Intermediate Frequency Magnetic Fields Research Articles

Behavioral testing of mice exposed to intermediate frequency magnetic fields indicates mild memory impairment.

Human exposure to intermediate frequency magnetic fields (MF) is increasing due to applications like electronic article surveillance systems and induction heating cooking hobs. However, limited data is available on their possible health effects. The present study assessed behavioral and histopathological consequences of exposing mice to 7.5 kHz MF at 12 or 120 μT for 5 weeks. No effects were observed on body weight, spontaneous activity, motor coordination, level of anxiety or aggression. In the Morris swim task, mice in the 120 μT group showed less steep learning curve than the other groups, but did not differ from controls in their search bias in the probe test. The passive avoidance task indicated a clear impairment of memory over 48 h in the 120 μT group. No effects on astroglial activation or neurogenesis were observed in the hippocampus. The mRNA expression of brain-derived neurotrophic factor did not change but expression of the proinflammatory cytokine tumor necrosis factor alpha mRNA was significantly increased in the 120 μT group. These findings suggest that 7.5 kHz MF exposure may lead to mild learning and memory impairment, possibly through an inflammatory reaction in the hippocampus.

Effects of intermediate frequency magnetic fields on male fertility indicators in mice

Human exposure to intermediate frequency (IF) fields is increasing due to new applications such as electronic article surveillance systems, wireless power transfer and induction heating cookers. However, limited data is available on effects of IF magnetic fields (MF) on male fertility function. This study was conducted to assess possible effects on fertility indicators from exposure to IF MF. Male C57BL/6J mice were exposed continuously for 5 weeks to 7.5kHz MF at 12 and 120μT. Sperm cells from cauda epididymis were analysed for motility, total sperm counts, and head abnormalities. Motile sperm cells were classified as progressive or non-progressive. Testicular spermatid heads were counted as well. The body weight development and reproductive tissue weights were not affected. No exposure-related differences were observed in sperm counts or sperm head abnormalities. Proportion of non-motile cells was significantly decreased in the 120µT group, and a corresponding increase was seen in the percentage of motile cells (significant in non-progressive motile cells). In conclusion, no adverse effects on fertility indicators were observed. Increased sperm motility is an interesting finding that needs to be confirmed in further studies.

Evaluation of biological effects of intermediate frequency magnetic field on differentiation of embryonic stem cell.

The embryotoxic effect of intermediate frequency (IF) magnetic field (MF) was evaluated using murine embryonic stem (ES) cells and fibroblast cells based on the embryonic stem cell test (EST). The cells were exposed to 21 kHz IF–MF up to magnetic flux density of 3.9 mT during the cell proliferation process (7 days) or the cell differentiation process (10 days) during which an embryonic body differentiated into myocardial cells. As a result, there was no significant difference in the cell proliferation between sham- and IF–MF-exposed cells for both ES and fibroblast cells. Similarly, the ratio of the number of ES-derived cell aggregates differentiated to myocardial cells to total number of cell aggregates was not changed by IF–MF exposure. In addition, the expressions of a cardiomyocytes-specific gene, Myl2, and an early developmental gene, Hba-x, in the exposed cell aggregate were not altered. Since the magnetic flux density adopted in this study is much higher than that generated by an inverter of the electrical railway, an induction heating (IH) cooktop, etc. in our daily lives, these results suggested that IF–MF in which the public is exposed to in general living environment would not have embryotoxic effect.

Acute and subchronic toxicity of 20 kHz and 60 kHz magnetic fields in rats

Despite increasing use of intermediate frequency (IF) magnetic fields (MFs) in occupational and domestic settings, scientific evidence necessary for health risk assessments of IF MF is insufficient. Male and female Crl:CD(SD) rats (12 per sex per group) were exposed to 20 kHz, 0.20 mT(root mean square, rms) or 60 kHz, 0.10 mT(rms) sinusoidal MFs for 22 h day−1 for 14 days (acute) or 13 weeks (subchronic). Experiments were duplicated for each frequency to ensure outcome reproducibility, and examinations were blinded for quality assurance. All rats survived without significant clinical signs until the end of experiments. Some changes in body weight between the MF‐exposed and control groups were observed over the course of exposure, although the directions of the changes were inconsistent and not statistically significant after subchronic exposure. There were significant differences between MF‐exposed and control groups in some organ weights and parameters in hematology and clinical chemistry, but these were minor in magnitude and not repeated in duplicate experiments. Histopathological findings reflecting toxicity were sporadic. Frequencies of other findings were similar to historic data in this rat strain, and findings had no specific relationship to changes in organ weight or parameters of hematology and clinical chemistry in each animal. The changes observed throughout this study were considered biologically isolated and were attributable to chance associations rather than to MF exposure. The results, in particular the histopathological evidence, indicate an absence of toxicity in IF MF‐exposed rats and do not support the hypothesis that IF MF exposure produces significant toxicity. Copyright © 2015. The Authors. Journal of Applied Toxicology Published by John Wiley & Sons Ltd.

Early Exposure to Intermediate-Frequency Magnetic Fields Alters Brain Biomarkers without Histopathological Changes in Adult Mice

Recently we have reported that intermediate-frequency magnetic field (IF-MF) exposure transiently altered the mRNA expression levels of memory function-related genes in the hippocampi of adult male mice. However, the effects of IF-MF exposure during brain development on neurological biomarkers have not yet been clarified. In the present study, we investigated the effect of IF-MF exposure during development on neurological and immunological markers in the mouse hippocampus in 3- and 7-week-old male mice. Pregnant C57BL/6J mice were exposed to IF-MF (21 kHz, 3.8 mT) for one hour per day from organogenesis period day 7 to 17. At adolescence, some IF-MF-exposed mice were further divided into exposure, recovery, and sham-exposure groups. The adolescent-exposure groups were exposed again to IF-MF from postnatal day 27 to 48. The expression of mRNA in the hippocampi was examined using a real-time RT-PCR method, and microglia activation was examined by immunohistochemical analysis. The expression levels of NR1 and NR2B as well as transcription factors (CaMKIV, CREB1), inflammatory mediators (COX2, IL-1 β,TNF-α), and the oxidative stress marker heme-oxygenase (HO)-1 were significantly increased in the IF-MF-exposed mice, compared with the control group, in the 7-week-old mice, but not in the 3-week-old mice. Microglia activation was not different between the control and other groups. This study provides the first evidence that early exposure to IF-MF reversibly affects the NMDA receptor, its related signaling pathways, and inflammatory mediators in the hippocampus of young adult mice; these changes are transient and recover after termination of exposure without histopathological changes.

Effects of 21-kHz intermediate frequency magnetic fields on blood properties and immune systems of juvenile rats

Purpose: Due to a lack of science-based evidence, we explored the effects of exposure to intermediate frequency magnetic fields (IF-MF) on experimental animals. We assessed several immunological parameters to determine the effect of exposure of the whole body to IF-MF.Materials and methods: Male Sprague-Dawley rats (4–5 weeks old) were divided into three groups: Cage-control, sham, and 3.8-mT (rms) exposure groups. The animals were exposed to IF-MF at 21 kHz under fixed conditions in an acrylic holder. Exposure was performed for 1 h/day for 14 consecutive days. On the 15th day following the exposure, biochemical and hematological parameters in blood were analyzed. The effects of the exposure on immunological functions such as the cytotoxic activity of lymphocytes, chemotactic and phagocytic activity of granulocytes, and T (cluster of differentiation 4 [CD4] and cluster of differentiation 8 [CD8])-cell frequency were also examined.Results: Hematological parameters were not affected by IF-MF exposure. Other immune functions such as the cytotoxic activity and phagocytic activity were not affected. Populations of T cells after exposure also did not show any significant differences. In blood biochemistry, there was significant difference in inorganic phosphorus level between sham and exposure group. However, this will not induce any pathophysiological status, because they were still within physiological range. Overall, no significant effect by exposure of IF-MF was observed under our experimental conditions.Conclusions: Our results suggest that exposure to 21-kHz sinusoidal IF-MF at 3.8 mT for 1 h/day for 14 days did not affect immune function in juvenile rats.

Intermediate frequency magnetic field generated by a wireless power transmission device does not cause genotoxicity in vitro.

The aim of this study was to evaluate effects of intermediate frequency magnetic fields (IFMF) generated by a wireless power transmission (WPT) based on magnetic resonance from the perspective of cellular genotoxicity on cultured human lens epithelial cells (HLECs). We evaluated the effects of exposure to 90 kHz magnetic fields at 93.36 µT on cellular genotoxicity in vitro for 2 and 4 h. The magnetic flux density is approximately 3.5 times higher than the reference level recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. For assessment of genotoxicity, we studied cellular proliferation, apoptosis and DNA damage by Cell Counting Kit-8 (CCK-8) assay, flow cytometry analysis, alkaline comet assay and phosphorylated histone H2AX (γH2AX) foci formation test. We did not detect any effect of a 90 kHz IFMF generated by WPT based on magnetic resonance on cell proliferation, apoptosis, comet assay, and γH2AX foci formation test. Our results indicated that exposure to 90 kHz IFMF generated by WPT based on magnetic resonance at 93.36 µT for 2 and 4 h does not cause detectable cellular genotoxicity.

Effect of an intermediate-frequency magnetic field of 23 kHz at 2 mT on chemotaxis and phagocytosis in neutrophil-like differentiated human HL-60 cells.

Public concerns about potential health risks of intermediate-frequency (IF) electromagnetic fields are increasing, especially as the use of induction-heating cooktops has spread extensively in Japan and Europe. In order to investigate the properties of IF electromagnetic fields, we examined the effect of exposure to a 23-kHz IF magnetic field of 2 mT for 2, 3, or 4 h on neutrophil chemotaxis and phagocytosis using differentiated human HL-60 cells. Compared with sham exposure, exposure to the IF magnetic field had no effect on neutrophil chemotaxis or phagocytosis. Previous studies demonstrated that exposure to a 23-kHz IF magnetic field of 2 mT (about 74-times the maximum value recommended by the International Commission for Nonionizing Radiation Protection guidelines) may affect the first-line immune responses in humans. To our knowledge, this is the first study to evaluate the effects of IF magnetic fields on cellular immune responses. We found that exposure to an IF magnetic field of 2 mT has minimal if any effect on either the chemotaxis or phagocytic activity of neutrophil-like human HL-60 cells.

Effects of intermediate frequency magnetic field on the solution treatment of Mg–Gd alloy

An intermediate frequency magnetic field (IFMF) was imposed upon Gd–Mg diffusion couples that were annealed at 773K. It was found that the average thickness of diffusion layer under the magnetic field was much wider than that without the magnetic field, indicating that the atomic diffusion ability was enhanced. The magnetic field was then applied to the solution treatment of Mg–16.66Gd–0.088Zr (wt%) alloy. Compared with the samples without magnetic field, the area fraction of the eutectic phase (Mg5Gd phase) was evidently lower at each time point when the IFMF was imposed during the solution treatment, i.e. the solution treatment process was accelerated by the magnetic field. These two phenomena are mainly due to the enhanced atomic diffusion ability in Mg–Gd alloy under IFMF.

Occupational exposure to intermediate frequency and extremely low frequency magnetic fields among personnel working near electronic article surveillance systems

Cashiers are potentially exposed to intermediate frequency (IF) magnetic fields at their workplaces because of the electronic article surveillance (EAS) systems used in stores to protect merchandise against theft. This study aimed at investigating occupational exposure of cashiers to IF magnetic fields in Finnish stores. Exposure to extremely low frequency (ELF) magnetic fields was also evaluated because cashiers work near various devices operating with 50 Hz electric power. The peak magnetic flux density was measured for IF magnetic fields, and was found to vary from 0.2 to 4 µT at the cashier's seat. ELF magnetic fields from 0.03 to 4.5 µT were found at the cashier's seat. These values are much lower than exposure limits. However, according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) occupational reference levels for IF magnetic fields (141 µT for the peak field) were exceeded in some cases (maximum 189 µT) for short periods of time when cashiers walked through the EAS gates. As the ICNIRP reference levels do not define any minimum time for exposure, additional investigations are recommended to determine compliance with basic restrictions. Even if the basic restrictions are not exceeded, persons working near EAS devices represent an exceptional group of workers with respect to exposure to electromagnetic fields. This group could serve as a basis for epidemiological studies addressing possible health effects of IF magnetic fields. Compliance with the reference levels for IF fields was evaluated using both broadband measurement of peak fields and the ICNIRP summation rule for multiple frequencies. The latter was generally more conservative, and the difference between the two methods was large (>10-fold) for EAS systems using a 58 kHz signal with complex waveform. This indicates that the ICNIRP multiple frequency rule can be unnecessarily conservative when measuring complex waveforms.

Intermediate frequency magnetic field and chick embryotoxicity

Intermediate frequency magnetic fields (MFs) have widely been used in industrial machines and home appliances, such as induction heating cookers, although toxicity studies to evaluate the potential health risks of such fields are insufficient. In induction heating cookers, the MF source (i.e. hobs), is located near the abdominal position of a person cooking. Hence, developmental effects on the fetus may be a concern in case the person is a pregnant woman. Fertile White Leghorn eggs (60/group) were either exposed to 20 kHz, 1.1 mT(rms) or 60 kHz, 0.11 mT(rms) sinusoidal MFs for 19 days during embryogenesis. The same number of eggs served as a control group. In addition, a sham-sham experiment was conducted to validate the equality between exposure and control facilities. After exposure, embryos were examined for mortality rate and stage. Live embryos were evaluated for developmental stage and gross and skeletal anomalies. Length of upper beak and leg digits was also measured. Examinations were conducted in a blinded fashion to ensure quality assurance; experiments were triplicated for each frequency to confirm the outcome reproducibility. Mortality rate and stage, incidence of malformed embryos, and developmental variables in live embryos were found to be similar between the MF-exposed and corresponding control group. Incidence of gross anomalies such as mandibular edema and skeletal anomalies such as coccyx defects were low across the experiments, and no significant group differences were noted. In conclusion, exposure to 20 kHz or 60 kHz MF did not produce any significant teratogenic developmental effects in chick embryos.

Alteration of gene expression by exposure to a magnetic field at 23 kHz is not detected in astroglia cells

The increasing use of induction heating (IH) cooktops has roused public concern in Japan and Europe regarding potential health effects. The purpose of this study was to evaluate the effects of exposure to a magnetic field at 23 kHz (which is the maximum output power frequency of most IH cooktops) on gene expression in a human-fetus-derived astroglia cell line, SVGp12. The cells were exposed to the magnetic field at 2 mTrms [which is approximately 74 times higher than the reference level in the most recent International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines], for 2, 4 and 6 h, using a previously reported exposure system. Gene expression was evaluated using an Agilent cDNA microarray. We did not detect any significant effects of the magnetic field on the gene expression profile. On the contrary, heat treatment at 43°C for 2 h used as a positive control significantly affected gene expression, including inducing heat shock proteins, which indicated that our protocol for microarray analysis was appropriate. From these results, we conclude that exposure of human-fetus-derived astroglia cells to an intermediate-frequency magnetic field at 23 kHz and 2 mTrms for up to 6 h does not induce detectable alteration of gene expression.

Can intermediate-frequency magnetic fields affect memory function-related gene expressions in hippocampus of C57BL/6J mice?

Recently, a cooking appliance based on the principle of electromagnetic induction has come to be used domestically on a widespread basis; this induction heating cooking hob mainly generates intermediate-frequency magnetic fields (IF-MF). However, whether electromagnetic fields originating from household appliances represent a health risk remains uncertain. We investigated the effect of IF-MF on the expressions of memory function-related genes and related transduction molecules in the mouse hippocampus. Male and female C57BL/6J mice were allotted to a control (sham-exposed), an exposure, or a recovery (one week after exposure) group and were exposed to IF-MF (21 kHz, 3.8 mT) one hour per day for 2 weeks. Twenty-four hour after final exposure, the expression levels of memory function-related genes and the mRNA levels for signal transduction pathway molecules in the hippocampi were examined using real-time RT-PCR. The relative mRNA expression levels of the N-methyl-D aspartate (NMDA) receptor subunits NR1, NR2A, and NR2B as well as transcription factors (calcium/calmodulin-dependent protein kinase (CaMK) -IV, cyclic AMP responsive element binding protein (CREB) -1) and neurotrophins (nerve growth factor (NGF), and brain-derived neurotrophic factors (BDNF)) were not significantly altered in the IF-MF-exposed mice. We also examined the morphology of the hippocampus using a histological analysis, but no changes in the IF-MF-exposed mice were seen. This is the first in vivo study to show that IF-MF exposure did not affect the expression levels of memory function-related genes in the hippocampus of C57BL/6J mice. The present findings suggest that IF-MF exposure may not affect cognitive function in the present animal model.

Absence of reproductive and developmental toxicity in rats following exposure to a 20-kHz or 60-kHz magnetic field

The use of intermediate frequency (IF) magnetic fields (MFs) in occupational equipment and domestic appliances, such as inductive heating cookers, is increasing. The WHO indicated a lack of scientific evidence needed to assess the health risk of exposure to IF MFs. Male and female rats (24/group) were exposed to a 20kHz, 0.2mT(rms) or 60kHz, 0.1mT(rms) sinusoidal MF for 22h/day from 14days prior to and during mating. Copulated females were exposed until gestation day 7 and sacrificed thereafter. Mated males were sacrificed to examine MF exposure effects on spermatogenesis. Reproductive examinations were blinded, and experiments were duplicated per frequency to ensure reproducibility. No statistically significant, exposure-related changes were found in the estrous cycle, copulation and fertility indices, numbers of corpora lutea and implantation sites, or pre- and postimplantation loss. No reproducible changes were observed in sperm count, motility, or morphological abnormality, or in the weights of testes and epididymides after MF exposure. No significant abnormalities were observed in gross pathology or histopathology of the uterus, ovary, testis, and epididymis in the MF- or sham-exposed groups. MF exposure during the preimplantation period was not toxic to fertility or early embryogenesis under the experimental conditions.

Intermediate frequency magnetic field at 23 kHz does not modify gene expression in human fetus‐derived astroglia cells

The increased use of induction heating (IH) cooktops in Japan and Europe has raised public concern on potential health effects of the magnetic fields generated by IH cooktops. In this study, we evaluated the effects of intermediate frequency (IF) magnetic fields generated by IH cooktops on gene expression profiles. Human fetus-derived astroglia cells were exposed to magnetic fields at 23 kHz and 100 µT(rms) for 2, 4, and 6 h and gene expression profiles in cells were assessed using cDNA microarray. There were no detectable effects of the IF magnetic fields at 23 kHz on the gene expression profile, whereas the heat treatment at 43 °C for 2 h, as a positive control, affected gene expression including inducing heat shock proteins. Principal component analysis and hierarchical analysis showed that the gene profiles of IF-exposed groups were similar to the sham-exposed group and were different than the heat treatment group. These results demonstrated that exposure of human fetus-derived astroglia cells to an IF magnetic field at 23 kHz and 100 µT(rms) for up to 6 h did not induce detectable changes in gene expression profile.

Design of Alternating Magnetic Field Stimulator Using Duty Factor

We have developed an alternating magnetic field stimulation system consisting of a switched-mode power supply and a digital control circuit which modulates a duty ratio to maintain a magnetic field intensity of a few mT even while the frequency increases up to 4 kHz with a controllable coil temperature below 30 oC in air. This duty ratio modulation and water circulation are advantageous for cell culture under ac-magnetic field stimulation by preventing the incubator from exceeding a cell-viable temperature of 37 oC. Although the temperature of the coil when subjected to a sinusoidal voltage rapidly increased, that of our system modulated by the duty factor did not change. This is a potentially valuable method to investigate the effects of intermediate frequency magnetic field stimulation on biological entities such as cells, tissues and organs.

Pre- and post-natal exposure of children to EMF generated by domestic induction cookers

Induction cookers are a type of cooking appliance that uses an intermediate-frequency magnetic field to heat the cooking vessel. The magnetic flux density produced by an induction cooker during operation was measured according to the EN 62233 standard, and the measured values were below the limits set in the standard. The measurements were used to validate a numerical model consisting of three vertically displaced coaxial current loops at 35 kHz. The numerical model was then used to compute the electric field (E) and induced current (J) in 26 and 30 weeks pregnant women and 6 and 11 year old children. Both E and J were found to be below the basic restrictions of the 2010 low-frequency and 1998 ICNRIP guidelines. The maximum computed E fields in the whole body were 0.11 and 0.66 V m−1 in the 26 and 30 weeks pregnant women and 0.28 and 2.28 V m−1 in the 6 and 11 year old children (ICNIRP basic restriction 4.25 V m−1). The maximum computed J fields in the whole body were 46 and 42 mA m−2 in the 26 and 30 weeks pregnant women and 27 and 16 mA m−2 in the 6 and 11 year old children (ICNIRP basic restriction 70 mA m−2).

An Accelerating Method of Growth of White Radish Sprouts using Intermediate-frequency Magnetic Fields

An Accelerating Method of Growth of White Radish Sprouts using Intermediate-frequency Magnetic Fields

Intermediate frequency magnetic fields generated by an induction heating (IH) cooktop do not affect genotoxicities and expression of heat shock proteins

The aim of this study is to evaluate the effects of intermediate frequency (IF) fields generated by induction heating (IH) cooktops from the perspective of cellular genotoxicity and stress responses. We evaluated the effects of exposure to 23 kHz magnetic fields at 6.05 mT(rms) for 2 h on cellular genotoxicity and stress responses in vitro. The maximum output power in most IH cooktops is at this frequency. The magnetic flux density is approximately 1000 times higher than the reference level in the International Commission on Non-ionising Radiation Protection (ICNIRP) guidelines. For assessment of genotoxicity, we studied cell growth, comet assay, micronucleus formation and hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene mutation. Heat shock protein (Hsp) 27, 70, 105 and phosphorylated Hsp27 were evaluated as indicators of the stress responses. We did not detect any effects of the IF magnetic fields on cell growth, comet assay, micronucleus formation, HPRT gene mutation, expression of phosphorylated Hsp27, or nuclear translocation of Hsp27, 70 or 105. Our results indicate that exposure to an IF magnetic field at 6.05 mT(rms) for 2 h does not cause detectable cellular genotoxicity, and does not induce detectable cellular stress.

Development of a higher power intermediate‐frequency magnetic field exposure system for in vitro studies

In a previous article we developed an in vitro 23 kHz magnetic field (MF) exposure system that generated an MF of 532 microT(rms). Using this system, the biological effects of 23 kHz MFs on cell functions have been reported. To further clarify the biological effect of intermediate-frequency (IF) MFs and investigate the dose-response relationship in cell lines, an exposure system that generates stronger MFs is required. To meet this requirement, we developed a 6.25 mT(rms) MF exposure system for in vitro study. This level is 1000 times the reference level for the general public in the ICNIRP guidelines. This system provides an MF of 6.25 mT(rms) at 23 kHz with a uniformity within +/-5%. To verify that in vitro experimental conditions are maintained, we examined the temperature, environmental MF, and MF leakage for a sham exposure system. In addition, we examined the harmonics, coil shape, and heat generated in the medium by the high-strength MF. As a result, it was confirmed that this system can be used to evaluate the biological effects of IF MFs. This article presents the design and successful construction of the in vitro exposure system.