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A baby's sex is determined by X and Y chromosomes
in the sperm. Researchers found exposure to a class of pollutants
which are a by-product of industrial and agricultural processes
increased the Y chromosome sperms. But the team from Lund University
in Sweden, which studied 149 fishermen, were unable to predict
if the effect would lead to more boys being born.
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2005/04/27
Lead researcher Professor Aleksander
Giwercman said a larger population sample would be needed
to confirm that.
But he added: "We think the fact that exposure to environmentally derived chemicals
can change the sex chromosome ratio in sperm is worrying in itself and requires
more attention from scientists and the public."
The researchers analysed the
effect of exposure to two persistent organochlorine pollutants - DDE and CB-153
- which is most likely to come from eating fatty fish such as salmon.
The 20%
of men with the highest exposure to DDE compared with the 20% with the lowest
exposure had 1.6% more sperm with the Y chromosome, the Human Reproduction journal
reported.
For CB-153 there was a 0.8% increase.
Dr Allan Pacey, a specialist
in male fertility at the University of Sheffield and secretary of the British
Fertility Society, said: "It is the first time I have heard of pollutants having
this effect.
"If this is so it is possible others could have a similar impact
and that could have huge consequences." A second study has also suggested environmental
factors can have an effect on male reproductive health.
Risk
The joint Denmark,
Finland and Lithuanian study, also published in Human Reproduction, showed an
incident rate of undescended testes, which increases the risk of testicular cancer,
in Lithuania of 5.7%.
This was lower than the 9% rate in Denmark, but higher
than the 2.4% rate in Finland.
Data on semen quality and testicular cancer in
the Nordic-Baltic region had led the researchers to expect similar rates of undescended
testes in Lithuanian and Finnish boys.
The fact that this was not so indicated
that something in the environment was having an effect on male foetuses developing
in the womb.
Report co-author Dr Niels Jorgensen said: "We need to look more closely at the
role of environmental factors, including those that can disrupt the hormone system,
and the role of genetics, lifestyle and other factors."
Peter Baker, director
of the Men's Heath Forum, said pollutants had been linked to a whole range of
problems. "This is an area that needs much more research."
Story from BBC NEWS
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Infertility