Joints around windows and between masonry panels in public buildings erected or renovated during the 1960s and 1970s were often sealed with a caulk containing polychlorinated biphenyls (PCBs). The oily PCBs kept the sealant pliable so that it could expand and contract with the weather. Although the Environmental Protection Agency banned PCBs’ production in 1977 owing to the compounds’ toxicity, some tainted caulk remains in place.