CELL PHONE RADIATION, CANCER, AND THE WHO
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.
As 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 make any sense at all?
Let 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?
DNA 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, “Tinkertoy” 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 ten to twenty 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.
The classical physics of Maxwell’s equations in the nineteenth 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 twentieth 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. 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.
How, 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 million.
It 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!”
So 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 fifty 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.
Of 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 with cancer.
So 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. 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 seventy 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 ten electron volts or more, corresponding to ultraviolet light and above. Cell phone microwaves have frequencies a million times too small to constitute ionizing radiation.
However, 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 epidemiological studies.
Okay, 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.
Let us synthesize a particular DNA sequence of a specified length (say, a thousand or ten thousand 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 one hundred to one thousand 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.
There will be some such damage due to natural radioactivity, particularly carbon-14, and due to cosmic ray muons. However, I confidently predict that 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.
So, 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.
Watch this column for experimental results, should anyone choose to produce them.
AV Columns Online: Electronic reprints of over 150 “The Alternate View” columns by John G. Cramer, previously published in Analog, are available online at: http://www.npl.washington.edu/av.
“Cellphone Radiation May Cause Cancer, Advisory Panel Says,” Tara Parker-Pope and Felicity Barranger, The New York Times, May 31, 2011,
“Cell phone cancer report comes amid industry lobby,” Cecilia Kang, The Washington Post, May 31 2011, http://www.washingtonpost.com/blogs/post-tech/post/cell-phone-cancer-report-comes-amid-industry-lobby/ 2011/05/31/AGLb3cFH_blog.html
“LexA-DNA Bond Strength by Single Molecule Force Spectroscopy,” F. Kühner, L. T. Costa, P. M. Bisch, S. Thalhammer, W. M. Heckl, and H. E. Gaub, Biophysical Journal 87, 2683-2690 (2004).
Copyright © 2011 John G. Cramer