Ora LSS Laenlied
:
PMR fal
exposure’ (Fig. 2B). The comparison of the amount of activity in the
various tissues followings
lation and gavage of the TypeIII simulant
is presented in ‘Table 2.|' Following gavage, approximately
1,3 + 0,2 per cent
of the activity in the GI 'tractfat’l "hr gained entry into the-blood stream and
was retained by the live?
tion of the simulant.
gudibkeldton, the primary sites’ of internal depnsi-
In cémparison, about 3.2 + 0.3 per cent of the GI
‘tract activity was found{wMEEbve x and skeleton following the inhalation
exposure-to the same simujant.? Thus, absorptionfrom the GI tract
accounts for an avcrage af'23’per cent of the activity deposited inthe
skeleton following an inhalation*exposure, and 50 per cent of both the
liver and respiratory trasaptivity:
Only half theiactivity in the respira -
tory system, therefore, |derives from material directly inhaled and absorbed through the alveolar‘tlegpue; the other half is obtained frommaterial
which enters the circulation;jpon absorption through the Gl tract, These
data emphasize the fact.that-the:GItract is a significant portal of entry of
a dry-particle aerosol into‘t
ystemic circulation following an inhalation ~
exposure<{! Thus, the phygicgicharacteristics (such as particle size)which |
have to befconsidcred inievaluating the absorption of particles must be cone }
sidered with respect to the intestinal membranes as well'as the alveolar
tissue.
Po
|
fe
.
a4
bee“ santo oa
a;
|
The radjoactivity in all'th tissu 8 except the skeleton,and thyroid
following both inhalationiandigayage decayed rapidly, decreasing toa
fraction of | per cent of theig’Ivhr activity by the 15th day. The skeleton
and thyroid, however, eptained from 4 to 9 per cent of their 1 hr activity
at the 15th day. The drop infactivity, in each tissue was afunction of two
simultaneous processes!’ the radioactive decay of the fission products
andithe biélogical loss’ o
Imiulant mate rial itself from the tigstes,
5
terredigprrpe
Radioactive Decayof
Hacioactive
.
vel
tivit
The composition of the vadioactive material deposited in a tissue is
reflected in the radioactive ecay ourveof that tissue. IA order to gain
information on (he selective pptake, the gamma activity of the tissues uf
animals sacrificed at | hr past-exposure was measured at intervals ove:
a 30-day period, ‘I'hese decay curves for various tissues’ (following ad.
The
i
ws
'in
im
i
amy
7%,
~8-
. Ug
etait ee”
4
rene +haat untieet m
mae enakeane.
i
iz
is
im
parent radionuclide,
ic
ting
7
ably reflects the growth of a‘gamma-emitting daughter from a heta-emil
|
cate SeeI ig ye eno
fission-product mixture due to the affinity of bone for certain of the elements which are characteriged by relatively long half-lives, The activily
of material, weposited inthe dine F decayed with a.somewhat higher rate
than other: soft (issues, Thetapparent increase, in activity.at | day prol.
“
similarityfof the curves (with the exception of the skeleton) indicates
that the isotopic distribution ‘of the internally deposited fission product:
in most offthe tissues was very similar, The lower rate of decay’ of the
activity infthe skeletal tissue reflects a fractionation in the uptake of the
em thee te
ministration by both inhalation‘and gavaye) are shown in Fig, 3.