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 tritiate d water and tritiated wheat were investigated to estimate the radiation dos e rates at the end of two modes of chronic exposure. Materials and methods: Wistar strain male rats continuously ingested tritia ted 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 sample s and organically hound tritium (OBT) in the freeze-dried samples were dete rmined. Results: The biokinetics of tritium was different between the two modes of exposure. The concentration of total tritium in the tissues exposed to trit iated water attained a steady-state condition by 2-3 weeks. The steady-stat e 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 relat ively efficient and prolonged OBT formation during chronic exposure to trit iated wheat resulted in relatively high incorporation and retention of trit ium 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 ingesti on 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.