Investigations on the role of soil organic components in the sorption of radioiodine

A batch experiment with I-125 revealed the general tendency of increasing distribution coefficients (Kd-values) with increasing organic C-content of different horizons of a chernozem and a podzolic soil profile. Experiments with different incubation conditions as insterile (aerobic and anaerobic), sterile and different incubation temperatures as well as with biologically relevant soil properties (water content, storage conditions) delivered indications for the participation of soil microflora in iodine immobilization. However, no occurence of a temperature optimum of the kinetic of the sorption was observed indicating that physicochemical processes are also involved in iodine immobilization. Experiments with artificially increased or decreased biomass showed a good correlation between biomass content and Kd-values emphasizing the important role of microorganisms in iodine fixation. As a further proof of microbial effects on iodine immobilization incorporation of radioiodine was tested with pure cultures of bacteria and fungi isolated from the soil. A considerable uptake of radioiodine was found in washed (NaCl, CaCl2) cells with both bacteria and fungi, but no incorporation was detected into cells incubated with radioiodine in the culture medium. This may be explained by the formation of nonavailable complexes of iodine with components of the medium and/or with cell exudates. 9 refs., 3 figs., 4 tabs. (Author)