Magnetic Fields and
Table of Contents
- Does anyone think that static electric or
magnetic fields cause cancer or any other human health problems?
- When evaluating whether there might be a
connection between cancer and static electric or magnetic fields, can all
electromagnetic fields be considered the same?
- When evaluating whether there might be a
connection between cancer and static electric or magnetic fields, do we have
to consider electromagnetic radiation as well as electromagnetic fields?
- When evaluating whether there might be a
connection between cancer and static electric or magnetic fields, do we have
to consider the electric as well as the magnetic component of the field?
- What units are used to measure static
- What sort of static magnetic fields are
common in residences?
- What sort of static magnetic fields are
common in workplaces?
- What is known about the relationship
between occupational exposure to static magnetic fields and cancer?
- How do scientists determine whether an
environmental agent, such as a static electric or magnetic field causes or
contributes to the development of cancer?
- How does the epidemiological evidence
relevant to a connection between static fields and cancer stand up to the
- How could laboratory studies be used to
help evaluate the possible relationship between static magnetic fields and
- Are static magnetic fields
- Do static magnetic fields enhance the
effects of other genotoxic agents?
- Do laboratory studies indicate that
static magnetic fields have any biological effects that might be relevant to
cancer or other human health hazards?
- Do static magnetic fields show any
reproducible biological effects in laboratory studies?
- Do static magnetic fields of the
intensity encountered in occupational settings show reproducible biological
- Are there known mechanisms that would
explain how static magnetic fields of the intensity encountered in
occupational settings could cause biological effects in humans?
- How does the sum of the laboratory and
epidemiological evidence relevant to a connection between static magnetic
fields and cancer stand up to the Hill criteria?
- Have any independent bodies reviewed the
research on static electric and magnetic fields and possible human health
- Do exposure standards for static
electric and magnetic fields exist?
- What is the basis for the safety
standards set by Lawrence Livermore, WHO, ACGIH, NRPB, and ICNIRP?
- Do static fields affect cardiac
- Do static fields decrease fertility,
cause birth defects or increase miscarriage rates?
- Annotated bibliography
Questions and Answers
1) Does anyone think
that static electric or magnetic fields cause cancer or any other human health
While most public concern about electromagnetic (EM)
fields and cancer has concentrated on power-frequency, microwave (MW) and
radiofrequency (RF) fields, claims have been made that static magnetic
fields cause or contribute to cancer.
There is very little theoretical reason to suspect that
static fields might cause or contribute to cancer or any other human health
problems (Q17), and there is very little laboratory (Q11-Q16,
Q23) or epidemiological evidence (Q8-Q10, Q23)
for a connection between static fields and human health hazards.
2) When evaluating
whether there might be a connection between cancer and static electric or
magnetic fields, can all electromagnetic fields be considered the same?
No. The nature of the interaction of an
electromagnetic source with biological material depends on the frequency of the
source, so that different types of electromagnetic sources must be evaluated
X-rays, ultraviolet (UV) light, visible light, MW/RF,
magnetic fields from electrical power systems (power-frequency fields), and
static magnetic fields are all sources of electromagnetic energy. These
different electromagnetic sources are characterized by their frequency or
The frequency of an electromagnetic source is the rate at
which the electromagnetic field changes direction and/or amplitude and is
usually given in Hertz (Hz) where 1 Hz is one change (cycle) per second.
The frequency and wavelength are related, and as the frequency rises the
wavelength gets shorter. Power-frequency fields are 50 or 60 Hz and have a
wavelength of about 5000 km. By contrast, microwave ovens have a frequency of
2.54 billion Hz and a wavelength of about 10 cm, and X-rays have frequencies of
10^15 Hz and, and wavelengths of much less than 100 nm. Static fields, or direct
current (DC) fields do not vary regularly with time, and can be said to
have a frequency of 0 Hz and an infinitely long wavelength.
The interaction of biological material with an
electromagnetic source depends on the frequency of the source. We usually talk
about the electromagnetic spectrum as though it produced waves of energy. This
is not strictly correct, because sometimes electromagnetic energy acts like
particles rather than waves; this is particularly true at high frequencies. The
particle nature of electromagnetic energy is important because it is the energy
per particle (or photons, as these particles are called) that determines what
biological effects electromagnetic energy will have .
At the very high frequencies characteristic of hard UV and
X-rays, electromagnetic particles (photons) have sufficient energy to break
chemical bonds. This breaking of bonds is termed ionization, and this part of
the electromagnetic spectrum is termed ionizing. The well-known biological
effects of X-rays are associated with the ionization of molecules. At lower
frequencies, such as those characteristic of visible light, RF, and MW, the
energy of a photon is very much below those needed to disrupt chemical bonds.
This part of the electromagnetic spectrum is termed non-ionizing. Because
non-ionizing electromagnetic energy cannot break chemical bonds there is no
analogy between the biological effects of ionizing and nonionizing
electromagnetic energy .
Non-ionizing electromagnetic sources can still produce
biological effects. Many of the biological effects of soft UV, visible, and IR
frequencies also depend on the photon energy, but they involve electronic
excitation rather than ionization, and do not occur at frequencies below that of
IR (below 3 x 10^11 Hz). RF and MW sources can cause effects by inducing
electric currents in tissues, which cause heating. The efficiency with which an
electromagnetic source can induce electric currents, and thus produce heating,
depends on the frequency of the source, and the size and orientation of the
object being heated. At frequencies below that used for broadcast AM radio
(about 10^6 Hz), electromagnetic sources couple poorly with the bodies of humans
and animals, and thus are very inefficient at inducing electric currents and
causing heating .
Thus in terms of potential biological effects the
electromagnetic spectrum can be divided into four portions:
- The ionizing radiation portion, where direct chemical
damage can occur (X-rays).
- The non-ionizing portion of the spectrum, which can be
- The optical radiation portion, were electron
excitation can occur (visible light, infrared light)
- The portion where the wavelength is smaller than
the body, and heating via induced currents can occur (MW and
- The portion where the wavelength is much larger
than the body, and heating via induced currents seldom occurs (lower-frequency
RF, power frequencies, static fields).
3) When evaluating
whether there might be a connection between cancer and static electric or
magnetic fields, do we have to consider electromagnetic radiation as well as
No. Static electromagnetic sources do not produce
In general, electromagnetic sources produce both radiant
energy (radiation) and non-radiant energy (fields). Radiated energy exists apart
from its source, travels away from the source, and continues to exist even if
the source is turned off. Fields are not projected away into space, and cease to
exist when the energy source is turned off. For static electromagnetic fields
there is no radiative component.
4) When evaluating
whether there might be a connection between cancer and static electric or
magnetic fields, do we have to consider the electric as well as the magnetic
component of the field?
No. Only the magnetic field component appears to be
relevant to possible health effects.
Magnetic fields are difficult to shield, and easily
penetrate buildings and people. In contrast to magnetic fields, electrical
fields have very little ability to penetrate skin or buildings. Because static
electric fields do not penetrate the body, it is generally assumed that any
biologic effect from routine exposure to static fields must be due to the
magnetic component of the field, or to the electric fields and currents that
these magnetic fields induce in the body [1,54].
5) What units are
used to measure static magnetic fields?
Static magnetic fields are generally measured in Tesla
(T), milliTesla (mT), and microTesla (microT, µT) where:
1000 mT = 1 T
1000 (µT) = 1 mT.
In the US, fields are sometimes still measured in Gauss
(G) and milliGauss (mG), where:
10,000 G equals 1 T
1 G = 100 microT
1 microT (µT) = 10 mG.
In the FAQ, mT (millitesla) will be the preferred term.
Magnetic fields can be specified in either magnetic flux
density or magnetic field strength. In the US and Western Europe field strengths
are usually specified in units of magnetic flux density (Tesla or Gauss). In
some of the Eastern European literature, however, magnetic fields are specified
in Oersteds (Oe), which are units of magnetic field strength. When
dealing with exposure of non-ferromagnetic material, such as animals or cells,
magnetic flux density and magnetic field strength can be assumed to be equal,
1 Oersted = 1 Gauss = 100 microT = 0.1 mT
6) What sort of
static magnetic fields are common in residences?
Residential and environmental exposure to static magnetic
fields is dominated by the Earth's natural field, which ranges from 0.03 to 0.07
mT, depending on location. Static magnetic fields under direct current (DC)
transmission lines are about 0.02 mT. Small artificial sources of static fields
(permanent magnets) are common, ranging from the specialized (audio speakers
components, battery-operated motors, microwave ovens) to trivial (refrigerator
magnets). These small magnets can produce fields of 1-10 mT within a cm or so of
their magnetic poles. The highest static magnetic field exposures to the general
public are from magnetic resonance imaging (MRI), where the fields range from
150-2000 mT [1,2].
Direct effects on ferromagnetic objects and electronic
equipment are the only things that most people would notice below about 1000 mT.
There is really no threshold for effects on ferromagnetic objects; a good
compass will twitch at fields as low as 0.01 mT, but it takes a much larger
field (above 1 mT) to make ferromagnetic objects move in a dangerous way.
Electronics can be affected by quite low fields; a high resolution color
monitor, for example, can show color distortions at static fields as low as 0.1
A source of exposure to static fields that blurs the
distinction between residential and occupational exposure is electric trains.
Static fields in electric trains can be as high as 0.2 mT .
7) What sort of
static magnetic fields are common in work places?
Persons with occupational exposures to static fields
include operators of magnetic resonance imaging (MRI) units, personnel in
specialized physics and biomedical facilities (for example, those working with
particle accelerators), and workers involved in electrolytic processes such as
aluminum production. Some aluminum manufacturing workers are reported to be
exposed to fields of 5-15 mT for long periods of time, with maximum exposures up
to 60 mT [2,3]; but another study reports
average fields of only 2-4 mT . Workers in plants using
electrolytic cells are reported to be exposed to fields of 4-10 mT for long
periods of time, with maximum exposures up to 30 mT [5,6].
Individuals working with particle accelerators are exposed to fields above 0.5
mT for long periods of time, with exposures above 300 mT for many hours, and
maximum exposures of up to 2,000 mT .
Another source of exposure to static magnetic fields is
the residual fields that can remain after strong static magnets are
removed. For example, after a clinical MRI unit is removed from a room, a
residual field of as high as 2 mT may remain from steel in the structure that
has been permanently magnitized. Such fields are not sufficiently strong to be a
concern for human health, but they may be strong enough to interfere with the
operation of sensitive electronic equipment. These residual fields can be
reduced (although not always eliminated) by professional "degaussing".
8) What is known
about the relationship between occupational exposure to static magnetic fields
There have been relatively few studies of cancer incidence
in workers exposed to static magnetic fields. Budinger et al 
found no excess cancer in workers exposed to 300 mT fields from particle
accelerators, and Barregard et al  found no excess cancer in
workers exposed to 10 mT fields in a chlorine production plant.
There are also studies of aluminum reduction plant workers
In general the studies of aluminum reduction plant workers were not designed to
analyzed the effects of static fields, but these workers are exposed to static
fields of 5-15 mT [2,3,4]. In
the aluminum reduction plant studies, the only excess cancer reported was
lymphoreticular tumors, and this was seen in one study . The
only aluminum reduction plant study to look specifically at static field
exposure and cancer reported no excess of nervous system or hematopoietic
9) How do scientists
determine whether an environmental agent, such as a static electric or magnetic
field causes or contributes to the development of cancer?
There are certain widely accepted criteria [11,63,64],
often called the "Hill criteria" , that are
weighed when assessing epidemiological and laboratory studies of agents that may
cause human cancer. Under these criteria one examines the strength, consistency,
and specificity of the association between exposure and the incidence of cancer,
the evidence for a dose-response relationship, the laboratory evidence, the
biological plausibility of the association, and the coherence of the proposed
association with what is known about the agent and about cancer.
- Strength of association: whether there a clear
increase in cancer incidence associated with exposure. The excess cancer
found in epidemiological studies is usually quantified in a number called
the relative risk (RR). This is the incidence of cancer in an
"exposed" population divided by the incidence of cancer of an
"unexposed" population. Since no one is unexposed to static
fields, the comparison is actually "high exposure" versus
"low exposure". A RR of 1.0 means no effect, a RR of less than 1.0
means a decreased incidence of cancer in the exposed group, and a RR of
greater than 1.0 means an increased incidence of cancer in the exposed
group. A strong association is one with a RR of 5 or more. Tobacco smoking,
for example, shows a RR for lung cancer 10-30 times that of non-smokers.
- Consistency: whether most studies show about the
same increased incidence of the same type of cancer. Using the smoking
example, essentially all studies of smoking and cancer have shown an
increased incidence of lung and head-and-neck cancers.
- Exposure-response relationship: whether cancer
incidence increases when the exposure increases. Again, the more a person
smokes, the higher the increased incidence of lung cancer.
- Laboratory evidence: whether there is there
experimental evidence suggesting that the cancer is associated with
exposure. Epidemiological associations are greatly strengthened when there
is laboratory evidence to support such an association.
- Plausible biological mechanisms: whether there
are any biological data or biophysical mechanisms that suggests that there
should be an association between the agent and cancer. When it is understood
how something causes disease, it is much easier to interpret ambiguous
epidemiology. For smoking, while the direct laboratory evidence connecting
smoking and cancer was weak at the time of the Surgeon General's report, the
association was highly plausible because there were known cancer-causing
agents in tobacco smoke.
- Coherence:is whether the association between
exposure to an agent and cancer is consistent with other things that we know
about the biophysics of the agent and the biology of cancer.
These criteria must be applied with caution [11,63,64]:
- It is necessary to examine the entire published
literature; it is not acceptable to pick out only those reports that support
the existence of a health hazard.
- It is necessary to directly review the important source
documents; it is not acceptable to base judgments solely on academic or
- Satisfying the individual criteria is not a yes-no
matter; support for a criterion can be strong, moderate, weak, or
- The criteria must be viewed as a whole; no individual
criterion is either necessary or sufficient for concluding that there is a
causal relationship between exposure to an agent and a disease.
10) How does the
epidemiological evidence relevant to a connection between static fields and
cancer stand up to the Hill criteria?
Application of the Hill criteria shows that the current
epidemiological evidence for a connection between static magnetic fields and
cancer is weak to non-existent.
- There is only a weak association between static
magnetic fields and cancer. There is only one study that shows any
indication of an association of static fields with cancer ,
and that association is not large, and is seen for only one type of cancer.
- The association between static magnetic fields and
cancer is not consistent. The studies of workers exposed to static
magnetic fields in industries other than aluminum reduction plants [6,7]
show no association between exposure to static fields and cancer, and all
but one of the studies in the aluminum industry show no association between
exposure to static magnetic fields and cancer.
- Since only one study reports an association between
exposure to static fields and cancer, the issue of specificity is moot.
- There is no evidence for a dose response
relationship between exposure to static fields and the incidence of
cancer. The only study reporting an association between exposure to static
fields and cancer shows no evidence of a dose-response relationship.
Thus the epidemiological evidence for an association
between static magnetic fields and cancer is weak and inconsistent, and fails to
show a dose-response relationship.
11) How could
laboratory studies be used to help evaluate the possible relationship between
static magnetic fields and cancer?
When epidemiological evidence for a causal relationship is
weak to non-existent, as in the case of static magnetic fields and cancer,
laboratory studies would have to provide very strong evidence for
carcinogenicity in order to tip the balance.
Carcinogens, agents that cause cancer, can be either
genotoxic or epigenetic (in older terminology these were initiators and
promoters). Genotoxic agents (genotoxins) can directly damage the genetic
material of cells. Genotoxins often affect many types of cells, and may cause
more than one kind of cancer. Genotoxins generally do not have thresholds for
their effect; so as the dose of the genotoxin is lowered the risk gets smaller,
but it may never go away. Thus evidence for genotoxicity at any field intensity
would be relevant to assessing carcinogenic potential [62, 75].
An epigenetic agent is something that increases the
probability that a genotoxin will damage the genetic material of cells or that a
genotoxin will cause cancer. Promoters are a particular kind of epigenetic agent
that increase the cancer risk in animals already exposed to a genotoxic
carcinogen. Epigenetic agents (including promoters) may affect only certain
types of cancer. Epigenetic agents generally have thresholds for their effect;
so as the dose of an epigenetic agent is lowered a level is reached at which
there is no risk. Thus evidence for epigenetic activity at field intensities far
above those actually encountered in residential and occupation settings would
not be clearly relevant to assessing carcinogenic potential [62,
12) Are static
magnetic fields genotoxic?
No. A broad range of whole organism and cellular
genotoxicity studies of static fields have been carried out. Together these
studies offer no consistent evidence that static magnetic fields are genotoxic.
Whole organism genotoxicity studies with static magnetic
fields have been somewhat limited. Beniashvili et al 
found no increase in mammary cancer in mice exposed to a 0.02 mT field. Mahlum
et al  found that exposure of mice to a 1000 mT field did
not cause mutations, and other investigators found a similar lack of mutagenesis
in fruit flies exposed to 1000-3700 mT [14,15,16]
have been two whole organism reports of possible genotoxicity. In 1995 Koana et
al  found evidence for increased mutations in repair
deficient fruit flies exposed to a 600 mT field for 24 hours. No effects was
seen in fruit flies that had normal DNA repair capacity. In 2001, Suzuki et al 
reported that exposure of mice to a 3000 or 4700 milliT static field for 24-72
hours caused chromosome damage in their bone marrow cells .
Cellular genotoxicity studies have been more extensive.
Published laboratory studies have reported that static magnetic fields do not
cause any of the effects that indicate genotoxicity. Static magnetic fields do
not cause DNA strand breaks , chromosome aberrations [18,19,20,21,22,23,79],
sister chromatid exchanges [18,20,22,24],
cell transformation [19,25], mutations [26,27,28,94],
or micronucleus formation .
In 2000 Teichman et al  reported
that 1500 and 7000 milliT static fields did not cause mutations in bacteria (the
Some studies of static electrical fields have also been
conducted. These have been reviewed by McCann et al , who
concluded that while there were some reports of genotoxicity for static
electrical fields, "all reports of positive results have utilized exposure
conditions likely to have been accompanied by auxiliary phenomena such as
corona, spark discharge, and transient electrical shocks, whereas negative
reports have not."
13) Do static
magnetic fields enhance the effects of other genotoxic agents?
Probably not. In general, static magnetic fields do
not appear to have this type of epigenetic activity. There are a few studies
that suggest that static magnetic fields might enhance the effects of other
genotoxic agents, but none of these studies has been replicated.
Three studies [14,30,31]
have found that 140-3700 mT static fields do not enhance the mutagenic effects
of ionizing radiation. A fourth study  reported that
1100-1400 mT static fields caused a slight increase in the number of chromosome
aberrations produced by exposure to high doses of ionizing radiation, and a
fifth study reported that a 4000 mT field slightly increased radiation-induced
cell killing .
Two studies [94, 101]
have found that 1500-7200 mT static fields do not enhance the mutagenic effects
of chemical carcinogens.
Repair of radiation-damage was reported not be affected by
a 140 mT field , but to be inhibited at 4000 mT .
Two studies [34,78] reported that 1300-4700
mT static fields did not enhance the mutagenic effects of a known chemical
genotoxins, and might even inhibit such activity.
Two studies [35,36]
found that 150-800 mT static fields did not enhance the development of
chemically-induced mammary tumors, but a third study 
reported that a 0.02 mT static field did enhance the development of
chemically-induced mammary tumors.
14) Do laboratory
studies indicate that static magnetic fields have any biological effects that
might be relevant to cancer or other human health hazards?
No. Laboratory studies of the effects of static
magnetic fields show that these fields do not have any consistent effects on
tumor growth, cell growth, immune system function, or hormonal balance.
Tumor growth : In general,
static magnetic fields of 13-1150 mT appear to have no effect on the growth of
either chemically-induced  or transplanted [37,38,39]
tumors. However, there is one report that suggests that a 15 mT static field
increases the growth rate of chemically-induced tumors .
Cell growth [69, 75]:
In general, static magnetic fields of 45-2000 mT appear to have no effect on the
growth of human [20,33,39,67,97],
or yeast  cells. However, there are 4 reports of static
fields effects on cell growth: inhibition of human lymphocyte growth at
4000-6300 mT , inhibition of tumor cell growth at 7000 mT
, stimulation of mammalian cell growth at 140 mT ,and
both stimulation and inhibition of DNA synthesis in fibroblasts at 610 mT .
Immune system effects [70, 75]:
In most studies, static magnetic fields of 13-2000 mT appear to have no effect
on the immune system of animals [38,40,41,42],
although one study reports that the implantation of small magnets into the
brains of rats enhanced their immune response . Two
studies of humans [5,44] have reported that
workers in aluminum reduction plants, where exposure to static magnetic fields
is common, have minor alterations in the numbers of some types of immune cells.
These minor alterations in cell number are of no known clinical significance,
and may not even be related to magnetic field exposure.
Hormonal effects : There are
some reports that static magnetic fields of the order of the natural earth field
(about 0.05 mT) can affect melatonin production in rats [45,46,47],
although other studies with stronger (e.g., 2000 mT fields )
have not seen such effects. The one study with human volunteers showed no
effects on melatonin production of overnight exposure to a 2-7 milliT static
field . While it has been suggested that melatonin might
have "cancer-preventive" activity [48,49],
there is no evidence that static magnetic fields affect melatonin levels in
humans, or that melatonin has anti-cancer activity in humans.
15) Do static
magnetic fields show any reproducible biological effects in laboratory studies?
Yes. While the laboratory evidence does not suggest
a link between static magnetic fields and cancer, studies have reported that
static magnetic fields do have "bioeffects", particularly at field
strengths above 2000 mT [1,50,51,52,53,54,55].
These "bioeffects" have no obvious connection to cancer.
16) Do static
magnetic fields of the intensity encountered in occupational settings show
reproducible biological effects?
Possibly. A few biological effects have been
reported in laboratory systems for fields as low as 20 mT, and some organisms
appear to be able to detect changes in the strength and/or orientation of the
Earth's static magnetic field (0.03-0.05 mT) [1,54].
In addition, the rates of some chemical reactions can be affected by magnetic
fields as low as 10 mT [56,57].
17) Are there known
mechanisms that would explain how static magnetic fields of the intensity
encountered in occupational settings could cause biological effects in humans?
No. There are known biological mechanisms through
which strong (greater than 2000 mT) static magnetic fields could cause
biological effects [1,50], but these
mechanisms could not account for biological effects of static fields with
intensities of less than about 200 mT [1,50].
It is conceivable that biological effects could be
mediated through effects on free radical reaction rates at field strengths as
low as 0.1 mT [56,57,71,98];
but there is no evidence that such effects have any biological significance [71,77].
18) How does the sum
of the laboratory and epidemiological evidence relevant to a connection between
static magnetic fields and cancer stand up to the Hill criteria?
Application of the Hill criteria [Q9]
shows that the evidence for a causal association between exposure to static
fields and the incidence of cancer is weak to nonexistent.
- A review of the epidemiological evidence shows a weak
to nonexistent association between exposure to static magnetic fields
and cancer [Q9].
- There is no laboratory evidence that static
fields cause the type of effects on cells, tissues or animals that point
towards static fields causing, or contributing to, cancer [Q12,Q13,Q14].
- From what is known about the biophysics of static
magnetic fields and the effects of static magnetic fields on biological
systems, the hypothesis that static fields would cause or contribute to
cancer has no biophysical plausibility [Q17].
19) Have any
independent bodies reviewed the research on static electric and magnetic fields
and possible human health effects?
Yes. There have recently been a number of such
reviews of the epidemiological and laboratory literature. None of these reviews
have concluded that static magnetic or electrical fields of the intensity
encountered in residential and occupational settings are human health hazards.
A 1993 review by the United Kingdom (British) National
Radiological Protection Board (NRPB)  concluded that
for static electric fields "there is no biological evidence from which
basic restrictions on human exposure to static electric fields can be derived...
" and that "for most people, the annoying perception of surface
electric charge... will not occur during exposure to static electric fields of
less than about 25 kV/m".
For static magnetic fields the NRPB 
concluded that: "there is no direct experimental evidence of any acute,
adverse effect on human health due to short-term exposure to static magnetic
fields up to about 2 T [2000 mT]... Effects on behavior or cardiac function from
exposure to much higher magnetic flux densities than 2 T [2000 mT] cannot be
ruled out... There is little experimental information on the effects of chronic
exposure. So far, no long term effects have become apparent... There is no
convincing evidence that static magnetic fields are mutagenic... Tumor
progression and, by implication, tumor promotion seems to be unaffected by
exposure to static fields of at least 1 T [1000 mT]"
In 1993, the American Conference of Governmental
Industrial Hygienists (ACGIH)  concluded in their
review of the literature of static magnetic fields that: "no specific
target organs for deleterious magnetic field effects can be identified at the
present time... Although some effects [of static magnetic fields] have been
observed in both humans and animals, there have not been any clearly deleterious
effects conclusively demonstrated at magnetic field levels up to 2 T [2000 mT]."
In 1994, the International Commission on Non-Ionizing
Radiation Protection (ICNIRP)  concluded that:
"current scientific knowledge does not suggest any detrimental effect on
major developmental, behavioral and physiological parameters in higher organisms
for transient exposure to static field densities up to 2 T [2000 mT]. From
analysis of the established interactions, long-term exposure to magnetic flux
densities of 200 mT should not have adverse consequences." The latest
ICNIRP guideline on time-varying magnetic fields  may also
20) Do exposure
standards for static electric and magnetic fields exist?
Yes. A number of governmental and professional
organizations have developed exposure standards, or have modified or reaffirmed
their previous standards. For pacemakers and implanted medical device standards
also see Q22.
- In 1987, the US Lawrence Livermore National
Laboratory developed and published guidelines for personnel exposure to
static magnetic fields . Under their guideline, people
with pacemakers and prosthetic devices are limited to a peak field of 1 mT,
training and medical surveillance is required for persons exposed to fields
above 50 mT, and time-weighted average fields are limited to 60 mT to the
whole-body and 600 mT to the arms and legs. Peak exposures are limited to
- In 1987, the World Health Organization (WHO)
published health criteria for workers exposed to static magnetic fields .
Their report concluded that: "from the available data it can be
concluded that short-term exposure to static magnetic fields of less than 2
T [2000 mT] does not present a health hazard."
- In late 1993, the UK National Radiation Protection
Board (NRPB) issued exposure guidelines for static fields .
For static magnetic fields, the limits recommended are 200 mT averaged over
24 hours, 2000 mT as a maximum whole-body field, and 5000 mT as a maximum to
arms and legs. For static electrical fields the limit recommended is 25
kV/m. This standard applies to both residential and occupational exposure.
- Also in 1994, the American Conference of
Governmental Industrial Hygienists (ACGIH) issued a standard for
exposure to static magnetic fields . The ACGIH static
magnetic field limit is 0.5 mT for pacemaker users, and for everyone else
the time-weighted limit is 60 mT for whole body exposure and 600 mT for
exposure of the extremities. Because of the nature of ACGIH this standard is
applied only to occupational settings.
- In 1994, the International Commission on
Non-Ionizing Radiation Protection (ICNIRP) published guidelines for
exposure to static magnetic fields . For the general
public the magnetic field exposure standard is 40 mT for continuous
exposure, except for persons with cardiac pacemakers and other implanted
electronic devices, where the standard is lower (0.5 mT). For occupational
exposure, the standard is 200 mT for continuous exposure, 2000 mT for
short-term whole-body exposure, and 5000 mT for exposure to arms and legs.
21) What is the
basis for the safety standards set by Lawrence Livermore, WHO, ACGIH, NRPB, and
The standards are based on several considerations.
- One objective is to keep the electrical currents
induced by movement through the static magnetic field to a level less than
those that occur naturally in the body.
- A second objective is to keep the electrical currents
induced in large blood vessels by blood flow to a level that will not
produce hemodynamic or cardiovascular effects.
- The pacemaker and prosthetic device restrictions are
considered in Q22.
22) Do static fields
affect cardiac pacemakers?
Effects on cardiac pacemakers have been reported for
fields as low as 1.7 mT . The most common effect was
triggering of the asynchronous mode; the effect is very model and orientation
dependent, and in the models tested normal operation resumed when the pacemaker
was removed from the field . Some pacemakers also
exhibited significant torque when exposed . For this
reason current static field guidelines restrict exposures for wearers of cardiac
pacemakers to 0.5 mT [50,58,59].
It would be prudent to apply this restriction to other implanted electronic
devices, and to prosthetic devices as well, although not all standards are
explicit on this point.
In contrast to the above, a 2000 study 
found that MR imaging could be safely performed at 500 milliT in patients with
23) Do static fields
decrease fertility, cause birth defects or increase miscarriage rates?
There is no consistent evidence for such effects.
Fertility: Mur et al  found
no significant effects on the fertility of men exposed to 4-30 mT static fields
in the aluminum industry; and Evans et al  found no effect
of fertility in female MRI operators. One animal study reported evidence for
decreased male fertility at 1500 mT , but two other
studies at 500-700 mT found no such effect [84, 95].
A fourth animal study reported decreased female fertility at 80 mT, but not at
30 mT .
Miscarriages: Baker et al 
found that MRIs done at 1500 mT in the second and third trimester did not
increase the miscarriage rate; and Evans et al  found no
significant effect on miscarriage rates in female MRI operators. Two animal
study reported decreased fetal viability at 30 mT [86,93]
and 80 mT , but other studies at 500-1000 mT [90,
95] and 6300 mT  found no such effect.
Birth defects: Baker et al 
found that MRIs done at 1500 mT in the second and third trimester did not
produce birth defects; and Evans et al  found no increase
in birth defects in children of female MRI operators. One animal study reported
adverse effects on fetal development at 1500 mT ; but
other studies found no increase in birth defects at 30 ,
500-1000 mT [13,90,92, 95]
or 6300 mT . Two animal MRI studies done at 1500 mT [88a,
88b] reported increases in birth defects, but heating due to the
radiofrequency (RF) radiation used in MRI cannot be ruled out as a factor. A
third MRI study at 1500 mT  found no such effect.
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and Additions Notes:
v3.1 (January, 2002):
- A report that exposure of mice to a 3000 or 4700 milliT
static field for 24-72 hours caused chromosome damage in their bone marrow
- Converted to one-piece document and simplified
- A report that overnight exposure to a 2-7 milliT field
had no effect on night-time melatonin production in human volunteers .
- A report that a 7000 milliT field had no effects on the
growth or drug sensitivity of normal or leukemic mammalian cells .
- A report that 1500 and 7000 milliT static fields do not
cause mutations in bacteria .
Initial conversion of the FAQ into html was done by Bob Mueller and Dennis
Taylor of the General Clinical Research
Center at the Medical College of Wisconsin
- This document reviews the laboratory and
epidemiological evidence relevant to the issue of whether static (direct
current, DC) magnetic or electric fields cause or contribute to cancer (or
any other health problems) in humans.
- This FAQ was designed for Netscape v4.77 and HTML
version 4 transitional.
- This FAQ is derived from an FAQ of the same name that
was developed in the sci.med.physics newsgroup of USENET.
- El documento "Preguntas y respuestas sobre campos
eléctricos y magnéticos estįticos y cįncer" estį disponible en
- There are two related FAQs:
This FAQ is Copyright©, 1996-2002, by John E. Moulder,
Ph.D. and the Medical College of Wisconsin, and is made available as a service
to the Internet community. Portions of this FAQ are derived from the following
four articles, and are covered by the Copyrights on those articles:
Permission is granted to copy and redistribute this document
electronically as long as it is unmodified. This FAQ may not be sold in any
medium, including electronic, CD-ROM, or database, or published in print,
without the explicit, written permission of John Moulder.
- JE Moulder and KR Foster: Biological effects of
power-frequency fields as they relate to carcinogenesis. Proc Soc Exp Med
Biol 209:309-324, 1995.
- JE Moulder: Biological studies of power-frequency
fields and carcinogenesis. IEEE Eng Med Biol 15 (Jul/Aug):31-49, 1996.
- KR Foster, LS Erdreich, JE Moulder: Weak
electromagnetic fields and cancer in the context of risk assessment. Proc
- JE Moulder: Power-frequency fields and cancer. Crit Rev
Biomed Engineering 26:1-116, 1998.