UNCLASSIFIED
Following ingestion, barely detectable levels of activity were present
in the liver and skeleton (0. 004 and 0. 011 percent) of the activity in the
G.I. tract. The La on the dry particle appears to enter the body almost
completely through the alveolar membranes. It is probable that because
of its insoluble nature the LaCl3 cannot be absorbed through the G.I.
membrane. The larger amounts which are able to penetrate the alveo-
lar tissue are probably transported as particles by macrophages and
subsequently leached from the particles into body fluids.
Thus it appears that only with soluble fission products is the G.I.
route of entry of importance.
Analysis of Biological Decay Curves
Studies made of the activity of the various tissues of the animals
after inhalation exposure or administration of radioactive material by
gavage were carried out over a period of 28 days in order to provide
data on the effect of the route of entry on the rates of clearance from
the individual tissues and on the doses received by these tissues. Fol-
lowing exposure to the dry-particle aerosol, the gammaactivity of each
tissue was determined at fixed intervals and was corrected for radioactive decay. Thus, the curve of the biological decay of Sr in each
tissue was determined.
The curves were analyzed mathematically, and it was found that in
most cases a simple sum of two exponentials was sufficient to characterize the decay curve over the 28-day period studied. The equations
took the form
At =Kj e Alt + K2 eA2t,
The constants determined for the various curves previously illustrated
in Fig. 3A are summarized in Table 5.
The activity of the G.I. tract and its contents decreased the most
rapidly, as would be expected from the system with the natural excre-
tory function (Table 5).
The initial component of biological loss of Sr
from the stomach (Aj * 6.06/day) and small intestine (j= 9. 09/day)
probably corresponds to the rapid loss of material by excretion.
The
second component (\2 = 0.128/day and 0.133/day) probably reflects
the appearance of lung "fixed" activity and the excretion of material de:
posited in internal tissues.
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