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.

Since the discovery of technetium (in 1937, by Perrier and Segre), technetium-99 and technetium-99m have become most familiar in the specialised literature, the behaviour of the former being of concern regarding its health impact, the latter having been used intensively in medical tests for many years. The knowledge of the characteristics and behaviour of this element in nature is currently increasing exponentially. It has become clear, however, that there is still a serious shortage of information needed to assess properly its burden and impact on man and his environment. Technetium may indeed be released from nuclear installations or as a waste product from medical applications. It is generally considered to be highly mobile as the anion TcOi, but it is also suspected to be readily reduced in soils and metabolised in living beings into lower oxidation states. The seminar was planned to analyse thoroughly the experimental results obtained up to now and to make recommendations of specific issues requiring further research. This book presents the papers of the different sessions in the order of presentation, and the conclusions drawn by three discussion groups which dealt separately with: problems of sources and distribution of man-made technetium and its radiological consequences; the chemical behaviour of technetium in different ecosystems; biochemical reactions and binding with macromolecules in various life systems. vi Preface The editors, together with the Programme Committee of the Seminar, wish to express their gratitude to the chairmen of the different sessions for their summary of the group discussions.