Rhizospheric Mobilization and Plant Uptake of Radiocesium from Weathered Micas

Abstract

Acute K depletion in the rhizosphere can lead to increased root uptake of radiocesium. Two processes can govern this increase: the very low uptake of potassium and the weathering of Cs-fixing clay minerals. Their respective importance is, however, unknown. We investigated the effects of these processes on radiocesium mobilization by roots of willow (Salix viminalis L.) from three micas: muscovite, biotite, and phlogopite. Willows were grown in a mixed quartz-mica substrate with the three respective (134)Cs-contaminated micas as sole sources of potassium and radiocesium. After 7 wk of plant growth, the micas were partially weathered. The degree of mica weathering and the prevalent potassium concentration in the solution increased in the order muscovite (5-11 microM K) < biotite (25-32 microM K) < phlogopite (25-35 microM K). The mobilization and root uptake of radiocesium were negligible with muscovite but increased in the same order. These results show that mica weathering directly and chiefly governs the mobility of radiocesium in K-depleted rhizosphere soil. The low mobility of trace Cs in the muscovite rhizosphere is linked with the dioctahedral character of this mica, and hence to its very low alterability.

Role and influence of mycorrhizal fungi on radiocesium accumulation by plants

“…Consequently, as ECM fungi can immobilize radiocesium and limit its accumulation in plants and especially shoots, they appear to be good candidates for phytoremediation strategies orientated towards the stabilization of radiocesium. It should nevertheless be noticed that along with ECM fungi, other soil-borne fungi are involved in radiocesium immobilization (Tegen et al, 1991;Brückmann and Wolters, 1994;Wirth et al, 1994;Rafferty et al, 1997) and are important agents in the radiocesium cycle in the upper layers of forest soils (Dighton et al, 1991;Thiry and Myttenaere, 1993;Guillitte et al, 1994). They indeed strongly affect radiocesium mobility and make it temporarily unavailable to the other components in the ecosystem.…”

“…This implies that radiocesium displays low mobility in the soil profile after its deposition due to its specific sorption on micaceous clay minerals (Cawse, 1983;Cremers et al, 1988Cremers et al, , 1990Smith and Elder, 1999;Rosén et al, 1999;Delvaux et al, 2000Delvaux et al, , 2001 and relatively high mobility in biological systems (Carter, 1993). This low mobility in soil is problematic as radiocesium tends to persist in the upper soil layers (Thiry and Myttenaere, 1993;Kruyts and Delvaux, 2002;Kruyts et al, 2004), which are extensively explored by plant roots and soil micro-organisms. Thus, in terrestrial ecosystems, the principal route of radiocesium entry into the food chain is the soil-to-plant pathway (Coughtrey and Thorne, 1983).…”

“…Thus, in terrestrial ecosystems, the principal route of radiocesium entry into the food chain is the soil-to-plant pathway (Coughtrey and Thorne, 1983). This route is strongly governed by intrinsic properties of soils, particularly their ability to specifically sorb radiocesium (Cremers et al, 1988(Cremers et al, , 1990Maes et al, 1999;Delvaux et al, 2000), the alterability of radiocesium-fixing minerals with respect to rhizosphere K-depleted environments Thiry et al, 2005), the relative contents of organic matter and clay minerals (Kruyts et al, 2004), and the key role played by the biologically mediated mixing process in humus-rich horizons (Kruyts et al, 2004). The strong dependence of radiocesium mobility upon mineralogical and physico-chemical properties, and biological activity largely explains why soils largely differ in terms of sensitivity towards 137 Cs plant contamination hazard (Delvaux et al, 2000;Kruyts et al, 2004).…”

Effect of waste mica on transfer factors of134Cs to spinach and lettuce

“…This was considered to be due to a slow and continued release of K from mica through the weathering process. Another reason might be due to high fixing capacity of waste mica for cesium (Zachara et al, 2002;Thiry et al, 2005;Sreenivasa Chari, 2010). The data revealed that soil type significantly influenced the 134 Cs transfer factors.…”

Adsorption and Transport Behaviors of Potassium in Vermiculitic Soils

“…It has been also reported the K depletion in rhizosphere result in increase in plant uptake of RCs. 10,22,23) It is also noted that vermiculite which originated from the weathering of granite is one of major clay minerals produced in Fukushima, Japan.…”