Preliminary tests have detected elevated levels of PCBs at three New York City schools.

The toxic chemical compounds were discovered as part of a pilot study designed to measure the amount of PCBS at the city’s public schools. Two more schools will be tested next year.

The Department of Education says the initial tests found PCB levels were higher than the federal recommendations for long-term exposure. After removing caulking and other material containing PCBs, air samples showed improved conditions. The agency says old fluorescent light fixtures also are being removed to further reduce PCB levels in the air.

PCBs were used in construction and electrical materials from the 1950s until 1978. Long-term exposure can cause cancer and other ailments.