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Static Fields

5. How may static fields affect cells or animals?

  • 5.1 What have studies on cells revealed about the effect of static magnetic fields?
  • 5.2 How can laboratory animals be affected by static electric or magnetic fields?
    • 5.2.1 Animal studies in general
    • 5.2.2 Effects on the nervous system in animals of various countries?
    • 5.2.3 Effects on the heart and blood flow of animal subjects
    • 5.2.4 Effect on the endocrine system of laboratory animals

5.1 What have studies on cells revealed about the effect of static magnetic fields?

The source document for this Digest states:

The results of in vitro studies are useful for elucidating interaction mechanisms, and for indicating the sorts of effects that might be investigated in vivo. However, they are not sufficient to identify health effects without corroborating evidence from in vivo studies.

A number of different biological effects of static magnetic fields have been explored in vitro. Different levels of organization have been investigated, including cell free systems (employing isolated membranes, enzymes or biochemical reactions) and various cell models (using both bacteria and mammalian cells). Endpoints studied included cell orientation, cell metabolic activity, cell membrane physiology, gene expression, cell growth and genotoxicity.

Positive and negative findings have been reported for all these endpoints. However, most data were not replicated. The observed effects are rather diverse and were found after exposure to a wide range of magnetic flux densities. There is evidence that static magnetic fields can affect several endpoints at intensities lower than 1 T, in the mT range. Thresholds for some of the effects were reported, but other studies indicated non-linear responses without clear threshold values.

Effects of static magnetic fields on cell orientation have been consistently found above 1 T, but their in vivo relevance is questionable. A few studies suggested that combined effects of static magnetic field with other agents such as genotoxic chemicals seem to produce synergistic, both protective and stimulating, effects. The current information is inadequate and needs to be confirmed before any firm conclusions on human health can be drawn.

Besides possible complicated dependence on physical dosimetersparameters such as intensity, duration, recurrence and gradients of exposure, biological variables appear to be important for the effects of static magnetic fields. Variables such as cell type, cell activation, and other physiological conditions during exposure have been shown to affect the outcome of the experiments. The mechanisms for these effects are not known, but effects on radicals and ions may be involved. in vitro studies provide some evidence for this.

If the very few studies employing MRI signals or other combined fields show any biological effects, they do not show any that are different from those of static magnetic fields alone.

Taken together, the in vitro experiments do not present a clear picture of specific effects of static magnetic fields, and they consequently also do not indicate possible adverse health effects.

Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
 Chapter 1, Section 1.1.3 In vitro studies

For more information on   See EHC 232
In vitro studies  Chapter 7, Section 7.1

5.2 How can laboratory animals be affected by static electric or magnetic fields?

    • 5.2.1 Animal studies in general
    • 5.2.2 Effects on the nervous system in animals of various countries?
    • 5.2.3 Effects on the heart and blood flow of animal subjects
    • 5.2.4 Effect on the endocrine system of laboratory animals

5.2.1 Animal studies in general

The source document for this Digest states:

Few animal studies on the effects of Static electric fields have been carried out. No evidence of adverse health effects have been noted, other than those associated with the perception of the surface electric charge.

A large numer of animal studies on the effects of static magnetic fields have been carried out. Most of those considered relevant to human health have examined the effects of fields considerably larger than the natural geomagnetic field. A number of studies have been carried out of fields in the millitesla region, comparable to relatively high industrial exposures. More recently, with the advent of superconducting magnet technology and MRI, studies of behavioural, physiological and reproductive effects have been carried out at flux densities around, or exceeding, 1 T. Few studies, however, have examined possible chronic effects of exposure, particularly in relation to carcinogenesis.

Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
 Chapter 1, Section 1.1.4 Animal studies

5.2.2 Effects on the nervous system in animals of various countries?

The source document for this Digest states:

The most consistent responses seen in neurobehavioural studies suggest that the movement of laboratory rodents in static magnetic fields equal to or greater than 4 T may be unpleasant, inducing aversive responses and conditioned avoidance. Such effects are thought to be consistent with magnetohydrodynamic effects on the endolymph of the vestibular apparatus. The data are otherwise variable. There is some evidence that several vertebrate and invertebrate species are able to use static magnetic fields, at levels as low as geomagnetic field strengths, for orientation. However, these responses are not thought to have any significance for health.

Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
 Chapter 1, Section 1.1.4 Animal studies

5.2.3 Effects on the heart and blood flow of animal subjects

The source document for this Digest states:

There is good evidence that exposure to fields greater than about 1 T (0.1 T in larger animals) will induce flow potentials around the heart and major blood vessels, but the physiological consequences of this remain unclear. Several hours of exposure to very high flux densities of up to 8 T in the heart region did not result in any cardiovascular effects in pigs. In rabbits, short and long exposures to fields ranging from geomagnetic levels to the millitesla range have been reported to affect the cardiovascular system, although the evidence is not strong.

The results from one group suggest that the static magnetic fields of mT intensities may suppress early blood pressure elevation via hormonal regulatory system. The same group has reported that low-intensity static magnetic fields of up to 0.2 T may induce local effects on blood flow that may lead to improvement of microcirculation. In addition, another group reported that high static magnetic field flux densities of up to 10 T may lead to reduced skin blood flow and temperature. In all these cases, however, the endpoints are rather labile, a situation that may have been complicated by pharmacological manipulation, including anaesthesia in some cases, and immobilisation. In general, it is difficult to reach any firm conclusion without some independent replication.

Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
 Chapter 1, Section 1.1.4 Animal studies

5.2.4 Effect on the endocrine system of laboratory animals

The source document for this Digest states:

Several studies described possible effects of magnetic field exposure on blood cells and the haemopoietic system. However, the results are equivocal, limiting the conclusions that can be drawn. The available evidence regarding effects of static magnetic field exposure on enzymatic and ionic constituents in serum comes primarily from one laboratory. These findings need to be confirmed by independent laboratories before conclusions can be drawn.

In terms of effects on the endocrine system, several studies from one laboratory suggest that static magnetic field exposure can affect pineal synthesis and melatonin content. However, some studies performed at other laboratories have been unable to demonstrate an effect. The finding of a suppressive effect of static magnetic field exposure on melatonin production needs to be confirmed in further research before firm conclusions can be drawn. On the whole, few studies have investigated static magnetic field effects on endocrine systems other than the pineal. No consistent effects have emerged.

Reproduction and development are very important issues in MRI exposure of both patients and clinical staff. In this respect, only a few good studies of static magnetic fields are available at field values above 1 T. MRI studies per se are uninformative because the effect of the static field cannot be distinguished from the possible general effects of the radiofrequency and pulsed gradient fields. Further examination is urgently needed to assess the health risk.

In general, so few animal studies have been carried out with regard to genotoxicity and cancer that it is not possible to draw any firm conclusions.

Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
 Chapter 1, Section 1.1.4 Animal studies

For more information on   See EHC 232
Effects on animals of static magnetic fields  Chapter 7, Section 7.2

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