Behavior of technetium-99 in soils and plants. Final report, April 1, 1974--December 31, 1978

Studies described in this report were aimed at establishing the magnitude and mechanisms of 99Tc sorption by soils and uptake by plants. Results show that 99Tc was sorbed from solution over a period to two to five weeks by 8 of 11 soils studies. The slow rate of sorption, the lack of sorption by low organic matter soils, the elimination of sorption following sterilization and increased sorption following addition of dextrose all point to a microbial role in the sorption process. However, it has not been established whether this is a direct or indirect role nor is it possible to clearly predict the conditions under which sorption will occur. Results of plant uptake studies show that 99Tc can be taken up and translocated into the photosynthetic tissue of higher plants with concentrations in seeds being much less than in vegetative tissue. Technetium-99 was also shown to be toxic to plants at low concentrations and evidence suggests that this is a chemically rather than radiologically induced toxicity. However, this remains to be completely resolved as well as whether there is a threshold level of 99Tc required before toxicity occurs. Studies of short-term, dynamic, aerobic systems indicated that 99Tc moves through the soil as a relatively large anion exhibiting characteristic miscible displacement with some asymmetric tailing. 99Tc exhibits greater retention that C1-, which may be attributed statistically to weak complexion by organic matter. It is unlikely that this retention phenomenon is related to the static sorption activity reported in the first part of this study