198 Health Physics August 2010, Volume 99, Number 2 Table A1. Six possible sets of parameter values for thyroid biokinetic model for Marshallese and for American military personnel on Rongerik. Parameter sets 1b and 2b were preferred for Marshallese (see text). Parameter sets Marshallese la 1b (preferred) Ic 2a 2b (preferred) 2c Average of data sets |b and 2b (applied to Marshallese) Military personnel (Rongerik Atoll) Water intake (Ld') Water loss via urine (Ld) Water loss via perspiration (L d“') Concentration of iodine in perspiration (ug L7') Iodine loss via perspiration (ug d7') Fractional uptake 1.5 2.0 2.5 1.5 2.0 2.5 — 0.5 0.5 0.5 0.5 0.5 0.5 — 1.0 1.5 2.0 1.0 1.5 2.0 — 37 37 37 37 37 37 — 37.0 55.5 74.0 37.0 55.5 74.0 — 0.35 0.32 0.30 0.42 0.42 0.42 — 2.0 1.1 0.9 37 33.3 0.30 quantitative estimates of the rate of iodine transfer among compartments, though, fortunately, iodine kinet- ics 1s relatively well understood. Iodine is essential in the body as it is accumulated by the thyroid gland in the production of the hormones thyroxine and triiodothyronine, which are essential for regulating the metabolic rate of the body. Several publications have shownthat 70 wg is the daily intake requirement to maintain adequate stores of iodine in the thyroid; this value has been assumed as the normal thyroid secretion of hormonal iodine. Intakes of iodine below 70 wg d' may cause symptomsof deficiency. The fraction of iodine ingested that is taken up by thyroid at 24 h after intake and the thyroid size vary according to long-term average dietary iodine intake (Stather and Greenhalgh 1983; Zvonova 1989). Zvonova (1989) derived a relationship between thyroid uptake and dietary iodine intake, which shows that the thyroid uptake increases with any deficiency of daily iodine dietary intake. This relationship is based upon the numerous human experimental data on '*'I uptake and thyroid secre- tion. It has also been shownthatlarger than typical values of thyroid mass tend to be associated with iodine intake deficiency and with larger than typical values of thyroid uptake. The fractional urinary excretions of iodine on the days of urine sampling were predicted using the ICRP compartmental recycling model (ICRP 1993) with a modification to include the perspiration loss pathway. A schematic diagram of the iodine biokinetic model assumedin this work is shown in Fig. Al. The assumptions used to derive the parameters of the iodine model were based on literature data. We assumed, for example, that the normal thyroid gland (adult) contains about 8,000 wg of stable iodine and that the organic iodine pool(protein- bound iodine, or PBI) is about 800 pg (Stather and Greenhalgh 1983; Zvonova 1989; ICRP 1993). The transfer rates from the inorganic iodide pool to the thyroid gland and from the thyroid gland to PBI are assumedto be 76 wg dd’. From the PBI compartment, 80% returns to plasma with a transfer rate of 61 wg d| and 20% is excreted by feces with a transfer rate of 15 wg d|. The parameters of our model are slightly different from the standard ICRP assumptions. Our assumption of 76 wg d| for the transfer rate from thyroid gland to PBI is based on the data reported by Rall and Conard (1966) for Marshallese. Those authors measured the thyroid uptake of iodine for the Rongelap inhabitants. Their estimate of 42%, based on measurements, was somewhat higher than might be expected for a population with good access to seafood. For most populations today, 30% uptake is typically assumed (CRP 1990, 1993). Rall and Conard (1966) also reported an averageurinary loss of 105 ug d', which was assumedto be equivalent to the daily intake of iodine. An amountof iodine secreted by the thyroid of 76 ug d' is inferred from a thyroid uptake of 42% and a urinary excretion rate of 105 yg d_' if both the perspiration and the fecal excretion losses are ignored. Applying the relationship developed by Zvonova (1989), the data reported by Rall and Conard (1966), constraining fecal losses to be 15 wg d', and using our assumption of perspiration as an additional pathway of excretion, we could not find complete concor- dance between a urinary excretion of 105 wg d ' and a fractional thyroid uptake of 0.42. We found that a fractional thyroid uptake of 0.42 is exactly consistent only with urinary losses of 32 to 69 wg d', and that the value 105 yg d' for urinary losses of iodine is precisely consistent only with fractional thyroid uptakes between 0.30 and 0.35. Based on these constraints, we proposed six plausible sets of physiological parameters (Table Al) by attempting to merge somewhat disparate historical information on various