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 werent 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 toxic
Contact: Jon Weiner
University of Southern California