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Anne Marie Helmenstine, Ph.D.

Bananas Are Radioactive

By July 10, 2011

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Kevin Rosseel, morguefile.comYou may have read about everyday objects setting off radiation alarms at border crossings between the US and Canada and Mexico. Newsweek has an article describing how medical radiation treatments (e.g., bone scans) may lead to traveling delays when they trigger radiation sensors. When the sensors are tripped, border officials conduct more intensive inspections to make sure you aren't carrying nuclear weapons. There are other ways to set off the alarms. Do you carry kitty litter in your car to help provide traction in icy weather or to absorb oil? It's slightly radioactive. Do you have tile or granite in your vehicle for a home improvement project? It has a relatively high radiation signature. Do you have a lot of bananas? They are also slightly radioactive.

It's pretty easy to understand why tile, granite, and kitty litter are radioactive. They contain low levels of minerals that naturally decay. Bananas are radioactive for a similar reason. The fruit contains high levels of potassium. Radioactive K-40 has an isotopic abundance of 0.01% and a half-life of 1.25 billion years. The average banana contains around 450 mg of potassium and will experience about 14 decays each second. It's no big deal. You already have potassium in your body, 0.01% as K-40. You are fine. Your body can handle low levels of radioactivity. The element is essential for proper nutrition. If you have a banana in your car for your lunch you aren't going to set off a Geiger counter. If you carry a produce truck full of them, you might encounter some problems. Ditto for a truck of potatoes or potassium fertilizer.

I guess my point is that radiation is all around you. After I read the Newsweek article I clicked off-site for more information and I found concern (panic?) over bananas being radioactive. Are they radioactive? Kinda. If you set a banana on a detector you won't hear mad clicking. It won't glow in the dark when you turn out the lights. There is a perception that radiation is bad, bad, bad. It's just a part of life. Bricks are radioactive. Anything containing carbon (you) is slightly radioactive. Bananas are radioactive and it's no big thing. Well... except maybe to Homeland Security.

Comments

August 11, 2008 at 3:14 pm
(1) Nancy says:

Oh, dear. One more thing I have to worry about…radioactive travel snacks!

August 12, 2008 at 8:10 pm
(2) Rosario Rajkumar says:

Novel points about banana. But harmless doses

of radioactivity.

Thank You,

Rosario

August 13, 2008 at 1:08 am
(3) ryan says:

so what do monkey have in them that there main food itself is banana’s and that they can have soo much of it and not increase there potassium value and get sick…and if they have any special thing, wouldnt it be wise to extract it from monkeys and use it as a medicine for people working in neuclear power plants or decay plants.

August 13, 2008 at 4:13 am
(4) kabir says:

If bananas are radioactive then they should heat up the body very soon but even excessive eating doesn’t produce such condition.
It means they are harmless.

August 14, 2008 at 8:57 pm
(5) Heather says:

Actually, it is a misconception to think that monkeys or primates only eat bananas. They eat a variety of fruits and vegetables just like humans. So they would be no more radioactive than us in that regard.

August 18, 2008 at 6:20 am
(6) George Karout says:

I love Ur banana article of radioactive isotopes and also Ur reflection on radioactivity as part of almost all mineral containing substances.
Iam a 1/2 vegetarian and consume 3 bananas a day. What do U think???
Thanks a lot Mrs Helmenstine

Best Regards // George

August 18, 2008 at 7:37 am
(7) MaD HaCkER says:

Standard sillyness from the “YOUR GOING TO DIE” croud. The dose is the poison. If you don’t drink any water, you die. If you drink the a lake, you drown and die. If you get no radas from the sun, vitaima D deficency, if you are are in the sun all the time, Skin Cancer. Just don’t worry about it, death is just the perod of life.

August 23, 2008 at 11:04 pm
(8) joe says:

so the half life is 1.25 billion years and decays 14 times a second?

are you sure you know what your talking about?

September 2, 2010 at 11:42 pm
(9) sydney says:

ah, ignorance at it’s very best…if you yourself do not know what you are talking about, do not leave a comment.

June 26, 2011 at 12:41 pm
(10) jo says:

half-life is the time it takes for the radioactivity of a specified isotope to fall to half its original value. A decay happens many times from each radioactive particle in a banana (there’s not just ONE radioactive molecule in a banana)
if you’re confused, http://en.wikipedia.org/wiki/Radioactive_decay

July 13, 2011 at 6:46 am
(11) bloggs says:

Means that 14 potassium atoms decay every second in one banana. 1.25b years is how long it takes for half of any given quantity of potassium to decay.

March 2, 2009 at 8:55 pm
(12) goober says:

i like this banana thing and think that you are right and wrong. just because bananas have like 0.01% radioactivity doesn’t mean that they are radioactive

OVER AND OUT
BANANAS RULE THE WORLD

June 30, 2009 at 1:35 pm
(13) Amasa says:

@joe: There are many, many, many, many, many molecules of potassium in 450 mg of potassium.

March 18, 2011 at 8:24 pm
(14) ole chem major says:

ever heard of Avogadro constant

— molecules in a mole of any material,,
6.02214179(30)10 to 23 power mol−1

14 decays per second is not much…
http://encyclopedia.thefreedictionary.com/Avogadro%27s+constant

worry about the economy and drunk drivers… those are critical…….

November 7, 2009 at 7:07 am
(15) Science Major says:

Yes — but so is just about ANY fruit or vegetable. They all contain Potassium, and a tiny fraction of all Potassium is radioactive. The amount of radioactivity is so small it is almost impossible to measure.

December 20, 2009 at 4:52 pm
(16) aka says:

I love the way the media is now making excuses for the radioactivity of our food supply. Never mind….everything was “always radioactive,” geiger counters were just created as a novelty, not to detect radioactivity that’s harmful and unnatrual. They’re trying to ban geiger counters in New York–for the people, of course. It’s in the people’s best interest NOT to know when a nuclear attack has happened. You know, nuclear attacks that pulverize concrete and metal by breaking them down molecularly. I wonder in those nano particals at Ground Zero that was places into trucks of soil made it into the soil of our food supply. Is our food radioactive as well? Oh wait…

January 20, 2010 at 3:21 pm
(17) rv8air says:

Do the math to put things into perspective. If the half life of P-40 is 1300 million years, it’s been there long before man set foot on the planet.

You can argue about WWII bombs which killed 240,000. Say what you will about that; it was war and it was intentional. The widest estimate from an unintentional exposure was Chernobyl is 4000 deaths, and that includes cancer related deaths not directly attributable.

Considering that our life on this planet depends upon a criticality at the center of our solar system, why do so many disclaim the value of naturally occurring activity in our food supply? Well, you can blame the media for that brand of histeria.

It’s important that we respect the power of nuclear physics, and use it to our wise advantage. However, wouldn’t we fare better, if the general public got serious, and did something about alcohol abuse, texting while driving, or smoking. All of these (and dozens of other voluntary activities) take far more lives every day, than radioactivity has EVER taken. Do the research and see for yourself.

Oh, and BTW, cigarettes are radioactive too, moreso than bananas- in addition to the P-40 they contain Polonium 210.

January 20, 2010 at 4:02 pm
(18) rv8air says:

P-40 has a very long half life. It was in the food chain long before mankind got involved. And then, there’s this huge reactor at the center of our solar system, bombarding us with cosmic beams 24/7. So let’s lighten up about what the media does and doesn’t do. After all, they’re the ones most responsible for the mass hysteria regarding radioactivity.

You want something to get serious about? On top of all the other ills associated with smoking, tobacco is radioactive too. You don’t hear much about that. Smokers enthusiastically suck that crud right into their lungs, where particulate radioactivity is deposited to do the most damage.

DUI, use of cell phones and texting while driving, are voluntary activities that take more lives every year, than involuntary radiation exposure has taken in the last fifty. If you want to get excited about something, start at home.

I’m not suggesting that radiation safety isn’t important. Of course, it is, and we owe a debt to those who’ve rightly enacted legislation to preserve our safety.

However, let’s not add to the hysteria playing the blame game. People need to get informed and make wise decisions. At the very least, let’s be intellectually honest about our activism, and focus on pressing problems.

Rad’s well understood and under control, so let’s move on to what’s fixable.

April 23, 2010 at 2:46 am
(19) Gastro Girl says:

Can anyone tell me how a nuclear medicine technician can actually compare radioactive dye with the radioactivity of a banana?…. Is it me or are our doctors wasting all that time in school, cuz they sure seem to be F-CKING idiots to me!!

April 23, 2011 at 9:30 pm
(20) Blacksheep says:

you are a goddess Lucy, Carol, and Rosie. Thanks for a chuckle. (I like to suck the sugar off.)

June 16, 2010 at 12:35 am
(21) Chris says:

@joe, the math looks a bit off, but not in the way you’re thinking, so let me break it down.
half life of K-40 = 1.248e9 years
natural abundance of K-40 = .012 %
molar mass of K-40 = 39.96399848 g/mol
450 mg * .012% = 5.4 mg
5.4 mg = .0054 g
.0054 g / 39.96399848 g/mol = 1.3512e-4 mol
1.3512e-4 mol * 6.022e23 particles/mol= 8.137e19 atoms K-40
4.0685e19 decay in the first 1.248e9 years
average of 3.26e10 per year
average of 1033 per second
Now I may have made an error in my math, and feel free to point it out if you find one, mind you this was quick and dirty done with the calculator built into windows. So to the layman, a banana is actually considerably radioactive, but you have to consider that K-40 decays into a weak beta particle, so the level of ionization is minimal.

June 16, 2010 at 12:47 am
(22) Mark Anderson says:

@Chris
Close, but its .012% which is really 0.00012 which works out to about 0.054 mg.

June 16, 2010 at 12:28 pm
(23) Chris says:

I can’t believe I made such a simple mistake, I blame it on doing that at around midnight. I’m half tempted to re-do the math to correct for that.
Well since it was such a simple mistake, all my numbers are only off by two decimal places, so it’s actually an average of 10.33 decays per second, not far off from the 14 given in the article.

June 16, 2010 at 2:50 pm
(24) Eliot says:

Good work Chris and Mark. However your estimate for number of decays per second will be off because you didn’t figure them using logs. Radioactivity is an exponential decay function. So the number of decays per time unit starts higher and then slowly gets lower over time. So one second now will have almost twice as many decays as one second 1.248e9 years from now. Of course we are interested in the rate of decays for seconds now not 1 billion years in the future. This is what pushed the number to 14 per second.

October 7, 2010 at 8:24 pm
(25) ThisGuy says:

Almost everything is radioactive. It’s no big deal. It’s actually pointless to display things that are slightly radioactive, since that’s almost everything. Very nice article though. (by 14 times per second I think he means molecules, not each half-life)

February 12, 2011 at 4:58 am
(26) Binkley says:

Good to see some of us can still do the math – high school was a long time ago for me and I have forgotten a lot of the math (especially logarithms haha)

But man, sure are a lot of ignorant people around too – and they still feel qualified to criticize an article written by someone with a Ph.D lol

And they vote too! 8-|

March 19, 2011 at 1:04 am
(27) huh says:

Avocados??? First bananas, now constant avocados…..life is going to kill us all!!

Last one in please shut the bunker door.

March 21, 2011 at 11:48 am
(28) James Aach says:

The current Japanese event is a very sad thing. I’ve worked in the US nuclear industry for 25 years. My novel “Rad Decision” culminates in an event very similar to the Japanese tragedy. (Same reactor type, same initial problem – a station blackout with scram.) The book is an excellent source of perspective for the lay person — as I’ve been hearing from readers. It is available free online at the moment at http://RadDecision.blogspot.com . (No adverts, nobody makes money off this site.) Reader reviews are in the homepage comments.

I believe there isn’t a perfect energy solution – just options – each with their good and bad points. And we’ll make better choices about our future if we first understand our energy present.

March 28, 2011 at 12:36 am
(29) Manmohan Dash says:

Hi Chris, Mark: you laid the ground work. Thanks. I will complete the calculation and show you this is exactly rounded to 14 decays per second (if you change your fraction of radioactive K-40 to 0.01 as in the article rather than 0.012 etc I think it will give the exact answer)

Here is the answer:

I take the calculation you two have done correctly, i.e. the 450 gram banana contains 8.137×10^17 nuclei of K-40 (not 10^19 as corrected by Mark)

Now the decay constant or transition probability as one may call it which gives the probability at any time of a single nucleus to decay at any time is w = 0.693/T_half_life. This is obtained by using Heisenberg Uncertainty principle for the nuclear decay. Here decay width which is given as a width of energy and mean life time which is given as a width or uncertainity in time must multiply to h-cross (time – energy uncertainty) Now Mean life is related to half life by the factor 0.693 (69.3% of nucleus would decay in the mean life where as 50% would decay in a half life)

SO the decay probability = w gives the probability or likelihood that any single nucleus will decay or not. SO we know this probability because we know the half life to be 1.25 billion years that is 1.25X365X24X3600X10^9 seconds = 1.25X3.15X10^16 seconds.

Since the banana has 450 grams of Potassium it has as many radioactive K-40 as we just counted, 8.137X10^17 nuclei, at the time of eating. SO the probability of decay is w and you know how many nuclei you got. Multiply them to get the exact number of radioactivity of your banana. Needless to say this product is 14.3.

(8.137X0.693)/(1.25X3.15)X10^(17-16) = 1.43X10 = 14.3

March 28, 2011 at 12:53 am
(30) Manmohan Dash says:

The calculations are correct as you can check, its 450 mg banana not 450 gram…just a typo

July 19, 2011 at 9:45 pm
(31) samuraishonan@blogspot.com says:

I live in Japan. Our bananas are very radioactive.

October 4, 2011 at 12:27 am
(32) rora says:

so what does this mean to the fruitarian, whos staple diet consists mainly of bananas?

is it a concern?

my MIL said humans should eat a lil bit of everything so that if a food is bad youre not eating large amounts.

October 4, 2011 at 8:24 am
(33) gunner tinkle says:

nice work !!!!!!

November 22, 2011 at 8:52 pm
(34) barnabyrks says:

My husband got stopped by TSA for carrying a banana in his backpack. Now it makes sense! (not really)

November 24, 2011 at 3:38 am
(35) Siddha says:

If bananas are radioactive with long half life, if you eat at least one in a day, all your life, how much radioactivity would you accumulate in 80 years of your life?

January 26, 2012 at 1:53 am
(36) welki says:

…and thats how primates evolved into hyper intelligent beings called humans.. radioactive mutation from excessive exposure and consumption of bananas

January 27, 2012 at 9:40 am
(37) omgyourmom says:

to Ryan,

wtf – go drown yourself as soon as possible.
Decay plants… goddamnit.

February 2, 2012 at 7:29 pm
(38) Eilzabeth says:

Bananas are not even the fruit with the highest level of potassium…so does that mean mean that young coconuts and dates which have a higher level of potassium have more radioactivity?

April 10, 2012 at 12:49 pm
(39) Rystik says:

Kabir,
your comment that if body does not heats up from eating bananas is scientifically flawed. A simple calculation will reveal that in order for your body temperature to increase by 1C (roughly 0.5F in our body temperature range) you will need to eat 200 billion! bananas to see an increase of 1 deg Celcius. (0.5 Farenheit). Even than is conservative estimate considering that your blood flow will equilibate that temperature quickly with the reset of the body.

On the other hand, each K-40 (which banana has) desintegration is theoretically capable of producing a mutation in DNA, potentially bad. But so are any sources of radiation that surround us.

I would worry more about the sun flares which can dump on you much more radiation than you think.

April 21, 2012 at 4:21 pm
(40) abc says:

You would have to gorge yourself on bananas before you would have any type of radioactive problems.

May 10, 2012 at 7:54 pm
(41) Dan Dookinsthyne The III says:

Daym Gurlll U sexeh

May 12, 2012 at 5:18 am
(42) Ishwar says:

Eh?oh,now I understand.there is definitely so many radioactive atoms in a banana.how else could the half life be 1250000000 years and decay 14 times a second?

May 14, 2012 at 12:02 pm
(43) Joe Neubarth says:

I caution everybody to keep their additional radiation exposure to a minimum. There is no safe dose of radiation regardless of the lies of the Nuclear Industry. The rampant increase in radiation exposure in our modern era is largely responsible for the six fold increase in Cancer in the United States in the past 100 years. We can thank nuclear bomb testing world wide, fabrication of radioactive fuel for nuclear power plants, the operation of nuclear power plants (Constantly releasing radioactive particulate to the atmosphere – Tritium, Krypton, Argon…… That is the reasons why all of the German speaking countries have banned nuclear power.), X-rays in medical procedures and the depletion of the Ozone layer in the upper atmosphere.

We need to control and limit those exposures that we have the ability to decrease. Thus, do not stand near the banana bin in the grocery store for very long, unless all of the banana’s are gone.

May 29, 2012 at 2:23 pm
(44) kd says:

Skimming through all of these finely honed responses, people taking hours to review, figure analyze and determine the levels emitted.

But, no one has mentioned the obvious… between TYPES of radiation and physiological maintenance, so I’ll quote a section of a good piece on why the difference: [note different isotopes and whether they are accumulated or exreted!]

” Potatoes, many types of seeds, kidney beans, and a variety of nuts are among the foods emitting the most radiation. Brazil nuts are near the top of the list with 12,000 picocuries per kg (2). …Bananas, by comparison, have an average radiation level of only 3520 picocuries per kg (3),

Those in the nuclear power industry use what they call the Banana Equivalent Dose as a way of putting radiation into perspective for the lay person …….. Using the banana to compare with the radiation emitted by a nuclear power plant or any other potentially dangerous radiation exposure is downright deceptive and gives people a false sense of security.

The comparison implies that all radioactive isotopes are created equal, and that there is no difference between our 3520 picocuries for a kg of bananas and the same amount of radioiodine, a major hazard involved in the production of nuclear power.

The first major problems with the comparison is that different types of isotopes have different characteristics in terms of half life, and whether it is alpha, beta, or gamma radiation.

The second is that the potassium in bananas does not stay in the body, but other types of radiation can, accumulating in organs and being absorbed by the blood stream.

Brazil nuts get their radiation from Barium, which the body can accumulate. …”

July 2, 2012 at 11:43 pm
(45) Baoli says:

Banana was chosen as the scape goat because the nuclear industry tried to dilute the fear on radiation.

January 18, 2013 at 10:44 pm
(46) Robert DeLaPlaza says:

To Rystik (comment 39)
Sorry I don’t know where you get your conversion constants;
but you got your numbers wrong.
1 Centigrade degree is 1.8 Fahrenheit ( not 0.5 F )

To huh.. (comment 27) well you have your screen name well
otherwise it looks like your reading level is more like a negative number…
is “Avogadro constant” nothing to do with Avocados.

I heard from an US Department of Education Government official; that kids reach High School with a reading level of third grade..?
How that can happen? what is wrong with US teachers, parents and kids… to much Nintendo shrinking their brains ?
It could be due to excess growth hormones used to make cattle more profitable, excess artificial colorants and preservatives, not to mention Tons of sugar, starches and fats, to make food more enticing (and profitable for the food industry) and fattening (profitable for the health and drug industries)
US Corporations create laboratory food; sold at supermarkets and everywhere; using scientific principles and studies to MAXIMIZE PROFITS and kill and stupidify Americans (and whoever gets in their way) in the process.

To Manmohan (comment 29)
A 450 gram banana is a 1 pound banana, where do you get those Jumbobananas ?
then you corrected… it’s a 450 mg banana; that will be a 0.0158733 ounce banana.
I think you meant that an average banana has 450 mg of potassium-40 ( K-40 )

The American public still having a disconnection from the world universal standard METRIC system, AND keep dragging from the court of the ancient kings and queens their own contorted system of inches, ounces weight and fluid, foot, yards, imperial and other gallons, full of odd numbers like Fahrenheit degrees were water freezes at 32 F ( 0 C )and boils at 212 F (100 C ) and several more, and a serious disconnection from a LOT of other things as geography, physics, math, reading… etc etc etc.

February 27, 2013 at 10:37 am
(47) nick says:

B-A-N-A-N-A-S!

March 4, 2013 at 2:05 am
(48) Celestine Olaprath says:

Very useful info to people who get scared when they hear the word Radiation.

April 29, 2013 at 8:12 pm
(49) kt says:

@Robert DeLaPlaza, fine analyses.

May 18, 2013 at 6:45 pm
(50) Honey Boo Boo. says:

I mean, what’s next?

May 18, 2013 at 6:46 pm
(51) SPARTAAAA says:

WHAT? I love babies. But why bananas? WHY?

June 1, 2013 at 1:11 pm
(52) aleksey b says:

potassium 40 not a molecula this is an atom or ions i guess.

July 5, 2013 at 2:11 pm
(53) Jason says:

@chris the math error was in multiplying 450mg by 1.2%, as opposed to .012%

September 13, 2013 at 4:37 am
(54) Gravation says:

We have some fine mathematician with some incredible Numerical analysis Whenever comes to k-40 ionization An deccaying process Yes it is a stable isotope that takes quite a while at half life or in a chemical induced state
With Other elements on the periodic table which is reactive to most My concern would be why worry about a banana Which is able to be metabolizied in the system When we should be Worried on a widescale issue people are importing chemicals through Russia and Germany and turkey and using the kitchen as a chem lab Trying to concentrate the conductivity Of uraniumRather than speaking such a small subject why not moveto something that will actually benefit The outcome of our society the government Expects things like Discussions and distribution really people should be making a larger movement To find out What our finest nuclear physicist are working towards It is not finding out the radioactivity of a banana and on a larger frame it probably has to do with mass destruction considering that the USofA survey is one of the finest facilitating Countries that the world has ever seen

December 8, 2013 at 2:01 pm
(55) Jesse says:

How many of you used your cellphone to leave your ridiculous comments? Worry about that radiation.

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