The 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 serial 24 -h personal magnetic field monitoring for 412 US and Canadian children and present the correlations between annual values. The mean time -weighted average ( TWA ) and geometric mean ( GM ) were similar for first, second, and third year measurements [ TWA: 0.11 T (n = 412 ), 0.13 T (n = 304 ), and 0.12 T (n = 134 ), respectively ]. There were no consistent differences in mean TWA or GM based on age or gender. Significantly lower mean TWA and GM were found for children living in rural areas. Higher exposures were noted among children living in urban areas, among apartments dwellers, and those living in rental homes. Measurements taken during summer months and among children residing in the northeast and Canada also tended to be higher. Correlations for most metrics were increased among children who had annual measurements performed during the same season. The metric with the highest year -to -year correlation was the GM. The lowest correlations were found for metrics estimating field intermittency and temporal stability. First to second year GMs were well correlated when taken in the same home ( Spearman rank correlation = 0.70 ), but a lower correlation ( 0.44 ) was noted among residentially mobile children. Our findings suggest that summarizing exposure using a single measurement of GM can estimate exposures for residentially stable children, but is not a good predictor of personal exposures among children who change residence during the study interval.

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.

0 s m o c on f o r m i ng L i m pe t s ( M o I I u sc a : ABSTRACTThe capacity to regulate body volume is important in the ability of soft-bodied osmoconforming marine animals to withstand osmotic stress. In the present study two intertidal limpets, Collisella digitalis and Notoacmea scutum, which differ in their tolerance of osmotic stress, are compared in their ability to regulate water content. Two direct measurements and two mathematical approaches developed by Oglesby (' 75) and Machin ('751, respectively, have been used. Both species are osmoconformers over the range 500-1,500 mOs/l but showed a slight tendency to hyporegulate C1-and Na' in the hemolymph. In weight and tissue hydration changes following a change in osmotic pressure of the medium, C. digitalis did not vary as widely as did N. scutum and so appears to have better control of body volume. This correlates well with the previous finding that C. digitalis tolerates a wider range of salinity than does N. scutum.