A scheme for incorporating DC magnetic fields into epidemiological studies of EMF exposure.

Experimental data on calcium-ion release in chicken brain tissue suggest that biological effects of electric and magnetic fields (EMFs) are concentrated near certain "active combinations" of DC magnetic field strength and "effective" AC magnetic field frequencies. We hypothesize that active AC/DC combinations may exist and suggest that epidemiologic data, coupled with DC magnetic field measurement, may be used to identify critical exposure conditions. An empirical model is used to calculate these multiple active combinations at any given DC magnetic field strength and to define a rating system that incorporates the proximity of AC magnetic field frequencies generated by electric power lines to the new, computed effective frequencies. Such an exposure score may be useful in investigating correlations of EMF exposure with disease incidence. For 60 Hz and 50 Hz, the highest EMF exposure scores occurred at DC field strengths of 506 mG and 422 mG, respectively. The exposure score contains a factor which may be adjusted to reflect the importance of harmonics of the AC magnetic field as well as of the fundamental frequency. Using this factor, we consider two important special cases consistent with chick brain data: 1) we consider active pairs associated with all detectable harmonics (up to 660 Hz) without regard to relative intensity of the harmonics, and 2) we use the relative intensities of the AC field frequencies to adjust their contribution to the exposure score.