"Most" of the air samples taken at 40 schools around Chicago were contaminated with PCB-11, says the Chicago Tribune. Banned over 30 years ago, polychlorinated biphenyls are highly toxic and linked to diseases like cancer, liver and kidney damage.
Though PCBs are known to linger in ecosystems, "bio-magnifying" in the fatty tissue of animals, researchers were surprised to find this particular type of PCB (11), as it was never specifically manufactured back before the chemicals were banned. There is some suspicion that the the source is yellow paint or factories that produce yellow paint of yellow pigments for paint, as that was a known source of PCBs in the past.
Why schools in particular as affected is also a mystery, though many schools are located in formerly industrial areas.
