Polychlorinated biphenyls are also long-lived chlorinated aromatic compounds. They include over 200 chemical compounds in the form of oily fluids to heavier grease or waxy substances. Production of PCBs began in 1929, and the compounds were used as coolants and lubricants in transformers and other electrical equipment. Because of their noncombustible insulating characteristics, PCBs were used to reduce the flammability of materials used in schools, hospitals, factories, and office buildings. A variety of commercial products, including paints, plastics, newsprint, fluorescent light ballasts, and caulking materials contained PCBs until production was banned in the 1970s.
Local sources of PCBs may be more important than local sources of dioxins and DLCs for contamination of aquatic organisms. PCBs were legally widely discharged into rivers, streams, and open landfills between 1940 and the early 1970s. In 1976, the Toxic Substance Control Act (TSCA) was passed, calling for a ban on the manufacture, processing, distribution, and use of PCBs in all products in which the PCBs were not totally enclosed. The TSCA was based on three concerns: first, PCBs persist in the environment and resist biodegradation; second, a population-wide incident of human poisoning in Japan in 1968 was attributed to introduction of PCB-contaminated oil into a community; and third, in 1975 the CDC reported that, in rat experiments, oral gavage with Aroclor 1260 (a mixture of PCBs) caused liver cancer (Kimbrough et al., 1975). As a result of the TSCA, transformers and electrical capacitors that contained PCB compartments were sealed. Such transformers remain in place unless the seals leaked or were damaged, and by 1990, any PCB transformer within 30 meters of a commercial or public access building should have been replaced, registered, or provided with protection (US EPA, 1994).
Bioaccumulation of PCBs A significant correlation has been observed between blood PCB levels and the quantity of fish consumed by humans (Fein et al., 1984; Humpfrey, 1988; Jacobson et al., 1990; Smith and Gangolli, 2002). Bioaccumulation of dioxins and PCBs in the fatty tissues of food animals contributes to human body burdens through ingestion of animal fats in foods such as meat and full-fat dairy products. These foods are the largest contributors of dioxins and DLCs from the US food supply. The levels of dioxins, DLCs, and PCBs in seafood are generally greater than those in meat; however, actual exposure levels are far lower because of the lower consumption of fish among the general population (IOM, 2003). Fish oils that are used for supplements tend to have lower levels of dioxins, DLCs, and PCBs than fatty or oily fish as a result of processing methods