sources, such as transmission and distribution lines and electric appliances, including shavers, hair dryers, water beds, and electric blankets. It must be emphasized, however, that the effects of exposure to different sources of electric and magnetic fields can be quite different, depending on their frequency and strength. Possible effects of the fields generated by high-voltage transmission lines or electric blankets, operating at 60 hertz (Hz),1 might be quite different from those generated by high-frequency (megahertz or gigahertz)2 devices.

Of primary interest to this committee is the concern about sources of low-frequency electric and magnetic fields associated with the generation, distribution, and use of electric power, including transmission lines, substations, distributions lines, and numerous electric devices ranging from personal computers to electric clocks.

Questions of the possible adverse health effects of exposure to electric and magnetic fields from 60-Hz power lines were first raised by Wertheimer and Leeper (1979). They reported epidemiologic data suggesting an association between the configuration of power lines near homes and the incidence of leukemia and other types of childhood cancer. Similar studies have been published in succeeding years in the United States and in numerous other countries. The results of these studies have increased the scrutiny of the possible association between raised levels of electric and magnetic fields in residences, as one site of exposure, and the incidence of cancer—the adverse health effect of most concern. Much of the early laboratory research on biologic effects of very low-frequency electric and magnetic fields focused on the study of electric fields, but results of epidemiologic and other studies have caused a gradual shift of interest toward magnetic fields as a possible cause of disease.

DEFINITIONS AND DESCRIPTIONS OF TERMS

Electric and Magnetic Fields

The term ''electromagnetic field," which is commonly used in the literature, applies to alternating fields. The electric and magnetic components of the fields generated by moving charged particles are formally linked and mathematically described by a set of coupled differential equations called Maxwell's equations. Electromagnetic fields are characterized by their wavelength, λ (expressed in meters), and their frequency, f (expressed in hertz); the frequency and wavelength

1  

 Electric and magnetic fields are characterized by their frequency and strength. Power-line fields are sinusoidal, meaning they alternately change from positive to negative voltage in smooth variation, with a frequency of 60 cycles per second. That frequency is described as 60 Hz. Hertz is an internationally accepted unit of frequency, 1 Hz referring to 1 cycle per second.

2  

 One megahertz (MHz) is 106 Hz; 1 gigahertz (GHz) is 109 Hz. A frequency of 109 Hz can also be represented as 1,000,000,000 Hz.



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