手机成为人类潜在的健康威胁

Nearly two-thirds of the people on Earth now use mobile telephones, according to a study by the International Telecommunications Union. But how safe are those phones? Scientists still aren't sure, but some evidence is starting to suggest there may be danger along with the convenience.

They go by various names — cellular telephone, cell phone, mobile, wireless, handy — and an estimated four billion people use them worldwide.

Each of those phones has a tiny radio transmitter to communicate with the wired telephone network, and for years, scientists have been trying to determine whether those RF, for radio frequency, transmissions might be harmful.

A U.S. Senate subcommittee this week brought together some experts to review the evidence and focus on whether more research is needed.

Not too long ago mobile phones were exotic and expensive, even seemed magical. Now, as subcommittee chairman Tom Harkin noted, we take them for granted.

"I would venture to guess that almost everyone in this room uses a cell phone on a regular basis, and most of us don't give a second's thought that it could harm us in any way," said the Iowa Democrat.

Measuring that harm is difficult. One problem is that mobile phones have been in widespread use for a relatively short period of time. Israeli researcher Siegal Sadetzki says cancers triggered by environmental factors, such as radiation, may take a decade or more to develop.

"In the case of brain tumors, it may reach even 30-40 years. For example, the atomic bombs in Hiroshima and Nagasaki occurred in 1945, while the first report demonstrating brain tumors among the survivors was not published until 1994, 50 years later."

Although many studies have been inconclusive, some newer studies are starting to turn up evidence that long-term use of mobile phones may be dangerous.

John Bucher is a senior official at the U.S. National Institute of Environmental Health Sciences: "There have been some hints recently that there is an increase in brain cancers in people who have used these cellular communication devices for a number of years."

Bucher's agency is funding a large scale animal test designed to simulate in rodents the kind of exposure that humans get when using cell phones. But results won't be in until 2013 or so.

In the meantime, Linda Erdreich of the consulting firm Exponent reviewed scientific evidence on potential health hazards and found no proven link.

"All of the agency reports that assess the evidence using a comprehensive approach reach similar conclusions: that the current scientific evidence does not demonstrate that wireless phones cause cancer or other health effects," she said.

Although quite a few studies have been published, the experts called before the Senate subcommittee saw a need for more research. Among them was Dariusz Leszczynski of Finland's Radiation and Nuclear Safety Authority

"We need international, well-designed, human volunteer studies," he stressed. "These studies should be aimed at proving or disproving whether human bodies respond to mobile phone radiation. In spite of years of research, we still do not have the answer to this basic question."

Until we do, mobile users who might be worried about the possible effect of emissions from their phones can take some precautions recommended by experts: Use a headset — a wired one is probably safer than a wireless Bluetooth earpiece — or use speakers. Use a low-radiation model handset. Keep the phone away from your body, while talking or between calls. Use text or SMS rather than voice mode. And limit children's cell phone usage, since young brains may be more sensitive to radiation emitted by the phones.