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To support research in this multidisciplinary area, our group at Information Ventures Inc. (IVI) reviews this literature for private subscribers and government agencies. IVI has collected more than 25,000 research papers related to the biological effects of EM fields for our commercially available electronic database, the EMF Database. The reports span the disciplines of physics and engineering, biophysics, molecular genetics, cell biology, plant and animal physiology, clinical applications, whole organism, and ecological studies. Understanding such a diverse literature exceeds the expertise of any individual scientist, and many of the better studies are themselves collaborations between physicist/engineers and biologists.
This article will introduce the reader to the literature in this field, and the major literature resources. I also describe several unusual aspects of this challenging area of research.
Many reviews of this literature have appeared in the past decade. Most focused on power frequency fields and reached substantially the same conclusion: that research to date is inconclusive and provides no basis to set reasonable exposure standards. They differ somewhat in their recommendations for additional research and the credence they place in the possibility of the existence of EM field effects.
Reviews have appeared in a variety of publications, and vary in approach and scope. These include book chapters or reviews in journals, which summarize the field and provide key references. Several government reports are available that provide more detail and more extensive bibliographies.
Some of these reviews have been peer-reviewed and some have not. The reviews cited below that appeared in scientific journals were peer-reviewed (although editorial practices and the rigor of the review can vary among journals). Those appearing as book chapters probably were not, although they may have been reviewed by the book's editors. Most of the government reports were subject to an extensive review process. Peer review is generally considered to be an important quality control mechanism in science, however the standards of peer review vary widely.
Several major government reviews have been completed in the last decade. Reports on health effects of EM fields, with emphasis on powerline fields, include those by Oak Ridge Associated Universities [2], the UK's National Radiological Protection Board (NRPB) [3], and the French National Institute of Health and Medical Research (INSERM) [4].
Several states (e.g. Connecticut [7], Kansas [8], and Virginia [9]) have commissioned reviews of the literature on possible health effects of power frequency fields. Some of these are very extensive: a September 1994 review prepared by IVI for the State of Maryland entitled "Status Report on Potential Human Health Effects Associated with Power Frequency Electric and Magnetic Fields" contains 789 references and detailed tables summarizing epidemiologic and animal research completed at that time [10].
Other government-sponsored reviews should be noted. Reports prepared for the Environmental Protection Agency and Department of Transportation review the scientific literature related to potential health effects of fields from proposed maglev (magnetic levitation) and other high-speed electric rail systems [5-6]. Major reports from the US National Council on Radiation Protection and Measurements (NCRP) and US National Academy of Sciences are expected to be released in 1996.
The journal and monograph literature contains numerous reviews of this field, which vary in scope and viewpoint. For example, Moulder and Foster wrote a skeptical review of the biological evidence related to cancer and power-frequency fields [11], while Savitz and Ahlbom gave greater credence to the epidemiologic evidence supporting a suggestion of risk [12]. A group of eight reviews introduced by Savitz [13] can be found in a 1993 supplement to the NIEHS journal Environmental Health Perspectives. Hendee and Boteler [14], Carstensen [15], Jauchem [16], Knave [17], Tenforde [18], Wood [19], and Zipse [20] reviewed various aspects of the issue of possible health effects of power frequency fields from epidemiology (e.g. Jauchem, Knave) to mechanisms of interaction of fields with biological systems (Tenforde).
Recent reviews about possible health effects of radiofrequency energy include one by Elder [21], who focused on radiofrequency fields and cancer and concluded that athermal levels of exposure are unlikely to increase cancer risk, while Goldsmith reviewed the limited epidemiologic evidence for microwave- or radar-induced health effects and gave greater consideration to the possibility of hazards implied by some unconfirmed positive results [22]. Such differences in interpretation may reflect subtle differences in weight that different experts may give to the same body of research evidence.
A recent two-volume book edited by Carpenter and Ayrapetyan contains several excellent reviews, including a review of neurological effects by Kholodov that emphasizes work conducted in the former Soviet Union [23]. Hitchcock and Patterson recently authored a comprehensive handbook which covers biological and physical aspects (including field measurement) of both extremely low frequency and radiofrequency range EM fields [24]. A handbook edited by Polk and Postow has stronger emphasis on physics and engineering [25]; a new edition is expected in early 1996. Somewhat older but still valuable overviews include collections edited by Wilson et al. (which emphasizes cancer [26]) and by Lin (which emphasizes radiofrequency fields [27]). Two older critical treatments of the health effects literature can be found in books by Carstensen [28] on biological effects of powerline fields, and Michaelson and Lin [29] on biological effects of radiofrequency fields.
Other more specialized reviews should be mentioned as well. Brent et al. [30] and Chernoff et al. [31] reviewed possible reproductive and teratogenic effects of EM fields, McCann et al. [32] and Murphy et al. [33] reviewed evidence for the genotoxic potential of EM fields, and Cadossi et al. [34] reviewed effects on lymphocytes. Loscher and Mevissen [35] and Holmberg [36] reviewed cancer-promoting effects of EM fields in animal tumor models. Stevens et al. [37] reviewed evidence related to breast cancer and the pineal melatonin hypothesis, and Reiter [38] reviewed melatonin responses in general. Delpizzo [39] reviewed studies of adverse reproductive effects associated with the use of video display terminals. With regard to more basic EM field bioeffects, Tenforde [40] reviewed biological effects of static magnetic field effects, Able [41] reviewed magnetic orientation and magnetoreception in birds, and Goodman et al. [42] reviewed cellular and subcellular EM field effects. Other specialized reviews, including one on behavioral effects of high peak pulse microwave exposures [43], appear as government reports.
Reviews often present a "bottom line" assessment of the literature that can miss its most interesting aspect, its diversity. Although research on the biological effects of EM fields has continued since the 1950s and even earlier, most of this research has been exploratory and few issues have been decisively resolved. Many reported studies involve small numbers of experiments on a single biological system exposed to a specific set of field conditions. Many studies are reported only as meeting abstracts and never appear in peer-reviewed journals. Some studies have obvious methodological problems; other apparently well done studies report bioeffects whose health significance is unclear, e. g., the reported changes induced by EM fields in calcium efflux from chicken brain hemispheres [44-45].
Inconsistencies and apparent contradictions abound in the literature. Carstensen [28] lists numerous examples of reported effects that could not be confirmed by independent investigators. However, in many instances, when a second research group has attempted to "replicate" the work of another group, it made small technical improvements, used different strains of cells or animals, used a different exposure system, or has otherwise varied the experimental design. When the results failed to confirm the initial study, some uncertainty remained due to differences in the experiments (for example, see the report of Prasad et al. [46]).
A recent conflict of this type between EM field research groups has attracted the attention of multidisciplinary journals like Science and Nature. In work spanning more than a decade, Goodman and Henderson have reported increased transcription of oncogenes and other specific mRNA sequences in several types of cells exposed to low-frequency magnetic fields [47-55]. Recently, two research groups in the US and the UK, using somewhat different methods, failed to observe field effects in one of the cell types used by Goodman et al. [56-57]. These groups all stand by the validity of their results, and it remains to be seen if additional independent experiments can resolve the issue.
Scientific disputes engendered by such conflicting results have created uncertainty about reported biological effects of EM fields in general, which extends to questions about possible health risks of the fields. The journal Nature exacerbated this problem when it presented contradictory results of the gene expression studies under the overly broad title "Cancer Risk and Electromagnetic Fields" [58].
In some cases, substantial efforts to resolve inconsistent research results have been made, without success. For example, Delgado [59] reported that exposure to magnetic field pulses caused abnormalities in chick embryos, depending on the specific frequency and intensity of exposure. Independent attempts to confirm these results using similar (but not identical) exposure parameters showed no effect [60-61], or showed effects that were smaller than Delgado's initial results [62]. Other investigators reported effects that depended on variables that were not controlled in the initial studies, such as a critical period of development [63], conditions of embryo storage [64], or the background geomagnetic field [65]. In an attempt to resolve the issue, the US Office of Naval Research sponsored "Project Henhouse", in which six independent laboratories conducted follow-up studies using the same protocol and identical incubators and exposures. Two laboratories reported highly significant increases in abnormal embryos, one found a marginal effect, and the remaining three laboratories (including that of Delgado's former coworkers who had been reporting significant effects for years) found no effect [66]. The problem may have been due to differences in the strains of the chickens or some other undefined factor [67]. However, the project received no additional funding and these possibilities were never explored. The results of this multicenter study, when results from all the laboratories were combined, indicated a small but statistically significant increase in abnormalities with magnetic field exposure.
The reports cited above provide good starting points for accessing the research literature in this field. However, the literature is so diverse and widely scattered that it is difficult to locate all pertinent studies. Most articles appear in journals related to the discipline of the studies rather than in journals dedicated to EM field bioeffects. For example, Bioelectromagnetics, which specializes in papers on biological effects of EM fields, represents less than 4% of the 18,000 citations in our EMF Database. The major epidemiologic studies involving EM fields were published in the epidemiology literature: American Journal of Epidemiology, American Journal of Industrial Medicine, Cancer Causes and Control, Epidemiology, International Journal of Epidemiology, Journal of Occupational Medicine, and others.
Biomedical databases like MEDLINE and MEDLINE PLUS can locate much of the literature in this field. However, they miss many articles, particularly those in the engineering literature and in the literature of the former Soviet Union and Eastern Europe. Many relevant publications appear as meeting abstracts, books, monographs, government reports, and theses, which are not systematically covered by the major commercial databases.
IVI staff began to abstract literature in this field systematically in 1972. Initially abstracts were published under the title Biological Effects of Nonionizing Electromagnetic Radiation (BENER) Digest, and have been published quarterly since 1989 by IVI under the title BENER Digest Update. Each issue contains approximately 200 detailed summaries of new research reports, written by scientific professionals. Also starting in 1989, IVI extended its coverage of the EM fields literature and to prepare a comprehensive computerized EMF Database which, by the end of 1995, contained over 18,000 summaries in electronically searchable form. The EMF Database is a unique resource for those who need to evaluate research on biological effects of EM fields.
Figure 1 shows the distribution of publications in the EMF Database for the past 18 years. The variations in the number of papers published each year may reflect, in part, changes in funding patterns and shifts of interest of scientists. Many readers of this journal may have only recently become aware of the possible biological effects of nonionizing electric and magnetic fields. As Figure 1 shows, there is a large and well-established research literature in this field. Indeed, this research tradition goes back many years.
Figure 1 also shows changes in research interests over time. As a fraction of the total literature, studies involving lower frequency fields have been increasing, with a corresponding decrease in studies related to radiofrequency fields. The "other" category in Figure 1 represents a diverse assortment. It includes health-related studies involving mixed exposures (e.g.. studies involving magnetic resonance imaging and video display terminals, which produce fields over a broad spectrum), clinical studies (e.g.. use of pulsed magnetic fields for bone and nerve healing, or stimulation of the brain), studies of magnetoreception, biological effects of static magnetic fields, and so on.
The Internet is a rich source of information in this field. EMF-Link, a World Wide Web server maintained by IVI (http://infoventures.com), is a comprehensive source that summarizes current research, EMF-related litigation, and other subjects. This server provides connections to other government and nongovernment Internet resources as well. Examples of the former include search services from MEDLINE and NIH CRISP. A notable example of the latter are two Frequently Asked Questions (FAQ) sheets maintained by J. E. Moulder, one on powerline fields and cancer, the other on possible health effects of static fields.
EMF-Link also provides connections to webservers maintained by various private groups with interests in this issue. These include FAB (The Swedish Association for the Electronically and VDT Injured), the Powerwatch Network, and Bridelwood Residents Hydro Line Committee. Possible health effects of EMF is a frequent subject of discussion on various Usenet groups (in particular, bionet.emf-bio, sci.physics.electromag, sci.environment).
Several specialized newsletters are available, which vary greatly in cost and editorial perspective. EMF Health Report, a lay-oriented newsletter published by IVI, covers recent scientific developments in this field. Other newsletters include Microwave News, EMF Health & Safety Digest, EMF News (a publication of Edison Electric Institute), and EMF Keeptrack. Information about these publications is available on EMF-Link.
Robert Bruce Goldberg received his Ph.D. from the Department of Medical Biophysics, University of Toronto, Ontario, Canada in 1975. He has a research and teaching background in cellular developmental biology and endocrinology. For the last decade, Dr. Goldberg has served as Information Ventures' Director of EMF Publications including the EMF Database, EMF-Link, BENER Digest Update, and the EMF Health Report. Together with members of IVI's biomedical group, he produces specialized technical reports and provides scientific analysis and review for private sector and government clients.