A new theory could solve the mystery of how weak electromagnetic fields
might damage the body鈥檚 cells. The theory has been proposed by Keith McLauchlan
of the University of Oxford.
Epidemiological studies in the 1980s raised fears that such fields might
cause some forms of cancer (see 鈥楢re power lines bad for you?鈥�, this issue).
Also, some biologists claim to have demonstrated that weak electromagnetic
fields affect the functioning of cells and tissues, although their experiments
have proved difficult, sometimes impossible, to replicate (New 女生小视频,
Science, 4 August 1990).
The major stumbling block to explaining how weak fields wreak havoc
is understanding how they can have any effect at all when dwarfed by fields
from the natural electrical processes in living things.
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McLauchlan thinks that small magnetic fields such as those generated
by the Earth and by electrical appliances may harm cells by allowing very
reactive chemical agents called free radicals to rove around in greater
numbers than normal, damaging DNA. He says that although chemists understand
and can prove the underlying theory, no one has yet demonstrated the effect
in living things.
Chemists know in great detail how magnetic fields affect the rates of
chemical reactions. McLauchlan says that, essentially, the fields cause
radicals that would otherwise react, to drift apart or vice versa, depending
on the size of the fields and the reaction they are involved in.
The important thing is that the effects occur at very weak fields of
a few milliteslas 鈥� the sort generated by electrical appliances, power
lines and the Earth. Also, the effects are no greater if the fields are
hundreds of thousands of times bigger.
In chemical reactions, bonds break and re-form. Most bonds consist of
pairs of electrons with opposite spins 鈥� one electron from each 鈥榩artner鈥�
in the union. In a reaction, the bond breaks, then both partners 鈥榬eclaim鈥�
their electron from the bond and rush off to find a new 鈥榩artner鈥�.
The ex-partners are now free-roving agents called 鈥榬adicals鈥�. To reform
a bond, two radicals that meet must have electrons with opposite spins 鈥�
a so-called 鈥榮inglet pair鈥�. But sometimes, radicals with the same spin encounter
each other. No marriage results, and the pair part rapidly, seeking to form
a singlet pair with a radical with an opposite spin.
However, unsuccessful pairings are more likely than successful ones
because there is only one way that a singlet pair can form but three ways
in which electrons with similar spins can unite. The two parallel spins
can point upward, downward or away from one another. Because their electrons
can adopt three configurations, they are called 鈥榯riplet鈥� pairs, or states.
When exposed to a very low static field, the triplet pairs readily break
and re-form into the successful marriage of a singlet pair. 鈥楢s the field
is increased, however (two of the three) triplet states become decoupled
from the singlet state entirely,鈥� writes McLauchlan in Physics World. 鈥楾his
may stop two-thirds of the radical pairs reacting (in a field of typically
only about 8 milliteslas) that could react in a low field 鈥� an enormous
effect of a small magnetic field on a chemical reaction.鈥�
鈥楾he field does not affect the nature of the product, only the amount
of it formed, although radicals which escape reaction at this stage enter
their surroundings and may, for example, initiate polymerisation.鈥�
McLauchlan says that when fluctuating fields are applied on top of the
static field, and they are correctly tuned, they can give the isolated triplet
states the precise amount of energy they need to return to the singlet state
and react together. In biological systems, exposure both to static, and
to static and alternating effects, could have unpredictable effects, he
says.
鈥業n all situations, weak static fields exist 鈥� even from the Earth鈥檚
magnetic field 鈥� alongside the varying ones, and it is not impossible that
this mechanism lies behind the apparent biological effects reported from
迟丑别尘.鈥�
