Regulatory models for atmospheric releases of tritium approved by the Environmental Protection Agency (CAP88, AIRDOS-PC, and COMPLY) calculate doses only from tritiated water (HTO) taken into the body. They do not deal with dose from emissions of tritiated hydrogen gas (HT) and conversion of HT to HTO in the environment, nor do they address the dose from ingesting tritium incorporated into organic compounds. A simple model (NEWTRIT) is proposed that accounts for all pathways to dose from atmospheric releases of HT and HTO. The model is formulated in terms of the tritium-to-hydrogen ratio in each environmental compartment. With each transfer, a small reduction in the ratio is introduced to reflect the dilution that occurs in nature. Conversion of HT to HTO in the environment is modeled using the latest experimental data. Concentrations of organically bound tritium are calculated in foodstuffs based on amounts of hydrogen in proteins, fats, and carbohydrates. Concentrations in foodstuffs and doses calculated by NEWTRIT are consistent with the predictions of existing regulatory models. In addition, the HTO component of NEWTRIT is tested using public bioassay data and the HT component is tested using results from a model intercomparison study for a hypothetical HT release. Although tritium doses probably have not been underestimated by regulatory models that account only for HTO (due to the high degree of conservatism built into these models), the explicit treatment of HT and organically bound tritium proposed here will make the dose assessments more comprehensive, defensible, and scientifically acceptable. Because NEWTRIT includes all pathways to dose and predicts conservative doses, it is a suitable model to replace the tritium models currently used for compliance.
*Terrestrial and Atmospheric Monitoring and Modeling Group, Operations and Regulatory Affairs Division, Environmental Protection Department, Lawrence Livermore National Laboratory, PO Box 808, L-629, Livermore, CA 94551; †Environmental Technologies Branch, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario K0J 1J0 Canada.
Manuscript received 23 December 2000;
revised manuscript received 3 May 2001, accepted 19 August 2001
For correspondence or reprints contact: S-R. Peterson, Terrestrial and Atmospheric Monitoring and Modeling Group, Operations and Regulatory Affairs Division, Environmental Protection Department, Lawrence Livermore National Laboratory, PO Box 808, L-629, Livermore, CA 94551, or email at email@example.com.