Refining risks of residential radon.

Though several studies have strongly suggested that relatively low residential concentrations of radon may pose a lung cancer risk, nearly all the data on this natural pollutant's carcinogenicity come from studies of underground miners exposed to very high amounts of this radioactive gas and its carcinogenic decay products. An international team of researchers has now pooled data from 11 populations of such miners--involving 65,000 men and more than 2,700 lung cancers--to tease out even more details on risks that might arise from the lower-dose residential exposures. Their analysis indicates that total accumulated dose isn't the best gauge of radon's danger.

Comparing equivalent total absorbed doses, those delivered more slowly appear more dangerous. This "inverse exposure rate effect could be interpreted as implying that miner-based models underestimate risk in homes, where exposure rates are generally lower," the researchers report in the June 7 Journal of the National Cancer Institute. Indeed, some residential exposures will result in total doses equivalent to those linked with cancer in the miners.

However, "there is also evidence--both theoretical and in these data--that that effect should decline as the total exposure goes down," points out Jay H. Lubin of the National Cancer Institute in Bethesda, Md., the report's lead author. That, Lubin says, argues that reducing residential concentrations to a value below EPA's action level--4 picocuries per liter of air--would offer long-term health benefits. The new data also show that risks associated with a given total absorbed dose diminish with time since exposure.

Another bit of reassuring news from the new analysis: Children appear no more vulnerable to radon's effects than adults. These findings derive from a long-term follow-up of workers, some of whom began their mining careers in pre-World War II China at the tender age of 8 or 9.