Radon may pose a greater cancer threat than has been thought.
4 December 2001
Radon damage to irradiated cells spreads to their neighbours, new research has found1. The result suggests that small amounts of this radioactive gas could cause widespread harm.
The study "is a reason for concern but not panic", says Gerhard Randers-Pehrson of Columbia University, New York, a member of the team that performed the study. "We're talking about the acceptable level of radon changing perhaps by a factor of two, not 100."
But even this change could mean a tenfold increase in the number of houses needing attention, Randers-Pehrson says. Many homes are exposed to levels of radon close to acceptable limits.
Radon is released by decaying uranium in granite rocks and soil. Where there is a lot of granite, such as in the US Appalachian region, water containing radon can seep through cracks in basement floors to produce potentially dangerous concentrations in homes. Proper ventilation and filling cracks in basement floors and walls can cut radon levels.
"We could be underestimating the magnitude of the problem and the benefits of remediation", says Jonathan Samet of Johns Hopkins University, who chaired the most recent US National Academy of Sciences panel to determine radon exposure risks.
The findings are for cells in culture. Radon exposure might not have the same effect on human bodies, cautions Barry Michael of the Gray Cancer Institute in London. "The mix of cell types in living organisms might lead to a very different picture," he says.
Radon causes about 17,000 lung-cancer cases in the United States each year, according to the US National Cancer Institute. Radioactive particles emitted by inhaled radon break DNA in cells, causing mutations that can lead to cancer.
Most estimates of the risk from low-level exposure come from measuring cancer in people exposed to high radon levels, such as uranium mineworkers. Experts tend to assume that a person who receives, for example, half as much radiation as another has half the risk.
But irradiating just 10% of the cells in a culture resulted in nearly as many mutations as irradiating them all, the Columbia team found. Many cells not directly hit showed mutations, suggesting that simple extrapolation may underestimate the risk of a low dose of radon.
"It seems that when a cell is irradiated, it sends a signal to neighbour cells that causes them to get damaged too," says Randers-Peterson. "We don't know why this happens."
Michael's studies, on the other hand, have found that neighbouring cells cause irradiated cells to age, so that they may die before becoming cancerous. "We need more research to understand the balance between damaging and protective impacts of low-dose irradiation," he says.
Extrapolating from miners seems to be valid, Samet says, although more studies are needed. Nevertheless, he says, the new findings "provide further support that there is no necessarily safe level of exposure".
Zhou, H. et al. Radiation risk to low fluences of alpha particles may be greater than we thought. Proceedings of the National Academy of Sciences, 98, 14410 - 14415, (2001).
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