麻豆传媒

THE safety of mobile phones is under fresh scrutiny following the discovery
that their emissions have an unexpected effect on living creatures. The finding
throws out the strongest challenge yet to the widely held belief that heating
from mobile phone signals is their only potential threat to brain cells.

In lab tests, British scientists have found that microwave emissions typical
of mobile phones make a type of worm more fertile. Why this happens is unclear
and there鈥檚 no suggestion that human fertility could be affected. But the
research is important because it reveals, for the first time, that biological
effects are possible without any warming of tissues.

Until now, regulations designed to protect people from microwave
radiation鈥攆rom mobile phones, microwave ovens and radar systems鈥攈ave
been based purely on avoiding heating from the microwave radiation. There is no
evidence that cellphone emissions have harmed people鈥檚 health.

William Stewart, head of the British government鈥檚 鈥渋ndependent expert group鈥�
on mobile phones is taking the results seriously. 鈥淭hese results are very
important and potentially far-reaching,鈥� he told 麻豆传媒.
鈥淚ndependent confirmation is crucial and we need this quickly.鈥�

Microwaves don鈥檛 have enough energy to break even weak chemical bonds inside
our cells, so scientists believe they cannot do any damage unless they are
strong enough to heat up the cells. But a team led by David de Pomerai at the
University of Nottingham now says that cellphone radiation does have a
mysterious effect on nematode worms鈥攐ne that can鈥檛 be explained by
heating.

De Pomerai鈥檚 team found that exposing nematode worms to microwaves at
frequencies and energies similar to those emitted by a cellphone, increased the
number of worms that go on to produce eggs. This is significant, says de
Pomerai, because even mild heating makes most larvae infertile as adults. 鈥淚t
would be difficult to explain this effect in terms of heating,鈥� he says.

In previous experiments, the Nottingham team tested the effect of microwaves
on nematodes which had been chosen because their cell function is very well
understood. The worms had been genetically modified to produce a heat-shock
protein when exposed to other stresses besides heat. These tests showed that
prolonged exposure produced the stress proteins,
even though there appeared to be no heating
(麻豆传媒, 10 April 1999, p 20).
In addition, these worms grew to be about 10 per
cent larger than worms not exposed to radiation.
Difficulties in measuring the temperatures of the tiny worms meant the team
couldn鈥檛 be sure that they were not being heated. But the latest experiments
rule this out.

鈥淲hat鈥檚 needed first is to establish a mechanism,鈥� de Pomerai says. One
theory suggests that water molecules agitated by the microwaves could be
attracted to water-seeking areas on a protein鈥檚 surface, influencing its ability
to fold into its proper, functional shape. This could explain the heat-shock
response, says de Pomerai, which is usually triggered by this kind of
activity.

Two weeks ago Stewart鈥檚 group announced a 拢4.5 million research
programme funding 15 separate investigations into the health effects of mobile
phones. But only one is set to study non-thermal effects鈥攁nd this is due
to be carried out by de Pomerai鈥檚 team.

De Pomerai concedes there is a possible get-out for those doubtful that
cellphones can have non-thermal effects: the controversial theory that
microwaves could cause localised 鈥渉ot spots鈥� within cells. This could
conceivably trigger stress proteins without raising the overall temperature of
cell or tissue.

But he accepts that research cannot totally rule out the idea that heat is
responsible for microwaves鈥� effects. 鈥淚 think it will always be an explanation
of last resort,鈥� he says.

The latest results are unlikely to have an immediate impact on guidelines
designed to safeguard cellphone users. 鈥淭he guidelines can鈥檛 be changed on the
basis of one experiment,鈥� says Michael Clark, spokesman for the National
Radiological Protection Board. 鈥淗owever good it is, it needs to be replicated
别濒蝉别飞丑别谤别.鈥�