A model of radioiodine transfer to goat milk incorporating the influence of stable iodine

Previously reported models for radioiodine in ruminants cannot account for the effect of variations in stable iodine intake including large countermea sure doses of stable iodine on the transfer of radioiodine to goat milk. A metabolically based model of radioiodine transfer in goats has been paramet erised using new experimental data on the effect of countermeasure doses of stable iodine on radioiodine transfer to milk. To account for the effect o f dietary stable iodine levels, the model represents the transfer of iodine from the extracellular fluid to milk with Michaelis-Menten kinetics. The m odel shows good agreement with the experimental data, and the estimated par ameters compare favourably with values which can be estimated from the lite rature. The parameterised model accounts for 95% of the variation in the ob served data for milk, faeces, urine and thyroid (n = 199). The model has be en used to predict the effects of variation in stable iodine intake and the extent of consequent chemical contamination of milk by stable iodine. The time taken for radio-iodine to reach peak concentrations in milk following a deposition event is predicted to vary significantly (ca. 2 days) over a r ange of expected stable iodine intakes. Doses of stable iodine sufficient t o reduce the radioiodine transfer to milk will result in stable iodine conc entrations in milk greatly in excess of internationally advised limits. The refore, we recommend that stable iodine supplementation not be used as a co untermeasure to reduce radioiodine transfer to milk. Indeed, model predicti ons suggest that reductions in stable iodine intake would be a more effecti ve countermeasure. However, this is unlikely to be feasible since the short physical half-life of I-131 may not allow adequate time to implement chang es in feed manufacture. The model de scribed in this paper is freely availa ble in ModelMaker 3.0 format (http://www.notingham.ac.uk/environmental-mode lling/).