Thursday, December 16, 2010

Dr. Mittleman at Rice University, provides a further discussion on the health effects of THz radiation


Hi Randy,
I'd be happy to write a short comment on the topic of the health effects of THz radiation.  I'm certainly not the expert on this topic, as it has not been a focus of my own research in recent years.  But I've kept up on it and can speak somewhat knowledgeably about what's known.

The key question here is whether irradiation by low-frequency electromagnetic waves can induce biologically significant effects in living cells, other than merely by heating them up.  It should be pointed out that this question (and probably the answer) are just as relevant for microwaves as for terahertz radiation.  All of these low-frequency waves are strongly absorbed by water.  Since all biology happens in water, it's clear that we can affect cells (or even cook them) by putting enough energy into the surrounding water. 

The hard part is determining if anything happens to the cells that is NOT merely the result of the water heating up.  And that's the important question, from the standpoint of setting safety standards.  If the only cell damage mechanism is thermal, then the minimum exposure limit for THz radiation would be set in the same way that it has been set for microwaves - we just avoid cooking people.  On the other hand, if cell damage can occur at a lower power density via some other mechanism, then the exposure limits would have to be correspondingly lower.

The conventional wisdom in the physics community is that there simply cannot be non-thermal effects.  The energy necessary to break a chemical bond is hundreds or thousands of times larger than the energy of a single terahertz photon.  Thus, ultraviolet or x-ray radiation can lead to genetic mutations (think: too much sun exposure leads to melanoma), but radiation at lower frequencies (with lower photon energies) does not.  If that conventional wisdom is correct, then the only danger from T-rays (or microwaves or radio waves or infrared radiation) is that it can induce thermal effects.

There have been a couple of proposals for mechanisms that would permit non-thermal effects from low-frequency radiation, most notably the recent paper by Alexandrov and co-workers (from Physics Letters A in 2010).  This paper got a lot of press when it came out.  It's a wonderfully inflamatory subject, after all.  But there are many reasons to believe that the analysis in that article (which, after all, contains no experimental evidence) is woefully over-simplified, and therefore completely inapplicable to the real world.  Most glaringly, the description neglects the absorption of THz radiation by the water bath in which the DNA chain resides.  That's like being worried about the effects of sunlight on your brain tissue - if you ignore the opaque skull that entirely surrounds your brain then you might actually need to consider that question, but for those of us with skulls it isn't exactly a pressing concern.  In my view, there is still no feasible proposal for a non-thermal mechanism.

Having said that, I do think that there is some experimental work that needs mentioning.  I refer specifically to the recent work from the lab of Dr. Peter Siegel at CalTech (more precisely, NASA JPL).  In these experiments, a collection of cells were irradiated with millimeter waves (not quite THz radiation), and certain changes were observed (e.g., induced cell poration, modulation of neuronal activity, etc.)  These folks were as careful as possible to monitor local temperatures and eliminate the possibility of thermally induced effects.  I would not call these results conclusive (neither would the authors), but they are suggestive that more work is needed. 

If these experimental results are correct, then the burden will still remain upon the researchers to come up with an explanation of how it's possible.  As far as I know, they've not even tried to explain anything yet, merely to observe and see what's going on.  I have great respect for Peter, but I remain skeptical simply because there is no plausible mechanism to explain non-thermal effects.


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Dr. Daniel Mittleman   
Rice University           
ECE Dept., MS-366 
 6100 Main St.           
 Houston, TX 77005
URL: www-ece.rice.edu/~daniel/Mittleman.html
Biographical InformationDr. Mittleman received his B.S. in physics from the Massachusetts Institute of Technology in 1988, and his M.S. in 1990 and Ph.D. in 1994, both in physics from the University of California, Berkeley, under the direction of Dr. Charles Shank. His thesis work involved the spectroscopy of semiconductor nanocrystals using laser pulses with durations of less than 20 femtoseconds, at wavelengths from 480 nm to 670 nm.  He then joined AT&T Bell Laboratories as a post-doctoral member of the technical staff, working first for Dr. Richard Freeman on a terawatt laser system, and then for Dr. Martin Nuss on terahertz spectroscopy and imaging. Dr. Mittleman joined the ECE Department at Rice University in September 1996, where he is a Professor.  At Rice, his research interests involve various aspects of spectroscopy, sensing, and imaging using terahertz radiation. Dr. Mittleman is a Fellow of the Optical Society of America.
Click here to see an up-to-date list of publications from the Mittleman group.

MY NOTE: THANK YOU VERY MUCH DR. MITTLEMAN FOR TAKING TIME TO HELP THE LAY COMMUNITY BETTER UNDERSTAND THz!

8 comments:

trailgenius said...

Dr.Middleman would you consider being on the board of Advanced Photonics Inc.?

trailgenius said...

I think that these last experiments must have been CW(continous wave)millimeter waves which is really apples to oranges in the amount of energy involved compared to pulse. API is exclusively pulse which is one reason why they are ahead of all their competition.Pulse domain terahertz energy is in an order of 10,000 times less than CW terahertz and 10,000,000,000 times less than an average microwave oven.I was in cancer research working on my doctorate for 5 years and we do know that dose or exposure is important in causing any mutation.That being said, what was the power in this experiment?Watts, kilowatts,microwatts milliwatts? Pulse domain terahertz is in the microwatts and of cource probably not to be compared with millimeter radiation anyway.
Just don't want people to be alarmed. This seems to be a no brainer in the health risks comparison with back scatter X-ray radiation.

jp_guillet said...

In most cases, the power of THz sources is low. With the attenuation in the water, the problem of the dangers of THz does not accurs in my opinion.

However, we must remember that this is not a question of power but power density. I got power densities much higher safety standards with a 1 mW CW source at f = 0.3 THz using Sommerfeld waveguide during my PhD work.

At one moment I thought I felt something touching the wire ... but this feeling exists even the source off. :) And my hands have not mutated yet!

As Dr. Daniel Mittleman said, I think that more work is needed.

Randy Knudson said...

I believe that one of the problems I see, in the discussion about THz allegedly damaging DNA, is that as Trailgenius points out, terahertz scanning processes are by no mean uniform. Time-domain terahertz is pulsed and not continuous.
I noticed that in looking at some of the millimeter-wave and continuous products, that they by no means are the same. Read the following from the Thru-vision webpage, and someone explain to me, how this could possibly damage DNA??
Safe technology

ThruVision Systems' technology is passive. Like CCTV cameras our products do not emit energy onto the people being screened. Some other body scanning technologies emit x-rays and other types of radiation during the screening process. Our products operate by receiving natural energy that emanates from all people.

ThruVision Systems recognises that it is important to balance security with civil liberties. Our products do not image intimate body details. This allows the screening of all age groups and removes the need for same gender operators. Our safe people screening systems can be used to screen women during pregnancy. As our products are completely passive people can be screened an unlimited amount of times with absolutely no risk to their health.
http://www.thruvision.com/Safe_Technology/Safe_Technology.htm

trailgenius said...

What is thruvision? Seems one could have a controlled release of some exothermic reactants into a water bladder "cover" maintaining 37C. if this is just thermal imaging.
Now onto physicist doing biophysical research:Great as we continually seem to unlock natures secrects. Everything may be eventually be explained by quantum mechanics but I have serious doubts. God (generator of diversity as we referred to during unrepeatable experiments) has made the biological system able to repair many environmental insults. Back in the 1970's I was living with a nuclear physist who did all his study on his Phd at Cal Tec then was hired at the Oak Ridge National Laboratory and finished his thesis at UT. Anyway the saccharine study came out where rats developed cancer given the equivalent ot 40,000 cans of pop a day. He thought this was bad research. This was good research as chemicals are either carcinogenic or noncarcinogenic. One can kill you with enough of anything(like water) but can only cause cancer if carcinogenic. The problem with the saccharine research was that people are afraid of the word cancer so non scientists took off the market a wonderful sweetener that was much healthier than the alternative of sugar which causes obesity and diabetes.The risk benefit ratio is schewed when ever talking about cancer!
"Cancer causing" are the most feared words. The trade centers arguably would still be standing if asbestos was allowed. and asbestos is another topic!
Well since it is snowing I will ramble on.
Nerve endings are superficial.Canines acquire two types of mange:sarcoptic which is pruritic not to be confused with prurient; and demodectic which does not itch-nonpruritic. I mention this because a previous comment said he felt something from terahertz exposure.The demodectic mange lives deep in the skin in the hair follicules below the nerve endings while the scabies lives on the surface where the nerve endings.
So this is good that a burn was felt. It means to me the energy was expended at the surface vs ionizing radiation like x-rays cause no sensation but go deep before expending their energy(and causing damage).
Finally in closing they may show the electromagnetic rays of certain wavelengths cause damage in certain situations. Just don't let people think that this is like putting your feet into the x-ray box to see if there is a correct fit. In my openion the benifit of being able to detect abnormalaties out weighs the harm even with back scatter X-rays. t-rays seem like the answere we have been after! At this energy level I don't see how they could cause any damage to the skin period.

trailgenius said...

Interesting synopsis on a paper by Zhou Yun whing helps understand poration.But once again not terahertz research.


Safe and efficient intracellular delivery of drugs and genes is critically important in targeted cancer treatment and gene therapy applications. Ultrasound has been demonstrated to increase the cell membrane permeability and exploited as a promising non-viral strategy for intracellular delivery of DNAs, proteins, and other agents. Despite increasing interest and progress made recently, challenges remain to achieve controllable outcome. Ultrasound energy mechanically creates nano- to micron- sized, non-specific pores on the cell membrane to allow entry of extracellular agents into the cell. However,the biophysical mechanisms of this process, often called sonoporation, has not been fully understood due to the lack of appropriate techniques to study the transient and submicronprocess. Sonoporation studies have been largely limited to static post-ultrasound assays. While important knowledge can be obtained through such analysis, such methods inevitably overlook the actual transient process of cell poration, therefore are inadequate to deterministically correlate ultrasound parameters with sonoporation outcome and to uncover cellular mechanisms of sonoporation in individual cells. This research aims to study the sonoporation dynamics at the single cell level to obtain better understanding of the mechanisms of sonoporation affected by relevant physical and chemical parameters. Using Xenopus oocytes as a model system, sonoporation of a single cell is monitored in real time via the voltage clamp techniques which provide a novel means to monitor the dynamics of sonoporation with high temporal resolution and sensitivity. The specific aims of this research are: 1) To investigate the roles of extracellular [Ca2+] in sonoporation; 2) To correlate sonoporation with acoustic cavitation activities at the single cell level; and 3) To estimate the pore size in sonoporation by using statistical analysis.

Randy Knudson said...

traigenius- I'm certainly happy to have your excellent posts! Thank you.

Lanet Khoda. said...

Let us irradiate YOUR children at high DARPA-funded "military" INTENSITIES 24/7 from drones overhead, or from the next room, and see how their brain myelenation fares. ...And never mind that those frequencies are blocked by our disappearing atmosphere. PS -- Do you people ever discuss ethics, while you pick up your paychecks?!