A hazard could be lurking in schools and other older buildings.
The Environmental Protection Agency says hundreds of school buildings across country have caulk around windows and doors containing potentially cancer-causing PCBs.
The agency is telling schools that they should test old caulk and remove it if PCBs turn up in significant amounts.
EPA Administrator Lisa Jackson says PCBs remain many buildings built before the chemicals were banned in the late 1970s. It's not yet clear how much of a danger this is, and the EPA says it will do more research.
In the meantime, officials say the danger can be diminished by improving ventilation, cleaning air ducts, washing hands often and avoiding using dry brooms or dusters near caulk that might contain PCBs.
The agency has set up a PCBs in caulk hot line, 1-888-835-5372, and Web site, www.epa.gov/pcbsincaulk/.