How toxic is tritium? Relevance of high-dose results and gamma-ray data to evaluating low-level, chronic exposure.

Interest in tritium toxicity stems from concern not only with 3H from small sources-its widespread use in research, for example, and in luminous paints (there have already been deaths from tritium exposure in the luminous paint industry)-but from the large source: nuclear energy. Tritium is a prominent by-product of nuclear fission, difficult and costly to contain, and impressive quantities find their way to the environment. When the fusion reaction becomes successfully harnessed for peaceful purposes, tritium will become even more important, because it is a fuel for nuclear fusion. Tritium will be increasingly with us in the foreseeable future, and it is essential that we possess a detailed understanding of its possible biological impact. As an isotope of hydrogen (the cell's most ubiquitous atom), tritium can be incorporated into essentially all portions of the living machinery. Its preferred chemical state is water, 3HOH, and as such it has free access to the body and to all living organisms. The main health and environmental concern is the possibility that significant biological effects may result from chronic exposure to very low concentrations of 3HOH. But there is a serious lack of data for such exposure; current understanding of protracted irradiation at low levels is based primarily on information obtained with -yrays. Therefore extrapolations are necessary for tritium, extrapolations from higher-level tritium doses, on the one hand, and from low-level -y-ray