Management of Commercially Generated Radioactive Waste - U.S. ...

E.13
E.6 SPECIFIC CONSIDERATION OF HEALTH EFFECTS FROM TRITIUM
Although tritium is subject to the uncertainties involved in any prediction of effects
at dose levels far below those for which there are experimental data, the relatively uniform
distribution of hydrogen throughout the body and our understanding of the metabolism of
hydrogen and water by the body do provide more confident dosimetry than is available for
most other radionuclides. If there is special concern about tritium effects, it relates
primarily to the difficulties of preventing its release to the environment, and to its
worldwide distribution and availability to man following release. Many aspects of the bio-
logical concerns for tritium in the biosphere are reviewed in the Proceedings of a symposium
on the subject, held in 1972 (Moghissi and Carter 1973).
There has been some concern that tritium incorporated in organic compounds, either
before or following ingestion by man, might present a substantially increased hazard. Such
an increased hazard might be due to: a) prolonged retention of the tritium-containing com-
pound, b) enhanced biological effectiveness of the radioactive disintegration due to conver-
sion of the hydrogen atom in a vital molecule to a helium atom (transmutation effect), or
c) an enhanced radiation effect due to origin of the beta ray within a vital molecule. If
the hydrogen of all molecules in the body were uniformly labeled with tritium, this would
add perhaps 50% to the whole body radiation dose from body water alone. Any larger
increased radiation dose from organically bound tritium could occur only if tritium were
preferentially incorporated or retained, in comparison with ordinary hydrogen. This possib-
ility was reviewed by Weston (1973) who concluded that, "it is apparent that large kinetic
isotope effects are often found for tritium-labeled compounds. In tracer experiments
utilizing tritium, observed rate constants could easily differ by an order of magnitude from
those for the analogous unlabeled compound. If tritium from a source of HTO at constant
specific activity is incorporated into a biological system by irreversible chemical reac-
tions, it will be discriminated against; and the tritium level in the biological system will
remain lower than that of the source. Conversely, kinetic isotope effects in the back
exchange to remove tritium after incorporation will favor retention of tritium in the.biological
system."
Although rather large isotope effects occur in individual chemical reactions, the over-
all effects in biological organisms seem relatively small, as discussed by Shtukkenberg
(1968). Thompson and Ballou (1954) compared tritium and deuterium in rats, as did Glass-
cock and Duncombe (1954). The effects were small, as they were in a study of algae (Crespi
et al. 1972). It therefore seems reasonable to assume, as was done in the dosimetric cal-
culations for this Statement, that tritium will behave like ordinary hydrogen; any error
introduced by such an assumption will probably overestimate the effects of tritium.
The significance of transmutation effects has been a controversial subject, but there
now appears to be agreement on the following conclusions, as expressed by Feinendegen and
Bond (1973): "The effects of intracellular tritium are overwhelmingly due to beta irradia-
tion of the nucleus. Transmutation effects do not produce a measurably increased effect
under most conditions and are detectable only, if at all, under highly specialized labora-
tory conditions. The origin of tritium beta tracks in, or their close juxtaposition to, the