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Electromagnetic fields and their effects on our lives.

The recent spate of newspaper and magazine articles about the health effects from exposure to electric and magnetic fields signifies growing public concern. People have come to realize that while electricity is the miracle worker of modern life-making our high standard of living possible with televisions, microwaves, computers -they have also become increasingly aware that where there is electricity, there is the potential for exposure to electric and magnetic fields.

Why all the alarm? First, to comprehend the potential effects of electric and magnetic fields, one must be familiar with their characteristics. Electric fields are the way to describe the electric force that an object exerts on other charges within its vicinity. They arise from the electric charge, and are present even when the current does not flow. Magnetic fields, on the other hand, result from the motion of electric charge, vary in strength with current and are present only when the current flows.

Together, electric and magnetic fields, also called electromagnetic fields or electromagnetic radiation, exist wherever there is electric power, via powerlines, household wiring, lighting fixtures and electric appliances. The units for electric magnetic fields are V/m (volts per meter) and uT (microtesla) or mG (milligauss), respectively. According to data compiled by the World Health Organization, electric field strengths of various home appliances measured at a distance of 30 cm (approximately 1 foot) ranged from 2 V/m from an incandescent bulb to 250 for an electric blanket. Coffee pots, color televisions, hair dryers, toasters and hand mixers range from 30 V/m to 50 V/m.

Electric and magnetic fields are found everywhere: They hold atoms together and are involved in the transmission of messages through the nervous system. The earth has a static electric field of about 130 V/m and a static magnetic flux density (a measure of field strength) of 50 uT (500 mG) at middle latitudes.

Electric and magnetic fields produced by power systems oscillate with the current. The frequency of this oscillation is 60 Hertz (Hz) in the United States and 50 Hz in other parts of the world. These frequencies are in the region of the electromagnetic spectrum called Extremely Low Frequency (ELF).

ELF electric and magnetic fields lose intensity rapidly as distance becomes greater. Electric fields are shielded by trees, tall fences, buildings and most other large structures. Magnetic fields are shielded only by structures containing large amounts of ferrous or other special metals. Scientists had previously assumed that exposure to 60 Hz ELFs would not be harmful because of the ELFs inherent lower energy. Indeed, ELFs do not break chemical bonds or significantly heat human tissue. Also, the earth and the human nervous system have electric and magnetic fields as strong or stronger than those produced by powerlines and other manufactured sources. However, those long-held views are now being challenged.

Cancer Risks

According to the United States Office of Technology Assessment (OTA), there have been five studies published that investigated the possible relationship between childhood cancer and exposure to electromagnetic fields. The study which triggered the most concern focused on children who had died of cancer in the greater Denver area between 1950 and 1973, totalling 344 cases, and a matched control population of the same number of children. By estimating the exposure to electromagnetic fields using a wiring configuration code, it was found that the rate of cancer deaths was approximately twice as high in children who lived in homes with potential electromagnetic field exposures as opposed to low potential exposures. Of the four studies conducted since then, two found no association between leukemia and exposure to electromagnetic fields while the other two studies did find an association.

Of the two studies which found a positive association, one centered on children who were diagnosed with cancer from 1976 to 1983. By using detailed exposure measurements and questionnaires to identify other possible confounding factors, the study found a 30-percent increase in risk for all cancers at fields of 2.5 mG and no increase for lower field ranges.

According to the OTA report, "Biological Effects of Power Frequency Electric and Magnetic Fields," there have been as many as 20 studies that have looked for an association between cancer, particularly leukemia and brain cancer, and exposure to ELFs. The OTA has concluded that "collectively the studies do not provide good evidence that ELF field exposure increases the risk of leukemia. At the same time, the evidence precludes categorical statements that no such risk exists."

Preliminary results of a study from Johns Hopkins University has created quite a sensation. As many as 50,000 telephone company workers in New York were studied and the overall cancer rate was found to be twice as high in line workers who were exposed to the most intense electromagnetic fields as among other telephone company workers. Exposure to ELFs did not cause chromosomal damage, but did seem to affect the cell membrane and circadian rhythms of humans and animals.

Reproductive Effects

By using birth announcements to examine the association between the use of electric blankets or electrically heated water beds, the potential for reproductive affects were also studied. The OTA report noted a seasonal pattern indicating a higher miscarriage rate, longer gestation periods and lower birthweights in babies born to mothers who used heated waterbeds and electric blankets. In general, animal studies have not shown effects on reproduction due to exposure to 60 Hz fields, although there have been some effects shown in studies using pulsed fields.

More conclusive information on reproductive effects should be available in the future. In fact, the Congenital Malformation Surveillance system at the Center for Disease Control in Atlanta has amassed data related to ELF exposure since 1985, focusing on the use of electric blankets and electrically heated waterbeds during and immediately preceding pregnancy.

The question of reproductive effects has also been raised in connection to visual display terminals. Most VDTs operate on the same principle as television sets, whereby the image is produced by an electron beam generated in a cathode-ray tube. Like television sets, the monitor of a VDT produces a variety of types of radiation, including very low frequency and extremely low frequency fields. A number of miscarriages and/or birth defects among VDT users have been recorded. However, they have not conclusively been shown to be caused by VDT exposure.

In assessing the data, the knowledge to date on the potential adverse health effects due to exposure to electromagnetic fields is currently inconsistent and inconclusive. A number of approaches can be followed to deal with this scientific uncertainty. One approach is to assume the worst and pass governmental regulations accordingly. Another approach would shelf the issue until conclusive evidence is developed, while a third approach recognizes that scientific uncertainties exist but adopts a response of prudent avoidance.

Currently, seven states limit field strengths on transmission line right-of-ways. These state limits are not based on scientific assessments of risk, since no one knows which attributes of electromagnetic fields, if any, produce ill-health effects. To date, electric blankets have not been regulated by any governmental agencies in response to potential cancer or reproductive effects.

Regarding VDTs, model safety regulations have been proposed in a number of locations and passed in Suffolk County, NY, which call for use of anti-glare screens, metal shielding to protect against radiation, mandatory eye exams and transfers for pregnant VDT operators upon request. However, Suffolk County has not implemented the regulations as a result of legal challenges.

Equipment is available to measure electromagnetic fields that could be used to document and record electromagnetic field levels. Since a correlation between exposure and effect does not currently exist, and since there are no established exposure limits, measurement cannot be used to effectively demonstrate safety or compliance.

Until further research clarifies whether or not there are adverse health effects due to exposure to electromagnetic fields, there are a number of precautions to take in order to minimize potential harm from electromagnetic field exposure, especially when it concerns the use of electric blankets and VDTs. For one, using electric blankets can be avoided completely.

In addition, because field strength falls off rapidly with greater distance, VDTs could be set up side-to-side with space between units rather than back-to-back. Using alternate technology screens such as liquid crystal displays will also reduce exposure. Carol J. Robinson is manager of safety and environmental engineering for Helene Curtis in Chicago.
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Author:Robinson, Carol J.
Publication:Risk Management
Date:Nov 1, 1991
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