Biological magnification.

Polychlorinated Biphenyls (PCBs) are non-flammable electrical insulators whose chemical stability allow them to persist in tissue and become concentrated up trophic levels.

Toxic effects include cancer and effects on the immune, reproductive, nervous, and endocrine systems. Congress banned their production in 1977.

Another example of biological magnification in raptors is the pesticide DDT, which was banned by the EPA in 1971.