The contribution of speciation studies to internal dosimetry.
Workshop on Internal Dosimetry of Radionuclides - Occupational, Public and Medical Exposure - 9-12 September 2002 - New College, Oxford, United Kingdom
F. PAQUET(1), G. COTE(2) and C. MADIC(3)
Speciation studies consist in the determination of the chemical form of elements and their concentrations in chemical or biological media. These studies are necessary to improve the understanding of trace element kinetics and metabolism. In case of internal contamination with radionuclides, speciation studies could therefore improve both the biokinetics models and the dosimetry of the radionuclides.
Computer speciation modelling and experimental speciation are two complementary approaches. The development of new thermodynamical databases, associated with new softwares gives new tools for a first estimate of the chemical forms and distribution of radionuclides in the various compartments of the body. The chemical forms often involved include free or complexed soluble ionic or neutral species, adsorbed species, precipitates and reversible or irreversible macromolecular complexes. Computer modelling should be completed by in vitro or in vivo experiments to both validate the results of speciation in fluids and partitioning between compartments, and derive appropriate thermodynamic and kinetic constant values.
State of the art description of what is known about speciation of radionuclides and what are the consequences in term of internal dosimetry is given for some actinides in blood, GI-tract, liver and skeleton. New data obtained in blood showed that most of the actinides are bound by transferrin, but that binding is strongly dependant of the initial valence state of the element. In liver, plutonium, americium and curium are bound to ferritin and lipofuscin whereas neptunium is bound to ferritin and calmodulin. All the data showed that this binding is time and mass dependant. In other organs, data are less abundant and most is known about the chemical form of uranium in saliva. These data need to be completed since GI-tract and skeleton are one of the main entry and deposition site, respectively, of the actinides in the body.
1.Institut de Radioprotection et de Sûreté Nucléaire, Département de Protection de la santé de l’Homme et de Dosimétrie, Service de Dosimétrie, Laboratoire d’Etudes Appliquées de Radiotoxicologie, BP 36, F-26701 Pierrelatte Cedex, France
2. Ecole Nationale Supérieure de Chimie, Rue Pierre et Marie Curie, F-75005 Paris, France
3. CEA/Saclay, DEN/SAC/DIR, 91191 Gif-sur-Yvette, France