Electromagnetic commute.

Epidemiologists investigating possible health effects of steady, weak electromagnetic fields usually measure people's exposures at home, school or work. But a new study suggests this approach overlooks a major source of such exposures: the daily commute.

Participants in the study wore electromagnetic-field detectors for 24 hours on a normal workday. EPA analyst Lynne M. Gillette, who directed the study, reports that riding in cars or electric subways exposed the volunteers to electromagnetic fields of 200 to 300 milligauss -- four to eight times stronger than those generated by computer terminals at work.

"People receive significant exposures during transport," she says. "So measurements made at schools, workplaces or homes may not be the best indicators of an individual's overall exposure."

The detectors also revealed that most electric alarm clocks generate 10-milligauss fields, which might possibly add up to a hazard over years of nighttime slumber, Gillette says.