Physical Science Concepts
Research History and Funding
Health Effects Studies
Exposure to electromagnetic fields, or EMF, has become an issue of concern for a great many people and is an active area of biophysical research. Discussion over the possible biological effects of electromagnetic fields first began to surface in the late 1960s following the introduction of new, higher voltage electric power transmission lines. An argument can be made that initial speculation regarding possible detrimental health effects of these lines arose among property owners who objected to their presence due to esthetic factors and the resulting loss of property values. In association with environmental action groups, who opposed construction of the lines on the basis of physical destruction and segmentation of habitat, an alliance was formed which worked to bring the issue into public awareness.
The first scientific study to attract serious interest in the issue came in 1979 following the work of epidemiologist Nancy Wertheimer, who was looking for possible causes for a number of childhood leukemia cases in the Denver metropolitan area. Her research, performed with physicist Ed Leeper, found that children with leukemia were more than twice as likely to have lived in homes near high current power lines, where the electromagnetic fields were stronger. Research on the issue has accelerated since that time, with mixed results, and will be discussed in greater detail later in this article.
Physical Science Concepts
The understanding of a few simple physical concepts is important to the discussion of any interaction between external physical agents and biological systems. Surrounding any wire or conductor that carries electricity, there exist both electric and magnetic fields, collectively referred to as electromagnetic fields, or EMF. These fields often extend for considerable distances around the wire. Although the early health effects studies looked primarily at the effects of large cross-country power transmission lines, and to some extent the public still associates EMF with these lines, it has become clear that anywhere electricity is in use, electric and magnetic fields will be present, often at significant intensities. This includes overhead and underground power distribution lines running throughout residential and commercial neighborhoods, certain types of interior structural wiring, as well as many common electrical devices. If detrimental bioeffects were to be confirmed, the ubiquitous nature of electricity in modern society could represent widespread public exposure to a potentially harmful physical agent.
The types of field that we are concerned about from a health effects standpoint are alternating current, or time-varying, fields whose strength and direction change regularly with time. They arise exclusively from man-made sources, specifically electric power and communications systems, and have been present in our environment for only about the past century. The earth's strong, steady-state magnetic field is often cited as a point of comparison with these fields, but this comparison is not especially meaningful since the influence on matter can be quite different between time-varying fields and static (non-time-varying) fields. It should be noted that naturally occurring time-varying fields, associated with geological and meteorological phenomena, do exist but are not considered detrimental. For the purposes of this article we will look at only a small part of the electromagnetic spectrum, the extremely low frequency, or ELF portion. Electric power distribution in the United States is at a frequency of 60 Hz, and falls within this region. This is the part of the spectrum where most of the research has been concentrated, although substantial work has also been done in relation to radio frequency and microwave fields.
Electromagnetic waves at these low frequencies contain relatively small amounts of energy and are often referred to as non-ionizing radiation. An important distinction must be drawn between this and the ionizing radiation with which most of us are familiar. Ionizing radiation, represented by X-rays, gamma rays, cosmic rays, and alpha and beta particle emissions from radioactive materials, has dramatic and well documented detrimental effects on living things. These high frequency waves or particles have enough energy to eject electrons from molecules, and can damage the structure of cells (including DNA) directly, or through the creation of highly reactive free radicals within cells. Low frequency, non-ionizing radiation does not react with matter in this way. It also differs from radiation in the microwave portion of the spectrum in that it lacks the energy to damage cells by thermal effects. For these reasons, well characterized interaction models which examine the effect of physical or chemical agents have proven inadequate for studying the effects of low frequency electromagnetic fields, and researchers have been presented with a new challenge in identifying biophysical mechanisms of interaction.
Research History and Funding
Many hundreds of studies have been conducted over the past two decades, with many more currently underway. Funding for this research in the U.S. has at various times come from the Environmental Protection Agency, the Department of Energy, the National Institute of Environmental Health Sciences, the National Cancer Institute, The National Institute of Occupational Safety and Health, the Food and Drug Administration, the Department of Defense, and a few state programs. The Electric Power Research Institute, a utility organization, has also funded a great deal of research. Some studies sponsored by the National Cancer Institute have incorporated EMF as one part of a broader epidemiological approach. Worldwide, at least 27 countries are involved in EMF research.
Most work currently underway in the U.S. is a part of what has come to be known as the Research and Public Information Dissemination (RAPID) Program. Mandated by Congress as a part of the Energy Policy Act of 1992, this was planned as a five year effort to determine if exposure to low level, low frequency electromagnetic fields is detrimental to health, and if so, to provide an assessment of risk. Funding was set at $65 million for the five years, with half this amount to come from industry and half from the government. This full sum was not forthcoming, since the industry contributions were not mandatory. The DOE and the NIEHS were charged with directing this research. A report to Congress is required in 1998.
At least four large scale literature reviews have been produced by or for agencies of the government in the last seven years. These reports often reached vastly different conclusions, and have served to heighten the controversy surrounding the issue. A report to the Congressional Office of Technology Assessment in 1989 concluded that there was clear evidence of biological effects related to electric and magnetic fields, but that the risk to health was unclear. The authors stressed the importance of additional research, and proposed a policy of "prudent avoidance," which refers to taking those steps to reduce EMF exposure that can be done with minimal cost, until more is known about the possible health effects. In 1990, the EPA produced their "Evaluation of the Potential Carcinogenicity of Electromagnetic Fields." This report, released only in draft form and then withdrawn under some controversy, classified magnetic field exposure as a potential human carcinogen. A report by the Committee on Interagency Radiation Research and Policy Coordination (CIRRPC) of Oak Ridge Associated Universities, at the request of the White House Office of Science and Technology Policy, reached the opposite conclusion. This report, released in 1992, found no convincing evidence of health hazards from electromagnetic fields. In 1991, before initiation of the RAPID Program, Congress had asked the National Academy of Sciences to review the available literature and provide information on the possible biological effects of EMF and, if possible, to perform a risk assessment. This National Academy of Sciences report, released in 1996, concluded that the current body of scientific data is insufficient to show that exposure to electric and magnetic fields constitutes a health hazard, primarily because no mechanism of action has been identified. It does, however, recognize that a clear association exists between residence near certain types of power lines and the incidence of childhood leukemia, although fields from the lines cannot be proven as the cause.
An extensive rewrite of the 1990 EPA report was completed, and progressed through several steps of scientific and administrative review, but has not been released to the public. Comments from reviewers indicate that it also recognizes an association between cancer and residence near power lines. Limited portions of the draft copy of another report, by the National Council on Radiation Protection, have been published in Microwave News, a scientific newsletter. This report recognized a possible EMF - cancer connection and proposed interim exposure guidelines. Release of these reports are not immediately anticipated.
Research into the possible biological effects of electromagnetic fields has proceeded along three tracks in the years since 1979: epidemiology, whole animal studies, and cell studies. Epidemiology is that branch of medical research which examines patterns of illness in human populations. As an observational technique, it can reveal a statistical association between an illness and a suspected causative agent, but taken alone it is insufficient to prove causality. Supporting evidence, in the form of cell or animal studies and a plausible mechanism of biologic action, is generally required to establish a cause and effect relationship. Most of these epidemiological studies have used some form of cancer as an endpoint.
As noted earlier, an association between childhood leukemia and proximity to power lines was the first realistic indication that exposure to electromagnetic fields may be harmful to health. To date several studies have examined the association between childhood cancer and power lines. The outcomes of these studies are complex and subject to varied interpretation, but at least eight have reported positive results. As the methodologic shortcomings of earlier studies have been overcome by better study designs, the trend of positive results has continued. Many of these studies have shown relative risks of around 1.5 to 2.0, indicating a doubling of the incidence of illness in the exposed population. A widely reported Swedish study, released in late 1992, revealed for the first time some indication of a dose-response gradient, with the number of cases increasing in the presumed higher exposure categories. Large meta-analyses that pool the results of several studies have been performed and the positive association still holds, even when individual studies with positive results are removed from the calculations. It is this consistent pattern of association in the childhood cancer studies that has continued to drive the research into EMF bioeffects.
Epidemiological studies of adult cancers in relation to occupational and residential exposure have shown some clear associations, but overall the results are mixed, with variation in both the strength of associations and in the cancer types noted. Studies which evaluate non-cancer endpoints, such as adverse reproductive outcomes, suicide and depression, and developmental problems have, with a few exceptions, produced negative results.
Laboratory research on cultured cell systems, referred to as in-vitro research, is often beneficial in establishing the response of a certain cell type to a suspected toxic or mutagenic agent, and in elucidating the molecular mechanism by which an effect may occur. Studies which expose cells to a wide range of electric and magnetic fields have examined the effect of these fields on signal transduction events, intracellular calcium concentrations, genotoxicity, and patterns of gene expression. Effects have been observed on some measures of cellular response, but in most cases at levels many times higher than those likely to be environmentally encountered. No genotoxic effects have been confirmed under any exposure conditions. Some insight into the means by which very weak signals may influence cellular processes has been gained, but no clear mechanism of action has been demonstrated.
Studies of animals exposed to suspected toxic agents are important in predicting potential toxicity to humans, and in confirming an effect indicated by an epidemiological study. They also provide valuable information for estimating the level at which toxicity may occur. Studies of animals, and to a lesser degree humans, exposed to electric and magnetic fields have produced interesting results; but these results neither confirm nor contradict the increased cancer incidence reported in some epidemiological studies.
There has been no evidence in any studies that EMF alone can cause cancer in animals. However, carcinogenesis is recognized as a multistage process. In a simplification of a clearly complex process, an agent recognized as an initiator can bring about the transformation of a cell in a manner that can lead to cancer. This process can be enhanced by, and is sometimes dependent upon, the effect of an additional agent called a promoter. A few studies of animals treated with a known chemical initiator have shown greater numbers of tumors, or greater tumor mass, in those animals subsequently or concurrently exposed to magnetic fields at moderate to high levels. This effect has most recently been reported in regard to mammary tumors in rodents.
Another effect that has been extensively investigated is suppression of the hormone melatonin, which is produced in the pineal gland of many animals, including humans. Animal studies have shown that certain types of magnetic field exposure can reduce the production of melatonin. Studies of human volunteers under exposure conditions have reported mixed results. Melatonin is important in regulating circadian rhythms in the animal. It is also recognized as having oncostatic properties and is thought to function as an antioxidant in preventing oxidative damage from intracellular free radicals. If it could be shown that EMF exposure alters melatonin production in any significant way, this would represent one mechanism whereby exposure influences cancer development.
Risk assessment, in regard to agents that are thought to pose a public health problem, is a well defined process that can produce meaningful and quantitative results. This information can be used by policy makers in developing programs to protect the public from these agents, if protection is warranted, and by individuals in making important life decisions. One of the steps in this process is exposure assessment. This involves determining the extent to which people are exposed to the agent in question. In regard to electromagnetic fields, this has been particularly difficult because the specific characteristics of exposure that may produce detrimental biological effects have not been defined. Examples of proposed exposure metrics include: the average field intensity over a period of time, time spent in the field over some threshold value, field variability, the presence of switching transients on the field waveform, time in the day-night cycle when exposure is received, and the strength and direction of the earth's geomagnetic field in relation to the power frequency field. Until the mechanisms by which electromagnetic fields interact with biologic systems are better understood, these questions cannot be answered, and a fully valid risk assessment will not be possible.
For most people, however, perception of risk is more subjective and qualitative, with perceived risk showing little correlation with actual risk. This has probably been the case in regard to electromagnetic fields, and for a number of reasons. First is the fact that the agent is invisible and not perceptible. Second, exposure is usually involuntary in that many people are financially unable to change their place of residence or place of employment in order to avoid a high exposure environment. Third, electricity and radiation of any type are mysterious, poorly understood, and inherently frightening to most people. On top of all this, the potential consequence of exposure, cancer, is very serious indeed. As an example, for an article in USA Weekend Sunday Magazine in 1993, readers' questions were solicited on a number of environmental health issues. Concern about EMF topped the list. A survey conducted in late 1995 by the Harvard Center for Risk Analysis showed that while most people were somewhat unsure about EMF risk, approximately 38% of them placed the risk in the high category.
The economic costs of a large scale response to the issue of electromagnetic fields in the environment is potentially very great. Transmission lines would have to be relocated out of densely populated areas, or the homes along the power line corridor would have to be abandoned and the property purchased to provide a buffer zone on both sides of the line. Neighborhood distribution lines would have to be replaced with new low field designs. Changes would also be required in the way power is distributed to individual homes and within large commercial buildings. Who pays for all these changes? If the electric utilities bear the burden, then everyone who pays an electric bill will pay a share. If the government picks up the tab, this translates into higher taxes for everyone. Public opinion surveys show that people in low field environments, who would be largely unaffected by these changes, are reluctant to pay even slightly higher bills to cover the cost of protecting the relative few who would immediately benefit.
The consequences of a premature response, based on fear and public pressure rather than on legitimate risk information, would be that we all pay substantial costs for unproven benefits, and that resources which could have been utilized in addressing more widely recognized public health problems may have been misdirected. If, on the other hand, no action is taken, and the detrimental health effects of EMFs are confirmed, then lives may be lost unnecessarily. This is the dilemma facing policy makers and the scientists who advise them.
Although the science is far from conclusive, a substantial base of data exists from years of research which is highly suggestive of an association between exposure to electromagnetic fields and the development of certain health problems. It is possible that a subset of the population, which may have a genetic predisposition to the development of these conditions, or who have been exposed to chemical or physical initiating agents, may experience enhanced sensitivity to the promotional effects of electromagnetic fields. Identification of these groups of people would be impractical given our current state of knowledge, but their risk would be greater than the general population. The need for continued research, carefully directed toward answering the salient questions raised by previous work, is clear. In the interim, until a realistic risk assessment can be performed and an appropriate societal or regulatory response initiated, the responsibility lies with each individual to learn more about their electromagnetic environment and to exercise a degree of caution consistent with their own approach to uncertain risks.
Important Research Update
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