People are terrified that they’re being exposed to radiation all the time, whether from distant nuclear accident or the mobile devices snuggled against their heads. Generally, they are wrong. Here are the most radioactive objects in the world around you, and the truth about which ones cause health problems.

What Do We Mean by “Radiation”?

Radiation is just a fancy word for energy that propagates out from a source in waves. This includes electromagnetic radiation, such as radio waves, microwaves, visible light, and x rays. It also includes certain elements which decay naturally over time, producing high-energy radiation in the form of alpha particles, beta particles, and free neutrons.

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When we’re trying to determine if a radiation source is harmful to humans, we look at two factors: The strength of the electromagnetic field surrounding the object (i.e., how much radiation), and “energy level” of the radiation waves, which is tied to their frequency (higher frequency waves pack more energy). Stuff that can damage biological tissues or DNA directly is called ionizing radiation. This includes high-energy electromagnetic waves — gamma rays, x-rays, and the higher part of the UV spectrum — and energetic particles produced by radioactive decay.

The EM spectrum, with higher-energy, ionizing radiation sources toward the right, via Wikimedia

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When humans first discovered that some forms of radiation are bad, we needed units to describe just how bad. Enter the sievert (Sv), a unit that incorporates the relative biological potency of different forms of ionizing radiation. Biologically speaking, one sievert is equivalent to a 5.5% chance of eventually developing cancer. Eight sieverts will kill you dead no matter what.

With that in mind, let’s have a look at some of the radiation sources we may encounter in our everyday lives.

Radiation Sources, Ranked

1. Bananas

Bananas bein’ bananas. Image via 24oranges / Flickr

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Everything with a temperature radiates energy, and bananas are no exemption. But they’re a pretty puny source of biologically effective radiation when it comes down to it. A banana equivalent dose (yep, the scientists went there) is approximately 0.1 microsieverts (µSv), or 0.0000001 sieverts. Watch out for those bananas, they’ll getcha. [Source]

2. Airport Security Screening

Those machines that scan you up and down for contraband (or loose change or earrings, as it were) also dose you with a small amount of x-ray radiation — anywhere between 0.015 and 0.88 μSv. To put those numbers in perspective, air travel itself can expose passengers to up to 0.04 µSv of cosmic radiation every minute. Put another way, a person would have to pass through an airport security scanner 1000-2000 times to equal the radiation dose of a single medical chest x-ray. In other words, security screens aren’t worth losing sleep over. [Source]

3. Chest X-Ray

Since we were on the subject, a routine medical chest x-ray doses you with approximately 20 µSv of radiation. Zap. [Source]

4. CRT Displays

Remember these? Image via Imrambi / Flickr

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Your displays emit EM radiation while they’re on, and naturally, you’re going to soak some of it up if you bask in their sweet glow all day. But only a small fraction of that radiation (the x-ray portion) is potentially harmful, and only if you’re using a CRT display. (LCD and plasma screens aren’t capable of emitting x-ray radiation). If you are still using a tube, the EPA reckons you’re absorbing 10 µSv of radiation a year from it. And if you’ve got an old CRT computer monitor to boot, toss on extra 1 µSv. [Source, Source]

5. Water

Water, life sustaining fluid that it is, contains trace amounts of radioactive material. The most significant source of radiation in water is tritium, a naturally occurring, radioactive form of hydrogen produced by the collisions of cosmic rays with molecules in the air. But tritium usually isn’t a big concern: On average, we absorb some 50 µSv of tritium radiation in our drinking water every year. [Source]

6. Concrete

Concrete is the second most used material on Earth after water, and it’s an even punier source of trace radioactive elements. On average, humans soak up 30 µSv of radiation every year from their sidewalks, road and building foundations. [Source]

7. Background Radiation of the Universe

All-sky image of microwave radiation in the early Universe. Image via NASA / WMAP Science Team

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The fabric of space itself is bleeding energy. Cosmic background radiation is everywhere, traces of the Big Bang that brought our Universe to life. Here on Earth, we’re shielded from the brunt of the stuff by our atmosphere. Still, some cosmic radiation filters into our world and through our bodies every year. At sea level, the annual dose is roughly 0.3 mSv — about 10 chest x-rays worth. [Source]

8. Your Own Body

Yes, your body produces biologically effective radiation, too! Mostly, we’re talking the decay of radioactive potassium atoms (damn those bananas!) with a sprinkling of carbon 14 atoms as well. The average human being contains about 30 mg of potassium-40, which produces radioactive beta particles as it decays. As a result, you dose yourself with approximately 0.39 mSv of radiation each year. Good job. [Source]

9. The Earth Itself

Image via Wikimedia

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Earth itself is radioactive, thanks to the slow decay of uranium and thorium isotopes in the crust and mantle. In fact, our planet’s natural radioactivity accounts for roughly 50% of the heat it gives off! It also accounts for some 0.48 mSv of the radiation we’re forced to absorb every year as Earthlings. [Source]

10. Hanging Out at Chernobyl

Unless you’re an environmental radiologist, you’ve really got no business loitering around one of the biggest nuclear disasters in human history. But say you really want to. You might be in for a mid-sized dose of radiation — anywhere from 1.7 to 192 mSv per year. Don’t stick around to find out. [Source]

11. Nuclear Reactors, When They’re Not Having Meltdowns

Image via Wikimedia

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Catastrophic meltdowns aside, safety protocols mandate that nuclear reactors keep their radioactive fission materials well-contained. The annual dose limit for a radiation worker in the United States is 50 mSv. [Source]

12. Outer Space

Space, as we know, isn’t a very human-friendly environment. Outside the protection of Earth’s ozone layer, UV and cosmic radiation levels are hundreds of times higher. A six-month stay on the International Space Station packs roughly 80 mSv of extra radiation, while a six-month journey to Mars could in theory dose you with up to 250 mSv (based on measurements taken by NASA’s Curiosity rover during its 350 million mile trip). Radiation exposure is one of the biggest health concerns for any future astronauts embarking on long-term space missions. [Source, Source]

13. Cigarettes

Image via Wikimedia

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Unless you’ve spent the last sixty years in a cave, you’ve heard that smoking the cigs causes cancer. In part, that’s because your cigarettes are literally radioactive! Researchers estimate that deposition of radioactive lead in the lungs of smokers results in an annual dose of 160 mSv. That’s roughly the same dose of radiation Scott Kelly’s getting from his year long stint in space! In practice, that number varies quite a bit, depending on whether you’re a heavy smoker or a dabbler. Still, I’d take a year in space over a year smoking cigarettes any day. [Source]

But What About Cell Phones, WiFi Routers, and Bluetooth?

Image via Daniel Chou / Flickr

You’ve probably noticed that I’ve failed to mention a few notorious devices— namely, WiFi routers, cellphones, and bluetooth headsets. Turns out, these technologies have no biological radiation dose whatsoever associated with them. Instead, they emit lower energy, non-ionizing forms of radiation that don’t directly damage human tissue.

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This isn’t some weird accident: Our telecommunications systems use low energy forms of radiation precisely because these types of radiation have been deemed harmless to living organisms. Says the World Health Organization:

Mobile phones communicate by transmitting radio waves through a network of fixed antennas called base stations. Radiofrequency waves are electromagnetic fields, and unlike ionizing radiation such as X-rays or gamma rays, can neither break chemical bonds nor cause ionization in the human body.

Huh. Even so, public concern over the health risks of phones and routers has prompted hundreds of scientific studies. What have the good scientists found? Mostly, a whole lot of nothing.

A large number of studies have been performed over the last two decades to assess whether mobile phones pose a potential health risk. To date, no adverse health effects have been established as being caused by mobile phone use.

Mobile phones operate at radio frequencies between 450 MHz and 2.7 GHz. The main danger in their frequency range, according to the WHO, is heat. But the maximum power output of our cell phones usually falls in the range of 0.1 to 2 Watts — placing them on par with energy efficient LED bulbs. If you tried really, really hard, you might be able to give yourself a first degree burn with an overheated phone.

Image via toprq.com / Flickr

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Wireless networks also fill the airwaves with radiation. In the case of WLANs, radiation is spat out at five distinct radio frequency bands: 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, and 5.9 GHz. Does any of this stuff pose a health hazard? Again, probably not, unless you’re worried about a little extra temperature:

To date, the only health effect from RF fields identified in scientific reviews has been related to an increase in body temperature (> 1 °C) from exposure at very high field intensity found only in certain industrial facilities, such as RF heaters. The levels of RF exposure from base stations and wireless networks are so low that the temperature increases are insignificant and do not affect human health.

Over the past 15 years, studies examining a potential relationship between RF transmitters and cancer have been published. These studies have not provided evidence that RF exposure from the transmitters increases the risk of cancer. Likewise, long-term animal studies have not established an increased risk of cancer from exposure to RF fields, even at levels that are much higher than produced by base stations and wireless networks.

However. The WHO does say that we can’t necessarily rule out certain long-term health effects of cell phones, since the devices didn’t become widespread until the 90s:

While an increased risk of brain tumors is not established, the increasing use of mobile phones and the lack of data for mobile phone use over time periods longer than 15 years warrant further research of mobile phone use and brain cancer risk. In particular, with the recent popularity of mobile phone use among younger people, and therefore a potentially longer lifetime of exposure, WHO has promoted further research on this group. Several studies investigating potential health effects in children and adolescents are underway.

While you wait the rest of your life for those study results to roll in, bear in mind that the power (and therefore RF exposure) of telecommunications devices decreases rapidly with distance. So if you’re worried about that extra daily dose of low-energy radiation, you can try only talking on your phone hands-free, or putting your router in the most remote corner of your house possible. Though seriously, most health experts will tell you that these “precautionary” measures are the equivalent of wearing sunscreen in a basement.

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And of course, if you do relegate your wicked router to a closet, your signal strength may suffer. As a result, you might have to spend more precious seconds refreshing Facebook, all the while absorbing additional nano-sieverts of radiation from your computer screen.

Personally, I’m a little more worried about the bananas.


Contact the author at maddie.stone@gizmodo.com or follow her on Twitter.