For the assessment of doses after inhalation of airborne uranium compounds by workers, the International Commission on Radiological Protection (ICRP) developed compartmental models that are used to calculate reference dose coefficients and retention and excretion functions. It is assumed that each acute intake has no effect on the biokinetics of later intakes. Consequently, retention and excretion after multiple or chronic exposure are predicted using the same models as after acute exposure. This assumption was tested here on rats exposed to repeated inhalation of uranium dioxide (UO₂). First, excretion and organ retention were determined after a single inhalation of UO₂. The follow-up of incorporated activity was used to design a biokinetic model for uranium inhaled by rats. Second, the biokinetics of uranium were monitored in two experiments of repeated inhalations of uranium dioxide under different intake patterns. For these two experiments, the organs' retention and excretion after repeated UO₂ inhalation were predicted using the biokinetic model and compared to the experimental measurement. Under the two sets of experimental conditions considered, the prediction of the biokinetic model based on acute exposure data was consistent with the biokinetics observed after repeated UO₂ inhalations, with the possible exception of retention in the skeleton.

In order to support animal experiments of chronic radionuclides intake with realistic dosimetry, voxel-based three-dimensional computer models of mice and rats of both sexes and three ages were built from magnetic resonance imaging. Radiation transport of mono-energetic photons of 11 energies and electrons of 7 energies was simulated with MCNPX 2.6c to assess specific absorbed fractions (SAFs) of energy emitted from 13 source regions and absorbed in 28 target regions. RODES software was developed to combine SAF with radiation emission spectra and user-supplied biokinetic data to calculate organ absorbed doses per nuclear transformation of radionuclides in source regions (S-factors) and for specific animal experiments with radionuclides. This article presents the design of RODES software including the simulation of the particles in the created rodent voxel phantoms. SAF and S-factor values were compared favourably with published results from similar studies. The results are discussed for rodents of different ages and sexes.

The interpretation of individual activity measurement after a contamination by ²⁴¹Am or its parent nuclide ²⁴¹Pu is based on the reference americium (Am) biokinetic model published by the International Commission on Radiological Protection in 1993 [International Commission on Radiological Protection. Age-dependent doses to members of the public from intake of radionuclides: Part 2 Ingestion dose coefficients. ICRP Publication 67. Ann. ICRP 23(3/4) (1993)]. The authors analysed the new data about Am biokinetics reported afterwards to propose an update of the current model. The most interesting results, from the United States Transuranium and Uranium Registries post-mortem measurement database [Filipy, R. E. and Russel, J. J. The United States Transuranium and Uranium Registries as sources for actinide dosimetry and bioeffects. Radiat. Prot. Dosim. 105(1–4), 185–187 (2003)] and the long-term follow-up of cases of inhalation intake [Malátová, I., Foltánová, Š., Becková, V., Filgas, R., Pospíšilová, H. and Hölgye, Z. Assessment of occupational doses from internal contamination with ²⁴¹Am. Radiat. Prot. Dosim. 105(1–4), 325–328 (2003)], seemed to show that the current model underestimates the retention in the massive soft tissues and overestimates the retention in the skeleton and the late urinary excretion. However, a critical review of the data demonstrated that all were not equally reliable and suggested that only a slight revision of the model, possibly involving a change in the balance of activity between massive soft tissues, cortical and trabecular bone surfaces, may be required.

Decommissioning fission and fusion facilities can result in the production of airborne particles containing tritium that could inadvertently be inhaled by workers directly involved in the operations, and potentially others, resulting in internal exposures to tritium. Of particular interest in this context, given the potentially large masses of material involved, is tritiated steel. The International Commission on Radiological Protection (ICRP) has recommended committed effective dose coefficients for inhalation of some tritiated materials, but not specifically for tritiated steel. The lack of a dose coefficient for tritiated steel is a concern given the potential importance of the material. To address this knowledge gap, a “dissolution” study, in vivo biokinetic study in a rodent model (1 MBq intratracheal instillation, 3-month follow-up) and associated state-of-the-art modelling were undertaken to derive dose coefficients for model tritiated steel particles. A committed effective dose coefficient for the inhalation of 3.3 × 10⁻¹² Sv Bq⁻¹ was evaluated for the particles, reflecting an activity median aerodynamic diameter (AMAD) of 13.3 µm, with the value for a reference AMAD for workers (5 µm) of 5.6 × 10⁻¹² Sv Bq⁻¹ that may be applied to occupational inhalation exposure to tritiated steel particles.

BIO Web of Conferences, open access proceedings in biology, life sciences and health