Various concerns about the effects that PCBs - synthetic organic chemicals that are used in hundreds of products - may have on the male reproductive system are well documented. But a new study seeking to quantify the effects of PCBs on male fertility appears to have raised more questions than it has answered. The impact of persistent organochlorine pollutants (POPs) , of which PCBs and DDT are two, on human fertility is still largely unknown and there are limited and contradictory findings as to whether PCBs and DDT damage human sperm. This study set out to see whether these two POPs damage sperm by altering its chromatin (the DNA and associated proteins that make up a chromosome) integrity. The new study has shown that polychlorinated biphenyls (PCBs) do damage sperm, but the levels of damage are not sufficient to cause major fertility problems. Despite this finding, the researchers said the findings "were a warning and further research was needed." The study, appearing in the journal Human Reproduction, also looked at dichlorodiphenyldichlorethylene (DDE) - a byproduct of the pesticide DDT - but found that it did not appear to damage sperm DNA.
The study, which is the first to assess data about reproductive effects of organochlorines from a general population, involved men from Greenland, Sweden, Poland and Ukraine. The international team of scientists tested sperm samples from the men and assessed the level of DNA damage. They also measured blood serum for levels of hexachlorobiphenyl, an indicator of total POPs in the body. The subjects also answered questionnaires on their lifestyle, occupations and reproductive history.
The results of the study were both intriguing and puzzling. Among the European men overall, the level of damaged sperm rose in tandem with rising levels of PCBs in the blood. Sperm DNA damage reached a 60 percent higher level in the group exposed to the highest levels of PCBs. But paradoxically, no such association was found among the men from Greenland.
"As usual, we wanted a simple answer and instead we found a lot of new questions," said researcher Marcello Span�. "We can only speculate, at this stage, that genetic make-up and/or lifestyle factors seem to neutralize or counterbalance the pollutants in this group." He said it was possible that the profile of the pollutants plays a role. "We measured only two important POPs as it would be a Herculean task to consider them all, so we are seeing only the tip of the iceberg."
While the results may appear contradictory, it would seem that there is enough evidence to justify concerns about PCB levels. But Span� said it was important to keep the results in perspective. The median level of damaged sperm DNA was 10 percent 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 percent and becomes negligible from 30-40 percent upwards. "PCB exposure might negatively impact reproductive capabilities especially for men who, for other reasons, already have a higher fraction of defective sperm," he said.
Span� added that research priorities should now include effects that may occur while infants are still in the womb. "What we badly need are data on exposure of unborn babies, as the endocrine disruption hypothesis suggests that foetal and peri-natal exposure could be more relevant as far as health and reproductive consequences are concerned," he concluded.
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