Answer to Question #317 Submitted to "Ask the Experts"

What are the effects of exposure to low levels of radiation?  Is a dose of 780 mrem dangerous?

In general, we do not expect to see any adverse health effects from exposure to low levels of radiation.  At exposures of less than about 10 rem to the whole body, the effects are so small that we simply cannot detect any effects at all because the magnitude of these effects (if they exist) is smaller than the amount of "noise" in the study. 

Since cancer (which is the health effect we expect to see at low levels of exposure) occurs randomly in the population and because background cancer rates are so high (about 30% of the population of the US will develop cancer during their lifetime and about 16% of the population will die of cancer), it is difficult to be certain whether or not a particular cancer is due to radiation exposure or simply to bad luck. 

For example, in a city of 100,000 people, we would expect that 16,000 will die of cancer.  If each of these people is exposed to 1 rem of radiation, the worst-case model suggests that we would see an additional 50 cancer deaths.  However, this is only an increase of about 0.3%, which is almost impossible to "see" through epidemiology.  In other words, there is no way to tell if 50 of these people had their cancer caused by radiation exposure.  This is why the Health Physics Society says that it is simply not appropriate to calculate a risk estimate for any radiation exposure of less than 10 rem to a person.  Andrew Karam, Ph.D., CHP