Overview of occupational exposure to electric and magnetic fields and cancer: advancements in exposure assessment.

For over ten years, there has been concern with the potential for increased risk of cancer among "electrical workers." In contrast to studies of residential exposure to magnetic fields, occupational studies include electric and magnetic field exposures and have much greater variability in field intensity, frequency, and temporal patterns. Studies of leukemia in electrical workers show a moderate consistency, with elevated risk ratios of 1.2 to 2.0 commonly observed. Brain tumors are similarly elevated with some consistency, and three recent studies have suggested increased risk of male breast cancer. Retrospective exposure assessment methods were advanced in recent studies of diverse occupations in a study in central Sweden, which yielded evidence of increased risk of chronic lymphocytic leukemia among men in more highly exposed occupations. A study of telephone workers in New York State incorporated measurements and found some indication of increased leukemia risk only when exposures were based on historical technology. Utility workers in southern California were studied and found not to have increased risks of leukemia and brain cancer based on exposures estimated with measurements. An ongoing study of electric utility workers at five companies in the United States incorporates an extensive measurement protocol. Randomly selected workers within occupational categories wore a time-integrating magnetic-field meter to provide estimates of exposure for the occupational category. We were able to estimate and partition the variance into between-day (the largest contributor), within occupational categories, and between occupational categories. Principal research needs concern optimal levels of worker aggregation for exposure assignment, historical extrapolation, study of diverse work environments, and integration of residential and occupational exposure in the same study.