A Mlange Of Environmental Issues Extremely Low Frequency ELF Magnetic Fields

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Wherever electricity is generated, transmitted, and used, electric and magnetic fields are created. It is impossible to use electrical energy without creating these fields; they are an inevitable consequence of the world 's reliance on electricity, and exist wherever any form of electricity is used. To say that electricity is an essential part of our lives cannot be overstated.

The earth itself is surrounded by a static magnetic field that varies between 25 and 65 microteslas (mT), and is hundreds of times greater than the alternating magnetic fields produced by the 110-volt (V) current in our homes, which produces about 0.01-0.05 mT.

As electromagnetic fields from high-voltage transmission lines, household appliances, and more recently mobile (cellular) phones, have received wide media attention, with concerns raised about possible adverse health effects of such exposure, we shall consider the underlying factors pertaining to electric and magnetic fields, and concern ourselves with the assessment and/or potential risks to health. After all, the human brain is an electromagnetic organ, and the most complex; shouldn't some effect be expected?

We begin by raising the questions, What is an electromagnetic field, what is the meaning of field, and how do they work? Additional questions will, of course, follow.

Electric fields exist around all copper wires and electrical appliances whenever they are plugged into a supply of electricity. On the other hand, magnetic fields are produced only when current flows and power is being used. Electric fields are produced by voltages and magnetic fields by currents. The higher the voltage—or greater the current—the stronger the field produced. These are, of course, invisible lines of force, but can become evident as static when driving an automobile near or under high-voltage transmission lines with the radio on. At much lower intensity, these fields also surround all electrical appliances. Twenty or thirty years ago it was not possible to operate an electric drill or clothes iron near a radio without static. Today that interference has disappeared because of the shielding provided.

As electric fields are produced by voltage, let us consider voltage—electric pressure, the ability to do work, measured in volts (V) or kilovolts (kV), which is equal to 1000 Volts. In the United States most domestic voltage is set at 110. Air conditioning systems pulling more energy often require 220 V. Home appliances are plugged into wall receptacles working on 110 V. When a lamp or toaster is switched on, an electric current flows that is measured in amperes (A). Think of voltage as water pressure in a hose with its nozzle in the off position. Turning the nozzle on allows the water to flow. In a copper wire, that's current.

With lamps, toasters, radios, TV's, coffeemakers, dishwashers plugged into wall receptacles, but switched off, an electric field exists around the cord or wire. But these fields are shielded by the covering around the wire, and field strength decreases rapidly with increasing distance from the wall receptacle. Turn these devices on, and current flows and magnetic fields develop around the cord, and exist along with the electric field. These magnetic fields are measured in gauss (G) (after the German mathematician Karl Frieidrich Gauss, 1777-1855) or teslas (T) (after Nicola Tesla, 1856-1943, a Croatian scientist/mathematician, and an American citizen), and its strength also decreases rapidly with increasing distance from the source. Magnetic field levels in either the domestic or occupational environments are less than 1 G; on the order of a milligauss, a thousandth of a Gauss. A person standing 4 feet from a copy machine may receive 1 mG of energy. At the copier, the magnetic field can be as high as 90mG:

1 tesla (T) = 10,000G 1 millitesla (mT) = 10G 1 microtesla (|T) = 10mG

To convert from microtesla to milligauss, multiply by 10. The gauss unit is most often used in the United States. The tesla is the internationally accepted unit.

Figure 8.1 depicts the magnetic field levels of common household appliances. Of particular importance is the fact that the electromagnetic spectrum spans a vast range of frequencies. Electric and magnetic fields can both be characterized by their wavelengths, frequencies, and amplitude or strength.

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Figure 8.1. Magnetic field levels near household appliances. [Figure courtesy of the Electric Power Research Institute (EPRI).]

Figure 8.2 shows the waveform of an alternating electric or magnetic field. The direction of the field alternates from one polarity to the opposite and back in a period of time of one cycle. Wavelength describes the distance between a peak on the wave, and the next peak of the same polarity. The frequency of the field measured in hertz (Hz) (after Gustave Ludwig Hertz, a German physicist, 1887-1875) describes the number of cycles occurring in one second. Electricity in the United States alternates through 60 cycles per second or 60 Hz. Recall that radiation includes X rays through ultraviolet light, visible light, infrared (heat), and microwaves, television to radiowaves along with electromagnetic waves—all forms of electromagnetic energy. A property

Figure 8.2. A waveform of an alternating electric or magnetic field in a period of one cycle.

One complete cycle

Wavelength /Crest h- -* Amplitude / Trough

Figure 8.2. A waveform of an alternating electric or magnetic field in a period of one cycle.

distinguishing different forms of electromagnetic energy is the frequency expressed as hertz—60 Hz carries little energy, has no ionizing effects, and has little to no thermal effects. Figure 8.3 provides several representations of the electromagnetic spectrum. Note that 60 Hz is at the tail end, close to zero frequency. Figure 8.4 shows the location of cellular phones, close to that of radio and TV broadcasts. The radio and microwave fields are different from the extremely low-frequency (ELF) electromagentic fields produced by high powerlines and most domestic appliances. Furthermore, all frequencies below ultraviolet are nonionizing, which means that they have insufficient energy to break chemical bonds. Concerns about EMFs and health most often focus on two distinct nonionizing frequency bands: the 60-Hz band, the frequency of electric power systems, and the 1-GHz band, where mobile phones operate. Typically, mobile phone frequencies range between 900 MHz and 1.8 GHz. Their power is measured in watts per square meter (W/m2 ) or more often million |W/m2, as opposed to electric fields, which are measured in volts/meter (V/m). Again, background fields in most homes arise from low-voltage electric wiring, while higher-power fields are produced by overhead powerlines. As for mobile phones, the highest fields stem from the phones themselves.

The main effect of electric fields can cause small currents to flow in the body but are not large enough to interfere with the action of nerves in the brain or spinal cord. In fact, a recently published article in the American Journal of Psychiatry informs us that individuals with diagnosed bipolar disorder exposed to the oscillating magnetic fields of an MRI scanner (a device used to produce high-resolution images of internal organs and tissues) reported improved moods after the scanning [32].

As all of us have experienced, very high electric fields can cause "microshocks" when metal objects are touched, much the same as walking across a nylon carpet does. These can be annoying or playful, but are not dangerous. With mobile phones, frequencies, if high enough, can induce heating—but current phone designs limit this to body temperature: 98.6°F (37°C).

Figure 8.3. A representation of the electromagnetic spectrum. (Figure courtesy of the National Academy of Sciences, Washington, DC.)

An interesting and instructive experiment that can, and actually should, be done in everyone's home every few years is a check of both the magnetic fields around all appliances, and a check of voltages at each receptacle. Rather than a Gauss meter and voltammeter, avail yourself of a multimeter, one that can measure both. Hold the meter close to each of your appliances—the microwave oven, the toaster, dishwasher, radio, TV, electric iron—which, of course, must be switched on. Readings on the Gauss scale in milligauss should be near or at zero. Be sure to check the cords and take several readings, close to the

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