United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/600/9-91/016F
December 1992
Electric and
Magnetic Fields:
An EPA Perspective on
Research Needs and
Priorities for Improving
Health Risk Assessment
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EPA/600/9-91/016F
December 1992
ELECTRIC AND MAGNETIC FIELDS: AN EPA PERSPECTIVE
ON RESEARCH NEEDS AND PRIORITIES FOR
IMPROVING HEALTH RISK ASSESSMENT
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C.
Printed on Recycled Paper
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Notice
This document has been reviewed in accordance with U.S. Environmental
Protection Agency policy and approved for publication. Mention of trade names
or commercial products does not constitute endorsement or recommendation
for use.
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ELECTRIC AND MAGNETIC FIELDS: AN EPA PERSPECTIVE
ON RESEARCH NEEDS AND PRIORITIES FOR
IMPROVING HEALTH RISK ASSESSMENT
CONTENTS
Executive Summary .......... .................. . [[[ ES-1
Chapter I. Introduction [[[ 1-1
Chapter II. Health Effects [[[ 11-1
A. Methodologic Issues for Epidemiology .................... ........... 11-1
B. Cancer [[[ II-3
C. Reproductive and Developmental Effects .......................... II-5
D. Nervous System Effects ........................................... ............. ll-7
E. Immune System Effects [[[ 11-10
Chapter III. Biophysical Mechanisms [[[ HI-1
A. Physical Interactions [[[ IH-2
B. Biological Interactions [[[ III-3
Chapter IV. Exposure Assessment [[[ IV-1
A. Source Identification and Characterization ....................... IV-1
B. Instrumentation and Calibration ......................................... IV-2
C. Environmental Measurement and Documentation ,. .......... IV-2
D. Exposure Modeling [[[ IV-3
E. EMF Coupling to Biological Objects . ................................. IV-4
F. Laboratory Exposure Systems ................ . ........................... IV-5
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Glossary
Appendix A. Research Recommendations
Appendix B. Acknowledgements
G-1
A-1
B-1
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DEDICATION
This report is dedicated to our colleague Ezra Berman, D.V.M., who is
internationally recognized for his research on the reproductive and developmental
effects of radiofrequency radiation and electric and magnetic fields. After 30 years in
the U.S. Public Health Service, Dr. Berman retired from the Environmental Protection
Agency during the preparation of this report. We are indebted to his prudent
research effort that produced a number of excellent research and review articles.
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SUMMARY
Recently, widespread media attention has been focused on whether adverse
human health effects could result from exposure to electric and magnetic fields (EMF).
Public and private concerns are based on research reports of a statistical association
between EMF exposure to human populations and some forms of cancer, as well as
measurable biological effects in laboratory animals, tissues, and cells. Although the
existing evidence does not prove a cause-effect relationship for EMF exposure and
human disease or injury, it does suggest the need for further research to allow for a
realistic evaluation of the possibility of public health risks and assessment of their
potential magnitude.
The goal of this document is to identify research needed to reduce
uncertainties in the risk assessment of EMF and to prioritize categories of these
research needs. The prioritization is based on a determination of which research
topics are most likely to provide near-term results that will improve and/or strengthen
our assessment of EMF health risks.
The discussion is devoted exclusively to EMF in the range of 0 to 500,000
Hertz (Hz). Sources of public exposure to EMF in this spectrum include electric
power lines (e.g., transmission and distribution lines, electric circuits in the home),
electrically powered devices in the home (e.g., electric blankets, televisions, hair
dryers, video display terminals, fluorescent lights), civilian and military communication
systems (e.g., LORAN, OMEGA, GWEN), and electric powered transportation
systems. Although EMF at frequencies above 500,000 Hz may also have potential
health effects, the lower range is emphasized because of the concern about EMF
from power lines and commonly used electric devices.
The strategy evaluates research needs in four major areas:
o Animal and human studies to determine if adverse health effects (cancer
and reproductive, nervous, and immune system effects) might result
from EMF exposure.
o Investigation of biophysical mechanisms, including both physical and
biological interactions, that underlie any effects which may occur from
exposure to EMF.
o Improved assessment of human exposure to EMF, including source
identification and characterization, instrumentation development,
exposure measurement and modeling, EMF coupling to biological
objects, and laboratory exposure systems.
o Identification and evaluation of mitigation options to prevent and reduce
human exposure to EMF.
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Those research topics deemed to be high priority are: carcinogenic health
effects; biophysical mechanisms; and human exposure assessment. Research on
possible effects on the reproductive and nervous systems was assigned a medium
research priority. A low priority was given to research on immune system effects and
control technology. Research recommendations are summarized in Chapter VI and
listed by topic in Appendix A.
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CHAPTER I
INTRODUCTION
The high standard of living in the United States is due in large measure to the
use of electricity. Our technological society developed electric power generation,
distribution, and utilization with little expectation that exposure to the resultant electric
and magnetic fields (EMF) might possibly be harmful beyond the obvious hazards of
electric shocks and burns, for which protective measures were instituted. Today, the
widespread use of electric energy is clearly evident by the number of electric power
lines and electrically energized devices.
Because of the extensive use of electric power, everyone in the United States
today is exposed to a wide range of EMF not present in the pre-techriological world.
More than 100,000,000 people - virtually all those born in the United States since
1940 - have been exposed throughout their lives to technology-generated electric
and magnetic fields. Recent research reports describe an association between
exposure to EMF and health effects in human populations, biological effects in
laboratory animals, and biological effects in cells and tissues derived from human
beings and laboratory animals. The epidemiological studies reporting a statistical
association between EMF exposure and some types of human cancer raise special
concern. Because of the potential for exposure of EMF to produce health effects,
especially cancer, the EPA conducted a review of the literature on cancer and related
biological effects. The external review draft entitled an "Evaluation of the Potential
Carcinogenicity of Electromagnetic Fields" (EPA/600/6-90/005B) was completed in
October 1990.
During the preparation of the literature review, the potential for health effects from
EMF exposure became more sharply focused as an emerging public health issue. To
address this issue, EPA initiated work on this report to identify the research needed to
reduce uncertainties in the risk assessment of EMF. The research needs effort was
enlarged to encompass all major health effects associated with exposure to EMF
including cancer and effects on reproduction, development, and the immunological
and nervous systems. In addition, the recommendations in this report describe
research needs in the areas of biophysical mechanisms, exposure assessment, and
control technology.
The document is written for scientists and engineers, managers, regulators,
and policy makers who are interested in the research issues associated with EMF. It
is meant to identify important research needs and to prioritize categories of these
needs based on their relevance for future decisions about the likelihood and
magnitude of human health effects resulting from EMF exposure. The research needs
outlined here are envisioned as a framework from which mission-oriented research
plans can be derived.
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The report format consists of two parts. First, an overview is presented of the
current state of knowledge for each of the four subject areas (health effects,
biophysical mechanisms, exposure assessment, and control technology); the overview
identifies research gaps and explains the rationale for the recommendations. Second,
research recommendations are given for important unresolved issues and emerging
technologies. The discussion of research needs and priorities is based on literature
reviews and other reports listed on page R-1. The literature is not reviewed in detail
and original research articles are not cited.
Important questions considered in this report are:
o What, if any, are the health effects in human populations exposed to EMF
in the home and public environments?
o
o
What, if any, are the other biological effects of EMF exposure?
What are the biophysical mechanisms that underlie interactions between
EMF and biological systems?
What electric and magnetic fields exist in the home and public
environments?
What are the sources of the fields?
If
necessary, how can exposure be mitigated?
Concerns about potential health effects associated with EMF were the stimulus
for recent interest by Federal agencies in the associated research questions. As
mentioned above, the EPA critically reviewed the literature on cancer in "Evaluation of
the Potential Carcinogenicity of Electromagnetic Fields" (External Review Draft,
EPA/600-6-90/005B, October 1990). The draft document was peer-reviewed by the
Nonionizing Electric and Magnetic Fields Subcommittee of the EPA Science Advisory
Board. The Subcommittee concluded that (1) currently available information is
insufficient to show electric and magnetic fields to be carcinogenic, and (2) there is
insufficient evidence to designate specific values of magnetic-field strength that may
be hazardous to human health. (Report to EPA Administrator from Science Advisory
Board, January 29, 1992.) Similar conclusions are found in the report written by the
Advisory Group on Non-ionizing Radiation to the National Radiological Protection
Board in the United Kingdom. (Electromagnetic Fields and the Risk of Cancer, 1992.)
The Science Advisory Board Subcommittee reviewed the penultimate draft of this
report on EMF research needs and their recommendations were used to prepare this
final report. The Subcommittee's support for EMF research is expressed clearly in the
following quote from their report submitted to the EPA Administrator:
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Research is needed. The Subcommittee therefore recommends that scientific
information sufficient to support credible formal risk assessment of exposure to
electric and magnetic fields be developed. Current scientific information
suggesting links between electric and magnetic fields and human health effects
is far less persuasive than that for chemical exposures related to workplace
settings, ambient air pollutants, indoor air pollution, or pollutants In drinking
water. The recommendation for research is justified by the almost universal
exposure of populations to electric and magnetic fields throughout life, the
limited options for individual exposure reduction, and the years needed to
implement widespread measures for reducing population exposure.
Furthermore, the health effect endpoints suggested by epidemiology studies
include childhood leukemia which results in many years of useful life lost per
case. In the absence of data to support a credible quantitative risk assessment,
public concern could result in sizable expenditures that may be unwarranted.
(Report to EPA Administrator from Science Advisory Board, May 1.1, 1992.)
The National Institute for Occupational Safety and Health (NIOSH) convened a
workshop on the health effects of electric and magnetic fields (1/30-31/91),to review
the literature which may have relevance for occupational exposure to EMF, to identify
knowledge gaps that might be filled by directed research, and to recommend a
national research agenda which, if implemented, would close the gaps and permit
reliable recommendations for protecting workers. The results of the workshop were
published in the "Proceedings of the Scientific Workshop on the Health Effects of
Electric and Magnetic Fields on Workers". The NIOSH report and this EPA report
together identify research to address uncertainties in risk assessment of exposure of
both workers and the public to electric and magnetic fields.
Other Federal agency activities include the following. The Food and Drug
Administration briefed (11/14/90) an advisory committee on EMF exposure levels and
possible human health effects associated with use of electric blankets. The National
Institute of Health held a workshop on Recent Developments in the Health
Consequences and Clinical Applications of Low Frequency Electromagnetic Fields
(2/11/91) to brief members of a research grant panel on the current state of
knowledge of EMF. More recent events involving the Department of Energy (DOE)
and the National Institute of Environmental Health Sciences (NIEHS) are described in
Chapter VI.
In addition to Federal agencies, a wide range of national and international
groups, industrial associations, and state agencies have recognized the importance of
EMF research. A sampling of comments is given below.
With advances in technology and the ever greater need for electric
energy, human exposure to 50/60 Hz electric and magnetic fields has increased
to the point that valid questions are raised concerning safe limits of such
exposure...From a review of the scientific literature, it is apparent that gaps exist
in our knowledge, and more data need to be collected to answer unresolved
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questions concerning biological effects of exposure to these fields. (International
Radiation Protection Association, Health Physics, vol. 58, pp. 113-114, 1990.)
Further study is needed on the influence of electric and magnetic fields on
cellular and animal systems, particularly in the areas of the nervous system and
the reproductive system...Emphasis should be given to validating recent findings
that suggest an association between cancer and exposure to ELF [extremely low
frequency] fields...Because the lack of exposure data is the greatest source of
uncertainty in investigations of human health effects, increased effort is needed
to improve exposure assessment techniques for future human studies. (World
Health Organization, Nonionizing Radiation Protection, Second Edition, pp. 223-
224, 1989.)
Research results available raise important scientific questions in the areas
of developmental biology, neural function, dosimetry, and mechanism. To
answer these questions and to assess their implications for potential health
hazards will require high quality research, fastidious reporting, and independent
replication of experiments. (Nonthermal Effects of Nonionizing Radiation, Final
Report, National Academy of Sciences, National Research Council, pp. 5-6,
1986.)
Although too little is known about field effects on cells and effects in the
whole animal to conclude that there is a causal connection between ELF
[extremely low frequency] fields and disease, there is also too much evidence
for effects of weak fields on important biological functions to ignore the
possibility that harmful health effects may occur. More research is needed to
decide if the biological interactions with ELF fields are only interesting laboratory
phenomena or are the signature of a widespread environmental health problem.
(Potential Health Effects of Electric and Magnetic Fields From Electric Power
Lines, Report to the California State Legislature, September 15, 1989, p. 100.)
The possibility of EMF playing a role in carcinogenesis cannot be ruled
out, but much work remains to be done in identifying a carcinogenic mechanism,
if any, and in providing an accurate assessment of human risk...However, much
additional research needs to be done on the issue. Exposure standards and
reliable estimates of human risk cannot be ascertained without such necessary
research. (Extremely Low Frequency Electric and Magnetic Fields and Cancer:
A Literature Review, Electric Power Research Institute, EPRI EN-6674, December
1989, see Report Summary.)
Particular emphasis should be given to experimental animal models for
those types of cancer for which there exist suggestive evidence for increased
cancer risk in human populations, based on residential and occupational
epidemiological studies or on general trends in cancer incidence; e.g., cancers
of the nervous system, leukemias, lymphomas, and melanoma. Other areas of
research that warrant further investigation are the effects of electromagnetic
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fields on the incidence of "spontaneous" cancers; repair of DNA damage; early
markers of tumor promotion, such as sustained hyperplasia; loss of intercellular
communication; cocarcinogenic agents, factors or processes; and the
expression of oncogenes and tumor suppressor genes. (Extremely Low
Frequency Electromagnetic Fields and Cancer: Focus on Tumor Initiation,
Promotion, and Progression. A report prepared for the National Electrical
Manufacturers Association, June 20, 1991, pp. 99-100.)
A critical need, at present, is significant increases in federal funding for
research on interaction mechanisms and animal studies, while maintaining efforts
in epidemiology but with greater emphasis on confounding factors and co-
carcinogens and agents with known carcinogenicity. Moreover, a measurement
program to identify and characterize sources of electric and magnetic fields
would be essential before procedures for exposure mitigation could be
implemented, if needed. (Statement to the Subcommittee on Natural Resources,
Agriculture Research, and Environment Committee on Science, Space, and
Technology, U.S. House of Representatives, James C. Lin, Chairman, Committee
on Man and Radiation, Institute of Electrical and Electronic Engineers, July 25,
1990.)
Recent years have seen dramatic developments in the science which have
prompted many observers to conclude that the issue of possible 60 Hz health
risks should be taken seriously... Already concerns have prompted vigorous
public intervention and litigation which has significantly impeded the ability of
private and public utilities to construct new power transmission facilities. Such
protests will probably grow and its seems likely that similar concerns about fields
will soon be raised at other levels. Without adequate science on which to base
answers, the resulting contention could go on for many years and have costs
significantly greater than the costs of the needed research. (Biological Effects of
Power Frequency Electric and Magnetic Fields-Background Paper, U.S.
Congress, Office of Technology Assessment, OTA-BP-E-53, May 1989, pp. 80-
81.)
This document addresses sources of EMF in the home and public environments
that emit electric and magnetic fields at frequencies of 0 to 500,000 Hertz (Hz). Such
sources include electric power lines, including transmission and distribution lines as
well as electric circuits within homes and public buildings, electric grounding systems,
and electrically powered devices such as home appliances, civilian and military
communication and navigation systems, and transportation systems. Specific
examples of the above include electric blankets, electrically heated water beds,
electric razors, hair dryers, video display terminals (VDTs), photocopiers, printers,
facsimile machines, fluorescent lights, light dimmers, televisions, navigational and
communication systems such as LORAN, OMEGA, and GWEN; and electric trains,
cars and other mass transit systems. Although exposure to EMF at frequencies
above 500,000 Hz is also a health concern, the lower range is emphasized because
of the heightened concern for possible health effects from exposure to 60 Hz EMF
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from power lines and to commonly used electric devices that emit EMF below 500,000
Hz. An EPA report entitled "Biological Effects of Radiofrequency Radiation" (EPA
600/8-83-026F), published in 1984 is a critical and comprehensive review of the
literature on frequencies above 500,000 Hz.
The goal of this document is to identify needs and specify priorities for research
to address the concern that exposure to EMF, aside from electric shocks and burns,
might have significant human health effects. This report describes research needs to
determine the possible health effects of EMF exposure, define exposure conditions,
and determine what type of control technologies might be needed to mitigate
exposure of the public to EMF. The recommendations in this report describe
research needs for (1) human health effects that specifically address cancer,
reproduction and development, the nervous system, and the immune system; (2)
biophysical mechanisms; (3) exposure assessment; and (4) possible control
technologies. Examples are given for each of these categories to illustrate the types
of important research needs.
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CHAPTER II
HEALTH EFFECTS
Many epidemiological studies report an association between EMF exposure
and health effects. The most frequently reported health effect is cancel. In particular,
EMF exposure has been reported to be associated with elevated risks of leukemia,
lymphoma, and nervous system cancers in children. Occupational studies of adults
describe an association between EMF exposure and leukemia, lymphoma, nervous
system cancer, and other cancers. Although there have been more than 40
epidemiological studies of children and adults conducted, uncertainties remain in our
understanding of the potential health effects of EMF. For example, uncertainties
surrounding exposure assessment are significant. Few epidemiological studies
contain measured exposure levels. In some studies, exposure levels have been
estimated by surrogate measures such as job title, broad occupational groupings, or
the configuration of electric power lines outside the home. In addition to cancer,
other health concerns are associated with the reproductive, nervous, and immune
systems. Further research is needed to clarify these reported associations.
The proposed research described below first addresses methodologic and
study design issues important to epidemiological studies. Following are discussions
of research for both human and laboratory animal studies for four major types of
health effects: cancer, alterations in reproduction and development, changes in
nervous system function, and effects on the immune system.
A. METHODOLOGIC ISSUES FOR EPIDEMIOLOGY
Exposure of the public to EMF results from residential exposure to fields from
sources inside the home and ambient exposure to fields from sources outside the
home and workplace. These exposure environments can vary greatly with respect to
intensity, duration, frequency, direction of the fields, and modulation, including the
number of on/off cycles. To assess the effect of EMF on human beings, a variety of
characteristics of the exposure field have to be considered. Attention "should focus on
resolving apparent discrepancies between magnetic field measurements and
surrogates of exposure, e.g., wiring configurations, so that the relevant: exposure
parameters) can be identified. Accurate exposure data will decrease misclassification
in epidemiological studies, improve the ability to develop exposure-response
relationships, and provide more reliable risk estimates.
RECOMMENDATION: EMF exposure of the public should be more fully
characterized to identify common and special exposure situations. Exposure data are
needed for statistically valid population estimates and to help identify the field
parameters that may be biologically active. The development and validation of
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personal external dosimetry methods to document and evaluate the exposure of
human beings to EMF should continue. Epidemiological research and exposure
assessment research must be integrated.
A major concern with the epidemiological data is the paucity of information on
factors which may distort the measure of risk associated with EMF exposure. This
concern is not unique to studies of EMF. Such distortions, if undetected, could
seriously affect the interpretation of the results. The concern for these factors in EMF
studies is due in part to our generally poor understanding of what causes cancer and
to relatively poor exposure assessment of all types of EMF environments. For the
latter, many studies were not designed to characterize total exposure. Some studies
of childhood cancer tried to address these other factors through extensive
questionnaires used to interview parents. Recent occupational studies have made
some advances in identifying exposure to agents in addition to EMF, but more
rigorous investigation is needed. Factors deserving examination include, but are not
limited to, health status, smoking history, chemical exposures, and occupational
information in studies of residential exposure.
RECOMMENDATION: Epidemiological studies on the effect of EMF should be
designed to identify and evaluate other factors which may distort the measure of
association with EMF exposure. Studies of humans in controlled laboratory settings,
animal studies, and in vitro studies should be evaluated for exposure parameters and
other information that would improve the design of epidemiological studies on EMF.
Most occupational studies are of men, but reports of increased miscarriages
and increased malformations suggest that women and children potentially exposed to
EMF may be at special risk. Emerging information about a possible link between
EMF exposure and breast cancer points to a need for more cancer studies of
women; breast cancer is the most common cancer in women and thus of significant
health concern.
RECOMMENDATION: Three major health effects to investigate in women
exposed to EMF are cancer, reproductive effects, and developmental effects. Cancer
studies should test the hypothesis that there is an association between EMF exposure
and breast cancer.
In general, epidemiological studies have chiefly examined exposure to EMF
associated with electric power use in the home and workplace, and studies of people
exposed to frequencies other than 60 Hz are neglected. Higher frequency fields as
well as 60 Hz fields are generated by switching transients and by devices such as
fluorescent lights, light dimmers, televisions, VDTs, and civilian and military
communications systems. Existing electrically powered transportation systems such
as mass transit systems and proposed systems such as magnetically levitated trains
and electric automobiles may generate EMF at frequencies above and below 60 Hz.
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RECOMMENDATION: Epidemiologies! studies should be conducted on
populations exposed to EMF other than electric power frequency fields;.
B. CANCER
B.1. HUMAN
Information on time-dependent factors that affect carcinogenesis is insufficient.
The length of time a person lived in a residential setting has not been adequately
addressed in residential studies. The length of residency in a particular EMF
environment may be an important component of exposure characterization and could
provide important information relevant to exposure-response relations. In a few
childhood cancer studies, the risk of cancer was substantially increased for children
who had the same "birth" address as the "diagnosis" or "death" address, compared to
those children who had moved sometime between birth and diagnosis., The influence
of latency and induction time have also not been rigorously examined in most
epidemiological studies. Different types of cancer have different latent periods. For
example, lymphoma, leukemia, and brain cancer have different latent periods that also
differ depending on cell type and whether the patients are children or adults.
Researchers may have been unable to determine the true risks of cancer, especially
the risk for specific types of cancer, because they did not consider the duration and
timing of EMF exposure.
RECOMMENDATION: Epidemiological studies on EMF and canicer should
assess the influence of time-dependent factors such as length of residency, duration
of exposure, and latency on the risk of specific types of cancer to (1) identify
exposure-response relations with length of residency as a surrogate for exposure and
to (2) validate whether or not specific cancer types have satisfied known latency and
temporal requirements for causality.
Another major problem with some epidemiological studies is the grouping of
cancers into broad categories. In some childhood cancer studies, the strongest
associations are between EMF exposure and all cancers combined. The specific
cancers associated with EMF exposure are leukemia, lymphoma, and nervous system
cancer. Yet, each of these categories contain separate and distinct disease subtypes.
Many reports do not distinguish between different subtypes of cancer. For example,
the risk of acute lymphatic leukemia, chiefly a childhood cancer, may not have been
considered separately from other acute and chronic nonlymphatic leukemias that
more typically affect adults. Lymphatic and nonlymphatic leukemias are different
diseases that may involve different mechanisms. Nervous system cancer is a generic
term that includes a number of histologically defined structures with different
etiologies, and lymphomas may constitute a class of different cancers with different
causes or processes. Often, studies group diseases because a low incidence of
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different types of cancer is found in the study population. However, specific cancers
associated with EMF may be missed in studies that group cancers into broad
categories.
RECOMMENDATION: Epidemiological cancer studies should emphasize
identification of distinct cancer types in populations exposed to EMF because the
reporting of cancer by general class may mask elevated risk for specific cancer types.
The reported association between EMF exposure and cancer suggests the
need for clinical research based on effects in biological models. Magnetic field
exposure of cells in culture is reported to increase the rate of DMA synthesis and
change their proliferative capacity. Human lymphoma cells exposed to 60 Hz fields
showed an increase in the activity of ornithine decarboxylase, an enzyme considered
to be essential for the growth of normal as well as cancer cells. Carcinogenic
chemicals can also increase the activity of ornithine decarboxylase. Breast cancer is
believed to be mediated by oncogenes and alterations in oncogenes and tumor-
suppressor genes are believed to be important in the development of colon cancer.
Since these biological changes are associated with the carcinogenic process, they are
candidate biomarkers for the disease.
RECOMMENDATION: Human clinical studies should try to identify possible
biomarkers of EMF exposure in the carcinogenic process, including alterations in
oncogenes and tumor-suppressor genes and ornithine decarboxylase activity.
BJ2. ANIMAL
Studies in animals and other biological test systems are needed to examine the
associations reported in human studies between cancer and exposure to EMF.
Laboratory studies provide an opportunity to discover cause-and-effect relations
between well-characterized biological systems and defined, controlled exposures to
EMF. Such definitive information cannot be obtained from human studies.
The EPA document on the potential carcinogenicity of EMF concluded that
several biological phenomena related to carcinogenesis are affected by these fields.
EMF exposures are reported to enhance DMA synthesis, alter transcription of
information from DMA into messenger RNA, alter normal patterns of protein synthesis,
delay the mitotic cell cycle, induce chromosome aberrations, induce enzymes normally
active during cell proliferation, inhibit differentiation and stimulate the growth of
carcinoma cell lines, and mimic the effect of phorbol esters, a class of cancer-
promoting chemicals.
The biological phenomena mentioned above are related to postulated
mechanisms of carcinogenesis; however, reports of EMF-induced changes in
biological systems do not prove that the fields are carcinogenic by themselves or that
exposure to them are risk factors for human cancer. Furthermore, the relevance of
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these findings is questionable because many occur at field strengths and conditions
(e.g., pulsing fields) different from the time-averaged ambient levels experienced by
human populations. Although a wide array of biological systems have been
investigated under a broad range of exposure conditions, independent confirmation of
specific experimental results remains important.
RECOMMENDATION: The potential role of EMF in carcinogenesis should be
studied in the laboratory (both in vitro and in whole animals) to discover the basic
nature of the field-dependence of effects. Gene expression, growth of transformed
cells, and intracellular reactions associated with chemical signalling are areas of
special interest.
The results of epidemiological studies suggest an association between
exposure to ambient power frequency magnetic fields and the development of cancer.
This hypothesis is being tested in a study now in progress investigating the
carcinogenic potential of 60-Hz magnetic fields in mice and rats exposed throughout
life. It may become necessary to conduct similar studies to test the carcinogenic
potential of other field parameters or combinations of field parameters representative
of those experienced by human populations. At this time, the carcinogenicity of EMF
has been tested in few animal studies under well-defined laboratory exposure
conditions. One of these studies found that magnetic fields about 1000 times greater
than household levels increased the rate of tumor development in mice treated with
both a chemical carcinogen and promoter. Recently, a possible link between EMF
exposure and a specific type of cancer (breast cancer) has been hypothesized.
RECOMMENDATION: Independent replication should be attempted of the
finding that magnetic fields appeared to increase the rate of tumor development in
mice chemically predisposed to cancer development. If similar results are found,
studies should be done to define the exposure-response relation and to investigate
mechanism(s) of interaction. Cancer studies in laboratory animals are needed to test
the hypothesis that there is an association between EMF exposure and breast cancer.
C. REPRODUCTIVE AND DEVELOPMENTAL EFFECTS
C.1. HUMAN
Environmental agents that cause reproductive and developmental effects are
important because they may directly influence health, lifespan, propagation, and
functional and productive capacity of our children. EMF exposure encompasses the
entire reproductive and developmental periods of life, including pre-conceptional germ
cell development in parents, the period from conception to birth, the postpartum
growth and development stage, and the reproductive ages.
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Epidemiological studies have reported reproductive and developmental effects
from exposure to EMF generated by devices in the workplace and home.
Investigations of women and the outcome of their pregnancies have included
operators of VDTs and users of specific home appliances (electric blankets, heated
water beds, and ceiling electric heat). The reports of increased miscarriages and
Increased malformations suggest that maternal EMF exposure may be associated with
adverse effects. In addition, other studies have reported an increased incidence of
nervous system cancer in children whose fathers had occupations with potential EMF
exposure. However, many studies have used surrogate measures of exposure, have
determined exposure at a time other than the one that is biologically relevant to the
health effect, and have examined in a limited fashion, if at all, other factors that could
distort the findings reported in.EMF studies. A recent study found that use of VDTs
and exposure to the accompanying electric and magnetic fields were not associated
with an increased risk of spontaneous abortion. Thus, the human data are not
adequate to support a definitive conclusion that EMF exposure has reproductive and
developmental effects.
RECOMMENDATION: Epidemiological studies should attempt to replicate
reported reproductive and developmental effects of EMF, especially any possible
relation between the use of electrically-heated beds and adverse pregnancy outcome.
Studies should be designed to include EMF exposure assessment, identify factors
other than EMF that may affect the study conclusions, identify relevant exposure
periods, and be guided by our understanding of reproductive and developmental
effects in laboratory animals.
C.2. ANIMAL
Studies of reproduction in laboratory animals include measures of sexual
behavior, capacity to fertilize, reproductive efficiency, sex organ morphology and
function, and synthesis of sex steroids. Although EMF exposure of the parent before
conception has been reported to affect several reproductive measures, including
sexual behavior and maturation, as well as male fertility, these results have not been
independently confirmed.
Laboratory mammals have been used also to study the potential consequences
of in utero exposure to EMF. A wide range of effects have been reported for rats and
mice exposed to such fields and their offspring. The effects include increased
embryonic death, decreased body weight, shifts in weights of hormonally-responsive
organs (including gonads and organs sensitive to steroid levels), changes in levels of
chemicals in serum and cells, and altered behavioral patterns. Most of the effects
reported in laboratory animals have not been independently confirmed.
There is evidence to indicate that magnetic fields may influence embryonic
development in laboratory animals. The most frequently used animal model for
demonstrating the effects of EMF is the chicken embryo. In 17 reports on the chicken
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embryo exposed to various EMF, 36 of 103 individual experiments showed a
statistically significant increase in abnormal embryos, while 67 did not.
RECOMMENDATION: Research should attempt to confirm independently
reported reproductive effects in mammals. Developmental studies with standard
laboratory models should employ exposure conditions reported to be effective in
nonmammalian systems. The relevance of developmental effects in nonmammalian
embryo models to permanent changes in mammals should be explored because of
the significance to epidemiological findings.
RECOMMENDATION: The reported association of increased cancer rates in
human offspring, or an association of any effect in offspring, to paternal exposure
requires a mechanistic link via paternal germ cell changes. Heritable genetic changes
in germ cells, as reported in epidemiological studies, need to be studied in laboratory
animals.
D. NERVOUS SYSTEM EFFECTS
D.1. HUMAN
Neurotransmitters and neurohormones are substances involved in
communication both within the nervous system and in the transmission of signals
from the nervous system to other body organs. These regulatory chemicals transmit
information and regulate or modulate various bodily functions that range from the
learning of new skills to the control of heart rate and blood pressure. Neuroregulatory
chemicals are released in pulses with a distinct daily or circadian pattern. Serotonin,
melatonin, dopamine, and noradrenaline have been the focus of much attention in the
brain sciences. Aberrant levels of these neurochemicals accompany clinical disorders
like depression and many of the drugs used to treat these diseases interact with
these neurochemicals. Their metabolites can be monitored in easily accessible body
fluids and provide information about the role of neuromodulators in disturbed nervous
system function.
Data of this type from exposed human subjects are not available! but relevant
animal experiments report that neurotransmitter metabolite levels are lowered in
primates and that circadian patterns of neurotransmitters and their metabolites are
desynchronized in rodents exposed to EMF. The few studies in which human
subjects have been exposed to EMF in controlled laboratory settings describe the
following effects: changes in brain evoked-potential indicative of possibly slowed
information processing, slowed reaction time and altered behavioral performance in
which ability to gauge the passage of time was a pivotal component, and altered
cardiovascular function including slowed heart rate and pulse that may indicate direct
action on the heart or the neurochemicals controlling cardiac function. Results also
indicated specific combinations of electric and magnetic fields may be necessary
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before alterations are observed.
Melatonin, a hormone released by the pineal gland during the dark period of
the daily cycle, may be an important marker for certain health effects of EMF.
Alterations in the circadian pattern of melatonin accompany depression, "jet lag," and
"shift lag," which can occur from rotating shift work schedules. Disruption of
physiological functions, such as sleep, that are synchronized with melatonin secretion
are symptoms for all three conditions. Body temperature is also synchronized with
melatonin rhythms. When humans isolated from external time cues are exposed to
electric fields their sleep-wake periods and core temperature patterns reportedly shift.
Manipulation of the light-dark cycle is used to treat depression, and "jet lag"
symptoms are ameliorated after treatment with light or melatonin. Night-time pineal
melatonin levels are reported to be suppressed in rats exposed to electric fields and
intermittent magnetic fields. EMF may also suppress nocturnally high levels of
melatonin in human beings. In one study, the use of electric blankets configured to
allow frequent on/off switching of the magnetic field that was 50% greater than that
associated with a conventional electric blanket, was shown to reduce the nighttime
urinary excretion of melatonin's major metabolite. A possible link between EMF-
induced alteration in melatonin synthesis and cancer has been hypothesized. Studies
with rats show that EMF can suppress the melatonin level in the dark phase of the
daily cycle. This action of reducing melatonin may possibly increase the potential for
cancer because melatonin is known to inhibit the growth of some cancers.
RECOMMENDATION: Work should continue with human subjects in controlled
laboratory settings where exposure to real and sham fields occur under double-blind
conditions. Physiological and behavioral endpoints previously reported to be
sensitive, as well as those reported in animal studies, should be monitored before,
during, and after exposure to EMF. Because of the suspected role of altered
melatonin rhythms in clinical disorders and in cancer, other studies should determine
if EMF can alter the circadian pattern of melatonin and its metabolites in body fluids.
Related research should assess the role of melatonin, if any, in the suppression of
cancer in human beings. Particular attention should be directed to whether the rate
of activation and deactivation of the field (intermittent exposure) has a more marked
effect than continuous application.
D.2. ANIMAL
Studies examining the related areas of behavior, circadian rhythms, and
neurochemistry have been the focus of laboratory animal research concerned with
EMF and the nervous system. Behavior is the integrated output of the nervous
system and alterations in circadian patterns or neurochemical levels are often
reflected in behavioral changes. Physiological and biochemical processes have a
synchronized daily cycle or circadian rhythm and aberrant rhythms have been linked
to a variety of disorders. Such disorders range from altered sensitivity to drugs and
toxins to sleep, performance, and psychiatric disorders, including chronic depression.
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The performance of both spontaneous and learned behaviors is affected by
EMF. Studies of spontaneous behavior have provided data on the threshold and
possible mechanism of perception of 60 Hz electric fields. Although detection
thresholds vary according to species, it is generally believed that fields are detected
by mammals with fur or hair, including humans, because hair vibration caused by the
oscillating electric field activates sensory mechanisms in the skin. No perception
mechanism for magnetic fields is known except for the visual effect in humans known
as magnetophosphenes or phosphenes (light flashes) caused by high intensity
magnetic fields. This phenomenon, which exhibits a threshold and is highly
frequency-dependent (maximum response in the 20 to 30 Hz range), \s apparently
caused by induced electric fields in the eye that stimulate the retina. Thus, a pulsed
magnetic stimulus is interpreted as flashes of light by the brain.
The performance of several learned behaviors in animals is reported to be
affected by EMF. The reaction time of non-human primates is compromised by
exposure to electric fields. Rats trained to respond with a certain pattern and rate of
behavior to earn rewards are less efficient when exposed to EMF. Magnetic fields
decrease the sensitivity of mice to the pain-relieving action of drugs such as morphine
and other opiates. Sixty-Hertz magnetic fields also reduce the number of seizures
induced in rats by an epileptogenic drug. The latter studies indicate that research
incorporating a drug challenge may help to identify the interaction of EMF with the
nervous system.
Research results also suggest that circadian rhythms can be altered by EMF.
In nonhuman primates, patterns of food and oxygen consumption were affected by
field intensity; for some monkeys, these altered biological rhythms persisted after the
cessation of exposure. Other work shows that 60 Hz electric fields produced phase
delays in activity and metabolism rhythms in mice. In addition, exposure to electric
fields has been shown to affect the circadian rhythm of serotonin, noradrenaline, and
dopamine in rats. As mentioned previously, alterations in the level and rhythm of
neurochemicals with respect to the natural daily light-dark cycle may have implications
for sleep and mood disorders, including chronic depression.
One of the most consistent neurochemical findings is that the circadian pattern
of melatonin synthesis in the rat can be altered by EMF. Melatonin levels vary with
the daily light/dark cycle and are higher in the dark phase. The finding that EMF can
suppress the higher melatonin level in the dark phase may possibly be related to
purported carcinogenic effects of EMF because melatonin inhibits the growth of some
cancers. A possible link between EMF-induced alteration in melatonin^levels and
cancer development requires study.
RECOMMENDATION: Studies of EMF effects on behavior of laboratory
animals should emphasize learned tasks and drug interactions. Other work should
determine whether the effects of EMF on circadian rhythms and neurochemical levels
are significant in related areas such as behavior and cancer. The consistent finding
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that EMF affects melatonin synthesis should be the focus of studies to determine the
sites and mechanisms of interaction. Related research should better define the role of
melatonin in suppression of cancer in animals. A primary goal of research on EMF
and the nervous system is to define causative exposure conditions; particular
attention should be given to the possible differential effects of electric versus magnetic
fields.
E. IMMUNE SYSTEM EFFECTS
E.1. HUMAN
The immune system defends against cancer and other diseases.
Environmental agents that compromise the effectiveness of the immune system could
potentially increase the incidence of cancer and other diseases. No research
recommendation is given for the human studies category because of the lack of data
on immune system effects in human beings and the preliminary state of knowledge of
such effects in both in vitro and in vivo laboratory studies (see below).
E.2. ANIMAL
A series of comprehensive investigations in the United States on the effect of
60 Hz electric fields on the immune system of laboratory animals found no effect of
chronic exposure of rats and mice. Thus, it was concluded that power frequencies
have small or no effects on the immune systems of exposed animals. However, the
role of magnetic fields was not investigated.
In vitro tests have also been used to investigate the effect of EMF on the
immune system. The results suggest that the magnetic field alone or in combination
with an electric field can affect immune function. Magnetic fields have been reported
to inhibit the proliferation of immune cells, inhibit killing of abnormal cells by the
immune system, and to change the proliferative capacity of cells in culture.
Independent confirmation of the in vitro immune results would open a promising
research approach to investigate the possible link between exposure to EMF and
cancer. In addition, these tests would help to define effective exposure parameters
because some immune effects are reported to be frequency-specific and to have a
nonlinear exposure-response relation. Also, work with modulated high-frequency
radiation indicates that the low frequency of modulation is the biologically effective
frequency.
RECOMMENDATION: Research should attempt to replicate independently the
reported in vitro immune effects. In addition, immune responses in laboratory animals
exposed chronically to magnetic fields warrants investigation.
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CHAPTER IH
BIOPHYSICAL MECHANISMS
Studies of biophysical mechanisms are important because the research
examines both stages of the interaction process: (1) the nature of the initial
physical/chemical interaction of EMF with biological systems and (2) the expression of
the physical/chemical change as a biological response. This information is needed to
identify field parameters and biological responses important for health research.
There is a substantial body of literature upon which the investigation of
biophysical mechanisms can be based. It is apparent from this literature that EMF
should not be considered a single entity, but rather a generic class of physical
agents, similar to classes of chemicals. Because of the infinite number of potential
combinations of exposure parameters, such as frequency, intensity, modulation, etc.,
it is possible that more than one mechanism may account for the variety of EMF
effects. Examples of reported biological responses to electric and magnetic fields
include: (1) alteration of melatonin synthesis in the pineal gland, (2) response of brain
tissue, e.g., ion flux changes and behavioral changes, (3) intervention in biochemical
signalling across the plasma membrane, including second-messenger systems and
protein-kinase action pathways that are important in hormone-induced responses, (4)
alterations in circadian rhythms, (5) effects on developmental and immune processes,
(6) bone fracture healing, and (7) alterations in gene regulation that are implicated in
tumor production.
The biological effects of EMF can be best understood by a three-step
paradigm: transduction, amplification, and expression. In the first step, energy in
electric or magnetic fields must be converted, or transduced, into a biochemical or
biophysical change to affect a biological system. The second step, amplification, is
needed to boost the initial biophysical changes triggered by the field. Amplification
would then lead to the third step, expression of the effect as an obseivable entity in
the laboratory; expression could occur through a constellation of both intra- and
extra-cellular biological changes.
There are known and predicted physical constraints on the transduction step.
It is known that the photon energy of frequencies in the 0 to 500,000 Hz range is very
small; there is insufficient photon energy to break chemical bonds even if the
transduction step were 100% efficient. A second constraint is predicted by a simple
physical model describing how lower frequency electric fields interact with an isolated
small spherical cell. The model predicts that electric fields do not affect the cell
because the electric current flows around and not through the cell. These two
physical constraints, the low energy of EMF and the physical model prediction,
contribute to the controversy on the biological plausibility of EMF interactions with
living systems.
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Although the physical model predicts that the interior of the cell may not be
affected directly by an external electric field, biomolecules in or on the cell surface
may act as transducers of the field. Thus, the assumptions of the simple physical
model involving an isolated small spherical cell may not be applicable to more realistic
models of cells and tissues. (Additional discussion of the model and relevant
research needs are given in Chapter IV.E: EMF COUPLING TO BIOLOGICAL
OBJECTS.) More realistic models should include known cellular mechanisms such as
single molecular events in or on the cell's membrane that activate a cascade of
biochemical pathways within the cell. The reports that weak electric and magnetic
fields cause a variety of biological effects such as those summarized above implies
that transduction, amplification, and expression processes occur. Theoretical models
have been limited to electric-field interactions and have not addressed emerging
information demonstrating that the magnetic field can interact directly with cells to
cause altered responses.
Advances in understanding the principles of physical interaction of EMF with
biochemicals and living cells will further define both transduction and amplification.
Well-known biochemical amplification systems are probably also important to study in
the context of EMF. Expression appears to be primarily caused by the interplay of
various biological and biochemical systems. The following discussion of biophysical
mechanisms is presented in two parts: physical interactions and biological
interactions.
A. PHYSICAL INTERACTIONS
In the past, characterization of the physical interactions of EMF with biological
materials emphasized electric field interactions. Recently, this focus has changed
because data from epidemiological studies suggest that the magnetic component
may be the active agent. Thus, interest has shifted to the biological consequences of
the induced current resulting from a changing magnetic field. The biological influence
of these magnetically induced currents has not been well characterized. Magnetic
fields may also affect biological objects by acting directly through naturally occurring
magnetic dipoles in the body.
RECOMMENDATION: The interaction of magnetic fields with biological
systems needs to be explored to test the hypothesis that induced currents from
oscillating magnetic fields are causative. It is also important to establish whether the
effects of currents induced by electric fields differ categorically from those produced
by magnetic fields. These two issues, in addition to the evidence that magnetic fields
also interact with biological systems via magnetic dipoles (e.g., magnetic resonance
imaging), need to be developed and examined for physiological significance and risk
implications.
Other physical parameters establish and define the electric and magnetic
conditions that cause biological changes. The field frequency can influence the
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reaction sites and processes that are affected. The biological response as a function
of frequency can be used to identify the number and character of response sites.
The intensity of the field is equally important, because it can provide information about
kinetics of the response, which leads to specific biological processes. Furthermore,
signal shape and temporal dynamics, including high peak-intensity single or multiple
pulses, can have a substantial effect. In more limited situations, the presence of a
static magnetic field and its orientation with regard to alternating electric and magnetic
components has been shown to be an important feature of exposure.
RECOMMENDATION: Principles established in ultraviolet radiation biology,
which examines biological responses as functions of field intensity, frequency and
time, should form the basis for the investigation of the biological effects of EMF.
Adjunct studies should include examination of frequency bandwidth, signal shape
and modulation, and the involvement of the earth's magnetic field with frequency-
specific effects. Furthermore, the interaction of combined electric and magnetic fields
in biological systems should be examined.
Models of the interaction of EMF with biological objects can identify the critical
physical aspects of the exposure situation that should be tested. Models that
successfully predict effects can provide a basis for extrapolating exposure outcomes
to other situations and to focus research planning. To utilize modeling) capabilities,
measurements and analyses must be performed at various levels of biochemical and
biological organization. These range from measurements of the dielectric constant
and magnetic susceptibility, and analysis of the thermodynamic models of chemical
reactions, to analyses incorporating complex reactions in non-equilibrium systems.
The emphasis of such models should be on intensities of EMF that would provide a
basis to understand ambient exposure levels in terms of risk identification and
assessment.
RECOMMENDATION: Models of possible mechanisms of action are needed.
Such models could be molecular, thermodynamic, or non-equilibrium in nature.
Some of the models developed for the study of EMF at frequencies above 500,000 Hz
should be examined for relevance to lower frequencies. New models may also be
required.
B. BIOLOGICAL INTERACTIONS
The health effects of EMF are described in general terms in Chaipter II. This
chapter emphasizes those biological effects and models important to guide research
on mechanisms of interaction.
Changing magnetic fields, because they are more penetrating than electric
fields, can induce electric fields and currents throughout biological systems. At the
cellular level, several sites of interaction and biochemical processes have been
identified as likely targets. Both models and experimental results indicate that
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membrane interfaces are a primary site of transduction of field energy to biochemical
change. The principal membrane involved is thought to be the plasma membrane
because of its role in the transfer of biochemical information between the exterior and
interior of the cell. Potential sites of action in the membrane include membrane lipids
and membrane/protein interfaces such as ion channels, gap junctions, and hormone
receptors. Biochemical transmembrane signal-transduction processes are reported to
be involved in EMF effects. In addition to possible membrane interactions, magnetic
fields have been reported to affect gene regulation, presumably at the nucleic acid
level. This interaction may occur through alteration of intermediate complexes of DMA
and repressor/inducer or polymerase molecules. Thus, electric and magnetic fields
could differentially influence various cellular components and processes.
RECOMMENDATION: Research is needed to identify and characterize the
influence of EMF on plasma membrane sites such as ion channels, gap junctions, and
transmembrane signal-transduction processes. Reports of altered gene expression
should be independently confirmed, and where warranted, models should be
developed to establish the exposure conditions necessary to cause changes.
Response dynamics of cellular or biochemical systems can provide critical
insight into mechanisms of action. Linear or monotonic exposure-response kinetics
have been observed in some experiments but nonlinear exposure responses also
have been reported in cells and tissues capable of excitation. In the latter studies,
only certain ranges of frequencies and intensities produce effects, whereas other
ranges have no effect. These nonlinear "windowed" results may reflect the
involvement of a resonant or a dynamic system. Such results could provide the basis
for amplification to account for changes at ambient exposure conditions that more
classical analyses can not address.
RECOMMENDATION: Research should continue to examine the "windows" of
intensity, frequency, and pulse repetition rate that cause responses. These conditions
need to be incorporated into a coherent physical and biochemical interaction scheme
in order to establish mechanisms of action.
Another way to view biological interactions of EMF is at the tissue/organism
level, particularly in tissues with cells in electrical contact with one another. The fact
that electrical currents normally occur in bone during growth and fracture repair, in
soft tissue during healing and nerve regeneration, and in tissues during development
and differentiation suggest that exogenous or external currents might alter biological
systems. For example, magnetic fields have been used in over 250,000 human cases
to enhance reunion of fractured bones. Understanding critical field parameters and
mechanisms involved in the healing process allow potential benefits to be optimized
and potential adverse effects to be assessed.
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RECOMMENDATION: Research on mechanisms should include studies of
endogenous electric currents and studies of EMF exposure characteristics reported to
have therapeutic action in biological systems.
This discussion of biophysical mechanisms deals primarily with cellular and
subcellular levels of organization. Whole animal studies also provide the opportunity
to examine mechanisms of action, particularly between interacting tissue systems.
Research needs involving whole animals in the areas of cancer, reproduction and
development, the nervous system, and the immune system are described in Chapter
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CHAPTER IV
EXPOSURE ASSESSMENT
This chapter describes engineering and physical science research needed to
reduce uncertainties in the exposure assessment of EMF. Although exposure
assessment is the most verifiable, least controversial, and best supported area of EMF
research, the following six areas require study: (1) source identification and
characterization, (2) instrumentation and calibration; (3) environmental measurements
and documentation; (4) exposure modeling; (5) EMF coupling to biological objects;
and (6) laboratory exposure systems.
A. SOURCE IDENTIFICATION AND CHARACTERIZATION
Electric and magnetic fields at the power frequency of 60 Hz are generated by
the production, delivery, and use of electric power. Sources of public exposure
include power transmission and distribution lines, electric circuits in homes and public
buildings, electric grounding systems, and electric appliances (e.g., hair dryers,
electric blankets, and electric razors). Higher frequency fields as well as 60 Hz fields
are generated by switching transients and by devices such as fluorescent lights, light
dimmers, televisions, and VDTs. A number of civilian and military navigational and
communication transmitters generate fields at frequencies below 500,000 Hz. Existing
electrically powered transportation systems such as mass transit systems or electric
trains and proposed systems such as magnetically levitated trains and electric
automobiles may generate strong magnetic fields at frequencies above and below 60
Hz.
Although many EMF sources in our environment have been identified, in
general, the electric and magnetic fields associated with these sources have not been
well-characterized. An exception is high voltage transmission lines. Less effort has
been expended on the characterization of fields associated with distribution lines
which, in comparison to transmission lines, are much more extensive and are a much
more common source of exposure in residential areas. Even less effort has been
devoted to field characterization in the home, schools, and other public environments
where people may be in close proximity to electric circuits in buildings, appliances,
and office equipment. Thus, a program on exposure assessment of EMF should
include characterization of sources in the home, and sources in public environments
including distribution and transmission lines.
RECOMMENDATION: The identification of sources of electric and magnetic
field exposure should be an explicit part of a program of exposure assessment. The
identification process requires some preliminary effort in source characterization
involving exploratory measurement and/or basic physical understanding of field
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sources. Logging of activities and location during personal exposure monitoring
studies can assist in source identification. Maintenance of a source inventory or data
base should be a continuing effort.
B. INSTRUMENTATION AND CALIBRATION
Instrument development in the private sector as well as in the government has
been responsive to perceived needs for field measurements. In particular, a number
of survey instruments that measure electric and magnetic fields that vary with time are
now available, and miniaturized pocket-size recording instruments have been
developed recently. Also available are instruments for measuring static electric and
magnetic fields. In addition to the purpose for which they were developed, these
instruments can be used as a development base to assemble devices that measure
and record a wide range of field parameters as the need arises. Important
measurement issues include the definition of appropriate meter characteristics and the
routine availability of calibration services. The question of what field parameter(s) to
measure requires the collaborative interaction of specialists in engineering, the
physical sciences and the biological sciences.
RECOMMENDATION: Specifications and calibration procedures for
instrumentation should be developed to provide appropriate measurements of fields
for health effects studies. This can be accomplished by a continuing series of
workshops to evaluate and update the methodology.
C. ENVIRONMENTAL MEASUREMENT AND DOCUMENTATION
Electric and magnetic fields have been measured in selected residences and
outside environments to help resolve uncertainties in the interpretation of
epidemiological results. Although state and local governments, utilities, private firms,
and individuals are currently measuring EMF, these measurements are often
conducted without adequate supervision and expertise. In general, measurements
have not been appropriate for determining public exposures. Moreover, no central
data base on EMF measurements exists.
RECOMMENDATION: EMF measurement training must be emphasized for
individuals responsible for field measurements and efforts to develop protocols for
electric and magnetic field measurements should continue to be supported. A
program to sample exposure of the general population and high exposure subgroups
should be initiated with emphasis on monitoring exposure during daily activities and
in specific environments such as schools and residences. Concurrently, an effort
should be initiated to develop a central file of measurement data by collecting and
indexing available information. Development of a certification program lor field
measurements is not recommended at this time because of the difficulty of defining
field parameters associated with health effects.
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D. EXPOSURE MODELING
Mathematical models to estimate EMF exposure have been developed because
measurement of fields at all locations and under all conditions of interest is not
practical. Two types of models, theoretical and statistical, are described here. The
application of theoretical models usually involves a numerical solution in which field
parameters are determined as a function of current or voltage on electrical
conductors. The frequency of interest has a wavelength that is large compared to the
dimensions of the exposed object and thus models, such as "quasi-static" models,
can be applied to a range of frequencies. For example, the same model used to
calculate 60 Hz fields near a power line may be used to determine higher frequency
transient fields generated by the power line.
Theoretical models can only be developed for well-documented configurations
of electric conductors and field-perturbing materials. Thus, most theoretical modeling
of 60 Hz fields has been applied to power transmission lines because such models
can be constructed easily. Home environments with a number of sources have not
been modeled, although some models have been made of ground currents in water
pipes. Individual appliances in which the primary sources are transformers, motors,
or heating elements have not been modeled except for electric blankets. Computer
programs are being developed to estimate fields in the home.
Statistical modeling makes use of magnetic field measurements of home
appliances at nonstandardized distances from the device. These models are used to
develop statistical estimates of average exposure. Statistical modeling does not
predict individual exposures, but provides estimates for groups of the" population, e.g.,
school children and homemakers. This approach could benefit from characterization
of important microenvironments where exposures occur, such as schools and homes.
Although microenvironmental modeling is a relatively new concept, it is readily
adaptable to EMF exposure modeling.
A combination of statistical and theoretical approximations of measurement
data could be used to develop specific source, microenvironmental, and general
environmental models to estimate EMF exposure. For example, in the general
environment, application of Geographic Information System (GIS) technology could be
used to analyze and display EMF levels measured outdoors from sources such as
power lines as well as comparative EMF levels measured indoors (microenvironmental
measurements), and to calculate the distribution of exposed populations. A
measurement and source data base could be used to create exposure models to
estimate human exposure to EMF sources and to evaluate the effectiveness of control
technologies.
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RECOMMENDATION: Research on exposure modeling is needed to develop
more refined models to estimate exposures resulting from sources in the home and
the outside environment Modeling data are needed to complement EMF
measurement programs and to support quality control programs.
E. EMF COUPLING TO BIOLOGICAL OBJECTS
The previous sections in this chapter have dealt strictly with determining the
unperturbed electric and magnetic field in the absence of a human body. In the
presence of a body, the electric field immediately outside the body is strongly
perturbed and the intensity of the field may differ greatly from that of the unperturbed
field. In contrast to the electric field, the magnetic field that penetrates the body is
essentially unchanged. Both external electric and magnetic fields that vary with time
induce electric fields internally and electric current inside the body is proportional to
the induced internal electric field.
It is a common assumption that biological effects are related to the induced
currents. However, it is not known whether low-level effects are caused by the
internal electric fields and associated currents, by the magnetic field acting directly on
magnetic dipoles or on moving electric charges, or by other exposure parameters. If
effects are due only to the magnetic field acting directly, then further study of
inductive field coupling would not be a priority. If the effects are at least in part due
to induced electric fields and currents, then field coupling research is critical. Internal
electric fields depend strongly on the size and shape of the exposed body or system.
Thus, EMF coupling analysis is necessary when scaling internal electric fields or
currents from animal and in vitro exposures to human exposures.
Much of the work on EMF coupling analysis has involved a model in which the
sample is assumed to be electrically uniform and linear. The internal field values
obtained under these assumptions may be misleading. At lower frequencies, for
example, it is likely that currents flow principally around and not through cells.
Therefore, extracellular current density may be much greater than the average current
density calculated over a mass of tissue. Even if the details of a model seem
complete from a physical perspective, caution needs to be exercised in extrapolating
the results to a living organism because of the complexity of biological systems.
(More discussion of this topic is on pages 111-1 and III-2.) The reports that weak
electric and magnetic fields cause biological effects implies that processes such as
amplification and frequency and intensity selectivity can occur. The latter includes
"windowed" responses, that is, discrete bands of frequency and intensity that produce
effects separated by bands that have no effect.
RECOMMENDATION: Exploratory research is needed to develop models to
explain how electric and magnetic fields interact with cells and tissue to produce the
reported biological effects. Efforts in progress to develop better cellular and
anatomical models of the electric characteristics of human beings, laboratory animals,
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and in vitro samples need additional support. Work on implantable probes for
macroscopic and microscopic measurement of internal currents, voltages, and other
field parameters in living systems should continue. A long-term goal is the
development of a standard formula and unit of "dose" that is dependent on external
exposure fields and is proportional to biological effect and/or human health risk.
F. LABORATORY EXPOSURE SYSTEMS
If the process by which biological effects occur were simple and relatively
straightforward, then minor variations in EMF exposure conditions or other parameters
might not affect the results significantly. If such were the case, independent
confirmation of experimental results should be a relatively simple matter of repeating
the experiment. If, however, effects are a complex function of several exposure
conditions that may not be well controlled, then confirmation becomes problematic.
The history of EMF research implies that careful control of important experimental
variables is needed.
It is important that laboratory exposure systems allow potentially critical
exposure variables to be controlled. For example, the steady magnetic field of the
earth has been implicated as an important exposure variable. This implies that the
earth's geomagnetic field in the exposure system needs to be controlled or at least
measured and reported. Also, exposure can easily be correlated with vibrations,
switching noises, and possibly heat from the EMF source. Thus, experimental
procedures must ensure that the treatment of exposed samples is identical to control
samples except for the intended EMF exposure. Incidental EMF in the laboratory
must be considered also. For example, steady magnetic fields are produced by
magnetized tools and magnetic door latches, whereas time-varying magnetic fields
are produced by magnetic stirrers and incubator heating coils.
Basic biological research aimed at testing specific theoretical models requires
relatively simple field configurations that can be varied in a controlled manner.
However, environmental exposure to EMF is far more complex than exposure
regimens typically used in the laboratory. This complexity may be an important factor
in determining the risk of a given exposure. Once biological responses are
established as markers of risk, they can be used to test the effectiveness of simulated
EMF environments.
RECOMMENDATION: Continued care is required in the design, exposure
characterization, and operation of exposure systems, including characterization of the
earth's geomagnetic field. A need may develop for exposure systems that simulate
ambient EMF environments.
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CHAPTER V
CONTROL TECHNOLOGY
For purposes of this research needs document, the issue of EMF control
technology is almost entirely dependent upon the results of health effects and
biophysical research programs discussed earlier. Clearly, if the scientific research
finds no relationship between EMF exposure and adverse health effects, there is no
rationale, from a human health standpoint, to develop exposure controls for EMF.
Research on control technology for EMF exposure is, therefore, a low priority
research area within the overall EMF research needs discussed in this document.
Despite the lack of demonstrated need for control technologies at present, identifying
and characterizing EMF sources by measurement or modeling is important. This
procedure defines the framework for possible future research on control technologies,
by surveying the current state-of-the-science for EMF control technology.
The major source of environmental exposure to EMF is the electric power
system, which includes transmission lines, the distribution system (substations, lines,
and transformers), and electric circuits in residential and other buildings to provide
power to appliances and machinery. Although considerable effort has been focused
on the control of EMF from electric utility systems, little work has been done on
controlling fields generated by electrically powered appliances, tools, and other
devices.
Concurrent with the increase in concern for the possible health effects of EMF
exposure has been the development and widespread use of devices like the VDT.
These devices, along with emerging technologies, such as electric automobiles and
magnetically levitated transportation systems may emit EMF significantly different than
that emitted by transmission or distribution lines. Furthermore, unlike transmission
and distribution facilities, these technologies are not generally controlled by one
segment of the electric industry. Control technologies may, therefore, need to be
developed so as to be available to producers of products that emit EMF, should a
need to control EMF be demonstrated.
In most circumstances, the strength of low-frequency EMF decreases with
distance from the source. One simple mitigation approach is therefore to increase
separation distance (e.g., increase the right-of-way for a transmission line). At low
frequencies, such as 60 Hz, the electric and magnetic components of EMF are
essentially uncoupled and each field component must be considered separately by
control technologies. Thus, techniques that reduce electric fields may or may not
reduce magnetic fields, and vice versa. Three mitigation methods are known to be
effective regardless of frequency: shielding; proper design, location, and choice of
components; and filtering. These methods are described in more detail below.
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Shielding: One of the most important components of EMF control technology
is shielding. The shielding effectiveness of a given material is a measure of the
reduction in field intensity. Magnetic fields cannot be effectively shielded with readily
available and inexpensive materials, especially at 60 Hz, because most materials are
essentially transparent to magnetic fields. Effective magnetic shielding requires a
special class of metals called ferromagnetic or MU metals. On the other hand, low
frequency electric fields including 60 Hz fields can be shielded by readily available
and inexpensive metals. Thus, electric fields can be effectively shielded by metal
enclosures, but the equivalent magnetic enclosure is not as practical or effective.
Design. Location, and Component Choice: After shielding, proper grounding
of power distribution systems in buildings is of utmost importance to reduce EMF,
especially magnetic fields. Improper grounding, in addition to increasing exposure
per se, can reduce shielding effectiveness. Ground currents result when a structure,
such as a house, has multiple grounds such as water pipes, ducts, anchors, etc., in
addition to the ground at the electrical service panel. In an electric conductor, the
magnetic field is proportional to the current in the wire. Thus, strong ground currents
produce strong magnetic fields. A single grounding connection would avoid ground
current loops.
Another important consideration for the mitigation of EMF exposure is the
location of electric conductors. For example, consider two wires in close proximity to
one another. One wire supplies the current and the other wire conducts the return
current back to the source (required to complete the circuit). Since the supply and
return currents are in opposite directions, they produce equal but opposite magnetic
fields that cancel each other. This illustrates a very important principle: for every
supply current there is an equal and opposite return current. The location of the
return current is the most crucial determinant of the strength of the magnetic field.
Thus, when wires are closely spaced and the currents are fairly well balanced (no
ground loops), the magnetic fields will be small. For this reason twisted-pair wiring
and coaxial cables produce little or no external magnetic fields.
Filtering: Transformers and motors may produce EMF with harmonic content,
that is, frequencies that are multiples of the primary frequency, which is usually 60 Hz.
Secondary distribution lines, grounding circuits, and appliances might have harmonic
frequencies up to the 11 to 17th harmonic (660 to 1020 Hz). Solid-state electronic
devices can also produce high-frequency emissions. Capacitors can be installed at
appropriate locations on circuits and electrical equipment to filter or reduce the
harmonic or high-frequency waveforms. Transmission lines and primary distribution
lines have little or no harmonic content.
A. TFtANSMISSION AND DISTRIBUTION LINES
Control technology for transmission and distribution lines has been developed
and could be applied if warranted. These techniques focus on compaction and
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shielding of transmission conductors. Compaction is based on the principle that for
three-phase, balanced, conductor systems, the net field, electric or magnetic, of the
three phases is zero. A disadvantage of compaction is that it results in an increase in
electrical arcing, which affects system reliability. For situations in which compaction
was an ineffective control technology, shielding techniques have been developed that
feduce the electric field at the edge of the right-of-way by approximately tenfold.
Compaction techniques and super-compaction techniques (cable technology) that
have been developed include gas-insulated transmission lines, super-conducting
cables, and direct-current cable technologies. In cable or gas-insulated transmission
technologies, conductors are inside a metallic sheath in which the electric field exists
only between the conductors and the sheath; electric fields external to cable sheaths
are essentially zero. Super-compaction or cable circuits significantly reduce magnetic
fields because the magnetic fields from the phase conductors are self-canceling.
Distribution circuits, unlike transmission circuits, rarely contain three-phase
balanced conductor systems. There is usually a net current flow and, if this net
current does not return in the cable sheath or in an immediately adjacent neutral
circuit, then large current loops exist between the cable circuit and the actual return
path of the net current. Therefore, distribution cable circuits can produce fields that
are similar to that of overhead transmission lines, even though voltage and current
levels are much smaller.
Two states have developed programs related to EMF control technology for
transmission and distribution lines. One program will identify and characterize
sources of magnetic fields and investigate means of reducing magnetic field levels
associated with power delivery and use. The other program requires; the utility
industry to allocate funds for research on management of magnetic fields from
transmission and distribution lines. One goal is to develop design options for the
reduction of ground level EMF from power lines.
RECOMMENDATION: Control technology research In this area is supported or
conducted by organizations with long-standing interest in the design and
development of transmission and distribution facilities; this effort should continue. A
future strategy for the reduction of public exposure to EMF from transmission lines
might include generation of electricity at the site of use by new technologies
(photovoltaic systems and fuel cells) as they become available and competitive.
B. RESIDENCES AND SCHOOLS
EMF inside the home and schools can be emitted from appliances, the wiring
system, including the grounding, underground and overhead distribution lines, and
transmission lines. Most mitigation research has focused on the magnetic field
because electric fields are fairly easy to shield. As stated earlier, the" characterization
(measurement/calculation) and control of EMF are intimately related, consequently any
mitigation program should be accompanied by a characterization effort.
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The power frequency magnetic fields in the home have been characterized in a
limited fashion. In most of these studies, fields were measured at unstandardized
distances from power lines and appliances, and frequencies other than 60 Hz, in
addition to field transients and other field parameters, were largely ignored.
Therefore, exposure to EMF in the home has not been well characterized.
The magnetic fields emitted by some appliances have been measured as a
function of distance from the appliance, although such data may not be particularly
useful in developing magnetic field control strategies. The devices that produce
strong magnetic fields have been identified, but how the field is produced has not
been well characterized. A few appliances, especially electric blankets and heated
water beds, have been identified as important sources of magnetic field exposure
because of their close proximity to the body for long periods of time. Electric blanket
and waterbed heater manufacturers have responded by developing low magnetic field
appliances. Procedures for making the measurements and therefore for determining
the effectiveness of the control technology have not been standardized.
It is important to standardize measuring procedures in the home and other
environments. These measurements should take into account use of electric
appliances and living habits. Actual exposure of different parts of the body should be
determined. Research volunteers, wearing dosimetric devices on various parts of the
body, could be used to determine the exposure characteristics of different home and
school environments. For magnetic field control in the home, a standardized
measurement strategy that can be adjusted to account for appliance usage is
required. This should be accompanied by an effort to create models that can predict
magnetic field exposure on the basis of home design and appliance installation. In
such models, emphasis could be placed on the devices that produce the strongest
fields, on chronic exposure, on strong transient fields, or on other exposure
conditions deemed important. If the field characteristics of an appliance were well
documented, then simple engineering principles such as twisted-pair wiring or control
of circular current loops might be sufficient to control the magnetic fields. Localized
shielding techniques may be effective on small volume devices.
RECOMMENDATION: Source Characterization/Mitigation. To characterize the
EMF from appliances, three-dimensional field maps should be generated by
measurement or calculation. These fields should be given as magnitudes as a
function of frequency for steady-state operation. Magnitude and frequency changes,
as a function of duty cycle, as well as transient fields, should also be documented.
Once the field sources have been identified and characterized, the development of
control techniques can be addressed.
Mapping living and school environments requires a methodical way to
accommodate the time and space variability of fields that are produced by randomly
positioned current paths. These current paths exist in electric devices, the leads
supplying the devices, the internal and external electric power supply lines, and stray
ground return paths. Thus, measurement protocols are required that will realistically
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assess exposure levels for complicated EMF environments:
RECOMMENDATION: Grounding Practice Review: National arid local electric
safety codes have specific requirements for electric service grounding to control the
hazard of shock. Yet, these current paths, intentionally created, contribute
significantly to magnetic field exposure. The advantages in terms of magnetic field
management versus disadvantages from interference, reliability, and safety should be
carefully evaluated for delta (ungrounded), single-point grounded, and multi-
grounded circuits. From the point of consumer interface and in the consumer
environment, single-point grounding, ground potential shift, and interference with
ground-fault interrupt circuits need to be carefully evaluated.
RECOMMENDATION: Shielding. Research should be devoted to the
development of new materials to shield magnetic fields, e.g., a malleable high
permeability material. Concurrently extending the range of permeability as a function
of low magnetic field strength could be very useful if the purported health effects of
magnetic field exposures identified in epidemiological studies are confirmed.
Research into magnetically modified polymers may be fruitful, since both fabrication
and field strength problems may be solved by one material.
Active magnetic shielding approaches should be investigated. In this
approach, magnetic fields are purposely generated to cancel other magnetic fields.
C. SPECIAL CONSIDERATIONS
Existing mass transit systems (subways and electric trains) and emerging
technologies such as magnetically levitated trains, electric automobiles, and
superconducting magnetic energy storage devices require special consideration.
These systems can produce magnetic fields over large areas at different frequencies.
Passengers on magnetically levitated trains will be exposed to static fields and to
frequencies up to about 1,000 Hz. Existing engineering control technologies may not
be sufficient to significantly reduce exposure, if mitigation is needed.
Another device that merits special concern is the VDT. In addition to being
energized by 60 Hz power, VDTs can produce EMF at frequencies of up to 250,000
Hz. This higher-frequency EMF is generated by the deflection yoke that controls the
horizontal deflection system and produces images on the VDT screen, VDT
manufacturers, however, have begun to reduce fields by shielding techniques. Metal
enclosures are used to shield electric fields, while active magnetic shielding
techniques are used to reduce magnetic fields. In the latter case, purposely
generated magnetic fields act to cancel the magnetic field produced by the deflection
yoke in VDTs.
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RECOMMENDATION: Both research on field characterization and shielding
technologies may be required for special devices. Recently developed magnetic field
monitoring equipment may need to be adapted to measure the unique magnitude-
frequency-time course characteristics of these fields.
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CHAPTER VI
SUMMARY AND CONCLUSIONS
International and national organizations, industrial associations, federal and
state agencies, Congress, and the public have expressed concern about the potential
health effects of exposure to EMF. This document describes research needed to
reduce uncertainties regarding possible health effects of EMF; to define exposure
conditions in the home and public environments; and to determine what types of
control technologies may be necessary to mitigate EMF exposure. EMF in the
frequency range of 0 to 500,000 Hz is the focus of the proposed research because
this range includes EMF emitted from power lines and from commonly used devices,
such as video display terminals. Research recommendations are presented for (1)
health effects that specifically address cancer, reproduction and development, the
nervous system, and the immune system; (2) biophysical mechanisms; (3) exposure
assessment; and (4) possible control technology.
The literature on EMF is substantial but considerably diverse because of the
variety of biological systems tested and the complex nature of the physical agent.
Rather than a single entity, EMF is more appropriately considered a generic class of
physical agents, similar to classes of chemicals. Because of the complexity of EMF
exposure conditions, most studies of biological effects have been hypothesis-
generating studies rather than hypothesis-testing research and many of the reported
effects have not been independently confirmed. Many of the research
recommendations emphasize the need to attempt replication of key findings in
biological studies.
The relative priorities for EMF research are summarized in Table 1. Highest
priority was assigned to those issues where targeted research could potentially
provide decision makers with better information upon which to base decisions about
the likelihood and magnitude of potential health effects from EMF exposure.
High-priority research areas are cancer, exposure assessment, and biophysical
mechanisms of action. Cancer research is a top priority because there are more than
40 human studies on this subject and it is most important to independently confirm
key human cancer studies with improved protocols and exposure assessments. A
major concern with the epidemiological data is the dearth of information on factors
that may confound the estimate of risk; therefore, human studies should address this
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TABLE 1. RELATIVE PRIORITIES FOR EMF RESEARCH
RESEARCH AREAS
RELATIVE PRIORITY
HEALTH EFFECTS
Cancer
Reproductive and Developmental Effects
Nervous System Effects
Immune System Effects
BIOPHYSICAL MECHANISMS
EXPOSURE ASSESSMENT
CONTROL TECHNOLOGY
High
Medium
Medium
Low
High
High
Low
issue. Epidemiological studies should assess the influence of time-dependent factors
such as length of residency, duration of exposure, and latency on the risk of specific
types of cancer to (1) identify exposure-response relations with length of residency as
a surrogate for exposure and (2) to validate whether or not specific cancer types have
satisfied known latency and temporal requirements for causality. In addition, a
continuing examination of the potential role of EMF in carcinogenesis should be
conducted in laboratory studies of animals and in cells and tissues to discover the
basic nature of the exposure-response relation and the effective exposure conditions.
Exposure assessment research is also high priority because it is essential to
the successful interpretation of the biological response and is critically important for
risk assessment. In all types of biological studies, exposure data are needed to
define exposure-response relations and to establish cause-and-effect relations. In
particular, cancer research, both in human populations and in laboratory studies,
requires definitive exposure data to judge the validity of the suggested causal link
between EMF exposure and cancer. The recommendations for exposure assessment
research identify needs in the following areas: source identification and
characterization; instrumentation and calibration; laboratory exposure systems; and
EMF coupling to biological objects. The text on EMF coupling to biological objects
concludes with the recommendation for exploratory research on physical models to
explain how electric and magnetic fields interact with cells and tissue to produce the
reported biological effects. Research needs for two additional areas of exposure
assessment research, environmental measurements and exposure modeling, reflect
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the fact that exposure to EMF in the home and public environments has not been well
characterized. Measurement and modeling efforts are needed to define exposure to
EMF from appliances, wiring systems including transmission and distribution lines,
grounding systems, and electric transportation systems. These data are also needed
to define the direction for control technology research.
Another high priority research area is biophysical mechanisms. An
understanding of how EMF interacts with biological systems is needed to minimize
uncertainty in extrapolating laboratory data to human exposure situations and to
identify effective exposure parameters. In particular, mechanistic research is needed
to test hypotheses that (1) the cell membrane is the primary site of interaction with
EMF and (2) the magnetic field, not the electric field, is the critical exposure parameter
in cancer development. A number of biological effects, including those reported to
have therapeutic potential, offer promising avenues for research on mechanisms of
interaction of electric and magnetic fields.
Research on human reproductive effects should emphasize the need to
attempt replication of isolated reports of increased miscarriages and increased
malformations, and reports of increased incidence of nervous system cancer in
children whose fathers had occupations with potential EMF exposure. The results of
laboratory studies of nonmammalian models that exhibit developmental effects from
exposure to EMF should be used to design studies with mammals. Research on
reproductive and developmental effects is a medium priority, but confirmation of
developmental effects in human beings or in laboratory mammals would elevate the
priority.
Research on the nervous system should further examine physiological,
neurochemical, and behavioral endpoints in human subjects reported to be sensitive
to EMF. Laboratory studies on the effect of EMF on the behavior of laboratory
animals should emphasize learned tasks and drug interactions. A primary goal is the
identification of effective exposure conditions, such as possible differential effects of
electric and magnetic fields. The consistent finding that EMF affects rnelatonin
synthesis in the pineal gland should be further investigated. Neurophysiological,
neurochemical, and behavioral effects in both human studies and laboratory
experiments may be generally regarded as hypothesis-generating and do not merit
the level of concern for cancer such as childhood leukemia. For these reasons,
research on the nervous system is a medium priority.
Research on the immune system is a low priority because reported effects
occur primarily in isolated cellular systems. The research recommendations for
immunology emphasize the need to attempt independent replication of reported
cellular effects and the need for screening studies of laboratory animals exposed to
magnetic fields. This research is related to the important role of the immune system
in cancer prevention.
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The potential need for future controls to reduce risks from exposure to EMF is
the rationale for control technology research. This research is a low priority because
no cause-and-effect relation between human health risk and EMF exposure has been
established. However, products from the control technology research recommended
in this report may ultimately be needed to mitigate EMF exposure of the public. The
research needs address electric grounding issues important to public health and
recommend that the ongoing effort to develop control technology for transmission
and distribution systems be continued. Similarly, other control technology research
should be done in concert with health and exposure assessment research so that
mitigation procedures and devices will be available if warranted by future health risk
assessments of EMF exposure.
This report concludes with summaries of three recent developments concerning
EMF research. The first is a report on "Health Effects of Low-Frequency Electric and
Magnetic Fields" (June 1992) that was prepared for the Committee on Interagency
Radiation Research and Policy Coordination (CIRRPC), Office of Science and
Technology Policy. The document is a scientific review and evaluation of the literature
on health hazards of exposure to these fields. Although not a comprehensive report
on research needs, the CIRRPC report states that additional EMF research is
warranted and a number of research needs are expressed. In agreement with our
three high priority research areas, the CIRRPC report emphasized cancer studies
(particularly studies of childhood leukemia and brain tumors), exposure assessment,
and mechanistic studies. Other CIRRPC recommendations for research on
reproduction and the nervous system are in agreement with our medium priority
recommendations.
Second, members of Congress expressed their support for continued research
on the potential health effects of EMF in the U.S. House of Representatives
Conference Committee Report on the 1992 Energy and Water Development
Appropriations Act and recommended that EMF research conducted by the
government be coordinated through the Department of Energy. In response to this
recommendation, DOE initiated a process to establish a National EMF Research and
Communication Program that would strengthen the coordination of EMF-related
activities among Federal agencies, states, and private organizations. Recently, a draft
of the national program was circulated for comment (National EMF Research and
Communications Program, Draft Program Strategic Plan, November 17, 1992). The
penultimate draft of this EPA report on EMF research needs was used by many
participants in the DOE effort to develop a national EMF research program.
Third, the Energy Policy Act of 1992 authorizes EMF programs for both
research and public information. Funds for the programs are to be cost-shared by
Federal and non-Federal sources. The Act authorizes a total of $65,000,000 for fiscal
years 1993-1997 to conduct the EMF programs with not more than $1,000,000 per
fiscal year for information dissemination activities; contributions from non-Federal
sources will be solicited to offset at least 50% of the total funding for all EMF program
activities. Federal responsibilities for the two programs are shared by NIEHS and
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DOE. NIEHS has responsibility for human health effects programs and DOE has
responsibility for exposure assessment and control technology programs.
Research needs that address potential human health, exposures assessment,
and control technology issues have been identified for workers in the NIOSH report
and for the public in this EPA report. Both reports identify high priority research
needed to reduce uncertainties in the risk assessment of EMF. These? reports provide
documentation for the research that should be included in future EMF research
programs such as those authorized by the Energy Policy Act of 1992.
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BIBLIOGRAPHY
Nonthermal Effects of Nonionizing Radiation. National Research Council, Advisory
Committee on the Nonthermal Effects of Nonionizing Radiation, Final Report,
National Academy Press, Washington, D.C., 1986, 16 pp.
Nonionizing Radiation: Extremely Low Frequency Electric and Magnetic Fields. In
EPA Indoor Air Quality Implementation Plan. Appendix A. Preliminary Indoor
Air Pollution Information Assessment. EPA/600/8-87/014. June 1987. Section
2.10, pp. 2-162 to 2-167.
Electric and Magnetic Fields at Extremely Low Frequencies. Anderson, L.E., and W.T.
Kaune. In Nonionizing Radiation Protection, M.J. Suess, and D.A. Benwell-
Morison, Editors, World Health Organization, Regional Office for Europe,
Copenhagen, 1989. Chapters, pp. 175-243.
Biological Effects of Power Frequency Electric and Magnetic Fields - Biackground
Paper, U.S. Congress, Office of Technology Assessment, OTA-BP-E-53,
Washington, DC, U.S. Government Printing Office. May 1989.
Potential Health Effects of Electric and Magnetic Fields from Electric Power Facilities.
A report to the California State Legislature by the California Public Utilities
Commission in cooperation with the California Department of Health Services.
September 15, 1989.
Extremely Low Frequency Electromagnetic Fields: The Question of Cancer. Wilson,
B.W., R.G. Stevens, and L.E. Anderson, Editors. Battelle Press, Columbus,
Ohio, 1990.
Federal Research on the Potential Health Effects of Power Frequency Electromagnetic
Radiation; Statement to the Subcommittee on Natural Resources, Agriculture
Research, and Environment; Committee on Science, Space, and Technology;
U.S. House of Representatives. J.C. Lin, Chairman, Committee on Man and
Radiation, IEEE-United States Activities, 1828 L Street, N.W., Suite 1202,
Washington, DC. July 25, 1990.
Evaluation of the Potential Carcinogenicity of Electromagnetic Fields. U.S.
Environmental Protection Agency, External Review Draft, EPA/600/6-90/005B,
October 1990.
Proceedings of the Scientific Workshop on the Health Effects of Electric and
Magnetic Fields on Workers. P.J. Bierbaum and J.M. Peters, editors. U.S.
Department of Health and Human Services, National Institute for Occupational
Safety and Health, Publication No. 91-111, 1991.
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Draft Statement on Research Needs and Funding Priorities in the Area of Health
Effects of Power Line Frequency Electric and Magnetic Fields. Ad Hoc
Subcommittee on Power Line Frequency Electric and Magnetic Fields,
Committee on Man and Radiation, The Institute of Electrical and Electronics
Engineers, Inc. March 4, 1991.
Extremely Low Frequency Electromagnetic Fields and Cancer: Focus on Tumor
Initiation, Promotion, and Progression. A report prepared for the National
Electrical Manufacturers Association. E.F. Walborg, Jr., June 20, 1991,
pp. 99-100.
Electromagnetic Fields and the Risk of Cancer. Report of an Advisory Group on
Non-Ionising Radiation. J.W. Stather. Radiological Protection Bulletin, No.
131, pp. 8-14, 1992.
Review of "Evaluation of the Potential Carcinogenicity of Electromagnetic Fields"
(EPA/600/6-90/005B). Report to EPA Administrator from the EPA Science
Advisory Board, January 29, 1992.
Review of "A Research Strategy for Electric and Magnetic Fields: Research Needs
and Priorities" (EPA/600/9-91/016A). Report to EPA Administrator from the EPA
Science Advisory Board, May 11, 1992.
Health Effects of Low-Frequency Electric and Magnetic Fields. A report prepared by
an Oak Ridge Associated Universities Panel for the Committee on Interagency
Radiation Research and Policy Coordination, Office of Science and Technology
Policy, June 1992.
National EMF Research and Communications Program, Draft Program Strategic Plan,
Department of Energy, November 17, 1992.
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GLOSSARY
Ambient. Encompassing or surrounding area.
Behavior. Action that can be observed directly and studied in relation to antecedent
conditions. In animals, a distinction can be made between learned arid spontaneous
behaviors. Learning is a long-lasting change that results from experience with
environmental events and includes actions such as solving a maze for food.
Spontaneous behaviors are actions that do not result from a response} to direct
stimulation and include behaviors like locomotor activity.
Biomarker. An indicator of variation in cellular or physiological components or
processes, structures, or functions that are measurable in a biological system or
sample.
Biophysical mechanisms. Physical and/or chemical interactions of electric and
magnetic fields with biological systems.
Capacitor. A device made of two electrically conducting surfaces, separated by an
insulator that stores electric charge.
Carcinogen. A chemical, biological, or physical agent capable of producing tumor
growth.
Carcinogenic process. A series of stages at the cellular level culminating in the
development of cancer.
Chromosome. A very long molecule of DNA, complexed with protein, containing
genetic information.
Orcadian rhythms. Biological processes that have synchronized daily cycles of
approximately one day (24 hours).
Circuit. A closed conducting path for the flow of electric current.
Conductor. A material that allows the flow of electric charge, e.g., wires on
transmission lines.
Control technology. The application of engineering approaches to manage or
mitigate exposure to environmental agents, e.g., electric and magnetic fields.
Current. The flow of electric charge.
Cytotoxicity. Toxic effects in cells.
G-1
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DMA. Deoxyribonucleic acid. The nucleic acid molecule in chromosomes that
contains the genetic information.
Developmental effects. Effects in the developing offspring due to exposure before
conception (either parent), prenatally, or postnatally to the time of sexual maturation.
Developmental effects may be expressed at any time in the life span of the organism.
Developmental effects are a subset of reproductive effects.
Electric dipole. Two separated electric charges; a molecule (or other structure)
having the effective centers of positive and negative charges separated.
Electric field. A field describing the electrical force on a unit charge in space.
Electrical charges are a source of electric fields. The electric field from "a power line is
an alternating, 60 Hz field.
Electric and magnetic fields (EMF). Energy in the form of electric and magnetic fields.
In this report, the frequency range of interest for EMF is 0 to 500,000 Hz.
Embryo. The early stages in the developing organism in which organs and organ
systems are developing. For humans, this stage lasts between the second through
eighth weeks after conception.
EMF. See Electric and magnetic fields.
Endpoint. An observable or measurable biological, chemical, or functional event used
as an index of the effect of a chemical, physical, or biological agent on a cell, tissue,
organ, organism, etc.
Epidemiology. The study of the occurrence and distribution of a disease or
physiological condition in human populations and of the factors that influence this
distribution.
Exposure. The joint occurrence in space and time of an organism and the agent of
concern, expressed in terms of the environmental level of the agent.
Exposure assessment. Measurement or estimation of the magnitude, frequency,
duration, and route of exposure of an organism to environmental agents. The
exposure assessment also describes the nature of exposure and the size and nature
of the exposed populations, and is one of four steps in risk assessment.
Exposure-response relation. A relationship between exposure and the effect
produced by the exposure. Response can be expressed either as the severity of
injury or proportion of exposed subjects affected.
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Extrapolation. An estimate of response or quantity at a point outside the range of the
experimental data. Also refers to the estimation of a measured response in a different
species or by a different route than that used in the experimental study of interest
(i.e., species-to-species, route-to-route, acute-to-chronic, high-to-low).
Field. Any physical quantity that takes on different values at different points in space.
Frequency. The number of complete cycles of a periodic waveform pier unit time.
Frequency is expressed in Hertz (Hz), which is equivalent to one cycle per second.
Gene. The simplest complete functional unit in a DMA molecule. A linear sequence
of nucleotides in DMA that is needed to synthesize a protein and/or regulate cell
function.
Geomagnetic field. The earth's natural magnetic field.
Germ cell. A cell capable of developing into a gamete (ovum [egg] or sperm).
Groundling. The connection of a conductor to something that will accept excess
electrical charge, for example, the earth.
Hertz (Hz). One cycle per second.
Hormone. A chemical substance, formed in one organ or part of the body and
carried in the blood to another organ or part where it alters the functional activity, and
sometimes the structure, of one or more organs in a specific manner.
Immune system. The body's primary defense against abnormal growth of cells (i.e.,
tumors) and infectious agents such as bacteria, viruses, and parasites.
Insulator. A nonconductor of electrical charges.
In utero. In the uterus; unborn.
In vitro. Isolated from the living organism and artificially maintained, as in a test tube
or culture dish.
In vivo. Occurring within the whole living body.
Ion efflux. The movement of ions, charged atoms or molecules, from a sample into a
surrounding solution.
Latency. The time between exposure to an injurious agent and the manifestation of a
response.
Learned behavior. See behavior.
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Leukemia. A progressive, malignant disease of the blood-forming tissues, marked by
an excessive number of white blood cells and their precursors.
Lympnoma. Any abnormal growth (neoplasm) of the lymphoid tissues. Lymphoma
usually refers to a malignant growth and thus is a cancer.
Magnetic dipole. Two separated magnetic poles; an object such as a permanent
magnet, particle, or current loop, that gives rise to a magnetic field. The object acts
as if it consists of two magnetic poles of opposite sign separated by a small distance.
Magnetic field. A field describing the force experienced by magnetic objects or
moving electrical charges in space.
Malformation. A permanent structural change in a developing organism that may
adversely affect survival, development, or function.
Mechanisms. See Biophysical mechanisms.
Messenger RNA. See RNA.
Metabolism. The biochemical reactions by which energy is made available for the use
of an organism from the time a nutrient substance enters, until it has been utilized and
the waste products eliminated.
Microenvironment The immediate local environment of an organism.
Mitosis. Cellular and nuclear division that involves duplication of the chromosomes of
a parent cell and formation of two daughter cells.
Model. (1) Mathematical model. A mathematical representation of a natural system
intended to mimic the behavior of the real system, allowing description of empirical
data, and predictions about untested states of the system. (2) Biological model. A
condition or disease in animals similar to the condition or disease in human beings.
Modulation. The process of varying the amplitude, frequency, or phase of EMF.
Neurotransmrtter. A chemical substance that transmits nerve impulses across the
space between nerve endings called the synapse.
Oncogene. A mutation of a naturally occurring gene involved in growth regulation
that results in uncontrolled growth. Oncogenes are associated with the development
of some forms of cancer.
Photon. A particle of electromagnetic energy.
Plasma membrane. The membrane surrounding plant and animal cells.
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Power. The time rate at which work is done. Electrical power is proportional to the
product of current and voltage.
Proliferation. Production of new cells through the process of cell division.
Promotion. The second hypothesized stage in a multistage process of cancer
development. The conversion of initiated cells into tumorigenic cells.
Reproductive effects. Effects on reproduction which may include, but not be limited
to, alterations in sexual behavior, onset of puberty, fertility, gestation, parturition,
lactation, pregnancy outcomes, premature reproductive senescence, or modifications
in other functions that are dependent on the integrity of the reproductive system.
Developmental effects are a subset of reproductive effects.
Risk assessment. The scientific activity of evaluating the toxic properties of an
environmental agent and the conditions of human exposure to it in order to ascertain
the likelihood that exposed humans will be adversely affected, and to characterize the
nature of the effects they may experience. May contain some or all of the following
four steps:
Hazard identification - The determination of whether a particular agent is or is
not causally linked to particular health effect(s).
Dose-response assessment - The determination of the relation between the
magnitude of exposure and the probability of occurrence of the health effects
in question.
Exposure assessment - The determination of the extent of human exposure.
Risk characterization - The description of the nature and often the magnitude of
human risk, including attendant uncertainty.
RNA. Ribonucleic acid. Messenger RNA, the nucleic acid in cells that is the template
for the sequential ordering of amino acids during protein synthesis, is synthesized in
the nucleus of the cell during the process of transcription.
Spontaneous behavior. See behavior.
Static fields. Electric and magnetic fields that do not vary in intensity or strength with
time.
Survey instrument. A portable instrument capable of measuring the strength of
electric and magnetic fields.
Time-varying fields. Electric and magnetic fields that change in intensity or strength
with time. Examples include 60 Hz, modulated, and transient fields.
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Transcription. The cellular process in which messenger RNA is synthesized, i.e., the
process in which the genetic information in DMA is transcribed in the form of a single
molecule of messenger RNA.
"Windowed" responses. Effects found within bands or ranges of frequency or
intensity separated by bands or ranges without effect; nonlinear exposure-response
relations.
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APPENDIX A:
RESEARCH RECOMMENDATIONS
1. HEALTH EFFECTS
A. METHODOLOGIC ISSUES FOR EPIDEMIOLOGY
RECOMMENDATION: EMF exposure of the public should be more fully
characterized to identify common and special exposure situations. Exposure data are
needed for statistically valid population estimates and to help identify 1he field
parameters that may be biologically active. The development and validation of
personal external dosimetry methods to document and evaluate the e:
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RECOMMENDATION: Human clinical studies should try to identify possible
biomarkers of EMF exposure in the carcinogenic process, including alterations in
oncogenes and tumor-suppressor genes and ornithine decarboxylase activity.
2. ANIMAL STUDIES
RECOMMENDATION: The potential role of EMF in carcinogenesis should be
studied in the laboratory (both in vitro and in whole animals) to discover the basic
nature of the field-dependence of effects. Gene expression, growth of transformed
cells, and intracellular reactions associated with chemical signalling are areas of
special interest.
RECOMMENDATION: Independent replication should be attempted of the
finding that magnetic fields appeared to increase the rate of tumor development in
mice chemically predisposed to cancer development. If similar results are found,
studies should be done to define the exposure-response relation and to investigate
mechanism(s) of interaction. Cancer studies in laboratory animals are needed to test
the hypothesis that there is an association between EMF exposure and breast cancer.
C. REPRODUCTIVE AND DEVELOPMENTAL EFFECTS
1. HUMAN STUDIES
RECOMMENDATION: Epidemiological studies should attempt to replicate
reported reproductive and developmental effects of EMF, especially any possible
relation between the use of electrically-heated beds and adverse pregnancy outcome.
Studies should be designed to include EMF exposure assessment, identify factors
other than EMF that may affect the study conclusions, identify relevant exposure
periods, and be guided by our understanding of reproductive and developmental
effects in laboratory animals.
2. ANIMAL STUDIES
RECOMMENDATION: Research should attempt to confirm independently
reported reproductive effects in mammals. Developmental studies with standard
laboratory models should employ exposure conditions reported to be effective in
nonrnammalian systems. The relevance of developmental effects Jn nonmammalian
embryo models to permanent changes in mammals should be explored because of
the significance to epidemiological findings.
RECOMMENDATION: The reported association of increased cancer rates in
human offspring, or an association of any effect in offspring, to paternal exposure
requires a mechanistic link via paternal germ cell changes. Heritable genetic changes
in germ cells, as reported in epidemiological studies, need to be studied in laboratory
animals.
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D. NERVOUS SYSTEM EFFECTS
1.
HUMAN STUDIES
RECOMMENDATION: Work should continue with human subjects in controlled
laboratory settings where exposure to real and sham fields occur under double-blind
conditions. Physiological and behavioral endpoints previously reported to be
sensitive, as well as those reported in animal studies, should be monitored before,
during, and after exposure to EMF. Because of the suspected role of iaftered
melatonin rhythms in clinical disorders and in cancer, other studies should determine
if EMF can after the circadian pattern of melatonin and its metabolites in body fluids.
Related research should assess the role of melatonin, if any, in the suppression of
cancer in human beings. Particular attention should be directed to whether the rate
of activation and deactivation of the field (intermittent exposure) has a more marked
effect than continuous application.
2. ANIMAL STUDIES
RECOMMENDATION: Studies of EMF effects on behavior of laboratory
animals should emphasize learned tasks and drug interactions. Other work should
determine whether the effects of EMF on circadian rhythms and neuroc:hemical levels
are significant in related areas such as behavior and cancer. The consistent finding
that EMF affects melatonin synthesis should be the focus of studies to determine the
sites and mechanisms of interaction. Related research should better define the role of
melatonin in suppression of cancer in animals. A primary goal of research on EMF
and the nervous system is to define causative exposure conditions; pai-ticular
attention should be given to the possible differential effects of electric versus magnetic
fields.
E. IMMUNE SYSTEM EFFECTS
1. HUMAN STUDIES
RECOMMENDATION: No research recommendation is given for this category
because of the lack of data on immune system effects in human beings and the
preliminary state of knowledge of such effects in both in vitro and in vivo laboratory
animal studies.
2. ANIMAL STUDIES
RECOMMENDATION: Research should attempt to replicate indespendently the
reported in vitro immune effects. In addition, immune responses in laboratory animals
exposed chronically to magnetic fields warrants investigation.
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II. BIOPHYSICAL MECHANISMS
A. PHYSICAL INTERACTIONS
RECOMMENDATION: The interaction of magnetic fields with biological
systems needs to be explored to test the hypothesis that induced currents from
oscillating magnetic fields are causative, ft is also important to establish whether the
effects of currents induced by electric fields differ categorically from those produced
by magnetic fields. These two issues, in addition to the evidence that magnetic fields
also interact with biological systems via magnetic dipoles (e.g., magnetic resonance
Imaging), need to be developed and examined for physiological significance and risk
Implications.
RECOMMENDATION: Principles established in ultraviolet radiation biology,
which examines biological responses as functions of field intensity, frequency and
time, should form the basis for the investigation of the biological effects of EMF.
Adjunct studies should include examination of frequency bandwidth, signal shape
and modulation, and the involvement of the earth's magnetic field with frequency-
specific effects. Furthermore, the interaction of combined electric and magnetic fields
in biological systems should be examined.
RECOMMENDATION: Models of possible mechanisms of action are needed.
Such models could be molecular, thermodynamic, or non-equilibrium in nature.
Some of the models developed for the study of EMF at frequencies above 500,000 Hz
should be examined for relevance to lower frequencies. New models may also be
required.
B. BIOLOGICAL INTERACTIONS
RECOMMENDATION: Research is needed to identify and characterize the
influence of EMF on plasma membrane sites such as ion channels, gap junctions, and
transmembrane signal-transduction processes. Reports of altered gene expression
should be independently confirmed, and where
warranted, models should be developed to establish the exposure conditions
necessary to cause changes.
RECOMMENDATION: Research should continue to examine the "windows" of
intensity, frequency, and pulse repetition rate that cause responses. These conditions
need to be incorporated into a coherent physical and biochemical interaction scheme
in order to establish mechanisms of action.
RECOMMENDATION: Research on mechanisms should include studies of
endogenous electric currents and studies of EMF exposure characteristics reported to
have therapeutic action in biological systems.
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III. EXPOSURE ASSESSMENT
A. SOURCE IDENTIFICATION AND CHARACTERIZATION
RECOMMENDATION: The identification of sources of electric and magnetic
field exposure should be an explicit part of a program of exposure assessment. The
identification process requires some preliminary effort in source characterization
involving exploratory measurement and/or basic physical understanding of field
sources. Logging of activities and location during personal exposure monitoring
studies can assist in source identification. Maintenance of a source inventory or data
base should be a continuing effort.
B.
INSTRUMENTATION AND CALIBRATION
RECOMMENDATION: Specifications and calibration procedures; for
instrumentation should be developed to provide appropriate measurements of fields
for health effects studies. This can be accomplished by a continuing sseries of
workshops to evaluate and update the methodology.
C. ENVIRONMENTAL MEASUREMENT AND DOCUMENTATION
RECOMMENDATION: EMF measurement training must be emphasized for
individuals responsible for field measurements and efforts to develop protocols for
electric and magnetic field measurements should continue to be supported. A
program to sample exposure of the general population and high exposure subgroups
should be initiated with emphasis on monitoring exposure during daily activities and
in specific environments such as schools and residences. Concurrently, an effort
should be initiated to develop a central file of measurement data by collecting and
indexing available information. Development of a certification program for field
measurements is not recommended at this time because of the difficulty of defining
field parameters associated with health effects.
D. EXPOSURE MODELING
RECOMMENDATION: Research on exposure modeling is needed to develop
more refined models to estimate exposures resulting from sources in the home and
the outside environment. Modeling data are needed to complement EMF
measurement programs and to support quality control programs.
E. EMF COUPLING TO BIOLOGICAL OBJECTS
RECOMMENDATION: Exploratory research is needed to develop models to
explain how electric and magnetic fields interact with cells and tissue to produce the
reported biological effects. Efforts in progress to develop better cellular and
anatomical models of the electric characteristics of human beings, laboratory animals,
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and in vitro samples need additional support. Work on implantable probes for
macroscopic and microscopic measurement of internal currents, voltages, and other
field parameters in living systems should continue. A long-term goal is the
development of a standard formula and unit of "dose" that is dependent on external
exposure fields and is proportional to biological effect and/or human health risk.
F. LABORATORY EXPOSURE SYSTEMS
RECOMMENDATION: Continued care is required in the design, exposure
characterization, and operation of exposure systems, including characterization of the
earth's geomagnetic field. A need may develop for exposure systems that simulate
ambient EMF environments.
IV. CONTROL TECHNOLOGY
A. TRANSMISSION AND DISTRIBUTION UNES
RECOMMENDATION: Control technology research in this area is supported or
conducted by organizations with long-standing interest in the design and
development of transmission and distribution facilities; this effort should continue. A
future strategy for the reduction of public exposure to EMF from transmission lines
might include generation of electricity at the site of use by new technologies
(photovoltaic systems and fuel cells) as they become available and competitive.
B. RESIDENCES AND SCHOOLS
RECOMMENDATION: Source Characterization/Mitigation. To characterize the
EMF from appliances, three-dimensional field maps should be generated by
measurement or calculation. These fields should be given as magnitudes as a
function of frequency for steady-state operation. Magnitude and frequency changes,
as a function of duty cycle, as well as transient fields, should also be documented.
Once the field sources have been identified and characterized, the development of
control techniques can be addressed.
Mapping living and school environments requires a methodical way to
accommodate the time and space variability of fields that are produced by randomly
positioned current paths. These current paths exist in electric devices,, the leads
supplying the devices, the internal and external electric power supply lines, and stray
ground return paths. Thus, measurement protocols are required that will realistically
assess exposure levels for complicated EMF environments.
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RECOMMENDATION: Grounding Practice Review. National and local electric
safety codes have specific requirements for electric service grounding to control the
hazard of shock. Yet, these current paths, intentionally created, contribute
significantly to magnetic field exposure. The advantages in terms of magnetic field
management versus disadvantages from interference, reliability, and safety should be
carefully evaluated for delta (ungrounded), single-point grounded, andi multi-
grounded circuits. From the point of consumer interface and in the consumer
environment, single-point grounding, ground potential shift, and interference with
ground-fault interrupt circuits need to be carefully evaluated.
RECOMMENDATION: Shielding. Research should be devoted to the
development of new materials to shield magnetic fields, e.g., a malleable high
permeability material. Concurrently extending the range of permeability as a function
of low magnetic field strength could be very useful if the purported health effects of
magnetic field exposures identified in epidemiological studies are confirmed.
Research into magnetically modified polymers may be fruitful, since both fabrication
and field strength problems may be solved by one material.
Active magnetic shielding approaches should be investigated. In this
approach, magnetic fields are purposely generated to cancel other magnetic fields.
C. SPECIAL CONSIDERATIONS
RECOMMENDATION: Both research on field characterization arid shielding
technologies may be required for special devices. Recently developed magnetic field
monitoring equipment may need to be adapted to measure the unique magnitude-
frequency-time course characteristics of these fields.
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APPENDIX B:
ACKNOWLEDGEMENTS
This report reflects the multidisciplinary talents and generous support of many
of my colleagues. Their timely, high quality contributions made it possible to meld
together the broad range of EMF research needs in time to meet the schedule for
submission of the penultimate draft to the Science Advisory Board's Nonlonizing
Electric and Magnetic Fields Subcommittee.
In particular, Carl Blackman and Diane Milier, contributed an extraordinary
amount of their time and expertise. They served as Special Assistants and were
especially helpful with the revision of the external review draft. This work was in
addition to their contributions of draft text on biophysical mechanisms (C. Blackman)
and the nervous system (D. Miller). Many times I sought their expertise and counsel
to help guide the project. Their willingness to help, sometimes on short notice that
necessitated rescheduling their work, is genuinely appreciated.
The multidisciplinary topics discussed in the chapter on health effects required
the assistance of several individuals. Those deserving special thanks for drafting text
and providing expert review are David Bayliss, Ezra Berman, Rebecca Calderon,
Doreen Hill, Robert McGaughy, Diane Miller, and Sherry Selevan.
A special acknowledgement goes to Edwin Mantiply for drafting the text on
exposure assessment. Ronald Spiegel was responsible for the information on control
technology. Norbert Hankin and James Walker provided very helpful technical
assistance with both topics.
The penultimate draft incorporated comments from 45 experts in other
organizations who responded to our request for technical review of the external
review draft. These experts, who volunteered their time and effort, are especially
appreciated because their reviews helped us focus on the important EMF research
needs and priorities described in this report.
Joe A. Elder, Ph.D.
Editor
- "J •fru.S. GOVERNMENT PRINTING OFFICE: 1993 - 750-002/60133
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