Polychlorinated biphenyls (PCBs) are mixtures of up to 209 individual chlorinated compounds called congeners. The compounds are man-made, with no known natural sources. PCBs appear as colorless to light yellow oily liquids or waxy solids. These chemicals have no known smell or taste. Many commercial PCB mixtures are known in the United States by the trade name Aroclor.
PCBs have been used as coolants and lubricants in transformers, capacitors, and other electrical equipment because they do not burn easily and are good insulators. The manufacture of the compounds stopped in the United States in 1977 because evidence showed that they build up in the environment and can cause harmful health effects.
Products made before 1977 that might contain PCBs include old fluorescent lighting fixtures and electrical devices containing PCB capacitors, old microscope and hydraulic oils, and in caulking compounds. They also were mixed with paints as a cutting agent and in this form can be found in quantity at some federal facilities.
Though PCBs are no longer manufactured in the United States, the levels of these compounds in various media with respect to health and safety are regulated by the EPA, Occupational Safety and Health Administration (OSHA), and the Food and Drug Administration (FDA).
PCBs have entered the air, water, and soil during their manufacture, use, and disposal; from accidental spills and leaks during their transport; and from leaks or fires in products containing PCBs.
The compounds can be released to the environment from hazardous waste sites, illegal or improper disposal of industrial wastes and consumer products, leaks from old electrical transformers containing PCBs, and burning of some wastes in incinerators.
PCBs do not readily break down in the environment and thus may remain there for very long periods of time. Some PCBs can exist as a vapor in air that can travel long distances and be deposited in areas far away from the point of release. In water, a small amount of PCBs might remain dissolved, but most stick to organic particles and bottom sediments. PCBs also bind strongly to soil.
PCBs are taken up by small organisms and fish in sediments and water. They also are taken up by other animals that eat these aquatic animals as food. PCBs accumulate in fish and marine mammals, reaching levels that may be many thousands of times higher than in sediments and water.
Although manufactured PCBs were banned in the late 1970s, lesser-known PCBs are still generated as an unintended manufacturing by-product including those used to make certain dyes, inks, and paints.
Below are some research papers identifying these compounds and the scope of the problem.