PCB chemicals were banned in the U.S. in 1979 because these chemicals harm human and environmental health. From the 1920s until their ban, an estimated 1.5 billion pounds of PCBs were made for things such as microscope oils, electrical insulators, capacitors, and electric appliances such as television sets or refrigerators. PCBs were also sprayed on dirt roads to keep the dust down prior to knowing some of the unintended consequences from widespread use.
Prior to the ban in 1979, PCBs entered the air, water, and soil during manufacture and use. Wastes from the manufacturing process that contained PCBs were often placed in dump sites or landfills. Occasionally, accidental spills and leaks from these facilities or transformer fires could result in PCBs entering the environment.
PCBs can be found worldwide. In the 1960s, when initial research results were released, traces of PCBs could be detected in people and animals around the world – not only in heavily populated areas such as New York City, but also in remote areas as far as the Arctic. These findings of such widespread and persistent contamination contributed to the banning of the chemical in 1979.
PCBs can degrade or breakdown in the environment, but the process greatly depends on the chemical makeup of the PCBs. The degrading process also depends on where the PCBs are in the environment. Typically, PCBs are either broken down in the environment by sunlight or by microorganisms. Sunlight plays an important role in the breakdown of PCBs when they are in the air, shallow water, or surface soils. Microorganisms, such as bacteria, algae, or fungi, biodegrade PCBs when found in soil or sediments.
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.