The tritium toxicity program in the Medical Department at Brookhaven National Laboratory

A summary of all the findings to date is given in Table 2. It appears from this information that it is possible to detect somatic, cytogenetic, and genetic effects resulting from exposures at 33 to 100 times the mpc's for HTO. Similar effects also result from exposure to external gamma rays at an equivalent dose. The reduction in bone marrow cells in animals maintaining normal total cellularity is of interest since it demonstrates both the presence of an effect at the primitive cell level and the animal's ability to compensate for this effect by recruiting stem cells from the G0 resting state. This evidence of damage together with the observed cytogenetic changes leads one to contemplate the possible importance of radiation exposures at these levels for the induction of leukemia or other blood dyscrasias. Studies to investigate this question are now under way. As predicted on the basis of established principles of radiobiology, exposure to tritium beta rays from HTO ingestion results in measurable effects on several animal systems. The importance of position of incorporation of H into molecules of biological importance has not been well defined, nor have the low-dose portions of the dose-response curve for several effects of interest. Experiments designed to address these questions and measure H turnover as a means for analysis of cell kinetics in several systems are now under way.