courtesy of Walter Mohn.
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This article is from the April, 1993 issue of
Research & Development Magazine, Des Plaines, IL, page 73.
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R&D ENVIRONMENTAL RESEARCH SECTION:
“Worry Over Power Lines Likely to Last,” by James Glanz
Potential hazards of extremely low frequency fields (ELF) have taken
an extremely low profile amid public accusations that microwaves
from cellular phones might cause brain cancer.
Far from the media crowd surrounding the cellular controversy ,
however, several researchers have expressed the opinion that studies
of ELF’s potential hazards are more likely to affect American
industry and society in the long run. ELF, defined as
electromagnetic radiation at frequencies below 300 Hz, includes the
60-cycle radiation emitted by everything from high-tension lines to
toasters to video display terminals.
“I think most of the heat is still on the power-line issue,” says
Bill Guy, professor emeritus at the Univ. of Washington’s
bioengineering center, Seattle. Guy, who has performed numerous
laboratory studies on the physiological effects of microwaves, says
there is “no documented literature that I know of that would
indicate any danger of cancer [caused by] cellular telephones.”
The scientific record on ELF is less reassuring, says Larry
Anderson, a researcher at Pacific Northwest Laboratories (PNL),
Richland, WA.
“I think what we’re seeing is that most recent epidemiological
studies tend to support the findings of earlier studies,” he says,
referring to elevated rates of leukemia for people who live near
power lines.
Other studies point to slightly increased rates of leukemia and
brain cancer for people occupationally exposed to ELF, such as
electricians and telecommunications workers.
The number of people habitually exposed to ELF is likely to be far
higher than those exposed to microwaves from hand-held cellular
Page 1
phones, even if the phones do turn out to be a threat.
Anyone whose sights are set on proving a link between microwaves and
cancer would do well to study the history of such attempts in the
ELF regime. Although many researchers are convinced of the link
between ELF and cancer, others (such as Robert Adair, a physicist at
Yale Univ.) point to the many conflicting studies or ridicule the
often marginal statistical certainty of the results.
In one case, an epidemiological study found an elevated incidence of
cancer among people who lived near power lines, but a later study
found that “residential traffic density is strongly associated with
childhood cancer…among the same study population,” report ed PNL’s
Thomas Tenforde in last year’s Annual Review of Public Health.
When they are not taken into account, such “confounding variables”
can invalidate statistical conclusions.
Particularly damaging to the persuasiveness of the cancer-ELF link
is the lack of any established mechanism by which the weak fields
that penetrate the body might have a deleterious effect on cells.
Adair has written down thermodynamic equations that he says describe
the current flowing through cell membranes, and he estimates that
random, fluctuating fields around the membranes would have effects
thousands of times larger than any external ELFs could have.
As a result of such considerations, many researchers are looking for
a mechanism by which this naturally occurring noise would ” average
out,” permitting the weak but steady 60-cycle oscillations to have a
noticeable effect on cells.
In one theory, the ELF fields resonate with natural oscillation
frequencies of cellular ions such as calcium and potassium. These
frequencies can be related to the cyclotron frequencies of the ions
in Earth’s magnetic field, or they can be determined by the
physiology of cell membranes. Other theories emphasize the spatial
coherence of ELF-induced currents over an entire cell. The random
currents are again presumed to cancel.
Still another approach to the ELF question is to directly examine
the effect of the fields on animals and cells in vitro. With these
methods, some groups have found deleterious effects – and others
have failed to.
Despite all this uncertainty, there is one thing the ELF researchers
can tell their cellular-phone counterparts for sure: Watch out for
politics. “It’s driven by factors other than just the science,”
warns PNL’s Anderson of such research. “The issue is one of public
interest. For that reason, whether or not there are health effects,
we need to get some resolution to it.”
More Information: Thomas Tenforde (509) 375-3738
FAX (509) 375-3686
Page 2
FIGURE 1
Humans and Power Lines
A Current Affair
_________
/ /
___/__/____ | 180 kV/m
* |/ | * |
* | /| * |
|/ | *** 60 nA/cm^2
____|_|_|____ /@ @
* |/|| * { V } 550 nA/cm^2
* |-/| * – /
|/^/| 200 nA/cm^2/ _
|/-/| / x—–190 nA/cm^2
|^/^/^| //^| |^\
||/|/|| // | | \
||/|^|/|| “”‘ | | `””
||/|||/|| [ ] 250 nA/cm^2
||/|^|/|| ||^||
||/|||/|| || || 370 nA/cm^2
||/|^|/|| || ||
|| ||2000 nA/cm^2
<_| |_>
Lightning-rod effect of human magnifies effect of a 60-Hz, 10-kV/m
electric field 18-fold. Such fields are commonly produced by over
head power lines. The field induces currents of up to 2000 nA/cm^2
in the person’s skin. Researchers are trying to find out whether
those currents can have adverse effects.
Source: William Kaune