We don't usually talk about stories published in Physics Today, a publication of the American Institute of Physics. But a recent one caught our attention for two reasons. One, it is about the effects of non-ionizing radiation (in this case an oscillating electric field) and a biological effect, cell division. The second reason is that physicists have been telling us for decades such effects are physically impossible. The only physical effect would be heating a cell, they said. They ridiculed epidemiologists who found an association between powerline frequency electromagnetic fields and childhood leukemia, saying such biological effects were outside the realm of modern physics. The magnetic fields from powerlines are two weak and much smaller than the earth's own field.
An important consequence of the low frequency and resulting low energy of electric and magnetic fields is that they are non-ionizing. An atom or molecule is said to be ionized when one or more of its electrons is dislodged by an energetic outside force such as very high frequency radiation. Gamma rays, X-rays, and high frequency ultraviolet light are termed "ionizing radiation" because their energy is so great that they are capable of ionizing atoms or molecules of ordinary matter.When that matter is human tissue, ionization can damage the DNA molecules of the cells, causing mutations and various forms of cancer. However, the energy carried in 60 Hz fields is much too small to break molecular or chemical bonds. Like visible light, infrared, microwaves, and television and radio waves, electric and magnetic fields are therefore termed non-ionizing radiation.
One form of non-ionizing radiation-microwaves-can nevertheless cause biological damage by a different process: microwaves are absorbed by the water present in tissue, and can induce currents strong enough to heat the tissue. But while 60 Hz fields can also set up currents in tissue, these currents are much weaker. The amount of heat they generate is trivial compared to the natural heat that comes from the cells of the body. There is no reason to believe that health effects can be caused by such minuscule amounts of heat. (From a 1997 Amicus Brief in an EMF legal case; the expert here is physicist Kenneth Foster)
These are incontrovertible facts from the science of physics. They are clearly true. Except when they aren't. These physicists are like the apocryphal professor of aeronautical engineering at MIT who every year patiently explains to his class why anything designed like a bumblebee couldn't possibly fly. Now physicists are acknowledging they not only fly, but they can be used to treat cancer:
Low-intensity electric fields can disrupt the division of cancer cells and slow the growth of brain tumors, suggest laboratory experiments and a small human trial, raising hopes that electric fields will become a new weapon for stalling the progression of cancer.
Alternating electric fields affect tumor cells by (a) slowing their division time from under one hour to more than three hours. The fields also (b,c) disintegrate cells in the later stages of cell division. (Credit: Physics Today, adapted from Kirson et al., Cancer Res. 64, 3288, 2004)
[snip]
In the studies, the research team uses alternating electric fields that jiggle electrically charged particles in cells back and forth hundreds of thousands of times per second. The electric fields have an intensity of only one or two volts per centimeter. Such low-intensity alternating electric fields were once believed to do nothing significant other than heat cells. However, in several years' worth of experiments, the researchers have shown that the fields disrupt cell division in tumor cells placed on a glass dish (in vitro).(Physics Today via ScienceDaily)
In the work reported in Physics Today patients with inoperable brain tumors (glioblastome multiforme) had electrodes with 200 kHz electric fields applied to their scalps for up to 18 hours a day. Preliminary results suggest the tumors progressed much more slowly than the usual clinical experience. This was undertaken because of accumulating information at the lab bench that electric fields at this frequency could slow cell division, and it happens not only with 200 kHz fields but with 50 Hz fields. 50 Hz is the frequency of powerline fields in Europe, almost the same as the 60 Hz fields used in powerlines in the US. . According to the physicists, this wasn't supposed to happen. But it does.
Now they are trying to explain how:
In the 200-kHz case, the electric fields hamper the formation and function of a key cell structure known as the mitotic spindle. The spindle is composed of cell components known as microtubules. The microtubules in turn contain components that have a high electric dipole moment, in which there is a large separation of opposite electric charges. Therefore, parts of the mitotic spindle are greatly influenced, and apparently disrupted, by an electric field.
The second effect of the 200 kHz fields is that they sometimes disintegrated the daughter cells just before they split off from their partners. The dividing cells sometimes destruct because a high-electric-field region develops between the two daughter cells. This leads to a large slope, or gradient, in the electric field from each daughter cell to this region. This gradient may rip organelles (cell structures) and macromolecules (such as proteins) from the scaffolding of the cells.
Ahh. So that's how the bumblebee flies!
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Hey! Is it the physicists' fault that the molecular biologists never say that some of their molecules have large dipole moments? You asked about heat, man, and we said that there couldn't be enough to worry about.
(-;
Also, now the "bumblebees can't fly" professor teaches at MIT! I thought he had tenure at Göttingen.
Blake: In my MIT days we always claimed him. If it wasn't done at MIT it wsn't worth rading or citing was the claim, even apochryphal claims. Regarding the other point, no, not really. The biologists didn't ask about heat. The physicists told us that heat was the only thing that could possibly result from non-ionizing EM and it was insignificant. So they set up the premise and then gave the answer.
Revere, is there any solid epidemiological evidence for a link between power transmission lines and cancer?
Epidemiology ain't my field, but IIRC, the interesting thing about the power lines/leukemia claims was that when the independent variable was actual measured field strength instead of "wire codes"- an arbitrarily determined constant based on proximity to power-carrying conductors- the correlation went right down the scuppers.
There's an awful lot of woo in this subject; reason to be cautious before hauling out the old bumblebee canard.
They ridiculed epidemiologists who found an association between powerline frequency electromagnetic fields and childhood leukemia, saying such biological effects were outside the realm of modern physics.
Well, that's just silly, isn't it? Boil 'em down and (surely) biology is just chemistry is just physics. No?
Ktesibios: There is a great deal of evidence. The question (as always) is how do you interpret it. The point of this post was that the claim that the way you should interpret the evidence is to reject any positive evidence out of hand because the proposition, on the face of it, is not scientifically credible (sort of like claiming you have a perpetual motion machine; you don't have to examine the details because we know at the outset you can't have siuch a machine) turns out to be wrong. There are now a number of demonstratable biological effects that are not thermal from EMF exposure, so much so, that the physicists themselves are now using physics to try to explain them. Hence the post.
Jun: You are treading in deep waters in the philosophy of science. As someone whose professional career is based on the application of mathematics to epidemiology I won't weigh in on one side or the other of the reductionist argument. However much of the discourse takes place at another level. As to the relation of my post to you comment, see my reply above.
"... physicists have been telling us for decades such effects are physically impossible. The only physical effect would be heating a cell, they said. They ridiculed epidemiologists ..."
Do "they" have a name? Got a reference here? The behavior of electric dipoles an alternating electric field is well understood. It sounds like "they" did not take a close look at the cell. In which case they rightly deserve some ridicule, speaking as a physicist.
JohnP: Kenneth Foster is one. I provided a quote from his amicus in the post. But this was a very common refrain and (I don't have the cite) I believe Foster even said it in the pages of Physics Today.
The problem (and it is a gigantic problem) with extrapolating these laboratory results into the field is that what is important in these effects is the electric field at the location of the molecule.
Electric fields are shielded by conductors. Metals are excellent conductors and a few microns of virtually any metal will very strongly attenuate any electric field. The reason that metals are shiny is because the metal is conductive, and the electric field component of light causes charge separation in that conductor and the resulting electric field cancels the field in the electromagnetic wave and the light is reflected.
If you wear an aluminum foil cap, a single layer of aluminum foil will completely attenuate any of the electric fields used in the study. The reason is because aluminum is perhaps 8 orders of magnitude more conductive than living tissues. A micron of aluminum attenuates as much as 100 meters of tissue (for DC fields, AC is more complicated).
Solutions of electrolytes (such as cytoplasm) are also conductive. These also shield electric fields.
The shielding of alternating fields is more complex than that of DC fields. Charge movement and relaxation takes some time, and so the shielding depends on the frequency. For the most part, the sources of AC fields (not in the laboratory) are only coupled capacitively through air, which is a very low dielectric constant media. In the lab, the electrodes are directly connected through water which has a very high dielectric constant. The difference in the capacitative dividing of the applied field due to an air gap vs a water gap can be very large.
Characterizing a field as "one or two volts per cm" isn't enough information. A field of 2 volts per cm in copper will cause the disspation of 2.4 megawatts per cm3. In air it is essentially zero and only depends on ion concentration.
Living materials are extremely complex electrically. Lipid bilayers are essentially non-conductive (except for ion channels which depend on voltage, ion species, and other things). Lots of the charges are not mobile, they are fixed to proteins and large molecules. Axons are somewhat more conductive than other tissues, which is why they get damaged more in electrical injury. But axons are surrounded by myelin, which is a lot less conductive than other tissues.
If you are going to estimate and evaluate a potential hazard, you have to consider a mechanism. A heating mechanism produces negligible heat and so there is negligible risk due to heating. An ionization mechanism produces negligible risk because there is no ionization. The mechanism considered in the paper was that of dielectrophoresis, which depends upoon the product of electric field and the electric field gradient. If either one of them is small, so is the dielectrophoresis force.
The suggested mechanim for the anti-cancer effect was disruption of DNA separation during cell replication. If cells are not replicating, that can't be affected.
A problem is that these results are being hyped (in my opinion) in an attempt to get more research funding.
Are environmental electric fields a problem? Maybe, but they are not a huge problem. Are they in the top hundred problems? I don't think so. If they were a huge problem, it would be obvious by now. People are not dropping dead in cities and from walking under power lines. Utility workers are not dropping dead.
A much bigger problem is that health resources are not allocated according to actual need, but rather by political whim based on hype, political expedience, xenophobia, and religious based notions of morality. There are easily dozens of diseases that are more important, HIV, TB, flu, STDs, hepatitis, malaria, and so on. Many orders of magnitude more people will die from lack of preventative care than from powerline EMF.
As I recall, a number of the epidemiological studies that related EMF to health did not measure actual exposures (and could not, because they were retrospective). Instead, they developed a proxy for exposure that was (I think) rather tenuous.
Ah, I see I posted before I read the bulk of ktesbios' comment, which Revere has yet to address.
They [power line skeptics] ridiculed epidemiologists who found an association between powerline frequency electromagnetic fields and childhood leukemia, saying such biological effects were outside the realm of modern physics. The magnetic fields from powerlines are two weak and much smaller than the earth's own field.
Revere(s), are you aware of the peer-reviewed epidemiological studies that found no connection between EMFs and cancer? They were not published by industry shills or in crappy journals. What is wrong with them, and why aren't they good evidence against the EMF/cancer connection?
hadindr: I am quite familiar with the many studies in this area. I have, in fact, published in the area (in IEEE, no less) so I am not at all ignorant of the issues involved. The epidemiology in this area is mixed, and as NJ points out, has not measured exposure prior to disease onset (they are case control studies). However this leads to nondifferential exposure misclassifcation which baises the effect measures toward the null, so this is not a reason to disbelieve positive studies but is a reason to discount negative ones. Epidemiology in this area is very difficult to do but there is a substantial number of positive results as well as nonpositive ones.
NJ: I believe I addressed ktesibios's comment directly.
But I think the point of this post is being missed by some commenters here. I did not say EMFs cause cancer. I said that the reason given for why it couldn't cause cancer are not valid. Non-ionizing emfs manifestly have biological ffects, contrary to the claim that thermal effects were the only physical consequence of exposure. I would point out to daedulus that the work reported on in Physics Today was not just in vitro but involved human subjects with glioblastome.
Are emfs a big health problem? Assuming measured ORs are roughly accurate (for the sake of argument) they are quite small, so any person's individual risk is elevated very little. A 30% increase in a small risk remains small. On the other hand the exposure source is ubiquitous, so if there is a risk, it makes sense to mitigate it (there are often very simple ways to do this that aren't costly) to lower exposures where they are high (which is very spatially dependent).
Since I've worked in this area in the past (no longer) I am not surprised at the reaction. This is a very emotional issue for physicists and engineers. Since I am an epidemiologist I am perhaps a bit less emotionally detached.
Revere, I appreciate your response. My question to you now would be what should regulatory agencies or utility companies do if the epidemiology for the EMF/cancer link is mixed, at best, and real experts (i.e. credentialed people who are not corporate shills or wackos) cannot agree if it is real or not?
I would also like to note that in the article you cited above the human trial was small and lacked a control group, so its findings are not yet definitive.
Not having studied biological systems electric characteristics (or even chemical systems), but IIRC the common argument is that lipid bilayers and water work to set up shielding dipoles around cells, apart from the water attenuation.
That would be some physicists and engineers, I'm sure. But even if I had studied biological systems I would have liked to see some good models and measurements, and at the moment it doesn't seem likely these things exist. (Due to the circumstances you now describe.)
Order of magnitude estimates are fine as far as they go, but as daedalus2u notes, biological systems are electrically (and chemically) complex.
I hate the bumblebee thing. It's a lame, anti-science myth, and it should never be mentioned except to debunk it.
...pet hate.
And strictly speaking the quote you gave does NOT say that non-ionising radiation has no health effect. It says that the heat generated has no health effect. As far as we know, that is still true.
It does NOT say that "the only physical effect would be heating a cell". Not at all. And if this effect here is found to "hamper the formation and function of a key cell structure" then that is completely in keeping with the quoted text from the wrong, wrong physicists.
Ad if this line seems a bit dubious: "...the energy carried in 60 Hz fields is much too small to break molecular or chemical bonds..." - I'd say that 1. it's pretty clear he's talking about the sort of damage done by ionising radiation, and 2. there's nothing in the new stuff to suggest that the effect is caused by the amount of energy carried by the fields, but is an interaction with a biological process.
I don't doubt that some physicists have scoffed at their biologically focussed comrades, but I'd tell 'em orf if'n I heard 'em, and I don't like bios bashing fizzies any more than I like fizzies bashing bios.
hardindr: No, there's nothing definitive. Definitive in controversial areas pretty much doesn't exist. When the stakes are high, there is controversy, and when there is controversy, it is not definitive by definition. Regarding what to do, there are a variety of relatively inexpensive fixes to reduce exposures, including ways to change connections so currents on the lines run in opposite directions and their fields cancer vectorially and to make the lines run closer together (this is the main reason buried lines have smaller fields; the lines are closer together and not separated as much). The utilities know this one is coming. They are putting disclaimers in their bills. But again, my post was not an examination of the underlying epi. It was about the physical basis for biological effects and what it has to do with the issue.
Torbjorn, ST: I don't bash physicists in general, just those that are so sure of themselves they act with arrogance and condescension towards others who look at evidence and say what they see (hence the bumblebee story, which I was careful to say was apochryphal, but which illustrates something real). It is a fact that many emf naysayers made free use of arguments that said thermal effects were the only possible basis for an adverse effect and implied that anyone who said differently was akin to denying the 2nd law (this is an analogy, don't take it literally; they didn't invoke the 2nd law). I can say quite confidently that the epidemiological evidence for emfs and cancer is as strong today as the evidence for asbestos and cancer in 1949 when it was generally accepted by the medical profession. The only thing that stands in the way of recognizing the link is some physical explanation or identification of a mechanism. Without that we are stuck where we are.
what has this thread to do with bumblebees ?
I don't like your headlines.
People are checking the headlines to decide which
thread to open, so please keep them informative.
Also used by search-engines for keyword-search.
anon,
In addition to the fact that you are a coward, how is it exactly that you get to tell the reveres how to run their blog?
Melanie: I choose to believe that Anon was joking. It makes my life less cranky to believe such things.
Revere: true true. Dunno why I was nitpicking when I agree with the substance. Musta been cranky yesterday.
Just to clarify my point, Revere, your initial response to ktesibios was a one line statement
that answered his lead question but did not elaborate on that evidence in the rest of the paragraph. Your subsequent response to hadindr, however, did explain in more detail, and for that I thank you.
NJ: OK. Fair enough. Rather than cite studies I think support the position of a relationship I'll send you to John Moulder's website that reviews the evidence, with cites. Moulder does not believe there is a relationship, but in my experience he is a fair and honest reporter of the evidence, although he has his own opinions. He is also not an epidemiologist, but he has compiled the citations. There is a section at the end of the FAQ with a bibliography. I haven't looked at it for awhile but I suspect he has kept it pretty up to date. You'll see all sides represented.
Everyone wants to cherry pick this harvest. My point is that there are abundant studies that show a relationship (and many that don't). So there is a lot of evidence. Again,everyone wants to interpret it their own way. However my post was trying to say that interpretations that start out by saying it is physically impossible are not supportable.
Here is the link to Moulder's site: http://www.mcw.edu/gcrc/cop/powerlines-cancer-FAQ/toc.html#A
200 V/M is small? That's an enormous field, I used to work at GM in the EMC department and that was about all we could get out of our multi-kilowatt test amplifiers. It's like sitting right next to a transmitter site, which is what we were trying to replicate in our anechoic chambers.
Back from the weekend and commenting again FWIW.
DC cables could be another means, lowering reactive losses (and so coupling to the envionment) and providing a stable gradient which could help (or be worse).
Thanks. That sounds even worse than I imagined it would be - the evidence emf to cancer is not recognized in the media.
But I don't understand the need for a full mechanism. Was that necessary in the asbestos case? Or is it still only a correlation, not tested as a causality?
Confusing. How does that square with the analogy with asbestos and "generally accepted by the medical profession"?
torbjorn: Asbestos was geneally accepted (via an editorial in JAMA) after a proporitonal mortality study was published iin 1949. There were far fewer positive studies then than for emfs now because there was a lot less epidemiology. Since the 60s we require epidemiological confirmation of everything and for emfs the data is mainly from epidemiology. By the nature of epi there is both positive and non-positive evidence. Once of the hallmarks of a causal association most important to \epidemiologists is "biological plausibility," in this case, an accepted mechanism whereby emfs could cause cancer. While we still don't have that for asbestos, we live in a different time and the arguments for non-ionizing radiation have a different weight than for a physical factor like an asbestos factor. So this is partly a story of legal rqluirements, philosopy of science and sociology of the profession, with politics and ecnomic interests thrown in, which is why it is confusing.
revere,
Thanks for the rundown.
Hmm, yes, it would be hard to show causality from epidemics only. I guess you would need a biological model to get some "knobs" to vary and prove causality over correlation - and then you would be halfway to some formal model anyway. (Though probably far from the detailed mechanism discussed.)
According the the Environmental Protection Agency, ELF electromagnetic radiation is a siginificant risk factor for developing cancer. Their conclusion is based on 8 studies of childhood cancer and more than 30 reports of cancer from electrical workers. In the early reports of the studies, it was suggested that ELF elevtromagnetic radiation be classified as "possible human carcinogens" but the recommendation was revoked due to need for further review of the findings. Other sources claim that the incidence of cancer in people living near power lines would be initiated by the behavior or aerosols in an electromagnetic field. If the aerosols in the electromagnetic field was causing cancer, it would be concentrated in parts of the body most exposed, such as the face and lungs. Studies show that people who live near power lines and workers do not have increased incidences of skin or lung cancer.
What to do with all the contrasting information out there?