Associated With Residential Exposure to Extremely Low
Frequency Electromagnetic Radiation
Roland J. Lamarine, HSD, is Associate Professor of Health Education and Richard A. Narad, DPA, is Assistant Professor of Health Services Administration, both in the Department of Health & Community Services at California State University, Chico, California.
Requests for reprints should be addressed to:-
Dr. Roland J. Lamarine, Department of Health and Community Services
California State University, Chico, CA 95929 0505, U.S.A.
Extremely low frequency electromagnetic radiation has received considerable attention recently as a possible threat to the health of persons living near high tension electric power lines, distribution substations,and even in close proximity to common household electric appliances. Results of epidemiological and laboratory research are examined to assess risks associated with magnetic fields generated by extremely low frequency electromagnetic sources. Health risks associated with such fields include a wide variety of ills ranging from disruption of normal circadian rhythms to childhood cancers. Risk assessment has been particularly difficult to determine in light of an ostensible lack of a dose response relationship. Current media sensation fueled in part by an equivocal position adopted by the United States Environmental Protection Agency has contributed to the controversy. Recommendations for prudent avoidance of possible dangers are presented along with policy implications concerning health risks associated with magnetic fields.
Since the advent of man made X rays and nuclear power, evidence has been accumulating concerning the health risks associated with ionizing radiation. Beginning in the 1970s, medical literature, and to a much greater extent, popular literature, have focused attention on a potential new health hazard associated with a different type of radiation, extremely low frequency electromagnetic radiation.
The electromagnetic spectrum includes forms of energy ranging from cosmic rays and X rays on the high frequency side to microwaves and electricity on the low frequency end, 2. Hertz (Hz) is the term commonly used to describe frequency or the number of times per second that electromagnetic waves alternate. Extremely high frequency radiation such as X rays and gamma rays are referred to as ionizing and are able to disrupt matter by stripping electrons from atoms. The current controversy focuses on the opposite end of the electromagnetic spectrum, extremely low frequency radiation (ELF).
ELF, which is defined as frequencies below 300 Hz, includes 60 Hz fields found in household electricity which had not been considered hazardous to health until the early 1970s. These fields are non ionizing; they are too weak to disrupt molecular bonds leading to genetic damage in living cells. They are not capable of generating significant amounts of heat like microwaves or radar. Electric fields are directly related to the level of voltage, while magnetic fields are produced by the movement of the charge. Both types of fields are produced by electric transmission and distribution lines and the vast array of electric appliances ubiquitous in modern society.
The strength of electric fields is directly related to voltage, the higher the voltage, the stronger the electric field. Electric fields are easily blocked by normal building materials from which houses are constructed. Their strength decreases rapidly with distance from the source, 3,4. The current controversy focuses not on electric fields but on magnetic fields which produce a series of force waves in concentric loops around electric currents.
Magnetic fields are produced by all electric charges and are even found within the human body. Magnetic fields also drop off rapidly with distance from the source, however, unlike electric fields, they are highly penetrating and cannot be easily blocked; they are capable of penetrating most objects including concrete and even lead. Magnetic fields are only detectable with the use of a magnetic field detector and are commonly measured in units called milligauss (mG), 5,6.
An ideal study to determine the health impacts of electromagnetic radiation would have several characteristics. First, it would include a process for identifying the dosage, including both amount and intensity of exposure. Second, it would control for other exposures to potential illness risk factors such as chemical carcinogens or occupational exposures to electromagnetic radiation. It would follow a sufficient number of cases to allow for considerable statistical power. If it were a cohort study, it would have to follow an extremely large cohort for a sufficient period of time to allow for the development of malignancies potentially associated with electromagnetic radiation. Because of practical, real world considerations, none of the studies completed so far on electromagnetic radiation have met these criteria.
It is difficult, if not impossible, to determine the exposure received by any individual, since magnetic fields vary according to electric usage during different times of day and seasons of the year. Instead, most studies have substituted configuration of wires near the study site as a proxy measure. The accuracy of this measure is particularly suspect in studies of patients from three decades earlier. The low number of childhood cancer patients does not allow many studies, even those which indicate positive findings, to reach statistical significance. Finally, most of the epidemiological studies, to date, have used case control or retrospective cohort formats; no prospective cohort study has been attempted.
In a recent editorial, Monson, 7, noted significant limitations associated with the case control format often including the absence of actual measures of electromagnetic fields (EMF) or empirical assessments of exposure to secondary sources of EMF, and biased reporting or incomplete histories related to self reports of exposure. Retrospective cohort designs, while less likely to suffer from recall bias, still do not adequately address the problem of providing actual measures of EMF exposure. Monson concluded there was a need for prospective cohort studies to examine the relationships between EMF and adverse health effects.
A chance observation in 1974 by Wertheimer, 8, led to an intense investigation of possible health effects associated with electromagnetic radiation generated by 60 Hz power lines. Wertheimer was investigating clustering among addresses of childhood leukemia deaths in Denver when she noticed that a large number of the victims' homes had been located near electrical transformers and distribution substations,9. This prompted the first of several epidemiological investigations into the possible association between residential electromagnetic field exposure and the occurrence of childhood cancers.
Wertheimer and Leeper conducted a case control study of 344 children who had died of childhood cancer in Colorado between 1950 and 1973, 8. Proximity to electric distribution lines was assessed and elevated cancer risks were indicated for residents of higher exposure dwellings. A dose response relationship was noted with greatest risk associated with length of residence in high exposure homes. Compared to children from low exposure homes, those dwelling in high exposure environments were two to three times as likely to have developed leukemias, lymphomas, or cancers of the central nervous system.
This study suffered from several weaknesses including the difficulty of accurately assessing exposure levels,since magnetic fields vary greatly with the levels of electric power usage and with distance from their source and may be produced by a variety of electric appliances within the home. Risk assessment was based on an electric distribution wire coding scheme assigned by the researchers without any type of blinding. Power line configurations proved, in later studies, not to be strongly correlated with magnetic field strength. In the Wertheimer study, actual magnetic field measurements were never conducted within the homes, 3,8,10.
Several studies have attempted to replicate Wertheimer and Leeper's results. Six additional case control studies have been performed examining the association between magnetic fields in homes of persons diagnosed with cancer compared to controls without cancer. The results have been mixed and inconclusive. Two studies found no increased risk for cancer related to magnetic fields, 11,12. Three studies found an increased risk that 13 15 did not reach statistical significance.
The best designed study was conducted by Savitz, Wachtel, Barnes, John, and Tvrdik 16 in Denver. These researchers studied a different group of children diagnosed with cancer than those examined by Wertheimer and Leeper in their original study. Exposure levels were assessed using wire configuration codes and magnetic field measurements within homes wherever possible. Results from this study, though not statistically significant, confirmed Wertheimer and Leeper's findings. Savitz and colleagues estimated that children from high exposure homes were 1.5 times more likely to develop cancer than were children from low exposure homes, a lower chance than that posited by Wertheimer and Leeper. It has been noted that as the rigor of these studies has increased the relative risks for cancer have tended to decrease, 10.
Perhaps the best summary of the implications of the findings from the Savitz study was given by the researchers themselves in the discussion section of their paper, "Although the present study has commonalities with the previous reports, it would be erroneous to interpret the literature as a series of replicated positive results. A more valid interpretation would be a literature of suggestive but inconclusive results, 16.
Several case control studies have been published recently reporting on the association between electric appliances (primarily electric blankets) in the home and risk for a variety of cancers, 17. Verreault et al. found little or no risk for testicular cancer related to the use of electric blankets.
Savitz et al,18, reported a weak, positive association between both prenatal and postnatal exposure to electric blankets and childhood cancers. These researchers felt their results warranted further study on the effects of magnetic field exposure produced by electric appliances, 19. Vera et al. found that electric blanket use was not generally associated with an increased risk for postmenopausal breast cancer. They also suggested a need for further research based on their finding that the most frequent users of electric blankets had slightly increased risks for breast cancer. Researchers in all three studies advised caution in interpreting results due to the absence of actual EMF measurements for which self report levels of exposure had been substituted.
Over two dozen studies have examined the effects of occupational exposure to electromagnetic fields on the development of a variety of cancers, primarily leukemias. Eighteen studies have indicated a significant increased risk of leukemia, while 11 have shown an association with brain tumors,20. As the experimental designs for occupational studies have grown more rigorous controlling for other carcinogenic risk factors such as chemical exposures, the relative risks for cancers associated only with electromagnetic fields have decreased, 10.
At best, epidemiological studies can demonstrate an association but to establish a causal link it is necessary to examine laboratory research and to elucidate a possible mechanism to explain how electromagnetic radiation might cause cancer. Carcinogenesis is believed to be a multistep process involving at least two major events. The first step, initiation, involves the genetic alteration of deoxyribonucleic acid (DNA) and does not appear to be linked to extremely low frequency magnetic fields. However, promotion, or the stimulation of cancerous growth in previously initiated cells, does appear to be a possible mechanism by which extremely low frequency electromagnetic radiation may increase the incidence of a variety of cancers. Laboratory research has indicated that electromagnetic radiation can affect calcium ion movements across cell membranes, activate enzyme systems, and alter DNA synthesis. Extremely low frequency magnetic fields could interfere with cell membrane function or with the flow of ions across cell membranes. Calcium ion concentrations are closely related to cell division; forces which affect these concentrations may serve to promote tumor growth. Stimulation of certain enzyme systems (ornithine decarboxylase) essential to cell growth has been demonstrated after exposure to 60 Hz fields. Such a mechanism could account for cancer promotion by magnetic fields, 5,20,21.
Research at the Battelle Pacific Northwest Laboratory has uncovered a connection between exposure to electromagnetic fields and breast cancer in rats. The underlying mechanism in this relationship may be the suppression of melatonin, a hormone believed to be protective against certain malignancies, especially cancers of the breast and prostate. These laboratory findings do not, however, correspond well to the types of cancers (leukemias, lymphomas, and nervous system tumors) being detected by epidemiological studies of electromagnetic field exposure, 21.
Interestingly, the usual dose response relationships have not been established. Several types of cellular activity stimulated by electromagnetic fields have been shown to occur at certain frequencies but to be absent at lower or higher frequencies. Such evidence is difficult to interpret. One explanation is that there are narrow ranges (effect windows) of frequencies or intensities that are harmful, 5. A different possibility could involve experimental protocols and technologies that are not adequate to assess true risks across a full range of frequencies and intensities.
Other Health Hazards
Both animal and human studies on the effects of ELF electromagnetic fields have shown a decrease in the secretion of pineal melatonin, a hormone which stimulates the daily cycle of sleep and wakefullness, 20, the circadian rhythm. Research on the effects of electromagnetic fields on reproduction have produced mixed and equivocal results. Studies of chicken eggs and miniature swine have indicated slight possibilities of abnormal development, while other studies have shown no measurable effects, 21.
Wertheimer and Leeper ,22, examined the relationship between the use of electric blankets or electrically heated water beds and pregnancy outcomes and found increased levels of miscarriage, birth defects, and low birthweights in those pregnancies where the mothers used the electrical appliances. A variety of methodological problems including small sample size and the possibility that elevated temperature was the etiological agent have interfered with extrapolation from these data.
What are the true risks associated with extremely low frequency electromagnetic fields? This is a difficult question to answer since the data currently available are equivocal. Though laboratory evidence is not clear, there is significant evidence that magnetic fields at certain frequencies and intensities can interfere with cell function. Epidemiological data are even more inconclusive with some studies showing no relationship while others point to a weak association. The question of a dose response relationship remains unanswered with current data supporting the notion of "windows" of risk at various frequencies.
The major reason for serious concern involves the ubiquitous nature of electromagnetic radiation in contemporary society. Since no major unexplained increase in cancer deaths has been associated with the fivefold increase in electrical usage in the U.S. over the last three decades, 10, 23, it is unlikely that electromagnetic radiation contributes substantially to elevated cancer risk. However, in view of the many positive associations in both laboratory and epidemiological studies, it is reasonable to assume that there may be a small risk, perhaps with magnetic fields acting as promoters for some cancers that have been previously initiated by more powerful carcinogens.
The Popular Press
The current media attention related to extremely low frequency magnetic fields has produced a mixture of beneficial and detrimental effects. The Environmental Protection Agency fueled the controversy by equivocating on whether to declare electromagnetic fields carcinogenic; EPA has even been accused of deliberately impeding the release of data fearing that the public might misinterpret EPA reports, 24. Many popular magazines and local television news reports have focused attention on the potential health hazards associated with electromagnetic fields.
Some reports have not been balanced presentations of research findings. The typical scenario involves elementary schools in the shadow of high voltage transmission lines, 25. Paul Brodeur's book, Currents of Death: Power Lines, Computer Terminals, & the Attempt to Cover Up Their Threat to Your Health 9, purports to chronicle the dangers associated with electromagnetic fields and to describe an alleged cover up by the electric utility industry. Like so many popular media health related messages, there is a basic core of facts embedded in an alarmist package which tends to generate hysteria among the public (but also increases sales or Nielson ratings).
Reducing Residential Exposure to Electromagnetic Radiation
If there is a health risk associated with exposure to magnetic fields produced by extremely low frequency radiation, it is a small risk. In those studies that indicated a health risk, 25, magnetic fields in the range of 2 3 mG appeared most culpable. Perhaps the best study to date, conducted by Savitz and colleagues 26 revealed that, in 207 Denver homes where magnetic measurements were actually taken, 90 percent were below 1.82 mG. and 50 percent were below .47 mG. Extrapolation from these data to other parts of the country may be inappropriate due to a variety of mitigating factors associated with individual utility company procedures.
A term introduced by Dr. M. Granger Morgan 5 of Carnegie Mellon University has gained wide acceptance in discussions of magnetic field hazards. "Prudent avoidance" suggests that reasonable preventive measures be adopted until research data suggest a need for more extreme actions. Such reasonable measures might include some of the following.
1. When dealing with magnetic fields, distance is an ally. Magnetic fields, particularly those generated by household appliances, drop off quickly in just a few feet from their source. Those who wish to minimize their exposure should not sleep or sit for long periods of time near electric devices particularly those with motors.
2. Much has been written about magnetic fields produced by video display terminals (VDTs). The larger, color monitors produce the strongest fields but some simple steps can be taken to minimize risks. Prudent avoidance includes sitting a minimum of 18 inches (an arm's length) from the monitor, turning it off when it is not being used, and not sitting close to the back or the sides of a monitor, even if it is in another room, magnetic fields can easily penetrate most objects. At least one manufacturer, Sigma Designs, has pledged to offer a low ELF emissions VDT, 27, for U.S. customers during 1991 and IBM has been able to reduce electromagnetic radiation 28 emissions from its VDTs.
3. Where feasible, unplugging water bed heaters and electric blankets before going to bed may be another "prudent" action. Turning them off removes the magnetic field but unplugging is necessary to eliminate the electric field. For individuals unwilling to unplug their electric blankets, Sunbeam offers a product which produces a 28 significantly diminished magnetic field.
4. Adults and especially children ,29, should be several feet away from all sides of a television. A television which is backed up against the wall of another room may unknowingly expose some other person to a magnetic field.
Currently 12 residential and 10 occupational studies are underway and several are near completion. Within the next four to five years the data base should be significantly improved, 20. Expectations for clear cut answers concerning the risks associated with electromagnetic fields may be unrealistic in view of the many constraints affecting this line of research. The population size of affected cancer patients will continue to be small in absolute numbers significantly reducing statistical power.
Surrogate measures of electromagnetic field exposure will also remain a major obstacle, since electromagnetic field levels vary continuously throughout the day and the season of the year. The current crop of studies will produce greater statistical power by adding larger numbers of subjects but they will not include prospective cohort studies due to the great expense and length of time involved in such research, expense that does not seem to be justified by past research results, 30.
The actions suggested above for individuals can minimize potential exposure to magnetic fields at little or no cost, however, public policy makers should react cautiously to proposed actions to minimize public exposure. As Morgan suggested "it may take some guts for a regulator to adopt a `prudent avoidance' strategy," but a stronger approach may require resources which 5
could be used better elsewhere. Until the studies called for by Monson 7 are available, prudent avoidance is preferable to any program aimed at elimination of EMR exposure.
Prudent avoidance might justify consideration of school location in siting of high voltage electrical lines (and vice versa), but there is no scientific evidence which can justify large expenditures to relocate either lines or (as has been suggested in some popular press stories regarding EMR) public facilities. Given the low probability of any negative impact, the cost of limiting exposure to magnetic fields, like other environmental protection issues, may not be justified by any 31
potential reduction in risk. In fact, as noted by the American Cancer Society, such efforts might take resources away from other cancer prevention programs which are likely to have a greater 32 impact.
Although electrical distribution may join garbage disposal on the "not in my back yard" list, few among us are willing to live without the benefits of electricity. Because of the quick fall off of magnetic fields, policy makers should not acquiesce to fears regarding the impact of electrical lines on residential communities.
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