Sources of low levels of radiation – such as radioactive radon gas seeping into houses – might cause more genetic damage and cancer than anyone realised, say a team of US researchers.
“The effects of radiation are very complex,” concludes Hongning Zhou of Columbia University in New York, a member of the team. “We should reconsider the risks of low levels.”
Current estimates of the risks of radiation come mainly from studies of cancer rates in survivors of the 1945 atomic bomb blasts in Hiroshima and Nagasaki, where the levels of radiation were very high. Scientists work out the risks of less intense radiation assuming that the cell damage falls off in direct proportion to the radiation dose.
But that might not be true. Over the past few years, experiments have shown that the effects of radiation in cells are unexpectedly complicated due to a so-called “bystander effect”, in which a radiated cell can alter the protein production of neighbouring cells.
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Now a team led by Tom Hei of Columbia University has measured the destructive effect of alpha particles on the genetic machinery of neighbouring cells.
Mystery damage
The team prepared layers of thousands of cells that are sensitive to mutations and targeted some of their nuclei with alpha particles. When they zapped 10 per cent of the cells with alpha particles, the number of cells with damaged DNA was similar to the number of casualties when they zapped all the cells.
Why the neighbours suffer damage is a mystery. But it seems to be linked to a type of chemical communication in which the targeted cell exchanges small molecules with its nearest neighbours. When Zhou’s team severed these chemical chat lines and repeated the alpha-particle assault, only the target cells were damaged.
Until there are detailed studies of low-level radiation on animal and human tissues, no one will know if this is cause for alarm. “The effects on animals and people are likely to be even more complicated,” says Richard Setlow, a biophysicist Brookhaven National Laboratory in Upton, New York. “But this is a clue what to look for.”
The result could fuel concerns over radon building up in confined spaces, such as the insulated basements of homes, as the gas leaks out of soil and rocks. The health risks of radon are controversial, but some scientists think it is responsible for thousands of deaths from lung cancer each year.
However, Setlow says that the risks of radon cannot be much higher than currently predicted. If they were, we would see far more cancer cases from regions where radon gas is a problem.
Journal reference: Proceedings of the National Academy of Sciences (vol 98, p 14,410)
