UNCLASSIFIED SUMMARY AND CONCLUSIONS Exposure of mice to a dry particle aerosol (Sr85ci2 adsorbed on kaolin particles) resulted in a G.I. tract/respiratory system activity ratio of 100,0.5 hr after exposure, Following administration of aqueous suspensions of the same material by stomach tube, the amount of gr85 deposited in the skeleton was 80 percent of that found in the skeleton following an inhalation exposure (in terms of initial gastrointestinal Sr activity). The findings of the high activity in the G.I. tract and the fix- ation of large amounts of Sr by the skeletal system following adminis-< tration by gavage suggest that a considerable fraction of the internally deposited activity after inhalation may have gained entry via the G.I. tract. After the mice were exposed to a liquid aerosol of SrCl2 in sea water, the ratio of activity in the G.I, tract/respiratory system at 0,5 hr after exposure was found to be 50, Three times as much Sr was found in the skeleton following exposure to the liquid aerosol as resulted from expo- sure to the dry particle aerosol. A two-fold increase in skeletal activity was also observed following administration by stomach tube of the ionic liquid SrCl2 aerosol over that found following the dry-particle suspension similarly administered. Thus, absorption of Sr into the body © was greater with the liquid aerosol than with the dry particle (2 to 3 times), due to either the greater solubility of the carrier or the nature of the association of the Sr with the carrier. Similar inhalation and gavage experiments performed with La adsorbed on an insoluble dry clay particle indicated that only a very small amount of this highly insoluble combination was able to penetrate to the internal tissues, The small amount gaining entry appeared to do so via the alve-~ olar tissue, possibly being transported as particles by macrophages. Calculation was made of biological decay constants and the relative dose to various organs that might be received by a man exposed toa dry-particle aerosol of Sr®Cl,. could be adequately described Most of the biological decay curves by the sum of two exponential functions, a rapid component and a much slower one. The first component reflects rapid clearance of activity from each organ, while the slower component corresponds to the biological loss of activity "fixed" in the organ, Calculation of the relative dose to the various organs indicated that the skeletal system received by far the highest dose over the 28-day period studied, as would be expected following exposure to a highly soluble bone-seeking metal, The high concentration of activity in the G.I, ys tract resulted in an initial dose rate to the small intestines many-fold -19UNCLASSIFIED ££ £€ KE FE &@ £E © fF fF if F 2 ae KE. E bk Gl UU