Virginia Department of Health
Since the submission of the last report, entitled "Monitoring of Ongoing Research on the Health Effects of High Voltage Transmission Lines (Ninth Annual Report)", dated April 20, 1994, several articles, reports, and reviews have been published in the literature on this subject. The following is an overview of the publications included in this report. Conclusions from the various publications are either extracted verbatim or represent the views of the investigators and authors of the publications.
The Maryland Department of Natural Resources Status Report (1)
The Maryland Department of Natural Resources, Power Plant Research Program issued its fifth periodic report entitled "Status Report on Potential Human Health Effects Associated with Power Frequency Electric and Magnetic Fields" (1). The report was prepared by Information Ventures, Inc. under a contract from the Maryland Department of Natural Resources. This report contains the results of reviews of various studies and research projects that are underway throughout the world to address the issue of possible adverse health effects from exposure to EMF produced by electric power lines. The report's conclusions are as follows:
Minnesota Environmental Quality Board Review (4)
An overview of more than 100 recent epidemiologic and laboratory research studies on EMF effects was prepared for the Minnesota Environmental Quality Board (4). The report summarized consensus views on the potential health effects from exposure to power frequency electric and magnetic fields. The central points of consensus are as follows:
Universities Consortium on EMF Literature Review - 1992 Supplement (5)
A Universities Consortium on EMF composed of scientists from Colorado State University, the University of Colorado Health Sciences Center, and the University of Denver reviewed recent scientific literature and submitted its report, "Investigation in Power-Line Frequency EMF and Its Risk to Health: A Review of the Scientific Literature - 1992 Supplement" (5) to Public Service Company of Colorado in February 1994. This supplement follows the 1991 review of EMF literature conducted by the consortium. The supplement concludes:
"This review of the 1992 published literature has not caused us to change our initial summary or recommendations. The "good" studies are retrospective and still suffer from confounding issues. Distance from wires may or may not correlate with EMF effects on public health, or may indicate other external factors. A small random effect - 1/3 of the studies show induced changes in embryogenesis - needs further evaluation. Considerations for future research include performing mainly animal and laboratory study research (determine the mechanism of action, if any) BEFORE considering additional epidemiology studies."
The 1991 literature review report (6) had concluded, "the childhood leukemia studies have a risk magnitude that is small enough that could easily be due to some type of sampling bias. The occupational studies consistently report higher rates of certain cancers, but the exposure in each occupation is not well measured, and no mechanism has been established that determines how the fields cause cancer or what aspect of the field may be involved. At this time electromagnetic fields do not appear to be a major health risk of the same magnitude as cigarette smoking or poor dietary habits, but the consistent (if small) increase in risk for childhood leukemia and certain occupational categories needs to be explained."
The Hawaii Department of Health EMF Policy (7)
The Hawaii Department of Health recently revised its EMF policy (7) recommending "prudent avoidance," based on continuing but inconclusive scientific evidence concerning health effects of EMF. The policy states:
"A cautious approach is suggested at this time concerning exposure to electric and magnetic fields (EMF) around low-frequency sources, such as electric appliances and power lines. The existing research data on possible adverse health effects including cancer, are inconclusive and not adequate to establish or quantify a health risk. For example, the biological mechanisms that might underlie any apparent relationship between EMF and cancer have yet to be clearly defined. Also, some epidemiological studies suggest that, if these fields increase the risk of cancer, it is a very small increase. Other epidemiological studies suggest that there is no increased risk."
The Utah Department of Health Report (8)
The Utah Department of Health, Division of Community Health Services, Bureau of Epidemiology submitted its position paper regarding EMF health effects to the Interim Health and Environment Committee of the Utah Legislature (8). The report concluded:
"In summary, some studies have demonstrated a positive association between ELF-EMF and adverse health effects; other studies, however, have found no association. Whether unrecognized exposures may be responsible for the positive associations, or whether ELF-EMFs themselves may be a cause of these effects is uncertain. The National Institute of Environmental Health Sciences (NIEHS) is currently sponsoring research to address this important issue. At the present time, it appears premature to draw conclusions regarding possible health effects from exposure to ELF-EMF."
The Utah Department of Environmental Quality Report (9)
The Utah Department of Environmental Quality, Division of Radiation Control submitted its position statement on the health effects of EMF to the Interim Health and Environment Committee of the Utah Legislature (9), concluding:
"After reviewing available scientific opinion, the Board finds that while there may be indications for further biomedical research on this question, the existing scientific evidence is not sufficient to warrant legislation or regulation at this time."
Institution of Electrical Engineers, U.K. Review (10)
A work group formed by the Institution of Electrical Engineers Health and Safety Committee in 1992 updated an earlier review by evaluating 245 recently published articles on EMF (10). The conclusions of the updated review are as follows:
Residential Study in Finland (11)
Verkasalo et al. (11) conducted a nationwide cohort study in Finland to investigate whether children exposed to the magnetic fields of power transmission lines have an increased risk of cancer, particularly leukemias, lymphomas, or nervous system tumors. The study included 134,800 children (68,300 boys and 66,500 girls) aged between 0 and 19 years. The children lived at any time between 1970 and 1989 within 500 meters of overhead power lines of 110, 220, or 400 kV. The exposure to magnetic fields in the residences was estimated to be above 0.1 mG. The study subjects were classified into categories according to two estimates of magnetic field exposure: strength of magnetic field and cumulative exposure (person years). Person years were calculated by multiplying average exposure to magnetic field and duration of such exposure. Calculation of person years began on January 1, 1974 at the earliest or on the day when the child met the exposure criteria (lived for the first time in residence with a magnetic field exceeding 0.1 mG). Calculation of person years ended when the child reached the 20th birthday, at death, or on December 31, 1990, whichever occurred first.
No statistically significant increased risk was observed for leukemias, lymphomas, or all cancers combined among children included in the study. During the 17 years observation period, 140 cases of childhood cancer were observed in the cohort which included 39 nervous system tumors, 35 leukemias, 15 lymphomas, and 51 other malignant tumors. The expected number of cases was 145. A statistically significant excess of nervous system tumors was found in boys (not in girls) who were exposed to magnetic fields of 2 mG per year. However, there were only five observed cases of nervous system tumors; three of these with different morphologies and locations were observed in one 18-year old boy.
Residential Study in Denmark (12)
In a population based childhood cancer study in Denmark (12), all 1,707 children diagnosed with leukemia, brain tumor, or malignant lymphoma during 1968-1986 were identified from the Danish Cancer Registry. Of these, 833 had leukemia, 624 had brain tumors, and 250 had lymphoma before 15 years of age. The control group consisted of 4,788 children randomly selected and matched for age and sex. Two controls (a total of 1,666) were matched to each leukemia case, three ( a total of 1,872) to each brain tumor case, and five (a total of 1,250) to each lymphoma case.
Exposure assessment was based on each child's residence near 50-400 kV transmission lines, underground cables, and substations. A calculated field level, based on distance and annual current flow on the lines was assigned to each residence.
Of 1,707 cases, there were only 10 cases of the three types of cancer in the group exposed to a calculated magnetic field at or above 1 mG. The relative risk for all three cancers combined was elevated (odds ratio 1.4; 95% confidence interval 0.7-3.0), but was not statistically significant. When the exposure was estimated at or above 4 mG, the excess relative risk for all three cancers combined was 5.6 (95% confidence interval 1.6-19). However, the excess risk was based on only 6 cases. Based on these results it was concluded that the proportion of childhood cancer possibly caused by EMF must be very small.
Residential Study in the Republic of China (13)
The incidence of childhood leukemia in five districts in the Taipei Metropolitan area in which at least one of the elementary schools is passed over by a high voltage (69-345 kV) electric transmission line was investigated by Lin and Lee (13). A possible association between residential EMF exposure and childhood leukemia was elevated over the ten year span of 1979-1988. A total of 67 cases of childhood leukemia (aged 0-14 years) were reported to the Cancer Registration Center in Taiwan. The expected number of leukemia cases in the study population was 42 during the ten year span. The standardized incidence ratio (SIR) of childhood leukemia in the five districts was elevated (SIR 1.49; 95% of confidence interval 1.16-1.91) and was statistically significant.
The study results were stratified in these age groups: 0-4 years, 5-9 years, and 10-14 years. Children in the 0-4 years group had the highest and statistically significant elevated SIR of 1.71 (95% confidence interval 1.20-2.35). The SIR of the school aged children (5-9 years group) was 1.24 (95% confidence interval 0.66-2.12). The SIR of children in the 10-14 years group was 1.32 (95% confidence interval 0.77-2.11). However, the SIRs in the two groups (5-9 and 10-14 years) were not statistically significant.
There were several inherent methodological limitations in the study. The major limitation was that the addresses of the leukemia cases were not well documented in the Cancer Registry. Therefore, it was impossible to identify which of the 67 cases of childhood leukemia in this study attended the EMF exposed school or lived in homes which were passed over by high voltage transmission lines. There was also an assumption that the children in the 0-4 years age group had a higher exposure to EMF in their homes, either from domestic appliances or from nearby transmission and distribution lines. The investigators also acknowledged that the differences in parental characteristics, such as occupations, medication use, exposure to pesticides, genetic factors, etc., might confound the results of their study.
Occupational Study in Los Angeles County, California (14)
A casecontrol study (14) examined potential association between electrical occupations and leukemia among electrical workers in Los Angeles County. The study included all males aged 20-64 years with a diagnosis of cancer reported to the comprehensive population-based cancer registry for Los Angeles County between 1972 and 1990 for whom an occupation at the time of diagnosis was recorded. Cases were 2,355 men with the diagnosis of leukemia. Controls were 67,212 men diagnosed with other cancers. Persons with malignancies of the central nervous system were excluded due to a proposed association with magnetic field exposure. Magnetic field measurements on workers in each electrical occupation and in a random sample of occupations presumed to be nonelectrical were used to estimate magnetic field exposures for each occupation. With the exception of electrical engineers, magnetic field exposures were higher among workers in electrical occupations than in nonelectrical occupations.
Among men in electrical occupations, 121 leukemias were diagnosed. Among men in nonelectrical occupations, the total cases of leukemia were 2,234. A weakly positive trend in leukemia risk across average occupational magnetic field exposure was observed (odds ratio 1.2; 95% of confidence interval 1.0-1.5). A slightly stronger association was observed for chronic myeloid leukemia (odds ratio 1.6; 95% confidence interval 1.2-2.0), but numbers in this subgroup were small. The authors concluded, "although not conclusive, these results are consistent with findings from studies based on job title alone that electrical workers may be at slightly increased risk of leukemia."
Occupational Study in Denmark (15)
A study (15) to determine the risk of cancer in occupations with potential exposure to EMF was conducted in Denmark. Subjects for this study were drawn from a cohort of 2.8 million men and women aged 2064 years employed in Denmark in 1970. The incidence of cancer was followed in these subjects for 17 years (1970-1987). Each person was classified by his or her industry and occupation in 1970. Each industry-occupation group was coded for potential exposure to magnetic fields above 3 mG. Some 154,000 men and 79,000 women were considered intermittently exposed to magnetic fields above 3 mG. The numbers of men and women continuously exposed to magnetic fields above 3 mG were 18,000 and 4,000, respectively. Intermittent exposure was not associated with an increased risk of leukemia, brain tumors, or melanoma. Men with continuous exposure had an excess risk of leukemia (39 observed versus 24 expected). The odds ratio was 1.64 (95% of confidence interval 1.2-2.24). These men had no excess risk of brain tumors or melanoma.
The incidence of leukemia was not increased in women with continuous exposure to magnetic fields. The investigators did not consider the study as conclusive, nor did they specifically implicate exposure to EMF as the cause for increased risk of leukemia. The investigators concluded, "The reason for the increased risk of leukemia is not clear. Besides electromagnetic fields other occupational exposures may explain the finding. Ongoing studies including measurements of exposure to electric and magnetic fields and assessment of exposure to chemicals will shed further light on these possible etiological agents."
Incidence of Leukemia and Brain tumors in Norwegian Railway Workers (16)
A nested case-control study of railway workers based on incident cases from the Cancer Registry of Norway was conducted by Tynes et al. (16). The study included a cohort of 13,030 male Norwegian workers who had worked on either electric or nonelectric railways. The cases were comprised of 39 men diagnosed with brain tumors and 52 men diagnosed with leukemia during the follow-up period from January 1958 to December 1990. Each case was matched on year of birth with four or five controls selected from the cohort. Controls must have survived to an age equal to or greater than the age at diagnosis of the corresponding case to be eligible. The exposure of each study subject to electric and magnetic fields was evaluated from cumulative exposure measures based on present measurements and historical data. The case-control analysis showed no association between leukemia or brain tumors and occupational exposure to electric and magnetic fields in electric railway workers.
Incidence of Cancer in Swedish Railway Workers (17)
In a study (17) of Swedish railway workers, all men 20 to 64 years of age and employed in 1960 were selected and compared with the population at large, concerning the incidence of leukemia, lymphoma, and tumors of the brain, breast, and pituitary gland. This study was a reanalysis of the 1961-1979 incidence data previously showing no increase in risk for leukemia and brain tumors among railway workers. In this reanalysis, the distribution of cancer cases for the total study population and for the occupational groups were computed by age at diagnosis in two 10-year periods. For the first decade, engine drivers and conductors combined had an elevated relative risk of chronic lymphocytic leukemia, acute myeloid leukemia, and lymphoma. The elevated relative risk was not found during the second decade. For brain tumors, no statistically significant associations were seen. Three cases of breast cancer (relative risk 4.9; 95% confidence interval 1.61-1.8) and nine cases of tumors of the pituitary gland (relative risk 3.2; 95% confidence interval 1.6-6.2) were reported. According to the authors, "these results give some support to the hypothesis of an association between EMF and certain types of cancer."
Personal Appliance Use and Risk of Adult Leukemia (18)
The hypothesis that use of personal electric appliances may be associated with increased risk of acute nonlymphocytic leukemia in adults was tested in a study (18) using interview data from a previously completed case-control study of 114 cases and 133 controls conducted between 1981 and 1984. Cases were selected from a population-based cancer registry in western Washington state. The controls were selected from the same area by random digit dialing. Of 32 electrical home appliances for which data on use were available for adult acute nonlymphocytic leukemia cases and controls, three motor-driven personal appliances (electric razors, hair dryers, and massage units) were selected. The results were compared on an "ever used" versus "never used" basis. Use of one or more of these appliances was not associated with increased risk of leukemia in the population studied. When the appliances were considered individually, massage units were more likely to have been used by cases than by controls. Hair dryers were more likely to have been used by controls than cases. There was a nonsignificant tendency for electric razor use to differentiate the cases from controls.
Occupational Exposure to EMF and Incidence of Breast Cancer (19, 20)
In a case-control study (19) of male breast cancer, 71 cases reported to the New York State Tumor Registry between 1979 and 1988 were compared with 256 healthy male controls. Controls were matched to cases by race, year of diagnosis, and age in 5-year intervals. No increase in disease risk was observed for males believed to have occupational exposure to EMF.
In another study (20), breast cancer mortality among female electrical workers in the United States was analyzed. The study was based on death certificates of women aged 20 years and over who died of breast cancer during 1985-1989 in 24 states. Four controls per case were selected from computer files of U.S. mortality data for the years 1985-1989. Sixty-eight women with breast cancer and 199 controls worked in electrical occupations. A total of 27,814 cases and 110,750 controls had occupations other than electrical. Electrical workers had excess mortality from breast cancer relative to nonelectrical workers (odds ratio 1.38; 95% confidence interval 1.04-1.82). The authors concluded, "In light of the limitations inherent in death certification data and the design of this study, any conclusions regarding the hypothesis that exposure to extremely low-frequency electromagnetic fields causes breast cancer among women must be limited. Nevertheless, our findings are broadly consistent with that hypothesis and encourage further investigation with improvements in study design and data quality."
Occupational Exposure to EMF and Incidence of Alzheimer's Disease (21)
Recently, preliminary findings of a study (21) were presented at the Fourth International Conference on Alzheimer's Disease (AD) and Related Disorders in Minneapolis, Minnesota. The results were published in the meeting abstracts reports. The study identified three independent groups of AD patients with different types of controls: (Group 1) 53 sporadic AD patients with 70 sporadic vascular disease (VD) patients as controls from the University of Helsinki (1982-1985); (Group 2) 198 AD cases and 299 matched hospital controls from another Helsinki hospital (1977-1978); (Group 3) 136 sporadic AD cases and 106 matched healthy controls with no family history of AD from the University of Southern California AD Research Center. Sporadic AD cases were individuals who do not have any relative affected by the disease. Primary occupation was classified as having high/medium or low EMF exposure. The results across the study population showed odds ratios of 2.9, 3.1, and 3.6 for Groups 1, 2, and 3, respectively. For females, the odds ratios were 7.3, 3.3, and 5.7, respectively. Combining the three groups gave odds ratios of 3.1 for all subjects and 4.2 for females. The confidence intervals were not given in the meeting abstract. The authors concluded, "Electromagnetic fields may be an important risk factor for AD. Odds ratios this high for EMF exposure have not been reported for any other disease, including leukemia and other cancers."
The study, giving details of methodology and results, is expected to be submitted for publication in a scientific journal.
Prevalence of Depression in Electrical Workers (22)
To address possible association between electric and magnetic field exposure and depression, a study (22) analyzed data from the Vietnam Experience Study conducted by the Centers for Disease Control and Prevention. The cohort included male veterans who served in the U.S. Army for the first time from 1965 to 1971. One hundred eighty three subjects were classified as electrical workers and 3,861 subjects were classified as nonelectrical workers. The risk of diagnosed depression, depressive symptoms, and elevations in personality scales indicative of depression was compared using the Diagnostic Interview Survey (DIS) and the Minnesota Multiphasic Personality Inventory (MMPI). The results suggest that electrical workers in general are not at increased risk for depression.
The studies published in the scientific literature during 1993-1994 do not provide any new convincing and conclusive evidence which would support the contention that residential exposure to EMF from high voltage transmission lines causes adverse health effects in humans. Neither a cause-effect nor a dose-response relationship has yet been established, and confounding factors or exposure to other etiologic agents continue to be a possible explanation of the association reported in some of the epidemiologic studies.