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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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