The team found an apparent link between levels of polychlorinated biphenyls (PCBs) in the bloodstream of more than 700 men and the degree of damage to the DNA in their sperm. The damage is insufficient to affect fertility, and the results are equivocal because one group of men — Inuit from Greenland — did not show any link even though they carried high levels of PCBs in their blood.

Nevertheless the findings, in Human Reproduction, seem certain to cause concern.

PCBs are ubiquitous in the environment and, like DDT, persist for decades. Originally produced in the 1950s and 1960s, they are synthetic organic chemicals, ranging from oily liquids to waxy solids, used for electrical insulation, as plasticisers in paint, plastics and rubber, as pigments and dyes and for many other purposes.

Millions of tonnes of PCBs were produced but when it was realised that they were persistent environment contaminants, production was phased out. Large amounts remain in the environment and can be detected in human fat and blood.

The team, from Italy, Denmark, Sweden, Poland and Ukraine, took blood and semen samples from 707 men — 193 Inuit, 178 Swedish fishermen, 141 men from Warsaw, and 195 men from Kharkiv, in Ukraine. They examined the sperm for signs of damage, looking for fragmentation of the DNA and comparing this with levels of PCBs in the bloodstream.

There was a clear trend for the Swedes and Ukrainians, with the highest levels of PCBs being associated with a 60 per cent increase in DNA damage. But PCB levels in the Warsaw men were very low and no trend was found. In the Inuit levels were high but damage relatively low.

Marcello Spanò, who led the team, said: “The results from the Inuit cohort are surprising and reassuring. We can only speculate, at this stage, that genetic make-up and/or lifestyle factors seem to neutralise or counterbalance the pollutants in this group.”

It could be, he said, that the profile of the pollutants played a role. PCBs are a class of compounds that include about 200 by-products. “We measured only two, so we are seeing only the tip of the iceberg.”

Dr Spanò added that it was important to keep the results in perspective. The median level of damaged DNA in sperm was 10 per cent 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 per cent and becomes negligible from 30 to 40 per cent upwards.

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