On May 31, 2011, screaming headlines in many news media were along the lines of the New York Times story “Cellphone Radiation May Cause Cancer, Advisory Panel Says”. On that date the World Health Organization (WHO) announced that a team of 31 scientists, from 14 countries including the USA, had made the decision to rank cell phone usage as a possible carcinogen after reviewing many peer-reviewed studies on cell phone safety. The WHO team claimed to have found enough evidence to categorize personal exposure by cell phone radiation as "possibly carcinogenic to humans." Interestingly, the body of evidence on which this pronouncement was based was the same as that available the previous year, at which time the WHO had stated that there was no evidence linking the radiation from cell phones with brain cancer. On the day of the announcement, I heard a radio interview with one of the WHO spokesman, in which he said that the decision to make the announcement was based on the fact that the uncertainties in the available epidemiological studies did not permit them to rule out a possible link between cell phone use and brain cancer. The epidemiological studies in question are large and expensive question-and-answer surveys that attempt to correlate the incidence of brain cancer with cell phone use and other possible causative factors.
a physicist, I am very troubled by the WHO proclamation and by the panicky
reactions it produced. Nowhere did I
find any indication that a key question had been asked: "Is there ANY plausible
physical mechanism by which the electromagnetic microwave radiation from cell
phones can possibly produce DNA damage leading to brain cancer?" Answer:
There is not.
It seems to me that before we expend huge research resources to undertake
these expensive and inconclusive epidemiological studies, we should be obligated
to ask if the hypothetical effect under study is consistent with the laws of
physics. In other words, does the
hypothetical link between microwaves and cancer that is being investigated makes
any sense at all?
me elaborate. In order to produce
cancer, the microwave radiation would have to cause a break or rearrangement of
cellular DNA, modifying the genetic code so that nerve cells in the brain become
cancerous. The microwave photons
must produce mutations. Is that
physically possible or plausible?
is a rather robust long-chain molecule. It
has been suggested (See my column AV-35
in the October-1989 issue of Analog) that DNA, because it is such a stable
and rigid molecule, could be used for structural engineering at the nanoscale,
constructing 3D mechanical scaffolding made from DNA chains. As structural
material DNA offers several very interesting advantages: the chains are
relatively rigid, can be made in the laboratory to designer specifications, and
will link, lock-and-key fashion, only to complementary sequence of bases of
another DNA chain. Thus,
“tinker-toy” DNA scaffolding at the nanoscale could be constructed, a
framework on which nanomachines could be assembled.
A key element of this nano-engineering concept is that it requires a considerable energy, around 10-20 electron-volts, to break a DNA bond. This is several times larger than the energy available from typical chemical reactions or from the energy content of photons of visible light. The DNA bond strength has been verified experimentally using the cantilever nano-manipulation of an atomic force microscope. A DNA strand is stretched like a spring until it reaches its breaking point and snaps. This only occurs when it has been given about 265 electron volts of stored energy by the cantilever system, implying a bond strength about 1/10 of that value. DNA is a tough molecule.
classical physics of Maxwell’s equations in the 19th century
described light and radio waves as perpendicular electric and magnetic fields
forming traveling waves moving through space at the speed of light with some
wave amplitude and frequency. The
energy of the wave was proportional to the square of the electric field.
This picture led to the conclusion that wave energy and wave intensity
were locked together, the more intense the light (or cell phone waves) the more
their energy content, and the more readily they might break a chemical bond.
This antique view still seems to be embraced by the segments of the
medical profession engaged in epidemiology.
However, the dawning of the 20th century brought a new
experimental result, the photoelectric effect, which demonstrated that the
energy delivered by light was correlated with frequency, not intensity.
Albert Einstein, who won the Nobel Prize in 1921 for this work, showed
that the energy content of light was quantized into individual photons, each of
which carried an energy content E
= hf, in other words, Planck’s constant h (4.14 x 10-15 electron volts per Hz) multiplied by
the frequency f of the radiation (in Hz). Interactions
between light and electrons, like those forming chemical bonds, happen one
photon at a time, and each photon can deliver only an energy of hf.
then, could microwave radiation break a DNA bond to produce a carcinogenic
mutation? As we sometimes say in
physics, it would require a visit from the Tooth Fairy.
What is the difference between the energy needed to break a DNA chemical
bond and the energy that might be supplied by the absorption of a photon of
microwave radiation? The most
energetic photons of cell phone microwaves are those of the 4G networks now
replacing the older cell network infrastructure, and the 4G system operates in
the frequency range 2.496 to 2.690 GHz (1 GHz = 1 billion cycles per second).
The corresponding energy content of 4G microwave photons is 0.00000103 to
0.00000111 electron volts. This
means that the mismatch between the energy carried by a cell phone microwave
photon and the energy required to damage a DNA molecule is a factor of about one
might be argued that it is possible for coherent microwave radiation interacting
with DNA to produce multi-photon events in which the energy of many photons is
absorbed in a particular quantum event. Such
“pile-up” quantum events do indeed happen with reduced probability, but
usually involve only two or three photons. One
would need a million-photon pileup to supply the needed energy for DNA breaking.
The probability of such a million-photon pile-up event is infinitesimally
close to zero, which is physics terminology for saying “No way!”.
what does produce DNA mutations? There
are two main culprits: carcinogenic chemicals, and natural radioactivity and
ionizing radiation. Cell division
involves replication of DNA and is a complex chemical process.
Alteration of the chemical environment in which the process takes place
can result in copying errors during DNA reproduction, and this is the most
likely cause of mutations. The cell
is also surrounded by a radioactive environment.
In particular, some of the carbon atoms in the DNA itself are the
radioactive isotope carbon-14, which decays by beta emission into nitrogen-14.
Every second about 50 carbon atoms in the DNA of the average human are
converted into nitrogen, directly producing mutations.
Fortunately, the cells contain DNA repair enzymes that compare one side
of the double helix with the other and repair such single-error damage.
course, the cell phone microwaves do interact with the brain.
After penetrating the skull with reduced intensity, their energy content
will generate tiny atomic and molecular vibrations that will show up as heat,
slightly elevating the temperature of the head in the region near the cell
phone. The body has a strong
interest in maintaining the brain in a narrow temperature range, so such
external heating will stimulate additional cooling blood flow in the heated
region. Recent MRI studies reporting
an increase in brain activity related to cell phone use may reflect this
phenomenon. But it has nothing to do
why do epidemiologist persist in attempting to link cancer to cell phone use?
I think that the answer is: “Because they can.”
And because one inconclusive epidemiological study provides a reason for
proposing and undertaking an even larger and more expensive epidemiological
study, leading to full employment of epidemiologists. There is no obvious end to
such a process.
I think part of the reason is also the confusion at many levels over the use of the word “radiation”. To the general public, radiation is a scary word associated with nuclear accidents and cancer. To a physicist, electromagnetic radiation simply means the traveling waves made of coupled electric and magnetic fields that are produced mainly by the acceleration of electric charges. Electromagnetic radiation may be of any frequency, with examples ranging from the 1 Hz ultra low frequency radio waves made by lightning strikes to the 70 million electron volt gamma rays, which have frequencies of about 3.3 x 1022 Hz and are made when neutral pi mesons decay. All of these are forms of electromagnetic radiation. The question that should be of interest is whether or not it is ionizing radiation, i.e., radiation that has a photon energy large enough to knock an electron loose from an atom. This occurs when the photon has an energy of around 10 electron volts or more, corresponding to ultraviolet light and above. Cell phone microwaves have frequencies a million times too small to constitute ionizing radiation.
some might argue that the link between cell phone microwaves and brain cancer is
not a theoretical physic question; it is an experimental question that must be
tested. We physicists have been
wrong before in our claimed understanding of the universe, and there might be
some presently unknown physical phenomenon that allows cell phone microwaves to
mutate DNA and produce brain cancer. If
the hypothetical effect is small, we could miss it without even larger
in the spirit of this approach, I’d like to propose an experiment (for someone
else to do) that would cost far less then the ongoing epidemiological studies.
The present state of molecular biology technology is such that DNA of a
specified sequence and length can be synthesized by commercial firms
specializing in the process. One can
also accurately measure the lengths of DNA strands by using electrophoresis
techniques, in which the mass of the DNA chain determines how slowly it
percolates through a porous medium in the presence of an electric field, with
the shorter, less massive DNA chains emerging first and the larger, more massive
chains emerging later.
us synthesize a particular DNA sequence of a specified length (say 1,000 or
10,000 bases) and place this in an aqueous solution in a vessel actively
maintained at body temperature. Two
such vessels should be prepared, with one held in isolation as a control and the
other exposed to intense microwave radiation for a given time, say 100 to 1,000
hours. Then the solutions should be
subjected to electrophoresis testing to look for shorter DNA chains resulting
from damage due to DNA breaks induced by cell phone microwave radiation.
will be some such damage due to natural radioactivity, particularly carbon-14,
and due to cosmic ray muons. However,
I confidently predict that, as long as the solution temperatures are constant
and carefully regulated, there will be no significant observed difference in
DNA breakage between the irradiated sample and the control sample, independent
of the intensity and duration of the microwave exposure.
does anyone out there in the molecular biology community want to undertake this
test? You could probably get
generous funding from cell phone companies that feel harassed by the WHO.
this column for experimental results, should anyone choose to produce them.
Radiation May Cause Cancer, Advisory Panel Says”, Tara Parker-Pope and
Felicity Barranger, The New York Times, May 31, 2011,
phone cancer report comes amid industry lobby”, Cecilia Kang, The Washington
Post, May 31, 2011,
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