Chronic toxicity/oncogenicity evaluation of 60 Hz (power frequency) magnetic fields in F344/N rats

Impact of Extremely Low-Frequency Electromagnetic Fields on Skeletal Muscle of Sedentary Adult Mice: A Pilot Study

Extremely low-frequency electromagnetic fields (ELF-EMFs) are ubiquitous in industrialized environments due to the continuous use of electrical devices. Our previous studies demonstrated that ELF-EMFs affect muscle cells by modulating oxidative stress and enhancing myogenesis. This pilot study investigated these effects on the skeletal muscles of sedentary adult mice, assessing physiological responses to ELF-EMF exposure and potential modulation by antioxidant supplementation. Male C57BL/6 mice were exposed to ELF-EMFs (0.1 or 1.0 mT) for 1 h/day for up to 5 weeks and fed a standard diet without or with N-acetyl-cysteine (NAC). The results showed transient increases in muscle strength (after 2 weeks of exposure at 1.0 mT), potentially linked to muscle fiber recruitment and activation, revealed by higher PAX7 and myosin heavy chain (MyH) expression levels. After ELF-EMF exposure, oxidative status assessment revealed transient increases in the expression levels of SOD1 and catalase enzymes, in total antioxidant capacity, and in protein carbonyl levels, markers of oxidative damage. These effects were partially reduced by NAC. In conclusion, ELF-EMF exposure affects skeletal muscle physiology and NAC supplementation partially mitigates these effects, highlighting the complex interactions between ELF-EMFs and antioxidant pathways in vivo. Further investigations on ELF-EMFs as a therapeutic modality for muscle health are necessary.

Long-Term Study on the Effects of Housing C57BL/6NCrl Mice in Cages Equipped With Wireless Technology Generating Extremely Low-Intensity Electromagnetic Fields

The recent development of mouse cages equipped with monitoring wireless technology raised questions on the potential effects on animals induced by electromagnetic fields (EMFs) generated by electronic boards positioned underneath the cages. The aims of this study were to characterize the EMF produced by digitally ventilated cages (DVC) and perform a clinicopathological study on mice maintained in DVC for up to 1 year. The EMFs were measured in empty individually ventilated cages (IVC) and DVC. Male (n = 160) and female (n = 160) C57BL/6NCrl mice were randomly housed in IVC and DVC in a single rack, 4 mice per cage. Body weight and food and water consumption were recorded at 14-day intervals. At sacrifice (days 60, 120, 180, and 365), body and testes weight was measured, and necropsy, hematology, bone marrow cytology, histology, and immunohistochemistry for cleaved-caspase 3 on the testes were performed. Digitally ventilated cages produced extremely low-intensity electric fields ranging from 5 Hz to 3 GHz. No exposure-related clinical signs and mortality occurred. Occasional statistical differences in body weight, food and water consumption, hematology, bone marrow, and histopathology were recorded, but considered without biological or clinical relevance. In conclusion, long-term maintenance in DVC had no definite effects on C57BL/6NCrl mice.

The carcinogenic potential of non-ionizing radiations: The cases of S-50 Hz MF and 1.8 GHz GSM radiofrequency radiation

Epidemiological studies have suggested that human exposure to extremely low-frequency electromagnetic fields from the electric power and to mobile phone radiofrequency electromagnetic fields induce an increased risk of developing malignant tumours. However, no adequate laboratory data, in particular long-term carcinogenicity bioassays to support the epidemiological evidence, have yet been available. This motivated the Ramazzini Institute to embark on a first project of four large life-span carcinogenic bioassays conducted on over 7000 Sprague Dawley rats exposed from prenatal life until natural death to S-50 Hz MF alone or combined with gamma radiation or formaldehyde or aflatoxin B1. Results now available from these studies, which started concurrently, have shown that exposure to Sinusoidal-50 Hz Magnetic Field (S-50 Hz MF) combined with acute exposure to gamma radiation or to chronic administration of formaldehyde in drinking water induces a significantly increased incidence of malignant tumours in males and females. A second project of two large life-span carcinogenic bioassays was conducted on over 3000 Sprague Dawley rats exposed from prenatal life until natural death to 1.8 GHz GSM of mobile phone radio base station, alone or combined with acute exposure to gamma radiation. Early results from the experiment on 1.8 GHz GSM alone show a statistically significant increase in the incidence of heart malignant schwannoma among males exposed at the highest dose.

Results of lifespan exposure to continuous and intermittent extremely low frequency electromagnetic fields (ELFEMF) administered alone to Sprague Dawley rats

BACKGROUND

Up to now, experimental studies on rodents have failed to provide definitive confirmation of the carcinogenicity of extremely low frequency electromagnetic fields (ELFEMF). Two recent studies performed in our laboratory on Sprague-Dawley rats reported a statistically significant increase in malignant tumors of different sites (mammary gland, C-cells carcinoma, hemolymphoreticular neoplasia, and malignant heart Schwannoma) when ELFEMF exposure was associated with exposure to formaldehyde (50 mg/l) or acute low dose of γ-radiation (0.1 Gy) (Soffritti et al., 2016a) (Soffritti et al., 2016b). The same doses of known carcinogenic agents (50 mg/l formaldehyde, or acute 0.1 Gy γ-radiation), when administered alone, previously failed to induce any statistically significant increase in the incidence of total and specific malignant tumors in rats of the same colony.

OBJECTIVES

A lifespan whole-body exposure study was conducted to evaluate the possible carcinogenic effects of ELFEMF exposure administered alone to Sprague-Dawley rats, as part of the integrated project of the Ramazzini Institute (RI) for studying the effects on health of ELFEMF alone or in combination with other known carcinogens.

METHODS

Male and female Sprague-Dawley rats were exposed 19 h/day to continuous sinusoidal-50 Hz magnetic fields (S-50 Hz MF) at flux densities of 0 (control group), 2, 20, 100 or 1000µT, and to intermittent (30 min on/30 min off) S-50 Hz MF at 1000 µT, from prenatal life until natural death.

RESULTS

Survival and body weight trends in all groups of rats exposed to ELFEMF were comparable to those found in sex-matched controls. The incidence and number of malignant and benign tumors was similar in all groups. Magnetic field exposure did not significantly increase the incidence of neoplasias in any organ, including those sites that have been identified as possible targets in epidemiological studies (leukemia, breast cancer, and brain cancer).

CONCLUSIONS

Life-span exposures to continuous and intermittent sinusoidal-50 Hz ELFEMFs, when administered alone, did not represent a significant risk factor for neoplastic development in our experimental rat model. In light of our previous results on the carcinogenic effects of ELFEMF in combination with formaldehyde and γ-radiation, further experiments are necessary to elucidate the possible role of ELFEMF as cancer enhancer in presence of other chemical and physical carcinogens.

Synergism between sinusoidal-50 Hz magnetic field and formaldehyde in triggering carcinogenic effects in male Sprague-Dawley rats

BACKGROUND

Experimental rodent bioassays performed up to now have failed to provide conclusive confirmation of the carcinogenicity of extremely low frequency magnetic fields (ELFMF).

OBJECTIVES

To evaluate the potential synergistic carcinogenic effects of concurrent exposure to ELFMF and formaldehyde in four groups of male and female Sprague-Dawley rats.

METHODS

One group was exposed from prenatal life until natural death to S-50 Hz MF and to formaldehyde in drinking water from 6 weeks of age for 104 weeks, two groups were treated only with formaldehyde or only with MF and one group served as untreated control.

RESULTS

Compared to untreated controls, exposure to MF and formaldehyde causes in males a statistically significant increased incidence of malignant tumors (P ≤ 0.01), thyroid C-cell carcinomas (P ≤ 0.01), and hemolymphoreticular neoplasias (P ≤ 0.05). No statistically significant differences were observed among female groups.

CONCLUSIONS

Life-span exposure to MF and formaldehyde induces statistically significant carcinogenic effects in male rats. Am. J. Ind. Med. 59:509-521, 2016. © 2016 Wiley Periodicals, Inc.

Life-span exposure to sinusoidal-50 Hz magnetic field and acute low-dose γ radiation induce carcinogenic effects in Sprague-Dawley rats

Background In 2002 the International Agency for Research on Cancer classified extremely low frequency magnetic fields (ELFMF) as a possible carcinogen on the basis of epidemiological evidence. Experimental bioassays on rats and mice performed up to now on ELFMF alone or in association with known carcinogens have failed to provide conclusive confirmation. Objectives To study the carcinogenic effects of combined exposure to sinusoidal-50 Hz (S-50 Hz) magnetic fields and acute γ radiation in Sprague-Dawley rats. Methods We studied groups of male and female Sprague-Dawley rats exposed from prenatal life until natural death to 20 or 1000 μT S-50 Hz MF and also to 0.1 Gy γ radiation delivered as a single acute exposure at 6 weeks of age. Results The results of the study showed significant carcinogenic effects for the mammary gland in males and females and a significant increased incidence of malignant schwannomas of the heart as well as increased incidence of lymphomas/leukemias in males. Conclusions These results call for a re-evaluation of the safety of non-ionizing radiation.

Regulatory Forum Opinion Piece*: The Value of Publishing Negative Scientific Study Data

Historically it has been easier to publish positive scientific results than negative data not supporting the research hypothesis. This appears to be increasing, with fewer negative studies appearing in the literature across many disciplines. Failure to recognize the value of negative results has important implications for the toxicology community. Implications include perpetuating scientific fields based upon selective or occasionally erroneous, positive results. One example is decreased vaccination rates and increased measles infections that can lead to childhood mortality following one erroneous positive study linking vaccination to adverse effects despite multiple negative studies. Publication of negative data that challenges existing paradigms enhances progress by stopping further investment in scientifically barren topics, decreases the use of animals, and focuses research in more fruitful areas. The National Toxicology Program (NTP) publishes both positive and negative rodent data. Retrospective analysis of the NTP database has provided insights on the carcinogenic process and in the gradual acceptance of using fewer animals in safety studies. This article proposes that careful publication of both positive and negative data can enhance product safety assessment, add robustness to safety determinations in the regulatory decision-making process, and should be actively encouraged by those determining journal editorial policy.

ELF magnetic fields: animal studies, mechanisms of action

Animal studies can contribute to addressing the issue of possible greater health risk for children exposed to 50-60 Hz extremely low frequency (ELF) magnetic fields (MFs), mostly in terms of teratological effects and cancer. Teratology has been extensively studied in animals exposed to ELF MFs but experiments have not established adverse developmental effects. Childhood leukaemia has been the only cancer consistently reported in epidemiological studies as associated with exposure to ELF MFs. This association has been the basis for the classification as "possibly carcinogenic to humans" by the International Agency for Research on Cancer in 2002. Animal experiments have provided only limited support for these epidemiological findings. However, none but one study used an animal model for acute lymphoblastic leukaemia (ALL), the main form of childhood leukaemia, and exposures to ELF MFs were not carried out over the whole pregnancy period, when the first hit of ALL is assumed to occur. Moreover, there are no generally accepted biophysical mechanisms that could explain carcinogenic effects of low-level MFs. The radical pair mechanism and related cryptochromes (CRY) molecules have recently been identified in birds and other non-mammalian species, as a sensor of the geomagnetic field, involved in navigation. The hypothesis has to be tested in mammalian models. CRY, which is part of the molecular circadian clock machinery, is a ubiquitous protein likely to be involved in cancer cell growth and DNA repair. In summary, we now have some clues to test for a better characterization of the interaction between ALL and ELF MFs exposure.

Evaluation of testicular degeneration induced by low-frequency electromagnetic fields

The population exposure to electromagnetic fields (EMF) has been growing in recent decades. The generation, distribution and use of electric energy can generate low-frequency electromagnetic fields. The present study investigates the effects of EMF (60 Hz and 1 mT) on spermatogenesis of rats during different periods of maturation. Wistar rats were exposed to EMF from day 13 of gestation to postnatal day 21 or 90 in three daily applications of 30 min. Plasma testosterone concentration was not changed by EMF exposure; however, histopathological and histomorphometrical analyses of the testes showed testicular degeneration in a subset of animals exposed to EMF. The magnitude of the degenerative process varied between those individuals affected, indicating different individual sensitivity to EMF. The main alterations observed through transmission electron microscopy were highly electron-dense mitochondria with loss of their organization and cristae. Exposure to 60 Hz and 1 mT EMF can disturb spermatogenesis and may produce subfertility or infertility.

The effects of chronic exposure to electromagnetic fields on thyroid parafollicular cells in rats

<br><br><b><font color="red">Withdrawn; published twice because of tehnical error. Link to the Editorial Decision <u><a href="http://dx.doi.org/10.2298/ABS1004251U">10.2298/ABS1004251U</a></u></font></b><br>

Chronic exposure to electromagnetic fields: Effects on thyroid parafollicular cells in rats

Based on the presented results and the previous data on thyroid follicles, it could be concluded that (i) PF cells and follicular cells reacted to EMF exposure similarly by their decreased activity, (ii) PF cells are the endocrine cell 'population' in the thyroid less susceptible to EMFs, and (iii) the activation of PF cells after the first recovery week following EMF exposure indicates a possible moderate involvement of these cells in overall thyroid reaction to certain environmental influences.

Lack of promotion effects of 50 Hz magnetic fields on 7,12-dimethylbenz(a)anthracene-induced malignant lymphoma/lymphatic leukemia in mice

New-born CD-1 mice were initiated with a single subcutaneous injection of 60 microg 7,12-dimethylbenz(a)anthracene (DMBA) within 24 h after birth. After weaning, the mice were randomly divided into five groups of 100, 50 males and 50 females each. One group served as a cage control. The other four groups of mice were exposed to either 0 (sham-exposed), 7, 70, or 350 microT(rms) circularly polarized 50 Hz magnetic fields (MFs) for 22 h/day, 7 days/week for 30 weeks. Animals were observed daily and the development of malignant lymphoma/lymphatic leukemia was examined histopathologically. The experiment was conducted twice. There was no observed sexual difference in the cumulative proportions of mice with malignant lymphoma/lymphatic leukemia and a 3-way analysis of deviance using the Cox regression model revealed no interactions between experiment, sex, or group. The cumulative proportions of mice with malignant lymphoma/lymphatic leukemia in the MF-exposed groups were not significantly higher than those in the sham-exposed group of each sex in individual experiments and in males and females combined in each experiment, and in all the animals from the two experiments combined. These data provide no evidence to support the hypothesis that power frequency MFs is a significant risk factor for hematopoietic neoplasia.

Power Frequency Magnetic Fields Increase Cell Proliferation in the Mammary Gland of Female Fischer 344 Rats but Not Various Other Rat Strains or Substrains

Epidemiological data have raised concerns about the relationship between exposure to power frequency magnetic fields (MFs) and breast cancer. We have shown previously that 50-Hz MFs at microtesla flux densities enhance mammary gland tumor development and growth in the 7,12-dimethylbenz[a]anthracene (DMBA) model of breast cancer in female Sprague-Dawley (SD) rats. We also demonstrated that MF exposure results in an enhanced proliferative activity of the mammary epithelium of SD rats, which is a likely explanation for the cocarcinogenic or tumor-promoting effects of MF exposure in the DMBA model. Comparison of different SD substrains indicated that the genetic background plays a pivotal role in these effects of MF exposure. This prompted us to compare the effects of MF exposure (100 microT, 2 weeks) on cell proliferation in the mammary gland in eight different strains and substrains of outbred and inbred rats. Proliferation of epithelial cells in the mammary tissue and adjacent skin was examined by labeling proliferating cells with bromodeoxyuridine (BrdU). In addition to the MF-sensitive SD substrain (SD1) previously used in our experiments, Fischer 344 rats were the only strain in which MF exposure significantly enhanced BrdU labeling in the mammary epithelium, indicating a marked increase in cell proliferation. The MF-induced increase in BrdU labeling in Fischer 344 rats was similar to that seen after DMBA application. Furthermore, whole mount analysis of mammary tissue from Fischer 344 rats demonstrated that MF exposure increased the number of terminal end buds, i.e. the site of origin of mammary carcinomas. By comparison with MF-insensitive inbred rat strains, Fischer 344 rats may serve to evaluate the genetic factors underlying sensitivity to cocarcinogenic or tumor-promoting effects of MF exposure.

Evaluation of spermatogenesis and fertility in F1 male rats after in utero and neonatal exposure to extremely low frequency electromagnetic fields

AIM

To determine whether in utero and neonatal exposure to a 60 Hz extremely low frequency electromagnetic field (EMF) results in spermatotoxicity and reproductive dysfunction in the F1 offspring of rats.

METHODS

Age-matched, pregnant Sprague-Dawley rats were exposed continuously (21 h/day) to a 60 Hz EMF at field strengths of 0 (sham control), 5, 83.3 or 500 microT from day 6 of gestation through to day 21 of lactation. The experimentally generated magnetic field was monitored continuously (uninterrupted monitoring over the period of the study) throughout the study.

RESULTS

No exposure-related changes were found in exposed or sham-exposed animals with respect to the anogenital distance, preputial separation, testis weight, testicular histology, sperm count, daily sperm production, sperm motility, sperm morphology and reproductive capacity of F1 offspring.

CONCLUSION

Exposure of Sprague-Dawley rats to a 60 Hz EMF at field strengths of up to 500 microT from day 6 of gestation to day 21 of lactation did not produce any detectable alterations in offspring spermatogenesis and fertility.

Lack of Effect of Extremely Low Frequency Electromagnetic Fields on Cyclin-Dependent Kinase 4 Inhibitor Gene p18INK4C in Electric Energy Workers

BACKGROUND

Long-term exposure to extremely low frequency magnetic fields (ELF-MFs) may be a risk factor for human cancer. One mechanism through which ELF-MFs could influence neoplastic development is the deletion/mutation of cancer-related genes. Cellular proliferation follows an orderly progression through the cell cycle, which is governed by different cyclins and cyclin-dependent kinase inhibitors (CDKIs). The putative tumor suppressor gene p18(INK4C) encodes a specific inhibitor of cyclin D-cyclin-dependent kinase 4 inhibitor complexes having an important role in cell-cyclin regulation. It has been found to be deleted/mutated in a variety of human cancers. Therefore, this study is to investigate whether or not long-term extremely low frequency electromagnetic field exposure may be a risk factor for human cancer due to the gene p18(INK4C) deletion/mutation.

METHODS

The study was carried out on 31 male electric workers and 30 healthy males between 30 and 40 years of age from the same geographic area and with similar lifestyles. We studied both groups by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP).

RESULTS

In comparison to the controls, band migration of exon 1 was found to be indifferent in all the subjects tested. However, only exon 2 of two electric workers was slow in migration with respect to both control and other subjects in the same class. This slow migration suggests that point mutations or polymorphisms may exist in this region of the p18(INK4C) gene. The relative risk (RR) for the unmatched analysis was 1,069 (95% confidence interval [CI] 0.975-1.172).

CONCLUSIONS

The results suggest that long-term ELF-MFs exposure does not significantly increase the risk of cancer.

Health effects relevant to the setting of EMF exposure limits

To date, electric and magnetic exposure limits for frequencies below 100 kHz have been based on vaguely defined neurobiological responses to electric fields induced in tissues in vivo by magnetic fields and on perceptual responses to external electric fields. Advances in tissue dosimetry, risk assessment methods, and biological research on stimulation thresholds and mechanisms are providing new bases for exposure limits. This paper reviews the historical basis for current electric and magnetic exposure limits in preparation for the development of the "next generation" of electric and magnetic occupational and public exposure guidelines. This is followed by an overview of reported neurobiological effects of electric and magnetic stimulation that should be considered in new exposure guidelines. For magnetic fields, there is stronger evidence for setting exposure limits to protect against adverse effects of nerve stimulation than for protecting against visual magnetophosphenes. Magnetophosphenes are not adverse, and the evidence that these perceptual responses of the eye are a precursor or surrogate for other adverse neurologic responses is weak. Rather than relying just on theoretical models to set exposure limits, data from human subjects exposed to pulsed magnetic fields should be used to estimate nerve stimulation thresholds. Such data can provide a solid basis for setting magnetic field exposure limits if uncertainties in the data and inter-individual variability are addressed. Research on sensory perception, spontaneous and evoked potentials, and epidemiologic studies of neuropsychiatric conditions in electric and magnetic exposed populations does not suggest a need for lower exposure limits. However, a report that a 60-mT magnetic field (below the threshold for peripheral nerve stimulation) produces prolonged alterations of brain excitability and "indisposure" of subjects should be investigated in future research.

Electric fields induced in humans and rodents by 60 Hz magnetic fields

Numerical computations are used to evaluate electric field dosimetry for high-resolution anatomically based inhomogeneous models of a human male child, and male and female rats and mice, under exposure to 60 Hz uniform magnetic field sources of three perpendicular orientations. The goal is to compare the child data to previously computed adult dosimetry and to evaluate the accuracy of linear scaling of organ dosimetry between species. It is expected that this work will aid in the design and interpretation of experiments involving rodents. It is found that child-to-adult and mouse-to-rat organ dosimetry shows the expected linear dependence on the geometric scale factor between models. The comparison between mice and the human child shows that postural and individual organ differences do have significant effects, and that care is required in scaling-based extrapolation of rodent experiment results to humans. However, for unrestrained animals, linear scaling appears to be a reasonable and conservative approach. Most of the rodent organ fields, for at least one field orientation, are greater than those expected from linear scaling.

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.

Effect of short duration electromagnetic field exposures on rat mass

Daily preexposure and postexposure mass measurements of 65 rats (young males and females, old males) a proprietary pulsed wound healing field, pulsed electromagnetic field, (PEMF), or their control fields for 4 h/day for 21 days. Statistical analysis of mass changes over time showed that young rats exposed to PEMF lost more mass and recovered it more slowly compared to controls (2-4% more loss) than did older PEMF exposed rats or any 60 Hz exposed rats. We conclude that daily preexposure and postexposure mass measurements are needed to adequately assess the effects of electromagnetic fields on body mass.

Leukemia and lymphoma incidence in rodents exposed to low-frequency magnetic fields

A weak association between residential or occupational exposure to electric and magnetic fields (50/60 Hz fields) and an increased incidence of leukemia has been reported. Numerous animal studies have evaluated the potential association between magnetic-field exposure and leukemia. These include long-term (up to 2(1/2) years) bioassays, initiation/promotion studies, investigations in transgenic models, and tumor growth studies. Exposure to 60 Hz circularly polarized magnetic fields at 1,400 microT for 28 months did not affect lymphoma incidence in mice. The study included over 2000 C57BL/6J mice. In another study, 1000 B6C3F(1) mice exposed to 60 Hz magnetic fields up to 1000 microT for 2 years showed no increase in lymphomas. Approximately 400 transgenic Emu-Pim1 mice exposed to 50 Hz fields up to 1000 microT for up to 18 months had no increased incidence of leukemia. Similarly, Trp53(+/-) mice and Pim1transgenic mice exposed to 60 Hz magnetic fields for 23 weeks showed no increased incidence of lymphoma. Three studies in F344 rats exposed to 50 or 60 Hz magnetic fields up to 5 mT showed no increased incidence of leukemia. The combined animal bioassay results are nearly uniformly negative for magnetic-field exposures enhancing leukemia and weaken the possible epidemiological association between magnetic-field exposures and leukemia in humans as suggested by epidemiological data.

The electric and magnetic fields research and public information dissemination (EMF-RAPID) program

In the United States, public concern that exposure to power-line fields was linked to cancer led to the establishment of a Congressionally mandated program, the Electric and Magnetic Fields Research and Public Information Dissemination (EMF-RAPID) Program. A major goal of the program was to "determine whether or not exposures to electric and magnetic fields produced by the generation, transmission, and use of electrical energy affect human health". Between 1994 and 1998, the EMF-RAPID program spent approximately $41 million on biological research. Much of the work funded by the EMF-RAPID program has not yet been published in the peer-reviewed literature. The U.S. National Institute of Environmental Health Sciences (NIEHS) asked that Radiation Research publish this special issue in an attempt to remedy this publication gap. The issue includes reviews of studies that were done to assess the biological plausibility of claims that power-frequency fields caused leukemia and breast cancer. The issue continues with two teratology studies and one immunology study. The section of the issue covering in vitro studies begins with an overview of the efforts NIEHS made to replicate a wide range of reported effects of power-frequency fields and continues with four papers reporting the absence of effects of power-frequency fields on the expression of stress-response genes and oncogenes. Other reports of in vitro studies and studies of mechanisms cover cytotoxicity, gap junction intracellular communication, calcium ion transport across the plasma membrane, and intracellular electric fields.

Magnetic fields and mammary cancer in rodents: a critical review and evaluation of published literature

Epidemiological data suggesting a possible increase in breast cancer risk in male electricians have raised concerns about the relationship between exposure to power-frequency magnetic fields and breast cancer. In this paper, we review the results of animal studies that are relevant to identifying possible increases in breast cancer risk resulting from exposure to 50 or 60 Hz magnetic fields. Three large-scale chronic bioassays of carcinogenesis in rats or mice exposed to magnetic fields for 2 years demonstrated no increases in the incidence of mammary cancer; it is generally accepted that power-frequency magnetic fields have little or no activity as a complete carcinogen in the rodent mammary gland. Findings from one laboratory, though inconsistent, suggest that magnetic fields may stimulate mammary neoplasia in rats treated with a chemical carcinogen. However, studies conducted in two other laboratories failed to confirm these findings; rats exposed to magnetic fields demonstrated patterns of tumor incidence, multiplicity, size and latency that were generally similar to those in sham-exposed controls. Where differences were seen, the groups exposed to magnetic fields generally had fewer mammary tumors than did sham-exposed controls. On this basis, evaluations of the activity of 50 or 60 Hz magnetic fields in models of multistage mammary cancer in rodents have generally been negative; positive findings have been reported from only one laboratory. The totality of rodent data does not support the hypothesis that power-frequency magnetic-field exposure enhances mammary cancer in rodents, nor does it provide experimental support for possible epidemiological associations between magnetic-field exposure and increased breast cancer risk.

Cell viability and growth in a battery of human breast cancer cell lines exposed to 60 Hz magnetic fields

Epidemiological data suggest that exposure to power-frequency (50/60 Hz) magnetic fields (MFs) may be a risk factor for breast cancer in humans. To determine whether MFs affect human breast cancer cells, we measured viability, growth and cytotoxicity in a battery of breast cancer cell lines after in vitro MF and sham exposure. Cells of three estrogen receptor-positive human breast cancer cell lines (MCF-7, ZR-75-1 and T-47D) and one estrogen receptor-negative human breast cancer cell line (MDA-MB-231) and normal (nontransformed) human breast epithelial cells were exposed to MFs (1 mT) or sham fields (<0.0001 mT) for 72 h. Cell viability was determined using the sulforhodamine B (SRB) assay at 0 and 72 h after the MF exposure period. Cell growth was measured as the change in SRB dye uptake over 72 h after MF exposure. MF exposure had no effect on cell viability or growth in any cell type examined. Similarly, MF exposure had no effect on cytotoxicity induced by exposure to the retinoid N-(4-hydroxyphenyl)retinamide. These data do not support the hypothesis that MF exposure stimulates growth of breast cancer cells.

Assessing the potential carcinogenic activity of magnetic fields using animal models

We update our 1997 publication by reviewing 29 new reports of tests of magnetic fields (MFs) in six different in vivo animal models of carcinogenesis: 2-year, lifetime, or multigeneration exposure studies in rats or mice; and promotion/progression models (rat mammary carcinoma, rat liver focus, mouse skin, several models of human leukemia/lymphoma in rats and mice, and brain cancer in rats). Individual experiments are evaluated using a set of data quality criteria, and summary judgments are made across multiple experiments by applying a criterion of rough reproducibility. The potential for carcinogenicity of MFs is discussed in light of the significant body of carcinogenesis data from animal bioassays that now exists. Excluding abstracts, approximately 80% of the 41 completed studies identified in this and our previous review roughly satisfy data quality criteria. Among these studies, the criterion for independent reproducibility is not satisfied for any positive results but is satisfied for negative results in chronic bioassays in rats and mice and for negative results in both promotion and co-promotion assays using the SENCAR mouse skin model. Results of independent replication studies using the rat mammary carcinoma model were conflicting. We conclude that long-term exposure to continuous 50- or 60-Hz MFs in the range of 0.002-5 mT is unlikely to result in carcinogenesis in rats or mice. Though results of most promotion/progression assays are negative, a weak promoting effect of MFs under certain exposure conditions cannot be ruled out based on available data.

Chronic toxicity/oncogenicity evaluation of 60 Hz (power frequency) magnetic fields in B6C3F1 mice

A 2-yr whole-body exposure study was conducted to evaluate the chronic toxicity and possible oncogenicity of 60 Hz (power frequency) magnetic fields in mice. Groups of 100 male and 100 female B6C3F1 mice were exposed to pure, linearly polarized, transient-free 60 Hz magnetic fields at flux densities of 0 Gauss (G) (sham control), 20 milligauss (mG), 2 G, and 10 G; an additional group of 100 male and 100 female B6C3F1 mice received intermittent (1 hr on/1 hr off) exposure to 10 G fields. A small but statistically significant increase in mortality was observed in male mice exposed continuously to 10 G fields; mortality patterns in all other groups of mice exposed to magnetic fields were comparable to those found in sex-matched sham controls. Body weight gains and the total incidence and number of malignant and benign tumors were similar in all groups. Magnetic field exposure did not increase the incidence of neoplasia in any organ, including those sites (leukemia, breast cancer, and brain cancer) that have been identified in epidemiology studies as possible targets of magnetic field action. A statistically significant decrease in the incidence of malignant lymphoma was observed in female mice exposed continuously to 10 G fields, and statistically significant decreases in the incidence of lung tumors were seen in both sexes exposed continuously to 2 G fields. These data do not support the hypothesis that chronic exposure to pure, linearly polarized 60 Hz magnetic fields is a significant risk factor for neoplastic development in mice.