Household radon risk low, study shows
January 18, 1999
By Environmental News Network staff
(ENN) -- Scientists performing controlled studies on mouse cells at Columbia University have released a study that shows homeowners exposed to radon gas may be less at risk for developing lung cancer than previously thought.
For the past two decades, researchers have been warning of the dangers from alpha radiation given off by radon, a gas that bubbles into homes from uranium-bearing rocks. The National Academy of Sciences puts the U.S. death toll at 18,000 a year, while the National Radiological Protection Board calculates Britain's death toll as 1,800 a year.
However, according to an article in the Jan. 16 edition of New Scientist Magazine, these estimates, which make radon second only to smoking as a cause of lung cancer, are calculated largely by extrapolating from deaths among uranium miners whose exposures to radon were 10 to 100 times higher. Researchers have struggled to find real effects among the general population.
Now David Brenner and colleagues at the Center for Radiation Research in Columbia University, N.Y., believe they have shown that extrapolating risk from high to low exposure is wrong, and that the real risks from radon in the home are much less than suspected. Most domestic exposures, says Brenner, involve a single alpha particle per cell over a year, whereas the miners were frequently exposed to several particles per cell over a short period.
In the first experiment of its kind, Brenner exposed 250,000 standard laboratory mouse cells to a single alpha particle. He found that only one in every 10,000 developed a cancerous mutation. This was almost indistinguishable from the mutation rate with no exposure at all.
He then repeated the experiment using a random distribution of particles. The average exposure of each cell remained one particle, but some received more and some none at all. In this case, the cells averaged three mutations per 10,000 cells. Brenner concludes that most of the damage must have been done to cells exposed to more than one particle -- far more damage than might be assumed if each individual alpha particle carried the same risk. Two particles hitting a cell in quick succession appear to be at least six times more dangerous than one.
The results appear to support the growing number of studies that have failed to find a link between domestic exposure to radon and lung cancer. They include a controversial survey by Bernard Cohen of the University of Pittsburgh that failed to find any connection between average lung cancer levels in U.S. counties and radon levels in half a million homes.
But they contradict the findings of a British study published last year by Sarah Darby of the Imperial Cancer Research Fund's Cancer Epidemiology Unit in Oxford. She followed up on 1,000 lung cancer victims in Devon and Cornwall and concluded that people exposed to radon levels above government limits faced a 20 percent greater chance of developing lung cancer.
Roger Cox, head of the radiation effects department at the NRPB, hails Brenner's "heroic experimental effort", but says that the number of mutations produced is too low to determine the true biological effect.
The current study is not without limitations and should not be used to draw conclusions warns Jay Lubin, radon expert at the National Cancer Institute in Bethesda, Md.
For more information, contact Claire Bowles, New Scientist, email: email@example.com.
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