A team of researchers from Lund University in Sweden have found that exposure to a class of environmental pollutants can change the ratio of sperm carrying male and female chromosomes.
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.