Work described in this report is aimed at establishing the magnitude and mechanisms of $sup 99$Tc sorption by soils and uptake by plants. Studies showed that sorption of $sup 99$Tc by soils was essentially stopped by sterilization of the soil, further indicating that the sorption process is related to microbial activity. Studies also showed that sorption can occur under aerobic as well as anerobic conditions. However, there was considerable difference in the extent of sorption for different soils which remains to be explained. $sup 99$Tc was shown to be toxic to germinating seeds at low concentrations, but not when added to more mature plants. Initial evidence suggests this is a chemically rather than a radiologically induced toxicity but this remains to be completely resolved as well as whether there is a threshold level of $sup 99$Tc required before toxicity occurs. (auth).

Studies described in this report were aimed at establishing the magnitude and mechanisms of /sup 99/Tc sorption by soils and uptake by plants. Results show that /sup 99/Tc 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 /sup 99/Tc 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 /sup 99/Tc required before toxicity occurs. Studies of short-term, dynamic, aerobic systems indicated that /sup 99/Tc moves through the soil as a relatively large anion exhibiting characteristic miscible displacement with some asymmetric tailing. /sup 99/Tc exhibits greater retention that C1/sup -/, 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.