Exposure to Environmental Ozone Alters Semen Quality

Newswise — Exposure to increased ozone levels adversely affects developing sperm, leading to lower sperm quality, according to a study accepted for publication today by the peer-reviewed journal Environmental Health Perspectives (EHP). The results of this study may contribute to a better understanding of the causes of infertility for the estimated 2.1 million couples in the United States who have difficulty achieving a pregnancy.

Researchers analyzed semen samples collected from 48 regular donors to a sperm bank in the Los Angeles area and compared the quality of the samples with available air quality data. They found that exposure to elevated ozone levels near donors' homes adversely impacted semen quality.

The study showed an inverse relationship between ambient ozone levels and sperm concentration at all points during the development of sperm (a 72-day process known as spermatogenesis). The results remained significant after adjusting for age, season and temperature.

"We noted an inverse relationship between ozone exposure and sperm concentration at all time points studied, suggesting that spermatozoa are susceptible to this toxic exposure throughout spermatogenesis," the authors wrote.Once sperm mature, it takes them approximately 10 days to reach the epididymis, where they become motile and capable of fertilizing an egg. Therefore, researchers studied the relationship between each semen sample and the air quality at 0-9, 10-14, and 70-90 days prior to its collection.

Besides ozone, the researchers also studied nitrogen dioxide, carbon monoxide, and fine particulate matter. Each of these air pollutants was believed to be capable of impacting sperm production. However, no similar association between sperm density and exposure to these air pollutants was found.

Ozone or ozone reaction products can cross the blood-gas barrier and be absorbed into the circulating bloodstream. But how ozone adversely impacts sperm in particular is still unclear. Ozone exposure is known to cause oxidative stress, which is documented to disrupt testicular and sperm function. As with smoking, exposure to ozone may induce either an inflammatory reaction in the male genital tract or the formation of circulating toxic species---both of which can cause a decline in sperm concentration.

Today's findings support an earlier study conducted in the Czech Republic by scientists from the U.S. Environmental Protection Agency. Young Czech men exposed to elevated air pollution in that study were more likely to have altered sperm quality as compared to those who lived in a locale with less air pollution.

"The most widely studied evidence of potential environmental reproductive hazards is the report that sperm counts have declined in certain industrialized countries. The validity of these findings continues to be controversial, yet most investigators agree that if a decline in semen quality does exist, these changes are probably related to geographic location," the authors of today's study wrote.

Subjects were healthy, educated males between the ages of 19 and 35. A period of sexual abstinence was required for three days before collection of samples. Donors were included if they provided multiple semen samples over at least a 12-month period from January 1996 through December 1998 and resided in the same zip code during that time.

The lead author of the study was Rebecca Z. Sokol of the University of Southern California. Other authors included P. Kraft, I.M. Fowler, M. Rizvan, E. Kim, and K.T. Berhane. The study was supported by a grant from the National Institute of Environmental Health Sciences (NIEHS). The article is available free of charge at http://ehp.niehs.nih.gov/docs/2005/8232/abstract.html.

EHP is published by the NIEHS, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal. More information is available online at http://www.ehponline.org/. Brogan & Partners Convergence Marketing handles marketing and public relations for EHP, and is responsible for creation and distribution of this press release.