.
SPECIAL REPORT!
C
66 HEALTH EFFECTS OF LOW-FREQUENCY ELECTRIC AND MAGNETIC FIELDS 33 BY THOMAS
T
d
he potential biological human health effects of ELFEMF have become an issue of scientific debate and public controversy with far-reaching social and economic implications for electric power transmission, distribution, and consumer end uses. The report of the ORAU panel typifies the response of many scientists and scientific committees that have undertaken a cursory examination of this subject. They conclude, and quite correctly in my view, that the evidence for biological and human health effects of ELF fields is very limited. They fnrther conclude that there is only weak evidence suggesting an increase in the relative cancer risk for children exposed to ELF fields in the home and for occupationally exposed electrical workers. However, the ORAU panel is misguided in concluding that the laboratory and epidemiological information is so weak that we . should assign a low priority ivesti
ELF-EMF (extremely low-frequem fields have frequencies below 3 Hz. As used by the ORAU par the abbreviation ELF-EMF refers electric and magnetic fields with f quencies below 30 kHz. ELF-El by this definition encompass three frequency bands: CLr
* ELF
I* vi
(the voice-frequency ba from 300 Hz to 3 kHz) * VLF ( t h e very low-frequen h = n A frnm 3 kH7 +n kU7\
ing what could ultimately prove to be a significant public health issue. At this stage, given the tremendous public interest in this subject, ignoring the existence of a possible problem will not make it disappear. On the contrary, failure by the federal government to invest in research on this subject will only increar- “-7 gridlock that currently exists hetween the public and the electric utilities over the siting and installation of new transmission and distribution lines. Epidemiological evidence for an elevated cancer risk in children residing near high-current distribution lines has been reinforced by the positive findings in recent studies conducted in Los Angeles County and in Sweden, which add credibility to the results of earlier studies by Wertheimer and Leeper and Savitz et al. in the greater Denver area ( I 4 ) . Similarly, there is now a substantial body of epidemiological evidence, including a large study recently completed in Sweden, indicating that individuals in the general class of “electrical workers” exhibit an elevated cancer risk (5,6 ) . The fact that the correlation between cancer risk and exposure to ELF field sources is significant only for surrogate measures of exposure such as power line configuration and electrical job title is perplexing. Few of the studies to date have demonstrated a correlation between actual ELF field exposures and cancer risk, and the possibility exists that confounding variables may be the true culprits instead of ELF fields per se. Nevertheless, the bulk of
S. T E N F O R D E available epidemiological evidence suggests that electric power sources are linked in some undefined manner to an elevated cancer risk among the high-exposure occupational and public groups. Although the relative risk factors are small (probably no larger than 1.5 to 2 and, quite possibly, less than 1.51, the total size of the exposed population ii i s large a t the national and international scales. Hence, the total number of individuals with an elevated cancer risk is sufficiently large to merit an expanded research effort. To suggest, as did the ORAU panel, that we should assign a low priority on the national research agenda to this potential problem serves only to undermine the efforts of those who are determined to get to the bottom of this socially and economically troublesome issue. Apart from the unfortunate concluding statements by the ORAU panel, there are a number of scientific oversights and inconsistencies in their report that merit discussion. In particular, four important issues were either overlooked, ignored, or given an inappropriate emphasis in the panel’s report.
l
The ORAU panel is misguided concluding that the laboratory and epidemiological information is so weak that we should assigr a low priority to investigating what could ultimately prove to be
I
ELF fields and biological tissues The ORAU panel report discusses the fact that thermally generated electric fields (Nyquist noise) are significantly larger than the local fields induced across individual cells by an externally applied ELF field at typical environmental levels. In other words, the signal-tonoise ratio (S/N] is expected to be much less than unity for ELF fields ~
56 Environ. Sci. Technol., Vol. 27, No. 1, 1993
0013-936X/93/0927-56$04.00/0 0 1992 American Chemical Society
from power lines and other common sources (7. SI.Althowh this is true at the level ofa single Cell, most biological tissues are composed of large cell aggregates that are electrically coupled via junctions between adjacent cell membranes. As a result, the S/N for an imposed ELF field improves roughly in proportion to the number of cells in the junctionally coupled aggregate (a rigorous treatment shows the S/Nto be proportional to the five-sixths
power of the number of cells [Reference 911. For instance, in 1 million electrically coupled cells, the S/N is predicted to increase by 100,000 relative t o t h a t for a single cell. Consequently, a typical environmental field on the order of 10-100 V/m will induce a local tissue field across this electrically coupled cell aggregate that exceeds the Nyquist noise field. Hence the argument that ELF field signals would be
"drowned" in a sea of background
electrical noise is incorrect.
Molecular events and ELF fields A glaring omission in the executive summary of the ORAU panel report is the failure to mention recent advances in understanding the molecular-level events that occur in cells exposed to ELF fields. These events include alterations in membrane functional properties [ligandreceptor interactions, ion binding Envimn. Sd. Technol., Vol. 27, No. 1, 1993 57
and transport), changes in secondmessenger signaling pathways mediated by Ca", cyclic nucleotides and kinases, and altered gene expression (transcription and translation) (30-12). In many cases, these altered functional properties of cells have been observed at E L F field levels typical of those induced by weak environmental fields. The overall pattern of membrane and cellular responses to E L F fields points toward membrane interactions and second-messenger signaling pathways as being responsive cellular elements. A further factor not mentioned in the report is that the observed response of the kinase C signaling pathway is consistent with a tumorpromoting effect of ELF fields, similar to that known to occur with phorbol esters (13).The importance of understanding the role of this biochemical transduction pathway is underscored by recent experiments that demonstrated a tumorpromoting effect of a 60-Hz magnetic field in mouse skin carcinogenesis ( 1 4 ) . Neuroendocrine responses The ORAU panel report discusses a variety of neurobehavioral and neuroendocrine alterations observed in response to ELF field exposure. Although noting that "changes in pineal melatonin production as a result of either electric or magnetic field exposure may be substantial," the authors make no attempt to relate this observation to possible uhvsioloeical or carcinoeenic outcomes. It is well established that reduced concentrations of melatonin in the circulation lead to increased prolactin release by the pituitary and increased steroid hormone release (estrogen and testosterone) by the gonads (15).An increase in the concentrations of steroid hormones stimulates breast tissue proliferation and also leads to immunosuppressive effects, on the basis of which it has been proposed that the decrease in melatonin production resulting from ELF field exposure could elevate the risk of breast cancer (16).This hypothesis is supported by the results of rodent studies in which it was demonstrated that melatonin injection suppresses mammary tumorigenesis and pinealectomy increases breast tumor formation (17).The results of recent epidemiological studies showing an elevated breast cancer risk in men who are occupationally exposed to 1~
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58 Environ. Sci. Technol., VoI. 27, No. 1. 1993
ELF fields are consistent with this
Acknowledgments
hypothesis (16-20).
The author wishes to thank L. E. Anderson, R. G. Stevens, and B. W. Wilson for helpful discussions on the content of this commentary. Research support is received by the author From the U. S. Department of Energy under contract DEAC06-76RLO 1830 w i t h t h e Pacific Northwest Laboratory. T h e Pacific Northwest Laboratory is operated for the U.S. Department of Energy by the Battelle Memorial Institute.
Electric power and cancer risk The ORAU panel report notes that a large increase in electric power generation and consumption has occurred over the past several decades without an accompanying increase in the rate of childhood cancer or adverse reproductive outcomes. This argument against a relationship between ELF field expos u r e a n d cancer risk, recently proposed by Jackson (211, is seriously flawed. First, the comparison of time trends in cancer risk with time trends in a suspected variable such as electric power use is a notoriously unreliable basis upon which to draw conclusions regarding a causal relationship. ( F o r example, cigarette smoking has been causally linked to bladder cancer, yet the mortality risk from this form of cancer has not increased since the turn of the century even though cigarette consumption has markedly increased.) Second, the types of electrical wiring used in homes and factories have changed significantly over the past several decades, with an accompanying decrease in the ambient ELF field levels. Any risk associated with the increased use of electric power could, in many instances, be offset by a decrease in the actual exposure levels experienced within the home or workplace. In summary, the report of the ORAU panel is seriously deficient in both content a n d logic, and should not be regarded as a definitive statement on the possible relationship between exposure to ELF fields and cancer risk.
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Thomas S . Tenforde is chief scientist of the Life Scie n c e s C e n t e r and manager of the Department ofEnergy's Health a n d Envimnmental Research Program a t the Pacific Northwest Laborotoi?.. HP rweived his B.A. degree in physics from Harvard University a n d a Ph.D. in biophysics from the University of California a t Berkeley. He h a s CORducted research in biophysics and radia t i o n b i o l o g y f o r 20 years a t t h e Lawrence Berkeley Loboratory and the Pacific Northwest Laboratory. a n d has authored or coauthored I85 publications a n d reports.
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