Outside 15 schools in eight states, government regulators have found elevated levels of a substance that - in a more potent form - was also used as a chemical weapon during World War I.

Those findings, based on samples collected for the Environmental Protection Agency, mark the first time the agency has expressed concern about the chemicals it detected as part of an ongoing effort to check for toxic chemicals in the air outside 63 schools nationwide.

The monitoring is part of a $2.25 million program that began in response to a USA Today investigation that identified hundreds of schools where chemicals from nearby industries appear to saturate the air. The preliminary results are meant to help determine only whether students face any immediate dangers from toxic chemicals. The EPA will use additional tests to evaluate long-term health risks.

The chemical that once was weaponized, acrolein, can exacerbate asthma and irritate the eyes and throat. It is a byproduct of burning gasoline, wood and cigarettes, but the EPA has not yet determined the specific sources for the elevated levels it found at each school.

EPA spokesman Brendan Gilfillan said the initial readings show "more must be done to reduce the amount of acrolein the American people, especially children, are exposed to."

At the 15 schools - in Alabama, California, Kentucky, Michigan, Mississippi, New York, Ohio and South Carolina - regulators found average acrolein levels at least 100 times higher than what the government considers safe for long-term exposure.

The highest level was recorded in August at Spain Elementary School in Detroit. On Wednesday, the 830 students at Spain were paying homage to the late Michael Jackson when Principal Ronald Alexander heard about the monitoring results. "We've had a very marvelous day today, but this is a concern," he said of the acrolein levels.

Alexander said he sometimes sends asthmatic students across the street to the Children's Hospital of Michigan. Despite 13 years as principal, Alexander said "we didn't really know anything about (the air quality) ... until they started this monitoring." The findings trouble him, he said, and he plans to call "a parent meeting to talk about what to do."