Even with discontinued use, PCBs, or polychlorinated biphenyls, are still present in the environment today because they do not breakdown quickly

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PCBs were banned in the U.S. in 1979 amid suggestions that these chemicals could have unintended impacts on human and environmental health.

The amount of time that it takes chemicals such as PCBs to breakdown naturally depends on their size, structure, and chemical composition. It can take years to remove these chemicals from the environment and that is why they are still present decades after they have been banned.

There are cleanup alternatives for chemicals in the environment, but this often requires considerable evaluation. Because PCBs exist in sediments, scientists need to determine if it is better to dredge and remove contaminated sediments from waterways or if it is safer to leave the sediments in place and cover with clean sediments, allowing them to naturally biodegrade. A cap or barrier can also be placed over contaminated sediments to prevent them from entering the environment. There are environmental, human health, and financial concerns with all of these alternatives.

PCBs are industrial products or chemicals that were used in the U.S. starting in the 1920s and until their ban in 1979. From the 1920s until their ban, an estimated 1.5 billion pounds of PCBs were made in the U.S. for things such as microscope oils, electrical insulators, capacitors, and electric appliances such as televisions or refrigerators.

For more information:
Office of Response and Restoration
PCBs (audio podcast)