Static Fields

6. How may humans be affected by static fields?

• 6.1 Have experiments on humans shown effects of static fields?
• 6.2 What health effects were seen in people exposed to static magnetic fields through their work?

6.1 Have experiments on humans shown effects of static fields?

The source document for this Digest states:

Static electric fields do not penetrate electrically conductive objects such as the human body; the field induces a surface electric charge and is always perpendicular to the body surface. A sufficiently large surface charge density may be perceived through its interaction with body hair and by other effects such as spark discharges (microshocks). The perception threshold in people depends on various factors and can range between 10 - 45 kV m⁻¹. Annoying sensation thresholds are probably equally variable, but have not been systematically studied. Painful microshocks can be expected when a person who is well insulated from the ground touches a grounded object, or when a grounded person touches a conductive object that is well insulated from ground. However, the threshold static electric field values will vary depending on the degree of insulation and other factors.

Endpoints investigated in human experimental studies have included peripheral nerve function, brain activity, neurobehavioural and cognitive function, sensory perception, cardiac function, blood pressure, heart rate, serum proteins and hormone levels, body and skin temperature, and therapeutic effects. exposure levels up to 8 T have been investigated, and both pure static fields and MRI imaging have been studied. The exposure duration ranged from a few seconds up to nine hours, but was usually less than one hour. The data available are limited for several reasons, including the facts that generally convenience samples of patients or healthy volunteers have been studied and the numbers of subjects have usually been small.

The results do not indicate that there are effects of static magnetic field exposure on neurophysiological responses and cognitive functions in stationary volunteers, nor can they rule out such effects. A dose-dependent induction of vertigo and nausea was found in workers, patients and volunteers during movement in static fields greater than about 2 T. One study suggested that eye-hand coordination and near visual contrast sensitivity are reduced in fields adjacent to a 1.5 T MRI unit. Occurrence of these effects is likely to be dependent on the gradient of the field and the movement of the subject. A small change in blood pressure and heart rate was observed in some studies, but were in the range of normal physiological variability. There is no evidence of effects of static magnetic fields on other aspects of cardiovascular physiology, or on serum proteins and hormones. Exposure to static magnetic fields of up to 8 T does not appear to induce temperature changes in humans.

Note, however, that most of the studies were very small, were based on convenience samples, and often included non-comparable groups. Thus, it is not possible to draw any conclusions regarding the wide variety of end-points examined in this report.

Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
 Chapter 1, Section 1.1.5 Laboratory Studies on Humans

6.2 What health effects were seen in people exposed to static magnetic fields through their work?

The source document for this Digest states:

Epidemiological studies have been carried out almost exclusively on workers exposed to static magnetic fields generated by equipment using large DC currents. Most workers were exposed to moderate static magnetic fields of up to several 10’s mT either as welders, aluminium smelters, or workers in various industrial plants using large electrolytic cells in chemical separation processes. However, such work is also likely to have involved exposure to a variety of potentially hazardous fumes and aerosols, thus confounding interpretation. Health endpoints studied in these workers include cancer, haematological changes and related outcomes, chromosome aberration frequency, reproductive outcomes, and musculoskeletal disorders. In addition, a few studies examined fertility and pregnancy outcome in female MRI operators, where the potential to have been exposed to relatively large static fields of up to ~ 1 T may have existed. Two studies examined pregnancy outcome in healthy volunteers exposed to MRI examinations during pregnancy.

Increased risks of various cancers, e.g. lung cancer, pancreatic cancer, and haematological malignancies, were reported, but results were not consistent across studies. The few epidemiological studies published to date leave a number of unresolved issues concerning the possibility of increased cancer risk from exposure to static magnetic fields. Assessment of exposure has been poor, the number of participants in some of the studies has been very small, and these studies are thus able to detect only very large risks for such rare diseases. The inability of these studies to provide useful information is confirmed by the lack of clear evidence for other, more established carcinogenic factors present in some of the work environments. Other non-cancerous health effects have been considered even more sporadically. Most of these studies are based on very small numbers and have numerous methodological limitations. Other environments with a potential for high fields have not been adequately evaluated, e.g. those for MRI operators. At present, there is inadequate data for a health evaluation.

Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
 Chapter 1, Section 1.1.6 Epidiemiological Studies

For more information on	See EHC 232
Laboratory studies on humans	Chapter 8, Section 8.1
Epidemiological studies	Chapter 8, Section 8.2