A baby's sex is determined by X and Y chromosomes in the sperm, and the team, which studied 149 fishermen, found exposure to a class of pollutants which are a by-product of industrial and agricultural processes increased the Y chromosome sperms, but were unable to predict if the effect would lead to more boys being born.
Professor Aleksander Giwercman, lead researcher, said a larger population sample would be needed to confirm that but he thinks the fact that exposure to environmentally derived chemicals can change the sex chromosome ratio in sperm is worrying in itself and demands more attention from scientists and the public. He says that if this chemical has such an effect it is possible others could have a similar impact
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, for CB-153 there was a 0.8% increase.
Dr Allan Pacey, of the British Fertility Society, a specialist in male fertility at the University of Sheffield and secretary of the British Fertility Society, says it is the first time he has heard of pollutants having this effect, if this is possible others could have a similar impact and that could have huge consequences.
A second study, the joint Denmark, Finland and Lithuanian study, has also suggested environmental factors can have an effect on male reproductive health.
Their study 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.
Previous data on semen quality and testicular cancer in the Nordic-Baltic region led the researchers to expect similar rates of undescended testes in Lithuanian and Finnish boys and the fact that this was not so indicated that something in the environment was having an effect on male foetuses developing in the womb.
Dr Niels Jorgensen, the study co-author says a closer look at the role of environmental factors is needed which should include those factors which can disrupt the hormone system, and impact on the role of genetics and lifestyle.
Peter Baker, director of the Men's Heath Forum, said pollutants had been linked to a whole range of problems and is an area that needs much more research.