Virginia Department of Health
The quest to confirm a causal association between exposure to EMF, specifically magnetic fields, and purported carcinogenic effects continues in the scientific literature. Several recent epidemiologic studies have focused their attention on the occurrence of leukemia and brain tumors among residents near high voltage transmission lines and among workers who were occupationally exposed to EMF. While some studies imply a possible link between EMF and certain types of cancer, others tend to impugn such a relationship. Most of the epidemiologic studies which incriminate exposure to EMF as a cause of cancer have been only suggestive of a relatively small increase in incremental risk over the background incidence. There is an eminent lack of statistical significance in many studies. Studies in which statistical association has been reported confer only a two- to three-fold increase of certain cancers. A relative risk of this magnitude is low and does not necessarily indicate a cause-effect relationship. These reported increases in cancer incidence might be expected to occur on the basis of chance alone or as a result of some unidentified factor or etiologic agent other than EMF. There is no unifying pattern in the published studies with respect to cancer types or site. Empirical estimates of exposure have been extrapolated from the historic line loads and do not accurately represent the extent or intensity of past exposures. There is no biological test to assess past exposure and current environmental measurements may be misleading. In view of the inconsistent and contradictory results in the currently available literature as well as the notable lack of a dose-response or an exposure-effect relationship, it is not yet possible to ascribe EMF from high voltage transmission lines as an etiologic agent for cancers in humans.
Laboratory experiments conducted on cells, tissues, and whole animals have shown that under certain conditions, exposure to EMF can produce changes in behavior, changes in nervous system activity, and alterations in biological rhythms and the production of certain hormones. Biological changes such as these are not necessarily physiologically significant. Hence, it cannot be determined that these biological effects translate into adverse human health effects. The observed effects depend upon various factors, including field strength, frequency, duration of exposure, variability of exposure, rate of change in intensity, and interaction with the Earth's magnetic field. Unlike ionizing radiation, power frequency EMF do not appear to cause direct damage to DNA or other genetic material. Thus, it is believed that exposure to EMF could not, by itself, initiate cancer. However, some scientists have postulated that electric and/or magnetic fields may potentially serve as cancer promoters (an agent which facilitates the growth of a cancer which has already been initiated). These hypotheses are now being tested by researchers.