USC Researchers Find Ozone Lowers Sperm Counts

Sokol reported on this work at the annual meeting of the Pacific Coast Reproductive Society.

She and her colleagues analyzed more than 8,000 sperm samples donated by 50 men in the Los Angeles area over a three-year period (January 1996 to December 1998), and compared them to more than 3,500 samples donated by 35 men from Northern California over the same time.

The original idea, says Sokol, was to see if there were geographic differences between the groups in terms of sperm quality. But, she says, the results were rather disappointing. "We found only minimal differences between Northern and Southern California, with only marginally higher motile sperm counts in Southern California," she reports. "And we weren’t even sure if those were real; there may very well have been some confounding factors."

But when she and her Keck colleagues compared the sperm data with air quality data donated by a private entrepreneur at Sonoma Technologies in Petaluma, Calif., they were startled by the pattern that emerged. "There was a significant correlation," says Sokol, "between decreases in sperm count and motility and increased ozone levels in the air, especially in Southern California."

In 2000, Sokol reported that sperm counts in general have remained virtually unchanged over the past 50 years, despite reports that the lives of men in the modern world were leading to a reduction in virility by as much as 50 percent.

This sort of epidemiology-based work is new to Sokol, who spent most of her career researching the effects of toxicants on male reproduction and infertility, and working in clinical studies in the field of male infertility. Then, in 2001, she was awarded a National Institutes of Health senior investigator fellowship award. Her award is supported by the National Institute of Environmental Health Sciences.

Just how ozone might be affecting sperm quality is somewhat of a conundrum, Sokol admits. "The blood-testis barrier is supposed to protect from these bad things," she says. [The cells lining the seminiferous tubules in the testes isolate sperm cells from the immune cells in the blood so as to prevent the body from launching an immune attack against the sperm, and to protect the sperm from any toxins in the blood.] "We know that oxygen radicals interfere with sperm function in the laboratory. So the question is, what physiological response does ozone inhalation trigger to affect sperm in the body?"

Sokol hopes to investigate that very question. In addition, she says, she would like to do another study of sperm quality—this one prospective rather than retrospective, and looking at sperm samples from a number of major cities known to have significant increases and decreases in ozone levels, such as New York and Mexico City. "I’m really starting to branch out," she says. "This is such a new area for me, and there’s so much to learn."