Epidemiological Studies and Surveys
Environmental studies. Suicide is a stress-related phenomenon that may be viewed as a specific manifestation of depressive mental illness. We studied the relationship between suicide and power-frequency field strength (2, 14). We were concerned with how the field strength at the residences of suicides compared with that at appropriately-chosen control addresses. The study group consisted of the 598 suicides that occurred within the study area (in the Midlands of England) during a 7-year period and an equal number of controls. We first examined the relationship between suicide and the computed electric and magnetic fields of nearby high-voltage power lines. We found a statistically significant correlation between both fields and the occurrence of suicide, but we could not determine whether more or less than the expected number of suicides occurred at locations of high field strengths (14). Since the total power-frequency field at any site is due to contributions from many sources- high-voltage lines, low-voltage lines, household wiring and appliances- we then proceeded with a study of measured field strengths. The mean measured magnetic field strength for the suicide group (867 µgauss), was found to be significantly higher than that of the control group (709 µgauss) (2). The proportion of suicide addresses in the high-field-strength region was 40% greater than the proportion of control addresses (Table 10.6).
Table 10.6. PROPORTIONS OF SUICIDE AND CONTROL ADDRESSES FOUND IN REGIONS OF VERY HIGH (1 500 µgauss) AND HIGH (1000 µgauss) MEASURED POWER-FREQUENCY MAGNETIC FIELD STRENGTH
Wertheimer and Leeper studied the association between childhood cancer (in Denver, Colorado), and living in proximity to power lines. Homes were classified on the basis of their distance to high-current (high magnetic field) and low-current (low magnetic field) line configurations. It was found that the death rate from leukemia, Iymphomas and nervous system tumors was about twice the expected rate in high-current homes (15). In a related study (16), which was different in several important respects (17), Fulton et al. failed to find an association between electrical wiring configuration and childhood leukemia in Rhode Island.
In a study involving children exposed to environmental high-frequency EMFs, differences were found in various cardiovascular indices between 100 children (aged 5-14) who lived in areas where the EMF ranged up to 30 v/m, and 70 control children who experienced fields of less than 0.l v/m (18). The exposed group had faster pulse and respiratory rates, increased blood pressure, and exhibited a slower recovery from a stress test.
These studies, and one other that failed to find an association between living near power lines and visits to a physician (19), are, so far as we have been able to determine, the only epidemiological studies that involve exposure to environmental EMFs.
Occupational exposure. There have been many surveys and studies of the side-effects of EMF exposure in the workplace. At high frequencies, the workers studied have included radar, radio, and TV technicians, and the operators of various specialized industrial equipment. In general, the most frequently found symptoms involved the hematological, cardiovascular, endocrine, and nervous systems of the exposed workers.
In 1970, Glotova and Sadchikova reported the development and clinical course of cardiovascular changes in 105 workers chronically exposed to 30 GHz, 2000-3000 µw/cm2 (20). They found that the EMF exposure resulted in cardiovascular and autonomic-system alterations, the nature of which varied with the individual. In some persons, there was sinus bradycardia and arterial hypotension without any signs of general or regional hemodynamic disturbances. In others, autonomic-vascular dysfunctions, often with symptoms of hypothalamic insufficiency were found. Subsequently, Sadchikova presented dinical observations on the health status of microwave equipment operators (21). There were three (predominantly male) groups that were matched with respect to age, sex, and job. The first group (1000 persons) was exposed to 2000-3000 µW/cm2, the second group (180) to 20-30 µW/cm2, and the third group (200) received no exposure. It was found that the first and second groups differed significantly from the controls in frequency of complaints of headache, tiredness, and irritability. Both groups exhibited various cardiovascular changes including bradycardia and abnormalities in blood pressure and ECG. Later studies on 885 radio and electronics workers yielded similar results (26).
In a study of 60 men exposed to 30-GHz EMFs during their working day (normally 10-170 µW/cm2, but up to 500 µW/cm2) six or seven times per month, bradycardia and a decrease in the pumping efficiency of the heart were found (23). Similar results were reported in 34 persons, aged 30-49 who had been exposed for 5-15 years (24). Various cardiovascular disorders were also seen in a study of 73 men and 27 women that had been occupationally exposed to microwave EMFs (25). Symptoms generally subsided 1-2 weeks after cessation of work around the radiation sources but in some cases they persisted for more than 2 years. Klimkova studied 162 workers who had been exposed to 3-30 GHz, and reported headache, fatigue, and EEG changes as a consequence of the EMF (26).
Sokolov et al. compared various blood and bone-marrow cell indices of 131 persons (115 males, 16 females)who had been occupationally exposed to high-frequency EMFs, with the corresponding values from 800 clinically healthy persons. Decreased leukocyte counts and an increased red blood cell formation were observed in the exposed individuals, and the results, which were progressive with increasing exposure, were found to be reversible upon cessation of exposure (27). Hematological disorders have also been reported in several other similar studies (29-32).
Prolonged occupational exposure leads to a stress reaction manifested by changes in corticoid metabolism (33) and in the general endocrine system (28, 34-36).
In a study of gonadal function in workers exposed to microwave EMFs (3.6-10 GHz, 10-100 µW/cm2, for an average of 8 years) significant differences between the exposed and control workers were found in the number, motility, and morphology of the spermatozoa. Following cessation of exposure, most subjects showed improvement in the various gonadal indices (37).
In an evaluation of the relationship between mongolism (Down's syndrome) and parental exposure to radiation, it was found that 8.7% of fathers of mongoloid children had contact with radar as compared to 3.3 % of control fathers-the difference was statistically significant (3 8). A later study failed to confirm this higher incidence of paternal radar microwave exposure in fathers of Down's cases (39).
Sadchikova has described three progressively more serious syndromes associated with exposure to high-frequency EMFs (collectively referred to as microwave disease) (21- 40).
1. Asthenic: seen in the initial stages of the disease and characterized by vagotonia, arterial hypotension and bradycardia.
2. Astheno-vegetative: more pronounced than asthenic phenomena and the most often observed form. Characterized by excitability of the sympathetic branch of the autonomic nervous system, with vascular instability and hypertension.
3. Hypothalamic: arises with increasing disease pathology. Characterized by the development of paroxysmal states in the form of sympathoadrenal crises. Frequently leads to ischemic heart disease.
Although the conclusion is hotly contested by industry spokesmen (41, 42), the evidence clearly indicates that exposure to high-frequency EMFs produces various abnormalities in the eye, particularly cataracts. In 1963, in one of the earliest studies of this relationship between EMFs and ocular anomalies, Zaret et al. (43) examined 73 6 workers involved in the maintenance and testing of radars, and 559 control individuals. The ophthalmic examinations included visual acuity tests, slit-lamp examinations, and stereophotography of the lens. They found significant differences between exposed and control groups in the frequency of polar defects and opacities. Subsequent re-evaluations of Zaret et al.'s data reinforced the original conclusions (44,45).
Mejewska (46) studied 200 workers who were exposed to 0.6-10.7 GHz and 200 control individuals: a statistically significant increase in lens opacities in the exposed individuals was found. The severity of the disease increased with the duration of exposure. In another study, which involved 600 workers and an age-matched control group of 300 individuals (47), it was found that exposure to 0.3-300 GHz correlated with an increased incidence of a specific kind of lens opacity. Appleton surveyed military personnel who had been exposed to microwave EMFs and found a trend in older age groups toward a greater incidence of opacities among exposed personnel (48). Odland (49) also studied the relation between exposure to military radars and ocular anomalies. There were 377 exposed individuals and 320 controls: among the exposed workers who had a family history of eye diseases, it was found that the incidence of eye defects was almost twice as great as that among the controls who had such a family history. Among 68 electronics workers and 30 control individuals, it was found that the incidence of lens opacities and retinal lesions were both greater in the exposed group (50, 51). Zydecki studied 1000 exposed workers (mostly between 100-1000 µW/cm2) and 1000 controls and found that the number of lenticular opacities was significantly greater in the exposed individuals (52).
Through painstaking analysis of many clinical cases, Zaret has been able to describe a particular lens opacification for which EMFs are the primary etiological factor (the microwave cataract) (53 -57). In contrast to other types of cataracts (heredity, metabolic, and senile) which originate in the lens, the microwave cataract originates in the elastic membrane that surrounds the lens (the capsule). Microwave cataracts occur following exposure to either thermal or nonthermal EMFs, and have a latency period of months to years.
The Soviet Union has enacted a high-frequency EMF occupational exposure limit of 10 µW/cm2 (58). Since the general public is a much more heterogeneous group than the work force-which does not generally contain the very young or old, or the sick-an additional safety factor of ten was incorporated in choosing a standard for the general environment, which was set at 1 µW/cm2 (59).
Personnel working in electrical sub-stations or near high-voltage power lines are exposed to relatively intense power-frequency electric and magnetic fields. In the early 1960's, Soviet scientists conducted several studies of the effects of power-frequency EMFs on exposed workers (60-62) and found a variety of ills including headaches, fatigue, chest pains, and sexual impotence. These studies led to the first (and only) health standards designed to regulate exposure to power-frequency EMFs in the workplace (63) (Table 10.7). Spanish investigators found similar problems among 9 workers (64), but among 11 American service personnel the only finding was a reduced sperm count in 2 workers (65).
Table 10.7. SOVIET OCCUPATIONAL-EXPOSURE SAFETY LEVELS FOR POWER-FREQUENCY ELECTRIC FIELDS
The original Soviet studies have led to an expanded effort to study the health risks of EMF exposure to service personnel (66). Studies in other countries have begun to confirm the early evidence that alterations in gonadal function are associated with workplace exposure. The results of a Swedish study seemed to indicate that fewer children were born to exposed high-voltage workers than to controls, and that the difference increased with the number of years of exposure (72). Later studies showed that 8% of the offspring of exposed workers suffered from birth defects as compared to 3 % of the offspring of the control-group members. In a Canadian study it was found that, prior to commencement of employment, the 56 high-voltage workers studied had fathered approximately equal numbers of male and female offspring, but that in children conceived thereafter, the number of males born was almost six times the number of females (67).