Extremely low frequency (ELF) fields (EHC 35, 1984)

INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

ENVIRONMENTAL HEALTH CRITERIA 35

EXTREMELY LOW FREQUENCY (ELF) FIELDS

This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.

Published under the joint sponsorship of
the United Nations Environment Programme,
the, World Health Organization, and the
International Radiation Protection Association

World Health Orgnization
Geneva, 1984

Reprinted 1992

ISBN 92 4 154095 8

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CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR EXTREMELY LOW FREQUENCY (ELF) FIELDS

1. SUMMARY AND RECOMMENDATIONS

1.1. Purpose and scope
1.2. Sources of exposure
1.3. Clinical applications
1.4. Field measurement and dosimetry
1.5. Characteristics of biophysical interactions
1.6. In vitro studies
1.7. Experimental animal studies
1.8. Effects on man
1.9. Exposure standards
1.10. Conclusions and recommendations

2. PHYSICAL CHARACTERISTICS, MEASUREMENT, AND DOSIMETRY

2.1. Quantities and units
2.2. Computational methods and measurements of ELF
electric fields
2.3. Field polarization and homogeneity
2.4. Energy carried by the field
2.5. Determination of ELF field exposure
2.6. The physical interaction of man and laboratory
animals with electric fields
2.6.1. Surface fields and internal current
density
2.6.2. Capacitive coupling of the electric
field to man and laboratory animals
2.6.3. Shock currents
2.7. Dosimetry and scaling between laboratory animals
and man
2.8. Magnetic induction of electric fields

3. NATURAL BACKGROUND AND MAN-MADE ELF FIELDS

3.1. Natural electric fields
3.2. Natural magnetic fields
3.3. Man-made sources of ELF
3.3.1. High-voltage transmission lines
3.3.2. Electric fields near transmission lines and substations
3.3.3. Magnetic fields near transmission lines
3.3.4. Man-made ELF fields in the home, workplace,
and public premises
3.4. Corona and noise effects of transmission lines
3.5. Electric shock
3.6. Interference of ELF fields with implanted
cardiac pacemakers

4. MECHANISMS OF INTERACTION

4.1. Biophysical mechanisms of electric field
interactions
4.2. Biophysical mechanisms of magnetic field
interactions

5. BIOLOGICAL EFFECTS IN CELLS AND ANIMALS

5.1. Cellular and membrane studies
5.2. Neurophysiological studies in animals
and animals tissues
5.3. Behavioural studies
5.4. Sensory phenomena
5.5. Effects on the haematopoietic system in animals
5.6. Cardiovascular effects
5.7. Effects on endocrinology and blood chemistry
5.8. Effects on the immune system
5.9. Growth and development studies
5.10. Reproduction and fertility
5.11. Mutagenesis
5.12. Circadian rhythms in animals
5.13. Bone growth and repair
5.14. The problems of extrapolating animal exposure
data to human beings

6. HUMAN STUDIES

6.1. Sources of information
6.2. Study design
6.3. Health status of occupationally-exposed
human beings
6.4. Studies on the general population
6.4.1. Studies on inhabitants of areas in the
vicinity of HV-lines
6.5. Studies on human volunteers
6.6. Summary

7. HEALTH RISK EVALUATION

8. STANDARDS AND THEIR RATIONALES

9. PROTECTIVE MEASURES

9.1. Goals
9.2. Groups to be protected
9.3. Protection rationale

GLOSSARY OF TERMS USED IN THE DOCUMENT

REFERENCES

APPENDIX I

APPENDIX I REFERENCES

NOTE TO READERS OF THE CRITERIA DOCUMENTS

While every effort has been made to present information in
the criteria documents as accurately as possible without
unduly delaying their publication, mistakes might have
occurred and are likely to occur in the future. In the
interest of all users of the environmental health criteria
documents, readers are kindly requested to communicate any
errors found to the Manager of the International Programme on
Chemical Safety, World Health Organization, Geneva,
Switzerland, in order that they may be included in corrigenda,
which will appear in subsequent volumes.

In addition, experts in any particular field dealt with in
the criteria documents are kindly requested to make available
to the WHO Secretariat any important published information
that may have inadvertently been omitted and which may change
the evaluation of health risks from exposure to the
environmental agent under examination, so that the information
may be considered in the event of updating and re-evaluation
of the conclusions contained in the criteria documents.

WHO/IRPA TASK GROUP ON EXTREMELY LOW FREQUENCY (ELF) FIELDS

Members

Dr J. Bonnell, Central Electricity Generating Board, London,
England

Dr B. Bosnjakovic, Ministry of Housing, Physical Planning, and
Environment, Rijswijk, The Netherlands^a

Dr J. Cabanes, Medical Committee, Electricité de France - Gaz
de France, Paris, France

Dr M. Grandolfo, Laboratory of Radiation, Institute of Public
Health, Rome, Italy

Dr B. Knave, Research Department, National Board of
Occupational Safety and Health, Solna, Sweden

Dr J. Kupfer, Occupational Hygiene Standardization, Central
Institute of Occupational Medicine, Berlin, German
Democratic Republic (Vice-Chairman)

Dr R. Phillips, Biology Department, Pacific Northwest
Laboratory, Richland, Washington, USA

Dr A. Portela, Institute of Biophysical Research, National
Council of Scientific and Technical Research (CONICET),
Buenos Aires, Argentin^a

Dr M. Repacholi, Royal Adelaide Hospital, Adelaide, South
Australia (Chairman)^a

Dr A. Sheppard, J.L. Pettis Memorial Hospital, Loma Linda,
California, USA (Rapporteur)

IRPA Secretariat

Mrs A. Duchêne, Commissariat à l'Energie Atomique, Déparement
de Protection Sanitaire, Fontenay-aux-Roses, France^b

WHO Secretariat

Mr G. Ozolins, Manager, Environmental Hazards and Food
Protection, Division of Environmental Health, WHO, Geneva,
Switzerland (Secretary)

Dr M. Shore, National Center for Devices and Radiological
Health, Food and Drug Administration, Rockville, Maryland,
USA (Temporary Adviser)

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^a Members of the International Non-Ionizing Radiation
Committee of IRPA.
^b Scientific Secretary of the International Non-Ionizing
Radiation Committee of IRPA.

Electric and magnetic field quantities and units in the SI system
-------------------------------------------------------------------
Quantity Symbol Unit
-------------------------------------------------------------------
Frequency f hertz (Hz)

Electric field strength E volt per metre (V/m)

Electric flux density D coulomb per square metre (C/m²)

Capacitance C farad (F)

Current I ampere (A)

Current density J ampere per square metre (A/m²)

Electric charge Q coulomb (C = A x s)

Impedance Z ohm (omega)

Volume charge density p coulomb per cubic metre (C/m³)

Magnetic field strength H ampere per metre (A/m)

Magnetic flux density B tesla^a (1 T = 1 Wb/m²)
(weber per square metre)

Permittivity epsilon^b farad per metre (F/m)

Permittivity of vacuum epsilon_o epsilon_o = 8.854 x 10^-12 F/m

Permeability µ henry per metre (H/m)

Permeability of vacuum µ_o µ_o = 12.57 x 10^-7 H/m

Time t seconds (s)
-------------------------------------------------------------------
^a 1 T = 10⁴ Gauss (G), a unit in the CGS unit system.
^b Designates a complex number.

ENVIRONMENTAL HEALTH CRITERIA FOR EXTREMELY LOW FREQUENCY (ELF)
FIELDS

Following the recommendations of the United Nations Conference
on the Human Environment held in Stockholm in 1972, and in response
to a number of World Health Resolutions (WHA23.60, WHA24.47,
WHA25.58, WHA26.68), and the recommendation of the Governing
Council of the United Nations Environment Programme, (UNEP/GC/10, 3
July 1973), a programme on the integrated assessment of the health
effects of environmental pollution was initiated in 1973. The
programme, known as the WHO Environmental Health Criteria
Programme, has been implemented with the support of the Environment
Fund of the United Nations Environment Programme. In 1980, the
Environmental Health Criteria Programme was incorporated into the
International Programme on Chemical Safety (IPCS). The result of
the Environmental Health Criteria Programme is a series of criteria
documents.

A joint WHO/IRPA Task Group on Environmental Health Criteria
for Extremely Low Frequency Fields met in Geneva from 5 to 9 March
1984. Mr. G. Ozolins, Manager, Environmental Hazards and Food
Protection, opened the meeting on behalf of the Director-General.
The Task Group reviewed and revised the draft criteria document,
made an evaluation of the health risks of exposure to extremely low
frequency electromagnetic fields, and considered rationales for the
development of human exposure limits.

The International Radiation Protection Association (IRPA)
initiated activities concerned with non-ionizing radiation by
forming a Working Group on Non-Ionizing Radiation in 1974. This
Working Group later became the International Non-Ionizing Radiation
Committee (IRPA/INIRC) at the IRPA meeting in Paris in 1977. The
IRPA/INIRC reviews the scientific literature on non-ionizing
radiation and makes assessments of the health risks of human
exposure to such radiation. Based on the Environmental Health
Criteria documents developed in conjunction with WHO, the
IRPA/INIRC recommends guidelines on exposure limits, drafts codes
of safe practice, and works in conjunction with other international
organizations to promote safety and standardization in the non-
ionizing radiation field.

This document is a combination of drafts prepared by Dr A.
Sheppard and Dr W.R. Adey (J.L. Pettis Memorial Veterans
Administration Hospital, Loma Linda, California), Dr M.G. Shandala,
Dr V. Akimenko and colleagues (A.N. Marzeev Institute of General
and Community Hygiene, Kiev, USSR), and Dr P. Czerski and Mr J.C.
Villforth (National Center for Devices and Radiological Health, US
Department of Health and Human Services, Rockville, Maryland). The
drafts were integrated at working group meetings in Grenoble
(1980), and Paris (1982). A subsequent draft of the document was
prepared by Dr P. Czerski, Dr B. Bosnjakovic, Dr M. Repacholi, Dr
V. Akimenko, Dr M. Grandolfo, Dr J. Cabanes, and Mrs A. S. Duchêne
at the WHO/IRPA working group in Paris in March 1983. A final
draft, incorporating the comments of reviewers from WHO National
Focal Points and many international experts, was prepared by Dr M.

Repacholi and Dr A. Sheppard in Geneva in December 1983.
Scientific editing of the draft, approved by the WHO/IRPA Task
Group in March 1984, was completed by Dr M. Repacholi and Dr A.
Sheppard. The efforts of all who helped in the preparation and
finalization of the document are gratefully acknowledged.

Subjects briefly reviewed, with particular reference to power
frequency (50 and 60 Hz) electric fields, include: the physical
characteristics of ELF fields; measurement techniques and
dosimetry; sources and applications of ELF; levels of exposure from
devices in common use; mechanisms of interaction; biological
effects in animals and animal tissues; human studies; health risk
evaluation and guidance on the development of protective measures
such as regulations or safe-use guidelines.

Although the emphasis of this document is on the effects of ELF
electric fields at 50 and 60 Hz, effects of ELF magnetic fields are
briefly mentioned since they always exist when electric current
flows. However, the specific problems related to static and time-
varying magnetic fields will be the subject of a separate
environmental health criteria document.

Health agencies and regulatory authorities are encouraged to
set up and develop programmes to ensure that the lowest exposure
occurs with the maximum benefit. It is hoped that this criteria
document will provide useful information for the development of
national protection measures against ELF fields.

1. SUMMARY AND RECOMMENDATIONS

1.1. Purpose and Scope

This document comprises a review of data on the effects of ELF
fields, predominantly ELF electric fields at 50 and 60 Hz, on
biological systems pertinent to the evaluation of health risks for
man. The purpose of the document is to provide information for
health authorities and regulatory agencies on the possible effects
of ELF field exposure on human health, and to give guidance on the
assessment of risks from occupational and general population
exposure. Areas in which uncertainties exist and further research
is needed are also indicated.

The document includes a review of the data on the biological
effects on human beings and animals of exposure to low frequency
electric and magnetic fields in the frequency range of zero to 300
hertz (Hz) (ELF).^a Data on the biological effects of exposure to
sinusoidally varying fields are mainly concerned with effects in
the range of 5 - 20 Hz or at 50 and 60 Hz, while limited data are
available on effects scattered throughout the ELF spectrum. Data
on studies with non-sinusoidal waveforms in this range have also
been considered. Effects of electrostatic and magnetostatic fields
are not included.

As the document mainly concerns effects directly attributed to
ELF electric fields, the effects of co-generated ozone, noise,
ultraviolet radiation (UVR) and X-rays from corona discharges,
induced short-circuit currents, etc., which may be important
factors in the overall transmission line environment, are discussed
only briefly.

In general, the effects of contact currents have not been
considered in detail since restriction of leakage currents from,
for example, household appliances and electromedical devices, is
already treated by national and international standards.

1.2. Sources of Exposure

Natural electric fields at extremely low frequencies are very
weak, while those of man-made origin are much stronger. The
strongest of the man-made electric fields are those surrounding
high voltage transmission lines ^b at 50 or 60 Hz, distribution
lines, and traction (transportation) systems that may operate at
16.67, 25, or 30 Hz. Within the home, the proximity of appliances

---------------------------------------------------------------------------
^a According to generally accepted usage in Europe, the region
from 30 Hz to 300 Hz is designated as extremely low frequency;
the region below this ELF band is unnamed. In the USA, the
ELF region is sometimes designated as 0 - 100 Hz (Polk, 1974).

^b These fields range up to about 10 kV/m within transmission
line corridors, and decrease to a background level of 10^-4 V/m
at approximately 10³ m.

and low voltage wiring produces ambient electric fields of 10^-1 -
10² volt/metre (V/m), depending on the mains voltage and the
distance.

The natural 60 Hz magnetic field is approximately 10^-9
millitesla (mT), which is low compared with the average fields (up
to 0.01 mT) found in private homes. Under the centre line at the
midspan of 1100 kV transmission lines, the 60 Hz magnetic field at
1 m above the ground is less than 0.035 mT. This is weaker than the
magnetic fields of up to 1 mT that occur close to common household
appliances.

It has become common practice to specify fields in terms of
their electric and magnetic field strength (E and H). The electric
field strength is specified in units of volts per metre (V/m). The
magnetic field is given by the field strength H in ampere/metre
(A/m) or the magnetic flux density B in weber/square metre (Wb/m²),
where 1 Wb/m² = 1 tesla.

1.3. Clinical Applications

The growth of bone tissue can be stimulated by electric
currents, and pulsed ELF fields are being used successfully in
clinical applications with patients suffering from intractable bone
disease or fractures. In the latter technique, electric currents
at ELF and higher frequencies are induced by pulsed magnetic
fields.

1.4. Field Measurement and Dosimetry

To characterize ELF fields, the strength, frequency, and
orientation of the electric and magnetic fields have to be
determined. Under power lines, the electric field has its major
component oriented vertically (perpendicular to the Earth's
surface), while the main magnetic field component is horizontal
(parallel to the Earth's surface). Principles of calculation and
measurements of these fields are outlined in section 2 of this
document.

A human or animal body located in an ELF electric field causes
perturbation of the field, resulting in an uneven distribution of
the field around the body. Both the electric and magnetic fields
induce electric currents in the exposed body. The electric fields
at the body surface and currents induced in man (a biped) and
quadruped animals are quite different, even at the same unperturbed
field strengths. The factors affecting the magnitude and
distribution of fields at the surface of the body and currents
induced inside the body are discussed below.

1.5. Characteristics of Biophysical Interactions

In regions of strong alternating electric fields, three
interactions occur:

(a) large surface fields exist, particularly at highly
curved regions, and may stimulate surface body
receptors, producing sensations;

(b) small currents flow within the body due to the large
surface fields; their magnitude is very small in
comparison with the currents that flow when contact
is made with charged conductors. The associated
internal electric field is some 10⁵ - 10⁷ times
smaller than the applied external electric field;

In most experimental situations with whole animals or in human
studies, the complex interrelationship between surface field
effects and possible internal electric field effects makes it
impossible to reach a clear conclusion on the importance of each
factor.

Although the non-magnetic nature of most biological materials
strongly suggests exclusion of magnetic field interactions,
alternating magnetic fields can induce electric currents similar to
the type of currents induced by coupling to electric fields. However,
in the transmission line context, the magnetically-coupled electric
currents are generally smaller, but within an order of magnitude of
the electric field-coupled currents. For exposures of prolonged
duration, currents produced by pulsed magnetic fields (peak
intensities of the order of 1 mT) are effective in modifying cell
functions (e.g., in the repair of bone fractures in human beings).
In laboratory studies with these same fields, changes have been
reported in bone growth, amphibian nucleated erythrocyte
dedifferentiation, nerve regeneration, and initiation and
alteration of DNA transcription, at current densities in fluid
bathing body cells of about 1 - 10 µA/cm² and electric gradients of
the order of 0.1 - 1 V/m.

The mechanisms by which a weak ELF field may interact with
biomolecular systems and tissues are incompletely understood.
However, from in vitro studies, there is now evidence of
field-induced interactions, including the phenomena of ionic
interactions with membrane surface macromolecules, which appear to
involve coupling of the cell interior to signals from neurotransmitters,
hormones, and antibodies.

1.6. In vitro Studies

In vitro studies are conducted for two main reasons:

(a) to elucidate mechanisms of interaction of ELF fields
with biological materials; and

(b) to provide information on end-points to search for in vivo.

These studies have included examination of interactions with
excised and cultured tissues, cell biochemistry, neurophysiology,
and growth of bone tissue. Electric fields were reported to affect
endocrine gland secretion, response to hormonal stimulation, brain
calcium ion exchange, immunoreactivity of lymphocytes, electrical
excitability of neuronal tissue, and tissue growth rates.

Some of these studies have revealed ELF field effects occurring
within certain "windows" in frequency and amplitude.

1.7. Experimental Animal Studies

The majority of ELF research has focused on effects directly or
indirectly involved with the central nervous system including
physiological, ultrastructural, and biochemical alterations, changes
in blood composition, behaviour, reproduction, and development.
Studies have been conducted almost exclusively on small laboratory
animals, except for a few studies carried out with miniature swine
and non-human primates.

Although some experimental data exist, one of the most serious
shortcomings of the studies on small animals results from an
inability to make extrapolations to human beings because of
uncertainty about applying the mechanisms proposed for the effects
seen so far. In particular, it is difficult to cite equivalent
human exposure because of vast differences in the distribution of
surface electric field strengths and internal current densities
between human beings and animals, and because there are no data on
the species dependency of effects.

Studies with small animals exposed to electric fields up to
100 kV/m have revealed effects on components of the nervous system,
including synaptic transmission, on circadian rhythms, and on the
biochemical properties of brain tissue. Results of behavioural
studies suggest that the nervous system may be affected by an ELF
electric field that is far too weak to stimulate synaptic function
or cell firing, although in vivo studies often do not exclude the
possible role of tactile sensory phenomena.

Field effects on peripheral blood composition and biochemistry
have been studied by numerous investigators with inconsistent
results. Generally, the changes in blood picture involve small
deviations from individual norms, but the values usually remain
within physiological norms. Results of studies on the influence of
ELF fields on immunocompetence in whole animals appear to be
negative.

Studies on swine exposed to 30 kV/m and rodents exposed to 65
kV/m for up to 18 months have revealed evidence of teratological
effects. These data are not conclusive and do not prove the
teratogenic potential of ELF fields in general.

Many studies on genetic effects and effects on cardiovascular
function have been reviewed and the conclusion reached that such
effects have not been convincingly demonstrated.

1.8. Effects on Man

Existing surveys of the state of health of high voltage (HV)
substation workers and HV line maintenance crews have been based on
small populations and have produced conflicting results. Soviet
authors noted an increased incidence of subjective complaints
attributable to effects on the nervous system and shifts in blood
biochemistry, but other authors have not reported such observations.
Differences in method often make comparison difficult, if not
impossible. Field strengths to which personnel were exposed were
only estimated, and only approximate data on the duration of
exposure to fields in a given strength range were available.

Some studies on volunteers exposed to electric fields up to 20
kV/m for short periods (days), under laboratory conditions,
confirmed the existence of slight changes (within the normal
physiological range) in populations of peripheral blood cells and
biochemistry, similar to those observed in experimental animal
studies.

Several recent epidemiological reports have presented
preliminary data suggesting an increase in the incidence of cancer
among children and adults exposed to magnetic fields through living
close to various types of electrical power lines or devices (e.g.,
power lines coming into the home, transformers, or other electrical
wiring configurations), and among workers in electrotechnical
occupations.

Slight increases in genetic defects or abnormal pregnancies
have been reported in one study. Epidemiological studies have been
performed on linemen and switch-yard workers, the groups considered
to be subjected to the highest electric-field exposure levels.
However, the exposure levels to which these people are subjected
have been found to be remarkably low. The preliminary nature of
the epidemiological findings, the low levels of exposure, and the
relatively small increment in the reported incidence of any
effects, suggest that, though the epidemiological data cannot be

dismissed, there must be considerable study before they can serve
as useful inputs for risk assessment.

No pathological effects resulting from ELF field exposure have
been established. However, thresholds for perception, startle, let-
go, respiratory tetany, and fibrillation due to contact currents
(electric shocks) have been quantified.

1.9. Exposure Standards

The few instances where countries have developed standards
limiting human occupational or environmental exposure to ELF fields
are discussed and compared in section 9 of the document.

1.10. Conclusions and Recommendations

1. In order to relate biological findings from in vitro and in
vivo studies on experimental animals to human beings, it is
recommended that dosimetry studies should be continued to
measure and relate external electric field strengths and
internal current density distributions in the whole body of
both animals and human beings.

2. From studies on man and animals, observed sensitivities are
consistent with two proposed models, one on the basis of
stimulation of peripheral sensory receptors in strong local
electric fields at the body surface, and the other on the basis
of current densities induced in the extracellular fluid. It is
recommended that models be devised that correlate exposure and
biological effects in terms of physical factors, such as
surface electric field, tissue current density, spark
discharges, and waveform.

3. The continuation of basic research on electric and magnetic
field interaction mechanisms is strongly recommended.
Investigations should be conducted on the possible synergism or
antagonism of field influences with physical and chemical
agents, since such data are not available.

4. In some studies, restriction of ELF effects to certain "windows"
in frequency and amplitude has been reported. It is recommended
that the window concept be further investigated to determine the
applicability of data obtained with various frequencies and
waveforms, and to relate the findings to potential health
detriment in human beings.

5. Studies have been performed on workers with long-term exposure
to electric and magnetic fields, but no adverse health effects
have been identified. However, these studies were not designed
to evaluate effects on reproductive functions, or long-term
carcinogenic risks. In two of the studies, electric field
exposure was carefully evaluated, and it was found that average
exposures in the occupationally-exposed groups were remarkably
low.

A suggestion of increased cancer incidence has been reported by
a number of investigators who have examined occupational and
general population groups exposed to electric and magnetic
fields. The studies performed have serious deficiencies in
epidemiological design and do not adequately characterize
levels and duration of exposure.

The limited knowledge of the potential human health risk
associated with exposure to electric and magnetic fields makes
it imperative that well-designed epidemiological studies should
continue to be undertaken to provide a firmer basis for risk
assessment.

6. Occupational exposure to strong electric fields is generally
intermittent and of short duration; exposed populations have
been identified, and there are some limited data based on
practical experience. At field strengths where spark
discharges are prevalent, prolonged exposures may impair
performance. Such exposures should be avoided, where possible.

7. Linemen working on energized extra- or ultra-high-voltage
conductors experience extreme electric field conditions, and
the use of appropriate protective clothing or devices is
desirable.

8. Whilst it would be prudent in the present state of scientific
knowledge not to make unqualified statements about the safety
of intermittent exposure to electric fields, there is no need
to limit access to regions where the field strength is below
about 10 kV/m. Even at this field strength, some individuals
may experience uncomfortable secondary physical phenomena such
as spark discharge, shocks, or stimulation of the tactile
sense.

9. It is not possible from present knowledge to make a definitive
statement about the safety or hazard associated with long-term
exposure to sinusoidal electric fields in the range of 1 - 10
kV/m. In the absence of specific evidence of particular risk
or disease syndromes associated with such exposure, and in view
of experimental findings on the biological effects of exposure,
it is recommended that efforts be made to limit exposure,
particularly for members of the general population, to levels
as low as can be reasonably achieved.

10. In principle, electric and magnetic field interference with
implanted cardiac pacemakers can lead to reversion to a fixed
rate, but cessation of stimulation is possible. Direct
interference has not been reported in fields below 2.5 kV/m.
Although body currents produced by contact with a vehicle in a
weaker field may cause interference, the risk of pacemaker
reversion is believed to be slight.

It is recommended that pacemaker designers and manufacturers of
other similar electronic equipment ensure that their devices
are resistant to failures caused by electric or magnetic field-
induced currents.

2. PHYSICAL CHARACTERISTICS, MEASUREMENT, AND DOSIMETRY

2.1. Quantities and Units

The electric (E) and magnetic (H) fields that exist near sources
of ELF electromagnetic fields must be considered separately, because
the very long wavelengths (thousands of kilometres) characteristic
of extremely low frequencies means that measurements are made in the
non-radiating near field. The E and H fields do not have the same
constant relationship that exists in the far field of a radiating
source.

In the vicinity of high-voltage transmission lines, the E and H
fields are typically of the order of a few kilovolts per metre
(kV/m) and a few tens of amperes per metre (A/m), respectively.
Persons standing under HV-transmission lines or in the vicinity of
charged conductors will have currents induced in their bodies as a
result of the interactions of these fields with the body tissues.
To fully assess the health implications of these ELF fields on man,
the fields must be measured accurately and interactions with the
body described quantitatively. The human body has a complex
geometrical structure making it difficult to obtain precise
theoretical or experimental descriptions of these interactions.

The quantities and units used in describing ELF electric and
magnetic fields are given on page 8.

The electric and magnetic fields are each described by a vector
defined by space components along three orthogonal axes. For
steady-state sinusoidal fields, each space component can be
represented as a phasor, i.e., a complex number having a magnitude
and phase. The magnitude is expressed as the root mean square
(rms) value of the field strength in volts per metre or amperes per
metre, respectively. The electric field strength is defined in
terms of a force exerted by the electric field on a unit charge and
the magnetic field by the force on a unit current in a unit length
of wire.

The flow of charge is the electric current measured in amperes
(A). The electric charge is the integral of electric current over
time and is expressed in ampere-seconds (A x s) or coulombs (C).
Derived quantities are surface charge density (A x s/m²) and volume
charge density (A x s/m³). The current density is defined as the
current flowing through a unit area perpendicular to the current
direction and is expressed in amperes per square metre (A/m²).

The electric flux density D is a vector quantity, the divergence
of which is equal to the volume charge density. The unit of the
electric flux density is A x s/m², and it is related to the
electric field strength by the equation D = epsilonE, epsilon being
the permittivity. Permittivity of the vacuum is epsilon_o = 8.854
x 10^-12 A x s/Vm. The relative permittivity, epsilon_r, a
dimensionless quantity, is defined as epsilon_r = epsilon/epsilon_o.
In free space, epsilon_r = 1, but in tissues, the values of epsilon_r
are significantly greater than 1. The capacitance between two

objects, measured in farads (1 F = 1 A x s/V), is defined as the
charge acquired by an object divided by the potential difference
existing between them.

The magnetic field can be described by the magnetic field
strength H and by the magnetic flux density B, where B = µH, µ
being the permeability. In free space, µ_o = 12.566 x 10^-7
V x s/Am. The relative permeability µr, a dimensionless quantity, is defined
as µ_r = µ/µ_o, µ_r = 1 in air, by definition, and also, for all practical
purposes, in biological tissues as well. The magnetic field is an axial
vector quantity, the curl (rotation) of which is equal to the total current
density, including the displacement current. Magnetic flux density, sometimes
called magnetic induction, is expressed in tesla, where 1 T = 1 V x s/m² = 1
Wb/m².

When describing exposure conditions, the electric and magnetic
field strengths and orientations should be indicated together with
the frequency. In the case of AC transmission lines, electric and
magnetic field components have a fundamental frequency equal to 60
Hz in North America and 50 Hz elsewhere.

Harmonic content is due to the distortion of sinusoidal wave-
form of the fundamental frequencies by waveforms of other frequencies,
and can be characterized by a Fourier series. The harmonic content
may be of importance at points near large industrial loads or in
laboratory installations.

Three-phase transmission lines generate fields, the space
components of which are not in phase. The field at any point close
to line current conductors can be described by the field ellipse,
i.e., the field vector describes an ellipse in any full cycle. At
distances of about 15 m or more away from the outer conductor, the
electric field of transmission lines can be considered practically
a single phase field.

The vertical component of the electric field under a
transmission line is the rms value of the component of the electric
field along the line perpendicular to the ground and passing through
the point of measurement. This quantity is often used to characterize
induction effects in objects close to ground level.

The space potential of a point is a phasor representing the
voltage difference between the point and the ground. The space
potential is perturbed by the introduction of an object into the
field. The "unperturbed space potential" that would exist if the
object were removed is often used in describing the field. This is
the induction field potential.

It is important to consider the action of an electric field on
the human body. Within the body, the low frequency electric field
is attenuated by about 10⁵ - 10⁷ from the value of the external
field. This is in contrast with a magnetic field. Because of the
high conductivity of the human body, the electric field is distorted
and localized at the surface of the body. In an alternating field,
a current is produced within the body, that has the same frequency
as the external field.

The human body acts as a conductor at ground potential, when a
person is in good electrical contact with earth, as when wearing
conducting shoes. A person wearing well-insulated shoes assumes a
free or floating potential above ground. However, the resistance
to earth of a person wearing shoes with leather soles is about
15 k ohms and with plastic shoes about 100 M ohms (Deno, 1977).
When the body is earthed, a current flows through the body to
ground. This current is approximately 14 µA (for 50 Hz) and 17 µA
(for 60 Hz) for each 1 kV/m of undisturbed field strength
(depending on the body size and shape). Of this current, about
one-third flows into the head (Hauf, 1982).

Kaune & Gillis (1981) formalized a number of concepts that
simplify the description of the interaction between an animal and
an ELF electric field. These authors showed that the electric-
field intensity at the surface of the body and induced currents
passing through various segments of the body are determined by:
(a) the characteristics of the applied electric field, i.e., field
strength, spatial structure, and frequency; (b) the shape of the
body; (c) the location of the body relative to ground and other
conductors; and (d) any conduction currents from the body to ground
or other conductors. Because these quantities do not depend on the
internal structures of the body, they can be measured using
conducting models, which may be hollow. The authors showed that
the electric field outside the body and the induced charge density
on the surface of the body are independent of frequency in the ELF
range for both grounded and ungrounded exposure conditions. They
also showed that the electric field outside and inside a body will
be unchanged by a scaled change in the size of the body. Finally,
these authors proved that the electric charge induced inside the
body of an exposed human being or animal is small compared with
that induced on the surface of the body.

The magnetic field is not perturbed by objects that are free of
magnetic materials. Magnetic field induction in objects causes two
types of electric currents (Zaffanella & Deno, 1978):

- a circulating current inside the object (eddy
current) induced by the magnetic flux density; and

- a current entering and leaving the object which may
be induced by the magnetic flux density through some
large loop external to, but including, the object.

2.2. Computational Methods and Measurements of ELF Electric Fields

Computational methods for the determination of electric and
magnetic fields are presented in standard textbooks on engineering
and physics. Detailed data on computational methods for in case of
HV transmission lines are presented in The Transmission Line
Reference Book (1975) and Zaffanella & Deno (1978).

There are basically two different approaches to the measurement
of 50 or 60 Hz E fields:

(a) free-body probes that measure fields at points remote
from the ground (Transmission Line Reference Book,
1975; Bracken 1976); and

(b) ground-reference instruments that measure the current
to ground that is collected by a metallic surface
(Miller, 1967).

The principles of operation of both types of instruments are
closely related. A free-body instrument consists of a hollow
metallic shell that is cut in half and the two halves insulated
from each other. The displacement current intercepted by a half-
shell is the time derivative of the surface unit charge, and for a
sinusoidal field:

I = dQ/dt = k omega epsilon_oE cos omega t Equation (1)

where E is the E-field strength, Q is the charge induced on one of
the half-shells, omega is the angular frequency, epsilon_o is the
permitivity of free space, and k is a constant.

The theory of operation for the ground-reference instrument is
quite similar to the above. A flat reference plate is placed on
the ground in electrical contact with the ground. A second plate
is placed a small distance above the reference plate and insulated
from it. The displacement current is again given by Equation (1).

The free-body approach is recommended for outdoor measurements
near power lines, since it does not require a known ground reference
for measurements anywhere above ground. The ground-reference probes
can be used only under special conditions as discussed in the
Transmission Line Reference Book (1975).

The electric field is perturbed (in some circumstances
significantly) by the presence of human beings, vegetation, or
other structures. Data presented in the literature show that, as
a general rule, in the presence of each perturbing influence, the
measured values are somewhat less than the unperturbed ones.

Three main procedures are used for the calibration of E-field
instruments:

(a) parallel plate techniques (usually with guard rings);

(b) single ground plate;

These three techniques have been reviewed by Kotter & Misakian
(1977). The first method is the best as it provides an accuracy of
1% or better for calibration of the field.

The electric field strength meter should be calibrated
periodically at intervals determined by the stability of the meter.
The instrument on a long (at least 2.5 m) handle is held between
the plates at the centre of the structure to take the appropriate
measurements while the plates are at a known voltage.

For some instruments, a correction for temperature and humidity
may be required. Therefore, these parameters should always be
recorded at the time of calibration and at the time measurements
are made.

In 1978, IEEE presented a technique using parallel plates to
calibrate power-line field survey meters. Two parallel, square
metallic plates separated by a distance d are supplied by an
alternating voltage source. The electric field strength E at the
midplane of the setting is given by:

E = V/d

where V is the voltage difference existing between the plates.
Fringing field effects at the periphery of the plates tend to
modify the field that would be expected to occur at the centre
point of the plates. It was found that for a pair of parallel
plates 1 m² each and spaced 0.5 m apart, the variation in field
magnitude was less than 1% from the simply computed value at the
centre in the midplane. This system constitutes a simple method of
evaluating survey meters.

For additional data, see the IEEE Standard for Recommended
Practices for the Measurements of Electric and Magnetic Fields from
Power Lines (IEEE 1978, 1979) and Tell (1983).

2.3. Field Polarization and Homogeneity

At ground level, beneath the transmission line, the electric
field is essentially a vertical homogeneous field with a horizontal
component that is about 20% of the vertical component (Poznaniak et
al., 1979). At distances of more than 15 m from the outer conductor,
this horizontal field drops to less than 10% of that of the vertical
field (Zaffanella & Deno, 1978).

Most experimental arrangements for the exposure of animals
involve a pair of horizontal parallel electrodes to produce a
vertical electric field that is quite homogeneous, if the electrode
spacing is adequate. Calculations (Ware, 1975; Shih & DiPlacido,
1980) indicate that the unperturbed electric field strength between
parallel plates is quite uniform in both the horizontal and vertical
directions, when the horizontal dimensions are two or more times
greater than the distance between the plates.

2.4. Energy Carried by the Field

A 10 kV/m electric field has an energy density of 4.42 x 10^-4
J/m³ producing an average power density in the body of man of about
10 µW/m³, which is about 10^-8 times the metabolic rate of the human
body (Sheppard & Eisenbud, 1977). Thus heating of a body by an ELF
field is completely negligible.

2.5. Determination of ELF Field Exposure

There are no universally accepted and clearly defined concepts
relating ELF field "dose" to biological effects, comparable with
ionizing or radiofrequency dosimetry in terms of exposure and
absorbed doses. Deno (1977), for example, suggests that exposure
to the electric field can be expressed as the product of electric
field strength and the duration of exposure. The current dose
(charge) on the various body surfaces and inside the body is a
constant ratio in the unperturbed field, if a person stays erect.
An "equivalent" E field is the vertical field at ground level (0.5
m), which would cause the same induction space potential at each
body position. The fields induced inside the body depend only on
the charges at the body surface (Deno 1979).

A "dose monitor" to measure the electric field exposure in
terms of the time integral of the unperturbed field in the ranges
of 0 - 5 kV/m, 5 - 10 kV/m, and above 10 kV/m has been constructed.
A separate device discharges the integrator monitors and gives a
reading of the doses after the exposure period. The actual
exposures were shown to be lower than those obtained by multiplying
the electric field strength in the area of work by the total time
spent in these areas. A similar device, constructed by Lövstrand
et al. (1979), was used to measure the exposure of workers in 50 Hz
EHV-substations. Lövstrand et al. (1979) stressed, however, that
the relationship between the unperturbed electric field strength
and the biological effect was by no means clearly established.
They maintained that further work was needed to develop dosimetric
concepts and to establish the relative significance of surface
charge densities, internal electric field strength, current, and
current densities for the "dose"-biological effect relationship.

2.6. The Physical Interaction of Man and Laboratory Animals with
Electric Fields

The exposure of intact organisms to ELF electric fields is
conventionally specified in terms of the unperturbed field
strength, in V/m or kV/m, which is measured or calculated before
the subject enters the field. The unperturbed field is not,
however, the field that acts directly on an exposed subject. The
fields to which a subject is actually exposed can be categorized as
follows:

(a) Electric fields acting on the outer surface of the
body. These fields can cause hairs to vibrate and
can thereby be perceived; they may also be able to
stimulate other sensory receptors in the skin.

(b) Electric fields induced inside the body. These
fields act at the level of the living cell, and their
presence is accompanied by electric currents because
of the conductivity of living tissues.

It has been shown that electric fields at the surface of a
conducting object are enhanced relative to the unperturbed field,
while induced fields inside the body are attenuated by about 10⁶
(Barnes et al., 1967; Deno, 1977; Kaune & Phillips, 1980).

2.6.1 Surface fields and internal current density

The electric field lines (the directions along which a charge
is moved by the force imposed by the field) are perpendicular to
the surface of the body. A greater concentration of electric field
lines (i.e., higher field strength) exists at a curved surface,
such as the human head, than on less curved surfaces of the body.
For this reason, it is useful to specify the surface electric field
that exists on various parts of the body.

A conducting object placed in an electric field carries a
current that is directly related to these surface fields. Thus,
the internal currents are greatest at the areas of the most intense
surface electric field. The current carried within the body (or a
portion thereof) can be calculated from the capacitance of the
body, a quantity that takes into account the size and shape of the
body and its proximity to other conducting objects such as the
ground and high voltage electrodes or wires, or perhaps other
animals, fences, trees, etc. (Deno, 1974, 1975, 1976, 1977;
Bracken, 1976; Zaffanella & Deno, 1978; Kaune & Phillips, 1980).

Within the body, the two quantities of interest are the current
and the current density. The total current is more easily measured
or calculated, but the current density is more directly relevant in
discussion of electric field effects in a particular tissue or
organ. The electrical complexity of the interior of the human
body, due to the presence of insulating membranes and tissues of
various impedances, has so far frustrated confident analysis of
precise interior current densities (Kaune & Phillips, 1980;
Spiegel, 1981).

2.6.2 Capacitive coupling of the electric field to man and
laboratory animals

A body is coupled to an electric field in proportion to its
capacitance such that the greater the capacitance the greater the
current flow in the body. For example, the capacitance of a rat is
about 5 picofarad (pF), while human beings have capacitances of
about 125 pF, when in close proximity with ground (Deno, 1974; Deno
& Zaffanella, 1975).

In many laboratory exposures of small animals, the distance
between the animal and the lower electrode is small or nonexistent
so that the animal's capacitance to this lower (usually earthed)
electrode represents a substantial portion of the total
capacitance.

By definition, in capacitive coupling, the body, according to
its capacitance C, "acquires" a certain amount of surface charge Q
and attains a potential V = Q/C. This view finds formal expression
in models that express any arbitrarily complex body as an equivalent
plate at an equivalent height, such that the total current collected
by the plate is the same as that for the actual body (Deno, 1974).
The capacitance, and thus the induced current, decrease for a body
separated from the ground and not close to the energized electrode.
The capacitance is dependent on the size, especially on the surface
area, shape, and orientation of the body, so that internal currents
will differ between fat and thin persons, between persons standing
and reclining, and between persons walking barefoot and those
wearing thick rubber-soled shoes or standing on a platform. It
would be useful, in all cases, to define the conditions under which
the capacitance has been measured.

A short-circuit current I_sc flows in a body placed in an
electric field and connected to the ground through a low resistance
path (paws, bare feet, a hand grasping an earthed pole). This
current is the sum of all the displacement currents collected over
the surface of the body. The only place on the body where a
current of the magnitude of the short-circuit current flows is
where there is connection with the ground.

2.6.3 Shock currents

In contrast with capacitive coupling to the field, a person
touching a conductor carries a "shock current", the magnitude of
which is determined by the total circuit impedance including the
electrical impedance of the skin and body. Exposure to an
extremely strong electric field would be needed to produce
displacement currents of several milliamperes, which would
represent a hazard similar to that of touching a live wire (Schwan,
1977).

2.7. Dosimetry and Scaling Between Laboratory Animals and Man

The surface and induced fields to which quadrupeds (e.g.,
laboratory animals) and bipeds (e.g., human beings) are exposed are
markedly different at the same unperturbed field strength. Hence,
it is necessary to scale exposures across species to compare
biological responses.

At present, there are several ways in which electric-field
exposure effects found in animals might be scaled to possible
effects in human beings. One way is to scale on the basis of
equivalent surface electric fields. Alternatively, the induced
currents or electric fields in corresponding tissues and organs
could be determined.

When scaling of exposure is made on the basis of equivalent
surface electric fields, it is assumed that the mechanism by which
biological effects are produced involves stimulation of receptors
on the surface of the body or currents at the surface of the body.
Stimulation of peripheral somatosensory receptors has been
demonstrated by Jaffe (1982, in press). Also, electric fields at
the surface of the body can produce oscillation of hairs on the
surface with a resultant stimulatory effect.

Classical neurophysiology suggests that induced current
densities could produce changes in cell physiology when
transmembrane current densities are of the order of 0.1 mA/cm²
(Schwan, 1982b). Large current densities are not normally possible
because such high E fields would be needed that electrical break-
down of the air would occur long before these current densities
could be induced. Novel mechanisms of interaction of the E field
with various biological systems would be needed to explain any
effects at the current densities of 10^-6 - 10^-9 A/cm² that may
be caused by fields found in the environment.

An erect grounded human being (biped) couples more strongly to
an ELF electric field than laboratory animals (quadrupeds).
Surface electric fields and axial current densities have been
measured in models of man, pig, and rat by Kaune & Phillips (1980)
(Fig. 1). At the tops of the bodies, surface electric fields are
enhanced over the unperturbed field strength present before the
subjects entered the field by factors of 18, 6.7, and 3.7 for human
beings, swine, and rats, respectively. For an unperturbed field
strength of 10 kV/m, average induced axial current densities in the
neck, chest, abdomen, and lower part of the legs are, respectively:
550, 190, 250, and 2000 nA/cm² for human beings; 40, 13, 20, and
1100 nA/cm² for swine; and 28, 16, 2, and 1400 nA/cm² for rats.

Recently an attempt has been made to determine human exposure
conditions simulated by animal exposures to 60-Hz electric fields
(Guy et al., 1982). A thermographic method for determining the
specific absorption rate (SAR) was used to quantify the electric
current distributions in homogeneous models of animals and human
beings exposed to uniform 60-Hz electric fields by exposing models
(of scaled size and conductivity) to 57.3 MHz fields. Although the

values of maximum current density predicted in the ankles of models
of human beings exposed to 60-Hz fields at 1 kV/m, 200 nA/cm,
agreed with independent measurements on full-scale models, the
simulation of the 60-Hz field with a 57.3-MHz field may not be
exact, when determining corresponding current densities in animals
and man.

Theoretical models of biological effects of electric fields
must distinguish between the importance of the microscopic electric
field versus the microscopic electric current, although these two
quantities will always be interrelated. If the model for inter-
action depends on transport of a certain quantity of charge, then
the microscopic electric field is not the quantity of interest, and
various experimental results should be scaled according to the
current density in the tissue. On the other hand, if the tissue is
sensitive to the electric field strength, independent of the charge
transported by that field strength, the model would require scaling
on the basis of internal electric field strengths. In general terms,
two such models would characterize the ultimate biophysical inter-
action measurement as either "voltmeter-like" or "ampmeter-like".

Whether an experimental result should be scaled according to
the current or the electric field can be very important because the
tissue conductivity that relates these two quantities varies

signficantly among various tissues and, even more widely, among the
tissue or subcellular components (e.g., plasma membranes) of
different species (section 5).

It is clear from these data that exposures in studies with
laboratory animals must be scaled to compare biological effects
from such studies to possible effects in man. Although
considerable progress has been made in the dosimetry of ELF
electric fields during the past several years, additional research
is needed before data from experimental animal studies can be
extrapolated to man. Information is needed on:

(a) interaction mechanisms;

(b) critical sites in the body that produce any effects;

(d) physiological differences between species.

2.8. Magnetic Induction of Electric Fields

An animal or human body does not appreciably affect a magnetic
field, but the magnetic field induces currents within the body.
The magnitude of these internal currents is determined by the
radius of the current path, the frequency of the magnetic field,
and its intensity at the location within the body. Unlike the
electric field, for which the internal field strength is many times
less than the external field strength, the magnetic field strength
is virtually the same outside the body as within. The magnetically-
induced electric currents are greatest at the periphery of the body
where the conducting paths are largest, whereas microscopic current
loops anywhere within the body would have extremely small current
densities. The magnitude of the current density is also influenced
by the conductivity of the tissues, and the exact paths of the
current flow depend in a complicated way on the conducting
properties of tissues.

The induced current density and power absorbed by a prolate
spheroid model of a man exposed to the magnetic-field component of
a transmission line have been calculated by Spiegel (1977).

3. NATURAL BACKGROUND AND MAN-MADE ELF FIELDS

3.1. Natural Electric Fields

The electric and magnetic fields of the Earth consist of a
static component, which is dominant, and a time-varying component,
which is smaller than the static component by several orders of
magnitude in the 50 - 60 Hz frequency range (Polk, 1974). The
fields are characterized by vertical components E_z and H_z for the
electric and the magnetic fields, respectively, as well as by two
horizontal components E_x,y and H_x,y.

The most important sources of man-made fields in the ELF range
operate at the power frequencies of 50 Hz or 60 Hz. The natural
electric field strength at the power frequencies of 50 Hz or 60 Hz
is about 10^-4 V/m, which means that fields in the close vicinity of
HV transmission lines are 10⁸ times stronger, and the fields
introduced into homes by wiring or appliances are still about 10³ -
10⁶ times stronger than the natural background.

The natural electric field near the Earth's surface is a static
field of about 130 V/m (Dolezalek, 1979). This is due to a
separation of electric charge between the atmosphere and the
ground, so that the Earth resembles a spherical capacitor and the
ground and upper atmosphere represent conducting surfaces. Daily
changes in the natural electric field are attributed to factors,
such as thunderstorms, that affect the rate of charge transfer
between the ground and the upper atmosphere. According to Chalmers
(1967), thunderstorms have electric fields of 3 - 20 kV/m.

The alternating fields at low frequency are related to
thunderstorm activity and magnetic pulsations that produce currents
within the Earth (telluric currents). The strength of the Earth's
electric field varies in time and over the frequency range 0.001 -
5 Hz (Krasnogorskaja & Remizov, 1975). Local variations occur
depending on atmospheric conditions and variations in the magnetic
field. The main characteristic of the Earth's electric field are
presented in Table 1.

3.2. Natural Magnetic Fields

The natural magnetic field is composed of an internal field,
due to the Earth acting as a permanent magnet, and to an external
magnetic field in the environment from such components as solar
activity, telluric currents, atmospheric activity, etc.

The internal magnetic field of the Earth originates from the
electric current in the upper layer of the Earth's core. There are
significant local differences in the strength of this field,
varying from about 50 A/m at the poles to about 23 A/m at the
equator (Presman, 1971; Benkova, 1975). These field strengths also
vary with time.

Table 1. Characteristics of the Earth's electric field in the ELF range
---------------------------------------------------------------------------
Frequency Nature of the field Field strength Reference
range (Hz) (V/m)
---------------------------------------------------------------------------
0.001 - 5 Short duration pulses 0.2 - 1000 Krasnogorskaja &
(magnetohydrodynamic for E_z Remizov (1975);
origin) Vanjan (1975)

7.5 - 8.4 3 - 6 quasisinusoidal On the average, Beresnev et al.
and pulses of undetermined (0.15 - 0.6) (1976)
26 - 27 origin during an 10^-6 for
interval of 0.04 - 1 s E_x,y with a
maximum of 10^-6

5 - 1000 Related to atmospheric 10^-4 - 0.5 Aleksandrov et al.
changes (atmospherics) for E_z, and (1972);
present all the time one order of Presman (1971);
magnitude lower Kleinmenova (1963)
for E_x,y. The
amplitude
decreases with
increasing
frequency
---------------------------------------------------------------------------
The external magnetic field consists of many components
differing in spectral and energy characteristics (Aleksandrov et
al., 1972; Polk, 1974; Benkova, 1975). The variations in the
magnetic fields are related to solar activity, particularly with
respect to the ELF components, which change over 11-year and 27-day
periods and also exhibit circadian variations. Other causes of
variations in the natural magnetic fields are thunderstorms,
atmospheric changes, and air ionization. About 2000 thunderstorms
are occurring simultaneously over the globe, and lightning is
striking the Earth's surface about 160 times per second; the
currents involved may reach 2 x 10⁵ A at the level of the Earth
(Kleimenova, 1963). Electromagnetic fields having a very broad
frequency range (from a few Hz up to a few MHz), originate the
moment lightning strikes and propagate over long distances,
influencing the magnitude of magnetic fields.

The characteristics of the Earth's magnetic field can be
summarized as follows:

(a) The amplitudes from 4 x 10^-2 to 8 x 10^-2 A/m are at
pulsation frequencies ranging from 0.002 to 0.1 Hz.

(b) The geomagnetic pulsations up to 5 Hz are of short
duration, lasting from a few min to a few h.

(d) At 50 or 60 Hz, the natural magnetic field is
approximately 10^-9 mT (Polk, 1974).

The geomagnetic field exhibits temporal and spatial variations
related predominantly to solar activity and local magnetic
aberrations.

3.3. Man-Made Sources of ELF

3.3.1 High-voltage transmission lines

The principal man-made sources of ELF are HV transmission
lines, and all devices containing current-carrying wire, including
equipment and appliances in industry and in the home operating at
power frequencies of 50 Hz in most countries and at 60 Hz in North
America.

Electrical energy is transmitted from the power plant, where it
is generated, along conductive, metallic transmission connections
(overhead power lines or underground cables) to substations and
finally to energy consumers.

A typical overhead line (Fig. 2) consists of supporting
structures (transmission towers or pylons) from which the live
conductors are suspended by sets of insulators. Each set of
insulators supports a single conductor or a bundle of two or more
conductors, which carries one electrical phase of the power supply.
The conductors of each phase are suspended far enough away from the
other conductors and the transmission tower to prevent flashover or
short-circuiting between one phase and another, or between the
phases and earth (via the supporting structure). In overhead
lines, the conductors consist of bare metal cables. Thus, any
approach to a live conductor presents a lethal danger due to
flashover and a resulting electric current flow that would precede
actual contact with a conductor.

High voltage lines are operated at standard voltages up to 750
or 765 kV and a line at 1100 kV is operating in the USSR. The
construction of 1000 - 1200 kV or 1500 kV lines is in progress or
at various stages in planning.

Most widely used are alternating current (AC) 3-phase HV lines.
One circuit of the 3-phase line comprises 3 single or 3 sets of
conductors under high-voltage and 1 or 2 grounded conductors that
protect the live conductors against lightning.

Typically, the unperturbed electric field at the height of an
average man, standing at the location of the maximum field (just
outside the outer conductor) of a high-voltage transmission line of
750 kV, is of the order of 10 kV/m. A lower value of about 1 kV/m
exists where the line is highest from the ground (20 m) and about
12 kV/m where it is lowest (13 m) (Zaffanella & Deno, 1978). The
electric field strength is a function of the lateral distance from
the centre of the HV line as shown in Fig. 3.

Occupational exposures that occur near high voltage transmission
lines depend on the worker's location either on the ground, or at
the conductor during live-line work at high potential. When working
under live-line conditions, protective clothing may be used to
reduce the electric field strength and current density in the body
to values similar to those that would occur for work on the ground.
Protective clothing does not weaken the influence of the magnetic
field.

3.3.2. Electric fields near transmission lines and sub-stations

At ground level, beneath high-voltage transmission lines, the
electric fields created have the same frequencies as those carried
by the power lines. The characteristics of these fields depend on
the line voltage, and on the geometrical dimensions and positions
of the conductors of the transmission line. The field intensity
selected for reference or comparison purposes is the undisturbed
ground level electric field strength. To avoid the effects of
vegetation or irregularities in the terrain, the unperturbed field
strength is usually computed or measured at a given height above
ground level (0.5, 1, 1.5, or 1.8 m).

There are several primary influences on the electric field
strength beneath an overhead transmission line. These include:

(a) the height of the conductors above ground (which is
influenced considerably by the ambient temperature
and heating caused by the current passing through the
conductor);

(b) the geometric configuration of conductors and
earthing wires on the towers, and in the case of two
circuits in proximity, the relative phase sequencing;

(d) the proximity of other tall objects (trees, fences,
etc.);

(e) the lateral distance from the centre line of the
transmission line;

(f) the height above ground at the point of measurement;
and

(g) the actual (rather than the nominal) voltage on the
line.

Inside buildings near HV transmission lines, the field
strengths are typically lower than the unperturbed field by a
factor of about 10 - 100, depending on the structure of the
building and the type of materials (Manders & van Nielen, 1981).

Conductor height, geometric configuration, lateral distance
from the line, and the voltage of the transmission line are by far
the most significant factors in considering the maximum electric
field strength at ground level. At lateral distances of about
twice the line height, electric field strength decreases with
distance in an approximately linear fashion. Reference to typical
measured or calculated field contours in the vicinity of the line
(Zaffanella & Deno, 1978) indicates that, for a 525 kV transmission
line (height about 10 m), the field is always less than 1 kV/m at
distances of more than 40 m from the outer conductor, while for a
1050 kV line, which has much higher conductors, the 1 kV/m field
occurs at a distance of about 100 m from the outer conductor.
Typically, where a right-of-way (RoW) is used for a transmission
line of 500 kV or more, it varies from 35 to 70 m, so that electric
fields at the edge of the RoW are of the order of 1 kV/m.

The electric field strengths at and above ground level from
various transmission lines are shown in Fig. 4 (Gary, 1976). The
electric field distribution within various voltage substations is
given in CIGRE (1980).

3.3.3. Magnetic fields near transmission lines

Just as an electric field is always linked with the presence of
charges, a magnetic field always appears when electric current
flows. A static magnetic field is formed in the case of direct

current, whereas time-varying electric and magnetic fields are
induced in the vicinity of alternating current power transmission
systems.

The magnetic field beneath high-voltage overhead transmission
lines is directed mainly transversely to the line axis. The
maximum flux density at ground level may be either on the route
centre line or approximately under the outer conductors, depending
on the phase relationship between the conductors.

Apart from the geometry of the conductor, the maximum magnetic
field strength is determined only by the magnitude of the current.
The maximum magnetic flux density at ground level for the most
common overhead transmission line systems is approximately 0.1
mT/kA (Hylten-Cavalius, 1975).

In contrast to an electric field, a magnetic field is more
penetrating and very difficult to shield. It easily penetrates
human beings and, in the case of an alternating or rotating field,
induces circulating or eddy currents that are not conducted to
ground. The internal voltage differences induced within the body
by a magnetic field from power lines may be as high as 1 mV, if the
magnetic flux density reaches approximately 0.028 mT (Hauf, 1982).

The maximum ground level magnetic field strengths associated
with overhead transmission lines are of the order of 0.01 - 0.05 mT
and are also related to line height. Unlike the electric field,
they are also directly affected by the current carried by the line.
The magnetic flux density decreases in an approximately linear
fashion with distance from the conductor (Lambdin, 1978; Zaffanella
& Deno, 1978).

In principle, these magnetic fields can induce electric
currents in the body and could induce effects via the same
mechanisms as electric field-produced currents. However, for
exposures near a HV transmission line, the smaller magnitude of
these magnetically-induced currents (generally no more than 25% of
the electric field-induced currents) has resulted in little
emphasis on their contribution. The largest current densities
occur at the periphery of the body and they are lower inside. Fig.
5 and 6 show the magnetic field distribution near a HV-transmission
line carrying only about 10% of the typical rated load current for
such lines.

3.3.4. Man-Made ELF Fields in the Home, Workplace, and Public
Premises

In the home or workplace, ELF electric field sources occur at
electric wiring, appliances, and light fixtures, or industrial
electrical machines. Measurements of electric fields in a typical
American home (115 V circuits) ranged from less than 1 V/m to about
10 V/m, while fields measured at 30 cm from some appliances varied
from 2 to 5 V/m near a light bulb to several hundred volts per
metre near an electric broiler (Miller, 1974; Zaffanella & Deno,
1978). As a rule, values appear to be greater than 10 V/m near
appliances, and will vary with the nominal voltage.

Typical values of electric field strengths and magnetic flux
densities in the vicinity of home appliances and the potential
leakage currents through the body if contact is made with these
appliances is given in Appendix I.

3.4. Corona and Noise Effects of Transmission Lines

A high-voltage electrode can create ozone (O₃) by means of
ionization of air near the high-voltage conductors. In the vicinity
of corona-free, high-voltage, overhead transmission lines (fair
weather conditions), no ozone is created. Under certain weather
conditions causing corona discharges in the vicinity of HV
transmission lines, formation of ozone occurs. However, since
ozone is a very unstable gas, it rapidly decomposes into harmless
oxygen compounds in the open air and biological effects should
not be expected. Measurement and calculations of ozone near
transmission lines show that local increments in levels of the gas
are insignificant (Frydman et al., 1972; Roach et al., 1973).

Noise is of concern in regions beneath or near power lines, and
in switch-yards. Techniques are available to reduce corona-induced
noise beneath power lines to acceptable levels or to standards set
by law. The switch-yard acoustic environment is special and can
differ considerably from that near the overhead lines. Both the
frequency spectrum of the noise and intensity in different spectral
regions should be taken into account. Effects of noise in terms of
annoyance, sleep disturbance, and community reaction in the case of
HV transmission lines in the USA are discussed in detail by
Pearsons et al. (1979). Results of their study indicate that
transformer and transmission line noise may create problems,
particularly in densely-populated urban and suburban areas.

3.5. Electric Shock

In regions of high electric field strength, objects, if
insulated from ground, can assume large potential differences.
If the human body becomes the pathway for currents between such
objects, substantial electric currents (of the order of 1 mA) can
flow. Investigation of these effects has revealed two exemplary
cases in which significant shock currents exist:

(a) a long unearthed metal fence running parallel to the
line; and

(b) a large vehicle beneath the conductors and
effectively insulated from ground.

It is necessary to distinguish between the transient short-
circuit current and the steady-state short-circuit current.
Zaffanella & Deno (1978) presented data, obtained under various
circumstances, that indicated that peak currents of up to 20 A can
flow for a few microseconds when a person draws a spark discharge
from an object with a hand-held metal key. The peak currents are
an order of magnitude smaller if the finger is used for contact.
The energy content of spark discharges obtained from a carpet are

found to be similar to those in a 10 kV/m electric field with the
important exception that the AC field continually recharges the
electrified body so that repeated frequent sparks are possible,
whereas several steps must be taken on a carpet to recharge the
body. The steady-state short-circuit current that flows when the
charged object is earthed depends on the capacitance to earth of
the object, and the open-circuit voltage to which the object is
charged, when disconnected from ground, according to the relation:
I_sc = omegaV_oc x C, where I_sc is the short circuit current,
omega is the angular frequency of the electric field, V_oc is the
open circuit voltage, and C the capacitance to earth of the object
(Deno, 1974).

For human beings standing on the ground with arms at the side
of the body in an electric field of frequency f, the short circuit
current I_sc in amperes is given approximately by the empirical
formula (Deno, 1974):

I_sc = 9.0 x 10^-11 h² E x f

where f is 50 or 60 Hz, h is the person's height in metres (m), and
E the electric field strength in volts per metre (V/m). Thus, in a
10 kV/m, 60 Hz electric field, a person 1.7 m tall carries a short
circuit of about 160 µA.

Typical capacitances for objects range from 700 pF for a small
vehicle to several thousand pF for buses and large trucks and about
1000 pF for a 150 m fence (Deno, 1974). Thus, the short-circuit
current for a 150 m fence could be as great as 2.2 mA, if the fence
were located in a field of 5 kV/m. Zaffanella & Deno (1978)
measured the short-circuit currents of a farm tractor, jeep wagon,
and a school bus. In a 10 kV/m electric field, these vehicles
conducted 0.6, 1.1, and 3.9 mA of current to earth, respectively.
Although the shock currents are of appreciable magnitude, they
should not present a hazard if appropriate safety procedures are
followed. Good engineering practice to reduce the risk of shocks
includes the carefully earthing of fences, gutters, and other long
metallic objects in a strong electric field.

Data (Zaffanella & Deno, 1978) concerning human beings exposed
to spark discharges of various intensities showed that 50% of the
population perceived spark discharges in a field of 2.7 kV/m and
that 50% of the population found the spark discharges annoying at 7
kV/m. To obtain these data, persons standing in an electric field
touched a metallic post with a finger; it is assumed that their
capacitance was of the order of 170 pF.

The sensations that result from microshocks do not appear
hazardous (except insofar as they may produce a startle reflex that
could result in an accident), but they may be highly significant in
the evaluation of effects attributed to the fields. Although the
scope of this document does not include the possible health effects
of such microshocks or transient spark discharges, more than
cursory mention is given to these effects because of their
importance.

For the human responses, it is useful to define 3 thresholds:

(1) Perception: the minimum current for perception by touch
is about 0.4 µA;

(2) the Let-Go Current: the maximum current for which a person
can release the involuntary muscular contraction (Fig. 7)
(Dalziel & Lee, 1968);

(3) the Fibrillation Threshold: the minimum body-current to
cause ventricular fibrillation is especially dependent on
the pathway of the current in the body and the duration
(Fig. 8) (Kupfer, 1979; Kupfer et al. 1981). If the
current is directly applied to the heart, the fibrillation
threshold is about 5 x 10² times lower (Kupfer, 1982;
Weirich et al., 1983).

3.6. Interference of ELF Fields with Implanted Cardiac Pacemakers

An implanted pacemaker is an electromedical device that
artificially stimulates the heart, thus making it possible for
persons with certain heart diseases to lead relatively normal
lives. Although pacemakers may be susceptible to some forms of
electrical interference, hazardous situations resulting from
ambient electromagnetic fields have not been reported. Results of
a research programme reported by Bridges & Frazier (1979), who
carried out bench studies and studies with implants in animals,
showed a wide range in interference sensitivity among various
devices and for different arrangements of the implanted leads.

Pacemaker reversion can be brought about via the following three
mechanisms (Bridges & Frazier, 1979):

(a) direct coupling to an ambient electric field (typical
threshold range, 3 - 600 kV/m);

(b) transient coupling to an ambient electric field
through vehicle leakage current ("microshock")
(typical threshold range, 60 V/m - 60 kV/m);

Butrous et al. (1983) studied 35 patients (fitted with 16
different pacemaker models from 6 manufacturers) who were exposed
to 50-Hz electric fields up to a maximum of 20 kV/m. Current flow
measures varied between 15 and 300 µA, depending on the field
strength and the position of the patient in the field. Four
different response patterns were encountered: (a) normal sensing
and pacing in all conditions (one manufacturer); (b) reversion to
the fixed (interference) rate; (c) slow and irregular pacing; and
(d) mixed behaviour over a critical range of field strengths and
then reversion to a fixed rate. Their responses depended on the
pacemaker units. The field strengths required to induce such
behaviour varied with unit and model. Generally, the interference

threshold depended on the magnitude and distribution of induced
body current relative to the pacemaker, as well as field strength,
and thus varied with patient height, build, and posture.

4. MECHANISMS OF INTERACTION

Several mechanisms have been proposed to explain the reported
effects of ELF electric fields on laboratory animals, and in
tissues and cells in vitro including:

a) stimulation of peripheral receptors in the skin;

b) induced electric fields and currents inside the body
acting at the level of cells; and

c) non-specific stress.

4.1. Biophysical Mechanisms of Electric Field Interactions

Electric field coupling occurs through capacitive and
conductive modes. Energy is transferred to the object from the E
field and an electric charge in the object is put into motion. The
amount of charge involved depends on the size and location of the
object with respect to the E field. When a path to ground is
provided, the charge movement results in a current flow. If the
object is insulated from the ground, a potential develops with
respect to the ground, the magnitude of which depends on the
capacitance to ground.

The penetration depth of the field lines into the body is very
shallow at low frequencies. There is evidence that the field
induces direct effects on skin sensors of the cat paw at a
threshold local field strength of over 200 kV/m (Jaffe, in press).
Some reported behavioural effects in chickens, mice, rats, and pigs
exposed to unperturbed fields of 30 - 100 kV/m may be related to
sensory stimulation. These effects are presented in reports on
field perception, arousal, avoidance, transitory activity changes,
and transitory increases in cortecosterone levels (Moos, 1964;
Graves et. al., 1978; Hjeresen et. al., 1980; Sagan et. al., 1981;
Rosenberg et. al., 1983; Stern et. al., 1983).

With large field strengths, discharges may be detected. Small
currents flow within the body due to capacitive coupling to the
fields. In principle, an electric field of sufficient magnitude
could have a direct effect on biological tissues by acting directly
on the free ions in the extracellular milieu, on the charged
portions of the biomolecules, or by interaction with electric
moments of molecular electronic structure. However, the very small
internal electric fields that result from capacitive or magnetic
coupling (Barnes et al., 1967; Sheppard & Eisenbud, 1977) could not
affect covalent molecular structures or the electrostatic bonds
between molecules, nor could there be direct effects on steric
structure.

In his consideration of ELF electric field interactions with
neural cells, Schwan (1977) stated that, under a wide range of
assumptions for cellular shape and cellular electrical properties,
it was impossible that the largest electric fields in air could

significantly affect neural membrane potentials by the passage of
transmembrane currents. Schwan added, however, that the anomalous
properties at frequencies below 100 Hz, though still poorly
understood, "provide for more possibilities of subtle effects if
there are any at all".

Adey (1980) suggested that it is important to take into
account the possibility that one cell may influence another in
brain and other tissues through modulation of their shared electro-
chemical environment. The same author (Adey, 1981) proposed that
amplification of the weak initial stimulus occurs by a cascade of
intracellular processes taking place at receptor sites on the cell
membrane surface. This model may be supported by data on the
coupling of the parathyroid hormone receptors to the cyclic
adenylase and cyclic AMP responses in bone cells (Luben et al.,
1982).

It was suggested by Cain (1981) that voltage-sensitive ion
channels play a role at sufficiently large field strengths. He
proposed that an alternating potential across the cell membrane may
change membrane conductance by interacting with the charged groups
of the protein macromolecules that gate voltage-sensitive ion
channels.

Pilla (1980) developed a model for electrochemical information
transfer at membrane surfaces that involves a minimal electrostatic
perturbation of the molecular structure. The essence of the model
is that specific surface adsorption is expected to exhibit a
significantly longer relaxation time than dielectric or electro-
static interactions, due to the number of aqueous and membrane
steps involved, so that the characteristic time for adsorption may
be about 10 ms. This is in agreement with data obtained from toad
bladder membrane (Pilla & Margules, 1977). This mechanism would
work in parallel with the charge transfer processes already known
to occur, and could mediate enzymatic reactions to have significant
effects on cellular chemistry.

Recently, Schwan (1982a,b) discussed the possible role of
alternating field-induced ponderomotoric forces, i.e., forces
exerted by electric fields on nonpolar particles. The theory
developed on this basis can be used to explain dielectrophoresis
(Pohl, 1978), rotation, deformation, destruction of cells (Schwan,
1982a), and electrical cell fusion (Pilwat et al., 1981; Richter et
al., 1981) in cases where electric field strength greatly exceeds
that which could be produced in tissue by an environmental ELF
field.

4.2. Biophysical Mechanisms of Magnetic Field Interactions

The eddy currents created by magnetic ELF fields in the human
body cannot be measured directly, but they can be calculated and
confirmed by measurements on phantom models. The biological effects
of such induced electric currents are discussed above, but any
direct magnetic field effects are not well understood at present.

5. BIOLOGICAL EFFECTS IN CELLS AND ANIMALS

Since human volunteers cannot be used for studies that could
potentially cause harmful effects, biological investigations are
normally conducted using various other animal species. Studies
have been performed, mainly using rats and mice, but a wide variety
of other subjects, including insects, birds, dogs, swine, and non-
human primates, have also been used. A broad range of exposure
levels have been employed, and an equally large number of
biological end-points have been examined for evidence of possible
electric-field effects. Since all animal studies cannot be
discussed, this review will be limited to studies having some
bearing on health risk assessment. Experiments not discussed will
be summarized in the tables. Some studies showed effects from
exposure, and others showed no effects. There is general consensus
among scientists that exposure to electric fields produces
biological effects; however, more data are still needed to
determine whether these effects constitute a hazard.

Many studies have been performed based on the explicit or
implied hypothesis that because electrochemical processes are
involved in nervous system functioning, there might be an
interaction of the electric field with the nervous system. Such
hypotheses became of greater interest when initial reports on
linemen and switch-yard workers (Asanova & Rakov, 1966; Korobkova
et al., 1972) suggested the occurrence of a generalized alteration
in central nervous system function. Other studies were based on
generalized physiological hypotheses, such as the expectation that
electric field exposure, continued over a long period of time,
might induce a stress response, alter cardiovascular function,
affect immune responses, or alter various biochemical and
physiological variables, especially blood chemistry and blood cell
populations. Study areas briefly reviewed below also include
growth and development, reproduction, fertility, and behaviour.

Studies on the effects of electric and magnetic fields on the
ecosystems involving plants, invertebrates (including insects),
birds, fish, and mammals have been summarized (Lee et al., 1979,
1982). As these studies do not have a direct relevance for human
health risk assessment they are not discussed further.

5.1. Cellular and Membrane Studies

The effects of electric fields on in vitro systems have
been studied in a few laboratories. With these studies, it is
possible to use large sample sizes and to have a high degree
of control over experimental variables. Such studies also
provide a more direct investigation of the possible mechanisms
of interaction between a biological system and an electric
field. However, the most serious problems with in vitro
experiments are those of dosimetry and extrapolation. The
dosimetric relationship between exposure in cellular systems
and in whole animals is unclear, and extrapolation of results
from less complicated systems to human beings is extremely
uncertain.

Preliminary experiments using cultured Chinese hamster ovary
(CHO) cells exposed to 3.7 V/m showed no effects on cell survival,
growth, or mutation rate (Frazier et al., 1982). Cell-plating
efficiency, however (reflecting a possible alteration in the cell
membrane), was reduced in cells exposed to 60-Hz fields at
strengths greater than 0.7 V/m. At the same field strength (0.7
V/m) (Marron et al., 1975; Goodman et al., 1976, 1979), after
several months of exposure, slime mold showed frequency-dependent
effects on mitotic rate, cell respiration, and protoplasmic
streaming. These effects were observed with both electric fields
and magnetic fields, alone or in combination.

Studies using a variety of models (Greenebaum et al., 1979a,b;
Miller et al., 1979) have given contradictory results. Effects on
cell division, growth, and metabolism may appear at field strengths
of the order of tenths of a V/m or tenths of a mT in the medium.
On the other hand, electrical cell rotation and fusion (Pohl, 1978)
appear in the range of 10 - 100 kV/m.

Experimental findings suggest that the principal site of
interaction between ELF fields and the interior of living systems
is the cell membrane (Adey, 1975, 1977, 1980, 1981; Bawin et al.,
1975, 1978; Sheppard & Adey, 1979; Adey et al., 1981). These
include a 10 - 20% alteration in the calcium exchange from chick or
cat brain tissues exposed to ELF electric fields, either amplitude-
modulated radiofrequency (RF) carrier waves of 50, 147, or 450 MHz,
or ELF sine wave fields (Bawin et al., 1975, 1978; Blackman et al.,
1979, 1980, 1982). The calcium effect is windowed in frequency,
where maximal effects occur for 16 Hz modulation, and in the case
of direct ELF exposures, Blackman et al. reported several windows
at 15 Hz and its harmonics up to 105 Hz, in fields of less than 100
V/m in air. A similar narrow amplitude window limits the range in
field strength (Bawin et al., 1978; Blackman et al., 1979, 1982).
Bawin et al. (1978) found a relationship between the observed
effect and the ionic composition of the bathing medium.

In the case of the ELF modulation of a RF field, the magnitude
of the effective ELF field (obtained by demodulation of the RF
field envelope) that acts on the calcium-binding sites depends on
an unknown efficiency for a demodulation process occurring at an
unidentified site. Assuming complete demodulation, the effective
ELF field would correspond to an ELF-only field in air of the order
of 100 kV/m (Adey, 1981), though by use of the RF carrier there is
no significant heating of tissue (Tenforde, 1980) and no known
artifact (such as spark discharges).

A calcium efflux effect is also reported for in vivo studies
on the cat (Adey, 1980). Possible underlying biophysical mechanisms
and a relationship to the electric properties of the brain (electro-
encephalograph waves or EEG waves) are discussed by Grodsky (1976).
However, the physiological implication of the calcium efflux
phenomenon is not known.

Electric field effects on synaptic transmission and peripheral
nerve function in rats exposed for 30 days to a 60 Hz field of
effective strength 65 kV/m were studied in replicate (Jaffe et al.,
1980, 1981). The exposure apparatus was designed to eliminate the
confounding influence of electric shock currents. Neurons of the
superior cervical ganglion showed significantly increased
excitability compared with the control group, as determined from
tests in which the amplitudes of paired compound action potentials
were measured (conditioning test response or C-T response). None
of several other indices of neural function was altered to a
significant extent. The authors interpreted the data as evidence
of an effect on pre- or post-synaptic mechanisms, possibly indicating
enhanced excitability, and as evidence against a significant effect
on nerve conduction mechanisms.

An investigation (Wachtel, 1979) in which invertebrate
neurons from the sea hare Aplysia were exposed in vitro to a low-
frequency electric field indicated a strong frequency dependence in
response to extracellular currents that included synchronization
with the applied field. The neuron was most sensitive at frequencies
below 1 Hz, close to the natural firing rate of Aplysia neurons,
and for a particular neuronal orientation with respect to the field.
Other data were reported by Sheppard et al. (1980) concerning the
ELF field exposure of Aplysia neurons, including transient changes
in the firing rate and increased variability during exposure to
an electric field of 0.25 V/m rms. Episodic synchronization between
the neuron and the applied field was reported at 1.4 x 10^-4 A/cm²
(rms).

In a study by Bawin et al. (in press) on rat brain tissue
slices exposed to either 5- or 60-Hz electric fields at field
strengths in the range of the EEG, 1 - 10 V/m, evidence was
presented of long-lasting changes in neuronal excitability that
differed with field frequency and exposure duration. While 5-Hz
fields were generally excitatory, brief 60-Hz fields either
potentiated or depressed the tissue response following field
exposure, and prolonged 60-Hz fields depressed the response.
Although potentiations (believed to be due to an effect on synaptic
mechanisms) can last indefinitely (observations have lasted for as
long as 7 h), the depressed response after 60-Hz exposures was
transient, lasting about 10 min.

In summary, the results of in vitro studies suggest that
time-varying ELF electric fields may change the properties of
cell membranes and modify cell function. Several theoretical
explanations have been proposed (section 4), and it seems
conceivable that several parallel mechanisms exist. No
comprehensive and experimentally confirmed theory has been

proposed. Some of the effects observed on cells and tissues in
vitro can be detected in vivo.

5.2. Neurophysiological Studies in Animals and Animal Tissues

Blanchi et al. (1973) reported changes in the electroencephalo-
graph (EEG) patterns of guinea-pigs exposed for 30 min to a 100-
kV/m, 50-Hz electric field. Gavalas et al. (1970) noted EEG
spectral power peaks in the hippocampus, and less frequently in the
amygdala and centrum medianum, in all three monkeys exposed in 7-
and 10-Hz electric fields (7 V/m peak to peak). Others failed to
see any EEG alterations in chicks exposed at 40 kV/m (Bankoske et
al., 1976), and cats exposed at 80 kV/m (Silney, 1979). EEG
effects have not been reported in other studies.

Hansson (1981a,b) reported that Purkinje cells of the cerebella
of rabbits exposed to the 14-kV/m (50-Hz) field of an outdoor
substation or exposed in the laboratory showed pathological changes
in the cellular cytoskeleton and alterations in the concentrations
of two glial cell proteins (S-100, GFA). When young rabbits were
exposed to a 50-kV/m electric field for 6 months, no ultrastructural
changes were found in cerebellar cells, nor changes in several
plasma hormones (Portet & et al., 1984).

Jaffe et al. (1981) found a significant effect of field
exposure (30 days, 65 kV/m) on neuromuscular physiology for one
type of muscle (slow-twitch soleus), but not for another (fast-
twitch soleus).

The data from neurophysiological tests in vivo and in vitro
indicate that electric fields may have effects on tissues, especially
components of the nervous system. The physiological significance
for human beings exposed to environmental fields has not been
determined. Information is needed on the relationships between
biophysical and biological effects. In some in vitro studies,
the fields or current densities clearly exceed the values estimated
for internal fields or current densities in human beings exposed to
environmental fields.

5.3. Behavioural Studies

Among the most sensitive measures of insult to a biological
system are tests that determine modifications in the behavioural
patterns of animals. This sensitivity is especially valuable in
studying environmental agents of relatively low toxicity (Anderson
& Phillips, 1984). Behavioural studies in several species provide
evidence of field perception and the possibility that the fields
may directly alter behaviour. In rats, the threshold of detection
varies from subject to subject in the range of 4 - 10 kV/m with an
average level at about 8 kV/m (Sagan et al., 1981; Stern et al.,
1983). In mice, responses to a 35-kV/m field were reported
(Rosenberg et al., 1983); perception was seen in pigeons at
approximately 30 - 35 kV/m (Graves, 1977), and in pigs at 30 - 35
kV/m (Kaune et al., 1978).

Hjeresen et al. (1980) reported on field avoidance among rats
exposed at 75 - 100 kV/m (60 Hz). Preference for shielded areas at
night was found among pigs exposed at 30 kV/m (Hjeresen et al.,
1982). However, at 25 kV/m, rats preferred the field region during
the inactive phase (Hjeresen et al., 1980). Tests of aversion in
rats exposed to fields of 32 - 130 kV/m produced a complex pattern
of null effects in some cases (Creim et al., 1980) or positive
effects in others (Lovely, 1982), depending on the behavioural
test.

Alterations in rat activity were noted at 1.2 kV/m by Moos
(1964). Other studies on activity indicated transitory
increased response on initial exposure of rats or mice at 25 -
35 kV/m (Hjeresen et al., 1980; Rosenberg et al., 1983),
depressed activity in chickens exposed at 26 - 40 kV/m
(Bankoske et al., 1976; Graves et al., 1978), and increased
activity among bees exposed at 4.2 kV/m (Greenberg & Bindokas,
1981).

Tests with monkeys at 7 - 100 V/m exposed to frequencies
typical of the EEG (1 - 32 Hz) showed altered behavioural
reponses in an operant conditioning task (Gavalas et al., 1970;
Gavalas-Medici & Day-Magdaleno, 1976), while in other tests
involving exposure to magnetic and electric fields, behaviour
was unaffected (DeLorge, 1972, 1973). Feldstone et al. (1980)
observed minor changes in behaviour among baboons exposed to 30
kV/m (60 Hz).

Tests on the behaviour of cats exposed to ELF-modulated radio-
frequency signals were reported to show evidence of long-lasting,
frequency-specific changes in brain rhythms (EEG), and studies of
brain rhythms in rabbits exposed to ELF-modulated radiofrequencies
were also reported to show specific changes in the EEG (Takashima
et al. 1979).

Behavioural tests which most frequently showed an effect of
exposure were those relating to detection of the field or to
activity. Most other behavioural tests did not change with
electric-field exposure at field strengths up to 100 kV/m. Table 2
includes a summary of experimental results from nervous system and
behavioural studies in animals.

5.4. Sensory Phenomena

Strong electric fields cause hairs to oscillate. The movement
of hairs on the ear tips of swine was detected photographically in
60-Hz electric fields at 50 kV/m (Kaune et al., 1980); rat
vibrissae movement was observed in a 50 Hz, 50 kV/m field by
Cabanes & Gary (1981). Stern et al. (1983) attempted to examine
field sensitivity thresholds in nude or shaved rats, but saw little
difference from results with fur-bearing subjects.

Jaffe (in press) observed a direct field effect on mechanoreceptors
of the cat paw above a threshold local electric field strength of
220 kV/m.

Extraordinarily sensitive electroreceptive capabilities exist
in some species (e.g., Elasmobranch fish), particularly where
there has been evolutionary adaptation to refine sensory organs
(Kalmijn, 1966; Bullock, 1973).

Cues, including magnetic field direction, seem important in
birds (Walcott, 1974) and in several species ranging from bacteria
and bees (where ferromagnetic materials have been found) (Gould et
al., 1978) to dolphins and man (Blakemore et al., 1979), although
the data in man are disputed. These findings highlight the fact
that extrapolation of the results of experimental amimal studies to
man is quite complex. Allowances must be made for differences in
species sensitivities to ELF fields.

5.5. Effects on the Haematopoietic System in Animals

Numerous studies on animals (Blanchi et al., 1973; Cerretelli &
Malaguti, 1976; LeBars & Andre, 1976; Graves, 1977; Graves et al.,
1979; Marino & Becker, 1977; Cerretelli et al., 1979; Phillips et
al., 1979; Conti et al., 1981; Ragan et al., 1983) concern field-
related variations in blood cell populations. There is evidence in
these studies of a prompt effect on neutrophilic cells and possibly
an effect on thrombocytes and reticulocytes. The data do not permit
determination of possible mechanisms that may involve either an
effect of the internal fields directly on haematopoietic tissues,
or an effect on tissues affected via the central nervous system as
a result of peripheral sensory stimuli. In all cases, the changes
in peripheral leukocyte counts have been within the range of
physiological norms. A summary of studies on the haematopoietic
system in animals is presented in Table 3.

Table 2. Nervous system and behavioural studies in animals
--------------------------------------------------------------------------------------------------------
Exposure Frequency Subject Effects examined Reference
(kV/m) (Hz)
--------------------------------------------------------------------------------------------------------
0.0074 60 monkey no effect on operant behaviour deLorge (1973)

up to 45, 60, monkey altered behaviour (frequency specific) Gavalas-Medici &
0.056 75 Day-Magdaleno (1976)

0.01 - 7, 10 monkey changes in interresponse time, dose- Gavalas et al. (1970)
0.056 dependent, EEG entrainment at field frequency

0.1 60 rat no effect in preference behaviour or in deLorge & Marr (1974)
temporal discrimination

up to 0.1 45 mouse no effect on brain and serum sertotonin Krueger & Reed (1975)

up to 0.1 45 rat altered brain acetyl transferase Noval et al. (1976)

0.8 - 1.2 60 mouse more active in dark periods Moos (1964)

4.2 60 bees increased activity during exposure Greenberg & Bindokas
(1981)

up to 25 60 rat initial startle reaction Stern et al. (1980)

2 - 10 60 rat detection threshold approximately 8 kV/m Stern et al. (1983)

25, 50 60 mouse initial sterile reaction Graves (1977)

25, 50 60 rat preference for area of exposure Hjeresen et al. (1980)

26 60 chick peck suppression, 28% decrease in motor Graves et al. (1978)
activity

30 60 swine perception of field, prefer shielded area Hjeresen et al. (1982)
at night

30 60 rat no effect in taste aversion Creim et al. (1980)

30 60 baboon small behavioural changes Feldstone et al. (1980)
--------------------------------------------------------------------------------------------------------

Table 2. (contd.)
--------------------------------------------------------------------------------------------------------
Exposure Frequency Subject Effects examined Reference
(kV/m) (Hz)
--------------------------------------------------------------------------------------------------------
32 60 pigeon perception of field altered in exposed Graves et al. (1978)
animals

10 - 75 60 mouse transient hyperactivity in inactive phase, Ehret et al. (1980b)
35 kV/m average threshold Rosenberg et al. (1983)

40 60 chicks decreased activity in exposed animals Bankoske et al. (1976)
Graves et al. (1978)

50 50 mouse, no effect on behaviour Le Bars et al. (1983)
rat,
guinea-
pig

10 - 75 60 mouse hyperactivity with intermittent exposure Rosenberg et al. (1983)
(commencing at 50 kV/m)

67 60 chicken no effect on activity or gross behaviour Bankoske et al. (1976)

67 60 mouse hyperactivity with intermittent exposure Ehret et al. (1980a,b)

75, 90, 60 rat rats spend more time out of field Hjeresen et al. (1980)
100

80 60 cat EEG changes Silney (1979)

65^a 60 rat increased excitability of sympathetic Jaffe et al. (1980)
ganglion

65^a 60 rat no effect on peripheral nerve function Jaffe et al. (1980)

65^a 60 rat excitatory changes in neuromuscular Jaffe et al. (1981)
function; slower recovery from fatigue

100 60 rat aversion behaviour Lovely (1982)
--------------------------------------------------------------------------------------------------------
^a Effective field strength.
5.6. Cardiovascular Effects

Cardiovascular function can be assessed by measuring blood
pressure and heart rate and by performing ECGs. So far, reported
evidence of changes in cardiovascular function has been limited and
contradictory. In early studies, a decrease was reported in the
heart rate and cardiac output of dogs exposed to 15 kV/m (Gann,
1976), and an increase in heart rate in chickens exposed to 80 kV/m
(Carter & Graves, 1975). Comprehensive studies in rats showed no
effects from exposure to 100 kV/m (Hilton & Phillips, 1980).
Transient increases in blood pressure in dogs exposed to field
strengths greater than 10 kV/m have been reported (Cerretelli &
Malaguti, 1976).

5.7. Effects on Endocrinology and Blood Chemistry

A large body of data has been collected under different
exposure conditions on measurements of different blood plasma
proteins, enzymes, etc. Some of these data are summarized in Table
4. No consistent picture of physiological or pathological changes
is evident.

Many of the major hormones have been examined for the effects
of electric-field exposure, particularly in rats and mice (Phillips
et al., 1979). Possible effects have been observed in only three:
corticosterone, testosterone, and melatonin. Because corticosterone
is produced by the body in response to stress, blood levels of the
hormone are extremely sensitive to the method used in obtaining
samples. Perhaps because of this sensitivity (rather than the
effects of electric-field exposure), a number of laboratories have
reported conflicting results.

5.8. Effects on the Immune System

In considering the pattern of effects on white cell populations,
it is of special importance to evaluate the immunocompetence of
electric-field-exposed animals. Schneider & Kaune (1981) did not
find any effects on the response to infection in chicks exposed to
2 kV/m. Morris & Phillips (1982, 1983) did not find any effects on
cell-mediated or humoral immune response in rats or mice exposed to
fields of 0.2 kV/m. No effect was observed from electric-field
exposure on infectivity by a leukemogenic virus in chickens (Phillips
et al., 1981). Lyle et al. (1983), however, observed significant
decrements in the cytolytic capacity of lymphocytes exposed to radio-
frequency fields modulated at 60 Hz. In an extensive study, Le Bars
et al. (1983) found no significant effects on immune response of
rats, mice, or guinea-pigs exposed to 50 kV/m, 50 Hz electric fields
for 8, 14, or 18 h/day over periods varying from 1 to 6 months.

Table 3. Haematopoietic studies in animals
----------------------------------------------------------------------------------------------------
Exposure Frequency Subject Effects Reference
(kV/m) (Hz)
----------------------------------------------------------------------------------------------------
0.01 50 mouse altered leukocyte distribution Blanchi et al. (1973)

0.01 50 rat altered leukocyte distribution Blanchi et al. (1973)

0.01 45, 60 rat all effects within normal range Mathewson et al. (1977)

5 60 mouse decrease in RBC concentrations Marino & Becker (1977)

10 50 dog no effect on haematology Cerretelli et al. (1979)

10 50 dog no effect on haematology Conti et al. (1981)

25 60 mouse higher WBC count Graves et al. (1979)

25 50 dog altered leukocyte distribution, Cerretelli & Malaguti
RBC count and haemoglobin (1976)

50 50 rabbit altered total leukocytes and RBC LeBars & Andre (1976)

50 50 rat no effect on haematology LeBars & Andre (1976)

50 50 rat, mouse, no effect on haematology LeBars et al. (1983)
guinea-pig

50 60 mouse higher WBC count Graves et al. (1979)

65 60 rat increased leukocytes in in utero- Phillips et al. (1979)
exposed offspring
----------------------------------------------------------------------------------------------------

Table 3. (contd.)
----------------------------------------------------------------------------------------------------
Exposure Frequency Subject Effects Reference
(kV/m) (Hz)
----------------------------------------------------------------------------------------------------
65 60 rat no effect on haematology Ragan et al. (1983)

65 60 mouse WBC increased in F₂ Phillips et al. (1979)
generation females

65 60 mouse RBC increased in F₂ generation Phillips et al. (1979)
offspring

90 60 rat no effect on polychromatic RBCs Phillips et al. (1979)

100 50 rat altered leukocyte distribution Cerretelli & Malaguti (1976)

100 50 rat significant changes in blood Cerretelli et al. (1979)
morphology and chemistry

100^a 60 rat no effect on haematology Ragan et al. (1983)

100 50 rat significant changes in blood Conti et al. (1981)
morphology and chemistry

100 60 rat increased leukocytes in in utero- Phillips et al. (1979)
exposed animals

100 60 rat no effect on haematology or serum Ragan et al. (1983)
chemistry
----------------------------------------------------------------------------------------------------
^a 65 kV/m effective.

Table 4. Studies on endocrinology and blood chemistry
----------------------------------------------------------------------------------------------
Exposure Frequency Subject Effects Reference
(kV/m) (Hz)
----------------------------------------------------------------------------------------------
0.1 45 rat altered plasma corticosterone Noval et al. (1976)
levels

0.1 45 rat no effects on serum chemistry Mathewson et al. (1977)

1.5 60 rat lower melatonin in pineal gland Wilson et al. (1981, 1983)

5 60 rat no effects on serum chemistry Marino & Becker (1977)

10 60 rat adrenal response elevated Lymangrover et al. (1983)

15 60 rat lower serum corticosterone Marino et al. (1976a)

15 60 rat lower albumin Marino & Becker (1977)

15 60 dog no effects on cortisol secretion Gann (1976)

25 50 dog no effects Cerretelli & Malaguti (1976)

25, 50 60 mouse transient effect on steroid Graves (1977)
concentrations
----------------------------------------------------------------------------------------------

Table 4. (contd.)
----------------------------------------------------------------------------------------------
Exposure Frequency Subject Effects Reference
(kV/m) (Hz)
----------------------------------------------------------------------------------------------
50 50 rabbit altered calcium, glucose, urea LeBars & Andre (1976)

50 50 mouse no effects on blood biochemistry LeBars et al. (1983)

50 50 rat no effects LeBars & Andre (1976);
LeBars et al. (1983)

50 50 guinea- no effects on blood biochemistry LeBars et al. (1983)
pig

65 60 rat lower testosterone levels Free et al. (1981)
(120-day exposures); no effects
in other hormones

80 60 rat no change in corticosterone level Seto et al. (1982)

100^a 60 rat no effects on serum chemistry Ragan et al. (1983)

100 50 rat no effects Cerretelli & Malaguti (1976)
----------------------------------------------------------------------------------------------
^a 65 kV/m effective.
Evidence from many blood studies on man or laboratory animals
shows slight changes in white cell populations, almost always
within the range of normal values. These shifts may, however,
indicate some alterations involving the immune system. Further
research is indicated, before a conclusion can be reached.
Overall, the evidence from many studies indicates that animal
morbidity and mortality in long-term exposures is unaffected,
suggesting that the immune response is generally unaffected.

5.9. Growth and Development Studies

Data from many studies on rats, mice, or chickens (Knickerbocker
et al., 1967; Marino et al., 1974; Krueger et al., 1975; Bankoske et
al., 1976; Cerretelli & Malaguti, 1976; LeBars & Andre, 1976; Noval
et al., 1976; Mathewson et al., 1977; Cerretelli et al., 1979;
Graves et al., 1979; Phillips et al., 1979, 1981; Fam, 1980; Conti
et al., 1981; Greenberg & Bindokas, 1981; Le Bars et al., 1983;
Portet, 1983) suggest that there are no effects on growth and
development. In particular, the data from multi-generation studies
on mice do not indicate any pattern of an effect on these parameters.

Exceptions are reported in two instances. Severe stunting was
reported in a wild strain of rabbits reared outdoors in a
substation electric field of 14 kV/m (50 Hz) in comparison with
rabbits in an electric field-free cage (Hansson, 1981a,b). The
same author did not find any growth changes in rabbits exposed
under indoor laboratory conditions. Secondly, the results of
multi-generation studies in electric-field-exposed swine (30 kV/m)
and rats (65 kV/m) revealed developmental defects that included an
increased incidence of fetal malformations in two successive
generations of miniature swine exposed for 18 months and in one of
two rat generations (Phillips, 1981, 1983; Sikov, 1982; Anderson &
Phillips, 1984). Because of the important implications of these
studies, additional research should be conducted to address
questions that, at present, preclude conclusions concerning a cause
and effect relationship between the various fields used in these
studies and the observed effects on development. In particular, in
the swine or rat studies, similar effects were not seen in all
generations, and the influence of environmental stress in the
rabbit study requires clarification. A summary of some of the
results of growth and development studies is given in Table 5.

5.10. Reproduction and Fertility

Studies on reproductive function have been carried out at many
field strengths (Knickerbocker et al., 1967; Krueger et al., 1975;
Phillips et al., 1979; Sikov et al., 1979) with no evidence of
consistent electric-field effects in rats or mice.

Effects on rat, swine, rabbit, and chicken growth and development
are described in the previous section. Swine conceived, born, and
then kept in the electric field for 18 months showed a deficit in
mating performance (Phillips, 1981).

A summary of effects on fertility and reproduction is presented
in Table 6.

5.11. Mutagenesis

Results of studies on Drosophila (Mittler, 1972; Bender,
1976) did not indicate any mutagenic effects, though those of an
earlier study (Coate & Negerbon, 1970) had suggested effects.
Other studies (Knickerbocker et al., 1967; Krueger et al., 1975)
did not show any effects.

No effects have been observed that would suggest that electric-
field exposure is mutagenic (Phillips et al., 1979; Frazier et al.,
1982).

5.12. Circadian Rhythms in Animals

Apart from the extensive investigations of Wever (1968) on
alterations in circadian rhythms in human beings, only a few
studies have been conducted to examine the effects of electric
fields on natural biological rhythms. Ehret et al. (1980a,b)
measured rat metabolism but did not observe any effects on the
circadian rhythms of metabolism in animals exposed to 8.2 kV/m, or
on ultradian rhythm in fields up to 100 kV/m. Wilson et al. (1981,
1983) examined circadian rhythms in rats in a more direct fashion,
measuring the cyclical pineal production of indolamines and
enzymes. A significant reduction in the normal night-time rise of
melatonin and biosynthetic enzymes was observed in rats exposed to
either 1.5 or 40 kV/m. Furthermore, the change in pineal indole
response occurred only after 3 weeks of chronic exposure (Anderson
et al., 1982).

5.13. Bone Growth and Repair

McClanahan & Phillips (1983) reported that bone growth in rats
did not appear to be affected by exposure to 100 kV/m. Marino et
al. (1979) and McClanahan & Phillips (1983) reported that bone-
fracture repair was retarded in rats and mice exposed to fields as
low as 5 kV/m but not in animals exposed to very low (1 kV/m) field
strengths. Exposure may affect the rate of healing but not the
strength of the healed bone (McClanahan & Phillips, 1983).

Table 5. Studies on growth and development
-------------------------------------------------------------------------------------------------
Exposure Frequency Subject Effect Reference
(kV/m or mT) (Hz)
-------------------------------------------------------------------------------------------------
0.1 45 rat no effect on body weight Mathewson et al. (1977)

0.1 45 rat altered growth Noval et al. (1976)

3.4 45 or 75 chick no effect on body weight Krueger & Reed (1975)

3.5 (0.1 45, 60, chick no effect on posthatching Durfee et al. (1975)
- 3 mT) or 75 growth and development

5 and 15 60 rat decreased body weight Marino et al. (1976, 1980)

7 60 bee no effect on bee or hive weight Greenberg et al. (1979)

10 and 15 60 mouse decreased body weight Marino et al. (1976)

14 50 rabbit stunted growth (raised outdoors) Hansson (1981a,b)

15 60 rat increased pituitary and adrenal Marino et al. (1976)
weights in exposed

25 60 mouse no effect on development Phillips et al. (1981)

25 50 rat lower growth rate Cerretelli et al. (1979);
Conti et al. (1981)

30 60 swine no effect on body weight Phillips et al. (1979)

30 60 swine increased rate of fetal malfor- Phillips et al. (1981);
mations (in 2 generations) Phillips (1983)
-------------------------------------------------------------------------------------------------

Table 5. (contd.)
-------------------------------------------------------------------------------------------------
Exposure Frequency Subject Effect Reference
(kV/m or mT) (Hz)
-------------------------------------------------------------------------------------------------
50 50 rabbit no effect on growth LeBars & Andre (1976)

50 50 mouse, no effect on growth LeBars et al. (1983)
rat,
guinea-
pig

50 50 rat no effect on growth Portet (1983)

65 60 rat increased rate of fetal malfor- Phillips (1983)
mations (1 of 2 generations)

67 50 chicken no effect on body weight Bankoske et al. (1976)

80 60 chick no effect on body weight Graves et al. (1979)

80 50 chick no effect on growth Bankoske et al. (1976)

100 50 rat no effect on embryo morphology Cerretelli & Malaguti
(1976)

100 50 rat lower growth rate Cerretelli et al. (1979);
Conti et al. (1981)

100 60 rat no effect on growth Phillips et al. (1979)

160 60 mouse lower body weight in offspring Knickerbocker et al. (1967)
of exposed males
-------------------------------------------------------------------------------------------------

Table 6. Studies on fertility and reproduction
--------------------------------------------------------------------------------------------
Exposure Frequency Subject Effect Reference
(kV/m) (Hz)
--------------------------------------------------------------------------------------------
1.6 (or 60 chicken reduced egg production Krueger et al. (1975)
1.2 G)

3.4 60 chicken no effects on hatchability, em- Krueger et al. (1975)
bryonic morphology, or sex ratios

3.5 (or 45, 60, chicken no effects on hatchability, Durfee et al. (1975)
1 - 3 G) or 75 embryonic survival

10 or 15 60 mouse no effects on litters or litter Marino et al. (1976)
size

30 60 swine (F₀) no effects on farrowing success Phillips (1981)
rate (1st breeding)

30 60 swine (F₀) increase in fetal abnormalities Phillips (1981)
(2nd breeding)

30 60 swine (F₁) poor breeding performance Phillips (1981)

30 60 swine (F₁) increased fetal abnormalities Phillips (1983)
(1st breeding)

50 50 rat no effect on estrus cycle LeBars & Andre (1976)

67 60 chickens no effects on hatchability or Bankoske et al. (1976)
time to hatch
--------------------------------------------------------------------------------------------

Table 6. (contd.)
--------------------------------------------------------------------------------------------
Exposure Frequency Subject Effect Reference
(kV/m) (Hz)
--------------------------------------------------------------------------------------------
100 50 rat effect on numbers of matings and Cerretelli & Malaguti
pregnancies (1976)

100 50 rat no effect on fertility Cerretelli et al.
(1979); Conti et al.
(1981)

100 60 mouse no effects on fertility, mor- Phillips et al. (1979)
tality, size of litter, sex ratio

100 60 rat no effects on mortality, litter Sikov et al. (1979)
size, or reproductive performance

100 60 rat earlier development of motor Phillips et al. (1979)
activity

160 60 mouse no effect on reproductive ability Knickerbock et al.
(1967)
--------------------------------------------------------------------------------------------

5.14. The Problems of Extrapolating Animal Exposure Data to Human
Beings

Because either the surface electric field or the internal
current density at a particular organ varies with the size, shape,
and orientation of the body, no single animal model can successfully
simulate the exposure conditions of a human being. At best, a
single study can approximate human exposures either to the surface
fields at a selected spot, or to the internal current density in a
selected organ (Sheppard & Eisenbud, 1977; Kaune & Phillips, 1980).

Kaune & Phillips (1980) calculated the current through various
sections of the body, and from the cross-sectional area, calculated
the average current density for the rat, swine, or human being
exposed to the same (unperturbed) electric field. The data showed
very large differences in currents as a function of animal posture.
For example, the total neck current in a horizontal rat exposed to
a 10-kV/m vertical E field was 1.6 µA, but, when the rat reared,
the current increased to 3.2 µA. The respective current densities
were 28 and 140 nA/cm². An even larger ratio of about 7-fold
occurred for the chest currents, while, in the abdomen, the resting
rat had a current density of only 2 nA/cm² compared with 85 nA/cm²
in the rearing rat. In either case, because of the larger capacitance
of the human body, the current density in the human neck will be
greater than that in the rat.

According to the foregoing considerations, for example, a study
designed to examine the effects of electric current density in the
neck of a man exposed to 10 kV/m would, if conducted on rats,
require an electric field of 200 kV/m, or in the case of pigs, 140
kV/m, whereas studies involving animals that stand erect more often
(such as primates) would require lower field strengths (Kaune &
Phillips, 1980). An electric field that produced a reasonable
match between man and the test animal in one part of the body would
tend to overexpose other parts of the animal body, for example, the
limbs.

Another approach to the determination of relative exposures
between man and animals considers the "enhancement factors" for the
surface electric field. Deno (1977) reported that, for human
beings, the surface electric field at the top of the head was 18
times that of the unperturbed electric field, whereas at the back
of the head the enhancement was 15 fold. At the upper arm, an 8-
fold enhancement occurred for the size and shape parameters given
by Deno. When a rat was exposed to a 10-kV/m unperturbed electric
field, the maximum field strength of 37 kV/m occurred at the back,
while an upright man in the same field had a maximum field of 180
kV/m at the top of the head (Kaune & Phillips, 1980).

These data indicate that man's size and posture make it
difficult to simulate in laboratory animals the current densities
that occur when man is exposed to strong electric fields. Because
of the interference of artifactual shocks, hair stimulation,
corona, and other problems of extremely high voltage, it is not
practical to expose animals to levels much higher than 100 kV/m.

The species differences between man and laboratory animals
may strongly affect the threshold for biological response, the
magnitudeof a physiological response, and the degree of adaption.
Biochemical differences among species may also prove significant.
None of these species-dependency factors is understood in the
context of ELF electric field exposures.

Magnetic field exposures may require scaling according to body
size, shape, and orientation if the primary action is due to the
induced electric field. The magnetic field itself is not perturbed
by either animal or human bodies and is essentially unchanged at
points outside or inside the body.

6. HUMAN STUDIES

6.1. Sources of Information

Three sources of information exist concerning the effects on
man of exposure to ELF fields:

(a) surveys of the state of health of high-voltage
linemen, utility, substation, and switch-yard workers;

(b) epidemiological studies of inhabitants near
high-voltage transmission lines, power distribution
lines, and substations; and

Additional information can be obtained from follow-up studies
of patients exposed to ELF fields as a result of medical applications.
Except for a report by Bassett (1981) on the state of patient health,
information is related to the effectiveness of the applied medical
procedure.

Although there is no good substitute for reliable epidedmiological
data for the evaluation of general population and occupational health
aspects of ELF exposure, data from present studies are insufficient
to draw any firm conclusions.

However, other epidemiological studies are in progress which
may provide further information needed to establish better health
criteria (Baroncelli et al., 1984; Checcucci, 1984; Knave, 1984).

6.2. Study Design

In epidemiological studies, it is difficult to obtain quantitative,
unbiased data that can be reliably interpreted. Two problems with
most of the human studies to date are the failure to obtain
measurement data on the level and duration of exposure, and the
failure to include an appropriate control group that is comparable
in all respects to the exposed group, except for exposure to the
electromagnetic field. While this does not necessarily invalidate
the results of such studies, these shortcomings must be taken into
account.

End-points can be selected to ascertain the health impact of
ELF exposure in areas of particular public concern. Effects on the
nervous system, behaviour, the cardiovascular system, tumour
incidence, reproductive success, or development are among the
appropriate end-points. Some authors (Utidjian, 1979) maintain
that, because there is no basis for postulating a specific disease
or cause of death related to ELF exposure, epidemiological studies
need to be cross-sectional, evaluating the general state of health
and the incidence of diseases. A basic problem is the selection of
appropriate matched control groups. Other, often overlooked
problems include those of obtaining appropriate information on

exposure duration and levels, the occurrence of confounding
factors, as well as the need for differentiation between the
effects of ELF exposure and the influence of collateral phenomena
such as noise, microshocks, ozone, or possibly the presence of
various ions and chemical substances.

Finally, to prevent the introduction of bias, all studies
should be "blind". This means that, whenever possible, personnel
who record data should be unaware of the subjects' exposure
history.

6.3. Health Status of Occupationally-Exposed Human Beings

A summary of studies on the health status of linemen and
switch-yard workers is given in Table 7.

Asanova & Rakov (1966) examined 45 high-voltage switch-yard
workers. This survey indicated a variety of symptoms in the
cardiovascular, digestive, and central nervous systems subsequent
to prolonged exposure of switch-yard workers to electric fields (up
to 26 kV/m). The disturbances noted were subjective. No control
group was examined. Furthermore, recent work in the USSR has
suggested that the observed effects might be the result of exposure
to microshocks or kerosene vapour rather than to electric fields
(Danilin et al., 1969; Savin et al., 1978; Bourgsdorf, 1980).

Results from the earliest comparable studies in the USA failed
to confirm those of the USSR studies. Kouwenhoven et al. (1967)
and Singewald et al. (1973) who studied 10 linemen exposed during
their work (4-year period) to unperturbed fields of up to 25 kV/m
did not observe any correlation between exposure and the health of
the subjects. However, this study included only a small number of
subjects, and descriptions of the experimental protocol and results
were incomplete.

Sazonova (1967) reported on physiological tests performed on
400 - 500 kV substation workers divided into 2 groups according to
the presumed extent of electric field exposure. The high electric-
field-exposed group had significantly lower blood pressure, greater
neuromuscular activity, and increased latent reaction times and
higher error rates in a stimulus-response test. The exposure
information was not adequate to determine either electric field
strength or duration of exposure.

Table 7. Studies on the health status of linemen and switch-yard workers
-----------------------------------------------------------------------------------------
Reference No. of Comments
subjects
-----------------------------------------------------------------------------------------
Kouwenhoven et al. 10 Linemen, 10-year period of observation, only general
(1967); Singewald medical data, no effects reported, no data on exposure
et al. (1973) levels, no control groups; same subjects in both
studies

Asanova & Rakov 45 Switch-yard workers (500 kV): subjective and objective
(1966) indications of functional neurovegetative disturb-
ances; exposure estimated; no control group; Danilin
et al. (1969) suggested that chemical pollution
(kerosene) may have been responsible

Sazonova (1967) 211 Switch-yard workers (400 - 500 kV): exposure
estimated; neurovegetative disturbances (as above);
increased latent reaction time and error rates; no
control group

Revnova et al. 114 Switch-yard workers (500 kV): findings as Asanova &
(1968) Rakov (1966); inadequate data on exposure; no control
group

Danilin et al. 12 Switch-yard workers: detailed clinical (hospital-
(1969) ization) study; average exposure 14 kV/m, maximum 26
kV/m; no effects; no control group

Fole et al. 9 Switch-yard workers transferred from a 200 kV to a 400 kV
(1974); Fole substation: exposures up to 15 kV/m; findings as Asanova
(1973) & Rakov (1966) plus visual troubles; no control group

Malboysson (1976) 160 84 switch-yard workers and 76 HV-linemen compared to 94
controls (low-voltage linemen): questionnaires and medical
examinations; no effects, better health of HV-workers;
inadequate data on exposure; no statistical analysis

Roberge (1976) 160 Switch-yard workers (735 kV): inadequate data on exposure;
no health effects; electric shock anxiety; ratio male/
female offspring 17:3; no control group

Stopps & 30 Linemen compared to 30 matched controls from among the
Janischensky power company employees: clinical studies, including ECG
(1979) and EEG; no effects; exposed group was preselected
(volunteers); exposures extrapolated from measurements

Knave et al. 53 400 kV station workers matched with 53 unexposed power
(1979) company employees: no differences in health status;
comprehensive medical and psychological study; good
exposure data

Issel et al. 110 Linemen working on 110 and 380 kV lines with protective
(1977) clothing; no effects; control group used
-----------------------------------------------------------------------------------------
Table 7. (contd.)
-----------------------------------------------------------------------------------------
Reference No. of Comments
subjects
-----------------------------------------------------------------------------------------
Broadbent et al. 390 Questionnaires on linemen and switch-yard workers; 28
(in press) exposed above level of detection threshold of monitor;
control group; no effects found
-----------------------------------------------------------------------------------------
Revnova et al. (1968) carried out a study on 114 workers (99
males, 15 females) in a 500 kV substation with findings similar to
those of Asanova & Rakov (1966). Danilin et al. (1969) did not
report any adverse health effects in a clinical study on 12 workers
exposed to an average field strength of 14 kV/m, which generated
whole body currents of 130 µA (maximum 26 kV/m and 230 µA).
Krivova et al. (1973) found no physiological changes at 10 kV/m,
but did identify some impairment of motor skills after exposure for
2 h to 16 kV/m.

To assess the health status of electricians on high voltage
systems, an investigation was started in the German Democratic
Republic in 1971 (Kupfer & Issel, 1975). The subjects included
linemen wearing protective clothing who worked bare-handed on 110 -
380 kV lines (Jahn et al., 1978). The men were examined according
to clinical criteria (locomotion system, cardiovascular system,
respiration system, haematopoietic system, kidney and liver
function, eyes, ears, and nose) and psychological criteria (risk-
taking behaviour, motivation, sensomotor coordination, reaction
time, intellectual abilities for technical thinking, personality).
Examination of 110 linemen and fitters did not reveal any health
changes or injuries attributable to the 50-Hz fields (Issel et al.,
1977). Electric fitters exposed under similar physiological and
psychological conditions, but at a field strength of 5 kV/m, served
as a control group.

In Spain, Fole (1973) and Fole et al. (1974) reported subjective
health effects among 6 workers from a 400-kV substation; there was
no control group. A group of 84 substation workers and 76 linemen
in Spain were compared with 94 linemen working on low voltage systems
(Malboysson, 1976). The linemen in both groups showed no apparent
adverse effects due to work in electric fields. No exposure
measurements were taken, and the data were not statistically analysed.

Knave et al. (1979) examined 53 workers at 400 kV-substations
in comparison with a matched reference group of 53 unexposed
workers. Only occasional exposures to field strengths above 5 kV/m
occurred (Table 8). Data on subjective complaints were collected
using standard questionnaires and interviews. Eight psychological
tests were performed. EEGs and ECGs were recorded, blood pressure
measured, and peripheral blood cell counts were made. No biochemical
tests were made. Comparison of substation workers and the reference
group generally showed no observation of a lower number of offspring.
However, a lower rate of male offspring was observed but not
attributed to electric field exposure.

Table 8. Percentage (%) of working time spent in electric fields
of different strengths by 400-kV substation workers^a
------------------------------------------------------------------
Type of work E-field strength ranges (kV/m)
0 - 5 5 - 10 0 - 15 15 - 20
------------------------------------------------------------------
Inspection rounds 66 37 2 1

Everyday work 34 61 4.8 0.2

Breaker work:

Revision 60 0 18 16

Testing 95 5 0 0
------------------------------------------------------------------
^a From: Knave et al. (1979).

In an earlier study (Roberge, 1976), 56 switch-yard workers at
735-kV substations in Quebec, Canada were examined. A questionnaire
oriented towards nervous system complaints was used, and a clinical
examination that included an ECG and a thorough examination of the
peripheral blood chemistry, was conducted. The data were compared
with "normal" reference values rather than those of a control group.
Differences in eosinophil number ( P < 0.05) were, however, within
clinical norms, and of doubtful statistical value.

Stopps & Janischewsky (1979) studied 30 high-voltage maintenance
men and 30 matched employees not exposed to electric fields. Clinical
and psychological investigations were made in a hospital. In the
exposed group, 19 linemen had estimated exposures of 7 kV/m h per day
(up to 8000 kV/m h over 10 years); and 11 substation workers had
average estimated exposures of 13 kV/m h per day (up to 36 000 kV/m
h over 10 years). No adverse health effects were found.

A health-questionnaire study (Broadbent et al., in press) was
conducted on 390 electrical power transmission and distribution
workers employed in the electrical industry in the United Kingdom,
of whom 28 were exposed to levels above the detection threshold of
the dosemeter. Actual exposure levels, measured during the two
weeks prior to the questionnaire interview, were considerably less
that the estimated exposures. About 150 interview questions were
administered by industrial nurses. Each man was asked to assess
his own experience of headaches in the last 6 months on a scale 0 -
3. Visits to doctors over six months and taking of prescribed or
unprescribed medicines were noted. A measure of cognitive failure,
i.e., frequency of minor episodes of forgetfulness or inattention,
was measured. Although there were significant differences in the
health effect measurements between different job categories and
different parts of the country, no significant correlation was
found between these effects and exposures to electric fields.

Five preliminary observations were reported, four published as
"letters to the editor", of an increase in the incidence of
leukaemia in groups of workers loosely defined as "electrical
workers" (Milham, 1982; Wright et al., 1982; Coleman et al., 1983;
McDowall, 1983; Vagero & Olin, 1983).

Milham (1982) reported on a data base of 438 000 deaths of men,
who were 20 years of age or older and were residents of Washington
State, USA, from 1950-79. A proportional mortality ratio (PMR =
observed/expected x 100) due to leukaemia, significant at the P <
0.01 level, was observed for "electricians", TV and radio repair-
men, power station operators, and aluminium workers. Wright et al.
(1982) sought to verify Milham's (1982) results by examining a
similar statistic, the proportional incidence ratio (PIR) of a
different and much smaller data base. They found significant
increases ( P < 0.05) in the incidence of acute myeloid leukaemia
(on the basis of a total of 4 cases) in power linemen and telephone
linemen, two groups for which the Washington data yielded
insignificant PMRs.

Additional data on occupational leukaemia rates in the United
Kingdom were provided in two letters. McDowall (1983) found an
increased evidence of leukaemia in occupationally-exposed
electrical workers using PMRs and also by a case-control study.
Coleman et al. (1983) also examined the leukaemia incidence for the
same electrical occupations with evidence of a 17% excess that was
especially strong for electrical fitters and telegraph operators,
for whom the extent of electric or magnetic field exposure was not
established.

These occupational groups have a number of environmental
factors in common, viz, exposure to electromagnetic fields and a
variety of metals and chemical fluxes. Electricians working in
homes usually work on equipment that is not operating or operates
at low voltages. Telecommunication and electronic personnel are
normally exposed to levels of power frequency electric or magnetic
fields no higher than those encountered in the average modern home.
These reports are inadequate in many ways for use in determining if
there is any association between leukaemia and exposure to electric
or magnetic fields. However, they merit further detailed study to
elucidate the signficance of the findings.

Finally, Vagero & Olin (1983) examined data from the Swedish
Cancer Environment Registry for the incidence of all types of
cancer among electrical or electronic industry workers compared
with the general working population. The authors claimed a nearly
two-fold excess of pharyngeal cancers among the test population.
However, the accuracy of the job classifications over the relevant
time periods was questionable. The authors were careful to point
out that caution was needed for any conclusions with regard to
relationships.

The association of electrical occupation with leukaemia
suggested in these studies was not consistent and often involved
very few disease cases in an occupational category. Deficiencies
these studies could be summarized as follows (Repacholi, 1984a):

(a) lack of consistency in designating occupational
classification;

(b) no account was taken of mobility between occupations;
and

(c) occupational groups sharing exposure to electric and
magnetic fields were undoubtedly exposed to other
physical and chemical agents.

In studies such as these, associations can be detected with a
reasonable degree of certainty, if appropriate statistics are
applied to a large enough data base of good integrity. The
suggestion of field-related leukaemia raises important questions
that should be addressed using studies of adequate statistical
power in which exposure is more accurately determined.

Bauchinger et al. (1981) examined the chromosomes in blood
lymphocytes of 32 switch-yard workers (380 kV) and did not find any
differences in comparison with matched, unexposed workers. However,
the control group demonstrated a rather high incidence of chromatid
gaps, 17 ± 1.3 per 1000 cells, compared with the "positive" control
group of nuclear power plant workers (15.0 ± 1.0 per 1000 cells).
In Sweden (Nordström et al., 1981), preliminary work has been
described in which increased frequency of chromosome breakage was
seen in a few workers exposed to 400 kV. Furthermore, congenital
deformities were found in 10% of 119 children of substation workers,
whereas only 2.7% of children of unexposed workers showed such
deformities (Nordström et al., 1983). Analyses of these data raise
major questions in the interpretation of the results, because the
highest percentage of abnormal progeny appears to be related to
type of job rather than to level of exposure (Anderson & Phillips,
1984).

More research is this area is necessary in properly-designed
human studies of significant magnitude to establish whether any
asociation exists between exposure to ELF and induction of
chromosome aberrations.

Nordström & Birke (1979) carried out a retrospective study on
the incidence of congenital malformation in the progeny of 542 male
employees of the Swedish State Power Board. The increased frequency
of malformations reported in this study occurred evenly throughout
the populations studied, irrespective of whether they worked in 400
kV, 130 - 200 kV, or 70 kV situations.

Employees exposed to very low level ELF electric fields
(generally less than 0.05 V/m and accompanying magnetic flux of
densities 10^-5 T) at the site of a test communications antenna
(Project Sanquine) did not show any pathological effects related to
the fields. In particular, an investigation for neurological
symptoms did not reveal any effects (Krumpe & Tockman, 1974).

6.4. Studies on the General Population

Wertheimer & Leeper (1979) reported a two- to three-fold
increase in the incidence of leukaemia among Colorado children
presumably exposed to magnetic fields of strengths up to 0.7 mT.
Magnetic fields were estimated by scoring the type of electrical
wiring configuration close to the homes (power lines of various
voltages and current-carrying capacity) into categories of high- or
low-current configurations.

The same authors (Wertheimer & Leeper, 1982), extended their
work to a study of the incidence of adult cancer in people living
near high-current electric wiring. The associations suggested were
not dependent on age, urbanism, neighbourhood, or socio-economic
level and were more clearly demonstrated when urban/industrial
factors were not present to obscure the pattern. The four types of
cancer that appeared to be particularly elevated in the exposed
adult populations were cancer of the nervous system, uterus,
breast, and lymphomas. The authors suggested that magnetic fields
might have a promoter effect since the increases were maximal, 7
years from the time of taking up residence in the area.

These preliminary studies have limitations common to many
epidemiological studies involving cohort selection. Additional
problems include possible biases in the techniques for scoring the
wiring configurations, and in the assumption that the scoring does
accurately segregate magnetic field strength levels among the cases
examined.

Further questions are raised since the data were not collected
blind and cases were ascertained after death, no account being
taken of cancer cases still alive. Furthermore, both birth and
death addresses were used, which introduces a potential for
observer bias.

Considerable interest has been provoked by these findings and
it is expected that many of the issues will be dealt with in
follow-up studies.

The hypothesis that such weak magnetic fields (of the order of
0.1 - 0.7 µT) induce biological effects has raised questions such
as those of Miller (1980), who criticized the Wertheimer & Leeper
studies on the basis that the magnetic field from electrical
appliances in the home would far exceed any contributions from
electrical wiring configurations in the environment.

A similar study carried out by Fulton et al. (1980) in Rhode
Island failed to reveal any evidence to support the Wertheimer and
Leeper hypothesis. However, Wertheimer & Leeper (1980) reanalysed
the Rhode Island data using their own study method and found a
slight association of childhood cancer with electrical wiring
configuration.

Tomenius et al. (1982) reported a similar finding of increased
leukaemia incidence in children living in homes where the levels of
the magnetic field measured outside the front door were 0.3 µT or
above. The data involved a small number of cases and, again, the
field measurement was questionable because the relation of actual
exposure to the field outside the home was not established. These
studies and the preliminary occupational data (see above) relating
some concern to electric or magnetic field exposure must be
investigated further to determine if the suggested link with cancer
induction or promotion can be established.

6.4.1. Studies on inhabitants of areas in the vicinity of HV-lines

A four-year study on 70 men, 65 women, and 132 children living
within 25 metres of 200 and 400 kV lines has been reported by
Strumza (1970). The control group consisted of 74 men, 64 women,
and 120 children living more than 125 metres from the lines. The
author failed to discover any differences between the exposed and
control groups on the basis of medical records, frequency of visits
to family doctors, or expenditure on pharmaceutical prescriptions.
Eckert (1977) tried to establish a relationship between the sudden
infant death syndrome and ELF fields, but the method and results
were questionable.

In a study by Dumansky et al. (1977), no effects were found in
farmers exposed to fields of 12 kV/m for 1.5 h/day. Similarly,
Busby et al. (1974) did not find any effects in 18 farmers working
on farms in the vicinity of a 765 kV line.

Reichmanis et al. (1979) and Perry et al. (1981) have suggested
a link between electromagnetic field exposure and suicide. It has
been pointed out (Bonnell et al., 1983) that the reports lack any
biological hypothesis. Suicide is frequently a symptom of a
pre-existing psychotic illness, and it is these diseases that are
important in studying suicide. Furthermore, these authors claimed
that the conclusions were contradictory and open to serious
criticism on the basis of incorrect use of epidemiological data.
The calculation of the magnitude of electric fields was also in
error by a factor of 10 000 (Bonnell et al., 1983).

6.5. Studies on Human Volunteers

There is only a limited amount of data on human volunteers
exposed to electric fields, low-level currents, or spark discharges
under laboratory conditions. These data are valuable because of
the greater control over extraneous influences compared with
occupational exposures and because they involve the human organism.

Of course, studies on human beings are limited to physiological and
behavioural observations that do not cause harm and the test
sessions are usually relatively short.

In considering these studies, it is important to remember that
microshocks can be felt in fields of above 3 kV/m (Takagi & Muto,
1971) and therefore can cause unease in subjects. To assess the
effects of the ELF field itself, it is necessary to take care to
eliminate the influence of microshocks in the experimental design.

In 1974, R. Hauf and co-workers reported studies on more than
100 human volunteers exposed to 50 Hz electric fields (up to 20
kV/m) during laboratory test sessions that involved relatively
brief exposures to the field. In the first report (R. Hauf, 1974),
no field-related effects were observed on reaction time, blood
pressure, pulse rate, electrocardiogram, or electroencephalogram.
Changes in some blood cell variables were seen, but these were
within the normal physiological range. Each of the 3-h test
sessions included 2 exposures for 45 min to fields at 1, 15, or 20
kV/m, and the testing lasted 3 successive days. Detailed
descriptions of the studies are available in the reports of R. Hauf
(1974) and Rupilius (1976).

Rupilius (1976) conducted a study on man where 3 days exposure
to a 20 kV/m electric field at 50 Hz was combined with exposure to
a 0.3 mT magnetic field at 50 Hz. Observations for up to 24 h
after exposure showed no changes in blood chemistry, including
triglyceride levels. Eisemann (1975) did not show any effects on
human subjects exposed for a period of 3 h to a conduction current
of 200 mA at 50 Hz, by means of electrodes placed on the ankles and
under the arms.

No significant behavioural changes were observed in 20 human
subjects exposed to an electric field of 20 kV/m (50 Hz) (Johansson
et al., 1973). The exposed subjects performed as well as controls
in tests of reaction time and in psychological tests, and responses
to a questionnaire did not show any significant differences in
perceived levels of discomfort between the test and control groups.

The results of several studies performed by Wever (1968)
indicated a significant influence of weak ELF electric fields on
human circadian rhythms. He found that the complete absence of
electric or magnetic fields led to desynchronisation of certain
biorhythms, but that synchronisation was restored by an applied
2.5-V/m, 10-Hz, square-wave electric field. These data are
difficult to interpret with reference to electric fields at
environmental levels. Wever postulated the existence of a
physiological detector of weak electric fields but did not
associate this finding with the possibility of health effects from
imposed ELF fields.

Human volunteers were also exposed to both electrical fields of
20 kV/m and magnetic fields of 5 mT by Sander et al. (1982).
Neither field produced any evident influence on the different
parameters studied, except some discontinuous variations in certain
of them.

Studies on the nervous system and behaviour in man are summarized
in Table 9, and studies on the haematopoietic system, in Table 10.

6.6. Summary

Few physiological or psychological effects in human beings have
been credibly related to electric field exposure. Such effects,
when reported, have often been questionable for the following
reasons (Anderson & Phillips, 1984):

(a) monitoring of symptomatology was subjective and was
frequently not well-defined;

(b) quantitative evaluation of effects was either not
performed or was not clearly described;

(d) electric fields had been confounded by secondary
factors (e.g., microshocks);

(e) observation periods were often short;

(f) exposure levels varied widely or were not documented,
making it difficult to estimate accurately the
magnitude and duration of exposure;

(g) numbers of subjects in many of the earlier studies
were insufficient to establish the statistical
significance of adverse effects.

Table 9. Studies on the nervous system and behaviour in man
--------------------------------------------------------------------------------------
Exposure Frequency Effects examined Reference
(Hz)
--------------------------------------------------------------------------------------
1, 15, or 20 kV/m 50 altered reaction time within G. Hauf (1974)
(up to 2 h) normal range; no effect on EEG R. Hauf (1974)
R. Hauf (1976)

20 kV/m, 0.3 mT 50 no effect on reaction time or EEG Rupilius (1976)
(for 3 h) R. Hauf (1976)

0.3 mT 50 no effect on reaction time or EEG Mantell (1975)
R. Hauf (1976)

200 µA (for 3 h) 50 no effect on reaction time or EEG Eisemann (1975)

6 kV/m (2 x 3 min) 50 effect on EEG when field "on" Waibel (1975)

380 - 400 kV 50 no effect on manual dynamometry Fole et al. (1974)
switch-yards

400 kV switch-yard 50 neuromuscular deficits among Sazonova (1967)
workers exposed workers

400 kV switch-yard 50 various clinical diagnoses related Asanova & Rakov
workers to CNS (1966)
--------------------------------------------------------------------------------------

Table 10. Haematopoietic studies in man
---------------------------------------------------------------------------
Exposure Frequency Effect Reference
(Hz)
---------------------------------------------------------------------------
1, 15, or 20 kV/m 50 altered total leukocytes, G. Hauf (1974)
(for 3 h) absolute neutrophils and R. Hauf (1974)
reticulocytes - all R. Hauf (1976)
within normal range

0.3 mT (for 3 h) 50 no effects Mantell (1975)
R. Hauf (1976)

20 KV/m, 0.3 mT 50 no effects Rupilius (1976)
R. Hauf (1976)

200 µA^a 50 no effects Eisemann (1975)
R. Hauf (1976)

5 mT (for 4 h) 50 no effects outside normal Sander et al.
range (1982)

20 kV/m (6.22 h/ 50 no effects outside normal Sander et al.
day) (for 1 week) range (1982)
---------------------------------------------------------------------------
^a No field, only conduction current via electrodes (approximately
equivalent to exposing man in a 12-kV/m field).

7. HEALTH RISK EVALUATION

In making an evaluation of the health risks of exposure to
ELF electric and magnetic fields, a number of factors must be
considered (Repacholi, 1984a). Criteria must be developed to
identify which effects are to be considered a hazard for human
health. A distinction needs to be made between the concepts of
interaction, biological effect, perception, and hazard.

Difficulty in defining the term health hazard occurs because
value judgements are involved that may not be based on scientific
analysis. Some may consider any field-induced interaction
hazardous. Others suggest that the field is hazardous if it is
capable of inducing a physiological perturbation in a biological
system that is either measurable or at least theoretically
possible. Still others note that a stimulus-producing sensation
without pain or discomfort is often assumed to be harmless, but
modern research has demonstrated that the opposite may be true
(Grissett, 1980).

Interactions that lead to measurable biological effects, which
remain within the normal range of physiological compensation of the
body and do not detract from the physical and mental well-being of
human beings, should not be considered hazardous. Interactions
that lead to biological effects outside the normal range of
compensation of the body may be an actual or potential health
hazard (Repacholi, 1983).

When making a health risk evaluation, strict guidelines must be
established prior to reviewing the literature on the biological
effects of exposure to static and ELF fields. Certain studies
(generally in vitro) are conducted to identify underlying
mechanisms of interaction. Health risk evaluations cannot be made
on the basis of in vitro experiments alone, because effects found
in vitro many not necessarily occur in vivo. With in vitro
experimentation, the toxicity of an agent can be determined in
increasingly complex steps. For example, effects on solutions of
biological molecules might be used as a model system to study a
predominant mechanism of action. Uncomplicated systems can assist
in the exploration and evaluation of mechanisms and may serve as a
useful basis for designing experiments at the cellular level - the
next level of biological complexity. By restricting the complexity
of the experimental system, there will be less chance of possible
subtle effects being masked by gross or dominant effects.

Thus, health agencies can place only limited value on in vitro
studies and must await the results of similar or related studies
conducted in vivo. The in vitro results may indicate that a
cautious or prudent approach should be adopted when setting
standards (Repacholi, 1983). This may be reflected in the
development of a safety factor which is applied to the lowest level
of exposure at which adverse effects are observed. Once the
mechanisms of interaction are understood and found to occur in
animals, the next step is to determine if it is possible to
extrapolate the results to man.

Unfortunately, the state of knowledge of the interacting
mechanisms operating when biological systems are exposed to
ELF fields is very limited. At present, it is impossible to
furnish any theory to predict the effects of exposure to these
fields. Because of this lack of information, care must be taken
in attempting to predict or extrapolate effects in man from effects
found in animals. Physical differences (size, shape, fur-bearing,
etc.) result in marked differences in the internal field distribution
(Kaune & Phillips, 1980), and in different behavioural and
homeostatic responses.

With such limited data available on biological effects and
interaction mechanisms, the only practical approach left for making
a health risk evaluation is to evaluate the available data on
exposure levels and effects to determine if thresholds for effects
occur (Repacholi, 1984a). In undertaking such an evaluation, it is
necessary to be selective as far as the data are concerned. Only
reports that provide adequate information on experimental technique
and dosimetry should form part of the evaluation. Ideally, from a
regulatory viewpoint, only data that have been established and have
a direct bearing on health risk should be considered. Publication
in a peer reviewed journal helps, but in the final analysis, unless
the data have been confidently reproduced, the results should be
considered tentative pending confirmation.

It would be ideal to make health risk evaluations on the basis
of well-conceived, well-conducted, and well-analysed epidemiological
studies. Unfortunately, all such studies on human beings exposed
to ELF fields have suffered from one or more deficiencies, as
indicated in section 6.

With such a limited scientific data base, the determination of
the existence of a true threshold exposure level below which no
adverse health effect occurs, cannot be made with confidence.
Thus, any health risk analysis for the development of standards
must inevitably adopt a phenomenological approach (Kossel, 1982;
Repacholi, 1983). In this case, a review of the literature is made
to determine the lowest exposure levels at which adverse biological
effects have been established. A biological effect that occurs in
living organisms or animals may be detected as some general or
specific alteration. If the change appears irreversible or
pathological, it might be presumed that it could be hazardous to
man under comparable exposure conditions. This assumption is made
only because insufficient information is available on the effect or
the underlying interaction mechanism to make an extrapolation to
exposure conditions producing similar effects in human beings and
to make a well-substantiated health risk evaluation.

The epidemiological studies (Wertheimer & Leeper, 1979, 1982;
Tomenius et al., 1982) suggesting a relationship between childhood
or adult cancer and residence in houses at various distances from
high current flow due to external electrical wiring configurations,
can only be considered as preliminary because of the many criticisms
that have been levelled at the studies (section 6).

The studies (Milham, 1982; Wright et al., 1982; Coleman et al.,
1983; McDowell, 1983; Vagero & Olin, 1983) suggesting an association
between electrical occupations (exposure to electric and magnetic
fields) and cancer were analyses of occupational mortality data and
subject to many sources of errors (section 6).

Thus, although these reports suggest potential adverse health
effects, they cannot be evaluated in terms of health risk until the
potentially confounding factors and sources of errors are eliminated.
It is of concern, however, that no studies have yet been published
following up these reports.

Laboratory studies on human volunteers exposed for short
periods to electric fields (up to 20 kV/m) have, in general, shown
no effects (Hauf & Wiesinger, 1973; Johansson et al., 1973; Hauf,
1974; Rupilius, 1976; Sander et al., 1982). The results of these
studies suggest that no apparent acute effects are likely from
exposure to strong electric fields. However, they cannot be used as
indicators that no health effects will occur from long-term
exposure (months or years).

Studies on the health status of linemen and switch-yard workers
have not revealed any differences between exposed and control
groups (Knave et al., 1979; Stopps & Janischensky, 1979). As
indicated in section 6, these epidemiological studies, although
among the more complete, have still suffered from a lack of numbers
of persons exposed to high electric field strengths for extended
periods. However, these workers are exposed to potentially the
highest electric field strengths albeit for short periods of time
(section 6, Table 7). These studies do not provide a good data
base on which to evaluate the possible health effects from long-
term exposure of the general public to electric fields near
transmission lines. More definitive information is needed, which
in general, can only be provided through both large-scale
epidemiological studies and developments in dosimetry that will
make it possible to extrapolate the experimental animal results to
human beings.

While attempting to arrive at general conclusions concerning
the health hazards of ELF electric fields for protection purposes,
the fundamental question that requires an answer is whether or not
exposure to these electric fields induces any physiological or
pathological effects in man.

From a careful review of laboratory studies in vivo and in
vitro, and from human studies, the following conclusions can be
drawn:

(a) Adverse human health effects from exposure to ELF
electric field levels normally encountered in the
environment or the workplace have not be established.

(b) Some human beings feel spark discharges in electric
fields of about 3 kV/m and perceive the fields
between 2 - 10 kV/m. At present, there are no
scientific data that suggest that perceiving a field
produces an adverse pathological effect.

(c) Exposure to ELF electric fields can alter cellular,
physiological, and behavioural events. Although it
is not possible to extrapolate these findings to
human beings, at present, these studies serve as a
warning that unnecessary exposure to electric fields
should be avoided.

(d) The preliminary nature of the epidemiological
findings on the increased incidence of cancer among
children and adults exposed to ELF fields from
electric wiring and the relatively small increment in
reported incidence, suggest that, although the
epidemiological data cannot be dismissed, there must
be considerable study before they can serve as useful
imputs for risk assessment.

8. STANDARDS AND THEIR RATIONALES

A standard is a general term incorporating both regulations and
guidelines and can be defined as a set of specifications or rules
to promote the safety of an individual or group of people. A
regulation is promulgated under a legal statute and is referred to
as a mandatory standard. A guideline generally has no legal force
and is issued for guidance only - a voluntary standard. Standards
can specify exposure limits and other safety rules for personal
exposure, or provide details on the performance, construction,
design, or functioning of a device.

To protect the general population and persons occupationally
exposed to ELF fields, exposure standards are promulgated. These
are basic standards of personnel protection that do not apply to
particular devices or equipment, but generally refer to maximum
levels to which whole or partial body exposure is permitted from
any number of radiation emitting devices. This type of standard
normally incorporates safety factors and provides the basic guide
for limiting personnel exposure.

To date, few regulatory exposure standards have been
promulgated limiting human exposure to ELF fields. Guidelines
have been developed in a number of countries, mostly as an interim
measure until sufficient information on adverse biological effects
becomes available to make some reasonable assessment of health
risks, and the exposure levels at which hazards occur.

This section includes a review of all known ELF electric field
standards known to the Task Group at the time of publication.

Standards

From a recent review of ELF standards, Repacholi (1984a) found
that the greatest interest in regulations or guidelines was in ELF
electric fields at power frequencies. With the growth in number
and length of high voltage transmission lines, increasing concern
has occurred among the public, regulatory agencies, and scientists
about possible human health effects from exposure to the electric
fields associated with these lines. While there is no definitive
evidence of such effects, mounting public fear and activism over
hypothesized health risks has caused delays in the licensing and
construction of major power transmission facilities, and encouraged
the formation of regulatory policy in some countries.

The primary basis for public concern was a series of studies
conducted in the USSR in the 1960s (Asanova & Rakov, 1966;
Knickerbocker, 1975). These studies resulted in the occupational
safety standard in the USSR (1975), which is summerized in Table
11. In addition, a guideline on the design of HV transmission
lines near residential areas recommends a limit of 1 kV/m (Lyskov
et al., 1975). However, this guideline may be under question
(Bourgsdorf, 1980).

Table 11. Electric field exposure limits for workers in
installations of 400 kV and higher in the USSR (1975)
------------------------------------------------------------------
Electric-field Permitted exposure duration
strength (kV/m) per day (min)
------------------------------------------------------------------
5 Unrestricted
10 180
15 90
20 10
25 5
------------------------------------------------------------------
Note:
1. If workers are exposed to electric fields of 10kV/m or more
for the full time permitted by the standard, they must remain
in fields of 5 kV/m or less for the rest of the day.

2. Workers exposed to 10 kV/m or above can remain for the
permitted time, provided they are not subject to spark
discharges.

The Soviet standard applies to workers in substations or on
transmission lines operating at 400 kV and above. The duration of
the standard was from 1 January 1977 to 1 January 1982, after which
it was to be reviewed and either changed or reaffirmed. At the
time of publication of this document, a new standard for electric
50 Hz power frequencies is being discussed by the Council of Mutual
Economic Assistance (incorporating Bulgaria, Cuba, Czechoslovakia,
the German Democratic Republic, Poland, Romania, and the USSR).

The basis for the Soviet standard is that studies conducted
since 1962 on the effects on workers on high-voltage power systems
revealed electric field influences on human beings. It is believed
that the reaction of the human body to the direct influence of an
electrical field is non-specific; it can develop after a
comparatively long time (2 - 5 months); it has a long-term
consequence, pronounced cumulative effects, and strong dependency
on individual physiological peculiarities of the body (Lyskov et
al., 1975).

In a design criteria for 1100 kV lines in the USSR, Lyskov et
al. (1975) and Bourgsdorf et al. (1976) reported that clearances to
ground were determined in order to limit the electric field to 10 -
12 kV/m, at points where the HV transmission lines cross roads, and
to 15 - 20 kV/m elsewhere along unpopulated sections of the line
routes; a limit of up to 20 kV/m was determined for difficult
terrain and hardly accessible areas. These field strengths must
not be exceeded at the centre of the span at a height of 1.8 m
above the ground and at the lowest sag (at the maximum 15-year
temperature).

In the United Kingdom, the National Radiological Protection
Board (NRPB, 1982) has issued a proposal for ELF fields. In this
consultative document it states: "The Board accepts that exposures
to power frequency fields of less than 10 kV/m are safe, although

the field may be perceptible at lower values, and that exposures to
fields up to 30 kV/m are unlikely to be harmful". The NRPB admits
that there is very little information that can be used as a
rational basis for limiting exposure and that at 50 Hz, perceptible
but harmless effects depend to a large extent on environmental
factors and individual sensitivities. However, steps should be
taken to prevent such effects from occurring with any degree of
regularity. This will generally be achieved if the root mean
square field strengths are kept below 10 kV/m. Prolonged exposure
to fields greater than 20 kV/m, which induce currents in excess of
0.5 mA in the body, is also undesirable, according to the NRPB.

In Japan, all electric power equipment is subject to the
regulation "Technical Practices of Electrical Equipment", an
ordinance of the Ministry of International Trade and Industry. The
ordinance (Repacholi, 1984a) includes such technical specifications
as:

(a) minimum height of electrical conductors;

(b) necessary clearance between a transmission line and
building; and

In summary, the ordinance states that the unperturbed electrical
field strength 1 m above the ground surface must not exceed 3 kV/m
rms. In addition, the line must be built so that it does not pose
any risk for human beings. However, in lightly-populated areas
such as rice fields, farms, and forests, this limitation is not
applied when the line is constructed so that there are no risks for
anyone.

A description of the technical basis for this 3 kV/m standard
is provided by the Japan IERE Council (1976). The standard is
based on the electrostatic induction sensed by a person who has his
cheek or finger in contact with the metallic part of the grip of an
umbrella.

In Poland (1980), the electromagnetic radiation standard for
frequencies from 0.1 - 300 000 MHz, includes a limit on electric
field strength at the single frequency of 50 Hz. The standard,
effective from 31 January 1980, establishes two "safety" zones.
For exposure to 50-Hz electric fields, the zones are:

1st zone (electric fields above 10 kV/m) - prohibited to
everyone except workers in electrical substations and
personnel working on power lines;

2nd zone (above 1 kV/m to 10 kV/m) - agriculture and
recreational activities are allowed, but not the
construction of housing, hospitals, schools or
kindergartens, except where buildings and farms existed
before the regulations were established.

The standard provides details of administrative controls, approval
procedures and electromagnetic field measuring authorities.
However, no rationale for the values in the standard appear to have
been published.

In the USA, there are a number of different standards with
regard to the control of electric fields at the edge of RoW (see
Glossary for definition) for high-voltage transmission lines.
General population and media pressure have prompted public hearings
and extensive debate over health effects from these lines. The US
Department of Energy, Bonneville Power Administration (BPA) has a
criterion on electric field exposure levels that results in a low
probability of human perception or annoyance from field effects
(Lee et al., 1982). BPA allows a maximum of 9 kV/m on the RoW,
when measured 1 m above the ground (Lee et al., 1982). It would
seem that the rationale for setting the 9-kV/m level is so that
induced body currents in human beings under the lines will not
exceed the current permitted by the National Electric Safety Code
(5 mA rms).

All 50 states in the USA have some legislation for regulating
the safety of the general population in the proximity of
transmission lines. Of these, 25 states have enacted legislation
requiring the preparation of environmental impact statements for
proposed overhead transmission lines with respect to electrical
effects. A comprehensive study was completed by the state of New
York (1979), in which testimony indicated potential impacts from
audible noise and from electrostatic shocks that people can receive
when they touch a large vehicle parked under the lines. The
testimony failed to demonstrate biological hazards from the field,
though further research is necessary to understand better the
effects of the fields on biological systems.

Many of the state regulatory agencies have carried out similar
studies (Shah, 1979; Montana, 1983) reaching the same basic
conclusions as New York (1979). Guidelines from each state on the
maximum electric field permitted at the edge of the RoW differ, but
are within the range of 1 - 3 kV/m (Table 12). Guidelines for
maximum field strength within the RoW varied from 7 to 11 kV/m.
Most states comply with the National Electric Safety Code (NESC),
which restricts currents in the human body to no more than 5 mA
(rms).

Table 12. Recommended electric field levels for high-voltage
transmission lines in the USA^a
-------------------------------------------------------------------
Max E field (kV/m)
State In RoW Edge RoW Comments Reference
-------------------------------------------------------------------
Minnesota 8 - Resolution Shah (1979)

Montana - 1 Resolution Montana (1983)

New Jersey - 3 Resolution New Jersey (1981)

New York - 1^b Temporary New York (1978)
resolution -
new EHV lines

7 - Public roads Shah (1979)

11 - Private roads Shah (1979)

North Dakota 9 - Resolution Shah (1979)

Oregon 9 - State law Shah (1979)
-------------------------------------------------------------------
^a From: Repacholi (1984a).
^b 1 kV/m for flat terrain - use 1.6 kV/m as criterion (Sheppard
(1983), personal communication).

Note: Most states have adopted NESC (5mA rms).

Only two states in Australia, Victoria and New South Wales,
have guidelines for the construction of 500 kV HV transmission
lines (Table 13).

In Victoria, the State Electricity Commission designs the 500
kV lines so that the electric field does not exceed 10 kV/m in the
RoW or 2 kV/m at the edge of the RoW, when measured 1 m above the
ground. Workers in switch-yards are normally restricted to
exposures below 10 kV/m, wherepractical.

The rationale for their guideline, contained in Johnson et al.
(1976), was also based on the fact that these values were generally
acceptable in many other standards, including the Soviet standard
(USSR, 1975).

Table 13. Guidelines for constructing 500 kV high voltage
transmission lines in Australia^a
-------------------------------------------------------------------
State Max. E field (kV/m)
In RoW Edge RoW
-------------------------------------------------------------------
New South Wales^b - 2

Victoria 10 2
-------------------------------------------------------------------
^a From: Repacholi (1984a).
^b Personal communication, Sydney, Australia, Electricity
Commission of New South Wales.

The Electricity Commission of New South Wales has an internal
design standard for 500-kV HVAC lines that states that the electric
field strength at the edge of the RoW should not exceed 2 kV/m.
However, in practice, the RoW is made sufficiently wide that values
of 0.5 kV/m are not exceeded at its edge.

9. PROTECTIVE MEASURES

9.1. Goals

This criteria document does not recommend specific values for
electric-field standards, but where a health agency finds that
standards are necessary, it provides guidance on the development of
standards.

It is understood that standards may be required when it is
necessary to ensure that physical agents are not introduced into
the environment at levels that may reduce the quality of life. The
overall assessment of the impact of electric power on the quality
of life involves the balance of positive and negative factors
implicit in a cost-benefit analysis. At this time, a cost-benefit
analysis cannot be conducted with quantitative precision.

9.2. Groups to be Protected

Protective measures may be considered for electrical utility
workers exposed near substations, transformers, capacitors, and
circuit breakers or workers exposed near live power transmission or
distribution conductors. Depending on the equipment, individual
policies and worker/job classifications, the extent of exposures
may vary widely, requiring careful review by each affected
organization. Workers primarily involved with communications
facilities may also be affected. In cases where joint facilities
are used (e.g., high-voltage lines near or having common RoWs with
low-voltage communications lines), the communications workers may
be considered together with electric power utility workers. Workers
in industry may also be affected, principally through magnetic
field exposures from low-frequency induction heaters and furnaces,
large motors, transformers, and similar devices to which personnel
are exposed, often at close proximity.

Exposure of the general population occurs during occasional
visits to electrical utility facilities, often for recreation in
RoWs or, in the case of farmers, for work. Exposures also result
from living in the vicinity of a high-voltage transmission line, in
the course of using electrical appliances, and generally as an
essential aspect of the widespread use of electric power for
illumination and power. It should be noted that high-voltage
direct current transmission also involves alternating currents as a
result of the AC/DC conversion process. These currents occur at
several harmonic frequencies in the range below 1 kHz at amplitudes
that are much below the level of direct currents. The specific
conversion technology and its operational mode must also be
considered.

At present, protective measures for the general population are
at issue with respect to dwellings located near power-transmission-
line corridors. Exposures that originate in the home or home
environment are generally weak and exposures to appliance-generated
fields are very intermittent. Although they are not thought to be
of concern, they have not been closely studied.

9.3. Protection Rationale

Occupational exposures among utility workers have been
characterized in data reviewed by Knave et al. (1979) and Male et
al. (1982). Relatively few hours are spent in fields at levels
above 5 kV/m, in any job. In fields above 10 kV/m, workers are
subject to recognised influences of perceptible shock discharges,
that reduce worker comfort and increase the possibility of
accidents with tools or accidents arising from faulty judgement.

The following protective measures can be taken with regard to
workers in fields of about 10 kV/m or more:

(a) the designing of equipment to reduce the likelihood
of large potential differences or large current flow
between a person and conducting objects;

(b) reduction of daily duration of exposure in proportion
to the degree of discomfort experienced; since job
assignments, weather, and clothing appear to be major
factors, rules can be developed on the basis of
practical experience;

(c) use of devices or clothing that reduce the strength
of electric fields acting on the body; particular
attention should be paid to the protection of linemen
working on HV lines with the bare-hand method, when
the total residual body current should not exceed
values that arise from exposure to external field
strengths of less than 10 kV/m.

Electric field exposure up to 20 kV/m, apart from effects due
to shocks, is not believed to be an occupational hazard on the
basis of information now available. For this reason, protective
measures, apart from an altered work schedule, are not suggested in
fields below 20 kV/m. Although an occupational hazard is not
established in fields above 20 kV/m, as a prudent measure it is
suggested that attempts should be made to reduce exposures to
levels where no unacceptable discomfort occurs.

In view of the fact that there is no health effect that could
be attributed specifically to ELF exposure, it is not practicable
to recommend any specific medical examinations, apart from those
that may be appropriate for electrical fitters and linemen in
general.

GLOSSARY OF TERMS USED IN THE DOCUMENT

ALTERNATING CURRENT: an electric current varying sinusoidally
in time.

ALTERNATING ELECTRIC FIELD: the electric field produced by a
sinusoidally-oscillating electric charge.

ALTERNATING VOLTAGE: a voltage varying sinusoidally in time.

BIOPHYSICAL: relating to the physical properties of biological
systems, e.g., the conductivity of tissue or its permittivity
are biophysical quantities.

CIRCADIAN RHYTHM: daily cycle of certain physiological
processes such as activity, temperature, and as indicated by
the levels of electrolytes, hormones, etc., in body fluids or
tissues. More generally, the term refers to a periodic
physiological or biochemical change.

CONTROLS: animals, tissues, etc., not subjected to the field
or other experimental treatment (see also SHAM-EXPOSED).

CURRENT DENSITY: the flow of electric current across a unit
area, a measure of the distribution of current within the
object or body tissues measured in amperes per square metre
(A/m²), or microamperes per square centimetre (µA/cm²).

EARTH: electrical ground.

EFFECTIVE FIELD: the time-averaged electric field to which a
biological system is exposed; this field is less than the
unperturbed field because of mutual shielding, e.g., by
animals housed as a group.

ELECTRIC FIELD: concept used to represent the force exerted on
the unit charge due to the location of electric charges at
various sites in a region; the high-voltage-transmission lines
electric field is an alternating (50- or 60-Hz) field due to
the sinusoidally-oscillating charges located on the conducting
wires of the transmission line. Electric fields are capable
of performing work on other electric charges moving between
points at different potential.

ELECTRIC-FIELD STRENGTH: magnitude of the electric field,
measured in volts per metre; (see VOLT PER METRE). The electric-
field strength beneath a HV transmission line is generally
measured at a fixed height above ground (usually 1 m).

ELF: abbreviation for extremely low frequency.

EXTREMELY LOW FREQUENCY: a frequency between 3 and 300 Hz; but
defined in this document as any frequency below 300 Hz.

FARADAY SCREEN: see FARADAY SHIELD CAGE.

FARADAY SHIELD CAGE: grounded cage made of conducting material
used to enclose an object subjected to an electric field; the
shield, usually composed of metal (eg., copper wire); reduces
the electric field strength inside the cage to nearly zero.

FIELD: a region of space in which certain phenomena occur,
described by a scalar or vector quantity, the knowledge of
which allows the effects of the field to be evaluated.

FREE SPACE: an ideal, perfectly homogeneous medium that
possesses relative dielectric and magnetic constants of unity,
and in which there is nothing to reflect, refract, or absorb
energy. A perfect vacuum possesses these qualities.

GROUND: zero potential, electric earth.

HERTZ (Hz): the unit of frequency for a periodic oscillation
corresponding to a complete oscillation per second (ops) or
cycle per second (cps).

HIGH TENSION LINE: a high-voltage transmission line.

HORIZONTAL ELECTRIC FIELD: an electric field directed parallel
to the Earth's surface; in the laboratory, such fields are
created by vertical plates.

HVTL: high-voltage transmission line; typically one operating
at or above 345 kV.

IMPEDANCE: the physical property of a material that determines
the relation between current flow and potential difference in
the material; for direct currents, impedance is identical to
resistance; for alternating currents impedance includes the
properties of resistance, capacitance, and inductance.

IMPEDANCE TO GROUND: an impedance measured between an object
and earth (ground); in caged laboratory animals, this property
depends on the caging materials, construction, and electrical
design, and the biophysical properties of the animal's
footpad; for human beings, skin, clothing, or shoe properties
are significant.

INTERNAL ELECTRIC FIELD: electric-field strength measured or
calculated for points within the body of an animal or human
being exposed to an external electric field.

MAGNETIC FIELD: a concept to describe the force exerted on a
unit current produced by moving electrical charges, such as
those in an electrical current; the transmission line magnetic
field is due to the flow of current in the wires. A magnetic
field exerts a force on moving electric charges, such as those
in another wire-carrying current or in a moving wire (dynamo
principle) always perpendicular to the direction of motion.

MICRO: prefix for 10^-6; e.g., microvolt, microampere,
micrometre; symbol - µ (Greek letter mu).

MILLI: prefix for 10^-3; e.g., millivolt, milliampere; symbol - m.

NANO: prefix for 10^-9; symbol - n.

NEUROPHYSIOLOGICAL: relating to the function of the nervous
system, e.g., peripheral nerves, the brain, spinal cord, the
sub-divisions of those organs and their cellular components,
including the nerve fibres.

PHASOR (vector): a phasor is a complex number. It is used in
connection with quantities related to the steady alternating
state in a linear network or system.

PICO: prefix for 10^-12; symbol - p.

PULSE POWER: the power averaged over the duration of a single pulse.

PULSE REPETITION RATE: the rate, usually given in cycles (or
pulses) per second, at which pulses are emitted by a pulse
system.

PULSE WIDTH: the duration of a pulse in the time interval
between the points on the leading and trailing edges.

RIGHT-OF-WAY (RoW): the provision of access to power lines for
inspection and maintenance purposes; the concept varies from
one country to another. It may take the form of the ownership
of land over which the power line passes, or the statutory
control of access to this land, or the negotiation of
agreements with the landowners. In some countries, the
right-of-way applies to a corridor (strip of land), of a
certain width, along the transmission line, in which the
public access or property rights may be restricted.

rms: root mean square, the square root of the temporal average
over a period of the square of the field strength magnitude.

SCALAR: a quantity that is completely specified by a single number.

SCALING: relating an exposure of one animal species to another
so that the effect of the electric field can be interpreted on
an equal basis; because of shape- and orientation-dependence
for both internal and external fields, human beings and
animals exposed to the same unperturbed field have very
different surface and internal fields.

SHAM-EXPOSED: a control experimental condition in which the
animals, tissues, etc., are treated identically to the exposed
objects, except that the field or other treatment is not
present; distinguished from "controls" by the use of apparatus
that is in all ways identical to the exposure apparatus which
is not operating.

SPECTRAL CHARACTERISTICS: the frequencies and amplitudes
inherent in a particular electric or magnetic field as
revealed by a mathematical or experimental technique that
"decomposes" the signal into its component frequencies and
field strengths (Fourier analysis).

SURFACE ELECTRIC FIELD: the electric field at the outer margin
of the object or body; this field is influenced by the shape
and configuration of a conducting body and, depending on the
degree of curvature, is locally greater than the unperturbed
electric field.

TERATOLOGICAL: relating to abnormal anatomy, resulting in
deformities, fetal death, still birth, etc., especially in a
developing or newborn organism.

UNPERTURBED ELECTRIC FIELD: the field that would exist at the
body's location if there were no body located in the electric
field. In the case of a uniform field, the field that exists
far from the location of a conducting object (such as the
human or animal body).

VECTOR: a mathematical-physical quantity that represents a
vector quantity - it has magnitude and direction.

VECTOR QUANTITY: any physical quantity in which specifications
involve both magnitude and direction and which obeys the
parallelogram law of addition.

VERTICAL ELECTRIC FIELD: an electric field directed
perpendicular to the Earth's surface; in the laboratory, such
fields are created by horizontal electrodes.

VOLT PER METRE: unit of electric field strength; a field of
one volt per metre is created in the centre of the midplane of
two parallel plates separated by 1 metre and having a
potential difference of 1 volt.

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APPENDIX I
----------------------------------------------------------------------------
The electromagnetic environment in the home^a
----------------------------------------------------------------------------
A. 60-Hz electric-field strengths at the centre of various rooms in a
typical home in the USA in 1974

Room V/m

Laundry room 0.8
Dining room 0.9
Bathroom 1.2 - 1.5
Kitchen 2.6
Bedrooms 2.4 - 7.8
Living room 3.3
Hallway 13.0

B. Typical values of electric-field strength (V/m) from 115-V, 60-Hz
home appliances (USA) at 30 cm from source

Electric blanket 250^b
Broiler 130
Stereo 90
Refrigerator 60
Electric iron 60
Hand mixer 50
Toaster 40
Hair Dryer 40
Colour TV 30
Coffee pot 30
Vacuum cleaner 16
Incadescent light bulb 2

C. Localized 60-Hz magnetic flux densities in the vicinity (a few cm)
of some electric appliances (mT)

1 - 2.5 325 watt soldering gun
Hair dryer

0.5 - 1.0 Can opener
Kitchen range
Electric shaver
Fluorescent desk lamp

0.1 - 0.5 Colour TV
Food mixer
Electric drill

0.01 - 0.1 Garbage disposal
Clothes dryer
Vacuum cleaner
Electric toaster
----------------------------------------------------------------------------

APPENDIX I (contd.)
----------------------------------------------------------------------------
D. Leakage currents passing through the body to earth from household
appliances (mA); the values should be compared to ANSI standards for
fixed appliances (750 mA) and for cord-connected appliances (500 mA)

Coffee mill 380
Refrigerator 40
Sewing machine 34
Coffee pot 6

E. Induced currents flowing in the earthed arm of an 80-kg, 1.75-m
human being with a heating pad or electric blanket in a
representative location

Heating pad 18 µA
Electric blanket 7 - 27 µA

F. Typical values of measured dispersed ambient magnetic flux
densities^c

Location Magnetic Flux Density
(µT)

University of Pennsylvania Hospital 0.2 - 0.4; 60 Hz
Princeton Hospital 0.03 - 0.1; 60 Hz
Park Falls (Wisconsin) Hospital 0.05 - 0.8; 60 Hz
Industrial Plant, Park Falls (Wisconsin) 0.3 - 6; 60 Hz
Scientific Laboratory, Pensacola, Florida 0.5 - 1; 60 Hz
IIT Research Institute office areas 5; 60 Hz
Stamford (Conneticut) railroad station 2 - 20; 25 Hz
Private dwelling 0.1 - 10.l; 60 Hz
----------------------------------------------------------------------------
^a From: Miller (1974), Bridges (1975), Sheppard & Eiisenbud (1977),
Atoian (1978), Bridges & Preache (1981).
^b Actual human exposure would be higher since the blanket would be at a
distance of less than 30 cm.
^c From: Miller (1974).

APPENDIX I REFERENCES

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    See Also:
       Toxicological Abbreviations