Thyroidal burdens of "'1 were calculated for 1-, 4-and 14-yr-olds, and adults, using available dietary data. Milk and milk products contributed 63, 57, 54 and 33% of the total thyroidal '"1 burden of the four respective age groups. As the contribution from dairy products decreased, that from meat increased from about 12% for 1-yr-olds to 35% for adults, while that from leafy vegetables remained relatively stable, from 17 to 21%. From ingested foods produced in air assumed to contain 1 pCi "' I per m3, daily dietary ' ' ' 1 intakes of 1.3, 1.2, 1.7 and 1.5 nCi were computed for the 1-, 4-, and 14-yr-old child and adult, respectively. For each nCi ingested daily, thyroidal dose rates for the respective age groups were calculated to be 4.9, 2.1, 1.7 and 2.6rem/yr, with the altered dose rates reflecting age-related differences in thyroid gland size and iodine kinetics.

A model is developed which allows mathematical treatment of the elimination of ingested fission products in milk. Equations are derived from the available experimental data which are used to predict the behaviour of a number of parent-daughter mixtures.IN MOST laboratory experiments on the transfer of fission products to milk, the change in concentration with time of a nuclide in milk has been studied following oral adminstration of a single dose. However, it is frequently desired to know what would be the course of events under more complex conditions of exposure of grazing animals. Prediction from single dose experiments to other situations has been shown to be but computation is tedious and would be eased if the curves relating change in concentration with time could be expressed mathematically. To date this has been attempted only for isotopes of iodine. (3) The purpose of the present paper is to postulate a simple model to provide a rational basis for mathemetical analysis of the existing experimental data and to use the model to predict the behaviour of parent-daughter mixtures which have not been studied experimentally. Udder I -Q m FIG. 1. Simplified compartmental model to describe metabolism of an ingested nuclide. &, , etc., represent the amounts of nuclide present in each compartment, rl, etc., are the rate constants describing transfer between compartments.

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