Application of a Canine 238Pu Biokinetics/dosimetry model to Human Bioassay Data

Abstract

Associated with the use of 238Pu in thermoelectric power sources for space probes is the potential for human exposure, primarily by inhalation and most likely as 238PuO2. Several models have been developed for assessing the level of intake and predicting the resulting radiation dose following human exposure to 239Pu. However, there are indications that existing models do not adequately describe the disposition and dosimetry of 238Pu following human exposure. In this study, a canine model that accounts for these differences has been adapted for use with human excretion data. The model is based on existing knowledge about organ retention of plutonium. An analysis of the sensitivity of the model to changes in aerosol-associated properties indicated that predictions of urinary excretion are most sensitive to changes in particle solubility and diameter and in the ratio of fragment:particle surface area. Application of the model to urinary excretion data from seven workers exposed to a 238Pu ceramic aerosol gave estimated intakes of 390-8,200 Bq and associated initial pulmonary burdens of 80-1,700 Bq. The resulting 50-y dose commitments to critical organs per Bq of 238Pu intake were estimated to be 0.5 mSv for the thoracic region, 0.2 mSv for the liver, and 1 mSv for the bone surfaces.

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

“…(2003) analysed 238 Pu in tissues of a whole-body donor (USTUR Case 0259) who accidentally inhaled plutonium (predominantly 238 Pu) in the form of a highly insoluble ceramic 238 PuO 2 -molybdenum. Along with six other workers exposed at the same time (Hickman et al., 1995), this donor excreted little or no 238 Pu in his urine for several months. Subsequently, however, and with no further intakes, the urinary excretion of 238 Pu increased.…”

“…Guilmette et al. (1994) and Hickman et al. (1995) developed the model further, adapted it to humans, and applied it to urinary bioassay data from workers who inhaled 238 Pu aerosols (see below). (777) In some of the studies outlined below, urinary excretion rates that increased with time were observed, indicating that the dissolution rate in the lungs increased with time.…”

“…Guilmette et al. (1994) and Hickman et al. (1995) developed the model further, adapted it to humans, and applied it to urinary bioassay data from workers who inhaled 238 Pu aerosols (see below).…”

“… (778) Guilmette et al. (1994) and Hickman et al. (1995) reported urinary excretion of 238 Pu for seven workers up to 18 y after inhalation exposure in the same incident.…”

Mobility, solubility and biokinetics of 238Pu

“…The observed excretion could be predicted by starting with an initial lung solubility of 1 X 10 -6 d -1 , increasing gradually to 4 X 10 -3 d -1 . A mechanistic model was developed for non-ceramic plutonium oxides in beagles [9], and was eventually adapted to fit the urinary excretion observed in cases involved in the 1971 incident [10,11]. The ICRP66/67 models were calibrated to fit the excretion and autopsy data of a worker who was exposed to ceramic 238 PuO 2 , but since this was only based on one individual, this modified ICRP model is not broadly applicable [12].…”