Observation of changes in urinary excretion of thorium in humans following ingestion of a therapeutic soil

The study investigated the changes in urinary thorium excretion by humans following ingestion of a therapeutic soil, which contains about 10 ppm of thorium. This well-known healing earth in Germany has been considered as an alternative medicine for diarrhoea and gastric hyper-acidity. Six adult volunteers ingested this therapeutic soil in varying quantities for 1-15 days at levels approximating those described in the package insert of the medicine (10-60 g of soil per day). The subjects ingested about 0.1-0.6 mg of thorium daily, which is 100-600 times higher than the normal daily intake of about 1 microg thorium in Germany. All 24-h urine samples collected from the subjects during pre-ingestion, ingestion and post-ingestion periods of the soil were analyzed for (232)Th using inductively coupled plasma mass spectrometry (ICP-MS). The measured excretion values varied in a wide range. Apparently, the high thorium amounts administered did not increase the (232)Th excretion in urine as expected, suggesting that this soil ingestion will not result in a considerably higher and harmful uptake of thorium into the human body.

Predicting the transfer of 137Cs to rice plants by a dynamic compartment model with a consideration of the soil properties

This paper describes the predictions of the transfer of 137Cs to rice plants following soil deposition during a non-growth season of rice by a dynamic compartment model considering the soil properties, and their comparison with experimental results. Major processes considered in the model were percolation, soil mixing by plowing, plant uptake, leaching to deep soil, fixation to clay mineral, and time-dependent growth of a plant. To consider the effects of the soil properties (pH, clay mineral, organic matter content, and exchangeable K) on plant uptake and the leaching rates of 137Cs in a root zone soil, the Absalom model was used for the present model. The 137Cs aggregated transfer factors (TFa, m2kg-1 dry plant) of rice plants for two consecutive cultivation years were obtained as a result of simulated 137Cs soil deposition experiments with 17 paddy soils of different properties, all of which were performed before transplanting of the rice. Observed 137Cs TFa values of the rice plants did not show an evident trend for the pH and clay content of the soil properties, while they increased with an increasing organic matter content and a decreasing exchangeable K concentration. Predicted 137Cs TFa values of the rice plants were found to be comparable with those observed.

Soil-to-grain transfer of fallout 90Sr for 28 winter wheat cultivars

In order to identify wheat cultivars with minimum soil-to-grain transfer of fallout 90Sr, 28 winter wheat cultivars were investigated at three different sites with different soil types in Upper Bavaria. Each cultivar was grown on an area of 10 m2 and harvested in August 1999. Mean soil-to-grain concentration ratios (C(r)) were 0.151 +/- 0.029, 0.205 +/- 0.035 and 0.060 +/- 0.012, respectively. The C(r) values obtained varied by factors of up to 2.6 for the different cultivars at a given site, and by factors of up to 5.0 for the different sites and a given cultivar. Site-averaged normalized concentration ratios (SANC(r)) ranged from 0.666 +/- 0.062 to 1.503 +/- 0.161. The cultivars Convent, Ludwig, and Semper, showed the lowest uptake of (90)Sr compared to the mean of all cultivars at each site. A cultivar that shows both minimum uptake of 90Sr and 137Cs could not be identified. The results suggest that 90Sr rather than 137Cs might be the limiting radionuclide concerning the use of contaminated land for wheat production. Thus, more efforts might be necessary identifying wheat cultivars with minimum 90Sr uptake.

Effects of phosphorus fertilization on the availability and uptake of uranium and nutrients by plants grown on soil derived from uranium mining debris

Subterranean clover and barley were grown on a soil derived from uranium mining debris and fertilized with phosphate as a U immobilizing additive for in situ remediation. We investigated the beneficial effect of P fertilization in the range 0-500 mg P kg(-1) soil in terms of U extractability, plant biomass production and U uptake. Increasing P in the mining debris caused a significant decrease of the water-soluble U and NH(4)-Ac extractable U at pH 7 and 5. For both plant species, P fertilization considerably increased root and shoot dry matter up to a maximum observed for soil receiving 100 mg P kg(-1) while the soil-to-plant transfer of U was regularly decreased by increasing P content in soil. These observations show that P fertilization represents an in situ practical option to facilitate the revegetation of U-mining heaps and to reduce the risks of biota exposure to U contamination.

Measurement of 224Ra uptake in a fern actively accumulating radium

A method is proposed for determining the level of 224Ra in plant samples by measuring its descendant nuclide 212Pb at 239 keV by gamma-ray spectrometry. Variations of 224Ra and 212Pb over time during sample preparation and counting were delineated prior to gamma-ray measurement. The 224Ra concentrations in plant samples were measured by their direct uptake from soil, which could be determined and distinguished from that resulting from decay of 228Th inside the plants. We propose that a field-growing Dicranopteris linearis, which actively accumulates radium, can be used as an indicator of the nutritional transportation and metabolic rate of radium and other alkaline earth elements. We investigated the influence of rainfall on 224Ra concentrations in fronds of D. linearis and the corresponding uptake rates. 224Ra could serve as a natural tracer of growth in plants over a several days. Its presence and content in plants implies a temporal mineral metabolic rate, which can provide useful information for plant physiological and environmental investigations.

[Imitation model of 90Sr behaviour in the soil and stand of pine forest]

The algorithm of display of 90Sr behaviour mechanisms in forest ecosystems by method of imitating modeling is developed. Distinctive features of algorithm: the 90Sr contents in vegetation is subdivided into two parts (outside and internal pollution), which dynamics is considered separately; dynamics of a radionuclide is considered in connection with dynamics of organic substance; it is supposed, that 90Sr behaviour in plants is similar to Ca behaviour; the biological availability 90Sr contained in a soil, is integrated function of time and physico-chemical properties of the given soil. On the basis of offered algorithm the model is constructed which is used for realization of a number of numerical experiments, including reconstruction of a situation of pollution of forest ecosystem on grey forest soils in result of Kyshtym accident. The quantitative estimations of intensity of 90Sr redistribution between stand components and soil are received. The modern problems of creation of prognostication models of 90Sr dynamics in the forest ecosystems are discussed.

[A mathematical model of 137Cs uptake and removal from the body of cattle in the event of chronic consumption of contaminated fodder]

A two-chamber mathematical model of 137Cs uptake and removal from the body of cattle chronically consuming contaminated fodder has been developed; the model takes into account age dependence of radionuclide absorption from the gastro-intestinal tract. The model parameters were taken from the experiment on calves with chronic peroral uptake of contaminated fodder. In accordance with the model and experiment, 137Cs transfer factor to the muscular tissue one month after birth reaches a maximum value of 56% of the daily uptake per 1 kg of the tissue. By the model, the equilibrium processes of uptake and removal set in two years after the calves birth. The equilibrium TF for muscles in adults approximates 2.8% of the daily uptake per 1 kg tissue. Because of 137Cs absorption from the gastrointestinal tract changes with age, doses of internal exposure of calves over the first two years will be about 5 times higher than doses for any one of the two subsequent years.

[137Cs distribution and accumulation in the tissues of cultivated fungi (Pleurotus ostreatus)]

The authors examined 137Cs accumulation and distribution in different structures and tissues of Pleurotus ostreatus cultivated under laboratory conditions. The fungi were shown to concentrate 137Cs. A higher concentrations of the radionuclides in the fungi compared to their substrate is manifested at the first stages of the fruit body formation, the maximum content of 137Cs is accumulated by fungi in the middle of bearing stage. The fungus tissues are different by their accumulative capacity as follows (ascending range): central, more dense part of the stipe < stipe < mycelium < cap < generative tissues. 137Cs accumulation in the fruit bodies depends also on the fungus size and age.

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

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

Modelling 137Cs uptake in plants from undisturbed soil monoliths

A model predicting 137Cs uptake in plants was applied on data from artificially contaminated lysimeters. The lysimeter data involve three different crops (beans, ryegrass and lettuce) grown on five different soils between 3 and 5 years after contamination and where soil solution composition was monitored. The mechanistic model predicts plant uptake of 137Cs from soil solution composition. Predicted K concentrations in the rhizosphere were up to 50-fold below that in the bulk soil solution whereas corresponding 137Cs concentration gradients were always less pronounced. Predictions of crop 137Cs content based on rhizosphere soil solution compositions were generally closer to observations than those based on bulk soil solution composition. The model explained 17% (beans) to 91% (lettuce) of the variation in 137Cs activity concentrations in the plants. The model failed to predict the 137Cs activity concentration in ryegrass where uptake of the 5-year-old 137Cs from 3 soils was about 40-fold larger than predicted. The model generally underpredicted crop 137Cs concentrations at soil solution K concentration below about 1.0 mM. It is concluded that 137Cs uptake can be predicted from the soil solution composition at adequate K nutrition but that significant uncertainties remain when soil solution K is below 1 mM.

Uptake and distribution of natural radioactivity in wheat plants from soil

The uptake of naturally occurring uranium, thorium, radium and potassium by wheat plant from two morphologically different soils of India was studied under natural field conditions. The soil to wheat grain transfer factors (TF) were calculated and observed to be in the range of 4.0 x 10(-4) to 2.1 x 10(-3) for 238U, 6.0 x 10(-3) to 2.4 x 10(-2) for 232Th, 9.0 x 10(-3) to 1.6 x 10(-2) for 226Ra and 0.14-3.1 for 40K. Observed ratios (OR) of radionuclides with respect to calcium have been calculated to explain nearly comparable TF values in spite of differences in soil concentration of the different fields. They also give an idea about the discrimination exhibited by the plant in uptake of essential and nonessential elements. The availability of calcium and potassium in soil for uptake affects the uranium, thorium and radium content of the plant. The other soil factors such as illite clays of alluvial soil which trap potassium in its crystal lattice and phosphates which form insoluble compounds with thorium are seen to reduce their availability to plants. A major percentage (54-75%) of total 238U, 232Th and 226Ra activity in the plant is concentrated in the roots and only about 1-2% was distributed in the grains, whereas about 57% of 40K activity accumulated in the shoots and 16% in the grains. The intake of radionuclides by consumption of wheat grains from the fields studied contributes a small fraction to the total annual ingestion dose received by man due to naturally existing radioactivity in the environment.

Can barium and strontium be used as tracers for radium in soil-plant transfer studies?

Radium is one of the prominent potential contaminants linked with industries extracting or processing material containing naturally occurring radionuclides. In this study we investigate if 133Ba and 85Sr can be used as tracers for predicting 226Ra soil-to-plant transfer. Three soil types were artificially contaminated with these radionuclides and transfer to ryegrass and clover was studied. Barium is considered a better tracer for radium than strontium, given the significant linear correlation found between the Ra and Ba-TF. For strontium, no such correlation was found. The relationship between soil characteristics and transfer factors was investigated. Cation exchange capacity, exchangeable Ca+Mg content and soil pH did not seem to influence Ra, Ba or Sr uptake in any clear way. A significant relation (negative power function) was found between the bivalent (Ca+Mg) concentration in the soil solution and the Ra-TF. A similar dependency was found for the Sr and Ba-TF, although less significant.

Uranium distribution and cycling in Scots pine (Pinus sylvestris L.) growing on a revegetated U-mining heap

We determined the uranium distribution in soil and its allocation in compartments of 35-year-old Scots pine developed on a revegetated U-mining heap. The processes controlling the dynamics of U recycling were identified and further quantified in terms of annual fluxes. As pine developed, an acid humus layer emerged leading to weathering of the alkaline mining debris but this had little effect on U mobility in the soil profile. Increased U mobility mainly involved a translocation of U to metal-humus chelates in surface layers. The root compartment accounted for 99.3% of the U budget in tree, thus serving as an effective barrier which restricts U uptake. The current root uptake and transfer of U to upper parts of the tree amounted to about 3g ha(-1) y(-1), i.e. less than 0.03% of the current NH4-exchangeable U pool in the soil (0-30 cm). Allocation and translocation pattern made it clear that a dominant fraction of the translocated U moves passively with the ascent xylem sap, most likely as a soluble complex, and steadily accumulates in the needles. Consequently, 97% of the U annual uptake is returned to the soil through litterfall. At the studied site, the risk of U dissemination due to biomass turnover or trunk harvest was low when considered in relation to the current "exemption level" for U.

Soil migration and plant uptake of technetium from a fluctuating water table

Soil columns (50x15 cm) were used to determine the potential for 95mTc (as a surrogate for 99Tc which is an important component of some radioactive waste) to migrate from a contaminated, fluctuating water table, through sandy loam soil and into perennial ryegrass. Upward migration was significantly retarded with, generally, only the bottom few centimetres of soil becoming contaminated over the 6 months of the experiment. This is thought to have been due to the presence of anoxic conditions within the water table leading to the reduction of pertechnetate to Tc(IV) species which are relatively insoluble. However, some evidence of very slow upward migration over time was found. Only a small and inconsistent transfer of activity into the perennial ryegrass was observed. Whilst these observations would suggest that 99Tc is less important than radionuclides such as 129I and 36Cl in terms of the risk associated with radioactive waste disposal, the potential for a slow upward migration, and/or a pulse-release following the re-oxidation of reduced soil in which 99Tc has accumulated should not be overlooked.

Bioavailability of radiostrontium in soil: experimental study and modeling

Parameters related to 90Sr mobility in the soil-plant system are reported: exchangeable content, selectivity coefficient, and transfer factor. Large mobility of 90Sr in different soil types was shown. The fraction of exchangeable 90Sr varied between 70 and 90%. The selectivity coefficient K(C)(90Sr/Ca) values were in the range 1.3-2.5. The radionuclide transfer factors (TF) varied by a factor of 9.6 for barley seedlings and by a factor of 6.6 for lupine seedlings. The exchangeable Ca content was the determinant soil parameter responsible for differences in 90Sr biological availability. A static model was devised that describes 90Sr sorption from soil solution by soil and on the root surface. The parameter of 90Sr bioavailability (A) has been suggested. Parameter A was calculated from data on soil exchangeable Ca content and 90Sr mobility indicators--exchangeable fraction of the radionuclide and the selectivity coefficient K(C)(90Sr/Ca). A correlation was found between TF and parameter A.

Effect of K and bentonite additions on Cs-transfer to ryegrass

Bentonite amendments are generally ineffective in reducing the soil-to-plant radiocaesium transfer but have previously been shown that bentonites in the K-form having been subjected to wetting-drying cycles had pronounced radiocaesium binding capacities. We have investigated the effect of wetting-drying (WD) on Radiocaesium Interception Potential (RIP) development in three K-bentonites and K-bentonite soil mixtures, using a variety of procedures: homogenisation of the bentonites with K through dialysis (K(B)), or partial transformation of the bentonite to the K-form in the presence of a solution of K2CO3 (K(L)) or in presence of solid K2CO3 (K(S)). Of the three strategies tested, addition of K2CO3 (solid) at a dose of 2 meq g(-1) clay and adding the K-bentonite mixtures to the soil resulted in the highest RIP increase after 20 WD cycles. The procedure giving the highest RIP yield is the most practical for further applications and was used in a pot experiment under greenhouse condition. When expressing the RIP increase of the soil-bentonite mixtures per unit bentonite added (RIP yield), 28- to 110-fold RIP increases were observed up to a value of approximately 60,000 meq kg(-1) (6 times higher than the RIP for illite). The beneficial effect following K-bentonite application was shown to be dependent both on a sorption enhancement effect (direct RIP effect) and fixation effects (indirect RIP effect). Greenhouse testing proved that the RIP effects observed in greenhouse could be predicted by making use of the sorption data from the laboratory tests. Optimum soil-amendment would be obtained with bentonites with high initial sorption RIP and a high sorption RIP increase when subjected to WD in the presence of potassium. Hypothised Transfer Factor (TF)-reductions of at least 10-fold could result when mixing approximately 1% bentonite, like Otay bentonite (RIP yield 99,000 meq kg(-1) after WD in presence of K if only fine particle size of <1mm considered) with the contaminated ploughing layer.

Thorium uptake by wheat at different stages of plant growth

Data on biogeochemistry of thorium are rather limited. So far little is known about toxic effects of small amounts of the radionuclide on higher plants. In this study the uptake of thorium by wheat seedlings was measured by greenhouse experiments. Germination of wheat seeds for 6 days in the presence of thorium resulted in accumulation of the metal in all parts of the seedlings. When the Th-rich seedlings were transferred to normal soil and were grown there further for 7 days, Th concentrations in roots and leaves decreased significantly (in leaves the Th content decreased up to the level of Th in the control plants). In seeds, however, Th content remained unchanged. An increase of Th content in roots and seeds was also observed as a result of addition of thorium to soil but in this case the concentration of Th in leaves did not change. The accumulation of Th in plants affected the uptake of other elements including essential macro-nutrients. The most strongly affected part of the plants was leaf.

Radiocaesium soil-to-wood transfer in commercial willow short rotation coppice on contaminated farm land

The feasibility of willow short rotation coppice (SRC) for energy production as a revaluation tool for severely radiocaesium-contaminated land was studied. The effects of crop age, clone and soil type on the radiocaesium levels in the wood were assessed following sampling in 14 existing willow SRC fields, planted on radiocaesium-contaminated land in Sweden following Chernobyl deposition. There was only one plot where willow stands of different maturity (R6S2 and R5S4: R, root age and S, shoot age) and clone (Rapp and L78183 both of age category R5S4) were sampled and no significant differences were found. The soils differed among others in clay fraction (3-34%), radiocaesium interception potential (515-6884 meq kg(-1)), soil solution K (0.09-0.95 mM), exchangeable K (0.58-5.77 meq kg(-1)) and cation exchange capacity (31-250 meq kg(-1)). The soil-to-wood transfer factor (TF) of radiocaesium differed significantly between soil types. The TF recorded was generally small (0.00086-0.016 kg kg(-1)), except for willows established on sandy soil (0.19-0.46 kg kg(-1)). Apart from the weak yet significant exponential correlation between the Cs-TF and the solid/liquid distribution coefficient (R2 = 0.54) or the radiocaesium interception potential, RIP (R2 = 0.66), no single significant correlations between soil characteristics and TF were found. The wood-soil solution 137Cs concentration factor (CF) was significantly related to the potassium concentration in the soil solution. A different relation was, however, found between the sandy Trödje soils (CF = 1078.8 x m(K)(-1.83), R2 = 0.99) and the other soils (CF = 35.75 x m(K)(-0.61), R2 =0.61). Differences in the ageing rate of radiocaesium in the soil (hypothesised fraction of bioavailable caesium subjected to fast ageing for Trödje soils only 1% compared to other soils), exchangeable soil K (0.8-1.8 meq kg(-1) for Trödje soils and 1.5-5.8 meq kg(-1) for the other soils) and the ammonium concentration in the soil solution (0.09-0.31 mM NH4+ for the Trödje soils compared to 0.003-0.11 mM NH4+ for the other soils) are put forward as potential factors explaining the higher CF and TF observed for the Trödje soils. Though from the dataset available it was not possible to unequivocally predict the Cs-soil-to-wood-transfer, the generally low TFs observed point to the particular suitability for establishment of SRC on radiocaesium-contaminated land.

Retention and phytoavailability of radioniobium in soils

Radioniobium is present in long-lived nuclear waste as a result of the activation of zirconium pellets associated with the nuclear fuel. The behaviour of niobium (Nb) in the environment and especially its fate in the soil-plant system has not been thoroughly investigated so far. In safety assessment of French long-lived nuclear waste disposal, data concerning the mobility and the bioavailability of Nb in soils are needed as well as general trends of its fate in the specific environment around the site of French underground research laboratory. Therefore, we investigated the mobility of 95Nb in three different soils typical of the area of north-eastern France and its uptake by two plants, rye grass (Lolium perenne L.) and winter wheat (Triticum aestivum L.). Soil:solution distribution of 95Nb was observed in 1:10 batch experiments with deionized water for a 3-day period. Results showed that K(d) values were high (in the order of 10(3) L kg(-1)) and were still significantly increasing after 3 days. A mathematical model, fitted to describe the decrease of the radioactivity after 3 days, is proposed to calculate sorption ratios--SR--(rather than K(d) values as equilibrium was not reached) over longer periods. Soil-to-plant concentration ratios (CR) were measured in shoots and roots of the two plants after cultivation on two soils spiked with (95)Nb (406kBqkg(-1)). Soil-to-root dry weight CR were high (0.30-1.52) and could probably be due to efficient uptake into the roots. However, no transfer of Nb to plant shoots was detected in any of the soils. Nb is thus a rather immobile element in soils and its transfer to plants seems limited to underground parts. It would therefore tend to accumulate in surface horizons of soils in case of long-term continuous surface release.

Uptake and distribution of 90Sr and stable Sr in rice plants

The stable Sr content in the aboveground parts of rice plants at various growth stages, and the distributions of 90Sr and stable Sr in rice plant components, such as polished rice, rice bran, hull, straw and root, at harvest time, were determined. The total Sr content in the aboveground rice plants was dependent on the growth stage and followed the sigmoidal shape of the growth curve. The concentration of 90Sr among the different components of rice plants varied within two orders of magnitude, whereas the 90Sr/Sr concentration ratio had a constant value. Therefore, the translocation rate of 90Sr in rice plants had similar values to that of stable Sr. However, the 90Sr/Sr concentration ratio for the rice plants was different for each study site. Only 0.6% of the total Sr was found in polished rice, while more than 99% was found in the non-edible components, of which 87% was present in the straw. These findings suggest that 90Sr in the non-edible parts could have been transferred to humans through the soil-plant system and/or feed-livestock pathway. The soil-to-plant transfer factor of 90Sr in polished rice was 0.0021 +/- 0.00007, which was two orders of magnitude lower than that in the straw. The percentage of 90Sr removed from the upper soil layer to the aboveground biomass of rice plants at harvest time was calculated as 0.094%. It is possible that approximately 0.1% of the total 90Sr content in the surface soil layer is removed from the soil-plant system by human activities every year.

Soil-to-plant halogens transfer studies 2. Root uptake of radiochlorine by plants

Long-term field experiments have been carried out in the Chernobyl exclusion zone in order to determine the parameters governing radiochlorine (36Cl) transfer to plants from four types of soil, namely, podzoluvisol, greyzem, and typical and meadow chernozem. Radiochlorine concentration ratios (CR) in radish roots (15+/-10), lettuce leaves (30+/-15), bean pods (15+/-11) and wheat seed (23+/-11) and straw (210+/-110) for fresh weight of plants were obtained. These values correlate well with stable chlorine values for the same plants. One year after injection, 36Cl reached a quasi-equilibrium with stable chlorine in the agricultural soils and its behavior in the soil-plant system mimicked the behavior of stable chlorine (this behavior was determined by soil moisture transport in the investigated soils). In the absence of intensive vertical migration, more than half of 36Cl activity in arable layer of soil passes into the radish, lettuce and the aboveground parts of wheat during a single vegetation period.

Comparison of transfer and distribution of technetium and rhenium in radish plants from nutrient solution

Tracer experiments were carried out to compare the plant uptake behavior of Tc and Re from nutrient solutions. Radish plants, transplanted to nutrient solution including various tracers, showed the same uptake and distribution of 95mTc and 183Re. The trend was the same when the 99Tc and stable-Re concentrations were increased in nutrient solution. The behavior of other elements was different from that of Tc and Re. These findings suggest the possible use of Re as the chemical analogue of Tc in soil solution to plant uptake experiments.

Comparative analysis of the in and ex situ determination of environmental radiation and dosimetry levels

A method is proposed to determine the activities of natural and artificial gamma-emitting radionuclides in soils using in situ spectrometry that is validated with conventional low-background laboratory gamma spectrometry. From the two sets of results, the dose-equivalent rate levels in the environment were reproduced and we are thus able to determine the principal components of those levels.

Radionuclide transport above a near-surface water table: IV. Soil migration and crop uptake of chlorine-36 and technetium-99, 1990 to 1993

Vertical distributions of (36)Cl and (99)Tc are presented from deep and shallow lysimeters above artificially controlled water tables for a 4-yr experiment from 1990 to 1993. Activity concentration profiles were all measured in late summer when a winter wheat (Triticum aestivum L. cv. Pastiche) crop was harvested. After harvest, activity concentrations in different organs of the crop were determined and crop uptake quantified as both an inventory ratio (IR) and a transfer factor (TF(w)), weighted to account for differential root and radionuclide distributions within the soil profile. Vertical distributions of radionuclides, crop roots within the soil, and IR and TF(w) values were each subjected to analysis of variance to estimate the individual and combined effects of soil depth and the year of the experiment on the results obtained. Chlorine-36 and (99)Tc exhibited highly significant variations in activity concentrations with soil depth and from year to year, indicating considerable physical mobility of both radionuclides. Soil-to-plant transfer was also high for both radionuclides compared with data obtained for gamma-emitting radionuclides. The IR values indicated that up to 40% of (36)Cl was incorporated in the crop's tissues at harvest, compared with a maximum of less than 1% for the less mobile gamma-emitting radionuclides. On the basis of the TF(w) values determined, (36)Cl uptake by winter wheat exceeded (99)Tc uptake, indicating that (36)Cl is highly bioavailable. Factors controlling the migration and bioavailability of both (36)Cl and (99)Tc in soils are discussed.

Soil-plant transfer of plutonium and americium in contaminated regions of Belarus after the Chernobyl catastrophe

Experimental data are presented for the soil to plant transfer of plutonium and americium into the main species of grass vegetation of Belarusian grasslands contaminated as a result of the Chernobyl catastrophe of 1986. The content of radionuclides in pore soil solutions and the total reserve of biologically available forms of plutonium and americium in rooting layers of different soil varieties have been established. The distribution coefficients of (239,240)Pu and 241Am between the solid phase and pore waters of soils have been evaluated. The migration ability and biological availability of radionuclides in soils with different structures of the absorbing complex have been analyzed for various landscape conditions. The dependence of soil to plant transfer of plutonium and americium on the content and composition of organic matter, and other characteristics of the soil complex has been studied. On the basis of these data, predictions of the contamination levels of the main grass species of natural and agricultural ecosystems by 241Am are presented.