It was used in schools, dormitories and hospitals all over the Puget Sound region. Now, new studies show it could be a hazard to your health.

KIRO 7 Eyewitness News Consumer Investigator Bebe Emerman uncovers a surprising new concern about a very old product.

There's no doubt that Polychlorinated Biphenyls -- better known as PCBs -- are dangerous, especially to children. Exposure can cause behavior problems and learning disabilities. Some studies even link it to cancer.

It was banned back in 1977. But we have uncovered a surprising new source of PCBs found in buildings all over the place.

They're everywhere -- in soil, in water, even in some of the fish we eat.

More On This Story Harvard School of Public Health: Caulking Found To Be Unrecognized Source of PCB Contamination Agency for Toxic Substances and Disease Registry: Polychlorinated Biphenyls (PCBs) Environmental Working Group and EWG Action Fund PCB – What You Need to Know

But who would ever think that caulk -- the rubbery substance used to seal windows and expansion joints -- could be loaded with PCBs?

A new study conducted by the Harvard School of Public Health shows certain types of caulk used in buildings constructed or renovated between 1959 and 1977 can be high in PCBs.

Dr. Robert Herrick, who headed the study, likens the problem to other hazards like asbestos and lead paint.

"I think we could have a similar case here where this material which was installed in the 70's is now a potential source of contamination throughout these buildings," Dr. Herrick said.

We wondered about caulk in buildings here in the Northwest so we took samples from the outside windows of five public school buildings built or renovated between 1959 and 1977. The schools were located all over the Puget Sound Region.

We then took our samples to Analytical Resources, Inc., a laboratory that specializes in environmental testing.

The results we got were troubling. We found PCB-laden caulk in four of the five schools we tested.

The lowest level we found was 2.9 parts per million; the highest was 26.

Now just to give you a comparison, the state clean-up level for PCBs in soil is just one part per million. Of course, that's soil. As far as building materials are concerned, there's really no "safe" standard for PCBs. Only if the level gets above 50 parts per million does the EPA consider it toxic waste.

But researchers say over time old, weathered caulk can break down and become crumbly -- possibly releasing PCBs into dust and air.

In fact, four years ago, an 8-story building at the University of Rhode Island was shut down after high PCB levels in dust and soil were traced back to the building's caulking and insulation. It took more than a year and $3 million to fix the problem.

So how does all this affect you and your kids? Right now, there is no federal requirement to test caulking in buildings for PCBs, but the subject is getting more attention.

Studies done in Switzerland, Sweden and Germany found a link between PCBs in caulking and PCBs in the air.

"And they've also found elevated levels in the blood of the people who live in the apartment building, and the teachers and the children that are in those school buildings," Dr. Herrick said..

And Dr. Herrick says just because caulking is found on the outside of a building, that's no guarantee of safety.

"The building does have a tendency to sort of 'breathe' in that air can move in and out of the building," he said. "And so this material that may be on the outside surface does in fact contaminate the interior of the building."

But without even seeing this report, several government agencies, including the EPA, were critical of it saying:

"Risks from consumption of PCB-contaminated foods far outweigh any risk from PCBs contained in masonry caulking."

The government agencies go on to say, however, "additional research into the cumulative effects of PCB's from other sources including caulk may be warranted."

Robert Duff of the Washington State Health Department agrees.

"I think, you know, the researchers in Boston have a point, you know they found it. It was a small survey, they asked for more research and I think there should be more research," Duff said.

We want to point out this kind of caulking was not used in single family homes, but in commercial and public buildings.

The EPA says there's no imminent threat. And while it's true we have no direct evidence that anyone inside these buildings is breathing unsafe levels of PCBs, again, it's an important question that should to be studied further.

The caulk you buy today, by the way, contains no PCBs.