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Rhizosphere Conference

Rhizospheric Mobilization and Plant Uptake of Radiocesium from Weathered Micas

II. Influence of Mineral Alterability

^a Radiation Protection Research Unit, Radioecology Section, SCK•CEN, Foundation of Public Utility, Boeretang 200, 2400 Mol, Belgium
^b Unité Sciences du Sol, Université catholique de Louvain, Place Croix du Sud 2/10, 1348 Louvain-la-Neuve, Belgium

^* Corresponding author (ythiry{at}sckcen.be)

Received for publication October 28, 2004. 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 ¹³⁴Cs-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 µM K) < biotite (25–32 µM K) < phlogopite (25–35 µM 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.

Abbreviations: FES, frayed edge sites • TF, transfer factor • XRD, X-ray diffraction