Biokinetics and dosimetry of titanium tritide particles in the lung

Doses of internal radiation from inhalation of metal tritide aerosols are potentially a major radiation protection problem encountered by nuclear industry workers. Based on results of experiments with rats intratracheally instilled with titanium tritide particles and on a self-absorption factor of beta particles determined by a numerical method, a biokinetic model was developed for inhaled particles of titanium tritide. Results showed that lung burdens of the tritide are well represented by a two-component exponential equation; biological half-lives derived for the retention of 3H in lung were 0.81 d and 66 d. The tritium clearance rate via urine or feces was described by bi-phase exponential components. At 121 d after instillation, 82% of the initial lung burden of 3H had been eliminated, of which 37% was excreted in urine, 29% via feces, and 16% through exhaled air. Based on simulation results of the biokinetic model, the cumulative absorbed dose and committed effective dose were calculated as well as the annual limit of intake (ALI) and derived air concentration (DAC). The ALI and DAC values for titanium tritide were a factor of 5 lower than values for tritiated water. This information will be useful in developing new guidelines for radiation protection purposes.