Teratological evaluation of mouse fetuses exposed to a 20 kHz EMF

As a continuation of our previous study, we performed a teratological evaluation of the importance of gestational age with regards to the exposure of 20 kHz intermediate frequency magnetic field (IF) on pregnant ICR mice. The pregnant mice were exposed to a 20 kHz IF magnetic field for 8 h/day in a carousel irradiator at 30 µT which is the limit standard for occupational population in Korea. The animals were sacrificed on the 18th day of gestation and the fetuses were examined for mortality, growth retardation, changes in head size and other morphological abnormalities. We concluded that exposure to 30 µT with 20 kHz IF did not cause any observable adverse effects on mouse fetuses. Bioelectromagnetics 30:330–333. © 2009 Wiley‐Liss, Inc.     

Effect of a 20 kHz sawtooth magnetic field exposure on the estrous cycle in mice

Female mice post weaning were exposed to 20 kHz sawtooth electric and magnetic fields (EMF) with 6.25 microT peak intensity for 6 weeks. Estrous cycles were checked using vaginal smears over the last 10 days of the experimental period. The vaginal smears from EMF-exposed mice revealed an increase in the frequency of one or two phases persisting. The number of estrous cycles less than 1 was more in the EMF-exposed group than in the sham control group. Furthermore, in the EMF-exposed group, the duration of proestrous and metestrous stages of the estrous cycle was significantly increased compared with the control group. In conclusion, our results suggest that exposure to 20 kHz sawtooth EMF may affect normal cycling of the estrous cycle by disrupting the female reproductive endocrine physiology. We should not disregard the possible adverse reproductive effect of the 20 kHz sawtooth EMF generated under the occupational exposure situation in females.     

A newly designed and constructed 20 kHz magnetic field exposure facility for in vivo study

Exposure to man-made electromagnetic fields has increased over the past century. As a result of exposure to these fields, concerns have been raised regarding the relationship between electromagnetic fields and human health. Interest in the biological and health effects of intermediate frequency (IF) magnetic fields has grown recently because of the increase in public concern. In order to investigate whether IF magnetic fields have biological effects, we have developed a 20 kHz (IF) magnetic field exposure system for in vivo studies. The exposure facility was designed to study the biological effects of IF magnetic field on laboratory animals. The facility consists of a 9 m x 9 m x 5 m high room containing seven separate rooms including a 5.3 m x 4.5 m x 3 m high specific-pathogen free exposure room. The dimensions of the exposure system are 1.6 m x 1.6 m x 1.616 m high located inside this exposure room. The system is designed to provide magnetic fields up to 200 microT at 20 kHz with the uniformity within +/-5% over the space occupied by animals. After constructing the facility, performance tests were carried out. As a result, it was confirmed that our facility met requirements for evaluation of the biological effects of IF magnetic field on small animal experiments. In this paper, the design, construction, and results of evaluation of an animal exposure facility for the in vivo biological effects of an IF magnetic field are described.     

Lack of chick embryotoxicity after 20 kHz, 1.1 mT magnetic field exposure

This investigation was undertaken because biological studies to evaluate the effects of intermediate frequency magnetic fields are insufficient. White Leghorn fertile eggs (60/group) were either exposed to a 20 kHz, 1.1 mT(rms) sinusoidal magnetic field or sham‐exposed during the first 2, 7, or 11 days of embryogenesis. Lower dose exposures at 0.011 and 0.11 mT(rms) for 2 days were also conducted to elucidate possible dose–response relationships. Additional eggs given all‐trans‐retinoic acid, a teratogen, were exposed to the 1.1 mT(rms) magnetic field for the same periods to investigate the modification of embryotoxicity. After exposure, embryos were examined for mortality and developmental abnormalities. Developmental stage, number of somite pairs, and other developmental endpoints were also evaluated. Experiments were triplicated and conducted in a blind fashion. No exposure‐related changes were found in any of the endpoints in intact embryos exposed to1.1 mT(rms) or to the lower doses of 0.11 and 0.011 mT(rms) magnetic fields. Retinoic acid administration produced embryotoxic responses, which were embryonic death and developmental abnormalities, in 40–60% of embryos in the sham‐exposed groups. The magnitude of these responses was not changed significantly by the magnetic field exposures. Under the present experimental conditions, exposure to 20 kHz magnetic field up to 1.1 mT(rms) was not embryotoxic in the chick and did not potentiate the embryotoxic action of retinoic acid. Bioelectromagnetics 30:573–582, 2009. © 2009 Wiley‐Liss, Inc.     

Toxicity bioassay in Sprague-Dawley rats exposed to 20 kHz triangular magnetic field for 90 days

Sprague-Dawley rats (10 each of male and female per group for sham and magnetic field exposed) were exposed in a carrousel irradiator to 20 kHz intermediate frequency (IF) magnetic field at 6.25 microT rms for 8 h/day, 5 days/week for 90 days. Urine analysis (pH, serum glucose, protein, ketone bodies, RBC, WBC, bilirubin, urobilinogen, and specific gravity), blood analysis [WBC, RBC, hemoglobin, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), thrombocyte count, and leucocyte count], blood biochemistry (total protein, blood urea nitrogen, creatinine, glucose, total bilirubin, total cholesterol, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and lactate dehydrogenase), and histopathological analysis for organs such as liver, kidney, testis, ovary, spleen, brain, heart, and lung were performed on day 90. Results showed no significant differences in the above analyses between IF magnetic field exposed and sham control rats. Therefore, we conclude that there were no significant toxicities in rats exposed to 20 kHz IF triangular magnetic field-exposure for 90 days.     

Teratological assessment of exposure to time-varying magnetic field

A teratological assessment was performed using rats that were exposed to an alternating magnetic field. The magnetic field had a sawtooth waveform similar to that produced by video display terminals (VDTs). Female rats were exposed 2 weeks prior to and throughout pregnancy at a rate of 7 h/day. Three intensities of magnetic field (5.7, 23 or 66 microT) were used. All of these field intensities were much greater than those to which VDT users are exposed. A slight but statistically significant decrease in maternal lymphocyte count for the highest intensity field was found as compared with the control group. However, the lymphocyte count was within the normal range, and the observed changes in hematological parameters were considered mild. No other maternal or fetal parameters that were examined showed a significant difference for any of the three field intensities. Where minor variations in skeleton development were observed they were known to be the common "noise" that appears in every teratological evaluation.     

Lack of promotion of mammary, lung and skin tumorigenesis by 20 kHz triangular magnetic fields

In order to evaluate possible tumorigenic effects of a 20 kHz intermediate frequency triangular magnetic field (IF), a frequency emitted from TV and PC monitors at 6.25 microT rms, which is the regulated exposure limit of magnetic field for the public in Korea, mammary tumors were produced in female Sprague-Dawley rats by oral intubation of dimethylbenz(a)anthracene (DMBA), lung tumors in ICR mice by scapular region injection of benzo(a)pyrene (BP), and skin tumors in female ICR mice by topical application of DMBA and tetradecanoylphorbol ester (TPA). IF was applied 8 h/day for 14 weeks beginning the day after DMBA treatment for mammary tumor experiment, for 6 weeks after weaning for lung tumor, and for 20 weeks beginning 1 week after DMBA application for skin tumor experiment. For skin tumors, TPA was applied once a week for 19 weeks. Results showed no significant differences in tumor incidence, mean tumor number and volume, and histological patterns between IF magnetic-field exposed and sham control rats in the above three tumor models. Therefore, we conclude that within the limitation or number of animals and the experimental conditions, 20 kHz IF triangular magnetic field exposure of 6.25 microT does not appear to be a strong co-tumorigenic agent in the chosen murine mammary, lung and skin models.     

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 µT_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. Bioelectromagnetics 31:156–163, 2010. © 2009 Wiley‐Liss, Inc.     

The effects of continuous exposure to 20-kHz sawtooth magnetic fields on the litters of CD-1 mice.

Mated CD-1 mice were exposed to 20-kHz sawtooth magnetic fields similar to those associated with video display terminals (VDT). Four groups of animals were continuously exposed from day 1 to day 18 of pregnancy to field strengths of 0, 3.6, 17, or 200 microT. There were no less than 185 mated dams in each exposure group. On day 18, the dams were sacrificed and assessed for weight gain and pregnancy. The litters were evaluated for numbers of implantations, fetal deaths and resorptions, gross external, visceral and skeletal malformations, and fetal weights. There were no less than 140 pregnant females in each group, and there were no significant differences between any of the exposure groups and the sham group (0 microT) for any of the end points. The results of this study do not support the hypothesis that the 20-kHz VLF magnetic fields associated with video display terminals are teratogenic in mammals.     

Neurochemical effects of a 20 kHz magnetic field on the central nervous system in prenatally exposed mice

C57/B1 mice were exposed during pregnancy (gestation days 0–19) to a 20 kHz magnetic field (MF). The asymmetric sawtooth-wave form magnetic field in the exposed racks had a flux density of 15 μT (peak to peak). After 19 days, the exposure was terminated, and the mice were housed individually under normal laboratory conditions. On postnatal day (PD) 1, PD21, and PD308, various neurochemical markers in the brains of the offspring were investigated and the brains weighed. No significant difference was found in the whole brain weight at PD1 or PD21 between exposed offspring and control animals. However, on PD308, a significant decrease in weight of the whole brain was detected in exposed animals. No significant differences were found in the weight of cortex, hippocampus, septum, or cerebellum on any of the sampling occasions, nor were any significant differences detected in protein-, DNA-level, nerve growth factor (NGF), acetylcholine esterase- (AChE), or 2′,3′-cyclic nucle-otide 3′-phosphodiesterase- (CNP; marker for oligodendrocytes) activities on PD21 in cerebellum. Cortex showed a more complex pattern of response to MF: MF treatment resulted in a decrease in DNA level and increases in the activities of CNP, AChE, and NGF protein. On PD308, the amount of DNA was significantly reduced in MF-treated cerebellum and CNP activity was still enhanced in MF-treated cortex compared to controls. Most of the effects of MF treatment during the embryonic period were similar to those induced by ionizing radiation but much weaker. However, the duration of the exposure required to elucidate the response of different markers to MF seems to be greater and effects appear later during development compared to responses to ionizing radiation. © 1995 Wiley-Liss, Inc.     

Development and evaluation of intermediate frequency magnetic field exposure system for studies of in vitro biological effects

We have developed an intermediate frequency (IF) magnetic field exposure system for in vitro studies. Since there are no previous studies on exposure to heating-frequency magnetic fields generated from an induction heating (IH) cook top, there is a strong need for such an exposure system and for biological studies of IF magnetic fields. This system mainly consists of a magnetic-field-generating coil housed inside an incubator, inside which cultured cells can be exposed to magnetic field. Two systems were prepared to allow the experiment to be conducted in a double-blind manner. The level of the generated magnetic field was set to 532 microT rms in the exposure space, 23 kHz, 80 times the value in the International Commission on Non-ionizing Radiation Protection (ICNIRP) guidelines, with a spatial field uniformity better than 3.8%. The waveforms were nearly sinusoidal. It was also confirmed that the parasitic electric field was 157 V/m rms and the induced electric field was 1.9 V/m rms. The temperature was maintained at 36.5 +/- 0.5 degrees C for 2 h. Furthermore, leaked magnetic flux density was 0.7 microT rms or lower at extremely low frequency (ELF) and IF in the stopped system when the other system was being operated, and the environmental magnetic flux density was 0.1 microT rms or lower at the center of the coils. As a result, it was confirmed that this system could be successfully used to evaluate the biological effects of exposure to IF magnetic fields.     

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. Bioelectromagnetics 33:662–669, 2012. © 2012 Wiley Periodicals, Inc.     

Carcinogenicity test in B6C3F1 mice after parental and prenatal exposure to 50 Hz magnetic fields

Some epidemiological studies suggest association of childhood cancer with occupational exposure of the parents to magnetic fields. To test this relationship, 50 each of C57BL/6J female and C3H/HeJ male mice were exposed for 2 and 9 weeks, respectively, to 50 Hz sham (group A), 0.5 (group B), and 5 mT (group C) sinusoidal alternating magnetic fields. They were mated under the exposure for up to 2 weeks, and the exposure was continued until parturition. All the B6C3F1 offspring, without adjusting numbers of animals, were clinically observed without exposure to magnetic field for a nominal 78 weeks from 6-8 weeks of age after weaning and then euthanized for pathological examination according to a routine carcinogenicity test. 540 pups entered the test, and the survival rate was 96.7%. No F1 mouse died of tumoral diseases before a male in A group died of stomach cancer at 43 weeks of age. The first animal death in the exposed groups due to tumor occurred at 71 weeks of age. Eighteen animals died before necropsy at 84-86 weeks of age. No significant difference was detected in the final number of survivors and incidence of tumors between groups A and B, or A and C. Concerning reproduction total implants in group B were less than in group A and the difference was on the borderline of significance (P=.05). This difference was not reproduced in a later duplicate experiment.     

Effects of prenatal exposure to 50 Hz magnetic fields on development in mice: II. Postnatal development and behavior

To investigate the potential of magnetic fields to act as a behavioral teratogen, pregnant CD1 mice were exposed or sham-exposed for all of gestation to a 50 Hz/20 mT magnetic field. Maturation of offspring was assessed using a range of standard developmental indices (eye opening, pinna detachment, hair coat, tooth eruption, sexual maturity, and weight) and simple reflexive behaviors (air righting, surface righting, forepaw grasp, cliff avoidance, and negative geotaxis). Activity and coordination levels were explored in juvenile and adult mice using an open field arena, a head-dip board, an accelerating Rotarod, and a residential activity wheel. All assessments were carried out without knowledge of exposure condition. Results from 168 sham-exposed mice from 21 litters and from 184 exposed mice from 23 litters were compared using survival analysis techniques and multivariate regression methods. Three possible field-dependent effects were found: Exposed animals performed the air righting reflex earlier (P < 0.01); exposed males (but not females) were significantly lighter in weight (P = 0.008) at 30 days of age; and exposed animals remained on a Rota-rod for less time as juveniles (P = 0.03). Some of these results have not been reported in other studies and may reflect spurious statistical significance, although some effect of magnetic field exposure cannot be ruled out. Overall, these results suggest that prenatal exposure to a 50 Hz magnetic field does not engender any gross impairments in the postnatal development or behavior of mice. This does not preclude such exposure affecting more subtle aspects of behavior. Published 1994 by Wiley-Liss, Inc.     

Effects of prenatal exposure to 50 Hz magnetic fields on development in mice: I. Implantation rate and fetal development

Pregnant CD1 mice were exposed or sham-exposed from day 0 to day 17 of gestation to a 50 Hz sinusoidal magnetic field at 20 mT (rms). Preimplantation and postimplantation survival were assessed and fetuses examined for the presence of gross external, internal, and skeletal abnormalities. There were no statistically significant field-dependent effects on preimplantation or postimplantation survival, sex ratio, or the incidence of fetuses with internal or skeletal abnormalities. Magnetic field exposure was, however, associated with longer and heavier fetuses at term, with fewer external abnormalities. The results lend no support to suggestions of increased rates of spontaneous abortion or congenital malformation following prenatal exposure to power frequency magnetic fields. © 1994 Wiley-Liss, Inc.     

Effects of exposure to a 50 Hz sinusoidal magnetic field during the early adolescent period on spatial memory in mice

Adolescence is a critical developmental stage during which substantial remodeling occurs in brain areas involved in emotional and learning processes. Although a robust literature on the biological effects of extremely low frequency magnetic fields (ELF‐MFs) has been documented, data on the effects of ELF‐MF exposure during this period on cognitive functions remain scarce. In this study, early adolescent male mice were exposed from postnatal day (P) 23–35 to a 50 Hz MF at 2 mT for 60 min/day. On P36–45, the potential effects of the MF exposure on spatial memory performance were examined using the Y‐maze and Morris water maze tasks. The results showed that the MF exposure did not affect Y‐maze performance but improved spatial learning acquisition and memory retention in the water maze task under the present experimental conditions. Bioelectromagnetics 34:275–284, 2013. © 2012 Wiley Periodicals, Inc.     

Deficits in spatial learning after exposure of mice to a 50 Hz magnetic field

A series of four experiments was performed to determine the effect of exposure to a 50 Hz magnetic field on memory-related behaviour of adult, male C57BL/6J mice. Experimental subjects were exposed to a vertical, sinusoidal magnetic field at 0.75 mT (rms), for 45 min immediately before daily testing sessions on a spatial learning task in an eight-arm radial maze. Control subjects were only exposed to a background time-varying field of less than 50 nT and the ambient static field of about 40 μT. In each experiment, exposure significantly reduced the rate of acquisition of the task but did not affect overall accuracy. This finding is consistent with the results of another study that found that prior exposure to 60 Hz magnetic fields affected spatial learning in rats. Bioelectromagnetics 19:79–84, 1998. © 1998 Wiley-Liss, Inc.     

ELF magnetic field exposure in a neonatal intensive care unit

In this paper, the magnetic flux density (MFD) distribution in a neonatal intensive care unit is described and MFD values inside a few open infant warming systems and incubators are reported. Typical measured values of the magnetic flux density at power frequency (50 Hz) in the "general environment" (the rooms of the unit) were lower than 0.2 microT, while higher MFD values were detected close to medical equipment and inside the open infant warming systems. In both cases, the magnetic flux density quickly decreases with increasing distance, so that measured values are reduced to "background" (i.e., general environment) levels 20-30 cm away from the sources. The total harmonic content over the 100-800 Hz frequency range was also evaluated. In the general environment, measured values in this band were negligible, while this was not the case close to medical equipment. Field levels inside the open and closed incubators depend on the position of the electronic control system, of the heating power generator and its winding conductor, and of the 220 V main plug. The magnetic flux density was also monitored for a prolonged period of time in a few types of open infant warming systems and incubators under standard intensive care unit operation with premature newborn present.     

Effect of exposure to extremely low electro-magnetic field during prenatal period on mice spleen

Total body weight of newborns, the volume of spleen, and the number of megakaryocytes decreased following the exposure to ELF-MF (6 x 10(-3) T and 50 Hz) at 1-5, 6-10, 11-15, and 16-20 days of pregnancy of mice. The complete period of gestation was sensitive to ELF-MF exposure; the initial days were more prone to exposure. The results suggest that the use of ELF-MF producing instruments should be limited during gestation.