Childhood leukemia and personal monitoring of residential exposures to electric and magnetic fields in Ontario, Canada

Objectives: To evaluate the risk of childhood leukemia in relation to resid ential electric and magnetic field (EMF) exposures. Methods: A case control study based on 88 cases and 133 controls used diffe rent assessment methods to determine EMF exposure in the child's current re sidence. Cases comprised incident leukemias diagnosed at 0-14 years of age between 1985-1993 from a larger study in southern Ontario; population contr ols were individually matched to the cases by age and sex. Exposure was mea sured by a personal monitoring device worn by the child during usual activi ties at home, by point-in-time measurements in three rooms and according to wire code assigned to the child's residence. Results: An association between magnetic field exposures as measured with t he personal monitor and increased risk of leukemia was observed. The risk w as more pronounced for those children diagnosed at less than 6 years of age and those with acute lymphoblastic leukemia. Risk estimates associated wit h magnetic fields tended to increase after adjusting for power consumption and potential confounders with significant odds ratios (OR) (OR: 4.5, 95% c onfidence interval (CI): 1.3-15.9) observed for exposures greater than or e qual to 0.14 microTesla (mu T). For the most part point-in-time measurement s of magnetic fields were associated with non-significant elevations in ris k which were generally compatible with previous research. Residential proxi mity to power lines having a high current configuration was not associated with increased risk of leukemia. Exposures to electric fields as measured b y personal monitoring were associated with a decreased leukemia risk. Conclusions: The findings relating to magnetic field exposures directly mea sured by personal monitoring support an association with the risk of childh ood leukemia. As exposure assessment is refined, the possible role of magne tic fields in the etiology of childhood leukemia becomes more evident.