Directorate-General for Health and Food Safety
7. Extremely low frequency fields (ELF) like those from power lines and household appliances
- 7.1 What are the sources of ELF fields?
- 7.2 What is the level of exposure to ELF fields?
- 7.3 Can ELF fields increase the risk of childhood leukaemia and other cancers?
- 7.4 Can exposure to ELF cause headaches or other health effects?
- 7.5 Can ELF magnetic fields have effects on human reproduction?
- 7.6 What can be concluded about ELF fields?
7.1 What are the sources of ELF fields?
Power lines generate ELF fields Credit: Miguel Saavedra
In this assessment, extremely low frequency (ELF) fields
fields with frequencies below 300 Hz, the frequencies
that are lower than intermediate frequencies. The main source of
ELF is alternating current carried in overhead lines of railways, power lines, electric
installations and household appliances. The magnetic field generated
has the same frequency as the current that produces it, i.e.
16 2/3 Hz, 50Hz or 60Hz (the latter predominantly in US). Additional important sources of ELF magnetic fields include power plants and substations, welding machines, induction heaters and tramway and subway systems.
ELF fields can be electric or magnetic:
- An electric field is the created by electric charges and characterised by forces acting upon other electric charges. It is measured in volts per meter (V/m).
- A magnetic field is created as a consequence of the movement of electric charges (electric current) and characterised by the force acting upon resting or moving electric charges. The strength of a magnetic field is usually measured in ampere per meter (A/m), alternatively, by accounting for the magnetic properties of material as magnetic induction, in tesla (T).
The amplitude of both electric and magnetic fields strongly decreases with distance from the field source.
ELF electric fields tend to be strongest below high voltage overhead power lines (up to several kV/m), and ELF magnetic fields are particularly strong near cables with high current load such as at welding machines and induction furnaces (up to a few mT). To determine compliance with exposure limits, the maximum possible exposure next to the source must be assessed, in general by comparing measured field quantities with the given reference level. The maximum field level of inhomogeneous fields next to a source may be several orders of magnitudes higher than the reference level of equivalent homogeneous fields.
7.2 What is the level of exposure to ELF fields?
The general public can be exposed to extremely low frequency (ELF) fields from various fixed sources that are operative in our environment, such as power lines and transformer stations, in particular if those are placed inside houses.
Passing directly below a high voltage power line, exposure to electric fields can be of several kV/m and to magnetic fields of several 10 μT. The amplitude of electric and magnetic fields decreases rapidly with increasing distance to the line;
At home, the magnetic fields are strongest close to distribution boxes and to household appliances in particular those, that contain motors, transformers, or consume high power such as electric ovens or heaters. The smaller the dimension of a source, the more effective is increasing distance in reducing field levels.
7.3 Can ELF fields increase the risk of childhood leukaemia and other cancers?
Studies on ELF MF are focusing on power frequency fields. In 2002, the International Agency for Research on Cancer (IARC) classified ELF magnetic fields as “possibly carcinogenic to humans” (Group 2B). This was based on epidemiologic studies that reported that children are more likely to develop leukaemia if their time-averaged exposure to ELF magnetic fields exceeds 0.3-0.4 μT, which is relatively strong. Experimental studies on animals did not support these findings. Furthermore, the IARC concluded, there was no evidence for a link between ELF magnetic fields and any other type of cancer.
This potential link between ELF fields and childhood leukaemia has been further addressed by a number of epidemiological studies which confirm an increased risk of leukaemia in children living close to high voltage power lines with estimated daily average exposures (above 0.3 to 0.4 µT) much higher than average magnetic field exposure at homes.
But it remains difficult to judge whether this apparently quite robust association is likely to be causal or a result of methodological shortcomings of the studies such as information bias, selection bias and confounding factors.
Indeed, little progress has been made in verifying the causality of the reported association or in explaining the finding, neither by a plausible mechanism nor in identifying an alternative explanation. Besides, a large and more recent study investigating childhood leukaemia survival in relation to ELF magnetic field exposure did not observe an association, adding no support to the hypothesis that ELF magnetic field may promote pre-leukemic clones both related to the risk of developing leukaemia as well as the risk of a relapse of leukaemia after successful treatment.
7.4 Can exposure to ELF cause headaches or other health effects?
As in the case of radio frequency fields, self-reported “electromagnetic hypersensitivity” is an issue that also comes up in the case of ELF field exposure including reports on a variety of symptoms such as skin redness, tingling and burning sensations, as well as fatigue, headache, concentration difficulties, nausea, and heart palpitations. There were several studies added to the existing pool of investigations. Overall, the studies do not provide convincing evidence for a causal relationship between ELF MF exposure and self-reported symptoms.
Studies investigating possible effects of ELF MF exposure on brain activity are too heterogeneous to draw a sound conclusion. Largely consistent with earlier results, recent studies have reported that exposure to ELF MF has no effect on activity or locomotion. There is some evidence from animal studies that exposure to ELF magnetic fields may affect the performance of spatial memory tasks (both deficits and improvements have been reported) and engender subtle increases in behavioural anxiety and stress.
Other studies have investigated potential molecular and cellular mechanisms, and despite a number of studies continue to report candidate mechanisms, particularly regarding effects on reactive oxygen species, none has been firmly identified that operates at exposure levels found in the everyday environment.
Epidemiological studies do not provide convincing evidence of an increased risk of neurodegenerative diseases, including dementia, related to power frequency MF exposure.
7.5 Can ELF magnetic fields have effects on human reproduction?
Epidemiological studies showed no evidence for adverse effects on pregnancy or on the health of the children. Some studies report some implausible effects but need to be replicated independently, before they can be used for risk assessment.
7.6 What can be concluded about ELF fields?
The new epidemiological studies are consistent with earlier findings of an increased risk of childhood leukaemia with estimated daily average exposures above 0.3 to 0.4 µT. As stated in the previous Opinions, no mechanisms have been identified and no experimental studies have been able explain these findings, which, together with shortcomings of the epidemiological studies prevent a causal interpretation.
Overall, existing studies do not provide convincing evidence for a causal relationship between ELF MF exposure and self-reported symptoms.
Studies investigating possible effects of ELF exposure on the power spectra of the waking EEG are too heterogeneous with regard to applied fields, duration of exposure, number of considered leads and statistical methods to draw a sound conclusion. The same is true for behavioural outcomes and cortical excitability.
Epidemiological studies do not provide convincing evidence of an increased risk of neurodegenerative diseases, including dementia, related to ELF MF exposure. Furthermore, they show no evidence for adverse pregnancy outcomes in relation to ELF MF. The studies concerning childhood health outcomes in relation to maternal residential ELF MF exposure during pregnancy involve some methodological issues that need to be addressed. They report implausible effects but need to be replicated independently before they can be used for risk assessment.
Recent results do not show that ELF fields have any effect on the reproductive function in humans.