ALTERNATE INDEXES OF ELECTRIC AND MAGNETIC-FIELD EXPOSURES AMONG ONTARIO ELECTRICAL UTILITY WORKERS

Epidemiologic studies examining the risk of cancer among occupational groups exposed to electric fields (EF) and or magnetic fields (MF) hav e relied on traditional summaries of exposure such as the time weighte d arithmetic or geometric mean exposure. Findings from animal and cell ular studies support the consideration of alternative measures of expo sure capable of capturing threshold and intermittent measures of field strength. The main objective of this study was to identify a series o f suitable exposure metrics for an ongoing cancer incidence study in a cohort of Ontario electric utility workers. Principal components anal ysis (PCA) and correlational analysis were used to explore the relatio nships within and between series of EF and MF exposure indices. Exposu re data were collected using personal monitors worn by a sample of 820 workers which yielded 4247 worker days of measurement data. For both EF and MF, the first axis of the PCA identified a series of intercorre lated indices that included the geometric mean, median and arithmetic mean. A considerable portion of the variability in EF and MF exposures were accounted for by two other principal component axes. The second axes for EF and MF exposures were representative of the standard devia tion (standard deviation) and thresholds of field measures. To a lesse r extent, the variability in the exposure variable was explained by ti me dependent indices which consisted of autocorrelations at 5 min lags and average transitions in field strength. Our results suggest that t he variability in exposure data can only be accounted for by using sev eral exposure indices, and consequently, a series of metrics should be used when exploring the risk of cancer owing to MF and EF exposure in this cohort. Furthermore, the poor correlations observed between indi ces of MF and EF reinforce the need to be take both fields into accoun t when assessing the risk of cancer in this occupational group. (C) 19 98 Wiley-Liss, Inc.