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 association between magnetic field exposure and survival of children with newly 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 microT was similar to earlier personal exposure studies involving children. A high correlation was found between 24 h TWA and alternative metrics: 12 h day TWA, 12 night TWA, geometric mean, 95th percentile value, percentage time over 0.2 and 0.3 microT, and an estimate of field stability (Constant Field Metric). Two measures of field intermittency, rate of change metric (RCM) and standardized rate of change metric (RCMS), were not highly correlated with TWA. The strongest predictor of TWA was location of residence, with highest TWAs associated with urban areas. Residence in an apartment, lower paternal educational level, and residential mobility were also associated with higher TWAs. There were no significant differences in the appliance use patterns of children with higher TWA values. Children with the 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 highly correlated with two metrics that estimate field intermittency.