Comparative biokinetics of tritium in rats during continuous ingestion of tritiated water and tritium-labeled food

PURPOSE: The biokinetics of tritium during continuous ingestion of tritiated water and tritiated wheat were investigated to estimate the radiation dose rates at the end of two modes of chronic exposure. MATERIALS AND METHODS: Wistar strain male rats continuously ingested tritiated water as drinking water and tritiated wheat as food for 14 weeks. Urine and tissue samples were obtained and total tritium in the fresh wet samples and organically bound tritium (OBT) in the freeze-dried samples were determined. RESULTS: The biokinetics of tritium was different between the two modes of exposure. The concentration of total tritium in the tissues exposed to tritiated water attained a steady-state condition by 2-3 weeks. The steady-state condition in the case of exposure to tritiated wheat was not observed for 10 weeks after the start of exposure in the majority of tissues. The relatively efficient and prolonged OBT formation during chronic exposure to tritiated wheat resulted in relatively high incorporation and retention of tritium in the tissues compared with those for exposure to the same activity of tritiated water. CONCLUSION: Radiation dose rates estimated at the end of continuous ingestion showed that tritiated wheat gave higher dose rates than tritiated water by a factor of 1.3 to 4.5, but the factors were within 2.0 in the majority of tissues except for small intestine and adipose tissue.