Worrying About Wireless
Scientific American
Journalist: Mark Alpert
September, 2000
Researchers are still unsure whether cellular phones are safe.
Like bursts of annoying static, questions about the safety of cellular phones have popped up repeatedly over the past decade. The controversy began in earnest in 1993, when a Florida man appearing on the television talk show Larry King Live claimed that his wife's brain cancer had been caused by the low-power radiation emitted by her cell phone. Other cancer victims soon made similar allegations in lawsuits against the phones' manufacturers. The Cellular Telephone Industry Association (CTIA) vigorously denied the claims, but at the same time it agreed to sponsor a six-year research program that would investigate whether cell phones pose any health risk.
Unfortunately, that question is still unanswered. The CTIA's research program, completed last year, yielded few worthwhile studies in return for the $25 million spent. The research on cell-phone safety has been wildly haphazard, and the results have created more confusion than ever.
In recent years scientists have found intriguing indications that cell-phone radiation may indeed have some effects on biological tissues. Whether those effects are harmful or benign, however, is another issue: no study to date has shown a clear link between cell-phone use and cancer or any other disease. Nevertheless, some scientists are urging cell-phone customers to take precautions. "With so many people using cellular phones over such a long time, even a slight effect could have many consequences," says Henry Lai, a professor of bioengineering at the University of Washington.
Many radiation experts maintain that it is physically impossible for cellular phones to have any biological effects. Cell-phone emissions range in frequency from about 800 to 2,000 megahertz. (Emissions below 1,000 megahertz are radio waves, whereas those above are microwaves.) At high power, such radiation can heat organic material-that's the way microwave ovens work-but cell-phone emissions are much too weak to cook human tissues. The average power transmitted by a typical mobile phone is about a quarter of a watt. If the phone's antenna is placed next to someone's head for a few minutes, the waves will raise the temperature of the nearby brain cells by a maximum of about 0.1 degree Celsius.
Because this heating is about one tenth the normal fluctuations of the brain's temperature, it is unlikely to affect the organ. What is more, cell-phone radiation is non-ionizing: unlike the high-energy photons in x-rays and gamma rays, which can shatter DNA molecules and thereby trigger cancer-causing mutations, radio and microwave photons are not energetic enough to break the chemical bonds of organic molecules.
Several experiments, however, suggest that low-power radio and microwaves can affect the mental performance of people and animals. For example, a 1999 study by Alan Preece of the University of Bristol in the U.K. asked a group of volunteers to perform an array of cognitive tasks while they were exposed to simulated cell-phone emissions from headsets. The emissions had no apparent effect on short- or long-term memory, but the exposure significantly decreased the subjects' reaction times as they pressed buttons to match the words "yes" and "no" flashed on a computer screen. In other words, the radiation made the volunteers quicker on the draw. Finnish scientists conducted a similar test and also found decreased reaction times. But when rats were exposed to low-power microwaves in several experiments done by Lai, the animals took longer to find their way through a maze than the rats in the control group did.
Research on health effects has yielded more disturbing results. A 1997 study conducted by investigators at the Royal Adelaide Hospital in Australia used mice that had been genetically engineered to be susceptible to lymphoma, the cancer of the lymphoid tissues. For one hour per day, the scientists exposed the transgenic mice to low-power radio waves similar to those emitted by digital cellular phones. After 18 months the incidence of lymphoma in the exposed mice was twice as high as that in the control group. In contrast, a 1999 study led by William Ross Adey of the University of California at Riverside found that digital cell-phone signals actually decreased the incidence of tumors in rats that had been exposed to a chemical carcinogen before birth. "We're seeing effects," Adey says, "but we can't figure out why."
Some biophysicists speculate that the electromagnetic fields generated by mobile phones could interfere with the body's sensitive electrical activities. For instance, one hypothesis proposes that the fields induce small movements in the positively charged calcium ions that activate key receptor sites on cell membranes. Under the right conditions, even a weak field could significantly increase or decrease the membrane's permeability. This would alter the concentrations of ions and free radicals in the cell and possibly lead to higher rates of DNA damage.
In 1995 Lai and his colleague Narendra P. Singh provided some evidence for this hypothesis. They exposed rats to low-power microwaves for two hours, then extracted the DNA from the rats' brain cells. They found a greater number of breaks in the DNA strands of the exposed rats than in those of a control group. But other researchers' attempts to replicate these results have failed. A group led by Joseph L. Roti Roti of Washington University found no changes in DNA strand breaks in half a dozen similar experiments.
A surer test of cell-phone safety would be a comprehensive epidemiological study that measured the incidence of cancer and other diseases in thousands of long-term cell-phone users. Preliminary results from a small CTIA-funded study suggest that cell-phone use could be associated with a higher rate of a rare type of brain cancer, but that research has not yet been published. A broader study conducted by the National Cancer Institute is expected to be out by the end of the year.
In the meantime many scientists are advising cell-phone users to be prudent. This past May a panel of experts commissioned by the British government released a report recommending that children be discouraged from using mobile phones for nonessential calls. The recommendation is partly based on evidence that a cell phone's electromagnetic field penetrates more deeply into a child's head than an adult's, so any possible health effects are likely to be more pronounced in children. The panel also recommended that wireless companies stop promoting the use of mobile phones by children. In the U.S., such promotions are commonplace. AT&T Wireless, for example, says it does not market to kids, but the company sells cell-phone faceplates with pictures of Mickey Mouse and other Disney characters.
In the end, though, the worries about wireless may be misplaced. Researchers have proved only one certain danger from cell phones: they lead to higher rates of traffic accidents when customers use them while driving (a practice that AT&T Wireless, to its credit, strongly discourages). And even the most pessimistic scientists admit that the potential health hazards from cell-phone radiation are meager compared with the dangers of, say, cigarette smoking. If you're still worried, you can buy a "hand-free" headset for your cell phone, which will at least shift the radiation from your head to another part of your body. You may also want to consider giving up hair dryers, which radiate powerful, low-frequency fields close to the head. But there's little sense in fearing the transmission towers used by cell-phone networks: beyond a few meters from the antennas, their fields fall off to practically nothing. Adds Singh: "Psychological stress may also cause DNA strand breaks. So simply worrying about cell phones could be unhealthy, too."