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CDC - Cancer Cluster archived website note

Historical Document

This document is provided by the National Center for Environmental Health ONLY as an historical reference for the public health community. It is no longer being maintained and the data it contains may no longer be current and/or accurate.

For current information about cancer clusters, please visit

What are polychlorinated biphenyls (PCBs)?

PCBs are mixtures of up to 209 individual chlorinated compounds (known as congeners). There are no known natural sources of PCBs. PCBs are oily liquids or solids that are colorless to light yellow. Some PCBs can exist as a vapor in air. PCBs have no 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 PCBs was stopped in the United States in 1977 because of evidence they build up in the environment and can cause health problems. Products made before 1977 that may contain PCBs include old fluorescent lighting fixtures and electrical devices containing PCB capacitors, and old microscope and hydraulic oils.

How do PCBs enter the environment?

PCBs 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.

PCBs still 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.

What happens to PCBs when they enter the environment?

PCBs do not easily break down in the environment, so they may remain there for a long time. PCBs can travel long distances in the air to areas far away from where they were released. In water, a small amount of PCBs may remain dissolved, but most stick to organic particles and bottom sediments. PCBs also attach strongly to soil. Small organisms and fish take up PCBs in water. Other animals take up PCBs when they eat these aquatic animals. PCBs accumulate in fish and marine mammals, reaching levels that may be many thousands of times higher than in water.

How can people be exposed to PCBs?

  • Breathing air that contains PCBs.
  • Eating food or drinking water that contains PCBs.

Can exposure to PCBs make people sick?

Probably not. In people exposed to large amounts of PCBs, the most common health problems are skin conditions such as acne and other rashes. Some exposed workers had changes in blood and urine that may indicate liver damage. In most people, PCB exposure probably will not cause skin and liver problems.

Animals that ate food containing large amounts of PCBs for short periods of time had mild liver damage, and some died. Animals that ate smaller amounts of PCBs in food over several weeks or months developed various kinds of health problems, including anemia; acne-like skin conditions; and liver, stomach, and thyroid gland problems. Other effects of PCBs in animals include changes in the immune system, changes in behavior, and reproduction problems. PCBs are not known to cause birth defects.

Can PCBs cause cancer?

PCBs probably cause cancer. Only a few studies of workers associated PCBs with certain kinds of cancer in humans, such as cancer of the liver and biliary tract. Lab rats that ate food with high levels of PCBs for 2 years developed liver cancer.

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