Power frequency magnetic fields and risk of childhood leukaemia: Misclassification of exposure from the use of the ‘distance from power line’ exposure surrogate

A recent study examining the relationship between distance to nearby power lines and childhood cancer risk re‐opened the debate about which exposure metrics are appropriate for power frequency magnetic field investigations. Using data from two large population‐based UK and German studies we demonstrate that distance to power lines is a comparatively poor predictor of measured residential magnetic fields. Even at proximities of 50 m or less, the positive predictive value of having a household measurement over 0.2 µT was only 19.4%. Clearly using distance from power lines, without taking account of other variables such as load, results in a poor proxy of residential magnetic field exposure. We conclude that such high levels of exposure misclassification render the findings from studies that rely on distance alone uninterpretable. Bioelectromagnetics 30:183–188, 2009. © 2008 Wiley‐Liss, Inc.     

0.2 T magnetic field inhibits angiogenesis in chick embryo chorioallantoic membrane

Inhibition of angiogenesis is a major target in the fight against cancer and other diseases. Although the effects of static magnetic fields on cancer development and cell growth have been investigated, effects on angiogenesis have received no attention so far. In this study we report the effects on angiogenesis of exposure to 0.2 T static magnetic field. Angiogenesis was analyzed using the chick embryo chorioallantoic membrane assay. Exposure to 0.2 T static magnetic field was achieved by placing the eggs for 3 hr in the isocentre of the magnet of a sectorial magnetic resonance tomograph used in clinical practice. In sham exposed specimens treated with phosphate buffered saline (negative control), no significant vascular reaction was detectable; 3 hr exposure to 0.2 T static magnetic field did not affect the basal pattern of vascularization or chick embryo viability. Prostaglandin E1 and fetal calf serum elicited a strong angiogenic response in sham exposed eggs. This angiogenic response was significantly inhibited by 3 hr exposure to 0.2 T static magnetic field. These findings point to possible use of static magnetic field in inhibiting angiogenesis; this effect could be exploited for treatment of cancer and other diseases where excessive angiogenesis is involved.     

Occupational exposure to magnetic fields from transformer stations and electric enclosures in Turkey

We aimed to provide a systematic evaluation of magnetic field (MF) exposure of staff working in the offices located above or close to transformer stations (TS) and electric enclosures (EE). Occupational short-term “spot” measurements with Narda EFA-300 and isotropic magnetic field probe were carried out in two National Banks and one Industrial Company having more than 500 employees. Extremely low-frequency (ELF) MFs up to several tens of μT were measured in the mentioned working environments. 25% of the measured MFs were found less than 0.3 μT, the background exposure level that staff receive at home, 75% were above 0.3 μT with the highest value of 6.8 μT. The mean and median personal exposures were calculated to be 1.19 μT and 0.56 μT, respectively. Most of the staff (83%) is under risk based on epidemiological studies that reported a statistically significant association between risk of leukemia and averaged magnetic fields of 0.2 μT or over. Results showed that risk evaluation should be considered to minimize the possibility of the workers being harmed due to exposure to work-related electromagnetic sources.     

Hypothesis: The risk of childhood leukemia is related to combinations of power-frequency and static magnetic fields

We present a hypothesis that the risk of childhood leukemia is related to exposure to specific combinations of static and extremely-low-frequency (ELF) magnetic fields. Laboratory data from calcium efflux and diatom mobility experiments were used with the gyromagnetic equation to predict combinations of 60 Hz and static magnetic fields hypothesized to enhance leukemia risk. The laboratory data predicted 19 bands of the static field magnitude with a bandwidth of 9.1 μT that, together with 60 Hz magnetic fields, are expected to have biological activity. We then assessed the association between this exposure metric and childhood leukemia using data from a case-control study in Los Angeles County. ELF and static magnetic fields were measured in the bedrooms of 124 cases determined from a tumor registry and 99 controls drawn from friends and random digit dialing. Among these subjects, 26 cases and 20 controls were exposed to static magnetic fields lying in the predicted bands of biological activity centered at 38.0 μT and 50.6 μT. Although no association was found for childhood leukemia in relation to measured ELF or static magnetic fields alone, an increasing trend of leukemia risk with measured ELF fields was found for subjects within these static field bands (P for trend = 0.041). The odds ratio (OR) was 3.3 [95% confidence interval (CI) = 0.4–30.5] for subjects exposed to static fields within the derived bands and to ELF magnetic field above 0.30 μT (compared to subjects exposed to static fields outside the bands and ELF magnetic fields below 0.07 μT). When the 60 Hz magnetic fields were assessed according to the Wertheimer-Leeper code for wiring configurations, leukemia risks were again greater with the hypothesized exposure conditions (OR = 9.2 for very high current configurations within the static field bands: 95% CI = 1.3–64.6). Although the risk estimates are based on limited magnetic field measurements for a small number of subjects, these findings suggest that the risk of childhood leukemia may be related to the combined effects of the static and ELF magnetic fields. Further tests of the hypothesis are proposed. © 1995 Wiley-Liss, Inc.     

Cortex reorganization of <Emphasis Type="Italic">Xenopus laevis</Emphasis>eggs in strong static magnetic fields

Observations of magnetic field effects on biological systems have often been contradictory. For amphibian eggs, a review of the available literature suggests that part of the discrepancies might be resolved by considering a previously neglected parameter for morphological alterations induced by magnetic fields – the jelly layers that normally surround the egg and are often removed in laboratory studies for easier cell handling. To experimentally test this hypothesis, we observed the morphology of fertilizable Xenopus laevis eggs with and without jelly coat that were subjected to static magnetic fields of up to 9.4 T for different periods of time. A complex reorganization of cortical pigmentation was found in dejellied eggs as a function of the magnetic field and the field exposure time. Initial pigment rearrangements could be observed at about 0.5 T, and less than 3 T are required for the effects to fully develop within two hours. No effect was observed when the jelly layers of the eggs were left intact. These results suggest that the action of magnetic fields might involve cortical pigments or associated cytoskeletal structures normally held in place by the jelly layers and that the presence of the jelly layer should indeed be included in further studies of magnetic field effects in this system.     

Correlations among indices of electric and magnetic field exposure in electric utility workers

Power-frequency electric and magnetic fields are known to exhibit marked temporal variation, yet in the absence of clear biological indications, the most appropriate summary indices for use in epidemiologic studies are unknown. In order to assess the statistical patterns among candidate indices, data on 4383 worker-days for magnetic fields and 2082 worker-days for electric fields collected for the Electric and Magnetic Field Project for Electric Utilities using the EMDEX meter [Bracken (1990): Palo Alto, CA: Electric Power Research Institute] were analyzed. We examined correlations at the individual and job title group levels among indices of exposure to both electric and magnetic fields, including the arithmetic mean, geometric mean, median, 20th and 90th percentiles, time above lower cutoffs of 20 V/m and 0.2 μT, and time above higher cutoffs of 100 V/m and 2.0 μT. For both electric and magnetic fields, the arithmetic mean was highly correlated with the 90th percentile; moderately correlated with the geometric mean, median, and lower and higher cutoff scores; and weakly correlated with the 20th percentile. Electric and magnetic field indices were generally weakly correlated with one another. Rank-order correlation coefficients were consistently greater than product-moment correlation coefficients. Job title group summary scores showed higher correlations among electric field indices and magnetic field indices and between electric and magnetic field indices than was found for individual worker-days, with only the 20th percentile clearly independent of the others. These results suggest that individuals' exposures are adequately characterized by a measure of central tendency for electric and magnetic fields, such as the arithmetic or geometric mean, and an indicator of a lower threshold or cutoff for each field type, such as the 20th percentile or proportion of time above 20 V/m or 0.2 μT. A single measure of central tendency for each type of field appears to be adequate when exposures are assessed at the job title level. © 1994 Wiley-Liss, Inc.     

Magnetic field direction differentially impacts the growth of different cell types

Magnetic resonance imaging (MRI) machines have horizontal or upright static magnetic field (SMF) of 0.1–3 T (Tesla) at sites of patients and operators, but the biological effects of these SMFs still remain elusive. We examined 12 different cell lines, including 5 human solid tumor cell lines, 2 human leukemia cell lines and 4 human non-cancer cell lines, as well as the Chinese hamster ovary cell line. Permanent magnets were used to provide 0.2–1 T SMFs with different magnetic field directions. We found that an upward magnetic field of 0.2–1 T could effectively reduce the cell numbers of all human solid tumor cell lines we tested, but a downward magnetic field mostly had no statistically significant effect. However, the leukemia cells in suspension, which do not have shape-induced anisotropy, were inhibited by both upward and downward magnetic fields. In contrast, the cell numbers of most non-cancer cells were not affected by magnetic fields of all directions. Moreover, the upward magnetic field inhibited GIST-T1 tumor growth in nude mice by 19.3% (p < 0.05) while the downward magnetic field did not produce significant effect. In conclusion, although still lack of mechanistical insights, our results show that different magnetic field directions produce divergent effects on cancer cell numbers as well as tumor growth in mice. This not only verified the safety of SMF exposure related to current MRI machines but also revealed the possible antitumor potential of magnetic field with an upward direction.     

Occupational exposure to magnetic fields from transformer stations and electric enclosures in Turkey

We aimed to provide a systematic evaluation of magnetic field (MF) exposure of staff working in the offices located above or close to transformer stations (TS) and electric enclosures (EE). Occupational short-term "spot" measurements with Narda EFA-300 and isotropic magnetic field probe were carried out in two National Banks and one Industrial Company having more than 500 employees. Extremely low-frequency (ELF) MFs up to several tens of μT were measured in the mentioned working environments. 25% of the measured MFs were found less than 0.3?μT, the background exposure level that staff receive at home, 75% were above 0.3?μT with the highest value of 6.8?μT. The mean and median personal exposures were calculated to be 1.19?μT and 0.56?μT, respectively. Most of the staff (83%) is under risk based on epidemiological studies that reported a statistically significant association between risk of leukemia and averaged magnetic fields of 0.2?μT or over. Results showed that risk evaluation should be considered to minimize the possibility of the workers being harmed due to exposure to work-related electromagnetic sources.     

3D Magnetopneumography Magnetic Dipole Model and Its Application Using Fluxgate Gradiometers

Magnetopneumography (MPG) as a non‐invasive method for pneumoconiosis diagnosis has been developed to evaluate the load and spatial distribution of particles within the human lungs through scanning of remanent magnetic fields after magnetization of the subject in a strong direct current field. The measurement of particle spatial distribution is very important for pneumoconiosis diagnosis because localized deposits may be associated with some pathological changes such as pulmonary fibrosis. Previous research found that loads of magnetite particles were proportional to their magnetic dipole moments. The three‐dimensional (3D) MPG magnetic dipole model (MDM) proposed in this paper and based on Biot–Savart Law and matrix manipulation provides a means of precise measurement of the particle distribution and load amount. A styrofoam + magnetite powder phantom with magnetization was laid on a nonmagnetic board. Two first‐order fluxgate gradiometers with 10^–12 T sensitivity were coaxially applied over and under the phantom and used for scanning remanent magnetic fields. This paper provides validation results using 3D MPG MDM through two experiments. The overall error of the simulation results is 0.2–2.7% in the center and 7.28–9.42% in the corners of the subject. Finally, this paper gives clinical experiments with a welder suffering stage‐II pneumoconiosis and states that the 3D MPG MDM shows similar results to X‐ray chest films in pneumoconiosis diagnosis. The results suggest that the 3D MPG MDM is potentially a reasonable and accurate algorithmic model to inversely track the load amount and distribution of magnetite particles within the lungs. Bioelectromagnetics. 2019;40:472–487. © 2019 Wiley Periodicals, Inc     

Magnetic field effects on assembly pattern of smooth muscle cells

Summary Under a strong magnetic field, the diamagnetic, properties of biological cells modulate the behavior of the cells themselves, under conditions of both floating and adherence. The morphological effects of strong static magnetic fields on adherent cells are less well understood than the effects of magnetic fields on red blood cells. In the present study, a high-intensity magnetic field of 14 T affected the morphology of smooth muscle cell assemblies, and the shapes of the cell colonies extended along the direction of the magnetic flux. The phenomenon was most notable, under magnetic fields of more than 10 T, where an ellipsoidal pattern of smooth muscle cell colonies was clearly observed. The ellipticity of the cell colony pattern with a 14-T magnetic field was 1.3, whereas that with a field of 0–8 T was close to a circle at about 1.0. The evidence that smooth muscle cells detect high-density magnetic flux and thus change their cell orientation was shown as a visible pattern of cellular colonies. The speculated mechanism is a diamagnetic torque force acting on cytoskeleton fibers, which are dynamically polymerizing-depolymerizing during cell division and cell migration.     

Myotube orientation using strong static magnetic fields

In this experiment, we evaluated the effects of strong static magnetic fields (SMF) on the orientation of myotubes formed from a mouse-derived myoblast cell line, C2C12. Myogenic differentiation of C2C12 cells was conducted under exposure to SMF at a magnetic flux density of 0-10 T and a magnetic gradient of 0-41.7 T/m. Exposure to SMF at 10 T led to significant formation of oriented myotubes. Under the high magnetic field gradient and a high value of the product of the magnetic flux density and magnetic field gradient, myotube orientation increased as the myogenic differentiation period increased. At the 3 T exposure position, where there was a moderate magnetic flux density and moderate magnetic field gradient, myotube orientation was not observed. We demonstrated that SMF induced the formation of oriented myotubes depending on the magnetic flux density, and that a high magnetic field gradient and a high value of the product of the magnetic flux density and magnetic field gradient induced the formation of oriented myotubes 6 days after myogenic differentiation. We did not detect any effect of the static magnetic fields on myogenic differentiation or cell number. To the best of our knowledge, this is the first report to demonstrate that myotubes orient to each other under a SMF without affecting the cell number and myogenic differentiation.     

The buoyancy-providing role of gas vacuoles in an aerobic bacterium

The heterotrophic, freshwater bacterium Prosthecomicrobium pneumaticum Staley possesses sufficient gas vacuoles to render it buoyant at all stages of growth. Although the cells have a turgor pressure of about 300 kPa, there is no evidence that this pressure is important in causing collapse of the constituent gas vesicles. A mutant of the bacterium, which produced only 0.2% of the amount of gas vacuoles produced by the wild type, was isolated. It always sank in liquid culture. Wild type and mutant bacteria grew at the same rate in shaken culture, but in static culture the wild type, which floated to the liquid surface grew more quickly than the mutant, which sank. Other competition experiments suggested that the advantage gained in floating at the surface was simply that oxygen was more readily available there to this obligate aerobe. Similar advantages may benefit gas vacuolate forms in natural habitats.A second mutant was isolated which produced about 40% fewer gas vacuoles than the wild type in corresponding stages of growth, insufficient to provide buoyancy, and unlikely to be of selective value. The occurrence of this mutant suggests there may be duplication of the gas vacuole gene.Abbreviations T turbidity - PST pressure sensitive turbidity - kPa kilo-Pascals (100 kPa=1 bar)     

Detection of intracellular macromolecule behavior under strong magnetic fields by linearly polarized light

Strong static magnetic fields on the order of 10 T have a diamagnetic force on cell components and generate a clear alignment of a smooth muscle cell assembly, parallel to the direction of the magnetic fields within an exposure period of 3 days. This work shows the effects of diamagnetic torque forces on cell component motion. Linearly polarized light was utilized to detect the displacement of intracellular macromolecules. The polarized light passed through a mass of cells in a magnetic field, and transmission of the light increased and reached a plateau 2 h after the beginning of magnetic field exposure at 14 T. However, no distinct change was observed in transmission of the light under zero magnetic field exposure. The change in polarized light intensity through the lamellar cell assembly under magnetic fields corresponds to behavioral changes in cell components. It was speculated that intracellular macromolecules rotated and showed a displacement due to diamagnetic torque forces during 2-3 h of magnetic field exposure at 14 T.     

Magnetic Susceptibility Difference-Induced Nucleus Positioning in Gradient Ultrahigh Magnetic Field

Despite the importance of magnetic properties of biological samples for biomagnetism and related fields, the exact magnetic susceptibilities of most biological samples in their physiological conditions are still unknown. Here we used superconducting quantum interferometer device to detect the magnetic properties of nonfixed, nondehydrated live cell and cellular fractions at a physiological temperature of 37°C (310 K). It is obvious that there are paramagnetic components within human nasopharyngeal carcinoma CNE-2Z cells. More importantly, the magnetic properties of the cytoplasm and nucleus are different. Although within a single cell, the magnetic susceptibility difference between cellular fractions (nucleus and cytoplasm) could only cause ∼41–130 pN forces to the nucleus by gradient ultrahigh magnetic fields of 13.1–23.5 T (92–160 T/m), these forces are enough to cause a relative position shift of the nucleus within the cell. This not only demonstrates the importance of magnetic susceptibility in the biological effects of magnetic field but also illustrates the potential application of high magnetic fields in biomedicine.     

Role of exchange and dipolar interactions in the radical pair model of the avian magnetic compass

It is not yet understood how migratory birds sense the Earth's magnetic field as a source of compass information. One suggestion is that the magnetoreceptor involves a photochemical reaction whose product yields are sensitive to external magnetic fields. Specifically, a flavin-tryptophan radical pair is supposedly formed by photoinduced sequential electron transfer along a chain of three tryptophan residues in a cryptochrome flavoprotein immobilized in the retina. The electron Zeeman interaction with the Earth's magnetic field (∼50 μT), modulated by anisotropic magnetic interactions within the radicals, causes the product yields to depend on the orientation of the receptor. According to well-established theory, the radicals would need to be separated by >3.5 nm in order that interradical spin-spin interactions are weak enough to permit a ∼50 μT field to have a significant effect. Using quantum mechanical simulations, it is shown here that substantial changes in product yields can nevertheless be expected at the much smaller separation of 2.0 ± 0.2 nm where the effects of exchange and dipolar interactions partially cancel. The terminal flavin-tryptophan radical pair in cryptochrome has a separation of ∼1.9 nm and is thus ideally placed to act as a magnetoreceptor for the compass mechanism.     

Inhibitory effects of a gradient static magnetic field on normal angiogenesis

Angiogenesis, the formation of new blood vessels, is critical in many normal and pathological processes such as development, reproduction, tumor growth, and metastasis. Recently, exposure to moderate‐intensity static magnetic fields (1 mT to 1 T) has attracted much attention for its potential therapeutic value as a noninvasive intervening method. Nevertheless, the effects of moderate‐intensity and spatial gradient static magnetic fields (GSMF) on angiogenesis have not received enough attention. In this study, the effects of GSMF (0.2–0.4 T, 2.09 T/m, 1–11 days) on angiogenesis were investigated both in vitro and in vivo. An MTT assay was used as an in vitro method to detect the proliferation ability of human umbilical veins endothelial cells (HUVECs). Two kinds of in vivo models, a chick chorioallantoic membrane (CAM) and a matrigel plug, were used to detect the effects of GSMF on angiogenesis. The results showed that the proliferation ability of HUVECs was significantly inhibited 24 h after the onset of exposure. With regard to the CAM model, vascular numbers in the CAM that was continuously exposed to the GSMF were all less than those in normal condition. In accordance with the gross appearance, the contents of hemoglobin in the models exposed to GSMF for 7–9 days were also less. In addition, similar to the CAM model, the results of vascular density and hemoglobin contents in the matrigel plug also demonstrated that the GSMF exposure for 7 or 11 days inhibited vascularization. These findings indicate that GSMF might inhibit or prevent new blood vessels formation and could be helpful for the treatment of some diseases relevant to pathological angiogenesis. Bioelectromagnetics 30:446–453, 2009. © 2009 Wiley‐Liss, Inc.     

Safety concerns related to magnetic field exposure

The recent development of superconducting magnets has resulted in a huge increase in human exposure to very large static magnetic fields of up to several teslas (T). Considering the rapid advances in applications and the great increases in the strength of magnetic fields used, especially in magnetic resonance imaging, safety concerns about magnetic field exposure have become a key issue. This paper points out some of these safety concerns and gives an overview of the findings about this theme, focusing mainly on mechanisms of magnetic field interaction with living organisms and the consequent effects.     

Exposure of children to residential magnetic fields in Norway: Is proximity to power lines an adequate predictor of exposure?

The aim of this work was to study the exposure to magnetic fields of children living at different distances from a power line and to evaluate how well theoretical calculations compared with actual exposure. Personal exposure instruments were carried for 24 h by 65 schoolchildren living 28–325 m from a 300 kV transmission line; the current load was 200–700 A. About half of the children attended a school far from the power line, whereas the other half attended a school located about 25 m from the line. Exposure to magnetic fields was analyzed for three categories of location: at home, at school, and at all other places. Time spent in bed was analyzed separately. The results indicated that children who lived close to a power line had a higher magnetic field exposure than other children. The power line was the most important source of exposure when the magnetic field due to the line was greater than about 0.2 μT. Exposure at school influenced the 24 h time-weighted average results considerably in those cases where the distance between home and power line was very different from the distance between school and power line. The calculated magnetic field, based on line configuration, current load, and distance between home and power line, corresponded reasonably well with the measured field. However, the correlation depends on whether home only or 24 h exposure is used in the analysis and on which school the children attended. The calculated magnetic field seems to be a reasonably good predictor of actual exposure and could be used in epidemiological studies, at least in Norway, where the electrical system normally results in less ground current than in most other countries. Bioelectromagnetics 18:47–57, 1997. © 1997 Wiley-Liss, Inc.