What are PCBs?

PCBs, or polychlorinated biphenyls, are a group of man-made chemicals. They were widely used in electrical equipment, in industrial processes, and in the manufacture and recycling of carbonless copy paper until research revealed that they pose risks to human health, wildlife and the natural environment. The federal government banned the production of PCBs in 1976, but PCB contamination remains widespread in the environment today because of improper disposal of products containing the chemicals and byproducts of the processes used to make such products.

PCBs bind readily with sediment particles and do not easily dissolve in water. In rivers, PCBs bind to sediment particles one million times more strongly than to water molecules. PCB molecules attached to sediment particles eventually sink to the river bottom, where they are eaten by tiny organisms. Small fish eat these organisms and retain the PCBs they carry in their body fat, and so on up the food chain to larger fish, birds of prey, and people. This process is called bioaccumulation or biomagnifaction, and PCB levels in top predators such as bald eagles, lake trout and humans can be millions of times those found in surface water. Because PCBs are soluble in fat, they stay stored in an organism's fatty tissue and can build to harmful levels over time. For information on their health effects, see PCBs and Health.