Leukemia in electric utility workers: The evaluation of alternative indices of exposure to 60 Hz electric and magnetic fields

Background Epidemiological studies have inconsistently demonstrated a posit ive relationship between magnetic and/or electric fields and leukemia. Alth ough exposure to both 60 Hz electric and magnetic fields can be characteriz ed in many ways, to date, risk assessment has been performed by using only a limited number of exposure indices. Methods The associations between adult leukemia and indices of electric and magnetic fields were explored within a nested case-control study of 31,453 Ontario electric utility workers. Results The percentage of time spent above electric field thresholds of 20 and 39 V/m was predictive of leukemia risk after adjusting for duration of employment and the arithmetic mean exposure to both electric and magnetic f ields (P < 0.05). Duration of employment was strongly associated with an in creased risk of leukemia. Those who had worked for at least 20 years, and w ere in the highest tertiles of percentage of time spent above 10 and 20 V/m had odds ratios of 10.17 (95% CI = 1.58-65.30) and 8.23 (95% CI = 1.2454.4 3), respectively, when compared to those in the lowest tertile. Nonsignific ant elevations in risk were observed between indices of magnetic fields and leukemia. Conclusions Our results support the hypothesis that electric fields act as a promoting agent in the etiology of adult leukemia. Exposure assessment ba sed on alternate indices of electric and magnetic fields should be incorpor ated into future occupational studies of cancer. (C) 2000 Wiley-Liss, Inc.