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Electromagnetic Fields Explained
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Conflicting
scientific studies concerning the possible health effects of
electromagnetic fields (EMF) have created widespread confusion among
consumers, driven largely by media reports rather than scientific
evidence. Power lines do depress the value of nearby homes, both due to
buyer's concern over the possible health effects and due to the more
basic reason that power lines are unattractive. Since it is nearly
impossible to prove a negative -- that is that something does not cause
cancer -- it is likely that the EMF controversy will be around for years
to come. What are EMFs? Electromagnetic fields are created whenever electricity passes through a conductor. There are actually 2 fields created: an electric field and a magnetic field. The strength of the electric field depends on the voltage being carried, while the magnetic field strength depends on the amount of current being carried (amperage). While it is easy to shield against the electric current, it is much more difficult to shield against magnetic fields. The magnetic field could be shielded by burying power transmission lines, but at a high dollar cost. Electromagnetic fields are both naturally occurring and manmade. There is a background EMF level created by the earth, with additional EMFs created by thunderstorms and solar activities. In addition, EMFs are created by a variety of household appliances as well as power lines and electrical substations. The strength of an electromagnetic field depends both on the flow of power at the source and the distance from the source. Thus, power transmission lines create much larger EMFs than do distribution lines or household appliances; however, transmission lines are also located much farther from inhabitants. Local distribution lines are usually located much closer to residences than are transmission lines, and thus may actually expose residents to greater EMFs than do transmission lines. In fact, many household appliances create EMFs far greater than those from transmission lines; however, these appliances only create EMFs while in use, while the transmission line EMFs are continuous. For example, the EMF 300 feet from a 230 kV transmission line is about 0.8 milligauss, while the EMF 6 inches from a typical hair dryer is around 300 milligauss. Obviously, people don't stand 6 inches from a hairdryer for long periods of time every day, but they may stay in their house for extended periods of time. For purposes of comparison, the earth's natural EMF is around 500 milligauss -- or over 600 times the field found 300 feet from a high voltage transmission line. History of the EMF Controversy The EMF scare can be traced back to a 1979 study by Wertheimer and Leeper, which found an increased risk of childhood cancer in Denver, Colorado children living near transmission lines. Over the nearly 20 years following this study, numerous studies have found widely conflicting results, using widely differing research methodologies. Epidemiological Studies In general, researchers have conducted two types of epidemiological studies: wirecode studies and exposure assessments. The first type, used in the 1979 Wertheimer and Leeper study, is referred to as a wirecode study. Researchers use information about the location and size of electric power transmission and distribution lines to estimate the exposure to EMFs of homes located near the transmission lines. The researchers then compare the incidence of disease in homes with high expected EMF exposures to the incidence of disease in homes with low expected EMF exposures. A number of wirecode studies have found a relationship between power lines and cancer. Specifically, researchers have found a 1.5 fold increase in childhood leukemia. While this result is statistically significant -- meaning that the relationship is unlikely to occur by chance -- scientists have not establisheda likely explanation for how the EMF effects cell biology to cause the leukemia. This is partially due to the fact that the causes of childhood leukemia are not well understood. The epidemiological studies have not linked EMFs to adult cancers, childhood cancers other than leukemia or effects on pregnancies. One possibility is that some other factor responsible for childhood leukemia is strongly correlated with the wirecode. For example, houses near power lines are often located near highways or railroad tracks. In addition the houses are older, and are built at a higher density. The other type of study is the exposure assessment. These studies differ from wirecode studies in that the EMF exposure estimates come from measured residential electromagnetic fields, rather than a wirecode. It is significant to note that the actual EMF readings are not strongly correlated with the wire code estimates -- meaning that a fair number of homes assumed to have high EMF exposures in wirecode studies have low EMF readings and vice versa. The exposure assessment studies generally have not found a link between exposure and childhood leukemia. However, these studies are done retrospectively -- the researchers take current measurements of the EMFs in homes of leukemia victims and in "control" houses. It is entirely possible that the EMFs were different in past years when the childhood leukemia victims were first exposed. The most recent study, conducted by the National Cancer Institute, used both wirecode and exposure assessments to study the current and past homes of 638 children with leukemia, as well as 620 control children. The study found "little evidence that living in homes characterized by high measured time-weighted average magnetic-field levels or by the highest wire-code category increases the risk of ALL [childhood leukemia] in children." In Vivo and In Vitro Studies Scientists have also studied the impact of EMFs on animals (in vivo studies) and human cells (in vitro studies). The animal studies found no evidence that residential EMFs caused cancer in laboratory animals. The standard concern with animal experimentation is that animals may not have the same response to EMF exposure as would humans. The cell studies also found no replicable effects from residential exposure levels. Cell effects were evident only at exposure levels far higher than typical residential levels. Based on the totality of the evidence available, the National Academy of Sciences, National Research Council (NRC) determined that there was no evidence showing that EMFs present a human health hazard. "Specifically, no conclusive and consistent evidence shows that exposures to residential electric and magnetic fields produce cancer, adverse neurobehavioral effects, or reproductive and developmental effects." Risk Assessment What the NRC did not say is that EMFs definitely do not cause cancer. There are two reasons for this. First scientists almost never say that something does or does not cause cancer. Finding no evidence of a link is about as strongly worded of a statement as scientists will ever use. Second, there is evidence that EMFs much greater than those found in residential settings can pose health effects -- much greater being 1,000 to 100,000 times larger. When scientists are confronted with evidence of health effects at high doses, and no evidence of health effects at low doses, they have great difficulty in determining a "safe" level. Often, scientists use a liner model -- meaning that they assume that the dose-response relationship is a straight line. Using the liner model, if you halve the exposure, you also halve the risk of cancer. The liner model starts with the assumption that zero exposure is associated with zero risk of cancer and that the first unit of exposure adds to the risk of cancer by the same amount as does the 100th unit of exposure or the 1,000th or the 10,000th. The linear model is often criticized by pointing out that it implies that if 100 men are killed from a 100 foot fall, this means that one man would be killed by a 1 foot fall; or that if 1,000 men drown in water that is 100 feet deep then 10 men would drown in 1 foot of water. This liner model is widely used -- but is often inaccurate, because it conflicts with the fundamental law of toxicology -- the dose makes the poison. Many commonly consumed chemicals are toxic in high enough doses. For example, one aspirin is probably good for you -- 1,000 aspirin would be fatal. One ounce of alcohol may provide health benefits, one gallon would kill you. The zero threshold, linear model doesn't explain these situations. Are there safe levels of EMFs? Scientists are unwilling to say so without much more research, but the NRC has reviewed all of the epidemiological and experimental evidence, and was unable to find any consistent evidence of harm from EMFs at residential exposure levels. Conclusions EMFs are created by the flow of electricity, and cannot be shielded against except at great cost. There have been a number of conflicting studies over the past 20 years, some purporting to find evidence of adverse health effects, and some failing to find any correlation. Recently, two highly respected groups -- the National Academy of Sciences and the National Cancer Institute -- have released major studies finding no evidence of a link between EMFs and cancer. These studies are not sufficient to "prove" that that there is no link between power transmission lines and cancer; but the studies do indicate that power transmission lines are much less likely to cause cancer than was previously assumed. Electric Power Lines: Not Guilty Electromagnetic Fields Unlikely Culprits in Childhood Leukemia, Says New Medical Study Magnetic fields generated by electric power lines near houses don't appear to cause childhood leukemia, an authoritative new medical study has concluded. The research by the National Cancer Institute is expected to ease fears about the hazards of exposure to electromagnetic fields (EMFs). It also provides credible new information that real estate practitioners can use to protect themselves from liability in transactions involving properties near high-voltage power lines. Practitioners have long-standing concerns about being named in lawsuits by buyers claiming they hadn't been adequately warned about the potential health hazards of electric lines near their house. Also, practitioners sometimes have difficulty marketing houses near power lines because of public anxiety about possible dangers. The new study, which was published recently in The New England Journal of Medicine, was conducted over an eight-year period and involved more than 1,200 children, 638 of whom were diagnosed as having acute lymphoblastic leukemia, the most common childhood cancer. The other children, used for comparison, didn't have the disease. Earlier studies depended on estimates of EMF exposure, whereas National Cancer Institute researchers used instruments to take one-day EMF measures in kitchens, family rooms, and bedrooms. Children with cancer were not exposed to EMFs that were stronger or more long-lasting than those experienced by the other participants, the study concluded. "Based on our results, is [EMF] likely to be an important cause of childhood leukemia? The answer is no," says Dr. Martha Linet, the lead researcher, in an article in the Los Angeles Times. Questions about possible EMF hazards first received widespread attention in 1979 when Colorado researchers reported that children with leukemia lived closer to high-voltage lines than did healthy youngsters. Further studies on the subject have produced varied conclusions; some supported the Colorado study, but others didn't. The National Cancer Institute research was designed to deal with scientific shortcomings in previous studies. The New England Journal of Medicine felt that the conclusions were so strong that it editorialized for an end to further EMF medical research. "The 18 years of research have produced considerable paranoia, but little insight and no prevention. It is time to stop wasting our research resources," the editorial said. What Should I Tell My Buyers About EMFs? Q: I have potential buyers who are interested in a property that has high-voltage electric lines nearby. They asked me about the health effects of electromagnetic fields. What should I say to them? A: As with any technical question about property condition or the implications of certain physical features, you must be careful to advise your buyers correctly without implying you have more expertise than you do. Some early EMF research indicated the possibility of a link between EMF exposure and certain health effects, including childhood leukemia and other cancers. Since that time a number of other studies have been inconclusive. The recent study by the National Cancer Institute didn't find a relationship between exposure to magnetic fields and childhood leukemia. Encourage your buyers to contact local or state environmental or health agencies to get more information. The U.S. National Institute of Environmental Health Sciences and the U.S. Department of Energy have published a booklet titled Questions and Answers About Electric and Magnetic Fields Associated With the Use of Electric Power (order online at www.niehs.nih.gov or by calling the Government Printing Office at 202/512-1800 and requesting document #061-000-00824-1). Some power companies have also developed publications. Practitioners should never offer their opinion to interested buyers on whether an EMF source, such as a power line, poses a hazard. The best practice is to give general, factual information about the potential hazards and to provide copies of or references to other information sources. That way, the buyers can determine for themselves the degree of risk they wish to accept. This procedure is particularly important with EMFs, whose risks, if any, are uncertain and incompletely understood. Response provided by Ralph Holmen, senior counsel, Legal Affairs, the NATIONAL ASSOCIATION OF REALTORS®. Expert Opinion What impact will this new medical study on EMFs have on the industry? Dr. Patrick Breysse, an environmental health scientist at the Johns Hopkins University School of Public Health, Baltimore, has researched the effects of magnetic fields on humans. The National Cancer Institute study represents an important contribution to the medical literature. This study suggests, contrary to earlier studies, that the lower levels of EMFs normally found in a residential environment are not a risk for causing cancer. The public should take some comfort from these results, which should lower anxiety about the potential health hazards of EMFs in residential areas. It doesn't, however, put to bed all the questions concerning EMFs. The study, for example, sheds little light on the potential cancer risks to utility workers who spend a lot of time working around high-level EMFs. More research is still needed. William N. Kinnard Jr., president of the Real Estate Counseling Group of Connecticut, Storrs, and an appraiser who has studied the impact of EMFs on property values. This was the most dramatic in a recent series of studies showing that there's no reliable scientific evidence that EMFs are associated with a cancer risk. This reinforces the study released last October by the National Academy of Sciences. The academy looked at 17 years of scientific studies dealing with EMFs and health and concluded that there's no danger. I doubt, however, that there'll be any serious decrease in the number of EMF lawsuits, at least for a while. What the popular belief is and what the scientific community knows to be true are two different things. People who are renting or buying houses tend to act on their prejudices rather than on scientific evidence. Paul Locke, director for the Center for Public Health and Law, Environmental Law Institute, Washington, D.C. The study suggests that EMFs are less of a health problem than was thought five years ago. I'm not sure whether that means the issue is going to disappear completely. When you talk about power lines, there are usually two concerns: One is health, the other aesthetics. This study may, in fact, lead to a reduction in concern about the health issue of EMFs, but concern about aesthetics maybe on the increase. The federal Telecommunications Act of 1996 limits the ability of local jurisdictions to control what types of communications towers may be erected in existing rights-of-way. In the future, I think, we'll see more problems with unsightly utility towers impacting residential property values. Summary of articles reprinted with permission from NAR web page and TODAY’S REALTOR® | ||||||||||||
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