Studies on the role of natural and anthropogenic organic substances in the mobility of radioiodine in soils

A batch experiment with 125I revealed the general tendency of increasing distribution coefficients (Kd-values) with increasing organic C-content of different horizons of a podzolic soil profile. Column experiments with four pedologically distinct horizons confirmed this trend. An addition of compost in a concentration of 0.1% to 1% resulted in a marked increase of 125I sorption in a soil layer with organic C-deficiency. Precipitation and dialysis of the eluted organic substances suggest that a considerable part of the radioiodine is fixed in humic and fulvic acids. Addition of anthropogenic complexing agents such as dibutylphosphate (DBP), nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) induced pronounced remobilization of iodine in the soil matrix. (orig.)