Electromagnetic fields (EMFs) have received a lot of attention in the last few decades. Some folks believe they cause cancer, especially childhood leukemia. Others argue that there is no risk.
Controversy and confusion continue. It seems like a good time to review the current thinking on the subject.
What are EMFs?
Electromagnetic fields are actually a combination of electric and magnetic fields. They occur when electrical current flows through cable or an electrical device. All electrical devices create an electromagnetic field when in use. The intensity of the field varies with the voltage. Higher voltage creates stronger electric fields. The current flow creates the magnetic field. Thus, primary transmission wires (those cables usually on towers or high poles) generate more intense EMFs.
The reason some folks are concerned about EMFs is that the charged particles created by EMFs have an effect on distant objects. The best example is to consider how a compass works. The North Pole attracts the compass’s needle because the electromagnetic field at the North Pole is greater than at any other location on earth.
How can I measure them?
EMFs are measured in milligauss (mG), or one-thousandth of a gauss. A gauss is a unit of measure of the intensity of an EMF, also known as magnetic flux density.
It is known that the intensity of an EMF decreases as you move away from the source. Many electrical appliances, for example, have relatively strong EMFs when you are within a few inches of the device, whereas virtually all EMFs created by electrical devices measure below 2 mG when you are three feet or more away. Electrical devices that use motors (can openers, saws, hair dryers, etc.) may have an EMF intensity of 1,000 mG or more within a few inches. That will drop to 100 mG or less one foot away and 10 mG or less three feet away.
For high-voltage power lines (transmission lines), the EMF often measures below 2 mG at 50 to 100 feet from the power line and virtually always drops below 2 mG by the time you are 300 feet from the power line.
What is safe?
What level of EMF is safe? To date, there is no known safe OR UNSAFE level. There are those who have suggested that levels less than 2 milligauss (mG) are “safe.” There is no credible, scientific basis for such a conclusion, however. Further, there may not be any level that is UNSAFE.
Are EMFs dangerous?
Other factors contribute to our risk of cancer. It is virtually impossible to isolate any one cause. Background EMF readings range from 1 mG to several mG. PCBs, herbicides, and ozone have been identified as possible contributory causes. Traffic density is a significant factor, because traffic exhaust contains known carcinogens.
It is important to note that the health effects of EMFs have been, and continue to be, EXTENSIVELY researched. As part of our preparation for this article, we found about 474,000 references on the Internet! Of course, not everything on the Internet is reliable or accurate, but the sheer number of references is note worthy.
According to our research, about $20 million is spent annually on investigations related to the health effects of EMFs.
The credible articles we encountered in our research are peer reviewed, which creates delays in publication; therefore, the most recent articles are a few years old. The following are some highlights of our research:
A 1996 review by a prominent group of scientists at the U.S. National Academy of Science concluded that:
No conclusive and consistent evidence shows that exposures to residential electric and magnetic fields produce cancer, adverse neurobehavioral effects, or reproductive and developmental effects.
A 2001 review by the U.K. National Radiation Protection Board (NRPB) concluded that:
Laboratory experiments have provided no good evidence that extremely low frequency electromagnetic fields are capable of producing cancer, nor do human epidemiological studies suggest that they cause cancer in general.
A review of the epidemiological literature by the International Commission on Non-Ionizing Radiation Protection concludes that:
In the absence of evidence from cellular or animal studies, and given the methodological uncertainties and in many cases inconsistencies of the existing epidemiological literature, there is no chronic disease for which an etiological [causal] relation to [power-frequency fields] can be regarded as established.
In an article written by Dr. John E. Moulder, Professor of Radiation Oncology, he states:
The largest studies of childhood leukemia and power lines ever done reported in 1997–2000 that they could find no significant evidence for an association of power lines with childhood leukemia. In contrast, a pair of studies published in 2000 reported that if all the studies in which magnetic fields could be measured or estimated were pooled, a statistically significant association could be found for childhood leukemia in the children with the highest average fields.
On the other hand, a series of studies have shown that life-time exposure of animals to power-frequency magnetic fields does not cause cancer.
There is a broad consensus in the scientific community that no causal association has been established between residential exposure to EMF and human health hazards.
In 1994, a report from the American Medical Association (AMA) Council on Scientific Affairs stated:
No scientifically documented health risk has been associated with usually occurring levels of electromagnetic fields.
However, it was recommended that the AMA continue to monitor developments and issues related to the effects of EMFs.
In June 1999, after six years of research, the National Institute of Environmental Health Sciences concluded that the evidence for the risk of cancer and other human disease from the electromagnetic fields (EMFs) around power lines is “weak.”
The bottom line appears to be that there is no scientifically conclusive relationship between EMFs and the risk of cancer, including leukemia. However, there are some studies that have seen some slight evidence of a relationship, making it impossible to conclude that there is absolutely no hazard related to EMFs.
In 1991, the U.S. Congress asked the National Academy of Sciences to review the literature on the possible health risks of residential exposure to power-frequency electric and magnetic fields. In response, the National Research Council, the research arm of the National Academy of Sciences, set up a committee of epidemiologists, biologists, chemists, and physicists who were experts in cancer, reproductive toxicology and neurobiological effects. The committee issued its report in November of 1996. The following are quotes from the executive summary:
Based on a comprehensive evaluation of published studies relating to the effects of power-frequency electric and magnetic fields on cells, tissues, and organisms (including humans), the conclusion of the committee is that the current body of evidence does not show that exposure to these fields presents a human-health hazard.
No conclusive and consistent evidence shows that exposures to residential electric and magnetic fields produce cancer, adverse neurobehavioral effects, or reproductive and developmental effects.
As recently as July 2002 (and followed by a similar statement in January 2003), the Wellness Letter published by the University of California, Berkeley, School of Public Health, stated:
An exhaustive study by a panel of leading scientists for the National Research Council has concluded that there is ‘no conclusive and consistent evidence that electromagnetic fields (EMFs) from power lines or household wiring cause cancer, miscarriages, birth defects, or other health problems.’
So, is there a risk to humans exposed to EMFs? After reviewing many credible, well-supported studies, the consensus seems to be a decisive “probably not.” And yet, for some, the concern will continue. We do not live in a safe world. Science cannot eliminate all risks. Cancer, like most other diseases, can seldom be attributed to a single cause. What is important for you, as a responsible adult, is to make well-informed decisions about managing the many risks you face.
发表于 25-8-2010 07:29 PM
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