Biological uptake and transfer of radium-226: a review

The theoretical basis of the biological uptake of radium is poorly developed. The simple linear concentration factor model has been used almost exclusively and often without any appreciation of its limitations. An analysis of the available data reveals that this model can be adequately validated only for freshwater algae. Deviations from this model are due to non-linearity of uptake response to increased radium concentration in the medium, to the lack of equilibrium being established within the time scale of the food-chain transfer, and to the existence of multiple sources (e.g. food and water) in some of the food-chain compartments. These theoretical weaknesses and the large errors of prediction indicate a need for more rigorous theoretical and experimental work. This need is further supported by the revised dose limits for the long-lived daughter products of uranium recently recommended by the International Commission on Radiological Protection (ICRP). These revised limits suggest that 226Ra may no longer be a singularly critical nuclide, and thus dose assessment models will have to incorporate more radionuclide transfer terms, for which the errors are additive, and so should be made as low as possible. (author)