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Cosmic Radiation

High altitudes may be bad for your health, writes Farrol Kahn

People are exposed to background radiation every day, but some, such as frequent fliers, are exposed more than others are. The radiation is-caused by electrically charged atoms known as ions that come from outer space. It is also produced by medical X-ray examinations and some industrial and pharmaceuticals products. 

Airline crew and frequent fliers receive bigger doses than the general population because at high altitude the Earth's atmosphere is thinner and offers less protection - the exposure can rise from 100 to 300 times more than at sea level. New UK research into the Biological effects of ionising radiation is reviving a long-running debate about the possible health risks and how, if at all, the aviation industry and regulators should be responding.

According to a study by Dudley Goodhead, who runs one of the world's leading radiation and genome stability units, ions can cause genetic mutations in human egg cells and sperm cells, and can damage a developing foetus. Professor Goodhead, who is based at the UK's Medical Research Council, has found that ionising radiation can produce a wide spectrum of damage to DNA, breaking single and double strands of its double-helix structure.

"This is exciting as we know that cancer grows from a single cell that experiences multiple changes;" says Professor Goodhead. "Cosmic radiation increases the chance of changes or aberrations in the cell
For most people, this should not raise any health issues. But, as Robert Souhami, dean of the Medical School at University College, London, observes: "The radiation risk is dosage related." So the more you fly the greater the risk. 

The average person in the UK receives an annual background dose of 2.6 millisieverts (mSv) of ionising radiation a year. Air crew and some frequent fliers, including couriers, are at the top of the occupational exposure league with 4.6 mSv a year, compared with nuclear workers who receive 3.6 mSv. The annual limit for nuclear power plant workers in Europe is 20 mSv, whereas 6 mSv is the limit for air crew.

Put into perspective, 200 hours on a subsonic aircraft would produce an annual dose equivalent to 1 mSv, but the same duration on Concorde is equal to 2 mSv, because the supersonic aircraft flies at a much higher altitude.

A frequent flier on conventional transatlantic routes between London and the east coast of the US, spending 700 hours in the air, could receive an annual dose of 5.7 mSv, including the average dose from background radiation.

Wallace Friedberg of the Federal Aviation Administration's Civil Aeromedical Institute, says this represents 170 chest X-rays a year (based on 4.1 hours at 37,000 ft equalling one chest X-ray).

Over the past decade, several air crew studies have been conducted. In a British Airways survey of 411 pilot deaths, incidences of malignant melanoma, colon and brain cancers were slightly higher than normal. Another larger research programme was carried out by Pierre Band, head of a cancer agency in Vancouver, on 2,740 Air Canada pilots. He found an increased incidence of prostate cancer and acute myeloid leukaemia, and slight increases - not significant statistically - in malignant melanomas, brain tumours and all types of leukaemia.

Another significant study on 1,577 female flight attendants working for Finnair between 1940 and 1992 showed twice the risk of breast cancer compared with the general population. 

Reaction to these studies has differed radically. US regulators and health experts believe any harmful effects would be minor. The European Commission, however, is playing safe by issuing a directive that requires all European airlines to start measuring dosages on each flight from next year.

Ionising radiation can be stopped from penetrating the body only by a thick shield of lead, concrete or water. But airlines and airframe manufacturers would be extremely reluctant to fit heavy lead lining to cockpits. 

James Currie, the Commission's director-general for environment, nuclear safety and civil protection, did suggest, however, that manufacturers could try to design aircraft with greater fuel efficiency at lower altitudes.

Financial Times. MONDAY APRIL 12 1999


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