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B.R. Scott, A.F. Fencl, Variability in PuO2 Intake by Inhalation: Implications for Worker Protection at the US Department of Energy, Radiation Protection Dosimetry, Volume 83, Issue 3, 1 July 1999, Pages 221–232, https://doi.org/10.1093/oxfordjournals.rpd.a032676
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Abstract
This paper describes the stochastic exposure (SE) paradigm where, at most, small numbers of airborne toxic particles are presented for inhalation. The focus is on alpha-emitting plutonium dioxide (PuO2) particles that may be inhaled by Department of Energy (DOE) workers. Consideration of the SE paradigm is important because intake of only a few highly radioactive PuO2 particles such as 238PuO2, could greatly exceed the annual limit on intake (ALI) used to control worker exposure. For the SE paradigm, credible intake distributions evaluated over the population at risk are needed, rather than unreliable point estimates of intake. Credible distributions of radiation doses and health risks are also needed. Because there are limited data on humans who inhaled PuO2, these distributions must be calculated. Calculated distributions are presented that relate to the intake of radioactivity via inhaling polydisperse PuO2 particles. The results indicate that a large variability in radioactivity intake is expected when relatively small numbers of PuO2 particles are inhaled. For the SE paradigm, one cannot know how many PuO2 particles were inhaled by an individual involved in a given inhalation exposure scenario. Thus, rather than addressing questions such as 'Did the calculated worker's intake of 238PuO2 exceed the ALI?', it is better to address questions such as 'What is the probability that 238PuO2 intake by a given worker occurred and exceeded the ALI?' Mathematical tools for addressing the latter question are presented, and examples of their applications are provided, with emphasis on possible DOE worker exposures at the Rocky Flats facility near Denver, Colorado. The alpha-emitting isotopes 238Pu, 239Pu, 240Pu and 242Pu are found at Rocky Flats. Although 238Pu is thought to be present in relatively small amounts there, intake via inhalation of only a few 238PuO2 particles could greatly exceed the ALI.
