The baloney about bananas

We often hear those in the business of pro-nuclear propaganda claiming that living around a nuclear power plant is less harmful than eating bananas — which contain a version of radioactive potassium (K-40). At the same time, nuclear advocates assert that releasing tritium (radioactive hydrogen) into the environment is harmless to human health.

But this is disingenuous — and likely deliberately misleading — nonsense. Dr. Ian Fairlie, an independent consultant on radioactivity in the environment, debunks the myths. Writes Fairlie:

First, the amount of K-40 in bananas is very small. All fruits and vegetables contain small variable amounts of potassium. It is true that some bananas can contain a very slightly higher amount than some other fruits and vegetables, but not much more. 

For example, similar amounts are found in dried fruits (raisins, apricots), beans, lentils, potatoes, spinach, broccoli and avocados.

Second, all naturally-occurring potassium contains 0.012% K-40 (12 K-40 atoms in 100,000 K atoms, i.e. a tiny amount). So you can eat bananas with few if any worries. In fact, the human body already contains potassium, so therefore it contains some K-40. This contributes a small fraction to our background radiation dose.

Third, potassium in our bodies is a vital mineral: it regulates fluid transport across cell membranes. Its main role is to maintain normal levels of fluid inside our cells. Therefore, the amount of potassium in our bodies is strictly regulated (i.e., it’s said to be under homeostatic control). 

No matter how much potassium we consume, the body will quickly and automatically excrete any excess amounts and along with it the K-40 in the natural potassium. Consequently, you can never have too much K-40 in your body. Again, this means there are no concerns about eating fruit and vegetables containing potassium.

Fourth, when these tiny amounts of K-40 decay, they mostly decay with the emission of a beta particle with a maximum energy of 1,300 keV. This is considerably larger than that of tritium’s beta particle maximum energy of 18 keV. Almost all of K-40’s betas will escape the human body as they are so energetic. But all of tritium’s betas will stay inside the body as its mean free path in tissue is 0.6 microns which is the diameter of a human chromosome. Tritium is therefore far more of a concern than potassium-containing bananas and other fruit and vegetables.

(Headline photo by Juan Emilio Prades Bel/Wikimedia Commons)