Pollutant chemicals called PCBs damage sperm but do not appear to have a dramatic impact on male fertility, scientists say.
However, they warn damage from PCBs could be enough to render infertile men whose sperm is already of less than optimum quality.
The synthetic organic pollutants are found widely in the environment.
Details of the pan-European study, which tested the sperm of 700 men, appear in Human Reproduction journal.
The study examined the effects of pollutants on men from four different places – some from Warsaw in Poland, some from Kharkiv in Ukraine, some Inuits from Greenland and some fishermen from Sweden.
Sperm samples were analysed for evidence of genetic damage and blood tests were carried out to determine the level of PCB exposure.
Geographical difference
The results showed that among the European men overall, genetic damage to the sperm rose in concert to exposure to PCBs.
However, no such association was found among the Inuit group.
Overall, around 10% of sperm DNA was damaged on average and the large majority of men in the study were fertile.
The probability of fathering a child starts to decrease when the proportion of damaged sperm reaches about 20% and becomes negligible from 30-40% onwards.
Lead researcher Dr Marcello Spanò said: "PCB exposure might negatively impact reproductive capabilities especially for men who, for other reasons, already have a higher fraction of defective sperm."
Dr Spanò said the results suggested that something in the Inuit group’s genetic make-up, or something about their lifestyle, might help to neutralise or counterbalance the damaging effects of PCB exposure.
However, he admitted the study was limited as there was no way the researchers could fully tease out the effect of each of the 200 closely related substances in the PCB family.
Complex relationship
The researchers say the effect of PCB exposure on the development of the foetus should be made a priority.
Dr Allan Pacey, senior lecturer at the University of Sheffield and secretary of the British Fertility Society, told the BBC News website: "This study confirms that the relationship between pollutants and sperm damage is a complex one.
"Thankfully, this report suggests that the damage done to sperm by PCBs is not sufficient to cause fertility problems.
"But the fact that the same chemical can have different effects on sperm from men in different part of the world is intriguing.
"Clearly we still have a lot to learn about how man-made chemicals interact with the male reproductive system."
The study also looked at DDE, a chemical produced by the breakdown of the insecticide DDT but found it did not appear to damage sperm DNA.
