ELECTROMAGNETIC FIELDS AND PUBLIC HEALTH
Physical Properties and
Effects on Biological Systems
Natural and many human-made sources generate
electromagnetic energy in the form of electromagnetic waves. These waves consist of
oscillating electric and magnetic fields which interact differently with biological
systems such as cells, plants, animals, or human beings. In order to better understand
these interactions, it is essential to be familiar with the physical properties of the
waves which make up the electromagnetic spectrum.
Electromagnetic waves can be
characterized by their wavelength, frequency, or energy. The three
parameters are interrelated. Each influences the effect the field may have on a biological
* The frequency of an
electromagnetic wave is simply the number of oscillations which passes a fixed point per
unit of time. It is measured in cycles per second, or hertz. One cycle per second
equals one hertz (Hz). Large divisions commonly used to describe radio
frequency (RF) fields include the kilohertz (kHz), or one thousand cycles
per second; the megahertz (MHz), one million cycles per second; and the gigahertz
(GHz), one billion cycles per second.
* The shorter the wavelength, the
higher the frequency. The middle of the AM broadcast band, for example, has a
frequency of one million hertz (1 MHz) and a wavelength of about 300 metres. Microwave
ovens use a frequency of 2.45 billion hertz (2.45 GHz) and a wavelength of 12 centimetres.
* An electromagnetic wave consists of
very small packets of energy called photons. The energy in each packet or photon is
directly proportional to the frequency of the wave: The higher the frequency, the
larger the amount of energy in each photon.
How electromagnetic waves affect biological
systems is determined partly by the intensity of the field and partly by the amount of
energy in each photon.
Electromagnetic waves at low frequencies are
referred to as "electromagnetic fields" and those at very high
frequencies are called "electromagnetic radiations". According to their
frequency and energy, electromagnetic waves can be classified as either "ionizing
radiations" or "non-ionizing radiations" (NIR).
* Ionizing radiations are extremely high
frequency electromagnetic waves (X-rays and gamma rays), which have enough photon energy
to produce ionization (create positive and negative electrically charged atoms or
parts of molecules) by breaking the atomic bonds that hold molecules in cells together.
* Non-ionizing radiations (NIR) is a
general term for that part of the electromagnetic spectrum which has photon energies too
weak to break atomic bonds. They include ultraviolet (UV) radiation, visible
light, infrared radiation, radiofrequency and microwave fields, extremely
low frequency (ELF) fields, as well as static electric and
* Even high intensity NIR cannot cause
ionization in a biological system. NIR, however, have been shown to produce other
biological effects, for instance, by heating, altering chemical reactions or inducing
electrical currents in tissues and cells.
Electromagnetic waves may produce biological
effects which may sometimes, but not always, lead to adverse health
effects. It is important to understand the difference between the two:
* A biological effect occurs when
exposure to electromagnetic waves causes some noticeable or detectable physiological
change in a biological system.
* An adverse health effect occurs when
the biological effect is outside the normal range for the body to compensate, and thus
leads to some detrimental health condition.
* Some biological effects can be
innocuous, such as the body's reaction of increasing blood flow in the skin in response to
slightly greater heating from the sun. Some effects can be advantageous, such as the
feeling of warmth of direct sunshine on a cool day, or can even lead to positive health
effects, such as the sun's role in helping the body produce vitamin D. However, some
biological effects lead to adverse health effects, such as the pain of sunburn or skin
The International EMF Project of the World
Health Organization is addressing the health concerns raised about exposure to
radiofrequency (RF) and microwave fields, extremely low frequency (ELF) fields, and static
electric and magnetic fields. These electromagnetic fields can produce different
biological effects that may lead to health consequences.
Radiofrequency (RF) fields
are known to produce heating and the induction of electrical currents. Other less
established biological effects have also been reported.
* RF fields at frequencies above about
1 MHz primarily cause heating by moving ions and water molecules through the
medium in which they exist. Even very low levels of RF energy produce a small amount of
heat, but this heat is carried away by the body's normal thermoregulatory processes
without the person noticing it.
* A number of studies at these frequencies
suggest that exposure to RF fields too weak to cause heating may have adverse
health consequences, including cancer and memory loss. Identifying and encouraging
coordinated research into these open questions is one of the major objectives of the International
* RF fields at frequencies below about
1 MHz primarily induce electrical charges and currents which can stimulate cells in
tissues such as nerves and muscles. Electrical currents already exist in the body as a
normal part of the chemical reactions involved in living. If RF fields induce currents
significantly exceeding this background level in the body, there is a possibility of
adverse health consequences.
Extremely Low Frequency (ELF) electric
and magnetic fields. The primary action in biological systems by these fields is the induction
of electrical charges and currents. This mechanism of action is unlikely to explain
the health effects, such as cancer in children, reported to occur from exposure to
"environmental" levels of ELF fields.
* ELF electric fields exist whenever a
charge (voltage) is present, regardless of whether any current is flowing. Almost none of
the electric field penetrates into the human body. At very high field strengths they can
be perceived by hair movement on the skin. However, some studies suggest that exposure to
low levels of these fields is associated with an increased incidence of childhood cancer
or other health consequences. Other studies do not. The International EMF Project is
recommending that more focused research be conducted to improve health risk assessments.
* ELF magnetic fields exist
whenever an electric current is flowing. They easily penetrate the human body without any
significant attenuation. Some epidemiological studies have reported associations between
ELF fields and cancer, especially in children, but others have not. Research on effects of
low-level (environmental) ELF fields is currently underway, including that monitored and
encouraged by the International EMF Project.
Static electric and magnetic fields. While
the primary action in biological systems by these fields is the induction of electrical
charges and currents, other effects have been established to occur that could
potentially lead to adverse health consequences, but only at very high field strengths.
* Static electric fields do not penetrate
into the body, but can be perceived by skin hair movement. Except for electrical
discharges from strong static electric fields, they do not seem to have significant health
* Static magnetic fields have virtually the
same strength inside the body as outside. Very intense static magnetic fields can alter
blood flow or change normal nerve impulses. But such high field strengths are not found in
everyday life. However, there is insufficient information about the effects of long-term
exposure to static magnetic fields at levels found in the working environment.
Safety Standards: In order to ensure that
human exposure to EMF should not have adverse health effects, that man-made EMF generating
devices are safe and their use does not electrically interfere with other devices, various
international guidelines and standards are adopted. Such standards are developed following
reviews of all the scientific literature by groups of scientists who look for evidence of
consistently reproduced effects with adverse health consequences. These groups then
recommend guidelines for standards for action by the appropriate national and
international bodies. A non-governmental organization, formally recognised by WHO in the
field of NIR protection, is the International Commission on Non-Ionizing Radiation
Protection (ICNIRP). ICNIRP has established international guidelines on
human exposure limits for all electromagnetic fields, including ultraviolet (UV)
radiation, visible light and infrared radiation, as well as RF fields and microwaves.
|Electromagnetic waves are generated by natural,
but mostly by human-made sources. Their spectrum includes both ionizing and non-ionizing
radiations (X-rays and gamma rays) have enough energy to create positive and negative
electrically charged atoms or parts of molecules by breaking the atomic bonds that hold
molecules in cells together. This effect is called ionization.
Even high intensity NIR cannot cause
ionization in the biological system. NIR, however, have been shown to produce other
biological effects, for instance, by heating, altering normal chemical reactions or
inducing electrical currents in tissues.
The International EMF Project of the World
Health Organization deals with the health effects of static, extremely low
frequency (ELF) and radiofrequency (RF) electromagnetic fields
Electromagnetic waves of different frequencies
interact differently with biological systems, such as cells, plants, animals, or
human beings. The extent they affect biological systems depends partly on their intensity
and partly on the amount of energy in photons.
Biological effects produced by
electromagnetic waves may sometimes, but not always, lead to adverse health effects.
For further information, please contact Health
Communications and Public Relations, WHO, Geneva. Telephone (41 22) 791 2532. Fax (41 22)
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