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Quantitative assessment of radiocaesium bioavailability in forest soils
Abstract
A method for quantitative characterisation of the radiocaesium availability to plants in forest ecosystems has been developed. For this purpose an expression has been proposed to calculate the radiocaesium availability factor in soils, which is a combination of key soil characteristics: radiocaesium exchangeability, exchangeable calcium in soil and effective selectivity coefficient. The experimental dependencies of the radiocaesium soil to plant concentration factors for fern and bilberry, on the availability factor calculated by the above equation were satisfactory described by linear function. The advantage of this method to characterise bioavailability of radiocaesium and to estimate site-specific values of concentration factor is that the necessary soil characteristics may be taken from the reference literature, evaluated by experts or determined with a simple experimental procedure. The method can be used in development of a radioecological Geographic Information Systems.
... The mechanistic models of different complexity describing the sorption of 137 Cs by soils and its accumulation by plants [6,18,20,21,24,25] have been put forward in the last decades due to the development of the theory of selective 137 Cs sorption [10,11,29,30]. In the mechanistic approach [3], the complex process of ion uptake by plants from the soil is divided into two stages: (1) the distribution of ions between the solid and liquid (soil solution) phases of the soil and (2) the uptake of ions from the soil solution by plant roots. ...
... At a specified temperature, the equilibrium can be characterized by the selectivity coefficient (K), which is independent of the composition of the ideal ion exchanger: (14) (15) where x and c denote the equivalent fractions of cations in the ion-exchanger phase and their activities in solution, respectively. In the case of homovalent exchange, the selectivity coefficient of the mixture can be calculated as a function of the ion-exchanger composition in the form of a positive solution of the equation (16) where (17) (18) Model 2 includes five input parameters (the sixth parameter is derived automatically), which is few taking into account that 10 or more parameters can be used in other models [10]. ...
The selective sorption of cesium by some soils, minerals, and natural mineral sorbents was studied using new methodological
and experimental approaches. It was found that the total capacity of two types of highly selective sorption sites significantly
differing (by several orders of magnitude) in the selectivity coefficients of Cs-K ion exchange makes up 0.5–6% of the total
capacity of the ion exchanger. The values of the radiocesium interception potential were determined for the studied soils
and minerals.
... Why does T ag -137 Cs of Koshiabura buds vary largely? As one important factor in the high variability of T ag -137 Cs, the variation of soil properties in the mineral soil horizon should be considered, such as the radiocesium fixation ability of the soil and the cation composition of the soil solution, especially the concentrations of potassium and ammonium [33][34][35] . Although 137 Cs fixation potentials were not measured at all four sampling sites in the present study, all of them have brown forest soils with granitic rocks as the surface geology 36 . ...
The aggregated transfer factor (Tag) is commonly used to represent the actual transfer of radiocesium from soil to wild edible plants, but the values have shown substantial variation since the Fukushima nuclear accident. To elucidate the factors causing this variation, we investigated the effects of spatial scale and vertical ¹³⁷Cs distribution in the soil on the variation of Tag-¹³⁷Cs values for one of the most severely contaminated wild edible plants, Eleutherococcus sciadophylloides Franch. et Sav. (Koshiabura). The variation in Tag-¹³⁷Cs values was not reduced by direct measurement of ¹³⁷Cs deposition in soil samples from the Koshiabura habitat, as a substitute for using spatially averaged airborne survey data at the administrative district scale. The ¹³⁷Cs activity concentration in Koshiabura buds showed a significant positive correlation with the ¹³⁷Cs inventories only in the organic horizon of soil from the Koshiabura habitat. The ratio of ¹³⁷Cs inventories in the organic horizon to the total ¹³⁷Cs deposition in soil exhibited substantial variation, especially in broad-leaved deciduous forests that Koshiabura primarily inhabits. This variation may be the cause of the wide range of Tag-¹³⁷Cs values observed in Koshiabura buds when calculated from the total ¹³⁷Cs deposition in soil.
... Hence, these micaceous minerals exhibit a very high selectivity and fixation capability for Cs + compared with the main cations in natural systems. Even a small amount of these mica-clay minerals in a soil may selectively fix a large amount of caesium, resulting in lower mobility in the environment and lower bioavailability [250,251]. ...
... Hence, these micaceous minerals exhibit a very high selectivity and fixation capability for Cs + compared with the main cations in natural systems. Even a small amount of these mica-clay minerals in a soil may selectively fix a large amount of caesium, resulting in lower mobility in the environment and lower bioavailability [250,251]. ...
... In this formula A is the ''availability'' factor, B, the proportionality coefficient between A and TF, is a plant specific property and characterizes the ability of a specific plant to sorb radiocaesium on the root exchange complex and transfer it through the cell wall, a ex is the exchangeability of radiocaesium in soil, RIP is a measure for the selective sorption of 137 Cs þ by soils, K c (NH 4 /K) is the selectivity coefficient of NH 4 þ ions with respect to the competing ion K þ , in rectangular brackets [ ] are the cation concentrations in the soil solution. This model was successfully tested for forest soils from Upper Swabia, Russia, Sweden and Switzerland (Konoplev et al., , 2000. If sorption both on frayed edge sites (FES) and regular exchange sites (RES) is considered, this factor A can be rewritten as: ...
Fertilization with 2.5t/ha limestone: (83% CaCO(3), 8% MgO, 6% K(2)O, 3% P(2)O(5)) reduces the (137)Cs transfer from spruce forest soil into plants like fern (Dryopteris carthusiana) and blackberry (Rubus fruticosus) by a factor of 2-5 during at least 11 years as measured by the aggregated transfer factor T(ag). In 1997 and 2006 these results were confirmed by additional measurements of the (137)Cs transfer factor TF, related to the root zone (O(h) horizon), which were explained by the selective sorption of (137)Cs in the root zone by measurements of the Radiocaesium Interception Potential (RIP) in fertilized (RIP>179meq/kg) and non-fertilized soils (RIP<74meq/kg).
... In this formula, A is the ''availability'' factor, B characterizes the ability of a specific plant to sorb radiocaesium on the root exchange complex and transfer it through the cell wall, a ex is the exchangeability of radiocaesium in soil, RIP is a measure for the selective sorption of 137 Cs þ , K c FES (NH 4 /K) is the selectivity coefficient of NH 4 þ ions with respect to the competing ion K þ , in rectangular brackets [ ] are the cation concentrations in the soil solution. This model was successfully tested for forest soils from Upper Swabia, Russia, Sweden and Switzerland (Konoplev et al., , 2000. Delvaux et al. (2000) discovered low concentrations of soluble K in the rhizosphere to be the cause of increased uptake of 137 Cs and they verified the above relation between TF and RIP for ryegrass (Lolium). ...
To give a quantitative description of the radiocaesium soil-plant transfer for fern (Dryopteris carthusiana) and blackberry (Rubus fruticosus), physical and chemical properties of soils in spruce and mixed forest stands were investigated. Of special interest was the selective sorption of radiocaesium, which was determined by measuring the Radiocaesium Interception Potential (RIP). Forest soil and plants were taken at 10 locations of the Altdorfer Wald (5 sites in spruce forest and 5 sites in mixed forest). It was found that the bioavailability of radiocaesium in spruce forest was on average seven times higher than in mixed forest. It was shown that important factors determining the bioavailability of radiocaesium in forest soil were its exchangeability and the radiocaesium interception potential (RIP) of the soil. Low potassium concentration in soil solution of forest soils favors radiocaesium soil-plant transfer. Ammonium in forest soils plays an even more important role than potassium as a mobilizer of radiocaesium. The availability factor - a function of RIP, exchangeability and cationic composition of soil solution - characterized reliably the soil-plant transfer in both spruce and mixed forest. For highly organic soils in coniferous forest, radiocaesium sorption at regular exchange sites should be taken into account when its bioavailability is considered.
The remediation of contaminated land using plants, bacteria and fungi has been widely examined, especially in laboratory or greenhouse systems where conditions are precisely controlled. However, in real systems at the field scale conditions are much more variable and often produce different outcomes, which must be fully examined if ‘gentle remediation options’, or GROs, are to be more widely implemented, and their associated benefits (beyond risk-management) realized. These secondary benefits can be significant if GROs are applied correctly, and can include significant biodiversity enhancements. Here, we assess recent developments in the field-scale application of GROs for the remediation of two model contaminants for nuclear site remediation (⁹⁰Sr and ¹³⁷Cs), their risk management efficiency, directions for future application and research, and barriers to their further implementation at scale. We also discuss how wider benefits, such as biodiversity enhancements, water filtration etc. can be maximized at the field-scale by intelligent application of these approaches.
The chapter reviews the studies of the behavior of Chernobyl-derived radionuclides in the soil–water environment that have been carried out over more than 30 years after the accident at the Chernobyl nuclear power plant on 26 April 1986, the worst nuclear accident ever. As a result of post-Chernobyl investigations, the role of released fuel particles in the environmental behavior of radionuclides has been revealed. A conceptual model accounting for transformation of radionuclide chemical forms in soils and sediments is outlined and data on key kinetic and equilibrium parameters for this model are presented. Newly introduced after Chernobyl accident, parameters of radiocesium selective sorption by soils and sediments (capacity of frayed-edge sites [FES] and radiocesium interception potential [RIP]) and methodologies for their determination and application are discussed. Another important addressed issue is establishing the exchangeable distribution coefficient Kdex, which can be estimated on the basis of ion-exchange equilibrium from commonly accepted characteristics of soils and sediments. Development of methods to parameterize radionuclide bioavailability through soil and soil solution characteristics is also examined. The reviewed advances in post-Chernobyl studies help to reduce significantly the uncertainty associated with predicting radionuclide fate and transport in the environment.
This chapter describes the consequences of the Chernobyl accident in forest ecosystems. We focus mainly on forests in the near zone of the accident at the territories of Ukraine and Belarus. Within this area, especially in the Ukrainian part of the 30-km Chernobyl zone, forests were exposed to high doses during the acute phase of the accident resulting in the slight to severe (up to lethal) damages to the ecosystems. Three decades after the accident, Chernobyl forests in the near 10-km zone remain heavily contaminated with long-lived radionuclides such as ¹³⁷Cs, ⁹⁰Sr, and isotopes of transuranium elements, which excludes the possibility of their economical utilization in the long term. At the most contaminated places, dose rates to the tree species may reach the level of mGy h⁻¹, that is, exceeding the safe levels for terrestrial ecosystems. We review the data on the radioactive contamination levels in Chernobyl forests, dynamics of radionuclides in the typical tree species at the early and late stages after the deposition, and the effects of acute and chronic radiation to plant species and analyze the contribution of forests to the doses to humans. Many important issues, such as radioactive contamination and effects on animals and others, are out of the scope of this chapter. Although this volume of the book is focused on the consequences of the Chernobyl accident, in some parts of this chapter, we find it necessary to refer to the situation after the Fukushima accident in order to emphasize the generic processes and their mechanisms in the radioactively contaminated forests. Materials of this chapter were partly presented in our recent reviews (Yoschenko et al., J Forest Res 23:3–14, 2018b; Yoschenko et al., Radiocesium dynamics in a Japanese forest ecosystem. Initial stage of contamination after the incident at Fukushima Daiichi Nuclear Power Plant, 2019); here, we present the extended version of the review.
This is Volume II in a three-volume set on the Behavior of Radionuclides in the Environment, focusing on Chernobyl. Now, so many years after the Chernobyl accident, new data is emerging and important new findings are being made. The book reviews major research achievements concerning the behavior of Chernobyl-derived radionuclides, including their air transport and resuspension, mobility and bioavailability in the soil-water environment, vertical and lateral migration in soils and sediments, soil-to-plant and soil-to-animal transfer, and water-to-aqueous biota transfer. The long-term dynamics of radionuclides in aquatic ecosystems are also discussed, in particular, the heavily contaminated cooling pond of the Chernobyl Nuclear Power Plant, which is in the process of being decommissioned.
Lessons learned from long-term research on the environmental behavior of radionuclides can help us understand the pathways of environmental contamination, which, in turn, will allow us to improve methods for modeling and predicting the long-term effects of pollution.
This book features a wealth of original data and findings, many of which have never been published before, or were not available internationally. The contributing authors are experts from Ukraine, Russia and Belarus with more than 30 years of experience investigating Chernobyl-derived radionuclides in the environment.
The content presented here can help to predict the evolution of environmental contamination following a nuclear accident, and specifically the Fukushima Dai-ichi nuclear power plant accident.
Fern accumulates radionuclides in abundance, including 137Cs. Tranfer of 137Cs and 40K in plants which have different root systems (fern or grass), or have no roots at all (moss) was compared. Samplings were performed in regions contaminated with 137Cs after Chernobyl Nuclear Power Plant (ChNPP) accident in 1994 and 1997–2000. The male fern (Dryopteris filix‐mas) most prevailing in Lithuania was studied. Fern accumulates 137Cs more effectively than grass or moss. The average 137Cs activity concentration in fern is 180±60 Bq kg−1 and the transfer factor is 0,074 m2kg−1. The fern stipe accumulates 137Cs most of all (200±90 Bqkg‐1), the transfer factor is 0,087 m2 kg−1. Accumulation of 137Cs is influenced by the content of K in the soil. 137Cs and 40K activity concentrations in fern are higher than those in the soil what shows that fern accumulates 137Cs better than 40K. Fern can clean the soil because this plant accumulates radionuclides in its stipe rather than roots.
137Cs kaupimosi sistemoje dirva – paparčiai tyrimai
Santrauka
Papartis efektyviai akumuliuoja radionuklidus, taip pat ir 137Cs. Šiame darbe palyginami 137Cs ir jo cheminio‐biologinio analogo gamtinės kilmės 40K kaupimosi augaluose, turinčiuose skirtingą šaknų sistemą (paparčiai, žolė) ir neturinčiuose šaknų sistemos (samanos) koeficientai. Bandiniai imti 1994 m. ir 1997–2000 m. po Černobylio AE avarijos 137Cs užterštuose Lietuvos regionuose. Tiriamas plačiausiai Lietuvoje paplitęs kelminis papartis (Dryopteris filix‐mas). Paparčiai kaupia 137Cs efektyviau negu žolės arba samanos, vidutinis 137Cs savitasis aktyvumas juose nustatytas 180±60 Bq×kg−1, kaupimosi koeficientas ‐ 0,074 m2×kg−1. Labiausiai 137Cs susikaupia paparčio stiebe (200±90 Bq×kg−1 kaupimosi koeficientas ‐ 0,087 m2×kg−1). 137Cs kaupimosi augaluose efektyvumui įtakos turi kalio kiekis dirvožemyje. 137Cs ir 40K savitųjų aktyvumų santykis paparčiuose yra didesnis negu šis santykis dirvožemyje, tai rodo, kad paparčiai geriau įsisavina 137Cs nei 40K. Galima teigti, kad paparčiai išvalo iš dirvožemio 137Cs, nes šis cheminis elementas gausiau kaupiasi stiebe negu šaknyse.
Reikšminiai žodžiai: 137Cs, 40K, Černobylio AE avarija, papartis, dirvožemis, kaupimosi koeficientas
First Published Online: 14 Oct 2010
April 2016 sees the 30(th) anniversary of the accident at the Chernobyl nuclear power plant. As a consequence of the accident populations were relocated in Belarus, Russia and Ukraine and remedial measures were put in place to reduce the entry of contaminants (primarily (134+137)Cs) into the human food chain in a number of countries throughout Europe. Remedial measures are still today in place in a number of countries, and areas of the former Soviet Union remain abandoned. The Chernobyl accident led to a large resurgence in radioecological studies both to aid remediation and to be able to make future predictions on the post-accident situation, but, also in recognition that more knowledge was required to cope with future accidents. In this paper we discuss, what in the authors' opinions, were the advances made in radioecology as a consequence of the Chernobyl accident. The areas we identified as being significantly advanced following Chernobyl were: the importance of semi-natural ecosystems in human dose formation; the characterisation and environmental behaviour of 'hot particles'; the development and application of countermeasures; the "fixation" and long term bioavailability of radiocaesium and; the effects of radiation on plants and animals.
Measurements of activity concentrations and speciation of 137Cs in bottom sediments of the Curonian Lagoon were carried out in samples collected in 1999–2003. In addition, the sorption-desorption processes of caesium in disturbed bottom sediments of fresh and sea water systems were investigated in long-term experiments (up to 375 days) in order to better understand the caesium behaviour during the Baltic Sea water flooding events to the Curonian Lagoon. The modified Tessier method was used to study caesium associations with geochemical phases of bottom sediments. The effect of carbonate coatings of bottom sediments on the Cs sorption-desorption process was observed. The comparative analyses of 137Cs solid phase speciation in bottom sediments after 241 and 375 days of the sorption experiment with that of the 137Cs speciation, determined in the same sediment sample before the sorption experiment, indicated that after 375 days of sorption the equilibrium was not reached, however, the Cs distribution in geochemical phases was found to be close to equilibrium. The desorption experiments evidenced the release of caesium into solution from regular exchange complex and transfer from other phases to the frayed edge sites on the layered clay minerals with its further fixation in the crystal lattice. The remobilization of “fixed” caesium was not observed, on the contrary, the redistribution of caesium with its subsequent fixation in clay minerals was observed, and on a time scale its fixation kinetics was comparable with the sorption experiment. This study showed that flooding events of sea water contaminated with caesium can cause a significant accumulation of caesium in the bottom sediments of the Curonian Lagoon and result in the redistribution of 137Cs activity concentration in the bottom sediments from one area to another.
Fern accumulates radionuclides in abundance, including Cs. Tranfer of Cs and K in plants which have different root systems (fern or grass), or have no roots at all (moss) was compared. Samplings were performed in regions contaminated with Cs after Chernobyl Nuclear Power Plant (ChNPP) accident in 1994 and 1997–2000. The male fern (Dryopteris filix‐mas) most prevailing in Lithuania was studied. Fern accumulates Cs more effectively than grass or moss. The average Cs activity concentration in fern is 180±60 Bq kg and the transfer factor is 0,074 mkg. The fern stipe accumulates Cs most of all (200±90 Bqkg‐), the transfer factor is 0,087 m kg. Accumulation of Cs is influenced by the content of K in the soil. Cs and K activity concentrations in fern are higher than those in the soil what shows that fern accumulates Cs better than K. Fern can clean the soil because this plant accumulates radionuclides in its stipe rather than roots.
The input of allochthonous plant material, largely terrestrial in origin, during the spring spate is a major source of primary
production for montane lake ecosystems such as Øvre Heimdalsvatn and is readily incorporated into the food chain leading to
fish. The transport from the lake catchment of allochthonous plant material contaminated with Chernobyl 137Cs in 1986 was investigated from 1989 to 2008. 137Cs activity concentrations were determined for both total samples before sorting and for the separate components in the two
main tributary streams, Brurskardbekken and Lektorbekken, as well as the outflow river, Hinøgla. The total samples showed
a similar long-term decline at all sites, although 137Cs activity concentrations were generally somewhat higher in Hinøgla compared to the tributary streams. For the total samples,
ecological half-lives were in the region of 4–5 years. However, there were major differences between components. The 137Cs activity content of most components, including mosses, leaves of willow and woody material, decreased significantly over
time. Lichens and juniper declined, but the relationship was not significant, while leaves of mountain birch and dwarf birch
showed no obvious trend over the 20-year period.
Spring wheat (Triticum aestivum L. cv. Tonic) was grown for 16 days in a sandy loam soil which was contaminated with 137Cs. The soil was fertilised with K at three rates (0,1 and 2 mmol K per 950 g dry soil) and with NO3--N at two rates (0 and 2 mmol per 950 g dry soil) in a factorial design. The 137Cs Activity Concentration (AC) in the shoot tissue significantly reduced 8.2-fold (nil N treatment, p<0.001) and 9.3-fold (highest N dose, p<0.001) with increasing K supply. In contrast, the K application increased the 137Cs AC in soil solution 1.7 fold (nil N treatment) or had no significant effect (highest N dose). At similar K application, the application of N increased the 137Cs AC in the shoot compared to the control. This effect is most probably due to the increased NH4+ concentration in soil solution which increased the 137Cs AC in soil solution. The soil solution composition (137Cs and K concentration) in the rhizosphere was estimated from the average soil solution composition at day 16 and solute transport calculations. The 137Cs AC in the shoot tissue was predicted from the estimated soil solution composition in the rhizosphere and the relationship between K concentration and 137Cs uptake derived from a nutrient solution experiment. The predictions of 137Cs AC's in the shoot are qualitatively correct for the fertiliser effects but underestimate the observations between 1.4 and 9.9 fold.
The effect of varying K supply on 137Cs uptake in spring wheat (Triticum aestivum L. cv. Tonic) was measured in a solution culture experiment. Wheat was grown in nutrient solution spiked with 137Cs. Treatments were four concentrations of K in solution (resp. 25 μM, 50 μM 250 μM and 1000 μM, added as KNO3) with twofold replication. 137Cs Activity Concentrations (AC, dry weight based values) in 18-day old plants decreased 123-fold in the shoot and 300-fold in the root between 25 μM K and 1000 μM K. Uptake of 137Cs was most sensitively affected by the K supply between 50 μM and 250 μM K. A comparison of the K/37Cs ratio in plant and in solution shows that K is from 3.9- to 25-times more selectively taken up than 137Cs. It is discussed that the sensitivity of the 137Cs uptake rate to the K concentration may explain the beneficial effect of increased K supply in reducing 137Cs uptake from contaminated soils.
Spring wheat (Triticum aestivum L. cv. Tonic) was grown for 16 days in a sandy loam soil which was contaminated with 137Cs. The soil was fertilised with K at three rates (0,1 and 2 mmol K per 950 g dry soil) and with NO3--N at two rates (0 and 2 mmol per 950 g dry soil) in a factorial design. The 137Cs Activity Concentration (AC) in the shoot tissue significantly reduced 8.2-fold (nil N treatment, pp137Cs AC in soil solution 1.7 fold (nil N treatment) or had no significant effect (highest N dose). At similar K application, the application of N increased the 137Cs AC in the shoot compared to the control. This effect is most probably due to the increased NH4+ concentration in soil solution which increased the 137Cs AC in soil solution. The soil solution composition (137Cs and K concentration) in the rhizosphere was estimated from the average soil solution composition at day 16 and solute transport calculations. The 137Cs AC in the shoot tissue was predicted from the estimated soil solution composition in the rhizosphere and the relationship between K concentration and 137Cs uptake derived from a nutrient solution experiment. The predictions of 137Cs AC's in the shoot are qualitatively correct for the fertiliser effects but underestimate the observations between 1.4 and 9.9 fold.
The effect of varying K supply on 137Cs uptake in spring wheat (Triticum aestivum L. cv. Tonic) was measured in a solution culture experiment. Wheat was grown in nutrient solution spiked with 137Cs. Treatments were four concentrations of K in solution (resp. 25 µM, 50 µM 250 µM and 1000 µM, added as KNO3) with twofold replication. 137Cs Activity Concentrations (AC, dry weight based values) in 18-day old plants decreased 123-fold in the shoot and 300-fold in the root between 25 µM K and 1000 µM K. Uptake of 137Cs was most sensitively affected by the K supply between 50 µM and 250 µM K. A comparison of the K/37Cs ratio in plant and in solution shows that K is from 3.9- to 25-times more selectively taken up than 137Cs. It is discussed that the sensitivity of the 137Cs uptake rate to the K concentration may explain the beneficial effect of increased K supply in reducing 137Cs uptake from contaminated soils.
Interionic effects on radiocaesium uptake in spinach (Spinacia oleracea L, cv. Subito) were measured in a solution culture experiment. In total, 15 different nutrient solutions, spiked with137Cs, were prepared in which K, NH4, Ca and Mg concentrations were varied at four different total salt concentrations between 5.3meql−1and 21.2meql−1. The range of cationic concentrations studied was: K, 0.53 to 10.4 mmoll−1; NH4, 0 to 8.47 mmoll−1; Ca, 0.15 to 5.0 mmoll−1; Mg, 0.08 to 2.0 mmoll−1. The plant/solution137Cs transfer factor (TF) varied between 41 lkg−1 and 117 lkg−1. Radiocaesium levels in the plants were poorly, but positively, correlated with the K concentration in solution. However, radiocaesium levels were significantly reduced by increasing Ca + Mg concentrations in solution. Between 10.06 and 1.06moll−1 K, radiocaesium levels in 20-day-old plants were only slightly affected if K was replaced by NH4 at almost constant Ca + Mg concentrations. The negative effect of Ca + Mg concentrations on137Cs uptake is interpreted from their effect on137Cs loading in the apoplast of the root cortex. A quantitative relationship is presented between the137Cs TF and the fractional loading of137Cs in the apoplast, which is calculated by ion exchange laws. This relationship is linear (R2 = 0.81) for the 15 different solutions studied.
A theoretical scheme is presented which considers the uptake of radiocaesium by roots of wheat and its subsequent translocation to above ground tissues. This is tested experimentally against data derived for actively growing plants in the presence of increasing concentrations of stable caesium (133Cs), potassium (K) and ammonium (NH4).Transfer functions for 137Cs are defined in the presence of each of these ions. Mean transfer factors derived for roots over the ion concentration ranges examined were approximately one order of magnitude greater than those for shoots and transfer functions in all cases were distinctly non-linear. Experimental data adhered closely to the model in all instances except that of K+ at an external concentration greater than 20 μM. This anomaly is identified as an ion-specific effect with important radioecological implications.The uses and limitations of the soil-to-plant transfer concept and simple mechanistic models such as that presented here are discussed with reference to the problem of modelling the movement of radioactive substances within the environment.
The bioavailability of radionuclides derived from the Chernobyl accident is discussed in terms of their speciation in soils. A scheme representing transformation processes of different chemical forms of these radionuclides in soil and soil solution is proposed. The rate constants of the main transformation processes were obtained experimentally. Various agrochemical countermeasures are evaluated in terms of their influence on the ratio of different radionuclide forms in soil and soil solution. The influence of soil characteristics on the potential effectiveness of countermeasures is discussed. Practically all agrochemical countermeasures currently in use have positive and negative effects. The most effective countermeasures for radiocaesium and radiostrontium were liming of the soil and the application of potassium containing fertilisers at elevated rates.
This chapter presents exchange studies concerned with pure systems—namely, the suspensions of clay minerals obtained from known sources and the clay fraction of soils known to contain predominantly a particular clay mineral. Partly because of its high exchange capacity, montmorillonite plays a major role in obtaining information about the mechanism of cation adsorption, covering almost complete ranges of composition for different ion pairs. The clay minerals vermiculite, kaolinite and illite (hydrous mica) have been used less frequently. The information about cation exchange involving the organic fraction of soils is scarce because of the difficulties of isolation and identification. In some cases, organic soils (peat soils) have been used. Cation-exchange properties of soil-borne oxides have recently received attention because of the increasing interest in the adsorption of heavy metals. Apart from investigations on specific soil constituents, samples of natural soils have also been used to obtain an estimate of the expected behavior in a field.
Field and laboratory experiments have been used to study the behaviour of long-lived radionuclides in the zone affected by the Chernobyl accident. Speciation of 90Sr and 137Cs in soils and bottom sediments was determined. The principal distinction of the Chernobyl fallout was that it contained a relatively small proportion of exchangeable forms because a considerable fraction of the radionuclides was incorporated as part of the insoluble fuel particles. Disintegration of fuel particles in soils and bottom sediments results in transition of non-exchangeable forms into exchangeable forms. Radionuclide species have different pathways and rates of migration in soils and bottom sediments. Migration of each chemical form was described by a convective-dispersive equation taking into account transformation processes of radionuclide species in soils or bottom sediments. Adsorption of 90Sr and 137Cs in the environment is controlled by the cation-exchange capacity and the selectivity of the solid phase (i.e., soil, bottom sediments and suspended matter) and the cationic composition of the liquid phase (i.e., soil solution, surface run-off and river or lake water). The corresponding parameters for the processes were obtained.
Purified cell walls were prepared from roots of Horse bean (Vicia faba L., var. minor) and Yellow Lupine (Lupinus luteus L.). Two methods were used: (a) grinding and (b) lysis of the endocellular contents by Triton X-100. The Ca(2+), Mg(2+), and K(+) contents were determined after incubation in various solutions in such a manner that the measurements gave access to the undisturbed equilibrium contents. The results were used to test a model which describes the ionic atmosphere in the cell walls as a result of simultaneous electrostatic interactions between free ions (Donnan effect) and specific association equilibria, including acido-basic ones. This model correctly accounted for the whole set of experimental results and predicted the values of the unmeasurable local concentrations and pH.
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