I.

I-131 THYROID BURDEN AT RONGELAP ISLAND BASED ON URINE BIOASSAY

Urine samples for 24-hour elimination were pooled and collected on the

17th day post detonation from persons evacuated from Rongelap Island (Co72).

The

urine was sent to Los Alamos Scientific Laboratory and an estimate of thyroid
absorbed dose from internal emitters was reported by Cohn (Cr56).

The 64-person

composite urine sample was 75% adult urine (18 2, >16 years of age), 20% adoles-

cent urine (4.8 2, 5-16 years of age) and 4.8% child urine (1.2 2, <5 years of
age) (Ja64).

The adult mean peak thyroid content of I-131 was estimated by

Harris to be 11.2 yCi (Ha54).

This estimate was based on the assumption that

0.1% of stable iodine intake on the first day would be eliminated via the urine

between the 15th and 17th days (Co72).

Harris indicated a mean activity of 1.31

x 107? uCi of I-13] in the Rongelap adult 24-hour urine taken on the 17th day
post detonation.
Table 1 is a tabulation of the fraction of an initial I-13] activity intake by ingestion that would be eliminated by an adult on a given day post the
intake.

These daily fractions were calculated by two methods, one was a model

by Johnson (Jo81, see Fig. 1) and the other was a model used by ICRP (ICRP 30,

see Fig. 2).

Both models incorporated feedback.

Both were solved using

catenary compartment kinetics and both led to similar values for elimination by

a reference man (see Table 1).

A comparison to an excretion curve in a normal

adult male was made and values tabulated for the case of stable iodine (see
Table 1).

Values for female individuals may be slightly higher or equivalent as

indicated by the comparison between reference male and female values.
On the basis of 1.31 x 107? uCi in adult urine on the 17th day post intake, a 93 pCi intake was estimated for I1~131.

Ingestion was assumed to occur

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