COMPARISONS BETWEEN MAGNETIC-FIELD EXPOSURE INDEXES IN AN AUTOMOBILE TRANSMISSION PLANT

Personal monitoring of extremely low frequency magnetic fields was con ducted at a large automatic transmission plant for a case-control stud y of primary brain cancer. Current workers were selected to represent the jobs most commonly held by study subjects. Several exposure indice s, corresponding to different plausible biological mechanisms, were co mputed for each of 81 workers who wore the monitoring instrument for o ne-half shift. Average exposures covered a range from 0.16 to 46 mG; m edian exposure was 1.3 mG. Nonparametric correlations were estimated t o learn whether all of these indices rise and fall together. Results w ere mixed, in that indices sensitive to high values showed correlation s above 0.7, but other correlations were between 0.4 and 0.6. Differen t indices may thus identify different groups as ''highly'' exposed. Th e authors also tested whether indices based on the fraction of time sp ent above hypothesized thresholds were accurately predicted by a logno rmal model. For 47% of the workers, the observed indices significantly exceeded those predicted by such a model suggesting that lognormality is not a good model for distributions of individuals' short-term expo sures.