This occasional column explores topics covered in Science Times 25 years ago to see what has changed — and what has not.
Everywhere
in the modern world, the throb of alternating current generates
electromagnetic waves — from the television, the blender, the light
bulbs, the wires in the wall.
Because
the oscillations are very slow (just 60 hertz, or cycles per second),
this type of radiation is called “extremely low-frequency.” It was long
thought harmless because it is too weak to knock out electrons and
directly damage molecules in the body.
But on July 11, 1989, Science Times reported the uncomfortable possibility that this ubiquitous background radiation might cause cancer.
An
epidemiological study comparing children in Denver who died of cancer
from 1950 to 1973 with a control group of other children found that
those who lived near electrical distribution lines were twice as likely
to develop the disease as those who did not. A subsequent study, by
other scientists who sought to eliminate what were seen as flaws in the
first study, had nearly identical conclusions.
Laboratory
experiments provided more reasons for concern. Electromagnetic
radiation, particularly the magnetic part of it, changed some
functioning in cells and altered the action of neurotransmitters. Pulses
of 60-hertz radiation increased the number of abnormal embryos in
chicken eggs.
The article quoted Dr. David O. Carpenter,
then the dean of the School of Public Health at the State University of
New York at Albany: “The whole thing is very worrisome. We see the tips
of the iceberg, but we have no idea how big the iceberg is. It ought to
concern us all.”
25 YEARS LATER Dr.
Carpenter is still at the same university, as the director of the
Institute for Health and the Environment. He still finds 60-hertz
radiation worrisome.
“Almost
nothing has changed in 25 years in terms of the controversy, although
the evidence for biological effects of electromagnetic fields continues
to grow stronger,” he wrote via email last week.
In reviewing the research, the World Health Organization
has categorized extremely low-frequency waves as “possibly
carcinogenic”: There appears to be an increase in leukemia rates with
long-term exposure to magnetic fields stronger than 0.4 microtesla. The
earth’s magnetic field is about 100 times stronger, but it is not
oscillating, a crucial distinction. (Concerns about other childhood
cancers have largely abated.)
But
only a small fraction of people are exposed to extremely low-frequency
waves that strong. “It’s not a very normal type of exposure,” said
Emilie van Deventer, the leader of a W.H.O. project to assess the health effects of electromagnetic fields.
One
reason for the continuing uncertainty is that scientists have yet to
explain how such waves could lead to cancer. Leukemia is a relatively
rare disease, striking fewer than one in 5,000 children in the United
States; its causes are hard to study, and even if a link were
established, any effort to shield the world from low-frequency radiation
would at best prevent a small number of cancers.
“In
terms of a public health perspective and in terms of what one would
think of suggesting in terms of regulations, you can see that the
risk-benefit ratio would be quite unbalanced,” Dr. van Deventer said.
“And this is if we were able to show causality.”
In
recent years, concerns have migrated to frequencies that oscillate not
60 times a second but millions to billions of times — those used by
cellphones, cordless phones and wireless networks. Dr. Carpenter, for
example, would like to keep Wi-Fi out of schools, even though there is
no direct evidence of harm as of yet and it broadcasts at lower energy
levels than cellphones; the W.H.O. calls the radio frequencies used by
cellphones, Wi-Fi and other telecommunication devices also “possibly
carcinogenic.”
“Which
is a little bit difficult to explain to the public,” Dr. van Deventer
said. “People like to have a black-and-white answer.
“Looking
at trends over the last 20, 30 years, we don’t see an increase” in
cancer, she said. “But again, we don’t know. If it takes cancer 10 years
to promote, maybe we will see it in the next 10 years.”
The
possible hazards have not deterred her from a modern lifestyle. “Yes, I
am calling you, talking to you using my cellphone,” she said. “I have a
microwave. I have everything. It doesn’t change anything for me.”
She added, ”But from a professional point of view, it’s important that we stay on top of it.”
The W.H.O. project is working on a new report summarizing the health risks of radio-frequency fields, to be published next year.
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