The Disposition of Americium-241 Oxide Following Inhalation by Beagles

The disposition of americium-241 in beagles was followed for up to 810 days after a single inhalation exposure to ^{241}{\rm AmO}{}_{2}$ aerosols having an activity median aerodynamic diameter (AMAD) of 1.3 μm and a geometric standard deviation (GSD) of 1.8 for medium (∼40 nCi/liter) and high (∼340 nCi/liter) concentrations. At low concentrations (< 1 nCi/liter), the aerosols were smaller (AMAD ∼0.6 μm) and the distribution broader (GSD ∼2.6). Excreta were analyzed for up to 30 days postexposure and where appropriate, during the last week before sacrifice. Tissue analyses for 241 Am were conducted on groups of three dogs sacrificed 10, 30, 90, 270, and 810 days postexposure. Forty percent of the final body burden of 241 Am was located in tissues other than the lung parenchyma by 10 days postexposure and only 6% remained in the lung by 810 days postexposure. Translocation was primarily to the liver and skeleton, with roughly equal fractions of the final body burden in each at all postexposure sacrifice times. There was very little retention in the thoracic lymph nodes (< 1%) and 241 Am activity found in the gonads was negligible (< 0.05%) for these dogs. Both the rate of translocation and the organ distribution as a function of time are different from those found in dogs that inhaled ^{238}{\rm PuO}{}_{2}$ or 239 PuO2. Therefore it is not appropriate to use data derived from 239 PuO2 experiments or observations to predict the behavior of other transuranic isotopes and elements.