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Is that a Banana in Your Pocket or Are You Radioactive?

Scott Edward Anderson's picture
EY (Ernst & Young)

Scott Edward Anderson is the founder of the popular blog, The Green Skeptic. A cleantech investor and entrepreneur, he founded VerdeStrategy, and is currently a director with EY's (Ernst &...

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Banana Equivalent Dose” was a concept new to me when it came to my attention via that font of much wisdom and arcana, Paul Kedrosky, who got it from William Gibson’s Twitter stream (@GreatDismal).

According to its Wikipedia entry,  “banana equivalent dose (or BED) is a concept   to place in scale the dangers of radiation by comparing exposures to the radiation generated by a common banana.”

Many foods are naturally radioactive, and bananas are particularly so, due to the radioactive potassium-40, or 40K they contain. Bananas are radioactive enough to regularly cause false alarms on radiation sensors used to detect possible illegal smuggling of nuclear material at US ports.[3]

A medium sized banana contains about 450 mg of Potassium.[4] 0.0117%, or about 53 μg of this being 40K. 53 μg of 40K produces 14 radioactive decays per second (dps), or 0.00037 μCi of radiation. If the banana is eaten, the dose equivalent is about 0.01 mrem.[1] 0.01 mrem is equivalent to 0.1 μSv.[5]

A radiation dose equivalent of 100 μSv (10 mrem, or 1,000 BED) increases an average adult human’s risk of death by about one micromort – the same risk as eating 40 tablespoons of peanut butter, or of smoking 1.4 cigarettes[6]

Here is a link to the full entry: Banana Equivalent Dose.

In the coverage of the Japan’s Fukushima nuclear plants SI multiples have been used, including the millisievert  and microsievert.  There was some confusion about this yesterday in the news as a spike was observed.

A millisievert (mSv) is a thousandth of a sievert and a microsievert is a millionth of sievert.  A chest x-ray has 0.1 mSv.  (Peter Wehrwein, editor of the Harvard Health Letter, has a good discussion of the topic at the Harvard Health Blog.)

Yesterday’s spike at the Fukushima Dai-chi plant was 400 mSv per hour.  Sounds like a bunch of bananas.

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David Lewis's picture
David Lewis on Mar 17, 2011

Radiation isn’t just coming at you from bananas.  The Earth is radioactive.  Radiation also enters the planetary system from space.  Life evolved on an even more radioactive planet.  Earth’s radioactivity is slowly declining.  But nevertheless, these days, measurements show that an average American’s exposure is dramatically increasing.   

This non news comes from the National Council on Radiation Protection (the NCRP), an organization chartered by Congress in 1964 to collect and disseminate information and recommendations about radiation in the public interest.  

The average yearly dose for an American in the 1980s was 360 millirem/yr

The green part of the pie is “normal” background radiation, the radon emanating from your basement, the cosmic rays coming into the system from space, etc.  The yellow slice is what medical imaging amounted to back then.  The entire rest of what an average person gets from consumer products and occupational exposure is the dark purple.  The nuclear industry’s total effect on your life could be cut out of this chart and it would not show up.  

By 2009 this picture has changed dramatically.  The entire pie is larger because the average dose level has increased 58% or by 260 mrem.  

Note also the relationship between slices.  Now Medical imaging contributes almost 300 mrem, which is getting close to the entire “normal” dose an average American received a few decades ago.  That 1980s “normal” is about what human beings have been receiving since apes first came out of the trees.  Medical imaging exposure is increasing so rapidly this 2009 chart is already obsolete:  the NCRP has announced since it published this that for the first time, medical imaging amounts to more than 50% of average total exposure.  

Another way to look at this:  early human beings in preindustrial civilization were exposed to a certain amount of radiation.  Now we’ve doubled it.  

The NCRP notes that some studies show that as much as 100 mrem of this medical imaging increase comes because of “defensive” medicine, i.e. because doctors are afraid of getting sued by their patients, which causes them to order unnecessary tests.  

We’re glowing in the dark because our doctors are afraid of getting sued by our lawyers, but the big public issues on the radiation front for decades are connected with the nuclear power industry.  

Coal plants emit more radiation than nuclear plants but get a free pass on this.  Coal contains uranium and thorium which survive burning, become part of the ash, and are emitted right out the stack.  

The big new US gas discoveries are taking place in shales once classed as uranium ore.  They are so radioactive that the resulting in gas is much more radioactive than previous gas, which already exposed users of it to an order of magnitude greater radiation dose than living next door to a nuke plant, but again, it can’t be pinned on the nuke industry, so it gets a free pass.  

On the other hand:  Public ignorance and uber-concern about radiation has led public officials to cater to radiation standards that are unevenly applied – the nuclear industry couldn’t convince the public to accept a plan to bury nuke waste in a place very near where almost 1000 nuclear bombs had already been exploded, in part because of public concern that someone wandering around the surface of the proposed area thousands of years from now might get an increased exposure of 15 extra mrem 10,000 years from now.  We’ve added almost 100 mrem to our exposure because we are trigger happy when it comes to suing our doctors.  That’s all of us who live here on average, not just the ones who would wander around at the surface near Yucca 10,000 years from now.  

Politics doesn’t have to make sense – if the public demands, the politicians will serve it up.  But we don’t have to pretend it makes sense.  Arguing that this radiation policy is ridiculous is deemed to be a sign that you are one of the pro nuclear special interest types always looking for a way to flog your favorite power source.  

Fear of radiation exposure is what is driving the hysteria in coverage of Fukushima today.  A year from now the zealots will be telling Japanese how many of them will be killed because their average exposure went up a few mrem.  This is insane, and it has been playing out for years.  The planet is being killed because we’re pretending we don’t have a low carbon power source.  

David Lewis's picture
David Lewis on Mar 20, 2011

Say Norm, could you tell us how much food you’ve eaten this year compared to how much you weigh?  What I read up there says if you eat a 400 gm banana you get 400 grams bigger.  It makes no sense to me.  

Personally, I don’t weigh 100 pounds more after eating 100 pounds of food over a long period of time.  I actually weigh about the same.   I go to the bathroom where my body disposes of a lot of things it doesn’t need.  

One point about bananas is if you walk by a bunch of them, you get a dose of radiation.  It is tiny, but measureable.  

Perhaps your organization doesn’t stoop to preposterous fear mongering over picocuries of radiation released from nuclear facilities, I don’t know if you do or not, but there are any number of organizations that do, even as they refuse to admit that standing next to a fellow protestor out there on the anti nuke protest line exposes them to more radiation than the picocurie leak they are protesting, because of the radioactive isotopes contained in their bodies.  

People just don’t realize Earth is radioactive and that the planet is bathed in radiation coming into the system from space.  Anti nuclear propagandists have pinned almost all radiation fears onto the nuclear industry, and the fact is, only a miniscule part of our exposure comes from that source.  Far more comes from the use of natural gas and coal.  Far more comes from medical imaging.  

If you want to “debunk” the banana dose, you’re going to have to do it a bit better than this.  

 

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