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INTRODUCTION

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The group of chemicals termed polychlorinated biphenyls is part of the larger class of chlorinated organic hydrocarbon chemicals. There are 209 individual compounds (congeners) with varying numbers and locations of chlorine on the two phenyl rings, with varying degrees of toxicity and adverse human and ecological effects.1 Some of the PCBs are structurally similar to dioxins and furans and these congeners may cause similar health effects.2 The higher chlorinated PCBs are particularly persistent in the environment,3 although not all potential congeners were manufactured and there was a shift toward lower-chlorinated PCB mixtures in later years. In 1976, the U.S. Congress passed the Toxic Substances Control Act which led to the ban of production of PCBs in the United States.

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PCBs were first produced by the Monsanto Company in the late 1920s in two U.S. states for use in electrical products; initially, polychlorinated biphenyls were found to have properties that made them desirable in electrical transformers and capacitors, because of their insulating and low flammability characteristics.4 Subsequently, PCBs were used in hydraulic fluids, microscope oil, paints, surface coatings, inks, adhesives, in carbonless copy paper, and chewing gum, among other products. Because of leaks in the production process, and spills or leaks from transformers and other products, fires and incineration of PCB products, and improper disposal of PCB-containing wastes in landfills, there is widespread contamination from PCBs in the environment and wide distribution in the food chain and human adipose tissue.1 There have been some dramatic examples of leakage and spills, including the Hudson River, in New York, and the New Bedford Harbor, in Massachusetts, and the town of Anniston, Alabama among many other examples. Indeed, PCBs have been found in mammalian blood and adipose tissue samples throughout the world,5 including remote Arctic populations with limited industrial production or use of these compounds.6 The likely source of PCB exposure in these remote settings is ingestion of PCBs accumulated through the food chain, especially in fish and marine mammals.

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Because of the many adverse health effects and widespread distribution of PCBs in the environment, these compounds have not been made in the United States since 19777 and are being phased out under the recent Stockholm Convention on Persistent Organic Pollutants (POPs). There are environmental and occupational exposure limits for PCBs in the United States that set allowable levels in workplaces, in drinking water sources, during transport or disposal, discharge into sewage treatment plants, and in food consumed by infants and adults. The current OSHA occupational limits are 1 mg/m3 for PCB mixtures with 42% chlorine and 0.5 mg/m3 for mixtures with 52% chlorine over an 8-hour day. Presumably, these limits would protect workers exposed during spills of old equipment containing PCBs. The U.S. Food and Drug Administration recommends that drinking water not contain more than 0.5 parts per billion PCBs and that foods such as milk, eggs, poultry fat, ...

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