Spontaneous genetic abnormalities occur with surprising regularity. Depending on the source of information, the rate for spontaneous genetic abnormalities is approximately 5 to 10%. Radiation increases the risk of genetic abnormalities. Radiation induced genetic abnormalities are indistinguishable from those that occur naturally. There are no changes that can be attributed to radiation effects that cannot be seen in naturally occurring genetic abnormalities.
At what rate do radiation induced genetic abnormalities occur, and with what levels of exposure? It has been estimated that by exposing the gonads directly to 10 Rads of radiation (twice the amount of radiation that a radiation worker can be legally exposed to over the period of a year) over a short period of time (seconds to minutes) there would be an increase in the incidence of genetic abnormalities by approximately 0.005% to 0.075%. This translates to an increase risk of genetic abnormalities of between 1 in 1,300 to 1 in 20,000. Without a doubt, measurable genetic effects occur due to radiation. These effects however, are significantly less than what might be commonly appreciated by the general public.
Remarkably, when studying the populations of Hiroshima and Nagasaki that were exposed to large amounts of radiation, the results of studies evaluating for genetic abnormalities approached but did not attain statistical significance.
The carcinogenic effects of radiation are well publicized. While such effects exist, they are often exaggerated. The lifetime risk of cancer for an individual is 25%. The lifetime risk of dying from cancer is 16%. Therefore, there are 160,000 cancer deaths per million deaths every year. By exposing a person to 1 Rad (10 times the legal limit for a member of the general public) of radiation over a short period of time (seconds to minutes), the cancer incidence is increased to somewhere between 10 and 500 deaths per million total deaths. This translates to an increased risk of between 1 in 2,000 and 1 in 100,000. Like the genetic effects, carcinogenic effects occur, but not as commonly as as portrayed by the media.
The fetus and embryo are believed to be more sensitive to the effects of radiation than adults. While there are phases during development when this is so, a substantial amount of exposure is required before we may identify statistically significant increases in abnormalities. Prenatal death from radiation may occur at doses as low as 10 Rads of acute exposure. Permanent growth retardation, malformation, and behavioral changes have not been observed at acute doses less than 25 Rads.
The popular media has exaggerated the effects of low levels of radiation. A common argument against the data presented above is that the results are based on animal data, and that animals are different from humans. Most radiation experiements are conducted on rats, and rats as a species are more sensitive to the effects of radiation than humans. Data obtained from these experiments therefore represent a conservative estimate of risks to humans and the true effect is probably somewhat less.