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Radon More Damaging to Genes Than Thought, Study Says

Copyright 1999 Nando Media
Copyright 1999 Associated Press

By PaulL Recer

WASHINGTON (April 26, 1999 6:05 p.m. EDT http://www.nandotimes.com) - Cells may be more sensitive to radiation damage from radon gas than previously believed, according to research that found high energy particles do not need to hit the nucleus of a cell to cause DNA changes.

In a laboratory study to be published Tuesday, researchers aimed alpha particles - a decay product from radon gas - at the fluid surrounding nuclei in cells taken from a hamster, and they found that radiation could cause genetic changes.

"The prevailing view has been that in order to cause genetic damage you have to irradiate the DNA directly in the cell nucleus," said Gerhard Randers-Pehrson of Columbia University, a co-author of the study in the Proceedings of the National Academy of Sciences. "What we find is that you can irradiate outside of the nucleus and still cause that type of damage."

Randers-Pehrson said scientists who calculate the health effects of radiation exposure will have to take this new finding into account, but that it is not yet clear how the research will affect the risk estimates.

"It may turn out there is more damage to the DNA at low doses than previously assumed, but that is something that scientists who make these extrapolations will have to determine," said Randers-Pehrson. "It is unclear as yet whether the results imply greater or lesser risk."

Exposure to radon gas, a natural byproduct from the decay of uranium and radium in soil and rocks, is thought to cause about 21,000 American lung cancer deaths annually, second only to smoking.

Radon gas can leak from the earth and collect in basements. When inhaled, the gas can leave in the lungs alpha particles that emit low levels of radiation over long periods of time.

Just how much radon poses a health risk has been controversial, but the Environmental Protecttion Agency recommends that the concentration of radon gas in homes be kept below 4 picocuries (a measure of radiation) per liter of air. A National Academy of Sciences study last year estimated that since 1980, Americans have spent about $400 million on radon gas tests and on renovations to vent buildings where the gas can collect. The study estimated that about 6 percent of American homes have radon concentrations that would merit corrective action.

Radon cancer risk estimates have been based, in part, on the belief that mutations that can lead to cancer occur only if radiation particles directly hit the cell nucleus that contains the DNA.

In the new study, Randers-Pehrson and his colleagues used a machine to zap cytoplasm, the part of the cell outside of the nucleus, with precise numbers of alpha particles. The number of particles is representative of the intensity of radiation exposure.

They found that cytoplasm hits of three to eight particles could trigger a genetic change in a cell. Randers-Pehrson said they also found that when the cytoplasm was hit, the cells tended to survive and were more likely to pass mutations into new generations of cells, a critical step in the formation of cancer.

Alpha particles striking the DNA directly tends to cause such extensive damage that the cell is generally killed and does not make new cells, he said.

Andrew J. Grosovsky, a radiation biologist at the University of California, Riverside, said the Columbia University study may "prompt a reassessment" of the risks of radon gas. But he noted that "it is way too early to tell what the consequences of this new understanding will be" in recommendations about radon gas exposure.

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