Adair gives the story on EMFs
by John L. Roeder
Throughout the years of debate about the risks of exposure to electromagnetic fields, the leading voice of reason countering claims that cancer could result from this exposure was that of physicist Robert K. Adair of Yale University. His approach has been consistently straightforward: look at what the effects should be of these fields on a human body or on a cell in a human body. Professor Adair shared this approach at the Northeast Regional Meeting of the American Association of Physics Teachers at Yale on Saturday, 7 November 1998, in a tutorial entitled "Biological Effects of Weak Electromagnetic Fields."
To begin with, Adair pointed out, the electrical conductivity of the human body shields the inside of the body from all but one ten millionth of whatever electric field is external, at a frequency of 50 Hz. For power lines, this is ten thousand volts per meter, so the electric field from a power line induces a field of only a millivolt per meter inside the human body. On the other hand, he also noted, magnetic fields are not shielded, and changing magnetic fields induce electric fields. For a magnetic field as strong as that of the Earth's but oscillating at a frequency of 60 Hz, the induced electric field equals another millivolt per meter, which Adair showed was equivalent to a 1.5 volt battery between two terminals separated by a mile.
The effects of 50 Hz electromagnetic fields on body cells is even less than that on the whole body, because the long wavelength (6000 km) compared to the size of body cells means that the fields are essentially static. The electric effects of magnetic fields of concern to epidemiologists turn out to be far weaker than electric fields in the human body, for example, the electric fields measured in electrocardiograms. In fact, Adair said, the heartbeat of a pregnant woman exposes her baby to a higher low frequency electric field than the external environment.
Electromagnetic fields, Adair noted, have meaning only in terms of forces on charges, and these forces are less than those of thermal jostling in cells. Thus, he said, there is no basis for believing that these fields have any biologic effect on humans. On the other hand, he was quick to add, some critters are more sensitive to magnetic fields: magnoteotactic bacteria, honey bees, and sharks. Sharks, he pointed out, are sensitive to induced electric fields as low as a microvolt per meter (corresponding to a 1.5 volt battery between terminals on the opposite sides of the Atlantic Ocean). They use this sensitivity to detect food by detecting the electrocardiac output from its prey. "This is the one situation in which weak electromagnetic fields are dangerous," he mused.
Sharks detect weak magnetic fields by their effect of admitting more calcium ions into an ampulla, but humans don't have this mechanism to detect weak electromagnetic fields. If we have no way to detect them, Adair said, they can't affect us.
Concerning the connection of electromagnetic fields to epidemiology, Adair felt that epidemiology suffers from being a non-falsifiable science. In contrast to the claims of cancers from electromagnetic field exposure, he showed two transparencies. One showed that nonrespiratory cancers declining slightly as the per capita electric power generation increased considerably. The other presented Danish data showing that childhood leukemia, if anything, decreased slightly while the per capita electric power generation increased.
Adair recognized that fears of electricity have permeated society since the beginning of electrification. Indeed, I recalled reading in an encyclopedia of St. Louis when I was an undergraduate at Washington University that St. Louisans feared that electricity in overhead trolley wires would kill street trees. But now science has developed to the point of being able to counter these fears. Adair closed by showing an amici curiae organized by Richard Wilson on behalf of a San Diego utility which included two physicists who won Nobel Prizes in Medicine -- Allan Cormack and Rosalyn Yalow. It was successful, thus showing that there is something physicists can do in societal interaction, particularly if they are prominent enough.
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