SOIL–SOIL SOLUTION DISTRIBUTION COEFFICIENT OF RADIOIODINE IN SURFACE SOILS AROUND SPENT NUCLEAR FUEL REPROCESSING PLANT IN ROKKASHO, JAPAN.

The soil-soil solution distribution coefficient (K_d) of radioiodine in soil samples with various total carbon (TC) contents was measured in a batch sorption experiment using ¹²⁵I tracer spiked as I⁻. The log values of K_d−¹²⁵I and TC concentration in low-TC soils (< 10g kg⁻¹) were positively correlated, whereas those of K_d−¹²⁵I in TC rich soils (> 10 g kg⁻¹) and dissolved organic carbon (DOC) in liquid phase were negatively correlated. The proportion of ¹²⁵I in the < 3 kDa fraction in the liquid phase is negatively correlated with the log of DOC, implying that ¹²⁵I is primarily combined with high-molecular-weight organic matter in soil solutions rich in DOC. The results suggest that K_d−¹²⁵I in soil with high soil organic material (SOM) content is governed by DOC via the combination of ¹²⁵I and DOC. In contrast, K_d−¹²⁵I in soils with a low SOM content was governed by SOM because the anion exchange capacity of SOM was vital for the sorption of ¹²⁵I⁻. [ABSTRACT FROM AUTHOR]