Radiation Exposure During Commercial Airline Flights
Q: What radiation doses do people receive from flying commercially?
A: We have summarized the following information from the articles referenced:
Feng YJ et al. Estimated cosmic radiation doses for flight personnel. Space Med Med Eng 15(4):265-9; 2002.
The average effective dose rate of all flights of Xinjiang Airlines from 1997 to 1999 was 0.238 mrem (millirem) per hour.
The average annual cosmic radiation dose for flight personnel was 219 mrem.
Annual individual doses of all monitored flight personnel are well below the limit of 2,000 mrem per year recommended by the International Commission on Radiological Protection (ICRP).
Bottollier-Depois JF et al. Assessing exposure to cosmic radiation during long-haul flights. Radiat Res 153(5 Pt. 1):526-32; 2000.
The lowest dose rate measured was 0.3 mrem per hour during a Paris-Buenos Aires flight.
The highest rates were 0.66 mrem per hour during a Paris-Tokyo flight and 0.97 mrem per hour on the Concorde in 1996-1997.
The corresponding annual effective dose, based on 700 hours of flight for subsonic aircraft and 300 hours for the Concorde, can be estimated at between 200 mrem for the least exposed routes and 500 mrem for the more exposed routes.
Waters M et al. The National Institute for Occupational Safety and Health/Federal Aviation Administration (NIOSH/FAA) working women’s health study: Evaluation of the cosmic-radiation exposures of flight attendants. Health Phys 79(5):553-559; 2000.
Radiation dose levels represent a complex function of duration of flight, latitude, and altitude.
Based on data collected for this study, radiation dose levels that would be experienced by a flight crew are well below current occupational limits recommended by the ICRP and the FAA of 2,000 mrem/year.
The National Council on Radiation Protection and Measurements (NCRP) recommends a monthly equivalent dose limit of 50 mrem. The ICRP recommends the radiation limit during pregnancy be 200 mrem.
Only flight crew flying both a large number of hours during pregnancy (for example, 100 hours per month) and strictly the highest dose-rate routes (typically global routesUnited States to Buenos Aires or United States to Tokyo, etc.) would exceed the NCRP monthly guideline.
Friedberg W et al. Radiation exposure during air travel: Guidance provided by the FAA for air carrier crews. Health Phys 79(5):591-5; 2000.
Seattle to Portland: 3 mrem per 100 block hours
New York to Chicago: 39 mrem per 100 block hours
Los Angeles to Honolulu: 26 mrem per 100 block hours
London to New York: 51 mrem per 100 block hours
Athens to New York: 63 mrem per 100 block hours
Tokyo to New York: 55 mrem per 100 block hours
Oksanen PJ. Estimated individual annual cosmic radiation doses for flight crews. Aviat Space Environ Med 69(7):621-5; 1998.
In this study, crew members averaged 673 block hours and pilots 568 block hours.
Average annual cosmic ray dose for cabin crews was 227 mrem.
Average annual cosmic ray dose for long-distance flight captains was 219 mrem.
Q: We plan to bring our 15-month-old grandson to Sicily for vacation, flying a commercial airline from the Philippines. Will the radiation while flying during our 12-hour trip plus the return flight be dangerous to his health?
A: There is no evidence to indicate that the low-level exposure which will be received on the single round-trip flight you have described will pose any harm to your grandson. The total dose from such a trip is only a few percent of the naturally occurring differences in background radiation that exist from one place to another on the Earth. People live healthy lives in areas where exposures over their entire lifetimes are differentially much greater than the in-flight exposure you have described.
Q: I work in the airline industry as a crew member and want to know if there is a way to find out what my radiation exposure might be.
A: There are several commercial firms that can provide individual dosimeters to interested passengers or crew members. It is extremely important to know that there are several types of radiation that contribute to a person’s dose at flight altitudes. Any dosimeter that will be useful in this application must contain a suitable neutron measurement system. To locate current vendors of these products, one can search on the Internet for “radiation dosimetry services,” “radiation dosimetry, or personnel radiation monitoring.”
Q: I understand that the radiation dose while flying diminishes as you get closer to the equator. Is this true?
A: Because incoming cosmic radiation particles are deflected by the Earth’s magnetic field, the intensity of in-flight radiation is a function of both altitude and latitude. In general, radiation shielding by the geomagnetic field is greatest at the equator and decreases as one goes north or south. At typical flight altitudes of 30,000 to 40,000 feet, the difference between the cosmic ray dose rates at the equator and at high latitudes is about a factor of 2 to 3, depending on where one is in the approximately 11-year solar cycle. So if all your flying is in the equatorial zone, you would expect that the dose rates at altitude are 2 to 3 times lower than for your colleagues flying more northern or southern routes. Of course, your total exposure will be a function of the hours you spend at altitude. In any case, your annual radiation burden will be well within the limits considered acceptable for occupational exposure by such organizations as the ICRP.
Q: Have there been studies of long-term, low-level exposure to radiation during commercial flights and the effects for flight crew?
A: At present, the Airline Pilots Association is conducting dosimetry studies for its membership and NIOSH is engaged in a study of reproductive disorders among flight attendants. Several studies have already been published; some show an increase in various malignancies among crew members while others show no increased risk. The following references all present data showing an increase in malignancies among flight crew members with the exception of the second British Airways paper which, as discussed above, reevaluates data published in the earlier reference. These papers can be obtained through your local library.
1. Pukkala E, Auvinen A, Wahlberg, G. Incidence of cancer among Finnish airline cabin attendants, 1967-1992. British Medical Journal 311:649-652; 1995.
2. Lynge E, Thygesen L. Occupational cancer in Denmark. Cancer incidence in the 1970 census population. Scandinavian Journal of Work, Environment and Health 16 (Sup 2):3-35; 1990.
3. Band PR, Nhu DL, Fang R, Deschamps M, Coldman AJ, Gallagher RP, Moody J. Cohort study of Air Canada pilots: Mortality, cancer incidence, and leukemia risk. American Journal of Epidemiology 143(2):137-143; 1996.
4. Grayson JK, Lyons TJ. Cancer incidence in United States Air Force aircrews 1975-1989. Aviation Space and Environmental Medicine 67(2):101-104; 1996.
5. Vagero D, Swerdlow AJ, Beral V. Occupation and malignant melanoma: A study based on cancer registration data in England and Wales and in Sweden. British Journal of Industrial Medicine 47(5):317-324; 1990.
6. Irvine D, Davies DM. The mortality of British Airways pilots, 1966-1989: A proportional mortality study. Aviation Space and Environmental Medicine 63:276-279; 1992.
7. Irvine D, Davies DM. British Airways flightdeck mortality study, 1950-1992. Aviation Space and Environmental Medicine 70:548-55; 1999.
8. Gundestrup M, Storm HH. Radiation induced acute myeloid leukaemias and other cancers in commercial jet cockpit crew: A population based cohort study. Lancet 354:2029-2031; 11 Dec 1999.
9. Reynolds P, Cone J, Layefsky M, Goldberg D, Hurley S. Cancer incidence in California flight attendants. California Department of Health. In Press.
Q: For pilots flying below 6,000 feet for 200 hours a year is there any danger from cosmic radiation?
A: Even at ground level, cosmic radiation is part of our normal environment. The Earth’s atmosphere absorbs this radiation, so its intensity is least at ground level. The altitude of interest in this question6,000 feet (1,800 m)is, of course, ground level in many places. Using the CARI-6 program available from the FAA, the calculated cosmic-ray dose rate at this altitude at high geographic latitude is about 0.0001 millisievert per hour. It would, therefore, require 10,000 hours of flying at this altitude to reach the 1 millisievert annual limit recommended as a maximum for members of the public exposed to ionizing radiation. It should also be noted that exposures well above this 1 mSv limit are not “dangerous.”
Q: Is there any specific limit for air travel for children?
A: An annual radiation dose limit of 1 mSv (100 mrem) for members of the public has been recommended by both the NCRP here in the United States and by its overseas counterpart, the ICRP. In June 2003 the Health Physics Society, the organization of radiation protection professionals that sponsors this website, reaffirmed that these limits are appropriate. This recommended limit, unchanged for more than 10 years, has generally been adopted into law or regulation by the government agencies that mandate radiation protection programs. No distinction is made between the exposure of adults or minors. However, radiation exposure to the flying public (versus someone who works as a crew member) is not regulatedit is considered a voluntary activity. So at least as far as any legal limits are concerned, there are none for this category of exposure, for adult flyers or anyone else.
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Bits of Mystery DNA, Far From ‘Junk,’ Play Crucial Role
By GINA KOLATA
Among the many mysteries of human biology is why complex diseases like diabetes, high blood pressure and psychiatric disorders are so difficult to predict and, often, to treat. An equally perplexing puzzle is why one individual gets a disease like cancer or depression, while an identical twin remains perfectly healthy.
Now scientists have discovered a vital clue to unraveling these riddles. The human genome is packed with at least four million gene switches that reside in bits of DNA that once were dismissed as “junk” but that turn out to play critical roles in controlling how cells, organs and other tissues behave. The discovery, considered a major medical and scientific breakthrough, has enormous implications for human health because many complex diseases appear to be caused by tiny changes in hundreds of gene switches.
The findings, which are the fruit of an immense federal project involving 440 scientists from 32 laboratories around the world, will have immediate applications for understanding how alterations in the non-gene parts of DNA contribute to human diseases, which may in turn lead to new drugs. They can also help explain how the environment can affect disease risk. In the case of identical twins, small changes in environmental exposure can slightly alter gene switches, with the result that one twin gets a disease and the other does not.
As scientists delved into the “junk” — parts of the DNA that are not actual genes containing instructions for proteins — they discovered a complex system that controls genes. At least 80 percent of this DNA is active and needed. The result of the work is an annotated road map of much of this DNA, noting what it is doing and how. It includes the system of switches that, acting like dimmer switches for lights, control which genes are used in a cell and when they are used, and determine, for instance, whether a cell becomes a liver cell or a neuron.
“It’s Google Maps,” said Eric Lander, president of the Broad Institute, a joint research endeavor of Harvard and the Massachusetts Institute of Technology. In contrast, the project’s predecessor, the Human Genome Project, which determined the entire sequence of human DNA, “was like getting a picture of Earth from space,” he said. “It doesn’t tell you where the roads are, it doesn’t tell you what traffic is like at what time of the day, it doesn’t tell you where the good restaurants are, or the hospitals or the cities or the rivers.”
The new result “is a stunning resource,” said Dr. Lander, who was not involved in the research that produced it but was a leader in the Human Genome Project. “My head explodes at the amount of data.”
The discoveries were published on Wednesday in six papers in the journal Nature and in 24 papers in Genome Research and Genome Biology. In addition, The Journal of Biological Chemistry is publishing six review articles, and Science is publishing yet another article.
Human DNA is “a lot more active than we expected, and there are a lot more things happening than we expected,” said Ewan Birney of the European Molecular Biology Laboratory-European Bioinformatics Institute, a lead researcher on the project.
In one of the Nature papers, researchers link the gene switches to a range of human diseases — multiple sclerosis, lupus, rheumatoid arthritis, Crohn’s disease, celiac disease — and even to traits like height. In large studies over the past decade, scientists found that minor changes in human DNA sequences increase the risk that a person will get those diseases. But those changes were in the junk, now often referred to as the dark matter — they were not changes in genes — and their significance was not clear. The new analysis reveals that a great many of those changes alter gene switches and are highly significant.
“Most of the changes that affect disease don’t lie in the genes themselves; they lie in the switches,” said Michael Snyder, a Stanford University researcher for the project, called Encode, for Encyclopedia of DNA Elements.
And that, said Dr. Bradley Bernstein, an Encode researcher at Massachusetts General Hospital, “is a really big deal.” He added, “I don’t think anyone predicted that would be the case.”
The discoveries also can reveal which genetic changes are important in cancer, and why. As they began determining the DNA sequences of cancer cells, researchers realized that most of the thousands of DNA changes in cancer cells were not in genes; they were in the dark matter. The challenge is to figure out which of those changes are driving the cancer’s growth.
“These papers are very significant,” said Dr. Mark A. Rubin, a prostate cancer genomics researcher at Weill Cornell Medical College. Dr. Rubin, who was not part of the Encode project, added, “They will definitely have an impact on our medical research on cancer.”
In prostate cancer, for example, his group found mutations in important genes that are not readily attacked by drugs. But Encode, by showing which regions of the dark matter control those genes, gives another way to attack them: target those controlling switches.
Dr. Rubin, who also used the Google Maps analogy, explained: “Now you can follow the roads and see the traffic circulation. That’s exactly the same way we will use these data in cancer research.” Encode provides a road map with traffic patterns for alternate ways to go after cancer genes, he said.
Dr. Bernstein said, “This is a resource, like the human genome, that will drive science forward.”
The system, though, is stunningly complex, with many redundancies. Just the idea of so many switches was almost incomprehensible, Dr. Bernstein said.
There also is a sort of DNA wiring system that is almost inconceivably intricate.
“It is like opening a wiring closet and seeing a hairball of wires,” said Mark Gerstein, an Encode researcher from Yale. “We tried to unravel this hairball and make it interpretable.”
There is another sort of hairball as well: the complex three-dimensional structure of DNA. Human DNA is such a long strand — about 10 feet of DNA stuffed into a microscopic nucleus of a cell — that it fits only because it is tightly wound and coiled around itself. When they looked at the three-dimensional structure — the hairball — Encode researchers discovered that small segments of dark-matter DNA are often quite close to genes they control. In the past, when they analyzed only the uncoiled length of DNA, those controlling regions appeared to be far from the genes they affect.
The project began in 2003, as researchers began to appreciate how little they knew about human DNA. In recent years, some began to find switches in the 99 percent of human DNA that is not genes, but they could not fully characterize or explain what a vast majority of it was doing.
The thought before the start of the project, said Thomas Gingeras, an Encode researcher from Cold Spring Harbor Laboratory, was that only 5 to 10 percent of the DNA in a human being was actually being used.
The big surprise was not only that almost all of the DNA is used but also that a large proportion of it is gene switches. Before Encode, said Dr. John Stamatoyannopoulos, a University of Washington scientist who was part of the project, “if you had said half of the genome and probably more has instructions for turning genes on and off, I don’t think people would have believed you.”
By the time the National Human Genome Research Institute, part of the National Institutes of Health, embarked on Encode, major advances in DNA sequencing and computational biology had made it conceivable to try to understand the dark matter of human DNA. Even so, the analysis was daunting — the researchers generated 15 trillion bytes of raw data. Analyzing the data required the equivalent of more than 300 years of computer time.
Just organizing the researchers and coordinating the work was a huge undertaking. Dr. Gerstein, one of the project’s leaders, has produced a diagram of the authors with their connections to one another. It looks nearly as complicated as the wiring diagram for the human DNA switches. Now that part of the work is done, and the hundreds of authors have written their papers.
“There is literally a flotilla of papers,” Dr. Gerstein said. But, he added, more work has yet to be done — there are still parts of the genome that have not been figured out.
That, though, is for the next stage of Encode.
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