California's Draft Health Goals
California found no epidemiological studies of tritium causing cancer in humans. It appears unlikely that tritium in the environment from present sources would produce detectable effects. Any carcinogenicity of tritium must be inferred.
A non-cancer public-health protective concentration was derived, based on changes in lifespan and hematopoietic tissues in chronic mouse studies cited in Balonov et al. (1993). Using a combined uncertainty factor (UF) of 100, which includes factors of 10 for intra- and interspecies extrapolation, a health-protective concentration for children is estimated to be 60,000,000 pCi/L, and for adults is estimated to be 2,100,000,000 pCi/L. Because these levels are much higher than the cancer risk-based estimates, a health-protective concentration based on cancer effects is assumed to protect against all non-cancer health effects. This concentration is also judged to be health-protective for all groups, including potential sensitive subpopulations. This level is for 2 liters per day consumption of tritiated water, for a lifetime.
All of the evidence of the ill effects of radiation in humans comes from studies of individuals exposed to very high doses, specifically Hiroshima bomb survivors. Data on the risk from low levels of exposure, come only from inferred mathematical models. Scientists have never observed any health effect in human populations from radiation doses less than 10,000 mrem. ( EPA's 20,000 pCi/L level gives a 4 millirem yearly dose.) This lack of observed effects could be because they occur too infrequently to be distinguished from normal occurrences, or it may be that there are no effects from these low levels because the body repairs itself (Hormesis). A 1990 National Institutes of Health study of populations living near nuclear facilities found no evidence that an excess occurrence of cancer had resulted from living near these facilities.
The mouse study used to infer results to humans, fed the mice 100,000,000,000 pCi/L tritium resulting in a dose of 20 rads. This is a massive amount of radiation, and can only be used to infer low-dose equivalents by assuming the Linear-no-Threshold Theory is true. Although useful for setting low level protective standards, Linear-no-Threshold Theory is not factually proven.