SUMMARY 



This account summarizes recent technical literature on the environmental 

 chemistry of polychlorinated biphenyls (PCBs); lists PCB background 

 concentrations in fish, wildlife, and invertebrates; documents their toxic and 

 sublethal properties; and reviews and provides recommendations for the 

 protection of sensitive species of aquatic organisms and wildlife. 



PCBs, a group of 209 synthetic halogenated aromatic hydrocarbons, have 

 been used extensively in the electricity generating industry as insulating or 

 cooling agents in transformers and capacitors. Due to human activities and 

 the chemical characteristics of the products, PCBs are now distributed 

 worldwide, with measurable concentrations reported in aquatic organisms and 

 wildlife from North America, Europe, the United Kingdom, and the Atlantic and 

 Pacific oceans. PCBs elicit a variety of biologic and toxic effects including 

 death, birth defects, reproductive failure, liver damage, tumors, and a 

 wasting syndrome. They are known to bioaccumulate and to biomagnify within 

 the food chain. As a result of legislation, virtually all uses of PCBs and 

 their manufacture have been prohibited in the United States since 1979. In 

 general, the ban has been accompanied by declines in PCB residues in fishery 

 and wildlife resources. However, the current environmental burden of PCBs in 

 water, sediments, disposal sites, deployed transformers, and other PCB 

 containers is now estimated at more than 82 million kg, much of it localized, 

 and this continues to represent a potential hazard to associated fish and 

 wildlife. 



The toxicological properties of individual PCBs are influenced primarily 

 by two factors: the partition coefficient based on solubility in 

 N-octanol /water (Kow); and steric factors, resulting from different patterns 

 of chlorine substitution. In general, PCB isomers with high Kow values, and 

 high numbers of substituted chlorines in adjacent positions, constitute the 

 greatest environmental concern. Unfortunately, basic chemical information is 

 lacking on many isomers. Also, biological responses to individual isomers or 

 mixtures vary widely, even among closely related taxonomic species. The issue 

 is further confounded by the presence of toxic impurities, such as 

 polychlorinated dibenzofurans, which may have been formed during the PCB 

 manufacturing process, or result from product usage. At this time, total PCB 

 residues give a more reliable measure of environmental PCB contamination than 

 do measurements of any Aroclor or other commercial mixtures. In view of the 

 demonstrated differential toxicities within the array of PCB congeners, it may 

 finally become necessary to modify existing standards and criteria based on 



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