Dioxins and polychlorinated byphenyls (PCBs) are groups of compounds that include chemicals that may be carcinogens at low levels of exposure over extended periods of time and may have other types of toxicological effects.

Since there are no tolerances or other administrative levels for dioxins in food or feed, the appearance of these compounds in a food or feed supply is of gravest concern. Tolerances for PCBs for feed and foodstuffs can be found in 21 CFR 109.30 and 509.30. FDA, in conjunction with the European Union and the USDA, is addressing both international and domestic dioxin and PCB concerns.