CANCER RISKS ASSOCIATED WITH OCCUPATIONAL EXPOSURE TO MAGNETIC-FIELDSAMONG ELECTRIC UTILITY WORKERS IN ONTARIO AND QUEBEC, CANADA, AND FRANCE - 1970-1989

To determine whether occupational exposure to magnetic fields of 50-60 Hz was associated with cancer among electric utility workers, the aut hors used a case-control design nested within three cohorts of workers at electric utilities: Electricite de France-Gaz de France, 170,000 m en; Ontario Hydro, 31,543 men; and Hydro-Quebec, 21,749 men. During th e observation period, 1970-1989, 4,151 new cases of cancer occurred. E ach participant's cumulative exposure to magnetic fields was estimated based on measurements of current exposure of 2,066 workers performing tasks similar to those in the cohorts using personal dosimetry. Estim ates were also made of past exposure based on knowledge of current loa ding, work practices, and usage. Workers who had more than the median cumulative exposure to magnetic fields (3.1 microtesla (mu T)-years) h ad a higher risk for acute nonlymphoid leukemia (odds ratio (OR) = 2.4 1, 95% confidence interval (CI) 1.07-5.44). The same observation holds for acute myeloid leukemia (OR = 3.15, 95% Cl 1.20-8.27). There was a lso an elevated risk for mean exposure above 0.2 mu T (acute nonlympho id leukemia, OR = 2.36, 95% Cl 1.00-5.58; acute myeloid leukemia, OR = 2.25, 95% Cl 0.79-6.46). However, there were no clear dose-response t rends with increasing exposure and no consistency among the three util ities. Men whose cumulative exposure to magnetic fields was above the 90th percentile (15.7 mu T-years) had an elevated risk for brain cance r (OR = 1.95, 95% Cl 0.76-5.00) that was not statistically significant . No association with magnetic fields was observed for any of the othe r 29 types of cancer studied, including skin melanoma, male breast can cer, and prostate cancer. Controlling for potential confounding factor s did not change the results.