Radon, a natural radioactive gas found in some structures, is the leading cause of lung cancer in non-smokers in the United States. 

It is responsible for about 21,000 deaths nationwide and about 400 deaths in Iowa every year, according to the Environmental Protection Agency. 

To curb the impact of radon locally, the city of Iowa City will require property owners and managers of single-family detached and duplex rental properties to verify units have been tested for elevated radon levels. The city estimates there are about 3,600 units across town.