The Influence of Aerosol Size on Retention and Translocation of 241Am Following Inhalation of 241AmO2 by Beagles

Abstract

Beagle dogs received a single inhalation exposure to a monodisperse or a polydisperse aerosol of 241AmO2 to determine the radiation dose to internal organs. Three monodisperse aerosol sizes (0.75, 1.5 and 3.0 micrometer activity median aerodynamic diameter) and one polydisperse aerosol (1.8 micrometer activity median aerodynamic diameter) were used to assess the role of particle size in clearance of 241AmO2 from the lung and the rate of translocation of 241Am to other tissues. Dogs were sacrificed in groups of two or three at 8, 32, 64, 128, 256, 365 and 730 days after exposure. The clearance rate of 241Am from lung was particle size dependent; this resulted in an increased radiation dose to lung at 2 yr by 70% as particle size increased from 0.75 to 3.0 micrometer aerodynamic diameter. Conversely, the radiation dose to liver and skeleton decreased by 20 and 35% respectively as particle size increased from 0.75 to 3.0 micrometer activity median aerodynamic diameter. When the radiation doses absorbed by lung, liver and skeleton were compared to those predicted by the ICRP 30 model, differences were noted.

Intracellular Particle Dissolution in Alveolar Macrophages

“…In fact, a translocation rate constant k = 6.9 x 10-8 g/cm2/day was determined for all canine lung clearance studies using Co304 particles (32). Interestingly, this constant was in the same range as the translocation rate constants found for other metal oxides in dogs (21)(22)(23)(24)(25)(26)(27)(28) (33).…”

“…This approach has also been applied to less soluble particles. Reasonable agreement was obtained when translocation in vivo was compared to dissolution of insoluble particles in lung fluid simulants (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). It has to be stated, however, that the particles used were not uniform and that their physical parameters, in particular their specific surface areas, were not known exactly, resulting in considerable uncertainty.…”

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

“… (927) As noted above, Mewhinney et al. (1978, 1982) and Mewhinney and Griffith (1983) studied the tissue distribution of americium in beagle dogs following inhalation of monodispersed (3.0-, 1.5-, and 0.75 µm AMAD) and polydispersed (1.8 µm AMAD) 241 AmO 2 aerosols over 6 y. They noted the long-term pulmonary retention of a small fraction, of the order of 1% (0.5–2%) ILD.…”

“…Biological half-times of americium in the liver are typically on the order of 5–15 d in rats and mice, 30–150 d in baboons and monkeys, and a few years in dogs and hamsters. Long-term studies on dogs (Lloyd et al., 1970; Mewhinney et al., 1982) indicate that a large portion of the initial liver burden gradually transfers to the skeleton. (950) Hamilton (1948) described the sites of bone deposition of americium and curium in rodents as indistinguishable from those of the trivalent elements cerium, promethium, and actinium, but different from sites of deposition of the tetravalent elements plutonium, thorium, and zirconium. Later studies involving a variety of animal species indicate that americium deposits on all types of bone surfaces, including resorbing and forming surfaces (Herring, 1962; Lloyd et al., 1972a; Durbin, 1973; Priest et al., 1983).…”

An Interspecies Comparison of the Phagocytosis and Dissolution of241AmO2Particles by Rat, Dog and Monkey Alveolar Macrophagesin Vitro

“…Among rat, dog and monkey, mechanical clearance by the mucociliary escalator is dominant in rat for short-term clearance, while the dissolution of particles is dominant for short-or long-term clearance of either moderately or highly insoluble particles in dog and monkey (Mewhinney et al 1982, Snipes et al . 1983) .…”