Radon gas in homes is directly linked to a small risk of lung cancer, according to a United Nations committee.

Officials at the UN Scientific Committee on the Effects of Atomic Radiation, or UNSCEAR, released a report Tuesday on what they called the first quantifiable evidence of risk from radon in homes.

Based in part on the report, the World Health Organization and other agencies are in the process of revising their recommendations on maximum radiation doses for homes and workplaces.

"There will be consequences in regulation through the lowering of recommended levels of radon in workplaces and homes," Wolfgang Weiss, UNSCEAR's vice-chairman, told a news conference in Vienna.

Health agencies are basing their updated recommendations on studies of tens of thousands of lung cancer patients in North America, Europe and China.

Until now, "radon has been a typical health risk no one wants to accept or take note of," said Weiss.

He called the report significant because it used 20 studies in homes where concentrations of radon where very low, rather than relying on estimates of radon risk that were extrapolated from studies of uranium miners who were exposed to high levels of the gas.

"We can see a risk," in homes, Weiss said. "It is small, but it is certainly there."

Source of radon

Radon is a colourless, odourless gas that is radioactive. It's formed by the disintegration of radium, which is produced when uranium decays.

Radon can accumulate in buildings, seeping in from the soil through cracks in the floor. The gas is also present in air and water, but if indoor levels are high enough, it can be a health hazard.

Health and radiation protection authorities in the United States and Germany have said radon is the second-leading cause for lung cancer after smoking.

The UN group suggested strategies for preventing radon from accumulating in homes, such as sealing basements with plastic foil. The first focus should be areas with very high levels where effects are seen, followed by measures for the general public, Weiss said.

The UN report was prepared in 2006. Its release was delayed because of financial problems that have been corrected, the agency said.

Other sections of the report assess the effects of radiation on the immune system and the effects of radiation on cells that were not irradiated directly.

UNSCEAR was established in 1955 and reports to the UN General Assembly. Its findings led to the partial test ban on atmospheric testing of nuclear weapons and helps set global standards on radiation protection.