The paper by Salvatore et al discusses a very broad, complex subject,
which, in some aspects, is quite controversial. The review touches
on many different topics but not always in enough detail to provide
clarity. Pertaining to the debated link between 50 to 60 Hz power
line field exposure and cancer, the authors characterize their
article as "... a review of the basic science that points
to this possible association [with cancer]." However, the
"basic science" that "points to" occupies
much of their presentation, while some major types of evidence
and reasoning that "points away" is not mentioned.
We agree that the possible human health hazards posed by environmental
electric and magnetic fields is an important issue, principally
because it concerns so many people. Thus, it is essential to understand
what basic science has found to date. An examination of the scientific
literature shows that while there are indeed reports of biological
effects associated with "weak" 50-60 Hz fields, there
are also  reports of initial findings not being confirmed by
other, independent research groups, and  strong theoretical
grounds for skepticism. With this in mind, in the space available,
we very briefly review some of the evidence on the "points
away" side of the intellectual ledger.
Electric and magnetic fields can, indeed, cause biologic effects
and induce changes in biochemical metabolic pathways. The response
of voltage-gated membrane proteins (channels, ionic pumps) has
a solid experimental  and theoretical foundation . Indeed,
nature has favored electrical signaling as the basis for important
interactions and control in many normal biologic processes. The
basic question is: what, if anything, happens to these electric
signals when they are exposed to external fields from power lines,
appliances, and other sources?
From Air to Tissue
In order to address this question, we must recognize the weakness
of the coupling between electric fields in air and biological
tissue. A reasonable upper limit for an electric field near a
powerline is around 10,000 V/m. The coupling through air is so
weak that 20 yards away from a power line, the intratissue electric
field directly induced is 1 million times as small, ie, approximately
E = 0.1! mV/cm. For a 100 micron diameter white blood cell precursor
in the bone marrow, this implies a change in the membrane potential
of approximately 0.1 µV (0.0001! mV). In contrast, the inescapable
thermal fluctuations in the transmembrane voltage have a root
mean square value of about 25 µV (2510!V)[3-4]. Furthermore,
the magnitude of the transmembrane voltage change normally associated
with a change in the conductance of a voltage-gated channel is
typically approximately 1 mV.
To make a long story short, for air fields less than 10 kV/m (extracellular
electric fields in the tissue less than approximately E = 10 mV/cm)
it is difficult to imagine that the external field can compete
with inescapable stochastic fluctuations in biochemical processes
[3-5]. Thus, any extra-cellular electric field less than 10! mV/cm
induced by 50-60 Hz magnetic fields can be considered "weak",
and any biological effect attributed to "weak" fields
deserves intense scrutiny above and beyond the normal diligence
given any experimental result.
Magnetic fields are not attenuated so strongly. However, for comparison,
the 50-60 Hz magnetic field needed to induce 10! mV/cm within
the human body is greater than about B = 0.01 T (100 G), while
the field associated with a typical power line is only 0.5 G.
Thus, any reported effects of "weak" fields cannot be
easily associated with typical voltage-gated proteins that nature
has so heavily favored during evolution .
Also missing from the Salvatore et al review are the "points
away" discussions based on other fundamental physical arguments
[3-6]. In the case of magnetically sensitive radical pair reactions,
the article fails to acknowledge that slow variations due simply
to walking in the earths geomagnetic field cause changes larger
than those due to powerline magnetic fields . For example,
a human approaching a large steel structure, such as a barge,
experiences a magnetic field change of about 7 microtesla (0.07
G), about 15% of the earth's field. Thus, reports of biologic
effects involving the radical pair mechanism at magnetic fields
smaller than about 10 microtesla (0.1 G) are difficult to accept
as support for potential hazards. These and other published arguments
are highly relevant to scientific progress towards understanding
this complex issue, but are not mentioned at all by the authors.
Theory has an important role in the current debate. A particularly
promising approach is reverse engineering-ie, taking the design
components appropriate for biological organisms and attempting
to construct the most sensitive device for field sensing possible.
This approach will identify not only fundamental limits but also
biological structures likely to be affected by weak electromagnetic
fields, if they do, in fact, exist. Such well-known biological
examples as sharks and skates, which can sense direct-current
(DC) electric fields in water of 10 !V/cm in water, and birds
and honeybees, which use differences in the earths magnetic fields
for navigation, serve as positive controls.
Some Misleading Points
In some aspects, such as the comparison of 50-60 Hz fields on
the scale of photon energy, the presentation of Salvatore et al
is grossly misleading. The photon energy is a measure of energy
stored in the field oscillation which is important only when the
period of oscillation is short in comparison to the time required
for field transmissions. The period for a 50-60 Hz sine wave is
approximately 20 milliseconds, over which time the field propagates
4,000 miles. Thus, for distances less than about approximately
10,000 miles, quantum mechanical considerations of photon energy
are not important in the field energy transmission. For the purposes
of the debate on whether electromagnetic fields pose a health
hazard, it is much more appropriate to consider the electromagnetic
field as a thermodynamic parameter, such as temperature or pressure,
rather than in terms of photons. The term "radiation,"
even when qualified by the adjective "nonionizing,"
is scientifically inaccurate when applied to this discussion,
and is particularly inappropriate because of the public's perception
Another erroneous concept is the discussion of the energy of the
field. Literally, the energy in the field is enough to energize
a city. The question is how strong is the coupling through air
to specific biochemical structures that can alter biochemical
processes. In order to foster a rational, scientifically balanced
discussion of these issues, it is important to assiduously avoid
these types of errors.
A Point of Disagreement
Regarding field-induced carcinogenesis, we do not agree with Salvatore
et al that nonpropagating fields are incapable of causing molecular
damage. Electroconformational denaturation of proteins with DC
fields have been documented . However, such strong tissue fields
are very unlikely without direct mechanical contact with the powerline.
Thus, we agree that ambient fields are more likely candidates
for tumor promoters. Powerline 50-60 Hz electric fields are excluded
from the cytoplasm of all but the largest cells (ie, skeletal
muscle and nerve cells which are larger than their electrical
space constant). The site of strongest interaction is the cell
membrane [3,8]. Thus, the plasma membrane is the most probable
site of interaction for commercial power-frequency electric fields,
and electric field interaction with plasma membrane processes
involved in growth control is an essential consideration.
Finally, there have been important experimental studies which
have sought to reproduce some of the widely discussed "gene
expression" studies [9,10], but no effect of "weak"
magnetic fields was found [11,12]. The combination of some experimental
studies that show no effects and theoretical grounds for doubting
the involvement of major classes of biophysical mechanisms strongly
suggests that scientific understanding of this controversial topic
is incomplete. Thus, we agree with the general conclusion of Salvatore
et al that "... funding of... research is essential to answer
the questions of possible carcinogenic or other health effects
of nonthermal, nonionizing electromagnetic fields."
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