Polychlorinated biphenyls (PCBs) are a family of 209 chemical compounds for which there are no known natural sources. Even though PCBs are no longer commercially produced in the United States, high levels of the chemicals remain in various parts of the country, in poultry, and in fish. This fact sheet will discuss what PCBs are, why they were so prominent, and why threats may still remain.
What are PCBs?
A phenyl is a univalent radical with a chemical equation of C6H5 (six carbon, five hydrogen atoms) with the symbol Ph. Valent refers to the measure of capacity to combine the number of atoms of hydrogen with one atom of chemical element in a reaction: a univalent is capable of replacing or combining with one atom of hydrogen or its equivalent. Radicals are a group of atoms that enter into and go out of chemical combinations without change. A radical forms one of the fundamental constituents of a molecule.
A biphenyl molecule is comprised of two benzene rings of hydrogen and carbon atoms. Benzene rings serve as the building blocks of petroleum, gasoline, and other fuels. These molecules are extremely flammable. By substituting chlorine for hydrogen atoms, the molecule becomes flame-resistant. Chlorinated biphenyls are any of a group of substances in which chlorine replaces hydrogen. Molecules with more than 1 chlorine atom are known as polychlorinated biphenyls. Polychlorinated biphenyls are toxic and accumulate in animal tissues.
The flame resistance of the polychlorinated biphenyls made them ideal for use in electrical products because they did not burn, break down, or react with other chemicals. Originally produced for use as flame retardants and as electrical insulators in transformers, capacitors, and other electrical equipment, PCBs were used in heating coils, carbonless carbon paper, lubricating oils for industrial drills, caulking compounds for skyscraper windows, electrical motors in refrigerators, in air conditioners, typewriters, power saws, and the like. At one time or another, a wide variety of products including cereal boxes, degreasers, varnishes, lacquers, waterproofing materials, and bread wrappers used PCBs. The unique properties of PCBs allowed them to be used in the manufacturing of many common products such as plastics, adhesives, paints, and varnishes. Between 1930 and 1970, 1.4 billion pounds of PCBs were manufactured in the United States.
In consistency, PCBs range from light oily fluids to greasy or waxy substances and are clear to yellow in color. During their manufacture and use, PCBs were released into the atmosphere through sewers, smokestacks, weathering of asphalt and other substances containing PCBs, and burning PCB- containing products. PCBs continue to be released from leakage of old equipment, leaching from landfills, and from previously contaminated sediments.
What happens to PCBs in the environment?
The very characteristic of the PCBs that made them wonderful for use in manufacturing makes them problematic in the environment. PCBs are very persistent: they are generally unalterable by microorganisms or by chemical reaction (they do not readily degrade). The stable nature of PCBs also lends to accumulation in the fatty tissues of animals once the PCBs are released into the environment. These accumulations increase as the tissue from contaminated animals moves through the food web. Because of bioaccumulation, the concentration of PCBs found in fish tissues is expected to be considerably higher that the average concentration of PCBs in the water from which the fish were taken.
Acute toxic effects in the environment include death of animals, birds, or fish, and death or low growth rate in plants. Chronic effects from PCBs may include shortened lifespan, reproductive problems, lower fertility, and changes in appearance or behavior. The primary concern of PCBs in surface water is the chronic effect of bioaccumulation.
During the mid-1960s
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