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A toxic, cancer-causing gas is threatening the health of students in thousands of classrooms across the country, but many districts aren't doing anything about it.
In an investigative report for TODAY, Jeff Rossen reports that radioactive radon gas -- which is invisible, odorless and tasteless -- exist in classrooms across the country at levels nearly twice the Environmental Protection Agency's accepted limit.
Radon is the second-leading cause of lung cancer, just behind smoking. Radon comes from the natural breakdown of uranium in soil, rock and water that seeps into the air. The EPA estimates that it causes about 21,000 lung cancer deaths every year.
"If a student's expose, even at the EPA's action level, 4 pico curies per liter, that's equivalent to smoking half a pack of cigarettes per day," radon expert Bill Field told Rossen.
Most schools in the U.S. don't test for radon, Rossen reports. With more than 70,000 classrooms at risk across the country, just five states -- Rhode Island, Connecticut, Virginia, Florida and Colorado -- require radon testing.
And when NBC News reached out to 40 different school districts across the country to offer free radon testing, all 40 either declined or didn't respond. Rossen says that one Indianapolis district said, "This can only make us look bad. If the levels are high, parents will get upset and want every school tested."
The reactions Rossen received echo sentiments in many districts nationwide. In a report last May by WHDH in Massachusetts, the station offered to pay for radon testing in districts that are radon "hot zones" where the threat is highest. None had ever been tested for radon, and all but one accepted the offer.
"If there's a finding… then parents are gonna go nuts," one school official told WHDH. "People panic, and I don't want that."
But even in Colorado, where testing is required by law, more than 300 of the state's 2,274 K-12 schools never completed radon testing, according to Education News Colorado. While the mandated testing did lead many schools that found high levels of radon to take measures against it, no law requires schools to retest, report findings or even fix any problems found.
In a statement to NBC News, the EPA "strongly recommends" that schools are tested for radon and despite "difficult budget challenges, EPA will continue the fight against radon exposure."
Watch Rossen's full report above.