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.

In vitro and in vivo genotoxicity of radiofrequency fields

There has been growing concern about the possibility of adverse health effects resulting from exposure to radiofrequency radiations (RFR), such as those emitted by wireless communication devices. Since the introduction of mobile phones many studies have been conducted regarding alleged health effects but there is still some uncertainty and no definitive conclusions have been reached so far. Although thermal effects are well understood they are not of great concern as they are unlikely to result from the typical low-level RFR exposures. Concern rests essentially with the possibility that RFR-exposure may induce non-thermal and/or long-term health effects such as an increased cancer risk. Consequently, possible genetic effects have often been studied but with mixed results. In this paper we review the data on alleged RFR-induced genetic effects from in vitro and in vivo investigations as well as from human cytogenetic biomonitoring surveys. Attention is also paid to combined exposures of RFR with chemical or physical agents. Again, however, no entirely consistent picture emerges. Many of the positive studies may well be due to thermal exposures, but a few studies suggest that biological effects can be seen at low levels of exposure. Overall, however, the evidence for low-level genotoxic effects is very weak.

Ornithine decarboxylase activity is affected in primary astrocytes but not in secondary cell lines exposed to 872 MHz RF radiation

PURPOSE

The effects of radiofrequency (RF) radiation on cellular ornithine decarboxylase (ODC) activity were studied in fibroblasts, two neural cell lines and primary astrocytes. Several exposure times and exposure levels were used, and the fields were either unmodulated or modulated according to the characteristics of the Global System for Mobile (GSM) communications.

MATERIALS AND METHODS

Murine L929 fibroblasts, rat C6 glioblastoma cells, human SH-SY5Y neuroblastoma cells, and rat primary astrocytes were exposed to RF radiation at 872 MHz in a waveguide exposure chamber equipped with water cooling. Cells were exposed for 2, 8, or 24 hours to continuous wave (CW) RF radiation or to a GSM type signal pulse modulated at 217 Hz, at specific absorption rates of 1.5, 2.5, or 6.0 W/kg. Cellular ODC activities of cell samples were assayed.

RESULTS

ODC activity in rat primary astrocytes was decreased statistically significantly (p values from 0.003 to <0.001) and consistently in all experiments performed at two exposure levels (1.5 and 6.0 W/kg) and using GSM modulated or CW radiation. In the secondary cell lines, ODC activity was generally not affected.

CONCLUSIONS

ODC activity was affected by RF radiation in rat primary neural cells, but the secondary cells used in this study showed essentially no response to similar RF radiation. In contrast to some previous studies, no differences between the modulated and continuous wave signals were detected. Further studies with primary astrocytes are warranted to confirm the present findings and to explore the mechanisms of the effects.

Ornithine decarboxylase activity of L929 cells after exposure to continuous wave or 50 Hz modulated radiofrequency radiation—a replication study

A replication study with some extensions was made to confirm enhancement of ornithine decarboxylase (ODC) activity in murine L929 fibroblasts after radiofrequency (RF) field exposure reported in earlier studies. L929 cells purchased from two cell banks were exposed for 2, 8, or 24 h to continuous wave or DAMPS (burst modulated at 50 Hz, with 33% duty cycle) signals at specific absorption rate (SAR) levels of 2.5 or 6.0 W/kg. Exposures were carried out in Crawford and waveguide chambers, at frequencies 835 and 872 MHz, respectively. The results did not confirm findings of previous studies reporting increased ODC activity in RF-exposed cells. When Crawford cell exposure system was used, ODC activity was either not affected (in the case of 8 or 24 h exposures) or decreased after 2 h exposure at the highest SAR level (6 W/kg). The decrease was most pronounced when cooling with air flow was not used, and is most likely related to increased temperature. The minor methodological differences (use of antibiotics, increased sensitivity of ODC assay) are not likely to explain the inconsistency of the findings of the present and previous studies. Different results were obtained in experiments with the waveguide system that involves more efficient temperature control. In this exposure system, ODC activity was increased after 8 h exposure at 6 W/kg. Further studies are warranted to explore whether this finding reflects a true non-thermal effect. The present study did not provide evidence for modulation-specific effects reported in earlier studies.

Modest increase in temperature affects ODC activity in L929 cells: Low-level radiofrequency radiation does not

The effects of low-level radiofrequency (RF) radiation and elevated temperature on ornithine decarboxylase (ODC) activity were investigated in murine L929 fibroblasts. The cells were exposed at 900 MHz either to a pulse-modulated (pulse frequency 217 Hz; GSM-type modulation) or a continuous wave signal at specific absorption rate (SAR) levels of 0.2 W kg(-1) (0.1-0.3 W kg(-1)) and 0.4 W kg(-1) (0.3-0.5 W kg(-1)) for 2, 8, or 24 h. RF radiation did not affect cellular ODC activity. However, a slight increase in temperature (0.8-0.9 degrees C) in the exposure system lead to decreased ODC activity in cell cultures. This was verified by tests in which cells were exposed to different temperatures in incubators. The results show that ODC activity is sensitive to small temperature differences in cell cultures. Hence, a precise temperature control in cellular ODC activity studies is needed.

Investigation of co-genotoxic effects of radiofrequency electromagnetic fields in vivo

We investigated the possible combined genotoxic effects of radiofrequency (RF) electromagnetic fields (900 MHz, amplitude modulated at 217 Hz, mobile phone signal) with the drinking water mutagen and carcinogen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Female rats were exposed to RF fields for a period of 2 years for 2 h per day, 5 days per week at average whole-body specific absorption rates of 0.3 or 0.9 W/kg. MX was given in the drinking water at a concentration of 19 microg/ml. Blood samples were taken at 3, 6 and 24 months of exposure and brain and liver samples were taken at the end of the study (24 months). DNA damage was assessed in all samples using the alkaline comet assay, and micronuclei were determined in erythrocytes. We did not find significant genotoxic activity of MX in blood and liver cells. However, MX induced DNA damage in rat brain. Co-exposures to MX and RF radiation did not significantly increase the response of blood, liver and brain cells compared to MX exposure only. In conclusion, this 2-year animal study involving long-term exposures to RF radiation and MX did not provide any evidence for enhanced genotoxicity in rats exposed to RF radiation.

Effects of mobile phone radiation on UV-induced skin tumourigenesis in ornithine decarboxylase transgenic and non-transgenic mice

PURPOSE

The effects of low-level radiofrequency radiation (RFR) on ultraviolet (UV)-induced skin tumorigenesis were evaluated in ornithine decarboxylase (ODC) and non-transgenic mice.

MATERIALS AND METHODS

Transgenic female mice over-expressing the human ODC gene and their non-transgenic littermates (20 animals in the cage control group, and 45-49 animals in the other groups) were exposed for 52 weeks to UV radiation or a combination of UV radiation and pulsed RFR. The UV dose was 240 Jm(-2) (1.2 x human minimum erythemal dose) delivered three times a week. One group of animals was exposed to Digital Advanced Mobile Phone System (DAMPS)-type RFR, the other group to Global System for Mobile (GSM)-type RFR at a nominal average specific absorption rate of 0.5 W kg(-1), 1.5 h day(-1), for 5 days a week. The skin was carefully palpated weekly for macroscopic tumours. Histopathological analyses of all skin lesions and of a specified dorsal skin area were performed on all animals.

RESULTS

UV exposure resulted in development of macroscopic skin tumours in 11.5 and 36.8% of non-transgenic and transgenic animals, respectively. The RFR exposures did not give a statistically significant effect on the development of skin tumours in either transgenic or non-transgenic animals, or in combined analysis, but tumour development appeared slightly accelerated especially in non-transgenic animals. No effects of RFR exposures were found on excretion of 6-hydroxymelatonin sulphate into urine or on polyamine levels in dorsal skin.

CONCLUSION

RFR exposures did not significantly enhance skin tumourigenesis. However, the slightly accelerated tumour development may warrant further evaluation.

Developmental effects of extremely low frequency electric and magnetic fields

Developmental effects of extremely low frequency (ELF) electric and magnetic fields are briefly reviewed in this paper. The results of animal studies on ELF electric fields are rather consistent, and do not suggest adverse effects on development. The results of studies on ELF magnetic fields suggest effects on bird embryo development, but not consistently in all studies. Results from experiments with other non-mammalian species have also suggested effects on developmental stability. In mammals, pre-natal exposure to ELF magnetic fields does not result in strong adverse effects on development. The only finding that shows some consistency is increase of minor skeleton alterations. Epidemiological studies do not establish an association between human adverse pregnancy outcomes and maternal exposure to ELF lields, although a few studies have reported increased risks associated with some characteristics of magnetic field exposure. Taken as a whole, the results do not show strong adverse effects on development. However, additional studies on the suggested subtle effects on developmental stability might increase our understanding of the sensitivity of organisms to weak ELF fields.

Effects of mobile phone radiation on X-ray-induced tumorigenesis in mice

The increased use of mobile phones has raised the question of possible health effects of such devices, particularly the risk of cancer. It seems unlikely that the low-level radiofrequency (RF) radiation emitted by them would damage DNA directly, but its ability to act as a tumor promoter is less well characterized. In the current study, we evaluated the effect of low-level RF radiation on the development of cancer initiated in mice by ionizing radiation. Two hundred female CBA/S mice were randomized into four equal groups at the age of 3 to 5 weeks. The mice in all groups except the cage-control group were exposed to ionizing radiation at the beginning of the study and then to RF radiation for 1.5 h per day, 5 days a week for 78 weeks. One group was exposed to continuous NMT (Nordic Mobile Telephones)-type frequency-modulated RF radiation at a frequency of 902.5 MHz and a nominal average specific absorption rate (SAR) of 1.5 W/kg. Another group was exposed to pulsed GSM (Global System for Mobile)-type RF radiation (carrier-wave frequency 902.4 MHz, pulse frequency 217 Hz) at a nominal average SAR of 0.35 W/kg. The control animals were sham-exposed. Body weight, clinical signs, and food and water consumption were recorded regularly. Hematological examinations and histopathological analyses of all lesions and major tissues were performed on all animals. The RF-radiation exposures did not increase the incidence of any neoplastic lesion significantly. We conclude that the results do not provide evidence for cancer promotion by RF radiation emitted by mobile phones.

Effects of 50 Hz magnetic field on cell cycle kinetics and the colony forming ability of budding yeast exposed to ultraviolet radiation

To investigate the effects of extremely low frequency magnetic fields on ultraviolet radiation (UV) exposed budding yeast, haploid yeast (Saccharomyces cerevisiae) cells of the strain SEy2101a were exposed to 50 Hz sine wave magnetic field (MF) of 120 microT with simultaneous exposure to UV radiation. Most of the UV energy was in the UVB range (280-320 nm). The biologically weighted (CIE action spectrum) dose level for the UV radiation was 175 J/m2. We examined whether 50 Hz MF affected the ability of UV irradiated yeast cells to form colonies (Colony Forming Units, CFUs). In addition, the effect of coexposure on cell cycle kinetics was investigated. Although the significant effect of MF on the cell cycle phases of UV exposed yeast cells was seen only at one time point, the overall results showed that MF exposure may influence the cell cycle kinetics at the first cycle after UV irradiation. The effect of our particular MF exposure on the colony forming ability of the UV irradiated yeast cells was statistically significant 420 min after UV irradiation. Moreover, at 240, 360, and 420 min after UV irradiation, there were fewer CFUs in every experiment in (UV+MF) exposed populations than in only UV exposed yeast populations. These results could indicate that MF exposure in conjunction with UV may have some effects on yeast cell survival or growth.

Development of preimplantation mouse embryos after exposure to a 50 Hz magnetic field in vitro

Effect of sinusoidal 50 Hz magnetic field (MF) on development of preimplantation CBA/S mouse embryos in vitro was studied. Superovulated and in vivo fertilized preimplantation embryos were collected at one cell stage and divided to control and MF-exposed groups. Sinusoidal 50 Hz MF with field strength of 10 A/m r.m.s., corresponding a flux density of 13 microT r.m.s., was used to expose the embryos in culture at 37 degrees C in a CO2-incubator. The developmental stage and abnormalities were recorded twice daily except once daily during weekends. The vitality and developmental stages of the embryos were similar in both groups although slightly more dead embryos were found during the 1st day in MF-exposed group (P<0.05) and the development of MF-exposed embryos was slightly impaired. In conclusion, the exposure to sinusoidal 50 Hz MF at field strength of 10 A/m did not significantly disturb the development of the mouse embryos in vitro up to the blastocyst stage.

Effects of 50 Hz magnetic fields on cancer induced by ionizing radiation in mice

PURPOSE

To evaluate the effects of 50 Hz magnetic fields (MF) on the development of cancer induced by ionizing radiation.

MATERIALS AND METHODS

A total of 150 female CBA/S mice were randomized into three equal groups at the age of 3-5 weeks. One of the groups served as a 'cage-control group'. The two other groups were exposed to ionizing radiation in the beginning of the study. One of these two groups was exposed 24 h per day, for 1.5 years, to a 50Hz vertical MF, the intensity of which varied regularly between 1.3, 13 and 130 muT. The other served as a control group and was sham-exposed to MF in similar, but unenergized, exposure racks. Body weights, clinical signs, and food and water consumption were recorded regularly. Haematological examination, and the histopathological analysis of all lesions and major tissues were performed on all animals.

RESULTS

MF exposure did not increase the incidence of any primary neoplasms. However, the incidence of basophilic liver foci, a probable pre-neoplastic change in liver, was increased. The incidence of hepatocellular adenomas was unchanged, whereas the incidence of hepatocellular carcinomas was slightly, but not statistically significantly, elevated.

CONCLUSIONS

It is concluded that overall the results of this study do not support a role for MF as a tumour promoter.

Effects of low-frequency magnetic fields on implantation in rats

Effects of 50-Hz sinusoidal magnetic fields (MFs) on embryo implantation, serum 17beta-estradiol, progesterone, testosterone, and melatonin levels, and on estrogen receptor (ER) and progesterone receptor (PgR) densities in the uterus were studied during the preimplantation and implantation periods in rats. Pregnant Wistar rats were exposed to magnetic r.m.s. field strengths of 10 or 100 A/m (13 or 130 microT) or sham-exposed (controls) from day 0 of pregnancy for 24 h/day and killed during light and dark periods between 70 h and 176 h after ovulation. MFs did not influence the mean total number of implantations. The nocturnal mean serum melatonin concentration decreased by 34 and 38% at 10 and 100 A/m, respectively. At the same time, the first embryos, at an early developmental stage, arrived in the uterus in the MF-exposed groups. Serum estradiol and progesterone levels did not significantly change. Nuclear PgR and ER densities in the uterus decreased before implantation and there was an increased incidence of early stage embryos and fewer hatched embryos were found in the uterus at 100 A/m. During the early implantation period, the uterine cytosolic ER/PgR-ratio was increased at 100 A/m and no implants were concomitantly found in uterus. The nuclear ER/PgR-ratio decreased during implantation in both MF-groups due to decreased nuclear ER density. At the same time, 19% and 15% of the embryos (calculated from the corpora luteae) at 10 and 100 A/m, respectively, were yet morulae and not implanted. In summary, the results show that MFs do not impair implantation in rats although there may be some borderline changes in the transport and development of embryos and associated endocrinologic parameters.

Epidermal ornithine decarboxylase and polyamines in mice exposed to 50 Hz magnetic fields and UV radiation

We studied the influence of magnetic fields (MFs) and simulated solar radiation (SSR) on ornithine decarboxylase (ODC) and polyamines in mouse epidermis. Chronic exposure to combined MF and SSR did not cause persistent effects on ODC activity or polyamines compared to the animals exposed only to UV, although the same MF treatment was previously found to accelerate skin tumor development. In an acute 24-h experiment, an elevation of putrescine and down-regulation of ODC activity was observed in the animals exposed to a 100-microT MF. No effect was seen 24 h after a single 2-MED (minimal erythemal dose) exposure to SSR. The results indicate that acute exposure to 50 Hz MF does exert distinctive biological effects on epidermal polyamine synthesis.

Increased resorptions in CBA mice exposed to low-frequency magnetic fields: an attempt to replicate earlier observations

This paper has two aims. First, it reports the findings of a study on the effects of low-frequency magnetic fields on reproduction. Second, it serves as an example of an attempt to replicate the results of an experimental study in an independent laboratory and discusses some of the problems of replication studies. To try to replicate the findings of a study reporting increased resorptions (fetal loss) in mice exposed to 20 kHz magnetic fields with sawtooth waveform and to study the possible effects of 50 Hz sinusoidal fields, pregnant mice were exposed to magnetic fields from day 0 to 18 of pregnancy, 24 h per day. The flux densities of the vertical magnetic fields were 15 microT (peak-to-peak) at 20 kHz and 13 or 130 microT (root mean square) at 50 Hz. Two strains of animals were used: CBA/S mice imported from the laboratory reporting the original observations, and a closely related strain CBA/Ca. The CBA/S mice were cleaned of pathogenic microbes and parasites before they were imported into our laboratory. The magnetic field exposures did not affect resorption rate in CBA/Ca mice. In CBA/S, the frequency of resorptions was higher in the exposed mice than in the control group. However, the increase was not significantly different from either the no-effect hypothesis or the results of the original study we were attempting to replicate. Differences between the two studies and difficulties in interpreting the results are discussed. It is concluded that the results tend more to support than argue against increased resorptions in CBA/S mice exposed to the 20 kHz magnetic field. The results demonstrate that animal strain is an important variable in bioelectromagnetics research: even closely related strains may show different responses to magnetic field exposure.

Effects of low-frequency magnetic fields on fetal development in CBA/Ca mice

Effects of alternating magnetic fields (MFs) on the embryonic and fetal development in CBA/Ca mice were studied. Mated females were exposed continuously to a sinusoidal 50 Hz (13 microT or 0.13 mT root mean square) or a sawtooth 20 kHz (15 microT peak-to-peak) MF from day 0 to day 18 of pregnancy for 24 h/day until necropsied on day 18. Control animals were kept under the same conditions without the MF. MFs did not cause maternal toxicity. No adverse effects were seen in maternal hematology and the frequency of micronuclei in maternal bone marrow erythrocytes did not change. The MFs did not increase the number of resorptions or fetuses with major or minor malformations in any exposure group. The mean number of implantations and living fetuses per litter were similar in all groups. The corrected weight gain (weight gain without uterine content) of dams, pregnancy rates, incidences of resorptions and late fetal deaths, and fetal body weights were similar in all groups. There was, however, a statistically significant increase in the incidence of fetuses with at least three skeletal variations in all groups exposed to MFs. In conclusion, the 50 Hz or 20 kHz MFs did not increase incidences of malformations or resorptions in CBA/Ca mice, but increased skeletal variations consistently in all exposure groups.

Nocturnal 6-hydroxymelatonin sulfate excretion in female workers exposed to magnetic fields

The objective of this study was to determine whether daytime occupational exposure to extremely low frequency magnetic fields (MFs) suppresses nocturnal melatonin production. Sixty female volunteers were recruited. Thirty-nine worked in a garment factory, and 21 office workers served as a reference group. Exposure assessment was based on the type of sewing machine used and MF measurements around each type of machine. Eye-level MF flux density was used to classify the operators to higher (>1 microT) and lower (0.3-1 microT) exposure categories. A third group of factory workers had diverse MF exposures from other sources. The reference group had average exposure of about 0.15 microT. Urine samples were collected on Friday and Monday for three consecutive weeks. Melatonin production was assessed as urinary 6-hydroxymelatonin sulfate (6-OHMS) excretion. The ratio of Friday morning/Monday morning 6-OHMS was used to test the hypothesis that melatonin production is suppressed after 4 days of occupational MF exposure with significant recovery during the weekend. Possible chronic suppression of melatonin production was evaluated by studying exposure-related differences in the Friday values by multivariate regression analysis. The Monday/Friday ratios were close to 1.0, suggesting that there is no increase in melatonin production over the weekend. The average 6-OHMS excretion on Friday was lower among the factory workers than in the reference group, but no monotonous dose-response was observed. Multivariate regression analysis identified MF exposure, smoking, and age as significant explanatory variables associated with decreased 6-OHMS excretion.

Possible cocarcinogenic effects of ELF electromagnetic fields may require repeated long-term interaction with known carcinogenic factors

Literature on cancer-related biological effects of extremely low frequency (ELF) magnetic fields (MF) is discussed in the light of the current understanding of carcinogenesis as a multistep process of accumulating mutations. Different animal models and study designs have been used to address possible cocarcinogenic effects of MFs. Based on a comparison of the results, we propose a hypothesis that MF exposure may potentiate the effects of known carcinogens only when both exposures are chronic. We also discuss possible mechanisms of MF effects on carcinogenesis and the adequacy of the classical two-step initiation/promotion animal experiments for simulating human exposure to the complex mixture of environmental carcinogens. We conclude that experiments designed according to the two-step concept may not be sufficient for studying the possible role of MF in carcinogenesis. Possible further animal studies are more likely to be productive if they include models that combine chronic exposure to MFs with long-term exposures to known carcinogens.

Dose-response of electromagnetic field-enhanced ornithine decarboxylase activity

Alteration of ODC activity in animals or cultured cells exposed to extremely low frequency electromagnetic fields, or to modulated microwave fields, has been documented by several laboratories. However, an evaluation of the dose-response relationship in these experiments has not been done. We examined ODC activity in L929 fibroblasts exposed for 4 h to 60 Hz magnetic fields of different amplitudes. Our results show a clear threshold response which could be fitted to a sigmoidal function, with the 50% point occurring at approximately 5 microT. This sigmoidal response is characteristic of biological responses which are governed by ligand-receptor binding, and has been previously observed in the incidence of magnetic-field induced morphological abnormalities in chick embryos. The implications of this study are discussed in terms of environmental exposures to EM fields.

Effects of gestational exposure to a video display terminal-like magnetic field (20-kHz) on CBA/S mice

Possible adverse effects of magnetic fields (MFs) on reproduction have been an open question. To verify the embryo-lethal effect of pulsed MF of the type emitted by video display terminals (VDTs) reported previously in CBA/S mice, a developmental toxicity study was conducted in animals of the same origin. Mated CBA/S mice (80-86 pregnant animals per group) were exposed to a 20-kHz MF with sawtooth waveform continuously from gestational day 0-18. The flux density of the vertical MF was 15 microT peak-to-peak (150 mG). This field was previously reported to increase the number of resorptions in CBA/S mice. On gestational day 18, the dams were killed and blood and bone marrow samples were taken for hematology and micronuclei analysis, respectively. The number of corpora lutea was counted and the content of the uterus examined. There were no statistically significant differences in maternal or fetal body weights, number of corpora lutea, implantations, resorptions, dead and live fetuses, or external and skeletal malformations. MF did not alter the number of blood cells or cause micronuclei in bone marrow erythrocytes in the dams. The mean number of resorptions was slightly but not statistically significantly, higher in the MF group than in controls. The results do not indicate marked developmental, hematological, or clastogenic effects of 20-kHz MFs.

Biological effects of amplitude-modulated radiofrequency radiation

Users of mobile telephones are exposed to radiofrequency radiation. One of the questions still open today is whether amplitude-modulated radiofrequency signals from digital phones exert specific bioeffects different from those of continuous (unmodulated) radiofrequency radiation. This paper reviews recent literature on the bioeffects of amplitude-modulated radiofrequency radiation, from cells to humans. The consistency of the results is discussed, and exposure parameters are compared to identify possible biologically active forms of amplitude modulation. Several studies have reported findings consistent with effects on the nervous system and cancer-related biological processes. However, the methods and exposure parameters vary widely, and no independent replications of the positive findings have been reported. The results available today fail to support the existence of well-defined modulation-specific bioeffects from exposure to radiofrequency radiation. Additional systematic studies are needed to identify possible reproducible modulation-dependent effects and biologically active modulation parameters.

Effects of 50 Hz magnetic fields on UV-induced skin tumourigenesis in ODC-transgenic and non-transgenic mice

PURPOSE

To study the possible role of 50 Hz magnetic fields (MF) in UV-induced skin tumourigenesis using a sensitive animal model.

MATERIALS AND METHODS

Transgenic mice (line K2) over-expressing the human ornithine decarboxylase (ODC) gene and their non-transgenic littermates were exposed for 10.5 months to UV-only or a combination of UV and a continuous (100 microT) or an intermittent MF with varying intensity (1.3-130 microT).

RESULTS

Both MF exposure and transgenicity enhanced the onset rate of macroscopically detectable tumours, but the effect was statistically significant only for the MF exposure (p < 0.015). The number of animals bearing malignant tumours was low and similar in all exposure groups. Epidermal cysts (EC) appeared to be strongly associated with both MF exposure and high ODC activity (transgenic animals). However, EC are not known to be associated with carcinogenesis. The UV-only or combined UV and MF exposure did not affect the ODC activities measured at the end of the exposure.

CONCLUSIONS

These results support the proposed tumour-promoting effect of MF, but do not suggest an important role for increased ODC activity in this process.

Evaluating alternative exposure indices in epidemiologic studies on extremely low-frequency magnetic fields

Choosing the right exposure index for epidemiological studies on 50-60 Hz magnetic fields is difficult due to the lack of knowledge about critical exposure parameters for the biological effects of magnetic fields. This paper uses data from a previously published epidemiological investigation on early pregnancy loss (EPL) to study the methods of evaluating the exposure-response relationship of 50 Hz magnetic fields. Two approaches were used. The first approach was to apply generalized additive modeling to suggest the functional form of the relationship between EPL and magnetic field strength. The second approach evaluated the goodness of fit of the EPL data with eight alternative exposure indices: the 24 h average of magnetic field strength, three indices measuring the proportion of time above specified thresholds, and four indices measuring the proportion of time within specified intensity windows. Because the original exposure data included only spot measurements, estimates for the selected exposure indices were calculated indirectly from the spot measurements using empirical nonlinear equations derived from 24 h recordings in 60 residences. The results did not support intensity windows, and a threshold-type dependence on field strength appeared to be more plausible than a linear relationship. In addition, the study produced data suggesting that spot measurements may be used as surrogates for other exposure indices besides the time average field strength. No final conclusions should be drawn from this study alone, but we hope that this exercise stimulates evaluation of alternative exposure indices in other planned and ongoing epidemiological studies.

Influence of short-term exposure of magnetic field on the bioelectrical processes of the brain and performance

The influence of an extremely-low-frequency (ELF) magnetic field on the bioelectrical processes of brain and performance was studied by EEG spectral analysis, auditory-evoked potentials (AEP), reaction time (RT) and target-deletion test (TDT). Fourteen volunteers were exposed for 15 min to an intermittent (1 s on/off) 45-Hz magnetic field at 1000 A/m (1.26 mT). Each person received one real and one sham exposure. Statistically significant increases in spectral power through alpha- and beta-bands, as well as in mean frequency of the EEG spectrum were observed after magnetic field exposure. Field-dependent changes of N100 were also revealed. No changes in the amplitudes or latencies of the earlier peaks were observed. No direct effects on RT, nor on TDT performance were seen. However, practice effects on RT (decrease of RT in the course of the test-sessions) seemed to be interrupted by exposure to the magnetic field.

Early pregnancy loss and exposure to 50-Hz magnetic fields

The possibility of an association of early pregnancy loss (EPL) with residential exposure to ELF magnetic fields was investigated in a case-control study. Eighty-nine cases and 102 controls were obtained from the data of an earlier study aimed at investigating the occurrence of EPL in a group of women attempting to get pregnant. Magnetic-field exposure was characterized by measurements in residences. Strong magnetic fields were measured more often in case than in control residences. In an analysis based on fields measured at the front door, a cutoff score of 0.5 A/m (0.63 microT) resulted in an odds ratio of 5.1 (95% confidence interval 1.0-25). The results should be interpreted cautiously due to the small number of highly exposed subjects and other limitations of the data.

Effects of 45-Hz magnetic fields on the functional state of the human brain

The influence of sinusoidal 45-Hz magnetic fields on the brain functions of 20 volunteers was investigated in a double-blind study using spectral analysis of EEG and measurements of Omega potentials and reaction time (RT). The field strength was 1,000 A/m (1.26 mT) and the duration of exposure was 1 h. Ten volunteers were exposed to a continuous field and ten received an intermittent exposure (1 s on/l s off). Each person received one real and one sham exposure. One half of the volunteers got the real exposure first and the sham treatment after at least 24 h. For the rest, the sequence was inverse. The measurements of EEG, omega potentials and RT were performed before and after each exposure. Several statistically significant changes were observed, most of them after intermittent exposure. In the EEG, an increase of alpha (7.6-13.9 Hz) activity and a decrease of delta (1.5-3.9 Hz) activity were observed. Beta waves (14.2-20 Hz) increased in the frontal derivations as did the total power in occipital derivations. The mean and peak frequencies of EEG increased mainly in the frontal derivations. No direct effects on RT were seen. Learning to perform the RT test (decrease of RT in repeated trials), however, seemed to be affected by the exposure. The persons who received real exposure first learned more slowly than those who got sham exposure first. Further experiments are necessary to confirm the findings and for understanding the mechanisms of the effects.

Effects of low-frequency magnetic fields on fetal development in rats

We studied effects of alternating magnetic fields on the embryonic and fetal development of rats. Mated females of the Han:Wistar-strain were sham exposed or exposed continuously to a 50-Hz field or to a 20,000 pulse-per-second (pps) sawtooth magnetic field from day 0 to day 20 of pregnancy for 24 h/day until necropsied on day 20. The respective peak-to-peak intensities of the fields were 35.6 microT (sinewave) and 15.0 microT (sawtooth). Each treatment group contained 72 bred females. Control animals were kept under the same conditions without the magnetic field. No adverse effects were seen in the dams. The mean numbers of implantations and living fetuses per litter were statistically significantly increased in the 50-Hz group. There were, however, three total resorptions of litters in dams of the control group, which contributed to the difference in the number of living fetuses. The corrected body-mass gains (gains without uterine content) of dams were similar in all groups. Pregnancy rates, incidences of resorptions, late fetal deaths, and fetal body masses were similar in all groups. The incidence of fetuses with minor skeletal anomalies was statistically significantly increased in both exposed groups. Only one serious malformation (anophthalmia, sawtooth-exposed group) and a few minor visceral malformations were found. In conclusion, the magnetic fields used in this study did not increase the incidence of major malformations or resorptions in Wistar rats. The increased number of skeletal anomalies and implantations we observed indicates, however, that some developmental effects in rats may attend exposure to time-varying magnetic fields.

Effects of low-frequency magnetic fields on embryonic development and pregnancy

Experimental and epidemiologic studies on the effects of low-frequency magnetic fields on pregnancy are reviewed. The literature suggests that these fields have adverse effects on chick embryo development. The interaction mechanism is not known. The results of experiments with mammals are inconsistent. There is more evidence of effects on mice than on rats, and the data suggest that fetal loss might be increased rather than malformations. Most of the epidemiologic studies related to pregnancy and low-frequency magnetic fields have concerned operators of a video display terminal (VDT). The results do not provide evidence for an association between adverse pregnancy outcome and use of a VDT. Other (stronger) sources of low-frequency magnetic fields have been addressed in only a few studies. It is not yet possible to conclude whether occupational or residential exposure to low-frequency magnetic fields affects human prenatal development. There is an apparent need for further investigation.

Incidence of leukaemia and brain tumours in Finnish workers exposed to ELF magnetic fields

The relative incidence of leukaemia, acute myeloid leukaemia (AML) and central nervous system (CNS) tumours among workers presumably exposed to extremely low frequency (ELF) magnetic fields (MFs) was studied. The study population consisted of all male industrial workers in Finland aged 25 to 64 years during 1971-1980 according to the Population Census in 1970. The occupations were grouped into three exposure categories according to the probability of exposure. The category of "probable" exposure included electrical occupations and the category of "possible" exposure included occupations where electric motors or welding are common. All other occupations were included to the category of "no exposure". Cancer incidence rates in different occupational groups during 1971-1980 were obtained after linking the census records with the national death certificates and the files of the Finnish Cancer Registry. The adjusted relative risks (with 95% confidence limits) in the categories of "probable" and "possible" exposure were for all leukaemia 1.9 (1.0-3.5) and 1.4 (1.1-1.8), for AML 1.5 (0.5-4.7) and 1.4 (0.9-2.1), and for CNS tumours 1.3 (0.7-2.3) and 1.3 (1.0-1.6), respectively. The results are concordant with earlier studies suggesting elevated risk among workers exposed to ELF magnetic fields.

Relationship between field strength and abnormal development in chick embryos exposed to 50 Hz magnetic fields

Chick embryos were exposed to sinusoidally oscillating 50 Hz magnetic fields during their first 2 days of development. In the first series of experiments magnetic field strengths of 0.1, 0.3, 1 and 10 A/m were used. The percentage of abnormal embryos (% AE) was 16 per cent in the sham-exposed control group. % AE was increased at 1 A/m (29 per cent) and 10 A/m (32 per cent), but not at 0.1 A/m (16 per cent) or 0.3 A/m (14 per cent). In the second series of experiments field strengths of 0.4, 0.6, 0.9 and 1.35 A/m were used. % AE was 17 per cent in the control group, 10 per cent at 0.4 A/m, 19 per cent at 0.6 A/m, 17 per cent at 0.9 A/m and 36 per cent at 1.35 A/m. Only the 1.35 A/m group was significantly different from the controls. The results of this study suggest that exposure of chick embryos to a 50 Hz magnetic field causes abnormal development, and that no abnormalities are induced below a threshold between 0.9 and 1 A/m.

Comparison of methods used for measuring the electrostatic field of video display terminals

The electrostatic field of video display terminal (VDT) operators was measured with different methods. Using the Wilson plate method the field strength at different locations at the face of three human subjects working with a VDT was determined. The strongest fields were found at protruding facial features. Measurements were also made with a measuring instrument known as a field mill. Comparative measurements were made with the field mill as such and combined with a metal plate or a hemisphere. The measured field strength was highly dependent on the method of measurement. A conducting hemisphere (diameter 0.20 m), used in combination with the field mill, was found to be a useful model of the human head in electrostatic measurements.

Measurements of extremely low-frequency magnetic fields around video display terminals

The extremely low-frequency (ELF) magnetic field emissions of seven video display terminal (VDT) models were measured. A measuring coil with a linearized frequency response (50 Hz to 25 kHz) was used. The dominating ELF magnetic field around the terminals was the 50 or 60 Hz asymmetric triangular waveform from the vertical deflection coil of the cathode ray tube. At the distance of 50 cm, the magnetic field strength was still slightly higher than the background level in usual office rooms, but several orders of magnitude lower than the thresholds of known interaction mechanisms. Some recent experiments suggest that certain biological effects may occur at field strengths only a few times higher than those found at the position of VDT operators, but the significance of these effects to human health is not known.