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HARDY, RIVERA, AND CONARD
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study the retention curve is best described as a series of exponentials
that level off after 140 days and approach a value of 25%. This isa
somewhat higher retention value than that reported in cther studies.”!
DISCUSSION
A number of investigators have shown that the whole-body veten-
tion for a single administration of “Cs can be expressed by a twocomponent exponential function of time: 4:45!"
Ry = (1 — a) e760899/T Ht 4. gg (0.698/T2)t
where R, is the fractional retention at t days, a is a constant, and T,
and T,
are biological half-lives in days. The short-term component
has a half-life, T,, of about one day,!*1617 and the principle compo-
nent has a half-life, T,, that varies from study to study, ranging from
50 to 150 days (Refs. 12 to 16 and 22 to 25). The comparison of biciogical haif-lives under conditions of both acute and chronic exposures is
tustified based on the work of Rundo,?® The short-term component was
not calculated in this study since the acute ingestion took place over a
seven-day period and the initial excretion collection periods were over
three-day intervals. The long-term component as determined by both
whole-body
counting
and
excretion data (74 and 64 days, respec-
tively) was within the range of biological half-life values found by other
investigators. Rundo™ has pointed out that a large partof the variations
in body burden can be attributed to the variability in biological asit-
life rather than to differences in dietary habits. The low excretion of
cs in feces relative to urine showed that the '’Cs in the Rongelap
food was rapidly and almost completely absorbed. Since the finding that
a single long-term component describes the excretion from the whole
body is in agreement with other studies, it can be said that the "Cs in
Rongelap food is not in a unique chemical form with respect to the
various accidental and experimental intake conditions under which the
behavior of "Gs in man has been studied.
The urinary to fecal ratio was found to be reasonably constant and
was within the range of 3 to 10 found by others.!?7!*® Rundo’® has used
the urinary to fecal ratio to estimate the uptake of Cs ingested in
food. The fraction of "Cs ingested in food which is transferred from
the gastrointestinal tract to blood was at least 0.9. The data obtained
in this study do not indicate that the Cs in Rongelap food behaves in
a@ significantly different manner.
The
excretion pattern of the %sr from the Rongelap food was
markedly different from that of “Cs. Most of the "Sr was not absorbed, as evidenced by the much higher fecal than urinary excretion.