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Magnetic Fields and Human Health

Table of Contents

  1. Does anyone think that static electric or magnetic fields cause cancer or any other human health problems?
  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?
  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 electromagnetic fields?
  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?
  5. What units are used to measure static magnetic fields?
  6. What sort of static magnetic fields are common in residences?
  7. What sort of static magnetic fields are common in workplaces?
  8. What is known about the relationship between occupational exposure to static magnetic fields and cancer?
  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?
  10. How does the epidemiological evidence relevant to a connection between static fields and cancer stand up to the Hill criteria?
  11. How could laboratory studies be used to help evaluate the possible relationship between static magnetic fields and cancer?
  12. Are static magnetic fields genotoxic?
  13. Do static magnetic fields enhance the effects of other genotoxic agents?
  14. Do laboratory studies indicate that static magnetic fields have any biological effects that might be relevant to cancer or other human health hazards?
  15. Do static magnetic fields show any reproducible biological effects in laboratory studies?
  16. Do static magnetic fields of the intensity encountered in occupational settings show reproducible biological effects?
  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?
  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?
  19. Have any independent bodies reviewed the research on static electric and magnetic fields and possible human health effects?
  20. Do exposure standards for static electric and magnetic fields exist?
  21. What is the basis for the safety standards set by Lawrence Livermore, WHO, ACGIH, NRPB, and ICNIRP?
  22. Do static fields affect cardiac pacemakers?
  23. Do static fields decrease fertility, cause birth defects or increase miscarriage rates?
  24. Annotated bibliography

Questions and Answers


1) Does anyone think that static electric or magnetic fields cause cancer or any other human health problems?

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 separately.

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 wavelength.

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 [62].

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 [62].

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 [62].

Thus in terms of potential biological effects the electromagnetic spectrum can be divided into four portions:

  1. The ionizing radiation portion, where direct chemical damage can occur (X-rays).
  2. The non-ionizing portion of the spectrum, which can be subdivided into:
    1. The optical radiation portion, were electron excitation can occur (visible light, infrared light)
    2. The portion where the wavelength is smaller than the body, and heating via induced currents can occur (MW and higher-frequency RF).
    3. 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 electromagnetic fields?

No. Static electromagnetic sources do not produce radiation.

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, so:
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 mT.

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 [80].

 


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 [4]. 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 [7].

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 and cancer?

There have been relatively few studies of cancer incidence in workers exposed to static magnetic fields. Budinger et al [7] found no excess cancer in workers exposed to 300 mT fields from particle accelerators, and Barregard et al [6] 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 [8,9,10,61]. 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 [8]. The only aluminum reduction plant study to look specifically at static field exposure and cancer reported no excess of nervous system or hematopoietic cancers [61].

 


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" [11], 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.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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 regulatory reviews.
  • Satisfying the individual criteria is not a yes-no matter; support for a criterion can be strong, moderate, weak, or non-existent.
  • 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.

  1. 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 [8], and that association is not large, and is seen for only one type of cancer.
  2. 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.
  3. Since only one study reports an association between exposure to static fields and cancer, the issue of specificity is moot.
  4. 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, 75].

 


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 [12] found no increase in mammary cancer in mice exposed to a 0.02 mT field. Mahlum et al [13] 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] fields.

There have been two whole organism reports of possible genotoxicity. In 1995 Koana et al [65] 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 [103] 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 [103].

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 [76], 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 [78].

In 2000 Teichman et al [101] reported that 1500 and 7000 milliT static fields did not cause mutations in bacteria (the Ames assay).

Some studies of static electrical fields have also been conducted. These have been reviewed by McCann et al [29], 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 [32] 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 [33].

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 [31], but to be inhibited at 4000 mT [33]. 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 [12] 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 [69]: In general, static magnetic fields of 13-1150 mT appear to have no effect on the growth of either chemically-induced [36] 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 [35].

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], animal [25,31,39,42,72,74,100] or yeast [66] cells. However, there are 4 reports of static fields effects on cell growth: inhibition of human lymphocyte growth at 4000-6300 mT [33], inhibition of tumor cell growth at 7000 mT [76], stimulation of mammalian cell growth at 140 mT [67],and both stimulation and inhibition of DNA synthesis in fibroblasts at 610 mT [72].

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 [43]. 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 [75]: 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 [68]) 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 [99]. 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.

  1. A review of the epidemiological evidence shows a weak to nonexistent association between exposure to static magnetic fields and cancer [Q9].
  2. 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].
  3. 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) [58] 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 [58] 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) [59] 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) [50] 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 [81] may also be relevant.

 


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 [54]. 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 2000 mT.
  • In 1987, the World Health Organization (WHO) published health criteria for workers exposed to static magnetic fields [60]. 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 [58]. 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 [59]. 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 [50]. 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 ICNIRP?

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 [73]. 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 [73]. Some pacemakers also exhibited significant torque when exposed [73]. 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 [96] found that MR imaging could be safely performed at 500 milliT in patients with cardiac pacemakers.

 


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 [82] found no significant effects on the fertility of men exposed to 4-30 mT static fields in the aluminum industry; and Evans et al [87] found no effect of fertility in female MRI operators. One animal study reported evidence for decreased male fertility at 1500 mT [83], 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 [93].

Miscarriages: Baker et al [85] found that MRIs done at 1500 mT in the second and third trimester did not increase the miscarriage rate; and Evans et al [87] 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 [93], but other studies at 500-1000 mT [90, 95] and 6300 mT [89] found no such effect.

Birth defects: Baker et al [85] found that MRIs done at 1500 mT in the second and third trimester did not produce birth defects; and Evans et al [87] found no increase in birth defects in children of female MRI operators. One animal study reported adverse effects on fetal development at 1500 mT [83]; but other studies found no increase in birth defects at 30 [86], 500-1000 mT [13,90,92, 95] or 6300 mT [89]. 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 [91] found no such effect.

 


Bibliography

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2) MA Stuchly: Human exposure to static and time-varying magnetic fields. Health Phys 51:215-225 (1986).

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Source: http://www.mcw.edu/gcrc/cop/static-fields-cancer-FAQ/toc.html


Revisions 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 cells [102].
In 2001:
  • Converted to one-piece document and simplified bibliography.
  • A report that overnight exposure to a 2-7 milliT field had no effect on night-time melatonin production in human volunteers [99].
  • A report that a 7000 milliT field had no effects on the growth or drug sensitivity of normal or leukemic mammalian cells [100].
  • A report that 1500 and 7000 milliT static fields do not cause mutations in bacteria [101].

 


Acknowledgments: 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

Last-modified: 14-Jan-2002
Version: 3.1.0
Maintainer: jmoulder@mcw.edu


Notice:

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:

  • 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 IEEE 85:733-746,1997.
  • JE Moulder: Power-frequency fields and cancer. Crit Rev Biomed Engineering 26:1-116, 1998.
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.

 

 

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