Cancer from Cellphones?
Well known for his outspoken views about the hazards of mobile phones, Lai concedes that he has no evidence to suggest people have problems handling alcohol or remembering where they are following a phone call. Yet he argues that mobiles should sometimes be switched off as a precaution--by aircraft technicians performing safety-critical maintenance work, for instance.
Last year, fears about mobiles affecting brain function received fresh impetus thanks to work by John Tattersall and his colleagues at the Defence Evaluation and Research Agency's labs at Porton Down in Wiltshire. Tattersall exposed slices of rat brain to microwave radiation. He found that it blunted their electrical activity and weakened their responses to stimulation. Because the brain slices were taken from the hippocampus, a structure with a role in learning, the results were seized upon as further evidence that mobile phones could scramble human memories.
In fact, the implications are far from clear. In people, the hippocampus is buried too deep in the brain to be influenced by emissions from mobile phones, says Tattersall. And his latest findings have undermined fears about memory loss. One result, for instance, suggests that nerve cell synapses exposed to microwaves become more--rather than less--receptive to undergoing changes linked to memory formation.
Taken together, the available data are very difficult to interpret. And some scientists suspect they may not even be reproducible. John Moulder, a radiation oncologist at the Medical College of Wisconsin in Milwaukee, says these experiments tend to work in one lab but fail in others, suggesting that technical glitches could be responsible for the results.
Perhaps the best reason for remaining sceptical is that the most worrying discovery ever made about low-energy microwaves remains mired in controversy four years after it was reported. In 1995, Lai claimed the DNA from the brains of rats exposed to microwaves suffered numerous strand breaks, a type of damage often seen in cells exposed to cancer- causing chemicals or powerful X-rays.
"If it was right, it would completely change the way we think about radiation," says Joseph Roti Roti, a radiation oncologist at Washington University in St Louis, Missouri. But so far, Roti Roti's team--funded by the mobile phone giant Motorola--has been unable to repeat the finding. Neither has Luc Verschaeve at the Flemish Institute for Technological Research in Boeretang, who has exposed white blood cells to microwaves.
In 1997 came another bombshell that is now being called into question. Researchers at the Royal Adelaide Hospital in Australia spent 18 months exposing mice to radiation mimicking the emissions of digital mobile phones. Michael Repacholi, who coordinated the study, didn't expect to find anything untoward. Yet twice as many of these mice developed lymphomas as did animals not exposed to the radiation.
But since then, three other teams have failed to find similar evidence of increased cancer rates among mice exposed to microwave emissions. To increase the sensitivity of the experiment, Repacholi's team used mice that had been genetically engineered to be susceptible to lymphoma. In the latest study, a team of microwave experts at the Brooks Air Force Base in San Antonio, Texas, used mice genetically engineered to be susceptible to breast tumours. They exposed the animals to microwaves for 20 hours a day for 18 months, yet saw no increases in tumour rates.
Repacholi, who is now coordinating the WHO's research into the health effects of electromagnetic radiation, says he is reserving judgment about the cancer link until researchers in Australia have repeated the original experiment using the same strain of mice and exposure conditions. "If they don't come up with the same result, that'll be a happy outcome," he says.
An even happier outcome would be if microwaves turned out to be good for you. It sounds crazy, but a couple of years ago a team led by William Ross Adey at the Veterans Affairs Medical Center in Loma Linda, California, found that mice exposed to microwaves for two hours a day were less likely to develop brain tumours when given a cancer-causing chemical.
But nobody has yet replicated that finding either, and Moulder doubts anyone will. He believes that what we're seeing is the variation from lab to lab that you would expect from technically demanding experiments that are trying to pick up tiny effects. "Study something enough times and by the laws of statistics you'll occasionally see something," he says.
Some of the experiments may also be plagued by systematic errors. One problem is that microwave emissions can interfere with electrodes and other instruments, leading to all manner of false readings. Another is that researchers often have a hard job ensuring their equipment doesn't induce heating effects that could never be caused by a mobile phone.
So should we forget about mobile phone radiation causing brain tumours and scrambling our minds? "If it doesn't reliably cause cancer in animals and cells at high doses, then it probably isn't going to cause cancer in humans," says Moulder. And while the results on the activity of the brain are too new to have been subjected to the same scrutiny, the consensus is: don't panic . . . but watch this space.