Polychlorinated Biphenyls are a group of man-made organic chemicals consisting of carbon, hydrogen and chlorine atoms. PCBs do not readily break down once in the environment. They can remain for long periods cycling between air, water, and soil. They are also taken up into the bodies of small organisms and fish. As a result, people who ingest fish may be exposed to PCBs that have bioaccumulated in the fish they are ingesting.