Long-term transfer of I-129 into the food chain

To investigate the transfer of Iodine-129 along the feed-animal-milk-pig thyroid pathway under conditions of short- and long-term contamination, two feeding experiments with dairy cows were carried out. Pasture grass radiolabelled with I-129 via root uptake was used as labelled feed in both experiments. During the first experiment the transfer of I-129 from feed to milk and the effective removal half-life of I-129 in the milk were determined after constant doses of I-129 in the labelled grass had been administered for a period of 8 days. In the second experiment the long term transfer of I-129 from feed-to-milk-to-cow-meat and to pig thyroid gland was followed for a period of 53 days. The pig was used because of the physiological similarity between pigs and humans. The effective half-life for removal of I-129 from milk was found to be 1.6 days. The values for the transfer factor from feed-to-milk (in units of day kg-1) resulting from the 1st assay ranged between 1.0.10(-3) and 1.7.10(-3). The long term feeding experiment exhibited a middle value for the transfer factor of 2.4.10(-3). The transfer factors pig thyroid/milk (as pig feed) and pig thyroid/cow feed exhibited values of 1.2 and 8.7.10(-3) respectively.