How Terahertz Waves (Body Scan Imaging Tech, eg) Tear Apart DNA

[BurtWorm]

This could--or maybe should--throw a big monkey wrench in plans to broaden the use of this technology at airport security areas. I was alerted to this article, which originally appeared at MIT's Technology Review Physics ArXiv blog, by Medgadget.com


http://www.technologyreview.com/blog/arxiv/24331/



Friday, October 30, 2009

A new model of the way the THz waves interact with DNA explains how the damage is done and why evidence has been so hard to gather

Great things are expected of terahertz waves, the radiation that fills the slot in the electromagnetic spectrum between microwaves and the infrared. Terahertz waves pass through non-conducting materials such as clothes , paper, wood and brick and so cameras sensitive to them can peer inside envelopes, into living rooms and "frisk" people at distance.

The way terahertz waves are absorbed and emitted can also be used to determine the chemical composition of a material. And even though they don't travel far inside the body, there is great hope that the waves can be used to spot tumours near the surface of the skin.

With all that potential, it's no wonder that research on terahertz waves has exploded in the last ten years or so.

But what of the health effects of terahertz waves? At first glance, it's easy to dismiss any notion that they can be damaging. Terahertz photons are not energetic enough to break chemical bonds or ionise atoms or molecules, the chief reasons why higher energy photons such as x-rays and UV rays are so bad for us. But could there be another mechanism at work?

The evidence that terahertz radiation damages biological systems is mixed. "Some studies reported significant genetic damage while others, although similar, showed none," say Boian Alexandrov at the Center for Nonlinear Studies at Los Alamos National Laboratory in New Mexico and a few buddies. Now these guys think they know why.

Alexandrov and co have created a model to investigate how THz fields interact with double-stranded DNA and what they've found is remarkable. They say that although the forces generated are tiny, resonant effects allow THz waves to unzip double-stranded DNA, creating bubbles in the double strand that could significantly interfere with processes such as gene expression and DNA replication. That's a jaw dropping conclusion.

And it also explains why the evidence has been so hard to garner. Ordinary resonant effects are not powerful enough to do do this kind of damage but nonlinear resonances can. These nonlinear instabilities are much less likely to form which explains why the character of THz genotoxic effects are probabilistic rather than deterministic, say the team.

This should set the cat among the pigeons. Of course, terahertz waves are a natural part of environment, just like visible and infrared light. But a new generation of cameras are set to appear that not only record terahertz waves but also bombard us with them. And if our exposure is set to increase, the question that urgently needs answering is what level of terahertz exposure is safe.

Ref: arxiv.org/abs/0910.5294: DNA Breathing Dynamics in the Presence of a Terahertz Field

[Orrex]

1. I don't know about all that, but that's the most realistic snowwoman I've ever seen!

[BurtWorm]

2. Why thank you. I made her myself out of unraveled DNA strands.

:hi:

[hobbit709]

3. The body scanners use millimeter wavelengths

A bit lower in frequency than THz.

[BurtWorm]

4. So MIT and Medgadget are barking up the wrong tree?

That's a relief.

[hobbit709]

5. 1 millimeter wavelength is 300GHz

[BurtWorm]

11. So you think there's nothing to worry about with this technology?

As I say, that's a relief.

[sui generis]

6. THz for this purpose is a range of frequencies

0.1 to 0.5 terahertz, which includes millimeter-range energy.

I dimly remember the primary difference is resolution in distance from the subject; i.e., across the room vs. point blank.

[hobbit709]

9. I don't consider 100 to 500 GHz a terahertz

anymore than I would consider a 100Gb hard drive a terabyte.

[sui generis]

10. Well good for you. I don't believe skyscrapers scrape the sky.

But the operational and generally accepted definition (give Wiki a shot) of this technology references it thus. And skyscraper sounds nattier than "really-tall-building", so I use that too.

:P

[hobbit709]

12. I played with a lot of EHF back in my military days

And we didn't consider that THz.

[BurtWorm]

13. Is your point just about the frequencies of the scans or about the alleged damage they do?

Are you arguing that because they're not really terahertz, MIT is off-base about the danger to human DNA from these scans? Or are you just saying they should be talking about gigahertz because the rays aren't really terahertz?

[hobbit709]

14. If they want to make claims, they should be accurate about the terminology.

It may all be part of the electromagnetic spectrum-but which part. Near infrared is not visible light nor is it considered regular radio waves.

Stand in the TX sun in Aug. for an hour and see how much DNA damage you get.

[BurtWorm]

15. Have you read the paper?

You're basing your opinion on terminology? You're just going to dismiss this out of hand because they're not using terminology as you would? What do you suppose caused the real DNA damage they're talking about? Texas sun that they accidentally let slip into the lab?

[Trillo]

7. "resonant effects"

That's the same generalized idea that Royal Rife claimed for his treatments.

http://www.rife.de/

[BurtWorm]

8. Rife was a drunken crackpot, though.

I don't know about these people. The MIT cachet lends them a bit more credibility in my book anyway.

[applegrove]

16. I knew those scans would be dangerous.

[StrawDog44]

17. How Would You..

Like to be the one looking at this all day. I mean, I'd be creeped out to see some old ladies kooch in this manner...or any manner for that matter.

[caraher]

18. Linguistic debates about whether "millimeter" waves are THz are irrelevant

The damage mechanism cited depends on certain resonances; all that matters is whether exposure to the radiation of the screening devices can initiate this mechanism, which in turn depends on the intensity of the radiation, its duration, and whether its spectrum included the appropriate resonances.

According to the investigators' paper, there are several studies that report DNA damage under specific circumstances. All of them show strong threshold effects in time or intensity. In other words, you need long (hours, not seconds) exposures or high intensities to see anything bad happen. The authors sum up the findings by saying, "...the available experimental data data strongly suggest that THz-radiation can affect biological function, but only under specific conditions, viz. high power, or/and extended exposure, or/and specific THz frequency."

The authors' simulation focused on higher frequencies than millimeter-wave devices use. While they focused on a range of about 1-2.5 THz (about 0.1-0.3 mm wavelengths), they were seeking mainly to establish a mechanism and only considered one model DNA molecule. I don't think it's much of a stretch to consider similar effects at longer wavelengths in different DNA molecules.

Given the numbers used in their simulations and the threshold values in the reports of damage they summarize, it seems unlikely that the duration of exposure and intensity of THz used in scanners would cause the kind of damage described. But the paper is not intended to establish safety; it is an argument that a mechanism for damage exists. Establishing a novel damage mechanism is a big deal. It provides a reason to be cautious about the technology, suggests future investigations that might lead to better understanding of potential risks, and provides the basis for science-based safety standards.

Bottom line: the "Airport scanners can unzip your DNA" headlines go way beyond what this paper suggests, but it does provide a sound scientific reason for caution and further study.

[BurtWorm]

19. Thank you. Very useful analysis of the data.

:toast: