Top 1. Introduction to electromagnetic fields
 Frequency ranges of electromagnetic fields
Electromagnetic fields are a
combination of invisible electric and
magnetic fields of force. They
are generated by natural phenomena, but also by human activities, mainly
through the use of electricity.
Most man-made electromagnetic
fields reverse their direction with time at a specific
frequency, ranging
from high radio frequencies (RF) – such as used by
mobile phones – through intermediate frequencies (IF) –
such as generated by computer screens – to extremely low
frequencies (ELF) – such as generated by power
lines.
The term static refers to fields that do not vary
with time. Static magnetic fields
are used in medical imaging and generated by appliances using
direct current.
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Exposure to electromagnetic
fields triggers immediate biological effects if they are strong
enough. Effects range from stimulation of nerves and muscles to heating
of the body tissues, depending on
the frequency. Exposure guidelines have been established to protect
against these effects.
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Top 2. What are the sources of exposure to radio frequency (RF) fields?
 Local wireless computer networks generate radio
fields Credit: Ramzi Mashisho
Radio frequency (RF) fields have many applications in modern
communications. Familiar sources include mobile phones, cordless phones,
local wireless networks and radio transmission towers. Medical scanners,
radar systems and microwave ovens also use radio frequency fields. Radio
frequencies range from 100 kHz to 300
GHz.
When exposed to radio frequency fields, the body absorbs energy over
time. How much radio frequency energy an individual absorbs every day is
not obvious as the exposure depends on many factors, especially distance
from the various sources. Field strength falls rapidly with distance,
meaning a person may absorb more energy from a device used at close
quarters – a handheld mobile phone, for example – than from a more
powerful source, like a radio transmission tower, that is farther away.
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Europe has set safety limits on exposure to radio frequency fields.
For handheld mobile phones, these limits are given in terms of the
energy absorbed by the head, the part of the body most exposed during
use. Other wireless devices used in close quarters, like cordless phones
and wireless computer networks, also generate radio waves but exposure
from these sources is generally lower than from mobile phones.
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Mobile phone base
stations and radio transmission
towers are structures designed to support antennas that
transmit radio signals. Because the field strength decreases rapidly
with distance, most people are exposed to only a fraction of the maximum
recommended. People who live or work near transmission towers are most
exposed because that is where the fields are strongest.
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In medicine, strong radio frequency fields are used to heat body
tissue, which can ease pain
or kill cancer
cells. Such fields are also used to
produce images of the brain and other body parts by
magnetic resonance imaging
(MRI). Exposure of patients
or medical staff could exceed the usual safety limits.
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Top 3. Can mobile phones cause cancer?
 More than 2 billion people use mobile phones
worldwide Credit: Juha Blomberg
In recent years many studies have investigated whether mobile phones
and radio frequency (RF) fields in general could cause
cancer.
Epidemiological studies on
mobile phone users have focused on
cancers originating in the head,
especially brain tumours. Overall,
research indicates that mobile phone use does not increase the risk of
cancer, especially when used less than 10 years. More research is needed
before a risk can be ruled out for use beyond 10 years.
Some studies have raised concern of a link between mobile phone use
and benign tumours of the auditory
nerve, which is responsible for balance and hearing. People who have
been using mobile phones for less than 10 years do not appear to have a
higher risk of this benign tumour
(acoustic neuroma). But
there is some evidence of a risk beyond 10 years, and more study is
needed.
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Animal studies have provided no consistent evidence
on whether radio frequency fields could induce
cancer, enhance the effects of
cancer-causing substances, or accelerate the development of
tumours. But most of these
studies involved relatively low exposure, calling for more research.
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In recent years, research on how radio-frequency energy affects
cells has expanded to
include more kinds of cell
cultures. Overall such studies show little evidence of
health-relevant effects when exposure is below existing safety
guidelines. But some studies suggest effects on
DNA at exposure levels close to
guidelines.
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Top 4. Can mobile phones or base stations trigger headaches or other health effects?
 Mobile phone base station Credit: Pyb
Some people attribute headaches, fatigue and dizziness to radio
frequency (RF) fields. Such complaints have raised concern that certain
individuals may be more sensitive than others to electromagnetic energy.
Present knowledge suggests that these symptoms are not linked to
exposure to radio frequency fields, but few studies have addressed this
issue directly.
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Because mobile phones are used near the head, there have been concerns
they could affect the brain.
Minor changes in the brain functions of people exposed to radio
frequency fields have been observed in some studies but not in others.
Suspicions that radio frequency fields could affect memory and learning
have not been confirmed.
Conflicting results were reported on whether low levels of radio
frequency fields increase the permeability of the barrier that keeps
harmful substances from reaching the brain (blood-brain barrier).
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Research on female health workers exposed while on the job revealed no
harmful effect on pregnancies.
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Few studies have addressed the possible effects of mobile phones on
children, despite concern that children could be more
vulnerable than adults and
will get more exposure over their lifetimes. One area for investigation
would be whether radio frequency fields can cause childhood brain
tumours.
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Top 5. Conclusions on mobile phones and radio frequency fields
 Few studies have looked at effects on children
Extensive research has been conducted in recent years on how radio
frequency fields, including those generated by mobile phones, might
affect health. A variety of possible effects has been studied, both
inside the laboratory and among human populations.
No health effect has been consistently demonstrated at exposure levels
below existing guidelines for the general public. Some studies suggest
an increased number of cases of benign
tumours of the auditory nerve
(acoustic neuroma) could
be linked to long-term mobile phone use, but overall results are not
conclusive at the present time.
Research indicates that a person who has used a mobile phone for up to
10 years does not have a higher risk of brain
tumours or other
cancers in the skull. This
also appears to be the case for someone who has used a mobile phone for
more than 10 years, but more study is needed.
Research has found no evidence that exposure to radio frequency fields
at levels below existing safety guidelines could cause symptoms like
headaches and dizziness.
Few studies have looked at possible health effects on children,
despite the growing popularity of mobile phones among the young and
concern that children might be more
vulnerable because of their
still developing nervous system.
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Top 6. Intermediate frequency fields like those from computer screens and anti theft devices
 Cathode ray tube screens generate intermediate frequency
fields Credit: Anissa Thompson
In this assessment, “intermediate” refers to frequencies ranging
from 300 Hz to 100 kHz.
These are lower than radio frequencies and higher than extremely low
frequencies.
Technologies generating intermediate frequency fields have increased
in recent years and include some anti-theft devices, induction
hotplates, cathode ray tube screens and radio transmitters. Intermediate
fields are also used by medical devices, and are generated by industrial
processes such as welding.
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Well-known biological effects in the intermediate frequency range are
nerve stimulation at the lower end of the range and heating at the upper
end of the range. Few data are available on the exposure of individuals
to intermediate frequency fields and on possible health effects. The few
studies conducted have focused on potential effects on the eyes, the
cardiovascular system,
cancer, and reproduction.
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Long-term studies on human populations are needed to evaluate the
risks to human health and to confirm that the current recommended limits
on exposure are adequate.
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Top 7. Extremely low frequency fields like those from power lines and household appliances

See also our Digest on Power Lines
Extremely low frequencies (ELF) are those
below 300 Hz. Such fields are
for instance generated by alternating
current (AC), the type of electricity used in most power
lines, wiring and appliances. Other important sources of extremely low
frequency fields are power plants, welding machines, induction heaters
as well as trains, trams and subway systems.
Extremely low frequency fields have electric and magnetic components.
ELF
electric fields
are particularly strong close to high voltage power lines, and
ELF magnetic fields are particularly strong near
induction furnaces and welding machines.
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In the areas that are accessible to the public, exposure to extremely
low frequency fields is below the set limits. When people pass directly
below a high voltage power line, their level of
exposure to such fields is relatively high though still below safety
limits. Low voltage power lines cause much lower exposure, and buried
cables virtually none. At home, fields are strongest very near electric
appliances such as vacuum cleaners.
Workers in the electric power industry and welders
can be exposed to high levels of
electromagnetic fields, and
adequate safety measures are needed. Some medical
applications also make use of extremely low frequency fields,
for instance to stimulate bone growth, to treat pain, or to detect
cancer.
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There is some evidence that ELF magnetic
fields can cause cancer
in humans but it is far from conclusive. This was concluded based on
studies indicating that children exposed to relatively strong ELF
magnetic fields from power lines were more likely to develop
leukaemia than those
exposed to weaker fields. These results have not been confirmed or
explained by experiments on animals and
cell cultures.
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No relation has been demonstrated between extremely low frequency
fields and self-reported symptoms such as fatigue, headache, and
concentration difficulties.
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For some other diseases, notably breast
cancer and cardiovascular
diseases, recent research indicates that a link to extremely low
frequency fields is unlikely, but further study is needed on how they
may affect the brain and spinal cord.
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Top 8. Static magnetic fields like those used in medical imaging
 MRI scanners use static magnetic fields Credit: Kasuga Huang
Static magnetic fields such as
those generated by a permanent magnet do not vary over time, and as such
do not have a frequency (0
Hz).
Man-made static magnetic fields
are generated wherever electricity is used in the form of
direct current (DC), for
instance in some rail and subway systems, in aluminium production and in
welding. In medicine, MRI scanners
use static magnetic fields to provide three-dimensional images of the
brain and other body parts. In this application the exposure can exceed
the usual recommended limit, both for the MRI operator and the patient.
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Evidence is insufficient for drawing conclusions about potential
health effects. Static magnetic
fields can exert small forces that result in changes in the
orientation or position of biological
molecules and cellular
components with magnetic properties. They can also exert forces on, and
affect the functioning of, implanted devices like pacemakers.
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Adequate data for risk
assessment of static magnetic
fields are almost totally lacking. The advent of new technology,
and in particular MRI equipment,
makes this a priority for research.
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Top 9. What is known about environmental effects of electromagnetic fields?
 Migratory birds rely on magnetic fields for
orientation Credit: Michael Hatherly
A few studies looked at effects of
electromagnetic fields on
certain plants and animals, either in the laboratory or near overhead
power cables.
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Some animal species might be particularly sensitive to
electromagnetic fields
generated by manmade equipment. Migratory birds, for instance, rely on
magnetic fields for
orientation and sharks possess electric sense organs.
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The few studies on how electromagnetic
fields may affect the environment focused on extremely low
frequency fields like those generated by overhead power cables. They
mostly considered plants – not species that might be particularly
sensitive to electromagnetic fields.
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There are insufficient data to determine whether a single exposure
standard is sufficient to protect all environmental species from
electromagnetic fields or
to judge whether standards for animals and plants should differ from
those for humans. Good quality data are needed on species that are
expected to be among the most sensitive to electromagnetic fields.
Long-term monitoring of relevant species and ecosystems may be valuable
to assess the potential of electromagnetic fields to influence human
health.
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Top 10. What comments were expressed on the findings of this assessment?
The public was invited to comment on this assessment by the European
Commission Scientific Committee on Emerging and Newly Identified Health
Risks (SCENIHR).
While interesting, many of the comments addressed aspects that were
beyond the task of this assessment.
Certain comments showed that some sentences or paragraphs could be
misinterpreted and that the wording did not accurately reflect the
viewpoint of the working group or the SCENIHR. In those instances the
text was revised accordingly.
Other than that, none of the comments received during the public
consultation process led to changes in the overall conclusions or in the
opinion.
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Top 11. Conclusions on electromagnetic fields
For many of the possible health effects the data available are still
very limited, especially for long-term low-level exposure.
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New scientific evidence does not call for a revision of the exposure
limits to radio frequency fields. There is some
indication of a link between long-term mobile phone use and a benign
tumour of the auditory nerve
(acoustic neuroma), but
more study is needed. Self-reported symptoms like headaches, fatigue, or
concentration difficulties have not been linked to exposure to radio
frequency fields. To date no epidemiologic studies on children are
available, even though they may be more sensitive than adults to radio
frequency fields from mobile phones.
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Because data for the intermediate frequency fields
are sparse, the assessment of health risks of short-term exposure to
high levels of intermediate frequency fields is currently based on known
biological effects at lower and higher frequencies. Proper assessment of
possible health effects from long-term exposure is important because
exposure to such fields is increasing due to new technologies.
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The past conclusion that extremely low frequency
magnetic fields
are possibly carcinogenic is still
valid. This was concluded based on studies indicating that children
exposed to relatively strong magnetic fields from power lines were more
likely to develop
leukaemia
. These results have not been confirmed or explained by
experiments on animals and cell
cultures. In European countries, the proportion of children
exposed to such levels is less than 1%. Whether recommended exposure
limits ought to be changed is a risk
management decision.
No consistent relationship between self-reported symptoms and
extremely low frequency fields has been demonstrated.
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New applications of strong static
magnetic fields
will require risk assessments for people who use the new technology at
work, as for instance operators of
MRI scanners.
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The data on how electromagnetic
fields may affect animals and plants are insufficient to
determine whether a single exposure standard is appropriate for all
plants/animals and whether the standards for animals and plants should
differ from those for humans.
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To fill the important gaps in knowledge, research efforts are
recommended, notably on long- term exposure and effects on children and
personnel dealing with equipment generating strong fields.
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© GreenFacts 2008. All rigths reserved. This text is a faithful summary of the produced in 2007 by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR): "Possible Effects of Electromagnetic Fields (EMF) on Human Health" Learn more... GreenFacts was contracted to prepare this summary by the DG Health and Consumers of the European Commission, which authorised its publication. |