Exposure assessment strategies in epidemiological studies of health effects of electric and magnetic fields

In the growing epidemiological literature on potential health effects of electric and magnetic fields in homes, from appliances, and in the workplace, exposure assessment persists as the principal challenge. Associations of concern are residential exposure and childhood cancers, occupational exposure and adult leukemia and brain cancer, and video display terminal use and pregnancy outcome. The biologically appropriate measure of exposure is undefined, there are a multitude of exposure sources, and because the concern is with such rare diseases as leukemia and brain cancer, all studies have retrospective exposure ascertainment. Residential exposure assessment has been based on wire configuration codes of nearby electric power lines or on in-home measurements, both proxies for historical exposures of interest. Each has theoretical and logistical advantages and disadvantages. Appliance exposures are based on self-report, focusing on those used for prolonged periods in close proximity to the user, such as electric blankets. Workplace exposures have been assessed by job title, more recently supplemented with measurements. Research is needed to: (1) develop and validate historical exposure models; (2) find ways to integrate exposure across diverse sources in the home and workplace; and (3) exploit laboratory findings to guide the selection of exposure metrics and relevant time windows.