Toxics can affect kids and adults differently

You can find this model in every school in the country. It indicates the presence of at least one or two chemicals that can cause a variety of ailments. The chemicals can cause harm and all depends on which are in the air and at what levels.

There are chemicals like butadiene that are classified as known carcinogens by the federal government. Any amount of this chemical can slightly increase the risk of contracting cancer. Authorities usually become concerned when the levels are high, especially if people are exposed to those levels for a long time.

One monitoring in elementary school in Addyston, Ohio, found butadiene levels that would cause a cancer risk far higher than what Ohio considers acceptable. And that led to the closure of the school.

Other chemicals have more limited effects. They will irritate the eyes of the children or cause headaches, even at heavy doses.  The American Lung Association says that others, such as ozone, can exacerbate asthma, a leading medical cause of school absences.

For those, regulators try to determine how much of a chemical a person can be exposed to without getting sick, a value the U.S. Environmental Protection Agency calls a "reference concentration."

Most assessments are based on the effect chemicals might have on adults, as shown in workplace studies.

"It's one thing to be able to detect the chemical," says Melanie Marty, a toxicologist with the California EPA. "It's another thing to know whether the concentration to which the kids are exposed is going to be harmful."