The determinants of Canadian children's personal exposures to magnetic fields

Study of the health effects of magnetic fields often depends on identifying determinants and hence indicators of personal exposure. This study identif ied determinants of children's exposure to magnetic fields and constructed a prediction model for them. For 632 children participating in a case-contr ol study of childhood leukemia, we made direct measures of exposure over 48 h using a portable device, together with observations on candidate determi nants. A child's age and sex, the proportion of time spent in the home, and their parents' education or income were very weak predictors of (logged) m ean 48 h magnetic field (R-2 < 1%). More important were province (R-2 = 8.0 %) and type of residence (R-2 = 11.3%). Low temperatures at the time of mea surement were associated with high fields (about 20% increase for each 10 < degrees>C below 14, R-2 = 4.9%). Several visible attributes of wiring aroun d residences predicted exposure, mostly captured in the Wertheimer-Leeper w ire code (R-2 = 13.5%). Stationary 24 h measurement in the bedroom (R-2 = 6 3.3%) and spot measurements outside the house (R-2 = 40.7%) predicted perso nal exposures best. Adding other minor;predictors increased only slightly v ariance explained by 24 h stationary (R-2 = 66.2%) and spot (R-2 = 46.8%) m easurements. Without spot or stationary measurements, the best model was mu ch less powerful (R-2 = 29.0%). We conclude that spot measurements outside the residence provide a moderately effective basis for estimating exposure for children living there, but do not perform as well as 24 h stationary me asurements in the child's bedroom. Although several other easily-observed v ariables were associated with personal exposure, they were weak determinant s, either individually or in combination. (C) 2001 Wiley-Liss, Inc.