Radio‐caesium fixation dynamics: measurement in six Cumbrian soils

Abstract

Five peat soils and a mineral soil were artificially contaminated with 137Cs. Soil solution activity and radio-lability of 137Cs were monitored over 709 days to quantify progressive 137Cs fixation. The peat soils fixed large amounts of 137Cs, but less than the mineral soil did. Distribution coefficients (&, cm3 g-') ranged from 30 to 5000 at the end of equilibration. A labile 137Cs distribution coefficient, Kdlr was estimated by a method involving solid e solution equilibration in dilute solution.In a separate study several concentrations of KC1 were added to soils in increasing concentration both before and after the addition of 137Cs. Differences in apparent adsorption strength of radiocaesium indicated that K+ induced the collapse of expanded mineral interlayers, thereby trapping ions. It seemed that 137Cs adsorbs at sites in the small micaceous clay fraction of the peat soils.The different rates of 137Cs adsorption and fixation in the peat and mineral soils, in which the rate of access of 137Cs to fixation sites in peat soils is less, seems to have been caused partly by lack of K, and partly by the scarcity of fixation sites.

Reversibility of radiocaesium sorption on illite

“…The amount of rapidly desorbed radiocaesium decreases with the adsorption time, in accordance with earlier observations of a progressively stronger binding between Cs and illite with increasing reaction time (e.g., Mundschenk, 1983;Comans et al, 1991;Absalom et al, 1995). The slow rate of desorption, operationally defined as the desorption occurring after more than 24 h desorption time, was interpreted in terms of a first order process.…”

“…The first is that the frayed edge site structure of the clay minerals collapses under the influence of high concentrations of adsorbed alkali metal ions, thus preventing the further release of radiocaesium (Madruga, 1993;Absalom et al, 1995;Absalom et al, 1996). Alternatively, Sparks (1989) argued that when the ion-exchange method is used in a batch procedure, a relatively high concentration of the desorbed species (i.e., 137 Cs) builds up in solution, which could inhibit further adsorbate release from the solids.…”

Effect of potassium (K) supply on the uptake of 137 Cs by spring wheat ( Triticum aestivum cv. Tonic): a lysimeter study

“…The exchangeability did not change substantially over the experimental period; however, statistical analysis did suggest that the exchangeability observed after harvest was significantly lower than that before harvest due mainly to plant uptake (Table 3). Rapid fixation of Cs + by soil has also been suggested by some laboratory studies [15,16] which demonstrated that fixation reached equilibrium less than 30 days after contamination. …”

Temporal variations of accumulated cesium in natural soils after an uncharacteristic external exposure

“…However, irrespective of the soil type, the total cesium content within the soil particle size fractions was more or less even and was in the range of 40 to 48 mg kg -1 (Figure 1). This pseudo-uniformity in the cesium distribution in the soil particle size fractions can be attributed to the shorter time-lag between the exposure period and concentration measurements [35]. The particle size can contribute to several effects when 137 Cs is used to estimate soil erosion rates.…”