PCBs (polychlorinated biphenyls), dioxins (polychlorinated dibenzo-p-dioxins), and furans (polychlorinated dibenzofurans) are groups of persistent organic pollutants (POPs) that have similar toxicity and share chemical characteristics. Dioxins and furans are created as an unintentional by-products from combustion, during the production of certain chemicals (such as pesticides), and in the pulp and paper industry during chlorine bleaching. Until their ban in 1979, PCBs were manufactured as insulator fluids in heat-exchangers and transformers, as hydraulic fluids, and as additives to paints and oils. PCBs remain in the environment even though they are no longer manufactured.
These compounds have the potential to be highly toxic to humans with exposure occurring through breathing contaminated air, drinking contaminated water, or eating contaminated food. About 90% of exposure comes from eating contaminated food due to the ability of these compounds to bioaccumulate in the fatty tissues of animals. These pollutants have been shown to cause liver problems, elevated blood lipids, and a skin condition called chloracne in people who have been exposed to large amounts. Extensive laboratory studies have also shown various effects to animal models, including cancer and reproductive problems.