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The notion that electric power lines can cause cancer arose in 1979 with a single flawed epidemiogical study that created a stir. Subsequent epidemiologic and animal studies have failed to find a consistent and significant effect. No plausible mechanism linking power lines and cancer has been found. In recent years, the verdict from large-scale scientific studies has been conclusively negative, and scientific and medical societies have issued official statements that power lines are not a significant health risk. In short, there is nothing to worry about.
Childhood leukemia can be used as an indicator that radiation exposure is sufficient to cause illness, because radioactivity elevates rates of leukemia before it produce other forms of cancer. Consequently, childhood leukemia ought to be the easiest to detect. In 1979, two researchers, Nancy Wertheimer and Ed Leeper, published an article based on their own epidemiologic study, alleging that the incidence of childhood leukemia was higher in Denver neighborhoods that were near electric power lines . Their article generated a flurry of other studies. The idea was picked up by Paul Brodeur, who wrote a frightening three-part article for The New Yorker that reached a large and influential audience. Subsequent books by Brodeur in 1989 and 1993 alleged that power lines were "Currents of Death" and that the power industry and the government were engaged in a cover-up [2,3]. The journal Microwave News has consistently echoed Brodeur's message.
The list of conditions purportedly related to electromagnetic fields has grown to include Alzheimer's disease, Lou Gehrig's disease, brain tumors, and breast cancer, and multiple chemical sensitivity. The alleged culprits include power lines, microwaves, radar, video display terminals (such as computer monitors), electric blankets, and household appliances in general. Because virtually everyone in developed countries is exposed to appliances that use 60 Hz power (50 Hz in Europe), this health scare would have been extremely important had it turned out to be valid.
By the mid-90s, at least 100 epidemiologic studies had been published. Most found no correlation between cancer and measured powerline magnetic fields in houses. The evidence accumulated that power lines are not a health risk. In 1995, the PBS-TV's Frontline aired a skeptical report, "Currents of Fear," that included interviews with Brodeur and his critics . By this time, a number of high-level review panels has assessed the published studies. One prominent panel, assembled by the Oak Ridge Associated Universities, concluded:
There is no convincing evidence in the published literature to support the contention that exposure to extremely low-frequency electric and magnetic fields generated by sources such as household appliances, video display terminals, and local power lines are demonstrable health hazards." 
Commenting on this report, Robert L. Park, Ph.D., executive director of the American Physical Society asked, "Will this report end the controversy? Of course not. An entire industry (including researchers) is now dependent on the fear of an EMF hazard."  In 1995, the society's executive council concluded:
The scientific literature and the reports of reviews by other panels show no consistent, significant link between cancer and power line fields. This literature includes epidemiological studies, research on biological systems, and analyses of theoretical interaction mechanisms. No plausible biophysical mechanisms for the systematic initiation or promotion of cancer by these power line fields have been identified. Furthermore, the preponderance of the epidemiological and biophysical/biological research findings have failed to substantiate those studies which have reported specific adverse health effects from exposure to such fields .
In 1996, a committee of the National Research Council concluded:
Based on a comprehensive evaluation of published studies relating to the effects of power frequency electric and magnetic fields on cells, tissues, and organisms (including humans), the conclusion of the committee is that the current body of evidence does not show that exposure to these fields presents a human-health hazard. Specifically, no conclusive and consistent evidence shows that exposures to residential electric and magnetic fields produce cancer, adverse neurobehavioral effects, or reproductive and developmental effects .
In 1997, the National Cancer Institute produced the largest epidemiological study to date, which found no association between childhood leukemia and either wiring codes or measured magnetic fields . The New England Journal of Medicine published the results together with an editorial calling for an end to wasting money on EMF research .
In 1999, The Lancet published a population case-control study covering the whole of England, Wales, and Scotland. All children diagnosed with leukemia or other childhood cancer during the previous four years were eligible. Each case was matched with two controls randomly selected for gender and date of birth from government registries. In the main study, 3838 cases and 7629 controls were interviewed. The EMF part of the study included only one control per case, and household EMF measurements and school measurements where relevant were taken on 2226 matched pairs. The measurements, adjusted for historical line load and appliance fields, were used to estimate average exposure in the year before the date of diagnosis, or an equivalent date for controls. To ensure that the EMF doses found inside the homes were the same as absorbed by the children, 100 of the children wore monitors for one week periods, three times a year. The study found no evidence that exposure to magnetic fields associated with the electricity supply increased risks for childhood leukemia, cancers of the central nervous system, or any other childhood cancer .
Thus, even though very hard to prove a universal negative, there have been so many studies over two decades that it is virtually certain that any significant hazard would have been discovered by now. The critics make a number of very telling points.
1. The fields produced by power lines are very small. Power lines produce both electric and magnetic fields. The electric field is greatly reduced in magnitude within the human body, because the body is an electrical conductor. In fact, power lines produce electric fields inside the human body that are much smaller than the electric fields that normally exist in the body. The magnetic field is not significantly shielded inside the human body, so the only realistic possibility of health effects come from the magnetic field. The magnetic fields from power lines are rather small. Typically they are about 2 milliGauss. By comparison, the earth's field is typically 300-500 milliGauss, with the exact value depending on the location on the surface of the earth. Magnetic fields from power lines are therefore hundreds of times smaller than the magnetic field from the earth. If the relatively weak magnetic fields from power lines had significant adverse health effects, you would expect the much stronger magnetic field from earth to be devastating. Yet no such effect has ever been found. In experiments on animals, mice have lived for several generations in 60 Hz magnetic fields as high as 10,000 milliGauss, thousands of times higher typical power line fields, without any adverse effects.
It is well known that fluctuating magnetic fields give rise to an electric field by the Faraday effect in physics. Yale physics professor Robert Adair demonstrated that these electric fields are very small in comparison with the naturally occurring electric fields arising from thermal fluctuations . This is a good benchmark to indicate that the powerline magnetic fields can't be important.
2. No plausible mechanism for adverse health effects has been postulated. It is well known that electromagnetic fields at high frequencies (e.g., ultraviolet light) can have adverse biological effects. This is why sunlight is a good disinfectant: it kills bacteria. However, the frequency of power line fields (60 cycles per second, or 60 Hz) is too low to have this effect by many orders of magnitude.
3. The initial study was flawed. Wertheimer and Leeper did not actually measure magnetic fields from power lines. Instead, they classified the homes according to their wiring code. The wiring code was then used as a surrogate for the powerline magnetic field, which was unmeasured and unknown. This is a flaw in the study. Later studies actually measured the magnetic fields from power lines and found no consistent relationship between measured magnetic field and incidence of cancer . It is important to realize that there are important possible confounding factors in such epidemiologic studies. For example, one possible confounding factor is an income effect. Living right under electric power lines is not a desired residence, and often is a low-income housing location. People living near power lines tend to be poorer than the control group, and there is a strong and well-known epidemiological relationship between poverty and cancer. Gurney and others showed that the homes with the presumably higher-current wiring code tended to be lower income . Thus the original Wertheimer-Leeper study was biased. In addition, it was based on a relatively few cases, and the statistics were consequently rather poor.
Later epidemiologic studies were properly designed, and some were much larger in scale. For example, the government of Finland performed a huge study of 134,800 children, with one million person-years of exposure. There were 140 cancers in the group, 5 fewer than would be expected by chance .
Consequently, the epidemiologic studies, taken as a whole, consist of a few early low-quality studies, some of which yielded positive effects, and later, higher-quality studies, which yielded negative studies. If power lines really caused cancer, it is natural to expect the later studies to confirm the earlier studies. Instead, this has all the earmarks of a nonexistent effect.
4. The incidence of leukemia has been decreasing. During the last few decades, the use of electric power and electric appliances has increased the 60 Hz powerline magnetic fields to which we Americans are exposed by roughly a factor of twenty. If power line fields were a significant cause of leukemia, there should have been a dramatic rise in leukemia. Leukemia rates, however, have slowly decreased. As noted by the physicist J.D. Jackson, this argues against any significant causal relationship .
Once the health scare was started in a big way, a number of factors have kept it going.
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In 1998, a 30-person panel convened by the National Institute of Environmental Health Sciences (NIEHS - a component of the National Institutes of Health) concluded—by a 19-9 vote—that electric and magnetic fields like those surrounding electric power lines should be regarded as a "possible human carcinogen."  Although described by NIEHS as as "an international panel of experts," the panel included the editor of Microwave News and several other well-known promoters of an EMF-cancer link. Dr. Robert L. Park said that most of the panelists have staked their reputations on such a link .
I believe that the panel's conclusion was not based on new data but represents a political effort to prevent the cutoff of research funds. Indeed, its chairperson declared:
This report does not suggest that the risk is high. It is probably quite small, compared to many other public health risks. However, I strongly believe that additional hypothesis-driven, focused research should be pursued to reduce uncertainties in this area .
In June 1999, the NIH Office of Research Integrity announced that Robert P. Liburdy, Ph.D., a former staff biochemist at Lawrence Berkeley National Laboratory, had engaged in scientific misconduct by intentionally falsifying and fabricating data and claims about purported cellular effects of EMF reported reported in two scientific papers . The papers [23,24]. published in 1992, had reported data indicating that EMF exert a biological effect by altering the entry of calcium across a cell's surface membrane. These claims were potentially important because they purported to link EMF and calcium signaling, a fundamental cell process governing many important cellular functions.
The power line "issue" illustrates how persistent a health scare can be when promoted by an author who tells a frightening tale. The power-line scare has certain things in common with other health scares: Magnetic fields are not understood by the public. Nor can they be felt, tasted, seen, or touched. This makes them mysterious, easily portrayable as threatening, and profitable to their advocates.
Dr. Farley is Professor of Physics at the University of Nevada, Las Vegas. He has never been employed by the electric power industry, or by its research organization, EPRI. He can be reached on the Internet or by email.