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Blank and Goodman [(1997): Bioelectromagnetics 18:111-115] suggest that weak extremely low frequency (ELF) electric and magnetic fields affect intracellular DNA directly. We show that such a conclusion is not in accord with physical principles.
It is widely accepted that moderate levels of nonionizing electric or magnetic fields, for example 50/60 Hz magnetic fields of about 1 mT, are not mutagenic. However, it is not known whether such fields can enhance the action of known mutagens. To explore this question, a stringent experimental protocol, which included blinding and systematic negative controls, was implemented, minimizing the possibility of observer bias or experimental artifacts. As a model system, we chose to measure mutation frequencies induced by 2 Gy gamma rays in the redox-sensitive hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene in Chinese hamster ovary cells. We tested whether a 12-h exposure to a 60 Hz sinusoidally oscillating magnetic-flux density (Brms = 0.7 mT) could affect the mutagenic effects of ionizing radiation on the HPRT gene locus. We determined that the magnetic-field exposure induced an approximate 1.8-fold increase in HPRT mutation frequency. Additional experiments at Brms = 0.23 and 0.47 mT revealed that the effect was reduced at lower flux densities. The field exposure did not enhance radiation-induced cytotoxicity or mutation frequencies in cells not exposed to ionizing radiation. These results suggest that moderate-strength, oscillating magnetic fields may act as an enhancer of mutagenesis in mammalian cells.
Slices of rat hippocampus were exposed to 700 MHz continuous wave radiofrequency (RF) fields (25.2-71.0 V m(-1), 5-15 min exposure) in a stripline waveguide. At low field intensities, the predominant effect on the electrically evoked field potential in CA1 was a potentiation of the amplitude of the population spike by up to 20%, but higher intensity fields could produce either increases or decreases of up to 120 and 80%, respectively, in the amplitude of the population spike. To eliminate the possibility of RF-induced artefacts due to the metal stimulating electrode, the effect of RF exposure on spontaneous epileptiform activity induced in CA3 by 4-aminopyridine (50-100 microM) was investigated. Exposure to RF fields (50.0 V m(-1)) reduced or abolished epileptiform bursting in 36% of slices tested. The maximum field intensity used in these experiments, 71.0 V m(-1), was calculated to produce a specific absorption rate (SAR) of between 0.0016 and 0.0044 W kg(-1) in the slices. Measurements with a Luxtron fibreoptic probe confirmed that there was no detectable temperature change (+/- 0.1 degrees C) during a 15 min exposure to this field intensity. Furthermore, imposed temperature changes of up to 1 degrees C failed to mimic the effects of RF exposure. These results suggest that low-intensity RF fields can modulate the excitability of hippocampal tissue in vitro in the absence of gross thermal effects. The changes in excitability may be consistent with reported behavioural effects of RF fields.
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Back pain and the whiplash syndrome are very common diseases involving tremendous costs and extensive medical effort. A quick and effective reduction of symptoms, especially pain, is required. In two prospective randomized studies, patients with either lumbar radiculopathy in the segments L5/S1 or the whiplash syndrome were investigated. Inclusion criteria were as follows: either clinically verified painful lumbar radiculopathy in the segments L5/S1 and a Laségue's sign of 30 degrees (or more), or typical signs of the whiplash syndrome such as painful restriction of rotation and flexion/extension. Exclusion criteria were prolapsed intervertebral discs, systemic neurological diseases, epilepsy, and pregnancy. A total of 100 patients with lumbar radiculopathy and 92 with the whiplash syndrome were selected and entered in the study following a 1:1 ratio. Both groups (magnetic field treatment and controls) received standard medication consisting of diclofenac and tizanidine, while the magnetic field was only applied in group 1, twice a day, for a period of two weeks. In patients suffering from radiculopathy, the average time until pain relief and painless walking was 8.2 +/- 0.5 days in the magnetic field group, and 11.7 +/- 0.5 days in controls p < 0.04). In patients with the whiplash syndrome, pain was measured on a ten-point scale. Pain in the head was on average 4.6 before and 2.1 after treatment in those receiving magnetic field treatment, and 4.2/3.5 in controls. Neck pain was on average 6.3/1.9 as opposed to 5.3/4.6, and pain in the shoulder/arm was 2.4/0.8 as opposed to 2.8/2.2 (p < 0.03 for all regions). Hence, magnetic fields appear to have a considerable and statistically significant potential for reducing pain in cases of lumbar radiculopathy and the whiplash syndrome.
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A clamped homogeneous electric field (CHEF) electrophoresis allowing the separation of DNA molecules in the range of 200 to 3000 kb in size was used to study the biological effects of electric and magnetic fields (EMFs). The results obtained did not show any detectable genomic damage on Saccharomyces cerevisiae.
Rat embryos (9.5 days old) were exposed for up to 36 h to various radio frequency (RF) electric and magnetic fields (modulation frequency: 16, 60, 120 Hz; electric field strength: 60, 600 V/m; magnetic induction: 0.2, 2.0 microT). A resonator technique was used to generate standing waves thus fulfilling three conditions: The site of maximum electric and magnetic oscillations could be separated, the field strengths were known exactly and a high homogeneity over the sample volume was achieved. In each frequency region the transmitter power levels were set to give specific absorption rate (SAR) values spreading from far below to far above the values met in the field of telecommunication (0.2, 1.0 and 5.0 W/kg). The criteria used to examine the embryos on day 11.5 for possible structural effects consisted of a scoring system, photographs, histology using both light and electron microscopy and determination of the protein content. All these data have been taken as sets of different intermediate frequency (IF) amplitude modulation of the RF carriers. Neither the electric nor the magnetic fields tested interfered significantly with the normal growth and differentiation of the embryos in vitro.
A nationwide case-control study of childhood leukaemia in New Zealand included measurements of electric and magnetic fields in children's homes. There was no significant association between leukaemia and the time-weighted average of the 50 Hz magnetic or electric fields in the bedroom and living (or daytime) room combined.
A detailed examination of the scientific foundations contained in a number of recent articles has revealed some serious errors. The careful application of advanced mathematical-physical methods to study the penetration of externally applied electric fields into the organs and cells of the human body has obtained new and significant results [8, 9, 32]. Specifically, Eqs. (11) and (12) establish a definite relationship between an incident low-frequency electric field and the current, current density, and electric field induced in the body when the arms are in contact with it and the incident field is parallel to its length. Corresponding formulas with the arms raised are available [10] as are formulas for the current density and electric field in the organs of the body [9]. It is these currents and electric fields that must be used by biomedical research workers to determine their effect on living cells. The proposed interpretation of epidemiological data [31] indicates a risk of leukemia in children when the incident 50-60-Hz electric field generated by a high-voltage transmission line is Einc > or = 61 V/m. (23). The corresponding maximum electric field at approximately 10 m from a 440-kV transmission line is Einc approximately 2100 V/m [8, 9]. The electric fields induced in the different organs of the body by these electric fields are in the range 25.2 < or = E1z < or = 119 microV/m for Einc2z = 61 V/m and 0.87 < or = E1z < or = 4.1 mV/m for Einc2z = 2100 V/m [9]. These are in the range of applied fields in in vitro experiments, which showed significant effects on cells [4], and should serve as guidelines for such experiments.
Open magnetic resonance imaging (MRI) systems enable performing image-guided medical procedures for long periods of time very close to, or inside, the patient imaging area. Medical personnel can be exposed to relatively high static, gradient, and radiofrequency fields compared to most other MRI systems. The Committee on Man and Radiation of the Institute of Electrical and Electronics Engineers calculated or used existing data on magnetic flux densities and field strengths in or near the patient area to assess occupational exposure levels. Potential exposures to each field type were analyzed and compared to relevant values specified in international exposure limits including those of the Institute of Electrical and Electronics Engineers and the International Commission on Nonionizing Radiation Protection. Exposures of the head or torso of a worker to gradient fields near the center of the patient-imaging area can exceed most exposure limits even for times less than a second. Exposures to radiofrequency fields can exceed limits if sustained exposures (minutes or more) occur to parts of the body. Static magnetic fields used by present Open MRI systems are below exposure limits of all of the standards that address these fields. Overall results of this study suggest that manufacturers and others who program or operate Open MRI systems should take care to ensure that operating parameters produce exposures that comply with the relevant exposure limits. Also, since field levels fall off rapidly with increasing distance, user practices may be implemented that reduce exposures significantly.
In recent years some people expressed concern about possible health effects of electric and magnetic fields produced by exposure to extremely low frequency bands (ELF: less than 300 Hz). This was first mentioned by epidemiological studies. However, the epidemiological method has several limitations that are difficult to overcome. One problem is the detection of relationships when the risk ratios are relatively low. Another obstacle may be how to define 'strength' of magnetic or electric fields. In animal studies, there have been published several papers that melatonin was depressed by exposure to magnetic fields. Levels of photon energy at the ELF bands are extremely low, hence it provides difficulty how to elucidate the 'positive' experimental results in terms of biophysical mechanisms.
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We present the results of current epidemiological research on the association between ELF magnetic fields and neoplasm. ELF magnetic fields were considered as 'possibly carcinogenic to humans (Group 2B)' by IARC. The evidence was limited to childhood acute leukemia and to chronic leukemia (associated to occupational exposure) in adults.
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Rabbits with a fibular ostectomy were exposed for 28 days to magnetic fields that satisfied the ion resonance conditions for calcium or magnesium. The rabbits were exposed to whole body treatment for 1/2 hour, 3 hours, or 24 hours per day. The fibulae from the experimental and control animals were removed surgically and were subjected to force-deflection testing to establish the stiffness of the healed fracture. The fibulae from the rabbits exposed to the ion resonance magnetic fields were found to be 55-299% (p < 0.01) more robust than the fibulae from the control animals.
The purpose of this randomized double-blind cross-over study was to investigate whether a low-dosed pulsed low-frequency magnetic field or a high-dosed pulsed low-frequency magnetic field improves the cutaneous microcirculation and alters the temperature of the foot. Twelve healthy subjects (five women, seven men) aged on average 25.8 years participated in the trial. Based on a randomization list, one of the following three interventions was applied for 30 min through a cushion placed below the non-dominant foot: either a pulsed low-dosed magnetic field (100 uT, basic frequency 30 Hz with a frequency modulation) or a pulsed high-dosed magnetic field (8.4 mT, 10 Hz), or sham treatment. The individual treatment sessions were applied in intervals of one week, at the same time of the day. Cutaneous microcirculation (laser Doppler flowmetry) and temperature (infra-red thermovision) were measured in the dorsum of the foot and the great toe every 5 min during the intervention, and 5 and 10 min post-intervention. With both pulsed low-dosed magnetic field and pulsed high-dosed magnetic field, just as with the sham treatment, a minor drop in temperature and decrease in microcirculation took place. A two-way repeated-measures analysis of variance revealed no significant difference between the interventions for any parameter. It was concluded that a local application of a pulsed low-frequency magnetic field to the foot did not enhance temperature or cutaneous microcirculation in healthy subjects.