Non-Hodgkin's lymphoma among electric utility workers in Ontario: the evaluation of alternate indices of exposure to 60 Hz electric and magnetic fields

Objectives-To examine associations between non-Hodgkin's lymphoma (NHL) and exposures to 60 Hz magnetic and electric fields in electric utility worker s with a series of indices that capture a variety of aspects of field stren gth. Methods-The study population consisted of 51 cases of NHL and 203 individua lly matched controls identified from within a cohort of male electric utili ty workers in Ontario. Odds ratios were calculated for several exposure ind ices with conditional logistic regression models. Aspects of exposure to el ectric and magnetic fields that were modelled included: the percentage of t ime spent above selected threshold field intensities, mean transitions in f ield strength, SD, and the arithmetic and geometric mean field intensities. Results-For the most part, there was a lack of an association between expos ure indices of magnetic fields and the incidence of NHL. Subjects in the up per tertile of percentage of time spent above electric field intensities of 10 and 40 V/m had odds ratios of 3.05 (95% confidence interval (95% CI) 1. 07 to 8.80) and 3.57 (1.30 to 9.80), respectively, when compared with those in the lowest tertile. Moreover, the percentages of time spent above these electric field thresholds were significant predictors of case status over and above the association explained by duration of employment and the arith metic or geometric mean exposure. Conclusions-These data suggest that exposures above electric field threshol d intensities of 10 and 40 V/m are important predictors of NHL. Consequentl y,the findings support the hypothesis that electric fields may play a promo ting part in the aetiology of this cancer. Further occupational studies tha t include assessment of exposure to electric fields and measures of field s trength above similar threshold cut off points are needed to confirm these findings.