Millions of American schoolchildren could still be exposed to toxic chemicals that were banned nearly half a century ago even after repeated attempts to clean up schools, according to a new study released Wednesday.

The analysis looked at 286 Environmental Protection Agency reports in 20 states from California to Maine and found as many as 14 million schoolchildren in elementary school through high school are potentially unprotected from the chemicals, known as PCBs or polychlorinated biphenyls. Those compounds are linked to a slew of negative health impacts like cancer, harmed immune systems, neurological damage, learning deficits, lowered birth weight and decreased thyroid function.

“PCBs are known to cause a reduction in learning ability and IQ. The last thing you want in a school is to have children exposed to a neurotoxic chemical that will reduce their ability to learn,” David Carpenter, the director of the Institute for Health and the Environment at the University of Albany, said in a statement that accompanied the release.

The analysis was conducted by the Environmental Working Group alongside the office of Massachusetts Sen. Edward Markey.

PCB map A map of states where EPA data on PCBs were analyzed. Photo: Environmental Working Group

PCBs were banned in 1979 by the EPA. Since then, a handful of lawsuits have made their way to Monsanto — the company most associated with manufacturing the chemical and one that made a concerted effort to deny their negative health impacts — and other entities. Those legal efforts have resulted in, among other things, a $46.5 million award in January to plaintiffs in St. Louis and a federal ruling last month in California that schools in Malibu need to remove PCBs by 2019.

PCBs can be found in a range of decaying products. In the schools, the chemicals are leaking from caulking, sealants and aging building fixtures, the report says. Any school built between the 1950s and 1970s is likely contaminated with PCBs. The EPA urges schools to remove any crumbling fluorescent light fixtures from their grounds.

But Monsanto’s PCBs aren’t the only chemicals banned long ago or simply dangerous that are still in schools. Kids can also be exposed to asbestos, radon, mold pesticides and lead in drinking water when they head to class.