When discussing proposed power lines, potential health effects are frequently cited as a concern by people who will live, work, or have children who attend school near the power lines.
Concerns about health effects related to transmission lines were brought to the public’s attention by a 1979 study in which epidemiologists linked the electromagnetic fields (EMF) from power lines to a slight increase in childhood leukemia.
“Obviously, [it was] a big deal,” Drew Thatcher, an expert in non-ionizing radiation, told TransmissionHub on June 28.
Studies similar to the 1979 study were repeated many times in subsequent years, but “there were a lot of weaknesses in those studies,” according to Thatcher, who is an adjunct professor at Vanderbilt University, and served as the Washington state health department’s expert on non-ionizing radiation for more than two decades.
In an effort to obtain more definitive data than the early studies yielded, scientists designed and performed more rigorous studies, Thatcher said.
The results were inconclusive.
In 1996, the U.S. National Academy of Sciences said it could not conclude that what appeared to be a slightly increased risk of childhood leukemia in children who lived near power lines could be explained by exposure to magnetic fields.
According to the National Cancer Institute’s web site, “Overall, there is limited evidence that magnetic fields cause childhood leukemia, and there is inadequate evidence that these magnetic fields cause other cancers in children.”
Other studies, conducted by such organizations as the World Health Organization (WHO) and the National Cancer Institute, showed no solid link between EMF and cancer, according to those organizations’ web sites. However, the WHO’s website adds, such studies receive little if any news coverage.
“Science cannot provide a guarantee of absolute safety yet but the development of research is reassuring overall,” according to the WHO’s web site.
“All of the epidemiology so far is based on fewer than 20 children for exposures greater than 4 milliGauss,” Thatcher said. “It’s too small a number to be a meaningful metric.”
The Gauss is the unit of measurement of a magnetic field.
“We’re not going to be able to say we’re 100% sure this isn’t a risk; that’s not how science works,” Thatcher said.
The International Agency for Research on Cancer (IARC), which is the part of the WHO focused on identifying causes of cancer, has classified very low frequency EMF – such as that from a 60 Hz power line – as a group 2B carcinogen.
A group 2B carcinogen, according to the WHO, is something that is “possibly carcinogenic to humans.” Coffee, Asian pickled vegetables, and talc-based body powder are also considered group 2B carcinogens.
A group 2A carcinogen is something that is “probably carcinogenic,” and includes polychlorinated biphenyls (PCBs) found in some transformers, as well as creosotes.
By contrast, a group 1 carcinogen is a “known carcinogen to humans” and includes asbestos, tobacco, and neutron radiation. Currently, only 100 substances have been classified as “known carcinogens.”
How much, how little
Whatever level of risk exists, it has not prompted the establishment of official exposure guidelines.
Neither the government of the U.S. nor of Canada has issued guidelines for power line EMF. However, agencies such as the International Commission for Non-Ionizing Radiation Protection (ICNIRP) and the Institute for Electrical and Electronic Engineers (IEEE) have developed such guidelines.
Set in 2010, the ICNIRP guideline for maximum exposure is 2,000 mG, a level the WHO’s policy recommendations said is a level “50 times lower than the exposure level at which any biological effects have been found.” Based on this 50-fold “safety factor”, “a high level of precaution is already built into” the ICNIRP guidelines, according to the WHO.
Thatcher said, “2,000 mG isn’t really relevant for public exposures; you can’t get that anywhere,” adding that the highest exposure level he has found in a public area was approximately 100 mG, in close proximity to an indoor transformer.
To put the EMF emissions from power lines into context, Thatcher met TransmissionHub on a right-of-way (ROW) in metropolitan Seattle, occupied by a 500-kV and three 230-kV power lines operated by the Bonneville Power Administration (BPA). Standing directly beneath the 500-kV line, approximately 20 feet away from the 230-kV line that also occupied the ROW, Thatcher’s meter detected a rating of slightly less than 25 mG.
But structures are not situated directly under power lines, and field strength drops off by a factor of “1/Distance from power lines2”, according to Thatcher, so a second reading was taken approximately 50 feet away, near the entrances to businesses – including a children’s gym – that occupy a strip mall adjacent to the ROW.
At that distance, the reading dropped to less than 12 mG.
Because weather was mild, the lines were operating at approximately 20% of their capacity, according to BPA.
“A peak magnetic field under these lines would be closer to 60 to 100 mG,” Thatcher said, adding, “As far as the science is concerned, any of these numbers is just fine. I wouldn’t be worried about any of them.”
Background exposure a factor
In addition EMF emissions, from power lines and virtually all types of electrical appliances, human beings are constantly exposed to background levels of EMF, according to the WHO.
The amount of background EMF exposure varies by latitude, with the least exposure at the equator and the highest at the poles. Background EMF in the Seattle area is approximately 550 mG, so increasing exposure by 11 mG would represent an increase of approximately 2% over the exposure people receive every day.
Arguably, the greater health risk associated with power lines is direct contact with the conductors themselves, whether from hot-air balloons or other aircraft colliding with the lines, thieves attempting to steal energized copper conductor for its scrap value, or people climbing the towers, like the 21-year-old Czech woman who authorities said climbed a transmission tower in the Czech Republic region of Zlin on June 22.
While science will not be able to say there is zero risk from EMF, Thatcher said, “We can say that, after 35 years of consistent research in this field, spending upwards of a half a billion dollars on this subject, we’re not able to find a consistent and definitive risk at all.”