Recently published research suggests that electric fields can influence the growth of brain tumors. This might suggest that low-energy electromagnetic fields, such as those near power lines, also have some health effect. When APS News asked several APS members with expertise in this area to comment, they expressed the view that this study should not change our thinking about the safety of power lines.
Beginning in 1979, various groups have claimed, based on statistical analysis, that those living near power lines have an increased risk of cancer. Later the claims were extended to include other devices that generate low-level electromagnetic fields, such as cell phones and electric blankets.
The scientific community generally refuted these claims, citing flaws in the analysis and an absence of any credible physical mechanism. In 1995, the APS Council passed a statement that said, in part, “The scientific literature and the reports of reviews by other panels show no consistent, significant link between cancer and power line fields.”
A National Academies panel also studied the possible connection between power lines and public health, and issued a report in 1996 that concluded that “the current body of evidence does not show that exposure to these fields presents a human-health hazard.”
The APS council reaffirmed its 1995 statement in 2005, stating that, “Since that time, there have been several large in vivo studies of animal populations subjected for their life span to high magnetic fields and epidemiological studies, done with larger populations and with direct, rather than surrogate, measurements of the magnetic field exposure. These studies have produced no results that change the earlier assessment by APS.”
Now, Yoram Palti of the Technion-Israel Institute of Technology, and colleagues have found that low intensity, alternating electric fields can disrupt cell division. The research is reported in PNAS (E. D. Kirson et al., Proc. Natl. Acad. Sci. USA 104, 10152 (2007); also see Search and Discovery, August 2007 Physics Today). The researchers found that electric fields applied to tumor cells in vitro and in mice and rats could slow the cells’ division and even kill dividing tumor cells. They then developed a treatment for an aggressive type of brain cancer, in which electrodes stuck to patients’ heads apply 200 kHz electric fields. A small clinical trial with 10 patients found that the treatment seems to slow the progression of tumors and lengthen the survival time of patients in the study.
Palti, said there is no connection between his studies and electric power lines or home appliances. The treatment uses alternating electric fields in the 100-200 kHz range, a much higher frequency than the 60 Hz power lines in the U.S. “If we move the frequency down, below 100kHz, or above 300kHz, we don’t get an effect,” Palti says. In addition, external electric fields would not penetrate the body. “The reason why we are using electrodes, is that there is a very bad impedance matching between the air and the tissue, so a very small fraction of the field penetrates the tissue. We are applying it directly to the tissue, so we get effectively much stronger field,” Palti said.
Another study by Damir Janigro, Luca Cucullo and colleagues at the Cleveland Clinic found that 50Hz low intensity alternating current can slow cell division in some cases. (Cucullo et al. Glia, 51, 65 (2005))The studies were done using several types of tumor cells in vitro. Janigro said, “We found that cell division was very much inhibited, in a very reversible way.”
Other experts didn’t think these studies should cause us to change our thinking about the safety of power lines.
The 1995 APS statement was based on a report written by David Hafemeister of CalPoly, San Luis Obispo. When asked about this new study, Hafemeister said he still sees no reason to think power lines cause cancer. “The basic physics makes it hard to believe there is cancer being caused. There could be some new paradigm, but that is shooting in the dark.” One has to look at the epidemiology for any connection between power lines and health, he said. The area of power lines and public health is “a well-researched area, with much conflicting data, and many have taken one item and ignored the rest,” he said.
Richard Wilson, emeritus professor of physics at Harvard, has studied the effects of extremely low-level doses of radiation. When asked about whether this new work might indicate electric fields such as those near power lines could affect the body, he said, “Indeed electric fields in the body have a great effect on cells. But the external fields do not penetrate the body.”
Charles Stevens, of the Salk Institute in La Jolla, CA, chaired the 1996 National Academies study. Referring to the recent research, he said, “The fields used were much larger than would occur near power lines or appliances. The fields produced by power lines are lower than those that occur naturally in the body because of currents flowing associated with nerve and muscle activity. These fields are more than an order of magnitude greater than what occur naturally.” He said he’d like to see the study confirmed by more research. “I would not take seriously the effect of electric fields on cell division until it has been repeated in another laboratory,” he added.