We have studied the effect of reduced dose rates of radiation on neoplastic transformation using the C3H/10T1/2 mouse embryo-derived cell line developed by Reznikoff et al. In this cell system, transformation can be measured by scoring the foci of piled-up cells that occur after the loss of contact inhibition of growth. We report here that reduction of the dose rates of fission-spectrum neutrons (of mean energy 0.85 MeV) from 38.5 or 10.3 to 0.43 and 0.086 rad min-1 has no effect on cell killing but increases transformation frequency. These data are in contrast to previously published results obtained with 60Co γ rays where reduction of the dose rate resulted in a marked reduction in transformation frequency. Although cancer induction in man involves many factors besides those at the cellular level, the implication from our findings is that the risk of cancer induction due to work-related exposure to neutrons in the nuclear power industry may be greater than previously thought.
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