Radiation damage accumulation over large time intervals: a descriptive model.

A simple model of DNA damage (mutation load) accumulation is considered. For time intervals exceeding average life duration, the kinetics of mutation load is determined. The major process determining these kinetics is shown to be natural selection (or any equivalent process of removal of the most affected lines). The characteristic time of this process (which is around three generations) is the approximate time of integration of the dose rate for determination of radiation damage. The conclusion is made that the maximum permissible dose should be established for this characteristic time, as it determines the remote effects of prolonged exposure to radiation. After this, the accumulated genetic damage presents "dose rate-effect" rather than "dose-effect" dependence. Dependence of mutation load on dose rate and parameters of selection processes is examined for different types of mutations. The cases of stable and exponentially decreasing dose rate are considered. The applicability of the model to human population is discussed.