What are PCBs?
Polychlorinated biphenyl materials were banned by the EPA in 1979, but the products had been in production for about 50 years before that and are still being thrown away.
According to the EPA website, "Due to their non-flammability, chemical stability, high boiling point, and electrical insulating properties, PCBs were used in hundreds of industrial and commercial applications including electrical, heat transfer, and hydraulic equipment; as plasticizers in paints, plastics, and rubber products; in pigments, dyes, and carbonless copy paper; and many other industrial applications."
The problem PCBs pose — and part of the reason they were so attractive to manufacturers — is that they do not break down easily. They are released through illegal or unmonitored dumping into nature, where they can last in soils or in lakes and rivers for centuries.
Eventually, they are taken up into the food chain by small organisms or fish, and then can be ingested by humans.
According to the EPA, "PCBs have been demonstrated to cause cancer, as well as a variety of other adverse health effects on the immune system, reproductive system, nervous system, and endocrine system."