Answer to Question #1147 Submitted to "Ask the Experts"

Q

As a student of radiologic technology 17 years ago, I was told peanuts were high in natural radiation. Is this true? I am now a clinical instructor and would like to pass this information on to my students.

A

To begin, it might be worth mentioning that a small segment of the population will experience severe (even life-threatening) allergic reactions to peanuts and peanut products—something totally unrelated to any radioactive content they may possess. I have been unable to find any information to the effect that peanuts contain an unusually high concentration of naturally occurring radionuclides. Ron Kathren's Radioactivity in the Environment states that the maximum alpha concentration that has been observed in peanuts and peanut butter is 0.012 picocuries per gram (pCi g^-1). Several fact sheets indicate a concentration in peanuts and peanut butter of 0.12 pCi g^-1 (unfortunately this is not particularly useful information because the identity of the radionuclides is not specified—presumably the activity is due to some combination of ⁴⁰K, ²²⁶Ra, ²²⁸Ra, etc.). In any event, these levels are not unusual and, in fact, are much lower than the concentrations in many other foods. Perhaps the individual who provided you with this information was thinking about Brazil nuts which have sometimes been referred to as the world's most radioactive food. The Brazil nut tree tends to accumulate high amounts of calcium. In the process, the nut also accumulates high levels of other Group II elements such as barium and radium. The radium, of course, is radioactive. The types of fact sheets mentioned earlier usually report concentrations of 14 pCi g^-1 for Brazil nuts—they may or may not state it but this represents the total alpha activity. The radioactivity in Brazil nuts is primarily due to an equal mix of the alpha emitter ²²⁶Ra and the beta emitter ²²⁸Ra. In a very extensive study, Oak Ridge National Laboratory (ORNL) found ²²⁶Ra concentrations in these nuts to range from 0.1 to 3.5 pCi g^-1. The concentrations of ²²⁸Ra ranged from 0.16 to 3.5 pCi g^-1. Since ²²⁶Ra and ²²⁸Ra produce various short-lived alpha-emitting decay products (for example, ²¹⁸Po, ²¹⁶Po, ²¹⁴Po, and ²¹²Po), the total alpha activity is higher than that of ²²⁶Ra alone. The ORNL study stated that the total alpha activity in Brazil nuts ranged from 0.9 to 19 pCi g^-1. The beta activity in these nuts is almost never reported. References:

• Eisenbud M, Gesell T. Environmental radioactivity. 4th ed. Academic Press; 1997.
• Kathren R. Radioactivity in the environment. Harwood Academic Publishers; 1984.
• Drury et al. Radioactivity in food crops. Oak Ridge National Laboratory publication ORNL-5963; 1983.

Paul Frame, CHP, PhD