INTRODUCTION

Humans have evolved, and live, in environments permeated with electric and magnetic fields (EMF) and radiation of many types, both natural and artificial. The electromagnetic spectrum common to our environment covers a broad range of frequencies and wavelengths1. These vary from the static geomagnetic field, to low-frequency emissions of a few hertz (Hz) to a few thousand Hz2 associated with lightning storms, to the much higher frequencies associated with visible light (near 1014 Hz), and still higher frequencies associated with X- and γ-rays (frequencies greater than about 1016 Hz). Radio transmitters and microwave ovens contribute high-frequency components to our electromagnetic environment; the transmission and distribution of electric power contributes at the extremely low-frequency (ELF) end of the frequency spectrum3.

Based on their frequency and intensity, electromagnetic fields vary greatly in their effect on biologic systems. For example, it is well known that exposures to ionizing radiation (X- and γ-radiation) at amounts well below those that produce acute biologic effects are associated with an increased risk of cancer in humans. Although there is not complete agreement about the magnitude of risk at very low exposures, the general principle of a dose-response relationship is widely accepted. This acceptance proceeds from an exceptionally large and consistent data base that demonstrates human response to exposures, from supporting data derived from laboratory studies with animals, and from experiments conducted at a basic mechanistic level in cell culture systems. Although a well-documented dose-response relationship has been established for the increased cancer rates induced by ionizing radiation at higher doses, direct epidemiologic study of exposure to environmental levels of ionizing radiation has not effectively demonstrated quantitative risks in human populations. For example, it has been impossible to use epidemiologic

1  

The frequency (f) and wavelength (λ) of electromagnetic fields/radiation are related by f = c/λ where c is the velocity of light; frequency is expressed in hertz (Hz), or cycles per second, and wavelength in multiples of meters, e.g., 1 nanometer, or 10-9 meters.

2  

1 Hz = 1 cycle per second, 1 kHz = 1,000 Hz; and 104 means 10×10×10×l0 = 10,000.

3  

It is common to use the term “extremely low frequency” (ELF) for frequencies of 3-3000 Hz.



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EMF Research Activities Completed Under the Energy Policy Act of 1992: [Interim Report, 1995] INTRODUCTION Humans have evolved, and live, in environments permeated with electric and magnetic fields (EMF) and radiation of many types, both natural and artificial. The electromagnetic spectrum common to our environment covers a broad range of frequencies and wavelengths1. These vary from the static geomagnetic field, to low-frequency emissions of a few hertz (Hz) to a few thousand Hz2 associated with lightning storms, to the much higher frequencies associated with visible light (near 1014 Hz), and still higher frequencies associated with X- and γ-rays (frequencies greater than about 1016 Hz). Radio transmitters and microwave ovens contribute high-frequency components to our electromagnetic environment; the transmission and distribution of electric power contributes at the extremely low-frequency (ELF) end of the frequency spectrum3. Based on their frequency and intensity, electromagnetic fields vary greatly in their effect on biologic systems. For example, it is well known that exposures to ionizing radiation (X- and γ-radiation) at amounts well below those that produce acute biologic effects are associated with an increased risk of cancer in humans. Although there is not complete agreement about the magnitude of risk at very low exposures, the general principle of a dose-response relationship is widely accepted. This acceptance proceeds from an exceptionally large and consistent data base that demonstrates human response to exposures, from supporting data derived from laboratory studies with animals, and from experiments conducted at a basic mechanistic level in cell culture systems. Although a well-documented dose-response relationship has been established for the increased cancer rates induced by ionizing radiation at higher doses, direct epidemiologic study of exposure to environmental levels of ionizing radiation has not effectively demonstrated quantitative risks in human populations. For example, it has been impossible to use epidemiologic 1   The frequency (f) and wavelength (λ) of electromagnetic fields/radiation are related by f = c/λ where c is the velocity of light; frequency is expressed in hertz (Hz), or cycles per second, and wavelength in multiples of meters, e.g., 1 nanometer, or 10-9 meters. 2   1 Hz = 1 cycle per second, 1 kHz = 1,000 Hz; and 104 means 10×10×10×l0 = 10,000. 3   It is common to use the term “extremely low frequency” (ELF) for frequencies of 3-3000 Hz.

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EMF Research Activities Completed Under the Energy Policy Act of 1992: [Interim Report, 1995] data alone to distinguish between a threshold model and a linear model of dose-response at or 10 fold higher than environmental exposures. The portion of the electromagnetic spectrum associated with ionizing radiation is characterized by very short wavelengths and extremely high frequencies, and the carcinogenic effects of exposures to small amounts of ionizing radiation are generally assumed to be proportional to the amount of ionization (energy) deposited in the tissues. Ionization creates highly reactive molecules that can damage DNA and produce mutational changes in the genes of mammalian cells. Electromagnetic radiation can deliver energy to biologic material in different ways depending on the frequency of the radiation. Radiation with frequencies greater than about 1015 Hz deposits energy primarily by ionization of the molecules of the absorbing material; this can cause damage directly to critical biomolecules of a living organism. Ultraviolet light, with frequencies somewhat smaller than that of ionizing radiation (less than about 1015 Hz), does not have sufficient quantal energy to cause direct ionization of the absorbing tissue constituents, but still can damage the molecular components of biologic material through excitation of the atomic and molecular constituents, thus initiating molecular reactions or altering chemical structures. At still lower frequencies, radiation has insufficient quantal energy to produce the excitation or ionization responsible for changes in the cellular DNA that are considered necessary to induce mutations or cancer. Depending on the frequency and intensity, however, some nonionizing electromagnetic radiation can produce increased agitation of molecules in human tissues—an effect that corresponds to increased tissue temperatures. This is common to microwaves—which have frequencies in the vicinity of 109 Hz—and led to their use for heating. If the fields in the tissue are of sufficient intensity, other effects can be produced in biologic material; excitation of nervous tissue can occur depending on the frequency and intensity of the radiation. Both the thermal and the nervous stimulation effect are well understood and can be repeatedly demonstrated. At 60 Hz, however, the frequency of power line fields is so low that the energy

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EMF Research Activities Completed Under the Energy Policy Act of 1992: [Interim Report, 1995] density that can be obtained in a biologic specimen is insufficient to produce such well-known effects. This situation also presents a problem for the measurement of a relevant dose parameter for exposures to 60 Hz electric and magnetic fields. In the cases of ionizing, ultraviolet, and microwave radiations, the doses from exposure can be well characterized (for example, ionizations per unit volume, photons per square centimeter) and related to quantifiable biological effects to define a dose-response relationship. This relationship invariably shows an increasing response with increasing dose and generally shows some decrease in response for the same dose delivered over increasing amounts of time. For the case of exposure to ELF-EMF, however, there are no certain biological or health effects and there is a large uncertainty with regard to what characteristics of the field to use for dose determination (for example, the root-mean-square field intensity multiplied by time, or the peak field intensity multiplied by a time factor, or a parameter involving the pulse shape or time variation of the pulses, etc.). Consequently, dose-response relationships for exposure of living systems to ELF-EMF have not been obtained. It is in this context that considerable controversy was created within the scientific community when it was first reported that exposure to power line fields was associated with increased incidence of disease. Wertheimer and Leeper (1979) reported that a two to threefold increased incidence of childhood leukemia was associated with residence in houses that had electrical-distribution wiring configurations which they expected to be associated with higher currents and higher than usual ELF-EMF. Not only were their findings unexpected, but they challenged prior insights and beliefs concerning both EMF and the causes of cancer. Since their work was published, other epidemiologic studies have been reported in which childhood and adult cancers, particularly leukemia and brain tumors, were observed to be elevated in association with surrogate4 measures of exposure to power frequency (50 to 60 Hz) EMF. When examined in 4   In most epidemiologic studies the actual electric or magnetic fields were not measured owing to many factors, such as difficulty in obtaining owner consent. Investigators, therefore, developed codes that described homes thought to present higher than average exposure to EMF based on their proximity to power transmission or distribution lines, presence of electrical transformers, and numerous other factors. These surrogate estimates of EMF were then used in lieu of actual measurements to explore associations with disease end points.

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EMF Research Activities Completed Under the Energy Policy Act of 1992: [Interim Report, 1995] relation to present day, time-averaged measured fields, however, no statistically significant association between cancer and greater than average EMF exposure has been reported. Recent epidemiologic studies of power frequency fields and cancer have been conducted in larger populations and with more detailed methodology, but they have not produced evidence that argues persuasively for a quantitative relationship between increased exposure to power frequency EMF and increased risk for any particular form of human cancer. Epidemiology can be a powerful tool for identifying potential risk factors when there is a strong correlation between increased risk of disease and specific environmental conditions. Epidemiologic studies also have been effective in identifying relatively weak associations between a putative risk factor and some cancers. However, as the association becomes weaker, the interpretations become more difficult, and the conclusions become less convincing. Epidemiologic studies are at a serious disadvantage if they are used in an effort to prove that such associations do not exist. One way to evaluate the credibility of epidemiologic findings of weak associations between surrogate estimates of EMF exposure and excess cancer risk is to assess the evidence for the biologic plausibility of such an association. The relatively few laboratory experiments that have sought to link 60 Hz EMF exposure and processes associated with any biologic precursors to carcinogenesis have not produced persuasive evidence that such a connection exists. Although there has been an extensive history of study of the response of biologic systems to exposure to EMF, no conclusive evidence about the potential for such fields to cause detrimental health effects has been produced. Some laboratory studies have reported evidence of biologic response to exposure to ELF-EMF, although, most either have not been reproduced, or have not been conclusively associated with detrimental health effects. Under such circumstances it is easy to see how serious controversy could develop about the interpretation of the available data. Public alarm about the possibility of incurring adverse health consequences from exposure to EMF associated with electric power transmission, distribution, and use is exacerbated by scientific uncertainty. The tragedy of cancer often provokes in a family, or a patient, a strong

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EMF Research Activities Completed Under the Energy Policy Act of 1992: [Interim Report, 1995] need to understand the cause. Cancer patients and their families can worry about the possibility that the disease might arise from previous exposures to EMF. Accounts in the popular news media offer examples of “clusters” of cases in which a small group exhibits an apparent and unusually high frequency of cancer. It is a simple step to draw a self-evident association between EMF exposure and cancer. When serious uncertainties in interpretation of available evidence arise in an area in which one or the other interpretation would have serious technical and economic consequences, it is important for government to help resolve the issues. As noted, there has been extensive study of the response of biologic systems to exposure to ELF-EMF, but there continues to be no conclusive scientific evidence about the potential for such fields to cause detrimental health effects. Literature reviews have been undertaken by the Oak Ridge Associated Universities, (ORAU, 1992), working under the sponsorship of the Committee on Interagency Radiation Research and Policy Coordination; by the Environmental Protection Agency (EPA, 1990); the National Radiation Protection Board of the United Kingdom (NRPB, 1992 and 1994); and by the government of Australia (Peach et al., 1992). These reviews all come to the same general conclusion: There is no conclusive evidence that ELF-EMF exposure leads to an increased incidence of cancer. Still, the popular media, and some in the scientific community, continue to make the connection. Many members of the public, as well as scientists, suggest additional research as the only way to provide a better understanding of the possible health consequences of ELF-EMF exposure. Because of scientific uncertainties and growing public concern, several workshops were held between 1990 and 1992 to discuss the kinds of research that would lead to a clearer picture of the potential health effects of ELF-EMF exposure. These workshops were conducted with the participation of representatives of the Department of Energy (DOE), the National Institute of Environmental Health Sciences (NIEHS), the Environmental Protection Agency (EPA), the Electric Power Research Institute (EPRI), the Health Effects Institute (HEI), public utilities, state governments, interested scientists, and others. The workshops explored strategies for research on the biologic effects of EMF exposure and the means by which information could be disseminated to the public in an

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EMF Research Activities Completed Under the Energy Policy Act of 1992: [Interim Report, 1995] accurate, unbiased, and timely manner. The workshops provided the basic framework for the establishment of an enhanced national program in EMF research that was ultimately authorized by Congress in the Energy Policy Act of 1992 (Public Law 102-486). Under Item 303, Section 2118, of the act, Congress established a 5-year program to investigate the possible effects of exposure to ELF-EMF on human health. The section outlines a national government-industry partnership to determine whether EMF exposure produced by the generation, transmission, and use of electric energy affects human health; to carry out research, development, and demonstration of technologies that would mitigate any adverse human health effects; and to disseminate information related to possible human health effects of EMF exposure. The program provided for the collection, compilation, publication, and dissemination of information on the types and extent of human health effects that might occur; the results of research on mechanisms of interaction of EMF and their relationship to possible human health effects; and research, development, and demonstration of technologies to improve measurement, characterization, and management of exposure to such fields. In the enabling legislation Congress authorized $65 million to be appropriated to the secretary of energy for fiscal years 1993 through 1997. The legislation also instructed the secretary to solicit contributions from nonfederal sources to offset at least 50% of the total funding for all activities under the program. The secretary was further instructed that funds could not be obligated in any fiscal year unless funds from nonfederal sources were available to offset at least 50% of the appropriations for that year. This legislation also established the National EMF Interagency Committee and the National EMF Advisory Committee to guide the research effort and directed the Department of Energy to enter into an agreement with the National Academy of Sciences to evaluate the research activities completed under the program. This report is the first of the periodic reports of the National Research Council, the operating arm of the Academy, to the National EMF Interagency and Advisory Committees. It reviews the activities completed under the National Energy Policy Act of 1992, as specified by the act.