Sunday, April 15, 2007

Killer Cellphones?

"Pronto? MoshiMoshi? Hello?"

I was reading Digg today, which pointed me to an article speculating that cellphones are causing "colony collapse disorder," the name for an alarming phenomenon whereby the majority of honeybees in every colony are mysteriously disappearing. (By the way, this isn't jsut about the honey bees produce. The value of their crop pollination is in the billions per year; would anyone like to post a comment with a more exact figure?) The article sounded interesting until they went off the deep end by vilifying cellphones with a few cherry-picked debunked claims:

Evidence of dangers to people from mobile phones is increasing. But proof is still lacking, largely because many of the biggest perils, such as cancer, take decades to show up.

Most research on cancer has so far proved inconclusive. But an official Finnish study found that people who used the phones for more than 10 years were 40 per cent more likely to get a brain tumour on the same side as they held the handset.

Equally alarming, blue-chip Swedish research revealed that radiation from mobile phones killed off brain cells, suggesting that today's teenagers could go senile in the prime of their lives.

Chilling. Let's go into an account of how much damage a cellphone can do, and let me cite a few studies of my own.

Traffic Dangers

We have lots of evidence that cellphones impair driving ability. A University of Utah study found that cellphone conversations impair about as much as a .08% blood alcohol content, the threshold for the legal drunk-driving limit in many North American states. The World Health Organization says talking on a cellphone while driving increases your risk of accidents by a factor of 3 to 4. Taking a 100-mile drive decreases your life expectancy on average by about one hour, i.e., it has and LED of one hour (see posts with the tags LED and EDD for more, or this one which introduces them). Talking on your cellphone bumps the LED up to three or four hours, meaning that the driving-related risk starts to overcome the old-age-related risk you'd incur anyways if you call people while driving.

Other than impairing driving ability (and repetitive stress injuries from thumb-typing), cellphones aren't going to hurt you. Let's take a look first at the physics of cellphones (which will show them to be benign) and then take a look at the epidemiology of cancer among cellphone users, citing the most thorough study ever done, which happens to be Danish (Long Live Fear-Dispelling Vikings!).

The Physics of Cellphones

Cellphones communicate by broadcasting microwaves to cell towers. They use one of two frequency ranges: either about 850 MHz (the PCS band) or about 1900 MHz (the cell band). The peak power of a cellphone's transmission is about 2 Watts, so the amount it broadcasts into your head isn't more than about 1 Watt.

There are three potential concerns which make cellphones potential health risks: heat, chemical damage, and brain interference. Let's assess each potential risk.

Of Cellphones and Sunbeams

It turns out many of you non-hat wearers heat your head with electromagnetic radiation on a daily basis. A fusion-powered blob of gases over 100 million km away bakes your melon with an intensity of over 1000 Watts per square meter on a cloudless day. If the cross-sectional area of your head is about 3% of a square meter, that means the sun warms your head with over 30 times the power intensity of a cellphone. If cellphone-related heat can cause damage, so can the sun.

Mutagenic Conversations?

The next most commonly-feared etiology of cellphone-related cancer is through the photons in the microwaves causing genetic damage by affecting our DNA. However, the energy in even the highest-energy cellphone photons is far too low: a 1900 MHz photon has an energy of less than 8 microelectronvolts: about 100 000 times less energetic than the kind of photon needed to make any chemical change. At body temperature, random thermal fluctuations give every molecule constant kicks of over 25 millielectron volts: over 1000 times as powerful as a cellphone photon. No cellphone is going to turn you into a toxic avenger.

Nokia Mind Control?

I've seen one more way in which fear-mongers propose that cellphones could harm you:. They think it's possible that the pulses of electromagnetic energy could interfere with brain functions. It's true that neuroscientists use pulses of transcranial magnetic energy to temporarily (and, we hope, reversibly) poke an area of gray matter to try to figure out what it does. Could cellphones be doing the same?

Again, the relative magnitudes are way off: neuroscientists use field strengths around 10 Tesla, while cellphones typically have much smaller magnetic field strengths: around 50 Gauss or 5 mTesla (1 Tesla = 10 000 Gauss: one of those Metric System anomalies). Once again there's a yawning, factor-of-1000 gulf between the strength of a cellphone and the effect size needed to make worrying sane. It's even worse when you take into account the fact that the energy associated with a magnetic field goes as the square of the field strength, so it's more like a factor-of-1-million difference between what a cellphone is and what we'd worry about.


By now, it shouldn't surprise you to find that the most extensive study done on cellphones (the Danish one I alluded to) "found no evidence for an association between tumor risk and cellular telephone use among either short-term or long-term users." The study followed 420 095 persons for up to 21 years each, and saw that cancer rates were not higher than among the population in general. Breath a sigh of relief, and don't believe the fear-mongers who say cellphones are risky.

What about studies which show a correlation between cancer and cellphone use? There's a dirty little secret in science called publication bias. In a nutshell, it's precisely those stories which seem to defy common thinking which seem most newsworthy, get the most press, and get published. In cases where there's a lot of public interest and attention, it's a good policy to disregard studies with small sample sizes, since there are probably 20 unpublished small studies with null results for every 1 study with a stunning effect that's significant at the 5% level.


I don't know that much about bees, but cellphones are safe to humans, provided that their attention isn't needed elsewhere and that it doesn't over-stress them to have a cellphone. It's not totally outrageous to guess bees might be confused by cellphones, since the Earth's magnetic field is only about 0.3 Gauss. I'm not an expert of bee navigation, but it shouldn't be to hard to experimentally verify the connection between active cellphones and bee death. In the meantime, color me skeptical, especially considering that the article repeats loony fears.


Quartz said...

So all those uv screen protection creams and skin tumors research are a bogus worldwide conspiracy driving money out of something nonexistant?

Quartz said...

screen<=skin, sorry

LeDopore said...

Hi Quartz,

Interesting point about skin creams! I'm not sure about their measured effectiveness, especially in view of the recent discovery that staying out of the sun may be more hazardous (due to lack of vitamin D) than getting the occasional sunburn.

However, I was talking about the issue that cellphones heat your head, which some people think might cause cancer. My point was that the sun heats your head way more than a cellphone, so you shouldn't worry. Unless the cream is highly reflective it won't change how much the sun heats your head, and I doubt that the heat is the main contributor to skin cancer anyways; I think it's the fact that UV sometimes ionizes electrons out of DNA, which can cause mutations.

It would be fun to figure out the net effect of sunscreen on cancer rates; I wonder if it's positive or negative!

Take care!


Knaldskalle said...

I concur with your scepticism about microwaves and bees. If that's the case, shouldn't we be experiencing similar sudden collapses in related species? Is there a relations between colony collapses and cell phone coeverage? I guess the bees should be safe in places where there's little to no coverage, then. From what I've heard the microwaves are supposed to disorient the bees (even though it's known that bees use sunlight for navigating), but that doesn't explain what happens to all the bees that aren't flying out and about. Where's the queen bee? Where are the non-nectar collecting workers (the ones that clean and maintain the hive)? Where are the drones? Do the microwaves suddenly make them fly off and vanish?

LeDopore said...

Dear Knaldskalle,

You make several excellent points which reinforce my skepticism about bees dying from cellphone radiation. Thanks!