I. 1-131 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% adolescent urine (4.8 2, 5-16 years of age) and 4.8% child urine (1.2 %, <5 years of age) (Ja64). The adult mean peak thyroid content of I-13] was estimated by Harris to be 11.2 ywCi (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 1072 uci of I-131 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-131 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 I-131. Ingestion was assumed to occur