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Biological and health effects of static fields
- Static magnetic fields exert forces on magnetisable metals as well as on moving electrically charged particles.
- As an example humans use strong magnetic fields for medical imaging methods.
- To date, investigations have not revealed any direct negative biological or health effects from static magnetic fields with magnetic flux densities of up to four teslas.
- Further research is needed on the effects of stronger static magnetic fields.
The Earth’s magnetic field deflects a part of the cosmic radiation, which has an ionising effect and is carcinogenic on living beings. At the equator the field has a magnetic flux density of about 30 microteslas, at the poles it is twice as high. In central Europe the flux density is about 48 microteslas.
Some species of fish are able to detect very weak static fields such as the Earth’s magnetic field and use these to orient themselves. Sharks and rays have very sensitive sensory organs in their skin which respond to electric fields induced by the magnetic field in salt water. Migratory fish like salmon use magnetite (a compound of iron and oxygen) in their nasal septum for the perception of the Earth’s magnetic field.
Many bird species are able to sense the Earth’s magnetic field and to orient themselves accordingly. To this end, they use several functionally independent sensory organs:
- Special receptors in the retina respond to the direction of the magnetic field.
- In the bird’s beak, there are cells containing magnetite which serve to detect the magnetic field strength.
- Parts of the inner ear also respond to magnetic fields.
Among mammals, only a few animals are able to orient themselves according to the Earth’s magnetic field. They live in darkness like for example bats, or underground like naked mole rats (rodents). Humans are not able to perceive the Earth’s magnetic field.
Strong static magnetic fields in magnetic resonance imaging
Employees and patients may come into contact with strong magnetic fields, for example in magnetic resonance imaging, a diagnostic imaging technique used in medicine. The scanners currently employed in clinical practice mostly have magnetic flux densities of 1.5 or 3 teslas. Scanners with 7 to 11 teslas intended for future clinical use are already being tested in research. Whether stronger fields have any health effects on patients or medical personnel is now being researched.
Indirect effectsshow / hide
Objects made of magnetisable metals, such as coins or scissors can turn into dangerous projectiles in the environment of magnetic resonance scanners. Already at magnetic flux densities above 3 milliteslas, magnetic fields exert strong forces on these objects.
These forces also act on implants containing magnetisable metals. For that reason, wearers of such implants can often not be examined in magnetic resonance scanners. Prior to the examination, the physician has to balance risks and benefits on the basis of the patient’s medical record and the information provided by the manufacturer of the implant.
Direct biological effectsshow / hide
Magnetic fields exert forces on electrically charged particles in the human body only when the particles are moving. This relates to blood flow or movements of the body within the magnetic field. To date, scientific investigations on magnetic flux densities below four teslas have not revealed any direct negative health effects on the human body.
Depending on their alignment, strong magnetic fields within the magnetic resonance scanner may slightly slow down the blood flow in large arteries of patients. Below eight teslas these effects are very minor and not relevant to health.
Furthermore, strong magnetic fields can directly exert forces on fluids and ions in the vestibular organ which can lead to impaired balance and dizziness in patients and medical personnel.
Individuals moving rapidly within strong static magnetic fields may experience sensations of dizziness, nausea and a metallic taste. This is due to the impact of induced electric fields on the vestibular organ and the taste buds. Moving rapidly within the spatial gradient of a strong static magnetic field may cause the perception of light flashes. These result from induced low-frequency electric fields in the retina.
In addition to strong static magnetic fields, time-varying gradient fields and high-frequency electromagnetic fields are employed in magnetic resonance imaging. Gradient fields are low-frequency magnetic fields.
The effects of stronger magnetic fields (above four teslas) have not yet been adequately investigated as the technology of magnetic resonance imaging using high magnetic flux densities is relatively new. In large scientific areas there are no established research findings on health effects.
Whether strong static magnetic fields have an influence on pregnancy and embryonic development has been investigated inadequately and only for low flux densities. This knowledge, however, is important for the safety of pregnant patients and medical personnel. As a precautionary measure, the German Commission on Radiological Protection (Strahlenschutzkommission - SSK) therefore recommends an especially careful balancing of the risks and benefits, particularly during the first three months of pregnancy. Nevertheless, this technology is increasingly used for diagnosing pregnant women, since it does not involve ionising radiation as is the case with X-ray or computer tomography.
Whether uncomfortable perceptions and impacts on the nervous system impair the performance of medical personnel also has to be investigated, as such impairment could be a hazard to the patients.
Research commissioned by the BfS
Several research projects commissioned by the BfS have investigated whether static magnetic fields of magnetic resonance imaging scanners may have health effects on patients or medical personnel.
It has been demonstrated that magnetic fields of up to seven teslas do not have any adverse health effects on the fertility of male mice, on the pregnancy of female mice, and on the embryonic development as well as on the further development of the offspring.
Investigations in humans have confirmed uncomfortable sensations, especially dizziness. This has, however, had no effects on cognitive performance such as reaction times and memory.
State of 2017.04.26