Do Not Fear the Banana

Zapperz has a short post on an article that appeared in the NY Times, chumming the waters of fear about radiation from granite countertops. I see that Chad has promised and delivered a bit of a rant, pointing out that popular media could and should do science. The problem is that they don’t — not in the living section, and sometimes not in the science section, and almost certainly not on the op-ed page.

But that’s not actually what piqued my interest here. It’s mediocre reporting, to be sure; the author makes sure to give “both sides” of the story, even though science boils down there being experimentally verified claims or not, so reporting knee-jerk reactions to the ticking of a geiger counter isn’t particularly responsible. But there was a snippet that reminded me of a conversation I was having last week.

Indeed, health physicists and radiation experts agree that most granite countertops emit radiation and radon at extremely low levels. They say these emissions are insignificant compared with so-called background radiation that is constantly raining down from outer space or seeping up from the earth’s crust, not to mention emanating from manmade sources like X-rays, luminous watches and smoke detectors.

And not to mention — because they don’t — people. That’s right: YOU are radioactive. An adult contains something like 140 g of potassium, of which about 16.5 mg will be K-40, which is radioactive with a 1.26 billion year half-life, yielding about 4400 decays per second. You also have C-14 in you, adding in another 3000 decays per second. The C-14 decay, and 89% of the K decays give betas, which will be deposited in your body. The other 11% of the K-40 decays have a 1.46 MeV gamma, and about half of them will be deposited in your body as well. This ends up being tens of millirem of dose per year.

The rest of the gammas escape, which means that you are a 6.5 nanoCurie gamma source. (Sleep with someone else 8 hours a night, all cuddled up? That’s around a millirem of dose each year. Not a cuddler? Here’s your excuse — your exposure decreases as you move away.) Do you use potassium in your water softener or as an alternative to table salt? What about bananas? That’s a 300 picoCurie source there, and you’re eating it. If you leave it alone, it’s only about 20 picoCuries of gamma.

The point here isn’t to make anyone afraid of bananas. You need potassium, and K-40 is along for the ride. But reporting like this gives no context, and paints a very simplistic “all radiation is bad” picture, when some dose is simply inescapable. It accentuates and panders to our inability to properly assess risk for unusual circumstances, especially with the mention of radon testing kits at the close of the article.

0 thoughts on “Do Not Fear the Banana

  1. Uncle Al demands government regulation! How much incremental harm could it do/dollar spent? Raid all machine shops and confiscate their granite surface plates. Curling stones demand armed response, then a nuclear strike against Ailsa Craig, Scotland to end the threat. Half Dome gets a radioactive warning trefoil blasted into its surface to Save Our Children! After the first year…