Dubbed 'naked' scanners because of the graphic image they give of the body, both machines have sparked widespread privacy concerns. But it's the backscatter devices, which emit small doses of ionzing radiation, that are worrying a group of scientists.
Four professors from the University of California at San Francisco (UCSF)-namely, Dr John Sedat, Professor Emeritus in Biochemistry and Biophysics, Dr Marc Shuman, an internationally recognized cancer expert, and Drs David Agard and Robert Stroud, who are X-ray crystallographers and imaging experts-recently wrote a letter to President Obama's Science and Technology advisor, John Holdren, about "the potential serious health risks" of airport backscatter scanners.
Their main concern was that the safety of these devices has not been adequately demonstrated. Consider-ing the plans to rapidly implement these scanners as a primary screening step for all air-travel passengers, thus exposing hundreds of millions of people to them, the scientists stressed the need for independent evaluation.
In particular, the letter voiced concerns over the dosage of X-ray energy delivered by the backscatter devices to a scanned person's skin.
"These new devices operate at relatively low beam energies (28 keV). The majority of their energy is delivered to the skin and the under-lying tissue. Thus, while the dose would be safe if it were distributed throughout the volume of the entire body, the dose to the skin may be dangerously high," they wrote.
Indeed, they believe that the X-ray dosages from these machines have misleadingly been compared with the cosmic-ray exposure we all encounter during airplane travel (see WDDTY vol 19 no 12) or chest X-rays. "Both the air-travel cosmic-ray exposure and chest X-rays have much higher X-ray energies, and the health consequences are appropriately understood in terms of the whole body volume dose," they state. "In contrast, these new airport scanners are largely depositing their energy into the skin and immediately adjacent tissue, and since this is such a small fraction of body weight/vol, possibly by one to two orders of magnitude, the real dose to the skin is now high."
The letter goes on to identify vulnerable groups that may be at particular risk from such high skin doses, such as children, pregnant women, the elderly and people with compromised immune systems, such as HIV and cancer patients. "There is good reason to believe that these scanners will increase the risk of cancer to children and other vulnerable populations," they state.
What's more, we could all be at risk if the devices malfunction. Any glitch in power at any point in the hardware or software that causes the device to stop could then deliver an intense radiation dose at a single spot on the skin. As no technology is perfect, this may happen at any time, even often.
The official response
So what did the White House say to all this? According to a recent posting on the White House's Office of Science and Technology Policy (OSTP) webpage, Office Director Holdren sent an e-mail to the UCSF professors, noting that the issue had been "studied extensively for many years by the Food and Drug Administration (FDA), Department of Health and Human Services, and Department of Homeland Security (DHS)". However, he conceded that the government needed to do a better job of explaining the safety issues surrounding the backscatter scanners, and so asked representatives from the FDA and DHS to address the concerns raised in the letter. Their reply to Holdren has now been posted on the FDA website.
After detailing the reviews and advisory committees that have certified the scanners as safe, the response concludes: "[T]he potential health risks from a full-body screening with a general-use x-ray security system are miniscule . . . we are confident that full-body x-ray security products and practices do not pose a significant risk to the public health."
However, this response doesn't satisfy John Sedat. When interviewed, he called the reply "deeply flawed" and "double-talk", and said it didn't answer any questions. "Sadly, I have to say we still don't have the information we need to decide what are the dan-gers of this device," he commented, and stated that the UCSF group will make a formal reply to Holdren.
Other scientists remain equally unconvinced by the government's response. As Dr David Brenner, who heads Columbia University's Center for Radiological Research, said, "I don't think anybody would argue the point that the individual risk is small," he said in an interview. "But multiply that times 700 million people-the number of people getting on planes currently-and that's the public-health risk."
Brenner also said there's reason to believe the radiation dose delivered per scan is higher that the government states, based on calculations by Arizona State University researchers, published online on 9 November ahead of print in the peer-reviewed journal Radiation Protection and Dosimetry. Although the estimated doses are still well below those associated with health effects, it's possible that certain groups, such as pilots and very-frequent fliers, could reach the recommended annual radiation-dose limit, Brenner said. The result? "You will end up with some number of cancers coming out of each year's scanning operations."
The wave of the future
An alternative full-body scanning technology also in use at airports around the world is millimetre-wave scanners, which don't use X-rays but, instead, bombard travellers with radiowave energy-tens of thousands of times lower than the radiowaves generated by mobile phones-and collect the reflected waves to generate images. Many argue that these are a much safer form of full-body scan, but a few reports claim that these devices, too, could pose serious health risks.
According to Mike Adams, editor of NaturalNews.com, the energy emitted from these scanners has the potential to damage human DNA. He cites a study, by scientists from both the Los Alamos National Laboratory in New Mexico and Harvard Medical School in Boston, which looked at the effects of terahertz waves-the high-frequency electromagnetic waves emitted by millimetre-wave scanners-on DNA.
"Based on our results, we argue that a specific terahertz radiation exposure may significantly affect the natural dynamics of DNA, and thereby influence intricate molecular pro-cesses involved in gene expression and DNA replication" (Phys Lett A, 2009; 374: 1214-7).
Clearly, considerably more research is needed on both types of scanners. But, in the meantime, what can we do to protect ourselves? Travellers within the US can still opt out of the full-body scan, and receive a slightly more intrusive pat-down than before as an alternative. However, in other places, such as the UK, restrictions have come into force which make it impossible for you to fly if you refuse to be subjected to a full-body scan. And this type of mandatory screening is likely to be enforced in the US and other countries in the near future.
To find out which airports are currently using full-body scanners, visit www.bigbrotherwatch.org.uk/ home/2010/06/airports-with-body-scanners.html.
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