TOWARD IMPROVED BIOKINETIC MODELS FOR ACTINIDES - THE UNITED-STATES TRANSURANIUM AND URANIUM REGISTRIES, A 25 YEAR REPORT

The origins and current activities of the United States Transuranium a nd Uranium Registries are traced with emphasis on biokinetic modelling , and new biokinetic models, for plutonium and americium, are proposed suitable for operational applications. Although started more than 25 years ago, the Registries remain the only formally organised human tis sue research programme devoted to the study of actinides in man. Using radiochemical techniques, the Registries determine the amount of acti nide elements in the tissues of volunteer donors at autopsy, using thi s information along with the individual's exposure and medical history , to evaluate the distribution, translocation, excretion and dose from Th, U, Pu, Am and other actinides in the body. The results of the Reg istries studies indicate that in addition to skeleton and liver, muscl e constitutes an appreciable reservoir for both Pu and Am, although th e dose to muscle is relatively low because of its large mass. The syst emic biokinetics of Pu and Am are well represented by a three-compartm ent model representing skeleton, liver, and other soft tissue (primari ly muscle) with different biokinetic constants for the two nuclides. F or Pu, the initial uptake fractions are 0.4, 0.4, and 0.2 with residen ce half-times of 50, 20, and 10 years, respectively for the skeleton, liver, and muscle. For Am, the comparable uptake fractions are 0.45, 0 .25, and 0.3 with residence half-times of 50, 2.5 and 10 years for the three compartments. Further to encourage radiobiology studies as well as to provide unique materials for research in other areas such as bi omarkers and oncogenes, the Registries have established the National H uman Radiobiology Tissue Repository, which includes more than 20,000 t issue samples and extracts, histopathology slides, and related materia ls from persons with internal depositions, including radium dial paint ers, plus a group of tissue solutions from the general American popula tion. On request, these materials are available to other investigators for collaborative or individual research purposes.