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DIVISION S-9—SOIL MINERALOGY

Specific Retention of Radiocesium in Volcanic Ash Soils Devoid of Micaceous Clay Minerals

^a CNRS–UMR 6532 HydrASA, Faculté des Sciences, Université de Poitiers, 40, avenue du Recteur Pineau, 86022 Poitiers cedex, France
^b Université Catholique de Louvain, Unité des Sciences du Sol, 2/10, Place Croix du Sud, 1348 Louvain-la-Neuve, Belgium

^* Corresponding author (emmanuel.joussein{at}hydrasa.univ-poitiers.fr).

The environmental availability of trace radiocesium (¹³⁷Cs) was studied in soils devoid of weathered micas. The soils were developed from basaltic ash, within a sequence Udand Tropept Udalf Udult from Cameroon. Tropepts and Udalfs are halloysite-rich and they exhibit a large cation exchange capacity (CEC) and a strong exchange selectivity for K probably due to the presence of halloysite-smectite mixed-layered clays. The ¹³⁷Cs mobility was evaluated in the B horizons through (i) a physicochemical approach using the radiocesium interception potential concept (RIP) and a sequential sorption–desorption procedure, (ii) a biological test assessing the ¹³⁷Cs rhizospheric mobilization (¹³⁷Cs-RM). In a constant K⁺–Ca²⁺ background solution, one of the Tropepts and the Udalfs fixed about 76% of the initial ¹³⁷Cs loading. The second desorption phase in acidic conditions was more discriminating: the Udalfs fixed about 40%, while the other soils fixed 5 to 20% of the initial ¹³⁷Cs⁺ loading. The ¹³⁷Cs-RM was generally small (3–15%) in all samples and was negatively correlated with the RIP (439–1836 µmol g^–1). The specific retention of ¹³⁷Cs in these soils was thus largely similar to that obtained in soils that contain weathered micas. It demonstrates the presence of ¹³⁷Cs specific sites in halloysitic soils devoid of such minerals. These sites might be associated with halloysite-smectite mixed-layered clays. They were probably formed following wetting-drying cycles in soils heavily fertilized with K.

Abbreviations: ¹³⁷Cs-RM, ¹³⁷Cs rhizospheric mobilization • CEC, cation exchange capacity • FES, frayed-edge sites • K_G, Gapon selectivity coefficient • PAR, potassium adsorption ratio • RES, regular exchange sites • RIP, radiocesium interception potential • TF, ¹³⁷Cs rhizosphere-to-plant transfer factor • TGA, thermal gravimetric analysis

This article has been cited by other articles:

				E. JOUSSEIN, S. PETIT, J. CHURCHMAN, B. THENG, D. RIGHI, and B. DELVAUX Halloysite clay minerals -- a review Clay Minerals, December 1, 2005; 40(4): 383 - 426. [Abstract] [Full Text] [PDF]