an environment containing such fields. Biologic responses to exposure to electric and magnetic fields have been shown in many laboratories, and often they appear to be associated with the nervous system. In addition, unconfirmed or controversial data have been reported on observed effects that might be due to field exposure (e.g., changes in brain chemistry and morphology and alterations in reproduction and development). It is not yet known whether confirmed or putative effects are due to a direct interaction of the field with tissue or to an indirect interaction (e.g., a physiologic response due to detection or sensory stimulation by the field).

Whether a biologic effect from exposure to electric or magnetic fields constitutes a health hazard has yet to be answered. Experiments have not confirmed pathologic effects, even after prolonged exposures to high-strength magnetic (10 mT) and high-strength electric (100 kV/m) fields. In the very few tumor-promotion studies that have been reported, results seem to be mixed; most studies show no association between exposure to electric and magnetic fields and increased tumor development.

Although the data are not strong or entirely consistent, some experimental results using animal cancer models suggest a possible association of exposure to electric and magnetic fields and adverse health outcomes. The strongest laboratory evidence for an association between magnetic-field exposure and cancer development is in promotion of mammary carcinogenesis initiated by chemical carcinogens; however, the results have not been consistent. In these experiments, tumors must be initiated with a chemical carcinogen for the magnetic-field exposure to have its apparent effect. Some data also support the possibility that magnetic fields can act as a copromoter; magnetic fields alone, however, have not been shown to be effective in promoting cancer development.