Friday, March 18, 2011

Murderous Microwaves

I have written previously on the topic of cell phone electromagnetic radiation and cancer, but the issue remains a concern among the general public. Kenneth Foster reviewed three new books about the risks associated with cell phones in the March issue of IEEE Spectrum (disclaimer: I have not read any of these books):
Disconnect: The Truth About Cell Phone Radiation, What the Industry Has Done to Hide It, and How to Protect Your Family, by Devra Davis;

Zapped: Why Your Cell Phone Shouldn’t Be Your Alarm Clock and 1268 Ways to Outsmart the Hazards of Electronic Pollution, by Ann Louise Gittleman

Dirty Electricity: Electrification and the Diseases of Civilization, by Samuel Milham.
Foster writes
Do you feel zapped, disconnected, electronically polluted by electromagnetic fields in your homes and workplace? Are you fearful of your electricity? These three books will feed your fears.

But are such fears justified? Public debates have been going on for more than a century about the possible health hazards of electromagnetic fields from power lines and radio-frequency energy from broadcast transmitters—and now cellphones. At the same time, health agencies have repeatedly reviewed the scientific literature and found no clear evidence of a problem. How can these totally different perspectives be reconciled?
Foster ultimately concludes that these perspectives can’t be reconciled. He counters these alarmist books with exhaustive scientific studies, such as Exposure to High Frequency Electromagnetic Fields, Biological Effects and Health Consequences (100 kHz–300 GHz), Edited by Paolo Vecchia et al., International Commission on Non-Ionizing Radiation Protection, 2009; and Risk Analysis of Human Exposure to Electromagnetic Fields, by Zenon Sienkiewicz, Joachim Schüz, Aslak Harbo Poulsen, and Elisabeth Cardis, report of the European Health Risk Assessment Network on Electromagnetic Fields Exposure, 2010. The first report concludes that
In the last few years the epidemiologic evidence on mobile phone use and risk of brain and other tumors of the head has grown considerably. In our opinion, overall the studies published to date do not demonstrate a raised risk within approximately ten years of use for any tumor of the brain or any other head tumor. However, some key methodologic problems remain—for example, selective non-response and exposure misclassification. Despite these methodologic shortcomings and the still limited data on long latency and long-term use, the available data do not suggest a causal association between mobile phone use and fast-growing tumors such as malignant glioma in adults, at least those tumors with short induction periods. For slow-growing tumors such as meningioma and acoustic neuroma, as well as for glioma among long-term users, the absence of associations reported thus far is less conclusive because the current observation period is still too short. Currently data are completely lacking on the potential carcinogenic effect of exposures in childhood and adolescence.
In the 4th edition of Intermediate Physics for Medicine and Biology, Russ Hobbie and I examine this topic in Section 9.10, Possible Effects of Weak External Electric and Magnetic Fields. We focus on power line (60 Hz) fields (another story….), but many of the same conclusions apply to cell phone (1 GHz) fields. A key factor is the energy of a microwave photon.
Radiated energy is in the form of discrete packets or photons, whose energy is related to the frequency of oscillation of the fields. The energy of each photon is E = , where h is Planck’s constant and ν the frequency. At room temperature, the energy of random thermal motion is kBT = 4 × 10−21 J. At 60 Hz, the energy in each photon is much smaller: 4 × 10−32 J. At 100 MHz it is 7 × 10−26 J.
Therefore, cell phone frequencies correspond to photon energies that are nearly 10,000 times less than thermal energies. Moreover, the energy required to break chemical bonds is hundreds of times greater than thermal energies. If cancer is caused by the breaking of bonds in DNA by photons, then cell phone photons are one millions times too weak to cause cancer. If enough photons were present, the tissue temperature could rise, but no one has evidence that there is a significant heating of the brain by photons; the fields are not that strong. We are left with no plausible mechanism connecting microwaves and cancer.

With weak epidemiological evidence and no mechanism, I remain a hard-boiled skeptic. In fact, my only reservation with Foster’s review is that his criticisms may have been too tame. My views are closer to physicist Bob Park, who is a vocal (and often sarcastic) critic of those who insist that cell phones cause cancer. Nevertheless, even Foster’s mild criticisms triggered a heated debate in the comments section following his review. Interestingly, most of the comments make emotional arguments, not scientific ones, indicating the need for a better understanding by the pubic of the basic physics of how electromagnetic fields interact with tissue. (At this point, I again plug our book, Intermediate Physics for Medicine and Biology, as the best source to learn the physics—although I admit on this one claim I may be slightly biased.)

So who should you believe in this debate? How about the National Cancer Institute? It is hard to think of a more unbiased or authoritative source of information. Their fact sheet provides a science-based analysis of the issue. But Ken Foster is a pretty reliable source of information too. He has spent nearly 40 years studying electricity and magnetism, with much of that analyzing the biological effects of E and M fields. His 1989 paper “Dielectric-Properties of Tissues and Biological Materials: A Critical Review,” (Critical Reviews in Biomedical Engineering, Volume 17, Pages 25–104), written with Herman Schwan, is a highly-cited classic. Foster’s article “Risk Management: Science and the Precautionary Principle” (Science, Volume 288, Pages 979–981, 2000) provides useful insight into the role of scientific evidence in evaluating risk. Russ and I cite several of Foster’s papers in the 4th edition of Intermediate Physics for Medicine and Biology, including
Foster, K. R. (1996) “Electromagnetic Field Effects and Mechanisms: In Search of an Anchor,” IEEE Engineering in Medicine and Biology, Volume 15, Pages 50–56.

Foster, K. R., and H. P. Schwan (1996) “Dielectric Properties of Tissues.” In C. Polk and E. Postow, eds. Handbook of Biological Effects of Electromagnetic Fields, Boca Raton, FL, CRC Press, Pages 25–102.

Moulder, J. E., and K. R. Foster (1995) “Biological Effects of Power-Frequency Fields as They Relate to Carcinogenesis,” Proceedings of the Society of Experimental Biology and Medicine, Volume 209, Pages 309–323.

Moulder, J. E., and K. R. Foster (1999) “Is There a Link Between Power-Frequency Electric Fields and Cancer?IEEE Engineering in Medicine and Biology Magazine, Volume 18, Pages 109–116.
(Note: when preparing this blog entry, I found that we have the title to the last paper incorrect in our book. It should be "Is There a Link Between Exposure to Power-Frequency Electric Fields and Cancer?" I will correct that in the erratum, found at the book website.)

In conclusion, I don’t believe the evidence supports the hypothesis that cell phones cause cancer. Give me some convincing new evidence or a plausible mechanism, and I’ll reconsider.

1 comment:

  1. For more information, see the April 13 article "Do Cellphones Cause Cancer" in the New York Time Magazine, by Siddhartha Mukherjee: