Adrien Cremers

Sorption-desorption dynamics of radiocaesium in organic matter soils

Abstract A systematic study has been carried out on the radiocaesium sorption properties of 25 soils (forest, peat) covering organic matter (OM) contents in the range of 10–97%. Predictions are made for radiocaesium partitioning between micaceous Frayed Edge Sites (FES) and regular exchange sites (RES) on the basis of specific radiocaesium interception potentials of the soil and overall exchange capacity. It is shown that for soils with a very high OM content (> 80%), significant fractions are present in a readily reversible form in the OM phase. In soils of low-medium OM content (

Plant-induced changes in the rhizosphere of maize and wheat

SummaryThe release of organic materials by roots of maize and wheat was studied using a growth chamber with a14CO2 atmosphere at constant total CO2 concentration and constant specific activity. The distribution of14C within shoots, roots and soil was determined for both plants after 4 and 6 weeks. After 6 weeks, 1.5% of the total amount of14C fixed by maize was found as a residue in the soil, while for wheat this figure was 2.0%.Rhizosphere14CO2 production was measured in a second experiment and plants were harvested after 3, 4, 5 and 6 weeks growth. The rhizosphere14CO2 evolution by wheat accounted for some 20% of the total amount of fixed14C and was a constant value throughout the growth period. Root-derived products were slowly incorporated by the soil microbial biomass to a maximum of 20% of the residual soil14C content after 6 weeks growth.

Availability of radiocaesium in soils : a new methodology

Two issues are addressed in this paper: (a) the partitioning of radiocaesium between the micaceous specific site pool and the reversible ion exchange pool in mineral soils characterized by relatively low contents of organic matter; (b) the presentation of a new methodology for measuring radiocaesium availability in soils. The partitioning of radiocaesium between specific sites and reversible ion exchange sites is predicted on the basis of soil characterization: specific sites and overall ion exchange capacity. It is predicted that, in mineral soils, only very small fractions of radiocaesium can be expected to be present in readily reversible ion exchange sites. Such predictions are confirmed by an experimental screening study on radiocaesium desorption in a sandy, loamy sand, loam and clay soil, using a variety of desorption agents. A new methodology is presented for measuring radiocaesium availability, using an infinite bath scenario. The method is illustrated by a series of radiocaesium desorption protocols on humic acid, a reference illite clay, a sand loam, loam and clay soil and a set of podzolic soils, including samples from the Chernobyl 30-km zone. It is demonstrated that the (Ca + Mg)/K ratio in soils may play a key role in accelerating the radiocaesium fixation process in the specific sites. The implications of the positive effect of a high CaMg status in the soil on its fixation potential are discussed in terms of the long-term effects of possible countermeasures.

Prediction of solid/liquid distribution coefficients of radiocaesium in soils and sediments. Part two: a new procedure for solid phase speciation of radiocaesium

Abstract A new procedure is developed for assessing the speciation of radiocaesium in soils and freshwater sediments. The method relies on the difference in the variation ofK D 137 Cs CS with NH4 concentration when Cs is present in the regular ion exchange complex or the micaceous frayed edge sites. The theoretical basis for the method is presented. The experimental procedure is based on the measurement ofK D 137 Cs as a function of NH 4 concentration in a mixed K Ca solution of constant composition. It is demonstrated that in most sediments and some soils, even some peat soils of 80% organic matter content,K D 137 Cs response to NH4 concentration coincides with the one obtained for a reference illite clay, thus showing quantitative adsorption of radiocaesium in the frayed edge sites of the micaceous clays.

Plant-induced changes in the rhizosphere of maize and wheat. II: Complexation of cobalt, zinc and manganese in the rhizosphere of maize and wheat

SummaryWater-soluble14C-labelled organic material, released into soil from roots of wheat and maize plants, was recovered with a mild percolation technique, without disturbing the root-soil interface. Extraction yields were relatively high for the14C materials (up to 11% of residual soil14C for 6 weeks maize) illustrating the water soluble character of the freshly added material. The complexation potential of the soil extracts was evaluated by adding57Co,65Zn and54Mn to the extract and determining their distribution among the organic fractions by a gel filtration technique. The results show that within four weeks a micro-environment is created around a plant root, characterized by an accumulation of root-derived organic materials. In parallel with this time dependent accumulation, a gradual shift from ionic metal to higher molecular weight forms occurred. The three metals were increasingly complexed throughout the growth period. Extracts from a fallow soil complexed minor amounts of the added tracer (6.4%; 1.9% and 0.2% for57Co,65Zn and54Mn respectively) while cropped soil extracts after 6 weeks complexed 61%; 16% and 6% of respectively Co, Zn and Mn in the case of maize, and 31%, 15% and 1% in the case of wheat. Although the effects are most pronounced in the case of Co and maize, evidence is given for similar effects with wheat and the other metals. The results indicate that the physicochemical status of transition metals in the rhizosphere is entirely different from that in the bulk soil.

Heterogeneity of charge density distribution in montmorillonite as inferred from cobalt adsorption

A comparison is made of the ion exchange behavior, towards the cobalt ion, of five sodium montmorillonite clays. The selectivity for the bivalent ion at low cobalt loading is correlated with the average dimensions of the particles in the various clays, as characterized by several methods. The data are interpreted in terms of a higher selectivity of the bivalent ions for the broken bonds located at the edges of the clay crystals. Using a model comprising two areas of different charge densities, the experimental differences in behavior can be predicted reasonably well.

Cationic interactions in radiocaesium uptake from solution by spinach

Abstract 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 with 137 Cs, were prepared in which K, NH 4 , Ca and Mg concentrations were varied at four different total salt concentrations between 5.3meql −1 and 21.2meql −1 . The range of cationic concentrations studied was: K, 0.53 to 10.4 mmoll −1 ; NH 4 , 0 to 8.47 mmoll −1 ; Ca, 0.15 to 5.0 mmoll −1 ; Mg, 0.08 to 2.0 mmoll −1 . The plant/solution 137 Cs 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 NH 4 at almost constant Ca + Mg concentrations. The negative effect of Ca + Mg concentrations on 137 Cs uptake is interpreted from their effect on 137 Cs loading in the apoplast of the root cortex. A quantitative relationship is presented between the 137 Cs TF and the fractional loading of 137 Cs in the apoplast, which is calculated by ion exchange laws. This relationship is linear ( R 2 = 0.81) for the 15 different solutions studied.

Mobility of radionuclides in undisturbed and cultivated soils in Ukraine, Belarus and Russia six years after the Chernobyl fallout

Six years after the accident at the Chernobyl Nuclear Power Plant, the behaviour of radionuclides in soils in rural areas of Ukraine, Belarus and Russia has been studied. Measurements were made to determine the total radioactive contamination, the fuel particle contribution, and the distribution and extractability of the radionuclides 137Cs and 90Sr. Inside the 30 km restriction zone around the plant, particles of highly irradiated fuel accounted for most of the radioactive contamination. The radioactivity in the soil, in decreasing order, was due to 137Cs > 90Sr > 144Ce ⩾ 134Cs > 241Am > 125Sb > 154Eu > 155Eu. Outside the 30 km zone, condensed radionuclides were dominant and here the radionuclide content of the soil was 137Cs > 134Cs > 125Sb > 90Sr. The mobility of 137Cs in the soil increased with increasing distance from the reactor: this was in line with the fact that the 137Cs in condensed form, relative to that in fuel particles, also increased with increasing distance from the reactor. There was greater migration of the γ-emitting radionuclides 125Sb, 137Cs and 144Ce in peaty soils than in soddy podsolic, sandy and loamy soils. In undisturbed soddy podsolic sandy soils, more than 95% of the 137Cs was found in the top 6 cm layer. Not surprisingly, in the cultivated soils, the radionuclides were found more or less homogeneously distributed in the 0–25 cm layer. In the undisturbed soils, the γ-emitters had all migrated down to about the same depth, except for the 125Sb which had moved rather deeper. Considerable amounts of the 137Cs and 90Sr were found to be extractable into ammonium acetate solution and the 90Sr was easily the most extractable radionuclide. This probably explains its enhanced migration in the soddy podsolic, sandy and loamy soils.

Formation of highly selective cesium-exchange sites in montmorillonites

Ion-exchange sites with very high selectivity for Cs (