Transferrin receptors and natural killer cell lysis. A study using Colo 205 cells exposed to 60 Hz electromagnetic fields.

The role of target cell transferrin receptors (TfR) in natural killer (NK) cell-induced cytolysis has been studied using Colo 205 cells in which prior exposure to 60 Hz electromagnetic fields produced constitutive expression of maximum numbers of TfR. It was found that NK cell cytolysis was decreased in those cells expressing the highest levels of TfR, while cells expressing the lowest level of TfR were lysed to the greatest extent. Furthermore, pretreatment of target cells with, and the continued presence in the assay medium of, iron transferrin produced, in general, only a slight decrease in cytolysis. Incubation of cells with apotransferrin also produced only a slight decrease in cytolysis, while incubation with zinc transferrin produced a greater decrease in cytolysis. This latter effect was particularly dramatic for cells that had been exposed previously to either a 60 Hz magnetic field alone (1.0 gauss) or to a combined electric + magnetic field (current density 300 mA/m2, 1.0 gauss). In addition to indicating a discordance between TfR expression on target cells and their sensitivity to NK cell cytolysis, the data presented provide a further indication of cellular membrane changes produced by exposure to 60 Hz electromagnetic fields.

Electromagnetic fields and public health.

A review of the literature is provided for the topic of health-related research and power frequency electromagnetic fields. Minimal evidence for concern is present on the basis of animal and plant research. General observation would accord with the implication that there is no single and manifest health effect as the result of exposure to these fields. There are persistent indications, however, that these fields have biologic activity, and consequently, there may be a deleterious component to their action, possibly in the presence of other factors. Power frequency electromagnetic field exposures are essentially ubiquitous in modern society, and their implications in the larger perspective of public health are unclear at this time. Electromagnetic fields represent a methodological obstacle for epidemiologic studies and a quandary for risk assessment; there is need for more data.

Mortality in workers exposed to electromagnetic fields.

In an occupational mortality analysis of 486,000 adult male death records filed in Washington State in the years 1950-1982, leukemia and the non-Hodgkin's lymphomas show increased proportionate mortality ratios (PMRs) in workers employed in occupations with intuitive exposures to electromagnetic fields. Nine occupations of 219 were considered to have electric or magnetic field exposures. These were: electrical and electronic technicians, radio and telegraph operators, radio and television repairmen, telephone and power linemen, power station operators, welders, aluminum reduction workers, motion picture projectionists and electricians. There were 12,714 total deaths in these occupations. Eight of the nine occupations had PMR increases for leukemia [International Classification of Diseases (ICD), seventh revision 204] and seven of the nine occupations had PMR increases for the other lymphoma category (7th ICD 200.2, 202). The highest PMRs were seen for acute leukemia: (67 deaths observed, 41 deaths expected; PMR 162), and in the other lymphomas (51 deaths observed, 31 deaths expected; PMR 164). No increase in mortality was seen for Hodgkin's disease or multiple myeloma. These findings offer some support for the hypothesis that electric and magnetic fields may be carcinogenic.

Effects of noise and electromagnetic fields on reproductive outcomes.

Much public health research has been directed to studies of cancer risks due to chemical agents. Recently, increasing attention has been given to adverse reproductive outcomes as another, shorter-term biologic indicator of public health impact. Further, several low-level ubiquitous physical agents have been implicated recently as possibly affecting human health. These physical factors (noise and electromagnetic fields) represent difficult topics for research with epidemiologic study methods. This paper provides a brief review of the published data related to the risk of adverse reproductive outcomes and exposure to noise or electromagnetic fields. The discussion includes ideas for possible biologic mechanisms, considerations for exposure assessment, and suggestions for epidemiologic research.

Cancer incidence among welders: possible effects of exposure to extremely low frequency electromagnetic radiation (ELF) and to welding fumes.

Epidemiological studies of cancer incidence among welders disclose a pooled total of 146 cases of leukemia observed versus 159.46 expected, a risk ratio of 0.92, and 40 cases of acute leukemia observed versus 43.39 expected, a risk ratio of 0.92. For respiratory tract cancer, the pooled total is 1789 cases observed versus 1290.7 expected, a risk ratio of 1.39. Most electric welders are exposed to extremely low frequency electromagnetic radiation (ELF) (magnetic flux densities of up to 100,000 microT), a suspected leukemogen, and to concentrated metallic aerosols (up to 200 mg/m3), which can contain the putative respiratory tract carcinogens Cr(VI) and Ni. The two exposures are usually coincident, since welding with an electric current produces welding fumes. The observation of an excess risk for respiratory tract cancer strongly suggests significant exposure both to fumes and to ELF. The absence of increased risk for all leukemia or for acute leukemia among ELF-exposed welders does not support the hypothesis that the observed excess risk for leukemia or acute leukemia among workers in the electrical trades is due to their ELF exposure, which on the average is lower than that of welders.

Proportionality of 60-Hz electric field bioeffect severity to average induced transmembrane potential magnitude in a root model system.

The postulate that electric field-induced bioeffects in the root model system are related to the induction of 60-Hz transmembrane potentials (Vim) was quantitatively tested. Root segment growth rate data and the calculated mean 60-Hz Vim which would arise in the cortical cells of a segment under specified exposure conditions were subjected to regression analysis. Statistically significant correlations between segmental growth rate and segmental-average Vim were obtained using data analyzed (1) within species at a constant applied field strength, (2) within species and pooled across field exposures, and (3) pooled across both species and exposures. In C. sativus roots, segmental growth is inhibited when segmental-average Vim attain a value of 3.4-3.6 mV. In C. maxima roots, growth inhibition occurs when Vim attain or exceed 2.3-2.7 mV. Segmental growth cessation is predicted to occur when segmental-average Vim exceed 7-9 mV.

DNA repair after gamma irradiation in lymphocytes exposed to low-frequency pulsed electromagnetic fields.

The effect of exposure to extremely low-frequency pulsed electromagnetic fields (EMFs) on DNA repair capability and on cell survival in human lymphocytes damaged in vitro with gamma rays was studied by two different micromethods. In the first assay, which measures DNA repair synthesis (unscheduled DNA synthesis, UDS), lymphocyte cultures were stimulated with phytohemagglutinin (PHA) for 66 h and then treated with hydroxyurea (which blocks DNA replication), irradiated with 100 Gy of 60Co, pulsed with [3H]thymidine ([3H]TdR), and then exposed to pulsed EMFs for 6 h (the period in which cells repaired DNA damage). In the second assay, which measures cell survival after radiation or chemical damage, lymphocytes were first irradiated with graded doses of gamma rays or treated with diverse antiproliferative agents, and then stimulated with PHA, cultured for 72 h, and pulsed with [3H]TdR for the last 6 h of culture. In this case, immediately after the damage induced by either the radiation or chemicals, cultures were exposed to pulsed EMFs for 72 h, during which cell proliferation took place. Exposure to pulsed EMFs did not affect either UDS or cell survival, suggesting that this type of nonionizing radiation--to which humans may be exposed in the environment, and which is used for both diagnostic and therapeutic purposes--does not affect DNA repair mechanisms.

Magnetic field exposure related to cancer subtypes.

Certain subtypes of cancer (notably nervous system cancer) showed an association with two indices of exposure to 60-Hz alternating magnetic fields (AMFs): Subtype similarities were seen in those people potentially exposed to AMFs by their occupations, and in those potentially exposed by high-current power lines near their homes. The incidence-age patterns observed in exposed and nonexposed groups suggest that prolonged AMF exposure may act as a cancer promoter.

Influence of power frequency electric and magnetic fields on human health.

Several reports have appeared in the last ten years in which the authors suggest an association between cancer/leukemia and exposure to electric and magnetic fields in the workplace or in the vicinity of distribution lines from overhead transmission systems. Several of these reports are reviewed and critiqued. The reports of clinical effects of electric and/or magnetic fields among human populations present serious difficulties which stem from the many publications in which pertinent material is not presented, and the data are variable or internally inconsistent. The reports presented so far are not very probing. The numbers of subjects are small, the epidemiologic methodologies are often weak, measurements of intensity of field are absent, and the statistical analyses utilized are not always appropriate. Although suggestive associations of electric/magnetic fields and cancer or leukemia have been made, no one has established a causal relationship between these fields and cancer or leukemia. All the reports on human exposure have numerous deficiencies which include: lack of or imprecise measurements of electric or magnetic field intensities, questionable subject identification, lack of statistical significance, confounding with uncontrolled variables such as socioeconomic differences, smoking, X rays, drugs, population mobility, and the unreliability of occupational classification. Nevertheless the possibility of a link between leukemia and cancer and exposure to electric and magnetic fields has been raised and only responsible research can refute or confirm these reports.

Exposure of rhesus monkeys to 20 000 G steady magnetic field: effect on blood parameters.

Sixteen monkeys were used in a study to determine the effects, or noneffects, of exposure to a steady magnetic field of 2 T (20 000 G). Arterial and venous blood samples were taken before, immediately after, and several weeks following the test. Blood gas analyses were made of arterial samples, and hemotologic cell data and Technicon SMAC analyses were made of venous samples. Differential and absolute white blood cell counts of segmented neutrophils and lymphocytes were considerably changed during the test, even for monkeys which were not exposed to the magnetic field. These changes have also been observed in monkeys whose environment and daily routine are modified appreciably. Eight of the 16 monkeys were tested twice: first, in the magnet with the magnet turned on, and second, two months later, in the magnet, but with the magnet turned off. A large superconducting magnet (0.63 m i. d. and 1.85 m long warm-air bore) was used, which accommodated two monkeys at one time. Paired-t tests of 45 blood parameters showed no significant differences between the two tests. Exposure to a gradient field compared with exposure to a uniform magnetic field showed no significant differences.

Effect of nuclear magnetic resonance on chromosomes of mouse bone marrow cells.

Three groups of six male Balb/c mice, subjected to 30 MHz continuous wave NMR exposure in a static magnetic field of 7.05 K Gauss for one hour, were each compared to another group of ten unexposed mice with respect to chromatid and chromosomal aberrations. The exposed groups were sacrificed at two hours, 24 hours and 48 hours following NMR exposure respectively. Control mice were sacrificed 24 hours after sham-exposure. All groups had approximately 0.02 apparent aberrations per cell. These apparent aberrations were in the form of metacentric chromosomes, possibly resulting from a union of chromosomes at their centromeres or possibly simply chromosomes in association. The results are consistent with earlier in vitro findings that NMR exposure causes no adverse cytogenetic effects.

Potential hazards of NMR imaging. No evidence of the possible effects of static and changing magnetic fields on cardiac function of the rat and guinea pig.

Clinical proton NMR imaging uses magnetic field strengths in the range 0.1 to 0.5 T. In addition to the large static magnetic field, patients are exposed to magnetic field gradients during imaging and under extreme conditions, such as power failure or quenching, the field may collapse precipitously. A potential source of hazard to patients under these conditions is the induction of thoracic currents which may trigger ventricular fibrillation. In the present experiments, a 0.16 T resistive magnet with a time constant of 60 ms, powered by a programmable power supply, was used to examine any possible effects of static and changing magnetic field on the ECG and arterial blood pressure of anesthetized rats and guinea pigs. Animals were exposed to the following field conditions: static fields of 0.16 T; sine, triangular, and square wave modulated fields from 0.1 to 2 Hz; rapid field switches in excess of 2.0 T/s for 25 ms timed to occur at different stages of the cardiac cycle, including the vulnerable period during ventricular repolarization; and AC fields of 50 Hz. No change was observed in the blood pressure, heart rate, or ECG under any of the field conditions examined.

Absence of mutagenic response to radiation from a video display terminal.

The standard Ames Salmonella test (TA 100) was used to detect the mutagenicity of radiation from a video display terminal. The Ames test is a sensitive assay that detects the ability of a chemical to damage deoxyribonucleic acid. It has also been employed to detect the mutagenicity of electromagnetic radiation. An extremely short distance (62 mm) from a video display terminal and an extremely high electrostatic field strength (250 kv/m) was employed. No mutagenic response was found in this test system.

Exposure to low-frequency electromagnetic fields--a health hazard?

Several epidemiologic studies indicate an association between exposure to low-frequency electromagnetic fields and certain types of cancer. However, there is no solid evidence from current experimental studies to support the hypothesis of carcinogenicity. Further research is needed, and in the present extended abstract Swedish epidemiologic studies projected for the future are briefly outlined. The studies will be time-consuming and will involve high costs. However, we anticipate that within the next four years the approach described will contribute significantly to knowledge about the possible health hazards caused by electromagnetic fields.

[Protection of personnel exposed to very high frequency electromagnetic fields (author's transl)]. / Protection du personnel exposé à des champs électromagnétiques de très haute fréquence.

After a short review of biological effects of non-ionising electromagnetic radiations, their pathological effects are examined, insisting on methods usable to gain informations. Techniques used for field surveys are studied with definition of various irradiation classes. Then protection methods are dealt with, either individual or global, together with medical surveillance.

[Chromosome studies of personnel exposed to electromagnetic radiation at radar centers]. / Indagini cromosomiche sul personale esposto a radiazioni elettromagnetiche che opera nei centri radar

The possibility that chromosome alterations take place in personnel exposed to electromagnetic radiation in radar centres has been studied. The study was carried out "blind" on short-term cultures of peripheral blood, some 450 metaphases being analysed for each case. No aberrations were found in either radar operators or controls and there was no statistically significant difference between them.

Effects of high-intensity power-frequency electric fields on implanted modern multiprogrammable cardiac pacemakers.

The effect on an implanted, multiprogrammable pacemaker of power-frequency (50 Hz) electric fields up to an intensity (unperturbed value measured at 1.7 m) of 20 kV/m were assessed in ten paced patients. Radiotelemetric monitoring of the electrocardiogram allowed supervision of the electrocardiogram throughout exposure to the alternating electric field. Displacement body currents of up to 300µA were achieved depending on the position and height of the patient. None of the pacemakers was inhibited, triggered or reverted to fixed rate operation during the exposure. The programmable functions, programmability or output characteristics were not affected. Small changes in cardiac rate and rhythm elicited the correct pacemaker responses. Unlike earlier models of pacemaker, this modern implanted pacemaker, which represents `the state of the art', is not affected by 50 Hz electric fields likely to be encountered when standing underneath power lines.

Extremely low frequency electromagnetic emissions from video display terminals and other devices.

Video display terminals (VDTs) are in widespread use and can be found in practically every modern office. Assessment of possible health effects of electromagnetic emissions from these devices is necessary. The intensity of the magnetic field and the frequency spectrum of the emissions at extremely low frequencies (ELF) (5-500 Hz) were measured for a few VDTs and compared with the background field intensities and emissions from other devices. The emissions in the frequency range investigated are of such low intensities that they are very unlikely to have any biological effects, let alone represent a health hazard.

Effect of electromagnetic interference by neonatal transport equipment on aircraft operation.

The number of civilian air ambulance services operating in the United States has been steadily increasing. The quantity and sophistication of electronic equipment used during neonatal transport have also increased. All medical equipment generates some electromagnetic interference (EMI). Excessive EMI can interfere with any of an aircraft's electrical systems, including navigation and communications. The United States military has strict standards for maximum EMI in transport equipment. Over the past 15 years, approximately 70% of neonatal transport monitors, ventilators, and incubators have failed testing due to excessive EMI. As neonatal transport equipment becomes more sophisticated, EMI is increased, and there is greater potential for aircraft malfunction. The Federal Aviation Administration should develop civilian standards for acceptable EMI, civilian aircraft operators must be aware of the possible dangers of excessive EMI, and equipment which does not meet future FAA standards should not be purchased.

Mechanisms of biological effects of radiofrequency electromagnetic fields: an overview.

Manmade sources of electromagnetic (EM) fields, and therefore human exposures to them, continue to increase. Public concerns stem from the effects reported in the literature, the visibility of the sources, and somewhat from confusion between EM fields and ionizing radiation. Protecting humans from the real hazards and allaying groundless fears requires a self-consistent body of scientific data concerning effects of the fields, levels of exposures which cause those effects, and which effects are deleterious (or beneficial or neutral). With that knowledge, appropriate guidelines for safety can be devised, while preserving the beneficial uses of radiofrequency radiation (RFR) energy for military or civilian purposes. The task is monumental because of the large and growing number of biological endpoints and the infinite array of RFR exposure conditions under which those endpoints might be examined. The only way to reach this goal is to understand the mechanisms by which EM fields interact with tissues. As in other fields of science, a mechanistic understanding of RFR effects will enable scientists to generalize from a selected few experiments to derive the "laws" of RFR bioeffects. This article gives an overview of present knowledge of those mechanisms and the part that the USAF School of Aerospace Medicine has played in expanding that knowledge.