Many Maine homeowners and apartment dwellers know the health risks posed by carbon monoxide, but another colorless, odorless gas also can prove harmful.

Radon, a naturally occurring radioactive gas found in high levels in Maine, can slowly seep from the ground into buildings through foundation cracks, gaps, and basement drains. Estimated to contribute to thousands of lung cancer deaths annually, radon also can dissolve into well water.

Simple air and water tests detect the presence of radon, and a new law will affect how Maine landlords and tenants respond to high radon levels in rental properties. Maine has required radon testing in apartment buildings since 2009, but under legislation passed last spring, landlords are no longer required to mitigate high levels, such as by installing venting systems.

Now, a landlord or tenant can terminate a lease within 30 days if high radon levels are detected and the landlord can’t or chooses not to mitigate, explained Bob Stilwell of the state’s radiation control program at the Department of Health and Human Services. All residential rental buildings must be tested for radon by March 1.

Found throughout the U.S., radon occurs in particularly high levels in Maine, Stilwell said. The gas is released into the air through the breakdown of uranium in soil, rocks and water, and can get trapped and concentrated inside buildings.

“There are not many states [with radon levels] equal to or higher than Maine,” he said.

While radon has been proven to cause lung cancer, health experts fiercely debate how many lung cancer deaths the gas contributes to, said Dr. Roger Inhorn, director of oncology and hematology at Mercy Hospital in Portland.

“You can read very different numbers depending on which study you’re looking at,” Inhorn said.

All major health organizations, including the U.S. Centers for Disease Control and Prevention, the American Lung Association and the American Medical Association, agree with estimates that radon causes thousands of preventable lung cancer deaths every year, according to the U.S. Environmental Protection Agency.

“The people at greatest risk are smokers — which is obviously a very clear, big risk factor — who are also exposed to radon,” Inhorn said.

Radon has been identified as the leading cause of lung cancer in nonsmokers.

Lung cancer patients often don’t know if they’ve been exposed to radon, Inhorn said. Testing their household level and extrapolating how long the person was exposed can lend a clue, he said.

Federal agencies and the state of Maine recommend mitigating radon at a level of four picocuries per liter of air or higher, based on research dating back to the 1970s. Newer studies on the health effects of radon haven’t determined the risks below two picocuries per liter, Stilwell said.

“We just know that there is an increased risk of lung cancer from radon at two picocuries per liter and up, and that risk gets significantly higher when you get to four picocuries per liter and up,” he said.

Approximately one in three Maine homes has air radon concentrations higher than four picocuries per liter, according to Maine DHHS.

The World Health Organization recommends homeowners take action at radon levels of 2.7 picocuries per liter and higher.

Research hasn’t conclusively determined at what level the gas poses a risk, Inhorn said.

“There has not been great statistical proof that at the levels typically found in residential settings that radon causes lung cancer,” he said.

Inhorn tested for radon in his own home, and while he questions the four picocuries per liter standard, he installed a venting system after his results came in higher, he said.

“I guess I speak with my actions. I had it put in,” he said. “I also felt bad spending the thousand dollars as well. I’m not quite sure, honestly, what kind of risk it is at these lower numbers.”

Radon testing kits are available at big box home improvement stores, and landlords and homeowners also can hire radon testing contractors. Those without mitigation systems should test for radon every five years, as levels can fluctuate, Stilwell said.

Rental tenants can test their units themselves, and the law prohibits landlords from retaliating against those who do, he said. If a tenant requests, landlords must re-test their properties for radon every 10 years unless a working mitigation system is installed.

Landlords must provide written notice to tenants within 30 days of receiving test results, regardless of the outcome. New tenants also must be informed before signing a lease or paying a security deposit.

Short-term rentals are exempt from the requirements.

Jackie Farwell

I'm the health editor for the Bangor Daily News, a Bangor native, a UMaine grad, and a weekend crossword warrior. I never get sick of writing about Maine people, geeking out over health care data, and...