Extremely-low-frequency Electromagnetic Fields--WHO classifies the cancer risk. (Update).
Whenever electricity is conducted through transmission lines, is transported through distribution lines, or is used in appliances, both electric and magnetic fields exist close to the lines or appliances. The power frequency used is 50 or 60 Hz. Use of electric power has become part of everyday life. Questions have been raised, however, as to whether these and other ELF fields are carcinogenic.
The International al Agency for Research on Cancer (IARC)--a specialized Cancer research agency of WHO--has recently concluded a first step in WHO's health risk assessment process by classifying ELF fields with respect to the "strength of the evidence" that they could cause cancer in humans.
In June 2001, an expert scientific working group of IARC reviewed studies related to he carcinogenicity of static and ELF electric and magnetic fields. Using the standard IARC classification that weighs human, animal, and laboratory evidence, the researchers classified ELF magnetic fields as possibly carcinogenic to humans based on epidemiological studies of childhood leukemia. Evidence for all other cancers in children and adults, as well as for other types of exposure (i.e., static fields and ELF electric fields) was considered not classifiable because of either insufficient or inconsistent scientific information.
"Possibly carcinogenic to humans" is a classification used to denote an agent for which there is limited evidence of carcinogenicity in humans and less-than-sufficient evidence for carcinogenicity in experimental animals. This classification is the weakest of three categories ("carcinogenic to humans," "probably carcinogenic to humans," and "possibly carcinogenic to humans") used by IARC to classify potential carcinogens according to published scientific evidence.
Do ELF Fields Cause Cancer?
ELF fields are known to interact with tissues by inducing electric fields and currents in them. This is the only established mechanism of action of these fields. The electric currents induced by ELF fields commonly found in the human environment are normally much lower than the strongest electric currents naturally occurring in the body, such as those that control the beating of the heart.
Since 1979, when epidemiological studies first raised a concern about a possible association between magnetic fields from power lines and childhood cancer, a large number of studies have been conducted to determine if measured ELF exposure can influence cancer development, especially leukemia in children.
There is no consistent evidence that exposure to ELF fields experienced in the living environment causes direct damage to biological molecules, including DNA. Since it seems unlikely that ELF fields could initiate cancer, a large number of investigations have been conducted to determine if ELF exposure can influence cancer promotion or co-promotion. Results from animal studies conducted so far suggest that ELF fields do not initiate or promote cancer.
Two recent pooled analyses of epidemiological studies, however, provide insight into the epidemiological evidence that played a pivotal role in the IARC evaluation. These studies suggest that, in a population exposed to average magnetic fields in excess of 0.3 to 0.4 microteslas ([micro]T), twice as many children might develop leukemia as in a population with lower exposures. In spite of the large-number database, some uncertainty remains as to whether magnetic-field exposure or some other factor(s) might account for the increased leukemia incidence.
Childhood leukemia is a rare disease, with four out of 100,000 children between 0 and 14 years of age diagnosed every year. Also, average magnetic-field exposures above 0.3 or 0.4 [micro]T are rare in residences. It can be estimated from the epidemiological-study results that less than 1 percent of populations using 240-volt power supplies are exposed to these levels, although the percentage may be higher in countries using 120-volt supplies.
The IARC review addresses the issue of whether it is possible that ELF-EMF poses a cancer risk. The next step in the process is to estimate the likelihood of cancers in the general population from the usual exposures and to evaluate evidence for other (non-cancer) diseases. This part of the risk assessment should be finished by WHO in the next 18 months.
Some National Responses
In response to increasing public concern over health effects from EMF exposure, several countries have established their own scientific reviews prior to the IARC evaluation. In 1998, a working group examining the issue for the U.S. National Institute of Environmental Health Sciences (NIEHS) classified ELF magnetic fields as possibly carcinogenic to humans. The U.S. government has since recommended "passive regulatory action," described as continued information and education of the public and encouragement of power utilities to voluntarily reduce human exposure where possible.
In the United Kingdom, the Advisory Group on Non-Ionizing Radiation recently reported to the National Radiological Protection Board on the topic of power-frequency EMF and the risk of cancer. The advisory group concluded that while the evidence is currently not strong enough to justify a firm conclusion that EMF fields cause leukemia in children, the possibility remains that intense and prolonged exposures to magnetic fields can increase the risk. The Health Council of the Netherlands, a major scientific advisory body of the Netherlands government, has reached similar conclusions.
While the classification of ELF magnetic fields as possibly carcinogenic to humans has been made, it remains possible that there are other explanations for the observed association between exposure to ELF magnetic fields and childhood leukemia. In particular, issues of selection bias in the epidemiological studies and exposure to other field types should be rigorously examined and will likely require new studies. WHO therefore recommends a follow-up, focused research program to provide more definitive information. Some of these studies are currently being undertaken and results are expected over the next two to three years.
WHO's EMF Project aims to help national authorities balance the benefits of electrical technology against possible health risks, and to help them decide what protective measures may be needed. It is especially difficult to suggest protective measures for ELF fields because researchers do not know what field characteristic might be involved in the development of childhood leukemia, or even if it is the ELF magnetic fields that are responsible for this effect. One approach is to have voluntary policies that aim to cost-effectively reduce exposure to ELF fields.
Some precautionary measures are outlined below:
* Government and industry should be cognizant of the latest scientific developments and should provide the public with balanced, clear, and comprehensive information on potential EMF risks, as well as suggestions for safe and low-cost ways to reduce exposures. These entities also should promote research that will lead to better information from which assessments of health risks can be made.
* Members of the general public might choose to reduce their EMF exposure by minimizing the use of certain electrical appliances or by increasing distance to sources that can produce relatively high fields.
* Entities siting new power lines could consult with local authorities, industry, and the public. Obviously power lines must be sited to provide power to consumers. Already, those making these decisions are often required to take into account aesthetics and public sensibilities.
* An effective system of health information and communication among scientists, governments, industry, and the public is needed to help raise general awareness of programs that deal with exposure to ELF fields and to reduce mistrust and fears.
(Adapted from WHO Fact Sheet 263. The complete text of the fact sheet can be found at <http://www.who.int/inf-fs/en/fact263.html>.)
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|Publication:||Journal of Environmental Health|
|Date:||Dec 1, 2002|
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