Tritium in rabbits after ingestion of freeze-dried tritiated food and tritiated water

Three groups of rabbits were exposed to freeze-dried tritiated food and/or tritiated water(HTO) for 29 days in daily doses of 185 Bq per gram body weight. The first group was exposed to tritiated alfalfa, the second group received half of the daily dose in the form of tritiated alfalfa and half in the form of HTO, and the third group was exposed to HTO only. The specific activity of nonexchangeable tritium in tissues of animals of the first group ranged from 1.67 to 8.63 times that of the same tissues in the third group. In animals of the second group the specific activity was close to the arithmetic mean of the values for the two other groups. The incorporation of tritium ingested with food was from 0.89 to 32.18% of the total activity given per gram body weight and from 0.44 to 7.21% when ingested as HTO. Dose rates, calculated for particular tissues at the end of the exposure, were lower in the tritiated food group than in the HTO group. However, considering the long biological half-time of tissue-bond tritium (T/sub b2/), the radiation dose absorbed after cessation of exposure was higher in the group exposed to tritiated food than in the group exposed to HTO. These studies demonstrate that calculation of the absorbed dose on the basis of body water tritium alone leads to underestimation of actual doses