Led by Jiri Rubes of the Veterinary Research Institute in the Czech Republic, the study, in collaboration with the United States Environmental Protection Agency, found a "significant association between exposure to periods of high air pollution (at or above the upper limit of US air quality standards) and the percentage of sperm with DNA fragmentation". The results were published in the latest issue of the journal Human Reproduction.

The research team studied a group of 35 young men in the Teplice district of the Czech Republic, an area which has considerably higher air pollution during winter because of coal-burning power stations and fossil fuels burned in homes. The volunteers donated samples over a two-year period and researchers looked at the number of sperm, their shape and how many moved properly. In addition they measured how much damage there was to the DNA of the sperm. They also accounted for other causes of damage, including drug and alcohol use and smoking. At its height, the amount of pollution regularly exceeded safe limits imposed on US cities.

"What's biologically important is that the air pollution is intermittent," said an author of the research paper. "If it created permanent damage, you would tend to see sperm quality go down over time. The fact that it didn't, it went up and down, would suggest that it was affecting the mature sperm late in their development."

 Alok Jha, science correspondent
 The Guardian 

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