AVAILABILITY AND FIXATION OF RADIOCESIUM IN A FOREST BROWN ACID SOIL

The organic and mineral horizons of a forest brown acid soil sampled in Belgium (Haute Ardenne, Vielsalm) were artificially contamined with a solution of (CsCl)-Cs-137. If the sequential extractions (CaCl2, NH4Ac, CuCl2 and HNO3, 1N) realised on a pure mineral substrate remove 40% of the total Cs-137 content, the same reagents can only remove 8% of total caesium when they react with the organic substrate (Of + OAh). Other controlled experiments with the different layers of the soil profile show, on the other hand, that if a pool of Cs-137 is available for exchange in the Of and B horizons (31 and 18%, respectively, of total caesium for NH4Ac), the quantities of exchangeable Cs-137 (CaCl2 and NH4Ac) and the present one in soil solution of the transition OAh and Ah horizons are near zero (0.1 and 2.7% of total caesium for NH4Ac, respectively). This result seems to contradict the available quantities of potassium cation. This suggests, firstly, that the organic matter, or more probably organomineral complexes, interact strongly on the behaviour of Cs-137 in the profile hemiorganic layers and, secondly, that the Cs-137 has a special behaviour of its own.