Risks of Hereditary Damage from Radiation: Viewed 70 Years Ago as Possibly Catastrophic but Now as Negligible, and Reasons for the Change

Estimates of the hereditary risks to humans from low-LET, low-dose or low-dose-rate radiation made by major committees of the US National Academy of Sciences and the United Nations have changed from exceedingly high to low over the past 70 years. It is now known that major complications were not reported by W. Russell for decades in his massive specific-locus mutation experiments on mice. The use of his data together with fears of the unknown and little other relevant data led to early estimates of hereditary risk that now appear absurdly large. The masses of specific-locus data produced over decades, taken together with L. Russell's 1964 hypothesis on the origin of clusters of identical mutations (an hypothesis developed and supported by specific-locus data) have recently led to the conclusion that the spontaneous mutation frequency per generation for recessive gene mutations exceeds, likely by orders of magnitude, what was generally assumed. There are many ramifications of this discovery. For example, the commonly used methods (doubling-dose and direct) to estimate hereditary risk are invalid and represent extreme overestimates of risk. To W. Russell's credit, even 70 years ago he was emphasizing the need to focus on studying the induction of dominant mutations in mice that could meaningfully be related to hereditary effects in humans in the first generation after radiation exposure. His desire for such information led to experiments studying skeletal malformations and cataracts, and in 1977 to the application of the direct method of hereditary risk estimation. While the new findings about the spontaneous mutation frequency also invalidate the direct method, extensions of that research have yielded evidence that an exposure of male mice to 600 R of gamma radiation delivered over about 110 days (~ 5 R/day) induces no dominant mutations relevant to health effects in humans by age 25. Indeed, the data suggest that there may even be hormesis, that being a beneficial effect of low-dose-rate radiation exposure.