Three schools sharing a single Manhattan building joined the growing list of public schoolswhere spot inspections have revealed elevated levels of polychlorinated byphenyls, or PCBs, leaking from aging light fixtures, the Environmental Protection Agency said Monday.

As many as two-thirds of public schools in New York City use the same type of fluorescent lights known to contain PCBs, according to a document prepared by the city's Department of Education and reviewed by The Wall Street Journal. To date, the EPA has examined...