Possible Health Effects of Exposure to Residential Electric and Magnetic Fields (1997) / Chapter Skim
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3 Cellular and Molecular Effects
3 Cellular and Molecular Effects
Pages 52-72
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From page 52... ...
Those effects are genotoxicity and carcinogenicity, changes in intracellular calcium concentrations, and changes in gene expression with emphasis on signal-transduction pathways. SUMMARY AND CONCLUSIONS From its review of the data on cellular and molecular effects from exposure to power-frequency electric and magnetic fields, the committee concludes the following: · Magnetic-field exposures of 50-60 Hz delivered at field strengths similar to those measured for residential exposure (0.01 to 1.0 `1T)
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From page 53... ...
For the positive results that have been observed, as in the bone-healing studies, the effects cannot be extrapolated to lower field strengths; therefore, it is not known whether the effects observed at higher field strengths are induced by mechanisms distinctly different from those that might cause effects at residential and occupational field strengths. The committee's overall conclusion based on analysis of in vitro experimentation is that magnetic-field exposures at 50-60 Hz have been shown to induce changes in cultured cells only at field strengths that exceed residential exposure levels by factors of 1,000 to 100,000.
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From page 54... ...
When experiments are initiated to determine whether such agents as power-frequency electric or magnetic fields produce patterns of response in multiple-cell systems that are similar to those produced by carcinogens, neurotoxins, or developmental toxins, the results can be regarded with confidence when those systems exhibit responses similar to those produced by documented toxins and when the responses are consistent with the mechanism that is hypothesized to underlie the hazard. GENOTOXICITY AND CARCINOGENIC POTENTIAL OF POWER-FREQUENCY ELECTRIC AND MAGNETIC FIELDS Substantial numbers of experiments have been performed in which cultured mammalian cells or prokaryotic cells were placed in an electric or magnetic field, a putative exposure delivered, and the cell response examined for a variety of end points.
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From page 55... ...
Thus, biologic systems that manifest changes in DNA sequence, such as mutations or chromosomal aberrations, are useful in identifying potentially genotoxic agents, most being potential carcinogens if acting on susceptible target cells in vivo. EXPERIMENTAL STUDIES OF IN VITRO EFFECTS Data on the biologic effects observed in cultured mammalian cells or selected prokaryotic cells exposed to electric and magnetic fields are divided in this section into two categories: heritable changes and transient changes.
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From page 56... ...
(19931. According to McCann et al., there is no convincing evidence that power-frequency fields induce direct genotoxic effects and that positive effects observed for high static electric fields might result from corona, arc, or spark.
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From page 57... ...
Although these data are difficult to interpret in terms of effects from exposure to fields at 50-60 Hz, they and data showing copromotion between pulse-modulated highfrequency electromagnetic fields and tumor promoters in some animal systems, as will be discussed subsequently, might warrant further study. Although some examples of positive effects exist, the great majority of effects are negative, and for those published studies that describe positive effects, similar studies describe negative effects.
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From page 58... ...
In particular, membrane signal-transduction processes have been an area of intense focus. One reason for the interest is that the cell membrane presents a substantial barrier to electric fields, especially in the range of field strengths and frequencies present in the ambient environment.
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From page 59... ...
A distinction should be made between the direct (biophysical) interactions of electric and magnetic fields with atoms or molecules in cells and the indirect (more general biochemical)
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From page 60... ...
Those studies are summarized in Chapter 4 of this report in the section on bone healing and will not be repeated here. It is important to emphasize, however, that most of the studies on bone and connective tissue have used field strengths much higher than those encountered in either residential exposures or most occupational exposures.
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From page 61... ...
These findings have been used as basis for a hypothesis that electric fields might act as a copromoter with tumor-promoting agents, producing more activation of ODC and more growth promotion of carcinogen-induced cells in the presence of low electric-field strengths than in the absence of electric
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From page 62... ...
Those data suggest that modification of the cellular response to tumor promoters might be an effect of the magnetic field at these relatively high field strengths. Uckun et al.
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From page 63... ...
If theist studies were replicated by other laboratories, they would be an exception to the observation that magnetic-field strengths near those encountered in households do not produce significant effects on cells in tissue culture. In summary, the body of work on signal transduction suggests that powerfrequency electric and magnetic fields, with magnetic fields at 100 AT (1 G)
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From page 64... ...
In subsequent studies, increases in mRNA transcripts were induced in the human promyelocytic cell line HL-60 by sinusoidal 60-Hz magnetic fields at 0.57-570 AT, 0.011-11 X 10-4 N7/m (Goodman et al., 1992) and by 60-Hz sinusoidal electric fields at 0.3 X 10-4 V/m (Blank et al.
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From page 65... ...
and a more-sophisticated exposure apparatus, along with more-specific and sensitive detection techniques, to examine the claims of increased gene transcription induced by powerfrequency magnetic fields. In Saffer and Thurston's (1995)
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From page 66... ...
In summary, the ultimate resolution of the controversy involving the magnetic-field-induced gene expression in mammalian systems remains to be determined; however, for the purposes of this report, it can be concluded that no effects of electric- and magnetic-field exposure on gene expression have been convincingly replicated by independent laboratories. It should also be pointed out that even the originally reported results were done mainly under conditions of 2 to 4 orders of magnitude higher field strengths than those encountered in residential households.
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From page 67... ...
Calcium Effllux from Chick Brains A large body of pre-1992 literature on the effects of electric and magnetic fields on calcium efflux from chick brains originally led to the concept of a complex set of "frequency windows," "powerdensity windows," "temperature windows," and a dependence on the local geomagnetic field. Although that concept is currently discounted because the effects were largely attributable to temperature or pH fluctuations that occurred during tissue analysis, the work is reviewed here to place into context the concept of windows and the concept that calcium is modulated by low-frequency electric and magnetic fields.
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From page 68... ...
/vc) FIGURE 3-1 Expenmental protocol for studies of the effects of EMF on calcium efflux in chick brain.
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From page 69... ...
field strength, and the responses are further complicated by the orientation between the oscillating ELF magnetic field and earth's dc magnetic field. It should be noted that although Blackman and co-workers observed an increase in calcium efflux, similar experiments performed earlier by Bawin and Adey (1976)
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From page 70... ...
Comment on Ior' Cyclotron Resonance Model Proposed to Explain How a Weak Magnetic Field Could Affect Calcium at the Membrane The ion cyclotron resonance (ICR) mechanism has been the subject of study as a possible source of interaction of low-frequency EMF with biologic systems for more than 20 years (Liboff et al.
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From page 71... ...
Therefore, whether or not 60-Hz EMF cause changes in calcium concentrations, the ICR model, as currently set forth, is not a viable mechanism for biologic systems. Even though the ICR mechanism is not viable, a number of experiments have been performed at charge-to-mass ratios (q:m)
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From page 72... ...
Of the recent experiments summarized in Table A3-2, only three meet the exacting requirements of replication by independent laboratories, publication in peer-reviewed journals, and explicit identification of exposure strengths. Those experiments were on thymic lymphocytes in which Con-A stimulated cells showed an increase in calcium transport resulting from exposure to pulsed magnetic fields having flux densities about 10,000 times larger than those found in the average human environment (Liburdy 1992b; Walleczek and Budinger 1992; Yost and Liburdy 1993~.
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