Radiocaesium Interception Potential Research Articles

The sorption of caesium to glauconite sands obeys local equilibrium at environmentally relevant water flow rates

Glauconite has a radiocaesium interception potential that is comparable to illite, suggesting that glauconite containing sands may be an effective geological barrier for radiocaesium. However, glauconite is present as coarse pellets (∼0.5 mm diameter) and considerable sorption non-equilibrium may occur during reactive transport in these permeable sands. Here, we analysed trace caesium (Cs) sorption kinetics in agitated batch suspensions to predict reactive transport at variable flow rates in glauconite containing sands. Batch sorption experiments showed that Cs+ sorption KD values in agitated suspension of glauconite sand of the Diest Fm (Dessel Member) increased by a factor 6 to 8 between 48 h and 94 days at trace Cs+ concentration (∼10−9 M). A breakthrough (BT) experiment was set up with 13 packed columns of the same Fm that were leached with 10−6 M Cs+ at variable flow rates equivalent to water residence times 0.07–3.4 days for a duration of 154 days. The BT was observed in treatments with the higher flow rates after 890–1170 pore volumes. The breakthrough expressed in pore volumes revealed earlier breakthrough at only the highest flow rate, indicating chemical non-equilibrium in that treatment. The BT curves were modelled with HP1 (Hydrus-PhreeqC), thereby relying on batch data obtained at 90 days and assuming local reaction equilibrium. The BT curves were well predicted with this model, corroborating local equilibrium except at the highest flow rates. It is concluded that Cs+ sorption on highly permeable glauconite sands is sufficiently fast to delay breakthrough with flow rates below 2.4 m d−1. Only in high flow rate, unrealistic for the Neogene and Paleogene formations, early breakthrough could occur.

Deriving probabilistic soil distribution coefficients (Kd). Part 2: Reducing caesium Kd uncertainty by accounting for experimental approach and soil properties

The solid-liquid distribution coefficient (Kd) is a key input parameter in radioecological models. However, its large variability hampers its usefulness in modelling transport processes as well as its accuracy in representing soil-radionuclide interactions. For the specific case of radiocaesium, the analyses of a Cs Kd soil dataset (769 entries) showed that values varied over a five order of magnitude range, and the resulting Cs Kd best estimate (calculated as a geometric mean = 2.5 × 103 L kg−1) lacked reliability and representativity. Grouping data and creation of partial datasets based on the experimental approach (short-term (< ~1 yr) vs. long-term experiments (> ~1 yr)) and soil factors affecting Cs interaction (i.e., the ratio of the radiocaesium interception potential (RIP) to the potassium content in soil solution (Kss); organic matter content (OM) and soil texture) succeeded in reducing variability a few orders of magnitude, with Cs Kd best estimates also differing by one-two orders of magnitude depending on the type of soil and experimental approach. The statistical comparison of the Cs Kd best estimates and related cumulative distribution functions of the partial datasets revealed a relevant effect of the sorption dynamics on Cs Kd values (with long-term values systematically higher than short-term ones), and that the RIP/Kss ratio was an excellent predictor of Cs Kd for short-term scenarios, whereas the RIP parameter could be predicted on the basis of texture information. The OM threshold to distinguish between OM threshold to distinguish between Mineral and Organic soils subclasses, regarding Cs interaction was determined to be 50% and 90% OM for short- and long-term scenarios, respectively. It was then recommended to select the Cs Kd input data depending on the soils and scenarios to be assessed (e.g., short- vs. long-term; OM %) to improve the reliability and decrease the uncertainty of the radioecological models.

Ability of micaceous minerals to adsorb and desorb caesium ions: Effects of mineral type and degree of weathering

AbstractTo evaluate the effects of type of micaceous mineral and degree of weathering on the ability to adsorb and desorb radiocaesium (RCs) ions, various levels of weathering were induced (K‐depletion) in three types of micaceous minerals: biotite, muscovite and illite. The ability to adsorb RCs was represented by RCs interception potential (RIP) and a desorption ratio was determined by the amount of 137Cs desorbed from the minerals by 1 M ammonium acetate (137Cs desorption ratio). The RIP values were in the order of illite &gt; biotite &gt; muscovite. The RIP values for biotite gradually increased with the release of up to ~50% of the K+ from interlayer sites but then decreased with the further release of K+, up to ~100%, which was associated with the formation of a fully expanded interlayer: vermiculite. The change from increasing to decreasing RIP due to the weathering of the biotite strongly indicated that the selective adsorption sites for RCs are not located in an expanded interlayer but in intermediate sites between non‐expanded and expanded interlayers: frayed edge sites (FES). In contrast, for both the muscovite and illite, the RIP only increased. The 137Cs desorption ratio, &lt;7% for all the samples, tended to decrease with increasing degrees of weathering and did not differ greatly by mineral type. These results contribute to a more accurate prediction of the risk of RCs transfer from soils to crops and the understanding of the weathering processes of micaceous minerals in soils.Highlights Radiocaesium adsorption and desorption was investigated for gradually K‐removed biotite, muscovite and illite. Vermiculitization of biotite via K removal firstly increased then decreased the frayed edge sites (FES). Adsorption was influenced by di/trioctahedral character and charge localization, and desorption by degree of weathering. These results lead to better understanding of the weathering processes of micaceous minerals and fate of RCs in soils.

Correlation between Different Type of Caesium Carrier in The Radiocaesium Interception Potential Measurement for Forest Soils

Radiocaesium, especially 137Cs, is one of major heavy fission product radionuclide that has a relatively long half-life and acts as a dangerous persistent pollutant to the environment. It could be dispersed widely through the atmosphere during nuclear weapon test and reactor accident such as Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) disaster in Japan. High retention of radiocaesium in the surface of forest floor surrounding Fukushima area is important issues to measure further potential risk of health and environment contamination. Radiocaesium Interception Potential (RIP) values are related to the sorption capacity of radioactive Cs in clay minerals, and in this study, we investigated the correlation between different type of Cs carrier to the RIP and their adsorption character in soil. The RIP values of all soil sample were varied from 27.27 to 522.66 mmol kg-1. The carrier effect on RIP was conducted using carrier 134Cs, carrier-free that contains 134Cs, 136Cs and 137Cs and 133Cs stable isotopes. Correlation between different type of carrier suggests a relatively lower RIP for stable caesium as a carrier. This phenomena could be caused by competitive adsorption among of caesium ions in the frayed edge sites of soil mineral. Organic carbon content and CEC also contributed to the RIP value. No significant difference found of C/N ratio and CEC values between deciduous and coniferous forest soil as they also have similarity of mineral content in soil.

Effects of zeolite and vermiculite addition on exchangeable radiocaesium in soil with accelerated ageing

Soil amendments with zeolite and vermiculite were expected to prevent radiocaesium (137Cs) dissolution and uptake from the soil by plants. In this study, we investigated how zeolite and vermiculite added to soil influence the radiocaesium fixation with ageing. Zeolite and vermiculite were mixed with soil (1 wt%) before or after the addition of carrier-free caesium-137 (137Cs) to soils with different radiocaesium interception potential (RIP), which is related to the capacity of the soil to fix trace radiocaesium. Then, the soils were exposed for repeated wet and dry cycles to accelerate 137Cs immobilization, and its extractability by 1 mol L−1 ammonium acetate was determined before and after 30 dry and wet cycles. Before accelerated ageing (i.e before dry and wet cycles), when 137Cs was adsorbed on the soil before the addition of the amendments, the addition of zeolite and vermiculite caused a decrease in the amount of exchangeable 137Cs in low-RIP soils but an increase in the amount of exchangeable 137Cs in high-RIP soils. The amount of exchangeable 137Cs was significantly decreased after accelerated ageing regardless of the application of amendments. However, radiocaesium fixation with accelerated ageing was partly inhibited by the addition of zeolite, regardless of the RIP values. The 137Cs adsorbed on highly selective sites in zeolite is exchangeable by 1 mol L−1 ammonium acetate. Thus, because a portion of the 137Cs is selectively adsorbed on highly selective sites in zeolite, the redistribution of 137Cs to frayed edge site followed by ageing-induced fixation was likely limited. However, when 137Cs was adsorbed on the soil before the addition of the amendments, the addition of zeolite and vermiculite had little influence on the amount of exchangeable 137Cs. In conclusion, the use of realistic doses of zeolite and vermiculite as agricultural amendments is not effective in enhancing the immobilization of radiocaesium in soil.

Phytoavailability of 137Cs and stable Cs in soils from different parent materials in Fukushima, Japan

Weathered micaceous minerals (micas) are able to release potassium ion (K+) and fix caesium-137 (137Cs), both of which reduce soil-to-plant transfer of 137Cs. Among micas, trioctahedral micas such as biotite is expected to have a stronger ability to supply nonexchangeable K+ and a higher amount of Cs fixation sites than dioctahedral micas such as illite. Although biotite is predominant in granitic soils (G soils), illite is mainly dominant in sedimentary rock soils (S soils). Therefore, we hypothesized that G soils have a lower 137Cs transfer risk than S soils because of this difference in mineralogy. The objective of the present study was to determine the transfer factor (TF) of 137Cs and stable Cs (SCs) and to elucidate the determinant factors of TFs for G and S soils in Fukushima, Japan. Pot experiments were carried out with rice (Oryza sativa L. cv. Hokuriku 193) in G and S soils to determine the TF of 137Cs (TF-137Cs) and stable Cs (TF-SCs) under K-deficient conditions. TF-137Cs and TF-SCs were highly correlated, and both were significantly lower for G soils than for S soils. Higher TF values were shown for soils with lower amounts of exchangeable and nonexchangeable K or with higher percentages of exchangeable 137Cs (ex137Cs). The percentage of ex137Cs was negatively correlated with the amount of Cs fixation sites, represented by the radiocaesium interception potential. Thus, we concluded that smaller TF values for G soils were caused by a stronger ability to supply nonexchangeable K+ and a higher amount of Cs fixation sites. These findings will contribute to the establishment of soil screening techniques based on 137Cs transfer risk in Fukushima prefecture.

Variability of the soil-to-plant radiocaesium transfer factor for Japanese soils predicted with soil and plant properties

Food chain contamination with radiocaesium (RCs) in the aftermath of the Fukushima accident calls for an analysis of the specific factors that control the RCs transfer. Here, soil-to-plant transfer factors (TF) of RCs for grass were predicted from the potassium concentration in soil solution (mK) and the Radiocaesium Interception Potential (RIP) of the soil using existing mechanistic models. The mK and RIP were (a) either measured for 37 topsoils collected from the Fukushima accident affected area or (b) predicted from the soil clay content and the soil exchangeable potassium content using the models that had been calibrated for European soils. An average ammonium concentration was used throughout in the prediction. The measured RIP ranged 14-fold and measured mK varied 37-fold among the soils. The measured RIP was lower than the RIP predicted from the soil clay content likely due to the lower content of weathered micas in the clay fraction of Japanese soils. Also the measured mK was lower than that predicted. As a result, the predicted TFs relying on the measured RIP and mK were, on average, about 22-fold larger than the TFs predicted using the European calibrated models. The geometric mean of the measured TFs for grass in the affected area (N = 82) was in the middle of both. The TFs were poorly related to soil classification classes, likely because soil fertility (mK) was obscuring the effects of the soil classification related to the soil mineralogy (RIP). This study suggests that, on average, Japanese soils are more vulnerable than European soils at equal soil clay and exchangeable K content. The affected regions will be targeted for refined model validation.

Predicting radiocaesium sorption characteristics with soil chemical properties for Japanese soils

The high variability of the soil-to-plant transfer factor of radiocaesium (RCs) compels a detailed analysis of the radiocaesium interception potential (RIP) of soil, which is one of the specific factors ruling the RCs transfer. The range of the RIP values for agricultural soils in the Fukushima accident affected area has not yet been fully surveyed. Here, the RIP and other major soil chemical properties were characterised for 51 representative topsoils collected in the vicinity of the Fukushima contaminated area. The RIP ranged a factor of 50 among the soils and RIP values were lower for Andosols compared to other soils, suggesting a role of soil mineralogy. Correlation analysis revealed that the RIP was most strongly and negatively correlated to soil organic matter content and oxalate extractable aluminium. The RIP correlated weakly but positively to soil clay content. The slope of the correlation between RIP and clay content showed that the RIP per unit clay was only 4.8mmolg−1 clay, about threefold lower than that for clays of European soils, suggesting more amorphous minerals and less micaceous minerals in the clay fraction of Japanese soils. The negative correlation between RIP and soil organic matter may indicate that organic matter can mask highly selective sorption sites to RCs. Multiple regression analysis with soil organic matter and cation exchange capacity explained the soil RIP (R2=0.64), allowing us to map soil RIP based on existing soil map information.

Relevance of Radiocaesium Interception Potential (RIP) on a worldwide scale to assess soil vulnerability to 137Cs contamination

The extent of radiocaesium retention in soil is important to quantify the risk of further foodchain contamination. The Radiocaesium Interception Potential (RIP – Cremers et al., 1988, Nature 335, 247–249) is an intrinsic soil parameter which can be used to categorize soils or minerals in terms of their capacity to selectively adsorb radiocaesium. In this study, we measured RIP for a large soil collection (88 soil samples) representative of major FAO soil reference groups on a worldwide scale and tested the possibility to predict the RIP on the basis of other easily accessible or measurable soil data. We also compared RIP values with those obtained from separate chemical extraction experiments. The range of measured RIP values (1.8–13300 mmol kg −1) was shown to include nearly all possible cases of agricultural soil contamination. Only Podzols, Andosols and Ferralsols were clearly characterized by a very low RIP (<2000 mmol kg −1). On a worldwide scale, RIP was in fact slightly related to soil reference type or other simple major physicochemical parameters such as clay percentage or organic matter. Conversely our results indicated a link between the RIP and radiocaesium extractability across very different soils. We showed that, with the proposed scale of RIP values, a simple acid extraction method can provide an operational result highly predictive of potential RIP despite very contrasting soil properties. The RIP could be estimated from the empirical equation: RIP = (−31.701 ∗ log(AER) + 58.886) 2 where AER is the fraction of acid-extractable radiocaesium.

Comparison of mechanistic and PLS-based regression models to predict radiocaesium distribution coefficients in soils

Radiocaesium sorption interaction descriptors were examined in 30 soil samples from Spain. Mechanistic and regression models were used to predict the solid–liquid distribution coefficients of radiocaesium (Kd(Cs)) based on soil properties, and the obtained values were compared with the experimental ones, which were derived from batch experiments. The batch experiments used two contact solutions: one simulated the composition of the soil solution, and the other was the wash-off from the soil. Several mechanistic models of different complexity were tested based on the Radiocaesium Interception Potential (RIP), with satisfactory agreement between experimental and predicted values. A simplified model based on either the RIP, or the clay content and K status of the soil was proposed. Various multivariant regression models, which were constructed using the Partial Least Square Regression (PLS), were also evaluated. The RIP, clay content, and the K and NH4+ contents were also identified by the regression models as the most relevant soil parameters to predict the Kd. As seen for the mechanistic models, the goodness of fit of the regression models was demonstrated by an excellent agreement between experimental and predicted values.

Landscape‐scale controls on the spatial distribution of caesium 137: A study based on an airborne geophysical survey across Northern Ireland

AbstractThe spatial distribution of 137Cs across the landscape and the processes controlling its redistribution are of interest because (i) 137Cs has been widely used to quantify the movement of soil and sediments and (ii) substantial fallout of 137Cs after the Chernobyl accident has led to contamination of foodstuffs in some places. A high‐resolution airborne geophysical radiometric survey of Northern Ireland has provided an opportunity to study the distribution and possible redistribution of 137Cs.The 137Cs activity (recorded at 1·2 million points) is distributed in a series of bands oriented approximately 160° and 115° clockwise from north. Geostatistical analysis of the data shows a strong, short‐range structure (correlation ranges between 0·6 and 8 km) in 137Cs activity across the vast majority of the region; the spatial distribution shows association with a published, coarse‐scale depositional pattern of 137Cs from Chernobyl. Two indices of land form derived from a digital elevation model, namely compound topographic index and the length–slope factor of the Revised Universal Soil Loss Equation, account for only 3% of the variance in 137Cs activity. In contrast, soil type and land cover in combination (including their interaction) account for 20% of the variance. In areas that received moderate fallout from Chernobyl, soil type alone accounts for a substantial proportion of the spatially correlated 137Cs activity. We attribute this to each soil type having a fairly uniform radiocaesium interception potential that differs from those of other soil types and that this potential controls the vertical migration of 137Cs. Over the granitic Mourne Mountains there is a strong spatial cross‐correlation between 137Cs activity and airborne estimates of soil potassium, suggesting that the latter provides a measure of the soil's radiocaesium interception potential; this is probably dominated by the quantity of the mineral illite. Copyright © 2010 John Wiley &amp; Sons, Ltd. and British Geological Survey

Characterization of Portuguese geomaterials, the clay component of rañas, as potential liners for low and intermediate radioactive disposal sites

Safety assessment of low and intermediate level waste (LILW) repositories requires the understanding of radionuclides sorption-desorption mechanisms, mainly the degree of interaction between radionuclides and min- eral surfaces. Among the different radionuclides that are part of the Portuguese radwastes' inventory 137 Cs is one of the most important from the radiological point of view due to its high radiotoxicity. The clay component of natural geomaterials termed ranas, originated from an area located in the NE Mainland of Portugal, was studied for their potential as effective barriers. These geomaterials (grains- size fractions \63 lm, \36 lm) were characterized in terms of cationic exchange capacity (CEC), frayed edge sites (FES) and radiocaesium interception potential (RIP). Organic matter content and pH were also determined. The fractions were mineralogically analyzed by X-ray diffrac- tion and by instrumental neutron activation analysis (INAA) for chemical elemental composition. Smectite (montmorilonite), illite, kaolinite were identified. The capacity of FES is related to the samples granulometry as opposed to what was observed for CEC and RIP. The behavior of ranas was not similar for all samples which may be related to differences in mineralogy. Future studies with regard to the behaviour of radiocaesium are expected to clarify the possible application of these geomaterials as liner/backfill/buffer for a LILW repository.

Influence of fertilizing on the 137Cs soil–plant transfer in a spruce forest of Southern Germany

Fertilization with 2.5 t/ha limestone: (83% CaCO 3, 8% MgO, 6% K 2O, 3% P 2O 5) reduces the 137Cs 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 137Cs transfer factor TF, related to the root zone (O h horizon), which were explained by the selective sorption of 137Cs in the root zone by measurements of the Radiocaesium Interception Potential (RIP) in fertilized (RIP > 179 meq/kg) and non-fertilized soils (RIP < 74 meq/kg).

Migration and bioavailability of 137Cs in forest soil of southern Germany

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.

Pedogenic alterations of illitic minerals represented by Radiocaesium Interception Potential in soils with different soil moisture regimes in humid Asia

SummaryA frayed edge site can be a significant indicator of alterations in illitic minerals in soils evolving under different climates, because illitic minerals are known to enlarge the frayed edge site through vermiculitization. We investigated the relative abundance of this site in soil clays (&lt;2 μm) using Radiocaesium Interception Potential (RIP) methodology, and determined the mineralogical factors controlling its amount (represented by RIP) for soils under ustic soil moisture regimes (northern Thailand, TH) and udic regimes (southwestern Japan, JP; East Kalimantan in Indonesia, ID) in humid Asia. We found three different correlations between RIP and mineralogical‐ or chemical‐indices: positive (amount of illitic mineral and Cs‐fixing capacity), negative (amount of kaolinite and hot‐citrate extractable Al‐Si) and no correlation (amount of DCB‐oxides). The variable that correlated best with the logarithm of RIP in each region was Alcit‐Sicit (JP), amount of illitic mineral (TH) and amount of kaolinite (ID). Under an ustic soil moisture regime in TH, there was little vermiculitization, as was evidenced by the direct correlation between the frayed edge site (or RIP) and the amount of illitic minerals and the very small Cs‐fixing capacity. A distinct dry season restricts water leaching, which may reduce alteration in illitic minerals. For ID soils under an udic soil moisture regime, illitic minerals weather to form vermiculite, which is reflected in the enlargement of the frayed edge site. However, for JP soils, hydroxy‐Al interlayering reduces the frayed edge site formed through vermiculitization. The release of hydroxy‐Al polymers from vermiculitic layers can induce the re‐exposure of the frayed edge site that can be progressive under a podzolization process.

Hydroxy‐Al polymers block the frayed edge sites of illitic minerals in acid soils: studies in southwestern Japan at various weathering stages

SummaryThe transformation of hydroxy‐interlayered vermiculite (HIV) to vermiculite in humid temperate soils may involve the gradual alteration of illitic minerals. However, it is difficult to detect such minor and progressive changes using conventional methods. We measured the amount of the frayed edge site (i.e. the weathering front of illitic minerals) in soil clays using Radiocaesium Interception Potential (RIP) methodology, and elucidated the effect of hydroxy‐Al polymers on the frayed edge site that may be occluded within HIV structures in the acidic soils of southwestern Japan. X‐ray diffraction patterns showed the progressive transformation of HIV to vermiculite, or further, to smectite in soil clays located in upper horizons and therefore subjected to more intensive podzolization. In this process, the amount of hydroxy‐Al polymers (represented by hot‐citrate Al) gradually decreased, while the vermiculitic charges increased (represented by Cs‐fixing capacity). However, the amount of the frayed edge site (represented by the RIP) firstly increased but then reversed and decreased in the upper layers of podzolic soils. After hot‐citrate extraction to remove the hydroxy‐Al polymers from HIV, the amount of the frayed edge site increased in HIV‐dominated clays, whereas there was a negligible increase in vermiculitic‐ or smectitic‐clays, thus indicating the blockage effect of hydroxy‐Al polymers on the frayed edge site. The sequential increase followed by the decrease that we documented in the amount of the frayed edge site along with the HIV‐vermiculite‐smectite transformation, suggested that the weathering front of illitic minerals was exposed as the HIV layers lose hydroxy‐Al polymers. Thereafter, the charges in the exposed frayed edge site might decline under the very acidic conditions of the upper layers of podzolic soils.

Acid extraction as a predictive tool of Radiocaesium Interception Potential (RIP) in a worldwide scale

The extent of radiocaesium in soil is very important to appreciate the risk of its recycling by the vegetation and thus the risk of food chain contamination. An intrinsic soil parameter, the radiocaesium interception potential (RIP), could be used to measure this retention. In this study, we tested the possibility to predict the RIP starting from a simple acid extraction in widely different soils coming from the whole world and pertaining to various soil reference groups of the WRB/FAO world soil classification. Our results show that a simple acid extraction could be used as an operational test to estimate the RIP whatever the soil type.

New best estimates for radionuclide solid–liquid distribution coefficients in soils, Part 1: radiostrontium and radiocaesium

Best estimates for the solid-liquid distribution coefficients ( K d) of radiostrontium and radiocaesium for various soil types, were derived from geometric means (GM) calculated from grouping soils by texture and organic matter content, and also using soil cofactors governing soil–radionuclide interaction. The K d (Sr) GM for Sand, Loam, Clay and Organic groups were similar, although the value for the Sand group was significantly lower. The Sr cofactor approach, based on the ratios of cation exchange capacity (CEC) to Ca and Mg concentrations in the soil solution, leads to K d (Sr) GM with a lower variability, from which best estimates could be proposed. The K d (Cs) GM for Sand and Organic groups differed, although similar values were obtained for Loam and Clay groups. Grouping the K d (Cs) according to the Radiocaesium Interception Potential (RIP) and the RIP divided by the K concentration in the soil solution also allows to suggest K d (Cs) best estimates with a lower variability.

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 K 2CO 3 (K L) or in presence of solid K 2CO 3 (K S). Of the three strategies tested, addition of K 2CO 3 (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 ∼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 ∼1% bentonite, like Otay bentonite (RIP yield 99 000 meq kg −1 after WD in presence of K if only fine particle size of <1 mm considered) with the contaminated ploughing layer.

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 (R 6S 2 and R 5S 4: R, root age and S, shoot age) and clone (Rapp and L78183 both of age category R 5S 4) 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 ( R 2=0.54) or the radiocaesium interception potential, RIP ( R 2=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 × m K −1.83, R 2=0.99) and the other soils (CF = 35.75 × m K −0.61, R 2 = 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 NH 4 + for the Trödje soils compared to 0.003–0.11 mM NH 4 + 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.