Polychlorinated Biphenyls (PCBs)
Polychlorinated biphenyls (PCBs) are a group of chlorinated hydrocarbon compounds that once were used widely as high-temperature insulators for transformers and other electric equipment and were also found in carbonless copy papers and some inks and paints. Since 1974, all uses in the United States have been confined to closed systems. Most PCB poisonings are chronic occupational exposures, with delayed-onset symptoms the first indication that an exposure has occurred. In 1977, the US Environmental Protection Agency (EPA) banned further manufacturing of PCBs because they are suspected carcinogens and highly persistent in the environment. The primary exposures occur from leaking transformers and other electric equipment, from hazardous waste sites, and environmentally from ingestion of contaminated water, fish, or wildlife.
Mechanism of toxicity. PCBs are irritating to mucous membranes. When burned, PCBs may produce the more highly toxic polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs [See Dioxins]). It is difficult to establish the specific effects of PCB intoxication because PCBs are nearly always contaminated with small amounts of these compounds. PCBs, and particularly the PCDD and PCDF contaminants, are mutagenic and teratogenic and are considered probable human carcinogens.
Toxic dose.
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