Alternative magnetic field exposure metrics: Relationship to TWA, appliance use, and demographic characteristics of children in a leukemia survival study

The ongoing Childhood Leukemia Survival Study is examining the possible ass ociation between magnetic field exposure and survival of children with newl y diagnosed acute lymphocytic leukemia (ALL). We report the results of the first year 24 h personal magnetic field monitoring for 356 US and Canadian children by time weighted average TWA and alternative exposure metrics. The mean TWA of 0.12 muT was similar to earlier personal exposure studies invo lving children. A high correlation was found between 24 h TVA and alternati ve metrics: 12 h day TWA, 12 night TWA, geometric mean, 95th percentile val ue, percentage time over 0.2 and 0.3 muT, and an estimate of field stabilit y (Constant Field Metric). Two measures of field intermittency, rate of cha nce metric (RCM) and standardized rate of change metric (RCMS), were not hi ghly correlated with TWA. The strongest predictor of TWA was location of re sidence, with highest TWAs associated with urban areas. Residence in an apa rtment, lower paternal educational level, and residential mobility were als o associated with higher TWAs. There were no significant differences in the appliance use patterns of children with higher TWA values. Children with t he highest field intermittency (high RCM) were more likely to sit within 3 feet of a video game attached to the TV. Our results suggest that 24 h TWA is a representative metric for certain patterns of exposure, but is not hig hly correlated with two metrics that estimate field intermittency. (C) 2001 Wiley-Liss, Inc.