Fertility and pollution: dirty air, ozone linked to sperm troubles.

Men might improve their fertility by reducing how much pollution they breathe in. The dirtier the air, the lower a man's sperm count and the more sperm with fragmented DNA he produces, two new studies suggest.

However, neither report directly links the decline in sperm quality to fertility problems.

"The decrease is not enormous," comments environmental chemist Brian McCarry of McMaster University in Hamilton, Ontario, who was not involved in either study. "There's no evidence that it has an impact on fertility."

In one study, ozone appeared to be a culprit behind diminished sperm counts, suggesting that it's a "sperm toxicant," say Rebecca Z. Sokol of the University of Southern California in Los Angeles and her colleagues. They had looked for a correlation between the quality of semen from 48 local sperm donors and air-quality data for the zip code in which each donor lived. The donors were healthy men who had given 10 or more donations to a sperm bank over at least a year.

Sperm counts were lower when ozone concentrations where the men lived had been high during the previous 90 days, Sokol and her team report in an upcoming Environmental Health Perspectives. Sperm take nearly that long to develop. The researchers took into account the effects that temperature and season have on men's sperm counts. Airborne particulate matter, nitrogen oxides, and carbon monoxide weren't associated with reduced sperm concentrations, the team says.

In the second study, Jiri Rubes and two of his colleagues at the Veterinary Research Institute in Brno, Czech Republic, worked with U.S. scientists. They examined up to seven semen samples from each of 36 men living in a polluted region of the Czech Republic.

Each September for 3 consecutive years, the researchers collected a sample from most of the men. The team took as many as four more samples from each man during the two winters of the study. Wintertime pollutant concentrations in the region tan be double to quadruple those measured in September.

In most winter-air samples, a cubic meter contained 60 to 80 micrograms each of particulate matter, nitrogen oxides, and sulfur dioxide and about 150 nanograms of polycyclic aromatic hydrocarbons, exceeding common regulatory limits. Semen samples had more fragmented DNA at those rimes than they did in September, the team reports in the October Human Reproduction.

"This is certainly an important finding," says Ashok Agarwal of the Cleveland Clinic. DNA damage to sperm has been linked to low pregnancy rates, although the damage found in the Czech study may not have been enough to impair fertility, he says.

Despite the heavy pollution, the researchers found no differences in sperm counts or several other measures of sperm quality. But, McCarry notes, "they didn't measure the ozone."