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2) When evaluating whether there might be a connection between EM fields and cancer, can all EM fields be considered the same?




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This article is from the Static Electromagnetic Fields and Cancer FAQ, by John Moulder jmoulder@its.mcw.edu and the Medical College of Wisconsin with numerous contributions by others.

2) When evaluating whether there might be a connection between EM fields and cancer, can all EM fields be considered the same?

No. The nature of the interaction of an EM source with biological
material depends on the frequency of the source, so that different types
of EM sources must be evaluated separately.

X-rays, ultraviolet (UV) light, visible light, MW/RF, magnetic fields
from electrical power systems (power-frequency fields), and static
magnetic fields are all sources of EM energy. These different EM
sources are characterized by their frequency or wavelength.

The frequency of an EM source is the rate at which the electromagnetic
field changes direction and/or amplitude and is usually given in Hertz
(Hz) where 1 Hz is one change (cycle) per second. The frequency and
wavelength are related, and as the frequency rises the wavelength gets
shorter. Power-frequency fields are 50 or 60 Hz and have a wavelength
of about 5000 km. By contrast, microwave ovens have a frequency of 2.54
billion Hz and a wavelength of about 10 cm, and X-rays have frequencies
of 10^15 Hz and, and wavelengths of much less than 100 nm. Static
fields, or direct current (DC) fields do not vary regularly with time,
and can be said to have a frequency of 0 Hz and an infinitely long
wavelength.

The interaction of biological material with an EM source depends on the
frequency of the source. We usually talk about the EM spectrum as
though it produced waves of energy. This is not strictly correct,
because sometimes EM energy acts like particles rather than waves; this
is particularly true at high frequencies. The particle nature of EM
energy is important because it is the energy per particle (or photons,
as these particles are called) that determines what biological effects
EM energy will have [62].

At the very high frequencies characteristic of hard UV and X-rays, EM
particles (photons) have sufficient energy to break chemical bonds.
This breaking of bonds is termed ionization, and this part of the EM
spectrum is termed ionizing. The well-known biological effects of X-rays
are associated with the ionization of molecules. At lower frequencies,
such as those characteristic of visible light, RF, and MW, the energy of
a photon is very much below those needed to disrupt chemical bonds.
This part of the EM spectrum is termed non-ionizing. Because non-
ionizing EM energy cannot break chemical bonds there is no analogy
between the biological effects of ionizing and nonionizing EM energy
[62].

Non-ionizing EM sources can still produce biological effects. Many of
the biological effects of soft UV, visible, and IR frequencies also
depend on the photon energy, but they involve electronic excitation
rather than ionization, and do not occur at frequencies below that of IR
(below 3 x 1011 Hz). RF and MW sources can cause effects by inducing
electric currents in tissues, which cause heating. The efficiency with
which an EM source can induce electric currents, and thus produce
heating, depends on the frequency of the source, and the size and
orientation of the object being heated. At frequencies below that used
for broadcast AM radio (about 106 Hz), EM sources couple poorly with the
bodies of humans and animals, and thus are very inefficient at inducing
electric currents and causing heating [62].

Thus the EM spectrum can be divided into four portions whose biophysical
characteristics and biological effects are quite different [62]:
1) The ionizing radiation portion, where direct chemical damage can
occur (X-rays, hard UV).
2) The non-ionizing portion of the spectrum, which can be subdivided
into:
2a) The optical radiation portion, were electron excitation can occur
(soft UV, visible light, IR)
2b) The portion where the wavelength is smaller than the body, and
heating via induced currents can occur (MW and higher-frequency RF).
2c) The portion where the wavelength is much larger than the body,
and heating via induced currents seldom occurs (lower-frequency RF,
power frequencies, static fields).

 

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previous page: 1) Does anyone think that static magnetic fields cause cancer?
  
page up: Static Electromagnetic Fields and Cancer FAQ
  
next page: 3) When evaluating whether there might be a connection between static EM fields and cancer, do we have to consider EM radiation as well as EM fields?