Physiology and Toxicology of Tritium in Man

¹ From the University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico

Using tritium water as a tracer in man, water absorption through the gastrointestinal tract began in 2–9 minutes and was complete in 40–45 minutes. The volume of water transferred from the intestine to the blood was linear with time and proportional to the volume of water ingested, within the range of 100–1000 ml. When exposed to HTO vapor via inhalation, man absorbed through the respiratory system 98–99% of the activity inspired. The activity in venous blood increased sharply during and shortly after inhalation exposure, after which it declined exponentially to equilibrium with a half-time of about 12 minutes. The average dilution volume in five experiments on three normal males was 62.2% and the biological half-time of tritium in body water of eight males on ad libitum water intake averaged 11.5 days. At equal vapor pressures man absorbed HTO inward through the skin at a rate comparable to the rate of insensible perspiration. HTO appeared to diffuse across the inert barrier of the outer skin with a half-time of about 3 minutes. When man was exposed to an atmosphere containing HTO, the HTO entering the body through the total skin area was approximately equal to that entering through the lungs. Both man and rat slowly oxidized inspired HT to HTO. The radiation hazard from exchange of tritium with hydrogen of the tissues after chronic or acute exposure to HTO was small compared to the hazard from the amount of HTO necessary to induce the activity into tissue components. On the basis of human data, the maximum permissible body burden of tritium was calculated to be 3.7 mc, and the maximum permissible concentrations of tritium oxide in air and water for continuous 24-hour exposure was estimated at 5 x 10^–6 µc/ml and 0.1 µc/ml, respectively. Adoption of the 1956 recommendations of the International Commission on Radiological Protection will result in the division of the above values by three.

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