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Cellular and other radio communications devices should be distinguished from low frequency electromagnetic fields found around electric power lines. Electric power systems in the United States operate at a low frequency of 60 cycles or hertz (Hz) and at high power, while cellular telephones operate at much higher frequencies, 800 to 900 megahertz (MHz), and at extremely low power levels. New PCS systems will operate at even higher frequencies, 2 gigahertz (GHz) and still lower power levels. Researchers have established that the effects of electromagnetic radiation vary greatly with frequency and power levels, and empirical work over the last several decades has been conducted to determine safe levels at various combinations. (see footnote 6) Because of this variability, however, effects found at one level are not generalizable to other frequency/power combinations-- independent research must be conducted.
Research Is Inconclusive
While considerable research has been conducted on the effects of electromagnetic fields generally, very little work has yet been done on the possible health effects of exposures in the specific frequency and intensity ranges generated by wireless communications devices and systems. A particular weakness in the existing literature is the lack of research on the impact of long-term exposures.
The data that does exist paints an ambiguous picture. Some-- but not all-- research conducted on cells and animals suggests that exposures to fields with characteristics similar to those generated by cellular phones may cause behavioral and biological effects, including abnormal cell growth and increased incidence of malignancies. (see footnote 7) The results of other studies involving claimed links between radio waves and cancer are inconsistent and difficult to interpret.
[GAO] has concluded that [no] research has been completed on long-term human exposure to low levels of radiation specifically from portable cellular telephones. Research findings on exposure to other sources of low-level radio- frequency radiation are inconclusive. Some laboratory studies show that biological effects can occur when animals and cells have undergone extended exposure to low-level radio-frequency radiation; others do not. Scientists at FDA and EPA said that existing research does not provide enough evidence to determine whether portable cellular telephones pose a risk to human health. (see footnote 8)
There are two fundamental issues concerning radio-frequency electromagnetic radiation and human exposure. The most obvious is the thermal or heating effect of such radiation on tissue. It is well known that high-power radio waves will generate heat in exposed tissues. Microwave ovens, high- powered radars, and other high-power microwave devices, for example, radiate energy--a small portion of which is absorbed by body tissues. The rate at which this energy is absorbed is called the specific absorption rate (SAR). Absorbed energy raises the temperature of the tissues through the excitation of water molecules (the typical microwave oven operates at about 600 watts at 2450 MHz). The higher the power level the more heat is generated at a given distance for a given sample, and the higher the frequency, the more of the incident energy is superficially absorbed.
The thermal effects of radio communication devices are generally not considered harmful. Wireless devices are required to comply with well- established standards governing human exposure to electromagnetic radiation. These standards incorporates a substantial safety factor as a cushion against unanticipated effects or exposure in unusual situations. As a result, researchers have been unable to measure heating of tissue at the low power levels used by hand-held cellular telephones. Microwaves do not penetrate metal, so shielding against them is fairly straightforward. In addition, power densities decline rapidly with distance from the source, so exposure can be reduced by lowering the power level and maintaining proper distances from operating antennas.
The second, and more controversial, issue is the possibility that RF radiation may cause nonthermal effects, including changes in genetic structure, the changes in the permeability of cell membranes, and disturbances in cell metabolism. These nonthermal effects theoretically could occur at lower power levels and under different modulation schemes than would be necessary to generate thermal effects. Much research in this area remains to be done, as government, industry and the academic communities agree. While there is no evidence that low-power, high-frequency radio signals cause cancer in cells, the possibility has been raised that such low-power radio waves could stimulate the growth of cancerous or precancerous cells, although early evidence is very weak (see box 11-1). Some preliminary evidence of microwave effects on DNA has also been reported, but not yet confi rmed. (see footnote 9)
Exposure Standards Are Still Being Debated
To protect people from harmful exposure to high levels of electromagnetic energy, the Institute of Electric and Electronics Engineers (IEEE) developed standard IEEE C95.1, which was revised and adopted by IEEE in September 1991 and approved by the American National Standards Institute (ANSI) in November 1992. (see footnote 10) Essentially, the standard says that devices operating between 100 MHz and 450 MHz are within permissible limits if they radiate less than 1.4 watts, and the radiating structure is at least one inch from the body. (see footnote 11) At higher frequencies, the permitted power levels drop: for example, at 1500 MHz, the limit is 0.4 watts. Most hand-held telephones used in the United States operate at no more than 0.6 watts. Mobile telephones (installed in cars) are permitted to emit up to 3 watts because car phone antennas are installed outside vehicles away from close human contact. These levels are considerably below the 4 watt per kilogram energy absorption threshold identified in the scientific literature as the lowest level at which adverse effects due to heating had been noted and replicated. In a December 1992 report, IEEE concluded that "prolonged exposure at or below the levels recommended in these guidelines is considered safe for human health."
The exposure limits in the standard were derived from work done by the U.S. Navy and the IEEE before 1960, and reviewed and revised every five years, according to ANSI policy. Because of this historical foundation, the standard principally addresses concerns about the thermal effects of microwave radiation. Nonthermal effects, while reportedly discussed in the standards committee deliberations, are not directly addressed by the ANSI/IEEE standard, in part because little research on them had been done when the standard was last revised. (see footnote 12) Too little is known about the mechanism(s) by which nonthermal effects operate to set standards for exposure, presuming harmful nonthermal effects exist. As the IEEE standard document notes:
Biological effects data that are applicable to humans for all possible combinations of frequency and modulation do not exist. Therefore, this standard has been based on the best available interpretations of the extant literature and is intended to prevent adverse effects on the functioning of the human body (see footnote 13). . . .
Research on the effects of chronic exposure and speculations on the biological significance of nonthermal interactions have not yet resulted in any meaningful basis for alteration of the standard. It remains to be seen what future research may produce for consideration at the time of the next revision of this standard. (see footnote 14)
Disputes over biological and health effects revolve around the continued acceptability of this standard as new research is performed. (see footnote 15) As of spring 1995, the FCC was still considering whether to adopt the C95.1-1992 standard for all devices operating at microwave radio frequencies. Analog cellular telephones are presently exempt from testing under FCC rules because of their low power levels. However, the FCC indicated in 1994 that PCS phones would be subject to testing and SAR level limitations unless their maximum power output was less than 0.1 watt and a 2.5 centimeter separation was maintained between the user and any radiating structures. (see footnote 16) The standard has been endorsed by the cellular industry and the FDA's Center for Devices and Radiological Health, but EPA, the National Institute for Occupational Safety and Health and others have objections. (see footnote 17)
Research Activities
Research into the possible health effects of radio communication devices and systems is under way in a variety of institutions, including work sponsored by the cellular telephone industry. Questions have been raised about the potential bias of such work, (see footnote 18) but these concerns appear to have been addressed. (see footnote 19) Planned research may provide some answers to recently raised questions about the health effects of wireless telecommunications.
Research is concentrated in epidemiology, dosimetry, toxicology, and clinical studies. Through statistical studies of large populations, epidemiological studies seek to determine whether the occurrence of a disease can be associated with characteristics of people or their environments (see box 11- 2). Dosimetry studies attempt to develop appropriate models of exposure relevant to human use of cellular and other wireless telephone use. Laboratory studies use controlled experiments with cell tissues or animals to ascertain the biological effects of particular radio-frequency emissions. These types of studies, epidemiological and laboratory, are necessary to assess whether there is a health risk to the population.
Two major research programs are being conducted in the United States. In the first, Motorola, a major manufacturer of cellular telephones and switching equipment, is funding a number of studies, some of which are published in the peer- reviewed literature. The other major research program is a three-to-five year effort, estimated to cost upward of $25 million, funded by the cellular telephone industry using an unrestricted deposit-only escrow fund that may be increased as research questions are refined. (see footnote 20) This effort is overseen by Wireless Technology Research (WTR) (formerly the Scientific Advisory Group (SAG)), (see footnote 21) and will support a number of multidisciplinary studies in epidemiology, cell cultures, test models, and genetics. (see footnote 22) Both analog and digital transmission formats will be examined at power levels and frequencies used by current cellular systems, as well as those of proposed PCS. The resulting scientific work is subjected to review through an independent peer-review board coordinated by the Harvard University School of Public Health's Center for Risk Analysis. (see footnote 23) Results will be submitted for publication in the scientific literature.
Research on cellular telephone health effects is also being conducted in Europe, although differences in transmission frequencies, power levels, and waveforms make it difficult to know the applicability of research findings in the United States. In the United Kingdom, the National Radiological Protection Board is developing computer models to characterize the fields induced in the human head by hand- held devices. Both German Telkom and the Research Association for Radio Applications--a consortium of manufacturers and cellular providers--are sponsoring behavioral and health effects research in Germany. The European Commission commissioned a study of thermal and nonthermal health effects from wireless device emissions in late 1994. The study is being conducted at the Center for Personkommunikation at Aalborg University, Denmark.
The credibility of industry-funded research depends on an open process, extensive peer and government review, adherence to accounting and auditing standards, no-strings- attached funding, appropriate research questions and methods, and timely disclosure of research results. For the CTIA-sponsored effort, the peer-review panels and the research itself are funded through an escrow account to provide for strict independence. GAO (see below) questioned whether the research efforts conducted under the cellular industry program could be considered truly objective and credible; the WTR established a new nonprofit administrative structure to manage the research funds and altered its funding and supervisory structures to respond to GAO's concerns. (see footnote 24) Government funds might be contributed to the effort, but the WTR believes that bureaucratic and budget constraints make this unlikely.
Government Initiatives
The General Accounting Office (GAO) completed a short study of research performed on the safety of analog cellular telephones in November, 1994. The report notes that no one federal regulatory agency in the United States has responsibility for wireless communications device emissions; EPA has overall responsibility for advising the government on EMF exposures, the FDA establishes standards for devices that emit radiation, and the FCC approves wireless communications devices for use and assures that their emission levels meet safety standards.
The study also concluded that little research on the health effects of wireless telecommunications devices on humans is planned by the federal government, with the exception of an epidemiological study by the National Cancer Institute to be completed in 1997 or 1998. In 1984, the Environmental Protection Agency convened an interagency working group on electromagnetic frequency radiation, composed of scientific specialists. The Food and Drug Administration is establishing an oversight group that includes policy specialists as well. (see footnote 25)