Natural and induced radioactivity in food

All natural foods are slightly radioactive, because they contain ⁴⁰K, ¹⁴C, and many other radioactive isotopes. This radioactivity may vary by a factor of 10 from one type food to another, and it varies with the region where the food is grown. The limit of detectable additional radioactivity is about 1 % of the natural radioactivity in food. This limit is usually considered as adequate for defining the limit for no health effects. Based on this criteria, it is generally recognized that no significant radioactivity is induced when the food is irradiated to a dose of 10 kGy by gamma rays from ⁶⁰Co and ¹³⁷Cs, 10 MeV electrons, and 5 MeV x rays. Theoretical estimates of induced activity can be made much more sensitive than direct measurements; and the health effects of the corresponding radiation can be estimated on the basis of the dose in mSv to the body from consuming irradiated food. The estimates show that the additional dose is about 2 x 10^-6 mSv/year from consuming 40 kg/year of food commercially sterilized with 60 kGy by 10 MeV electrons. Had the food been sterilized by 5 MeV x rays, the dose would be about 10^-4 mSv/year. These doses are insignificant and may be compared with the additional dose of about 1.1 x 10^-2 mSv each passenger receives when flying from Boston to San Francisco, or with the average background radiation of about 3.6 mSv/year, and the corresponding health effects