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Acute (2 h) exposure of rats to a 60 Hz magnetic field (flux densities 0.1, 0.25, and 0.5 mT) caused a dose-dependent increase in DNA strand breaks in brain cells of the animals (assayed by a microgel electrophoresis method at 4 h postexposure). An increase in single-strand DNA breaks was observed after exposure to magnetic fields of 0.1, 0.25, and 0.5 mT, whereas an increase in double-strand DNA breaks was observed at 0.25 and 0.5 mT. Because DNA strand breaks may affect cellular functions, lead to carcinogenesis and cell death, and be related to onset of neurodegenerative diseases, our data may have important implications for the possible health effects of exposure to 60 Hz magnetic fields.
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 rats. Groups of 100 male and 100 female F344/N rats were exposed continuously 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 F344/N rats received intermittent (1 hr on/1 hr off) exposure to 10 G fields. Mortality patterns, body weight gains throughout the study, and the total incidence and number of malignant and benign tumors in all groups exposed to magnetic fields were similar to those found in sex-matched sham controls. Statistically significant increases in the combined incidence of C-cell adenomas and carcinomas of the thyroid were seen in male rats chronically exposed to 20 mG and 2 G magnetic fields. These increases were not seen in male rats exposed continuously or intermittently to 10 G fields or in female rats at any magnetic field exposure level. No increases in the incidence of neoplasms, which have been identified in epidemiology studies as possible targets of magnetic field action (leukemia, breast cancer, and brain cancer), were found in any group exposed to magnetic fields. There was a decrease in leukemia in male rats exposed to 10 G intermittent fields. The occurrence of C-cell tumors at the 2 lower field intensities in male rats is interpreted as equivocal evidence of carcinogenicity
Our results do not support the original conclusions: we did not see MF-inducible gene expression for field intensities and exposure durations investigated previously
Extensive testing using both coded and uncoded analyses was negative for an MF effect. Using the same exposure conditions as in the transformation studies, no MF-induced changes in ornithine decarboxylase expression were observed in C3H/10T1/2 cells, casting doubt on a promotional role of MF for the tested cells and experimental conditions.
The results of the present studies demonstrate that exposure to EMF has no statistically significant effects on the expression of c-myc and a battery of other cancer-related genes in two in vitro human breast epithelial cell model systems. These results supplement a growing body of evidence (30–35) which suggests that alterations in oncogene or tumor suppressor gene expression are unlikely to be involved in a mechanism of EMF-induced cancer.
These data, when considered as a whole, are interpreted as indicating that chronic exposure to pure linearly polarized 60 Hz magnetic fields has little or no effect on cancer development in the F344/N rat.
An unexpected association was also observed for colon cancer, using geometric indexes of exposure, but no other association was seen for any other type of cancer. Our study indicates that electric fields may have a specific effect on the risk of brain tumor, and that this should be taken into account in future analyses on the carcinogenic effects of 50- to 60-Hz fields.
Measured magnetic fields under low power use conditions had a modest association with cancer incidence; a cutoff score of 2.0 milligauss resulted in an odds ratio of 1.4 (95% confidence interval (CI) = 0.6– 2.9)
. In addition, there appears to be a dose threshold between 2 and 12 mG. The mechanism(s) of action is unknown and may involve modulation of signal transduction events associated with melatonin's regulation of cell growth.
Abstract: In this study we investigated whether a 60 Hz magnetic field can act at the cellular level to influence the growth of human estrogen-dependent breast cancer cells. Our experimental design assessed cell proliferation of a human breast cancer cell line, MCF-7, in the absence or the presence of melatonin which inhibits growth at a physiological concentration of 10-9 M. In three experiments, continuous exposure to average sinusoidal 60 Hz magnetic fields of 1.90 ± 0.01, 2.40 ± 0.70, and 2.53 ± 0.50 mG, or simultaneous exposure in matched incubators to average 60 Hz magnetic fields of 10.4 ± 2.12, 11.95 ± 2.73, and 11.95 ± 3.28 mG, respectively, had no effect on cell proliferation in the absence of melatonin. When MCF-7 cells were cultured in the presence of 10-9 M melatonin, an 18% inhibition of growth was observed for cells in a 2.40 ± 0.70 mG field. This effect was blocked by a 60 Hz magnetic field of 11.95 ± 2.75 mG. In a second experiment, a 27% inhibition of MCF-7 cell growth was observed for cells in a 2.53 ± 0.50 mG magnetic field, and this was blocked by a 60 Hz magnetic field of 11.95 ± 3.28 mG.
These results provide the first evidence that ELF frequency magnetic fields can act at the cellular level to enhance breast cancer cell proliferation by blocking melatonin's natural oncostatic action
The occurrence of C-cell tumors at the 2 lower field intensities in male rats is interpreted as equivocal evidence of carcinogenicity; data from female rats provides no evidence of carcinogenicity in that sex. These data, when considered as a whole, are interpreted as indicating that chronic exposure to pure linearly polarized 60 Hz magnetic fields has little or no effect on cancer development in the F344/N rat.
Children Living Near High Voltage Power Lines Have Increased Risk of Leukemia
Researchers from England have reported that children living within 200 meters of high voltage power lines have a 70% increased risk of developing leukemia. The details of this large case control study were published in the June 4, 2004, issue of The Lancet .
Some early research suggested that exposure to electromagnetic fields through living next to high voltage power lines was a possible risk factor for developing childhood leukemia. However, more recent studies have failed to document an increased incidence of childhood acute lymphocytic leukemia (ALL) in individuals living near power lines. The details of this report appeared in the June 6, 2005, issue of the British Medical Journal .
The current study is the largest to examine the relationship between living close to high voltage power lines and the incidence of childhood leukemia. These researchers looked at the records of over 29,000 children between the ages of 0 and 14 years with cancer; including 9,700 with leukemia. They found that children who lived within 200 meters of high-voltage power lines had a 70% increased incidence of leukemia compared to individuals who lived more than 600 meters away. They also observed a 23% increased incidence in those living between 200 and 600 meters.
This study has a few important limitations. First, case-control studies are by nature susceptible to sampling bias. In other words, the researchers may have selected control patients that lived further away from power lines by chance; another set of controls may have lived closer to the power lines than the case patients. Second, the researchers were not able to estimate or measure the magnetic field from the power lines, so the researchers could not know what level of magnetic fields the children were actually exposed to.
Even if proximity to high voltage power lines increased the risk of childhood leukemia as much as reported in this study, power lines would only be associated with about five of the 400 to 420 cases that occured in England and Wales each year.
There is an association between childhood leukaemia and proximity of home address at birth to high voltage power lines, and the apparent risk extends to a greater distance than would have been expected from previous studies. About 4% of children in England and Wales live within 600 m of high voltage lines at birth. If the association is causal, about 1% of childhood leukaemia in England and Wales would be attributable to these lines, though this estimate has considerable statistical uncertainty. There is no accepted biological mechanism to explain the epidemiological results; indeed, the relation may be due to chance or confounding.
Leukemia following Occupational Exposure to 60-Hz Electric and Magnetic Fields among Ontario Electric Utility Workers Anthony B. Miller1,, Teresa To1, David A. Agnew2, Claus Wall1 and Lois M. Green2 1Department of Preventive Medicine and Biostatistics, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada 2Health and Safety Services, Ontario Hydro, Toronto, Ontario, Canada Reprint requests to Dr. A. B. Miller, Department of Preventive Medicine and Biostatistics, Faculty of Medicine, University of Toronto, 12 Queens Park Crescent West, Toronto, Ontario M5S 1A8, Canada. In a nested case-control study of 1,484 cancer cases and 2,179 matched controls from a cohort of 31,543 Ontario Hydro male employees, the authors evaluated associations of cancer risk with electric field exposure and reevaluated the previously reported findings for magnetic fields. Pensioners were followed from January 1, 1970, and active workers (including those who left the corporation) from January 1, 1973, with both groups followed through December 31, 1988. Exposures to electric and magnetic fields and to potential occupational confounders were estimated through job exposure matrices. Odds ratios were elevated for hematopoietic malignancies with cumulative electric field exposure. After adjustment, the odds ratio for leukemia in the upper tertile was 4.45 (95% confidence interval (Cl) 1.01–19.7). Odds ratios were also elevated for acute nonlymphoid leukemia, acute myeloid leukemia, and chronic lymphoid leukemia. For cumulative magnetic field exposure, there were similar elevations that fell with adjustment. Evaluation of the combined effect of electric and magnetic fields for leukemia showed significant elevations of risk for high exposure to both, with a dose-response relation for increasing exposure to electric fields and an inconsistent effect for magnetic fields. There was some evidence of a nonsignificant association for brain cancer and benign brain tumors with magnetic fields. For lung cancer, the odds ratio for high exposure to electric and magnetic fields was 1.84 (95% Cl 0.69–4.94). Am J Epidemiol 1996; 144: 150–60. electromagnetic fields; leukemia; neoplasms; occupational diseases