New recommendations for indoor radon...

below the current Environmental Protection Agency (EPA) guidelines made by the Health Physics Society (HPS). Key bit:

"At levels of 4 pCi/L or more, EPA encourages members of the public to take steps to reduce the radon concentrations and to consider action at levels above 2 pCi/L. The HPS concurs with the EPA’s guideline of 4 pCi/L. However, because 4 pCi/L is not a definite line between “safe” and “unsafe,” the HPS also recommends that the public consider action at levels below 4 pCi/L. Recent residential epidemiological studies have demonstrated that there is a statistically significant increased risk of lung cancer at concentrations as low as 2.7 pCi/L."