Natural Radioactivity in Food
Trace amounts of naturally occurring radionuclides can be found in some foods. The most well-known foods containing radioactivity are bananas and Brazil nuts. These foods do not pose a radiation risk because the amount of radiation is so small.
Radioactivity is the spontaneous emission of radiation by an unstable atomic nucleus that "wants" to give up some energy in order to shift to a more stable configuration. Natural radioactivity of this kind can be found in the food we eat and the water we drink. The levels of natural radionuclides in food and drinking water are generally very low, making them safe for human consumption, though they can vary greatly depending on local geology, climate and agricultural practices.
Some foods contain naturally occurring radionuclides such as potassium, carbon and radium, along with their decay products. These foods do not pose a radiation risk because the amount of radiation involved is so small. Food acquires this radioactivity in three main ways: uptake, where plant roots absorb radionuclides from the soil; deposition, where airborne radioactive particles settle on crops; and bioaccumulation, where radionuclides accumulate in animals that consume radioactive plants, feed or water.
Commonly cited naturally radioactive foods include Brazil nuts, bananas, lima beans, red meat, potatoes, low sodium salt, carrots and beer. Brazil nuts are the most radioactive food. Each banana has the ability to emit .01 millirem of radiation — a very low level of radiation. Knowing the content of naturally radioactive substances in food is useful to estimate man's radiation exposure from food consumption.