Radon may pose a greater cancer threat than has been thought

[Guest guest]

Radiation zaps bystanders

4 December 2001

ERICA KLARREICH

 

Radon damage to irradiated cells spreads to their neighbours, new research

has found^1. 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.

 

Collateral damage

 

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 " .

 

References

 

1. 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).

© Nature News Service / Macmillan Magazines Ltd 2001

 

 

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