Two well characterised Pu inhalation cases show some remarkable similarities between substantially different types of Pu oxide. The circumstances of exposure, therapy, bioassay data, chemical solubility studies and dosimetry associated with these cases suggest that highly insoluble Pu may be more common than previously thought, and can pose significant challenges to bioassay programmes.

The reconstruction of internal doses under Part B of the Energy Employees Occupational Illness Compensation Program Act differs in multiple ways from that used in a typical operational setting. There are, for example, no limits at or above which doses must be assessed; all doses, including unmonitored or potentially undetected doses, must be reconstructed. In addition, the primary dose of concern is that delivered to the organ in which the cancer originated, and only the dose delivered to that organ prior to the time the cancer was diagnosed is relevant. Additional challenges are presented in the requirement to partition dose by radiation type and energy rather than by radionuclide, the need to include any potential dose that could have been received but was unmonitored or undetected, the inability to collect follow-up samples, and, in many cases, a general lack of information regarding the employee's work history, such as specific duties or location within a site. To overcome these challenges, the NIOSH dose reconstruction program has adopted a set of default values that include assumptions that are favorable to the claimant when there is more than one plausible choice. Due to the large number of claims that must be reconstructed, efforts are continuously underway to expedite the rate at which they can be processed. This is being achieved by taking advantage of situations in which it can be documented that more detailed evaluations would not change the outcome of the adjudication of the claim.

This paper describes a way of obtaining and gives applications of intake retention functions. These functions give the fraction of an intake of radioactive material expected to be present in a specified bioassay compartment at any time after a single acute exposure or after onset of a continuous exposure. The intake retention functions are derived from a multicompartmental model and a recursive catenary kinetics equation that completely describe the metabolism of radioelements from intake to excretion, accounting for the delay in uptake from compartments in the respiratory and gastrointestinal tracts and the recycling of radioelements between systemic compartments. This approach, which treats excretion as the 'last' compartment of all catenary metabolic pathways, avoids the use of convolution integrals and provides algebraic solutions that can be programmed on hand held calculators or personal computers. The estimation of intakes and internal radiation doses and the use of intake retention functions in the design of bioassay programs are discussed along with several examples.

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