New estimates show the rate of Portland-area homes with elevated levels of radon is double the national average.
The Oregonian reports that a Portland State University professor and five students compiled radon tests from homes and businesses statewide.
Their research suggests one in every four houses in the Portland area accumulates radon above the level the U.S. Environmental Protection Agency says should prompt fixes to keep the gas outdoors.
The EPA says the odorless, invisible radioactive gas is the leading cause of lung cancer for nonsmokers.
Outside the Portland area, high levels were found in parts of Astoria, Myrtle Creek and Milton-Freewater.