SD23 - Monitoring of Ongoing Research on the Health Effects of High Voltage Transmission Lines

  • Published: 1998
  • Author: Department of Health
  • Enabling Authority: Senate Joint Resolution 278 (Regular Session, 1993)

Executive Summary:
Pursuant to Senate Joint Resolution No. 126 of the 1985 Session and Senate Joint Resolution No. 278 of the 1993 Session, this thirteenth annual report on monitoring of ongoing research on the human health effects of high voltage transmission lines is submitted to the members of the 1998 Virginia General Assembly. Since the submission of the last report, entitled "Monitoring of Ongoing Research on the Health Effects of High Voltage Transmission Lines (Twelfth Annual Report)," dated March 20, 1997, several articles , reports, and reviews have become available in the literature on this subject. An overview of these publications is presented in this report.

The possible health effects of electromagnetic fields (EMF) exposure in an occupational environment were first reported in the literature from the former Union of Soviet Socialist Republics (USSR) in the mid-1960s. Several subjective complaints, involving the cardiovascular, digestive, and central nervous systems, were reported by electric switchyard workers. Subsequent studies of electric utility linemen in the United States failed to observe the same adverse health effects reported by their counterparts in the former USSR. Since that time, scientific interest has continued to increase in an attempt to ascertain an association between residential and occupational exposures to EMF and detrimental health effects.

Over the past several years, burgeoning public concerns, as well as scientific uncertainty regarding potential health effects from exposure to power frequency EMF emanating from nearby high voltage electrical transmission lines, have generated considerable controversy among scientists, courts, regulatory bodies and public policy makers. Since 1979, numerous epidemiologic studies have appeared in the literature exploring a possible causal association between exposure to EMF and cancer, especially leukemia and brain tumors. Nonetheless, the subject still remains controversial. This is because the results of these investigative studies have been contradictory, inconclusive, and far from establishing an unequivocal dose-response or a cause-effect correlation. Some investigators have suggest statistically significant, but weak positive associations between EMF and the increased risk of cancer from occupational exposure or proximity to high voltage transmission lines. The relative risk inferred in some of the studies is low in magnitude and is within the range where experimental bias or confounding factors cannot be completely ruled out. The reported incremental increases in cancer incidence are also discordant with respect to cancer types or site. The reported increases in risk have been observed only in relation to estimates of magnetic fields based on extrapolation of historical data., but not to actual contemporaneous field measurements. Many scientists are of the opinion that since there is no plausible biological basis, it is inconceivable that power frequency EMF at field strengths typically encountered in and around residences in the proximity of high voltage transmission lines could pose an increased risk of cancer in humans.

To what extent high voltage transmission lines incrementally contribute to daily exposure of EMF is still an enigma. This is because exposure to EMF is unavoidable due to ubiquitous sources other than high voltage transmission lines, such as wall wiring, lighting fixtures, distribution lines, substations, and from the use of a vast array of electrical appliances, such as televisions, clocks, computers, ovens, ranges, toasters, blenders, hair-dryers, irons, shavers, blankets, power tools, etc. Admittedly, some of these appliances are used for short intervals, yet cumulative daily exposure to EMF from these devices is most likely to exceed that from high voltage transmission lines.

The preponderance of evidence in the scientific literature available to date for causation of cancer or any other deleterious effects in humans from exposure to EMF from nearby high voltage transmission lines is neither convincing nor consistent. The studies published in the literature lack clear demonstration of a significant causal relationship and a definitive dose-response gradient. There is no widely accepted biological mechanism or a theory of how power frequency EMF could cause a disease. There are no specific clinical signs or symptoms for disease(s) possibly associated with exposure to low frequency EMF. To date, there are no specific clinical confirmatory tests or biomarkers that could assess past exposure to EMF or potentially help in either confirming or excluding diagnosis of a disease, if any, linked to either electric or magnetic fields or both. Evidence from the laboratory studies has thus far failed to show that exposure to EMF causes cancer in experimental animals. Experiments have also failed to show how EMF could initiate or promote the growth of cancer. Both in vivo and in Vitro experimental studies therefore, do not lend support to an implied association between exposure to EMF and cancer.

Epidemiologic studies examining the possible association between EMF and cancer have some inherent strengths and weaknesses. In order to detect an association between a given risk factors and disease, an epidemiologic study must control for other potential risk factors that may be confounding this association. Even when all potential risk factors are known and controlled to the maximum extent possible, it is frequently impossible to rule out confounding when the strength of an association observed between the risk factor of interest and disease is weak. In reality, it is seldom possible to control for all other potential risk factors, because for many diseases, like various forms of cancer, those other risk factors, because for many diseases, like various forms of cancer, those other risk factors are unknown. Some epidemiologic studies have found that exposure to EMF may confer a two to three-fold increased risk of certain cancers. This is a fairly small increase when compared to the association between cigarette smoking and cancer, where the risk is increased by ten-fold or greater. Furthermore, exposure to EMF is universal and unavoidable. Thus, it is not possible to find a control group of individuals who would be unexposed; only populations with relatively greater or lesser exposure can be compared. Also, past exposure can only be estimated based on wiring configuration. There is no biological test to assess past exposure and current environmental measurements may be misleading. The assumption that the exposed group would have had a higher exposure to electromagnetic fields than the rest of the population may not be true and therefore, may skew the interpretation of the results of epidemiologic studies.

Although epidemiologic studies may fail to find an association between a given risk factor and disease, it is practically impossible for any epidemiologic study to rule out the possibility of a weak association. This is because the power of a study to confirm a negative association hinges on the prevalence of the disease of interest and the size of the study population. Because of the rarity of most tumors, any competent epidemiologic study that attempts to rule out very small associations between EMF and one type of cancer would have to include an exceedingly large population. Such a study would almost certainly be cost-prohibitive.

Scientific proof of a cause and effect relationship cannot be readily inferred from a single epidemiologic study. Causality is established using multiple criteria, only one of which is epidemiologic association. Other important factors in confirming a cause and effect relationship include strength of association, consistency and specificity of observations, appropriate temporal relationship, dose-response relationship, biological plausibility, and experimental verification. none of these factors by itself is sufficient to approve or disprove that an observed association represents a true cause and effect relationship. In the case of EMF, these tests for causality have not been satisfied for the implicit deleterious effects.

Laboratory experiments conducted on cells, tissue, and whole animals have shown that under certain conditions, exposure to EMF can produce changes in behavior and 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.