.0005-0.0184 depending on site, respectively. 40K results are less variable with TF values covering a range of 0.31-2.01. Only at one site was a significant decrease of 137Cs concentration (decay-corrected) in meadow vegetation observed during the observation period 1992-1999. Seasonal trends of 40K and 137Cs were investigated at one site in 1996. Both elements show decreasing concentrations in plants from beginning of May-July, followed by a peak in September. Although this pattern was not very pronounced, there are some hints that it may explain deviations of long-term trends in 137CS levels in grass caused by unusual weather conditions as indicated by phenological climate data (beginning of sweet cherry and black elder blossoming). Finally, TF values were correlated with soil characteristics, revealing a negative correlation of radiocaesium soil-plant transfer with soil pH, exchangeable and extractable fractions of Mg, Ca and Na as well as a positive correlation with exchangeable Al.

A simple method for the estimation of the bioavailability of radiocaesium from herbage contaminated by adherent soil

Adherent soil may contribute a large proportion of the radiocaesium content of sampled vegetation. Consequently, inadvertent ingestion of adherent soil can contribute significantly to the radiocaesium intake of grazing animals, and needs to be accounted for within radiological assessments. However, accurate estimation of the degree of soil adhesion on vegetation is acknowledged to be difficult. To determine the relative contributions of vegetation and soil to the radiocaesium contamination of milk and tissues, soil-specific estimation of radiocaesium bioavailability values would be required. Here we suggest that a previously developed in-vitro bioavailability assay (involving a 2 h extraction with 0.1 M stable CsCl) can be used to estimate the true absorption coefficient of radiocaesium associated with sampled vegetation directly. Using this technique, seasonal trends in bioavailability are demonstrated to vary in accordance with estimations of the degree of soil adherent to vegetation collected from an upland pasture. The use of this technique would negate the need for detailed measurements of the amount of soil adhering to sampled vegetation and soil-specific radiocaesium bioavailability assessments.

The role of fungi in the transfer and cycling of radionuclides in forest ecosystems

Fungi are one of the most important components of forest ecosystems, since they determine to a large extent the fate and transport processes of radionuclides in forests. They play a key role in the mobilization, uptake and translocation of nutrients and are likely to contribute substantially to the long-term retention of radiocesium in organic horizons of forest soil. This paper gives an overview of the role of fungi regarding the transfer and cycling of nutrients and radionuclides, with special emphasis on mycorrhizal symbiosis. Common definitions of transfer factors, soil-fungus and soil-green plant, including their advantages and limitations. are reviewed. Experimental approaches to quantify the bioavailability of radionuclides in soil and potential long-term change are discussed.

Environmental processes affecting plant root uptake of radioactive trace elements and variability of transfer factor data: a review

Soil-to-plant transfer factors are commonly used to estimate the food chain transfer of radionuclides. Their definition assumes that the concentration of a radionuclide in a plant relates linearly solely to its average concentration in the rooting zone of the soil. However, the large range of transfer factors reported in the literature shows that the concentration of a radionuclide in a soil is not the only factor influencing its uptake by a plant. With emphasis on radiocesium and -strontium, this paper reviews the effects of competition with major ions present in the soil-plant system, the effects of rhizosphere processes and soil micro-organisms on bioavailability, the factors influencing transport to and uptake by roots and the processes affecting long-term uptake rates. Attention is given to summarizing the results of recent novel electrophysiological and genetic techniques which provide a physiologically based understanding of the processes involved in the uptake and translocation of radiocesium and -strontium by plants.

An overview of the effect of organic matter on soil-radiocaesium interaction: implications in root uptake

This paper aims to give an overview of the effect of organic matter on soil-radiocaesium interaction and its implications on soil-to-plant transfer. Studies carried out after the Chernobyl accident have shown that high 137CS soil-to-plant transfer persists in organic soils over years. In most of these soils, the specific sites in clays control radiocaesium adsorption, organic compounds having an indirect effect. Only in organic soils with more than 95% of organic matter content and negligible clay content does adsorption occur mostly on non-specific sites. After a contamination event, two main factors account for the high transfer: the low solid-liquid distribution coefficient, which is due to the low clay content and high NH4+ concentration in the soil solution, and the low K+ availability, which enhances root uptake. The estimation of the reversibly adsorbed fraction, by means of desorption protocols, agrees with the former conclusions, since it cannot be correlated with the organic matter content and shows the lack of specificity of the adsorption in the organic phase. Moreover, the time-dependent pattern of the exchangeable fraction is related to soil-plant transfer dynamics.

Soil organic horizons as a major source for radiocesium biorecycling in forest ecosystems

Here we review some of the main processes and key parameters affecting the mobility of radiocesium in soils of semi-natural areas. We further illustrate them in a collection of soil surface horizons which largely differ in their organic matter contents. In soils, specific retention of radiocesium occurs in a very small number of sorbing sites, which are the frayed edge sites (FES) born out of weathered micaceous minerals. The FES abundance directly governs the mobility of trace Cs in the rhizosphere and thus its transfer from soil to plant. Here, we show that the accumulation of organic matter in topsoils can exert a dilution of FES-bearing minerals in the thick humus of some forest soils. Consequently, such accumulation significantly contributes to increasing 137Cs soil-to-plant transfer. Potassium depletion and extensive exploration of the organic horizons by plant roots can further enhance the contamination hazard. As humus thickness depends on both ecological conditions and forest management. our observations support the following ideas: (1) forest ecosystems can be classified according to their sensitivity to radiocesium bio-recycling, (2) specific forest management could be searched to decrease such bio-recycling.

Generic values for soil-to-plant transfer factors of radiocesium

There is a need for soil-to-plant transfer factors of radionuclides that take into account all possible crops on all soil varieties to support dose assessment studies. Because only limited experimental data exist for worldwide soil systems, such values should necessarily have a generic character. This paper describes a generic system for 137Cs, mainly based on a reference soil-to-plant transfer factor which depends solely on soil properties such as nutrient status, exchangeable K-content, pH and moisture content. Crops are divided into crop groups, cereals serving as reference group. The transfer of other crop groups can be calculated by multiplying data for cereals by a conversion factor. Existing data present in the IUR (International Union of Radioecologists) databank and in large part the work of a FAO (Food and Agriculture Organisation)/IAEA(International Atomic Energy Agency)/IUR project on tropical systems provided the basis for the derivation of the conversion factors and reference values.

Transfer of 137Cs and 60Co from irrigation water to a soil-tomato plant system

An experiment has been performed at the nuclear power plant of Garigliano (Caserta, Italy), aiming at the measurement of transfer factors of 137Cs and 60Co radionuclides from the irrigation water to a soil-plant system, with particular attention to the influence on such transfers of the irrigation technique (ground or aerial). Tomato plants were irrigated weekly with water contaminated with 137Cs and 60Co (about 375 Bq/m2 week), using both irrigation techniques. After 13 weeks, fruits, leaves, stems, roots and soil were sampled, and radionuclide concentrations were measured by high-resolution gamma spectroscopy. It was found that the activity allocated to the plant organs is significantly dependent upon the irrigation technique, amounting to 2.1% and 1.6% of the activity given in the cultivation for aerial treatment and 0.4% and 0.3% for the ground treatment, for 137Cs and 60Co respectively. The activity absorbed by plants is allocated mainly in leaves (> 55%), while less then 10% is stored in the fruits, for both irrigation techniques. Transfer factors (soil-plant and irrigation water-plant) of tomato plants and of weeds have been determined for 137Cs and 60Co, as well as for natural 40K in the soil.

Plant uptake of 134Cs in relation to soil properties and time

134Cs uptake by sunflower and soybean plants grown on seven different soils and its relation to soil properties were studied in a greenhouse pot experiment. Soil in each pot was contaminated by dripping the 134Cs in layers, and sunflower and soybean plants were grown for three and two successive periods, respectively. 134Cs plant uptake was expressed as the transfer factor (TF) (Bq kg(-1) plant/Bq kg(-1) soil) and as the daily plant uptake (flux) (Bq pot(-1) day(-1)) taking into account biomass production and growth time. For the studied soils and for both plants, no consistent trend of TFs with time was observed. The use of fluxes, in general, provided less variable results than TFs and stronger functional relationships. A negative power functional relationship between exchangeable potassium plus ammonium cations expressed as a percentage of cation exchange capacity of each soil and 134Cs fluxes was found for the sunflower plants. A similar but weaker relationship was observed for soybean plants. The significant correlation between sunflower and soybean TFs and fluxes, as well as the almost identical highest/lowest 134Cs flux ratios, in the studied soils, indicated a similar effect of soil characteristics on 134Cs uptake by both plants. In all the studied soils, sunflower 134Cs TFs and fluxes were significantly higher than the respective soybean values, while no significant difference was observed in potassium content and daily potassium plant uptake (flux) of the two plants.

A comparison of 90Sr and 137Cs uptake in plants via three pathways at two Chernobyl-contaminated sites

Foliar absorption of resuspended 90Sr, root uptake and contamination adhering to leaf surfaces (i.e. soil loading) were compared at two Chernobyl-contaminated sites, Chistogalovka and Polesskoye. Although foliar absorption of resuspended 90Sr was quantifiable, its contribution amounted to less than 10% of the plants' total, above-ground contamination. Root uptake was 200 times greater than foliar absorption at the near-field site of Chistogalovka and eight times greater at Polesskoye, where the fallout consisted of the more soluble condensation-type, rather than fuel particles. Strontium's bioavailability exceeded that of 137Cs (analyzed in the same plants) by orders of magnitude when compared using concentration ratios. Simplistic, cumulative effective dose calculations for humans ingesting 90Sr- and 137Cs-contaminated plants revealed that the dose at Chistogalovka was greater from 90Sr (185 mSv vs. 3 mSv from 137Cs), while at Polesskoye the dose from 137Cs (66 mSv) was 30 times greater than from 90Sr (2 mSv).

Distribution and mobilization of U, Th and 226Ra in the plant-soil compartments of a mineralized uranium area in south-west Spain

The activity concentrations of natural uranium isotopes (238U and 234U), thorium isotopes (232Th, 230Th and 225Th) and 226Ra were studied in soil and vegetation samples from a disused uranium mine located in the Extremadura region in the south-west of Spain. The results allowed us to characterize radiologically the area close to the installation and one affected zone was clearly manifest as being dependent on the direction of the surface water flow from the mine. The activity concentration mean values (Bq/kg) in this zone were: 10,924, 10,900, 10,075 and 5,289 for 238U, 234U, 230Th and 226Ra, respectively, in soil samples and 1,050, 1,060, 768 and 1,141 for the same radionuclides in plant samples. In an unaffected zone, the activity concentration mean values (Bq/kg) were: 184, 190, 234 and 7251 for 235U, 234U, 230Th and 226Ra, respectively, in soil samples and 28. 29, 31 and 80 in plant samples. The activity concentrations obtained for 232Th and 228Th showed that the influence of the mine was only important for the uranium series radionuclides. The relative radionuclide mobilities were determined from the activity ratios. Correlations between radionuclide activity concentrations and stable element concentrations in the soil samples helped to understand the possible distribution paths for the natural radionuclides.

Uptake of 40K and 137Cs in native plants of the Marshall Islands

Uptake of 137Cs and 40K was studied in seven native plant species of the Marshall Islands. Plant and soil samples were obtained across a broad range of soil 137Cs concentrations (0.08-3900 Bq/kg) and a narrower range of 40K soil concentrations (2.3-55 Bq/kg), but with no systematic variation of 40K relative to 137Cs. Potassium-40 concentrations in plants varied little within the range of 40K soil concentrations observed. Unlike the case for 40K, 137Cs concentrations increased in plants with increasing 137Cs soil concentrations though not precisely in a proportionate manner. The best-fit relationship between soil and plant concentrations was P = aSb where a and b are regression coefficients and P and S are plant and soil concentrations, respectively. The exponent b for 40K was zero, implying plant concentrations were a single value, while b for 137Cs varied between 0.51 and 0.82, depending on the species. For both 40K and 137Cs, we observed a decreasing concentration ratio (where concentration ratio=plant concentration/soil concentration) with increasing soil concentrations. For the CR values, the best-fit relationship was of the form CR = aSb/S = aSb(-1). For the 40K CR functions, the exponent b - 1 was close to - 1 for all species. For the 137Cs CR functions, the exponent b - 1 varied from -0.19 to -0.48. The findings presented here, aswell as those by other investigators, collectively argue against the usefulness of simplistic ratio models to accurately predict uptake of either 40K or 137Cs in plants over wide ranges of soil concentration.

Transfer of 137Cs and stable Cs from paddy soil to polished rice in Aomori, Japan

Rice is a staple food in Japan and other Asian countries, and the soil-to-plant transfer factor of 137Cs released into the environment is an important parameter for estimating the internal radiation dose from food ingestion. Soil and rice grain samples were collected from 20 paddy fields throughout Aomori Prefecture, Japan in 1996 and 1997, and soil-to-polished rice transfer factors were determined. The concentrations of 137Cs, derived from fallout depositions, stable Cs and K in paddy soils were 2.5-21 Bq kg(-1), 1.2-5.3 and 5000-13000 mg kg(-1), respectively. The ranges of 137Cs, stable Cs and K concentration in polished rice were 2.5-85 mBq kg(-1) dry wt., 0.0005-0.0065 and 580-910 mg kg(-1) dry wt., respectively. The geometric mean of soil-to-polished rice transfer factor of 137Cs was 0.0016, and its 95% confidence interval was 0.00021-0.012. The transfer factor of 137Cs was approximately 3 times higher than that of stable Cs at 0.00056, and they were well correlated. This implied that fallout 137Cs, mostly deposited up to the 1980s, is more mobile and more easily absorbed by plants than stable Cs in the soil, although the soil-to-plant transfer of stable Cs can be used for predicting the long-term transfer of 137Cs. The transfer factors of both 137Cs and stable Cs decreased with increasing K concentration in the soil. This suggests that K in the soil was a competitive factor for the transfers of both 137Cs and stable Cs from soil-to-polished rice. However, the transfer factors of 137Cs and stable Cs were independent of the amount of organic materials in soils.

Assessment of plant uptake of radioactive nickel from soils

As a result of isotopic dilution, the availability to plants of radioisotopes introduced into the soil solution should be directly related to the size of the isotopically exchangeable pool (E(t))-value). This work was undertaken to test this hypothesis for the radionuclide 63Ni. The demonstration was based on pot experiments conducted with seven soils representing a large range of Ni content (from 9.9 mg kg(-1) to 862.6 mg kg(-1)) which were mixed with a 63NiCl2 solution (100 kBq kg(-1)). Three plant species varying in Ni uptake, Triticum aestivum (wheat), Trifolium pratense (clover), and the Ni-hyperaccumulator Alyssum murale, were grown for 90 d, and their total Ni and 63Ni content determined at harvest. In parallel, the isotopically exchangeable kinetics method (IEK) was run on each soil sample to measure the E(t)-value. Results showed that plant uptake of radioactive nickel was negatively correlated with the E(t)-value with wheat and clover as a result of the dilution of 63Ni added in the isotopically exchangeable pool of soil Ni (alpha=5%); correlation was positive with the A. murale (alpha=10%). Hence, this provides a new approach for the assessment of soil-to-plant transfer of 63Ni at larger scale avoiding the carrying out of time consuming experiments.

A validation study for the transport of 134Cs to strawberry

The paper presents results on model validation by field experiment for transport of 134Cs to strawberry. The transfer of 134Cs to herbaceous plants was investigated following a wet deposition after an acute release during 2000. Leaf-to-fruit, soil-to-fruit and direct fruit pathways were examined. The available meteorological and local soil information together with the experimental data were taken into account by the model RUVFRU. The processes are described by first order differential equations. In the case of foliar contamination scenarios measured and calculated results for fruit are in good agreement. However, the results of soil contamination scenarios provide large differences of up to three orders of magnitude between model predictions and experimental values for either fruit or other parts of the plant. The bias could be explained by the underestimation of the interception of the plant at the beginning of the season, in the soil contamination scenario. The model output permits prompt assessment of emergency situations and provides aid making decisions concerning mitigation of the consequences of the accident.

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.

Accumulation of 137Cesium and 90Strontium from abiotic and biotic sources in rodents at Chornobyl, Ukraine

Bank voles (Clethrionomys glareolus) and laboratory strains of house mice (Mus musculus BALB and C57BL) were relocated into enclosures in a highly contaminated area of the Red Forest near the Chornobyl (Ukraine) Reactor 4 to evaluate the uptake rates of 137Cs and 90Sr from abiotic sources. Mice were provided with uncontaminated food supplies, ensuring that uptake of radionuclides was through soil ingestion, inhalation, or water. Mice were sampled before introduction and were reanalyzed every 10 d for 137Cs uptake. Levels of 90Sr were assessed in subsamples from the native populations and in experimental animals at the termination of the study. Uptake rates in house mice were greater than those in voles for both 137Cs and 90Sr. Daily uptake rates in house mice were estimated at 2.72 x 10(12) unstable atoms per gram (whole body) for 137Cs and 4.04 x 10(10) unstable atoms per gram for 90Sr. Comparable rates in voles were 2.26 x 10(11) unstable atoms per gram for 137Cs and 1.94 x 10(10) unstable atoms per gram for 90Sr. By comparing values from voles in the enclosures to those from wild voles caught within 50 m of the enclosures, it was estimated that only 8.5% of 137Cs was incorporated from abiotic sources, leaving 91.5% being incorporated by uptake from biotic materials. The fraction of 90Sr uptake from abiotic sources was at least 66.7% (and was probably much higher). Accumulated whole-body doses during the enclosure periods were estimated as 174 mGy from intramuscular 137Cs and 68 mGy by skeletal 90Sr in house mice over 40 d and 98 mGy from 137Cs and 19 mGy from 90Sr in voles over 30 d. Thus, uptake of radionuclides from abiotic materials in the Red Forest at Chornobyl is an important source of internal contamination.

Uptake and mobility of uranium in black oaks: implications for biomonitoring depleted uranium-contaminated groundwater

In a preliminary study, the uptake and the mobility of uranium (U) by black oak trees (Quercus velutina) were assessed by measuring the isotopic composition of tree rings in two mature oak trees in a heavy metal contaminated bog in Concord, MA. The bog is adjacent to a nuclear industrial facility that has been processing depleted uranium (DU) since 1959. Over the past 40 years, DU has been leaking from an onsite holding basin and cooling pond down gradient to the bog where the oaks are located. Because DU has no source outside the nuclear industry, contamination from the industrial facility is readily discernable from uptake of natural U by measuring isotopic compositions. Isotope ratio analysis confirms the occurrence of DU in bark, sapwood and heartwood tree rings dating back to 1937, pre-dating the introduction of DU at the site by at least 20 years. Isotope dilution analysis indicates high concentrations of U (>3 ppb) in sapwood that drop rapidly to relatively constant concentrations (0.3-0.4 ppb) in heartwood. These data indicate that once incorporated into tree cells, U is mobile, possibly by diffusion through the tree wood. Concentrations of U in sapwood are approximately equal to average U concentrations in groundwater onsite over the past 10 years, suggesting that oak trees can be used as present-day bioindicators of U-contaminated groundwater. We suggest that regional sampling of oak bark and sapwood is a reasonable, inexpensive alternative to drilling wells to monitor shallow groundwater U contamination.

Siderophore mediated plutonium accumulation by Microbacterium flavescens (JG-9)

Uptake of plutonium and uranium mediated by the siderophore desferrioxamine-B (DFOB) has been studied for the common soil aerobe Microbacterium flavescens(JG-9). M. flavescens does not bind or take up nitrilotriacetic acid (NTA) complexes of U(VI), Fe(III), or Pu(IV) or U(VI)-DFOB but does take up Fe(III)-DFOB and Pu(IV)-DFOB. Pu(IV)-DFOB and Fe(III)-DFOB accumulations are similar: only living and metabolically active bacteria take up these metal-siderophore complexes. The Fe(III)-DFOB and Pu(IV)-DFOB complexes mutually inhibit uptake of the other, indicating that they compete for shared binding sites or uptake proteins. However, Pu uptake is much slower than Fe uptake, and cumulative Pu uptake is less than Fe, 1.0 nmol of Fe vs 0.25 nmol of Pu per mg of dry weight bacteria. The Pu(IV)-DFOB interactions with M. flavescens suggest that Pu-siderophore complexes could generally be recognized by Fe-siderophore uptake systems of many bacteria, fungi, or plants, thereby affecting Pu environmental mobility and distribution. The results also suggest that the siderophore complexes of tetravalent metals can be recognized by Fe-siderophore uptake proteins.

Radionuclide transport above a near-surface water table: III. Soil migration and crop uptake of three gamma-emitting radionuclides, 1990 to 1993

This paper summarizes the vertical distributions of 22Na, 137Cs, and 60Co above controlled water tables in deep and shallow lysimeters during a four-year experiment. The activity concentration profiles were all determined at the time of harvest of a winter wheat (Triticum aestivum L. cv. Pastiche) crop. Activity concentrations in different crop tissues were determined and crop uptake expressed as both an inventory ratio (IR) and a transfer factor (TFw), weighted to account for root and radionuclide distributions within the soil profile. Experimental variates were subjected to analysis of variance to determine the single and combined effects of the soil depth and the year of the experiment on the results obtained. Each radionuclide showed significant variations in activity concentration with soil depth, but the significance of these variations from year to year was dependent on radionuclide. A distinction in the behavior of weakly sorbed (22Na) and more highly sorbed (137Cs and 60Co) radionuclides was observed. The former exhibited significant variations in its distribution in the soil profile from year-to-year whereas the latter did not. Relatively high TF, values for 22Na were maintained throughout the experiment, whereas for 137Cs and 60Co, the highest TFw values were recorded in 1990 followed by a significant decline in 1991, with TFw remaining low in 1992 and 1993. The TFw values were, in general, significantly higher for deep lysimeters than for shallow lysimeters. This is thought to provide evidence of enhanced radionuclide absorption by the relatively small fraction of roots in the vicinity of the deeper water table.

A dynamic compartmental food chain model of radiocaesium transfer to Apodemus sylvaticus in woodland ecosystems

A study was undertaken to quantify the activity concentrations of 137Cs in Apodemus sylvaticus (the woodmouse) in two woodland sites, Lady Wood and Longrigg Wood, adjacent to British Nuclear Fuels Ltd. (BNFL) Sellafield, Cumbria, UK. A deterministic dynamic compartmental food chain model was also constructed to predict 137Cs activity concentration [Bq kg(-1) dry weight (dw)] in A. sylvaticus on a seasonal basis given the activity concentrations in its diet. Within the coniferous woodland site (Lady Wood), significant differences were found between seasons (P < 0.05, summer vs. autumn cohort; P < 0.001, spring vs. autumn cohort), with an autumn peak in activity concentration (geometric mean = 140 x/divided by 2.3 Bq kg(-1) dw) being attributed to mycophagy. Fungal concentrations ranged from 2-3213 Bq kg(-1) dw. The modelled activity concentrations fell between the confidence intervals of the observed data in four of the six seasonal cohorts sampled. Disparities between predicted and observed activity concentrations are attributed to uncertainties surrounding the fundamental feeding ecology of small mammals.

Long-term studies on transfer of 137Cs from soil to vegetation and to grazing lambs in a mountain area in northern Sweden

Studies were made during 1990-1997 on the transfer of 137Cs from soil to vegetation (herbage) and to grazing lambs on a mountain farm with an uncultivated grazing area of about 10 km2. The farm is situated in an area in Northern Sweden which was contaminated by the Chernobyl fallout in 1986. The mean concentration of 137Cs in the soil to a depth of 10 cm for eight sampling sites observed in the 8-year period was 14.51 kBq/m2, while in the cut herbage the average concentration was 859 Bq/kg d.w. and in lamb meat 682 Bq/kg w.w. A slow vertical migration of 137Cs in the 0-10 cm soil layer was indicated. Although the 137Cs concentration in herbage gradually decreased, the concentration in lamb meat varied from year to year. Soil ingestion by the lambs as a pathway for activity transfer was shown to be negligible, while ingestion of fungi with high concentrations of 137Cs was demonstrated to occur, as large numbers of fungi spores were counted in samples of the lambs' faeces. Fungi ingestion might therefore partly explain the varying mean yearly 137Cs concentrations in lamb muscle. The mean transfer parameters were as follows: for "soil to herbage" 61.3 Bq/kg d.w. herbage per kBq/m2 soil, for "herbage to lamb meat" 0.81 Bq/kg w.w. meat per Bq/kg d.w. herbage, and for "soil to lamb meat" 47.1 Bq/kg w.w. meat per kBq/m2 soil. A trend of decreasing values of the transfer parameter for "soil to herbage" indicated that 137Cs was becoming less available for root-uptake with time. The effective ecological half-life of 137Cs in soil, herbage and lamb meat was calculated to be 19, 7 and 16 years, respectively. It can be concluded that natural areas are vulnerable to 137Cs contamination, resulting in high concentrations in plants, fungi and lamb meat for a long time.

Soil- and plant-based countermeasures to reduce 137Cs and 90Sr uptake by grasses in natural meadows: the REDUP project

The effectiveness of a set of soil- and plant-based countermeasures to reduce 137Cs and 90Sr transfer to plants was tested in natural meadows in the area affected by Chernobyl fallout. Countermeasures comprised the use of agricultural practices (disking + ploughing, liming and NPK fertilisation), addition of soil amendments and reseeding with a selection of grass species. Disking + ploughing was the most effective treatment, whereas the K fertiliser doses applied were insufficient to produce a significant increase in K concentration in soil solution. The application of some agricultural practices was economically justifiable for scenarios with a high initial transfer, such as 137Cs-contaminated organic soils. The use of soil amendments did not lead to a further decrease in transfer. Laboratory experiments demonstrated that this was because of their low radionuclide sorption properties. Finally, experiments examining the effect of plant species on radionuclide transfer showed that both transfer and biomass can depend on the plant species, indicating that those with high radionuclide root uptake should be avoided when reseeding after ploughing.

The influence of clay mineralogy on the mobility of radiocaesium in upland soils of NW Italy

137Cs extraction experiments were performed on 14 contaminated soils from NW Italy with different characteristics and mineralogical composition. Solutions of HCl (pH = 0.5) and buffered EDTA/ammonium acetate (Lakanen solution) were used to assess bioavailability. The results show that less than 2% of 137Cs is available for leaching and/or root uptake. Even within a complex natural system it was possible to identify the amount of swelling clays (vermiculite + smectite) as the main control on Cs mobility under acidic conditions. The ammonium ion appears to be effective in desorbing Cs and its role is briefly discussed in terms of crystal chemistry. The relevance of mineralogy in assessing soil vulnerability is underlined.

The presence of some artificial and natural radionuclides in a Eucalyptus forest in the south of Spain

Long-lived artificial radionuclides (137Cs, 90Sr) were studied in a Eucalyptus plantation located in the south-west of Spain. Radionuclide concentrations were determined in different types of samples corresponding to specific forest components (soil, trees, herbs and litter). Depth profile distributions were obtained in two selected core soils. Two layers were separately measured in three other cores. The concentration factor, defined as the ratio between the mean activity concentration in a component and the mean activity concentration in the soil, was calculated for each component. The biomass of different components was estimated in order to evaluate the total density concentration (Bq/ha) of the artificial radionuclides (137Cs, 90Sr) in the Eucalyptus plantation. The transfer of the radionuclides between the different forest components can be inferred from the results. Additionally, other naturally occurring radionuclides (40K, 226Ra, 228Ra, 228Ac) were determined for comparison. Transport of radionuclides from forest to a nearby pulp mill is also discussed.

Sorption of radioactive contaminants by sediment from the Kara Sea

The purpose of this study is to quantify some of the parameters needed to perform near-field modelling of sites in the Kara Sea that were impacted by the disposal of radioactive waste. The parameters of interest are: the distribution coefficients (Kd) for several important radionuclides, the mineralogy of the sediment, and the relationship of Kd to liquid-to-solid ratio. Sediment from the Kara Sea (location: 73 degrees 00'N, 58 degrees 00'E) was sampled from a depth of 287 m on August 23/24, 1992. Analysis of the material included mineralogy, grain size and total organic carbon (TOC). Uptake kinetics were determined for 85Sr, 137Cs, 241Am, 99Tc, 1251, 232U and 210Pb and distribution coefficients (Kd) were determined for these radionuclides using batch type experiments. Sorption isotherms, developed for 137Cs, 85Sr and 99Tc, were linear in each case. Increasing the liquid-to-solid ratio strongly increased uptake of 137Cs and moderately increased uptake of 99Tc. Analysis for anthropogenic radionuclides indicated the presence only of 239/240Pu in the sediment with the highest activity (at the top section of the core) being 0.420 Bq kg(-1). Other anthropogenic radionuclides were below detection limits.

Short rotation coppice for revaluation of contaminated land

When dealing with large-scale environmental contamination, as following the Chernobyl accident, changed land use such that the products of the land are radiologically acceptable and sustain an economic return from the land is a potentially sustainable remediation option. In this paper, willow short rotation coppice (SRC) is evaluated on radiological, technical and economic grounds for W. European and Belarus site conditions. Radiocaesium uptake was studied in a newly established and existing SRC. Only for light-texture soils with low soil potassium should cultivation be restricted to soils with contamination levels below 100-370 kBq m-2 given the TFs on these soils (5 x 10(-4) and 2 x 10(-3) m2 kg-1) and considering the Belarus exemption limit for firewood (740 Bq kg-1). In the case of high wood contamination levels (> 1000 Bq kg-1), power plant personnel working in the vicinity of ash conveyers should be subjected to radiation protection measures. For appropriate soil conditions, potential SRC yields are high. In Belarus, most soils are sandy with a low water retention, for which yield estimates are too low to make production profitable without irrigation. The economic viability should be thoroughly calculated for the prevailing conditions. In W. Europe, SRC production or conversion is not profitable without price incentives. For Belarus, the profitability of SRC on the production side largely depends on crop yield and price of the delivered bio-fuel. Large-scale heat conversion systems seem the most profitable and revenue may be considerable. Electricity routes are usually unprofitable. It could be concluded that energy production from SRC is potentially a radiologically and economically sustainable land use option for contaminated agricultural land.

Radionuclide transfer from soil to fruit

The available literature on the transfer of radionuclides from soil to fruit has been reviewed with the aim of identifying the main variables and processes affecting the behaviour of radionuclides in fruit plants. Where available, data for transfer of radionuclides from soil to other components of fruit plant have also been collected, to help in understanding the processes of translocation and storage in perennial plants. Soil-to-fruit transfer factors were derived from agricultural ecosystems, both from temperate and subtropical or tropical zones. Aggregated transfer factors have also been collected from natural or semi-natural ecosystems. The data concern numerous fruits and various radionuclides. Soil-to-fruit transfer is nuclide specific. The variability for a given radionuclide is first of all ascribable to the different properties of soils. Fruit plant species are very heterogeneous, varying from woody trees and shrubs to herbaceous plants. In temperate areas the soil-to-fruit transfer is higher in woody trees for caesium and in shrubs for strontium. Significant differences between the values obtained in temperate and subtropical and tropical regions do not necessarily imply that they are ascribable to climate. Transfer factors for caesium are higher in subtropical and tropical fruits, while those for strontium, as well as for plutonium and americium, in the same fruits, are lower; these results can be interpreted taking into account different soil characteristics.

The influence of the development of temperate fruit tree species on the potential for their uptake of radionuclides

This paper reviews the published literature that describes the phenological development of above and below ground organs of temperate fruit trees (top fruit), particularly with respect to apple (Malus domestica). Critical information is presented which is considered appropriate in developing an understanding of the potential for top fruit species to take up radionuclide contaminants from the atmosphere and the soil. Information is cited on how climatic and edaphic factors influence the growth and development of temperate fruit trees, the phenological production of their leaf area and the development and growth of their fruit and hence the potential for foliar and fruit uptake of radionuclides from the atmosphere. The study also reports on the importance of the distribution and phenological development of roots in the soil and the potential for their uptake of radionuclides from the soil. The effects of above and below ground management procedures, within temperate fruit orchards, on potential radionuclide uptake are also considered. It is concluded that the potential for the uptake of radionuclides by temperate fruit tree species will depend on a number of phenological and physiological factors. For uptake from the soil these factors include; root distribution and density in the soil profile, seasonal changes in the production and distribution of roots, and the presence and amount of water in the soil. These factors are themselves influenced by rootstock type and its growth vigour, scion type and its growth vigour, tree age, spacing of trees in the orchard, orchard management practices (presence or absence of weeds or grass under the trees) and soil type and depth. Direct uptake by the shoot, however, will be influenced by the climatic conditions at the time of exposure and the presence of foliage. Deposition and uptake are likely to change with leaf area development and the ability of radionuclides to penetrate the cuticle of the leaf changes with seasonal development. Transport of radionuclides to the fruit may also depend on the time of season, as the importance of the xylem and phloem transport routes can change with the growth and development of the fruit.

Predicting the transfer of radiocaesium from organic soils to plants using soil characteristics

A model predicting plant uptake of radiocaesium based on soil characteristics is described. Three soil parameters required to determine radiocaesium bioavailability in soils are estimated in the model: the labile caesium distribution coefficient (kd1), K+ concentration in the soil solution [mK] and the soil solution-->plant radiocaesium concentration factor (CF, Bq kg-1 plant/Bq dm-3). These were determined as functions of soil clay content, exchangeable K+ status, pH, NH4+ concentration and organic matter content. The effect of time on radiocaesium fixation was described using a previously published double exponential equation, modified for the effect of soil organic matter as a non-fixing adsorbent. The model was parameterised using radiocaesium uptake data from two pot trials conducted separately using ryegrass (Lolium perenne) on mineral soils and bent grass (Agrostis capillaris) on organic soils. This resulted in a significant fit to the observed transfer factor (TF, Bq kg-1 plant/Bq kg-1 whole soil) (P < 0.001, n = 58) and soil solution K+ concentration (mK, mol dm-3) (P < 0.001, n = 58). Without further parameterisation the model was tested against independent radiocaesium uptake data for barley (n = 71) using a database of published and unpublished information covering contamination time periods of 1.2-10 years (transfer factors ranged from 0.001 to 0.1). The model accounted for 52% (n = 71, P < 0.001) of the observed variation in log transfer factor.

In vitro penetration of soil-aged mercury through pig skin

The dermal bioavailability of mercury "aged" in soil for 3 mo was compared to that of pure mercury (without soil) and to mercury in brief contact with soil (16 h). Studies were conducted in vitro with [203Hg]mercuric chloride on dermatomed male pig skin by flow-through diffusion cell methodology. Less than 0.5% of the initial mercury dose penetrated through skin into receptor fluid after each treatment. The majority of pure mercury became covalently bound to skin. However, a short contact time with either an Atsion (sandy) or Keyport (clay) soil significantly decreased the total penetration of mercury (sum of receptor fluid and skin) by 40%. After aging, a 95% reduction in total penetration was observed for the compound relative to chemical without soil. Both soils bind mercury more strongly with time, as evidenced by larger quantities of radioactivity in soil and smaller amounts in skin decontaminate after aging than in soil for 16 h. Decreased mercury bioavailability with aging indicates lower health risk and reduced need for soil cleanup.

Plant uptake of radiocaesium: a review of mechanisms, regulation and application

Soil contamination with radiocaesium (Cs) has a long-term radiological impact because it is readily transferred through food chains to human beings. Plant uptake is the major pathway for the migration of radiocaesium from soil to human diet. The plant-related factors that control the uptake of radiocaesium are reviewed. Of these, K supply exerts the greatest influence on Cs uptake from solution. It appears that the uptake of radiocaesium is operated mainly by two transport pathways on plant root cell membranes, namely the K(+) transporter and the K(+) channel pathway. Cationic interactions between K and Cs on isolated K-channels or K transporters are in agreement with studies using intact plants. The K(+) transporter functioning at low external potassium concentration (often <0.3 mM) shows little discrimination against Cs(+), while the K(+) channel is dominant at high external potassium concentration with high discrimination against Cs(+). Caesium has a high mobility within plants. Although radiocaesium is most likely taken up by the K transport systems within the plant, the Cs:K ratio is not uniform within the plant. Difference in internal Cs concentration (when expressed on a dry mass basis) may vary by a factor of 20 between different plant species grown under similar conditions. Phytoremediation may be a possible option to decontaminate radiocaesium-contaminated soils, but its major limitation is that it takes an excessively long time (tens of years) and produces large volumes of waste.

90Sr and 137Cs in environmental samples from Dolon near the Semipalatinsk Nuclear Test Site

The (90)Sr and (137)Cs activities of soil, plant, and milk samples from the village of Dolon, located close to the Semipalatinsk Nuclear Test Site in Kazakhstan, were determined. The areal deposition at the nine sampling sites is in the range of <500 to 6,100 Bq m(-2) and 300 to 7,900 Bq m-2 for (90)Sr and (137)Cs, respectively. Similar values have been reported in the literature. At some of the sites both nuclides mainly have remained in the top 6 cm of the soil profiles; at others they were partly transported into deeper soil layers since the deposition. For most of the samples the (90)Sr yield after destruction of the soil matrix is significantly higher than after extracting with 6 M HCl indicating that (90)Sr is partly associated with fused silicates. The low mean (90)Sr activity concentrations of vegetation samples (14 Bq kg(-1) dw) and milk samples (0.05 Bq kg(-1) fw) suggest that this has favorable consequences in terms of limiting its bioavailability.

Radiocaesium and radiostrontium uptake by fruit bodies of Pleurotus eryngii via mycelium, soil and aerial absorption

There has been an extraordinary increase in interest concerning the transfer of radioactive contamination to the fruit bodies of fungi since the Chernobyl nuclear power plant accident. These investigations, however, have focused exclusively on field studies aimed fundamentally at quantifying the behaviour of the radiocaesium component of the contamination. The results have shown great variability. As a contribution towards this body of knowledge, we have made a comparative study of the temporal evolution of the transfer of 85Sr and 134Cs via three routes of radioactive contamination--from the mycelium, from the surface layer of the soil, and directly onto the caps of the fruit bodies--for the saprophyte species, Pleurotus eryngii, under controlled laboratory conditions. The results indicate that the last of the above three uptake routes is the most efficient, and that the temporal evolution of the transfer is closely related to the radionuclide and the radioactive contamination route being considered.

[An estimation of 137Cs accumulation in forest fungi by the soil properties]

A method of calculation of radiocaesium uptake by forest mushrooms as a function of soil properties is presented. Calculated value of 137Cs transfer factor for Xerocomus badius in the contaminated area of Bryansk Province of Russia is in a good agreement with experimental data.

Investigation of the soil-plant transfer of primordial radionuclides in tomatoes by low-level gamma-ray spectrometry

The paper presents actual data from investigations of the soil-plant transfer of the primordial radionuclides 40K, 238U, 226Ra, 210Pb and 227Ac for tomatoes growing at soils from former uranium mining areas. The analysis were carried out using low-level gamma-ray spectrometry in a 47 m deep underground laboratory. For tomato fruits transfer factors of (0.0007 +/- 0.0006) for 235U, (0.0021 +/- 0.0017) for 226Ra, (0.0015 +/- 0.0009) for 210Pb and (0.0018 +/- 0.0012) for 227Ac were obtained. The investigation of the soil-plant transfer by low-level gamma-ray spectrometry is often limited by the Compton-continuum from the always present high-energy gamma-ray emitter 40K.

Soil-to-plant transfer factors for radiocesium and radiostrontium in agricultural systems

A database of soil-to-plant transfer factors for radiocesium and radiostrontium has been compiled for arable crops from published and unpublished sources. The database is more extensive than previous compilations of data published by the International Union of Radioecologists, containing new information for Scandinavia and Greece in particular. It also contains ancillary data on important soil characteristics. The database is sub-divided into 28 soil-crop combinations, covering four soil types and seven crop groups. Statistical analyses showed that transfer factors for radiocesium could not generally be predicted as a function of climatic region, type of experiment, age of contamination, or soil characteristics. However, significant relationships accounting for more than 30% of the variability in transfer factor were identified between transfer factors for radiostrontium and soil pH/organic matter status for a few soil-crop combinations. Best estimate transfer factors for radiocesium and radiostrontium were calculated for 28 soil-crop combinations, based on their geometric means: only the edible parts were considered. To predict the likely value of future individual transfer factors, 95% confidence intervals were also derived. A comparison of best estimate transfer factors derived in this study with recommended values published by the International Union of Radioecologists in 1989 and 1992 was made for comparable soil-crop groupings. Whilst there were no significant differences between the best estimate values derived in this study and the 1992 data, radiological assessments that still use 1989 data may be unnecessarily cautious.

Radionuclide behaviour and transport in a coniferous woodland ecosystem: vegetation, invertebrates and wood mice, Apodemus sylvaticus

Activity concentrations of radionuclides (134Cs, 137Cs, 238Pu, 239 + 240Pu and 241Am) were measured in vegetation, invertebrates and wood mice, Apodemus sylvaticus, collected in Lady Wood, a coniferous woodland in the vicinity of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, UK. Vegetation was of low diversity and biomass with activity concentrations ranging from 1 to 5 Bq kg-1 (134Cs), 0.3-0.5 Bq kg-1 (238Pu), 0.8-8 Bq kg-1 (239 + 240Pu), and 0.6-16 Bq kg-1 (241Am), dry wt. Caesium-137 activity concentrations were high compared to the reference site in Cheshire, varying between 65 and 280 Bq kg-1. Marked inter-specific and temporal differences in radionuclide activity concentrations were recorded for invertebrate populations. Caesium-137, 238Pu, 239 + 240Pu and 241Am activity concentrations in detritivorous invertebrates were consistently higher than in all other invertebrate groups reflecting contamination of the leaf litter. The activity concentrations in detritivores increased during the autumn and winter, reflecting changes in diet as food sources varied throughout the year. Activity concentrations in invertebrates caught in Lady Wood were generally an order of magnitude higher than for the reference site. Activity concentrations in wood mice varied between 7 and 150 Bq kg-1 (137Cs), 0.1-0.3 Bq kg-1 (238Pu), 0.1-0.6 Bq kg-1 (239 + 240Pu) and 0.2-0.4 Bq kg-1 (241Am). There were clear differences in the activity concentration of 137Cs (P < 0.01), 239 + 240Pu (P < 0.05) and 241Am (P < 0.05) in animals caught in Lady Wood compared to the reference site. However, the activity concentrations for 238Pu were similar at both sites, reflecting a low gastrointestinal transfer. Seasonal variation in activity concentrations was observed for 137Cs, 238Pu and 241Am. This variation is attributed to changes in the age structure of the population and diet throughout the year.

Soil to plant uptake of fallout 137Cs by plants from boreal areas polluted by industrial emissions from smelters

To study the impact of industrial pollution on the soil-to-plant uptake of fallout-radiocesium in a boreal forest ecosystem, four study sites were selected at distances of 7, 16, 21 and 28 km from the large copper-nickel smelter at Monchegorsk on the Kola Peninsula (Russia). At each site, soil and selected plant species were sampled from five plots and analysed separately for 137Cs and 40K. The data show that the root-uptake of 137Cs, as characterised by the median aggregated transfer-factor T(ag), decreased significantly (P < 0.05) with decreasing distance from the smelter for the plants Vaccinium myrtillus (from 0.023 to 0.007 m2 kg-1) and Empetrum nigrum (from 0.015 to 0.007 m2 kg-1), but increased for Deschampsia flexuosa (from 0.013 to 0.031 m2 kg-1). For Vaccinium vitis-idaea a significant trend for the T(ag) was not observed. The median 40K activity concentrations in these plants also decreased significantly (P < 0.001) with decreasing distance from the smelter for Vaccinium myrtillus (from approx. 140 to 20 Bq kg-1 dry wt.), Empetrum nigrum (from approx. 90 to 40 Bq kg-1 dry wt.), and also for Deschampsia flexuosa (from approx. 270 to 40 Bq kg-1 dry wt.). For Vaccinium vitis-idaea such a continuous significant trend was not observed. The results for the Cu-Ni polluted soils thus show: (1) that the soil-to-plant transfer of radiocesium can be significantly modified; (2) that these modifications are quite specific; and (3) that modifications of the uptake of potassium do not always correspond to those of radiocesium.

Detection limits for 90Sr, Pu, Am and Cm in soil and pasture vegetation shortly after a nuclear accident

This work estimates the critical activity concentrations of 90Sr and the alpha-emitting isotopes of Pu, Am and Cm in soil and pasture vegetation that would be required to exceed the action levels for foodstuffs recommended by the IAEA. The results show that the common detection limits for environmental analysis of these nuclides may be increased by orders of magnitude if the aim of the analysis is to determine whether or not the action levels will be exceeded. This information is useful in the development of more simple and rapid analytical methods to be used shortly after a nuclear accident. In addition to activity concentrations, the critical deposition densities on soil and grazing areas are estimated. Critical limits are also derived for 137Cs and 131I.

Radiocaesium and radiostrontium uptake by turnips and broad beans via leaf and root absorption

One of the immediate consequences of massive radioisotope release into the atmosphere is contamination of the biosphere. This contamination can affect plants either by direct deposition onto the leaves, or by contaminating the soil followed by absorption by the roots. Knowledge of the efficacy of the two routes of radionuclide incorporation into the food chain is fundamental to understanding the mechanisms by which radioactive contamination reaches man. The present work analyzes the incorporation of 134Cs and 85Sr via root and leaf uptake into the parts consumed by man, for two very different crops: turnip (Brassica napus) and broad bean (Vicia faba). The root uptake studies consider the available soil fraction for these two radionuclides, and indicate greater availability for 85Sr than for 134Cs which is fixed rapidly in the soil. For the study of leaf uptake, leaves were contaminated at three different stages of plant growth; the results indicate an inverse dependence of the transfer coefficients on the time elapsed from the moment of the contamination to harvesting of the edible parts.

Accumulation of 210Pb, 226Ra and radioactive cesium by fungi

Fungi sampled in three areas in France were analyzed by gamma-spectrometry for their concentrations of 134Cs, 137Cs, 210Pb and 226Ra. In most of the samples radioactive cesium was detected with a maximum of 2860 Bq kg-1 (dry wt.). Activity concentrations of 210Pb were in the range < 1.76-36.5 Bq kg-1 (dry wt.). Activity concentrations of 226Ra were consistently lower, often by one order of magnitude. Models are developed to estimate the contributions of atmospheric 210Pb deposited onto the fruit bodies to the measured 210Pb concentrations and of the uptake of 222Rn soluted in soil pore water which subsequently decays into 210Pb. It is shown that both pathways are of only minor importance. Comparison with the soil-mushroom concentration ratios of stable lead, which were determined for some of the samples, confirmed that 210Pb in mushrooms mainly originates from direct uptake of 210Pb present in the soil. Despite of the high concentrations of 137Cs detected in most of the mushrooms, radiation doses to individuals due to mushroom consumption are dominated by 210Pb for the majority of the edible mushrooms sampled.

Development of an approach to estimating mid- to long-term critical loads for radiocaesium contamination of cow milk in western Europe

This paper describes the application of the critical load methodology, developed to set emission targets for atmospheric pollutants, to radioecology. The critical load can be redefined within radioecology as the radionuclide deposition at which radionuclide activity concentrations in a specified food product will exceed the maximum permitted level. An empirically based approach is described which provides estimates of critical load values for cow milk in the mid- to long-term after an accident when soil-to-plant transfer of radiocaesium is largely responsible for plant radiocaesium contamination. The areas identified as being most potentially vulnerable to radiocaesium deposition using this approach are those with extensive areas of organic soils such as western Scotland, parts of Ireland, The Netherlands and Denmark. The classification of European soil types into soil groups with significantly different soil-to-plant transfer of radiocaesium, and the allocation of a transfer value to each soil group provide the greatest uncertainties within this approach. Potential problems and deficiencies affecting the estimation of parameter values are discussed.

[Dynamics of decrease of the transfer coefficient of Cs-137 to agricultural plants after the Chernobyl AES accident]

Data on the dynamics of the decrease of 137Cs transfer factors to agricultural plants after the accident at the ChNPP are presented. The ecological half-life periods of decrease in transfer factors in the first period after the accident (1987-1989) have been shown to vary between 1.2 and 2.9 years. Subsequently the decrease slowed down and in 1990-1994 the half-life periods amounted to 4-11 years depending on plant species peculiarities and soil properties.

Foliar and soil uptake of 134Cs and 85Sr by grape vines

The foliar and soil uptake of 134Cs and 85Sr by grape vines and their subsequent translocation to fruits and to the other plant compartments is described. Grape vine plants growing in pots and kept in an open field were contaminated with 134Cs and 85Sr in ionic form by sprinkling on the aerial part, or by addition to the soil. Sprinkling was effected at the stage of ripening of the grapes. Interception, determined by analysing all the leaves picked from three plants after the sprinkling, was approx. 50% of the sprayed activity. Soil contamination was effected after the fruit setting, 1 month earlier than sprinkling. At ripening, the whole plant was picked. Berries, leaves, shoots, stems, roots and soil were analysed by gamma spectrometry. Activities of the different parts of the plant were expressed as: (a) translocation factors of intercepted activity for foliar treatment; (b) transfer factors of activity applied to the soil for soil treatment. Both factors were calculated per unit of fresh weight, or referred to the total biomass of the plant compartment. Leaf-to-fruit translocation factors per unit of weight are of the order of magnitude of 10(-1) for 134Cs and of 10(-2) for 85Sr. One/two order of magnitude lower are soil-to-fruit transfer factors: 10(-3) both for 134Cs and for 85Sr. Radiocesium behaves quite differently from radiostrontium, but the behaviour of both radionuclides within the grape vine is independent of the path of absorption, by leaves or by roots. 134Cs is absorbed more easily than 85Sr by plant foliage, but is absorbed with more difficulty than 85Sr by roots. After absorption by either route, radiocesium concentrates mainly in the fruit compartment of the plant, whereas radiostrontium concentrates in the foliar compartment. Loss from the aerial part of the plant is higher for 85Sr than for 134Cs. 85Sr remains more available in soil than 134Cs, is more absorbed by roots and is more leached downward. After foliar contamination, the dominant pathway of radionuclides to reach the soil is by dislodging of non-absorbed radionuclides or senescent cells from the aerial part of the plant by action of wind and rain.

Gastrointestinal absorption of plutonium by the Marshall Islanders

The gastrointestinal absorption constant (f1) is a critical parameter in assessing systemic uptake following the ingestion of a radioactive material and in monitoring such intakes. This study addresses the latter, particularly for plutonium, and from environmental measurements derives an f1 value of 4 x 10(-4) for the Marshallese population. The uncertainty associated with the methodology and measurements used in this f1 value assessment is evaluated. This evaluation takes into account the results from 24-h urine samples and the particular lifestyle of the Marshallese. Plutonium intake resulting from soil consumption is a primary parameter in this evaluation; for this study, it was assumed to be 500 mg d(-1). The f1 value determined here is consistent with the values in ICRP Publication 67 of 5x10(-4) for ages 1 to adult, and is the same as that suggested by the NRPB.

Dynamics of 137Cs in the forests of the 30-km zone around the Chernobyl nuclear power plant

Dynamics of the 137Cs content in the components of the forests in the 30-km zone around the Chernobyl nuclear power plant (NPP) in 1986-1994 are associated mainly with such factors as the size of radioactive particles in the fallout, ecosystem humidification and soil type, tree age. The influence of particle size was especially noticeable between 1986-1987 and was displayed by low biological availability of radionuclides in the near part of the zone (within the 10-km radius circle around the NPP) in comparison with more distant regions (within the 30-km radius circle). Later, the expression of this influence decreased and transfer factor (the ratio of 137Cs content in overground phytomass to the soil contamination density) became approximately the same for all plots with similar ecological and fallout characteristics. Humidity of landscape and soil type determined the velocity of radionuclide vertical migration in the soil and 137Cs biological availability. These parameters were maximum for the hydromorphic soils of wet landscapes enriched in organic substance and poor clayey minerals. Differences of 137Cs accumulation in overground phytomass of trees caused by tree age are displayed in the higher 137Cs concentration in structural parts of young trees as compared with old ones.

[137Cs accumulation by grasses from peat soil under increasing amounts of potassium and nitrogen fertilizers]

The three-chamber model of radionuclides uptake from soil was proposed. This model permit to analyse the transfer factors as the function of the some properties of the radionuclides, macroelement-analogs, soil and plants. The field experiment results (Novozybkov District) was analysed. In this experiment the uptake 137Cs in Bromopsis inermis L. from peat soil under increasing K- and N-fertilizer doses was investigated.

[The biogeochemistry of the radionuclides of the Chernobyl release in the forest ecosystems of the European portion of the CIS]

The 9-years dynamic of Chernobyl-derived radionuclides in the vegetation and soil covers of the forest ecosystems of the European part of the CIS is considered. The quantitative estimation has been done for main fluxes of Cs-137 in the forests of automorphic landscapes: influx to the vegetation, return with the litterfall, stem flow and throughfall, vertical migration in the soil profile (including intrasoil flow), and redistribution within the system of geochemically connected landscapes.