‘data to the
(Eq. 4)
Q = 500 uro7 4,
amination
clearance mechanisms.
One can then describe trans-
fer to the systemic circulation as:
rer, whether
iterized data
Substitution of known values for t and U
lations as
allows one to estimate total-body burden at time.
ures are
‘of exposure in the same units that are used for U
mic model of
(i.e.,
count rate, Mass, or activity).
(Eq. 6)
Assuming that each increment transferred is
Similarly,
data ob-
‘the body burden (Q,) at any time t following re[peated exposure may be calculated by using the total
excreted according to the function shown in Eq.
£ short life
elimination coefficient and assuming multiple in-
the excretion rates from each increment.
lutonium
puts as 4 summation process.
m and col-
5.
Langhan
l,
the total excretion may be described as the sum of
Time (t)
is relative to elapsed time since transfer from the
lung rather than time since inhalation.
A major difficulty in evaluating human expo-
Using R
r function
gures has been the problem of reservoirs of pluto-
as the time urine samples are obtained after inhala-
te to body
pium in various organs
tion, the excretion rate (EY) is:
(not bone) that are slowly
sed to
released to the circulatory system at rates that
ons char-
depend on many factors such as location within the
and release body, particle size,
E, = 0.002 A_ Q, f° et (R - cy 70774 dt.
and physiochemical form.
(Eq. 7)
'This slowly translocated plutonium is subsequently
ecent analents and
deposited in other tissues and ultimately lost from
either the
the body via urinary and fecal excretion.
Unfortunately, Eq. 7 is not integrable and must
be solved for individual values of 4, R, and t by
expansion of the exponential term and solving until
The concept of slow, continuous release of
functions
the series converges.
on patterns .° bound plutonium into the body fluids, first formtained dur-
several groups of investigators.°??
some
The overall transfer rate
(A) was thought to be composed of two components:
alized by Healy,’ has been built into models by
(1)
The rate of
rate of transfer into the systemic circulation
periods up
urinary or fecal excretion of plutonium in persons
(ADs and (2} rate of loss via ciliary clearance
ed on the
chronically exposed can be estimated from Eqs. 1
mechanisms (A).
expressions " and 2 by summation of individual administrations.
as 4.
Healy's model regards relatively insoluble pluto-
ecal excre-
excretion and for the amount of plutonium in blood.
nium in che lung as a reservoir tsolated from
ra period
Figure 1 shows the calculated relation between
| normal body metabolism yet continually releasing
plutonium into the bloodstream.
The model has no
any portion of the lung or body; therefore, particles transiocated from the lung to lymph nodes
(Eq. 2)
behave in the same manner as those in the lung,
1ttom of the
provided the rate of solution and entry into the
2 days fol-
systemic circulation is the. same.
iown time,
lung and then utilizes the systemic model developed
by Langham, 29
fF ing acute deposition after initial clearance of an
, Smount (Q\) of insoluble plutonium is:
(Eq. 5)
(Eq. 3)
=
The overall elimination rate (A) actually represents
both solubilization and transfer to the systemic
circulation and discharge from the lung by ciliary
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LUNG EXPOSURE MODEL
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SYSTEMIC EXPOSURE MODEL
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The quantity (Q) in the lung at time t follow-
irine speci-
ired ina
The model assumes
a constant fractional removal per unit time from the
time of
ig Eq. 1 and
iot,-
, constraints regarding the positionof plutonium in
(Eq. 1)
Healy assumed that As was the same
Similar expressions were derived for fecal
&
c
2
4
°
1
x
10-4
a
0°
Ie
Fig. 1.
ft A hed
ro!
a
oe
aa
ee eee
Dertahrreetieriedatal-
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10°
TIME AFTER EXPOSURE (DAYS)
10°
heedee
cd tL
10
Fractional urinary excretion as a function
of time after acute exposure based on the
systemic and lung exposure models.
27