Considerable experience with radioecological and related ecological research on terrestrial and aquatic ecosystems has been achieved, especially after the Chernobyl accident. The combined effects of the radiation, chemical and biological factors, after a contamination of the environment and during its remediation have shown an interactive complexity that highlights the need for equidosimetrical evaluations of the influence of the various stressors and the need for their ecological normalization.

In radioecology and radiation protection, methods of radiation dosimetry are key for dose assessment. It is therefore highly desirable to develop a clear theoretical approach as well as a practical method of equidosimetry that would allow for an ecological normalization of the different stressors in unified uniform units, especially for comparison purposes.

This text contains the proceedings of the Workshop on The Transfer of Radionuclides in Natural and Semi-Natural Environments, held at the Villa Manin, Passariano (Udine), Italy, 11-15 September 1989.

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.

Assessment of the radiological impact of planned or existing practices involving the (actual or potential) release of radionuclides to the environment are largely based on the use of modelling techniques which allow prediction of the relationship between environmental levels and releases and the associated radiation dose to man. Models are imperfect means of representing environmental transfer processes, and it is essential to know the reliability which can be associated with the predictions of these models for each and every assessment situation. Such information is necessary in order to establish confidence in model predictions and, in particular, to allow adequate safety margins to be set in the design of nuclear facilities. This knowledge is also a prerequisite to determine release limits or to decide whether further research is justified in order to improve predictive accuracy. Therefore a number of distinguished pilpers have been presented during this workshop which focused both on practical aspects of variability of observations of facts occuring in nature, but also on learned aspects of the science of statistics. It is not very clear, however, whether much insight in mechanisms is gained by such an approach. This insight is probably rather reached by a straightforward judgment of the quality of the primary data and by the willingness to think over carefully the experiments and measurernents before doing them. The book is composed such as to give the reader the chance to quietly study the presented papers in good order.

Considerable experience with radioecological and related ecological research on terrestrial and aquatic ecosystems has been achieved, especially after the Chernobyl accident. The combined effects of the radiation, chemical and biological factors, after a contamination of the environment and during its remediation have shown an interactive complexity that highlights the need for equidosimetrical evaluations of the influence of the various stressors and the need for their ecological normalization.

In radioecology and radiation protection, methods of radiation dosimetry are key for dose assessment. It is therefore highly desirable to develop a clear theoretical approach as well as a practical method of equidosimetry that would allow for an ecological normalization of the different stressors in unified uniform units, especially for comparison purposes.