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Living dangerously -- Standard radiation safety limits used around the world
may have to be revised to protect the young and old
by Rob Edwards
New Scientist magazine, 28 February 1998
YOUNG children and old people around the world could be exposed to damaging doses of radiation from nuclear plants and other sources because the database that is used to set safe limits is flawed. A new analysis by a leading British epidemiologist suggests that the young and old are more sensitive to radiation damage than was previously thought.
The international system of radiation safety limits is mostly based on epidemiological studies of 76,000 people from Hiroshima and Nagasaki who were still alive five years after their cities were obliterated by American atom bombs in 1945. The rates at which they have contracted cancers compared with people from other Japanese cities are used by regulatory agencies to estimate the risks of exposing people to radiation from nuclear plants, bomb tests and fallout from accidents such as that at Chernobyl in 1986.
But Alice Stewart, famous for her work in the 1950s revealing the dangers of X-raying pregnant women, argues that the atom bomb survivors are not a normal, homogeneous population. She says her analysis shows that children and old people are more vulnerable to radiation, and that a high proportion of them died between 1945 and 1950 before studies of the Hiroshima and Nagasaki residents began. The young and old are therefore under-represented among the survivors. "The atom bomb data are no good as a basis for radiation safety regulations," she says.
Aged 91, Stewart is an honorary professor at the University of Birmingham School of Medicine. Her study, which is due to be published by the Scientific and Technological Options Assessment unit of the European Parliament in the next few weeks, compares 2601 survivors who suffered from acute radiation injuries with 63,072 survivors who did not. Stewart found that of those with acute injuries, children who were under 10 when the bombs exploded were a thousand times as likely to die of cancer as people aged between 10 and 55.
People over 55 at the time of the explosions were twice as likely to die of cancer as those aged between 10 and 55, the study shows. Among those who did not suffer acute injuries, children under 10 at the time of the explosions were three times as likely to die of cancer as other age groups.
Stewart says her results show that the very young and very old are particularly sensitive to radiation. She suggests that the immune systems of the young and old are more easily harmed because they are either still developing or are breaking down. A damaged immune system makes people more vulnerable to cancers and infections, she says.
The National Radiological Protection Board, which advises the British government, accepts that the Japanese database is not perfect because it lacks information on the first five years of exposure. But the board's spokesman, Mike Clark, points out that safety limits are also derived from other databases-including Stewart's earlier work on X-rays.