Polychlorinated biphenyls generalized structures

Chlorinated ethanes are chemical compounds of the general structure C2HxCl x(X 5) and are widely used in the industrial world as solvents, chemical intermediates, cleaning fluids, fumigants, and for numerous other purposes including uses in petroleum-refining. Likewise,.the chemicals in the class of compounds known as polychlorinated biphenyls Cl (2< < 10) (PCBs) have... 

Although this public health statement will focus on CDDs, it is important to note that CDDs are found in the environment together with other structurally related chlorinated chemicals, such as chlorinated dibenzofurans (CDFs) and polychlorinated biphenyls (PCBs). Therefore, people are generally exposed to mixtures of CDDs and other classes of toxicologically and structurally similar compounds. 2,3,7,8-TCDD is one of the most toxic and extensively studied of the CDDs and serves as a prototype for the toxicologically relevant or dioxin-like CDDs. Based on results from animal studies, scientists have learned that they can express the toxicity of dioxin-like CDDs as a fraction of the toxicity attributed to 2,3,7,8-TCDD. For example, the toxicity of dioxin-like CDDs can be half or one tenth or any fraction of that of 2,3,7,8-TCDD. Scientists call that fraction a Toxic Equivalent Factor (TEF). More information on TEFs can be found in Section 2.5. 

Figure 3.2 General structure of the envirotoxic polychlorinated biphenyls and examples of two congeners, one coplanar with affinity for the Ah-receptor and one not coplanar.

Polychlorinated biphenyls (PCBs) are a group of chloro-snbstitnted biphenyl compounds having the following general structure ... 

FIGURE 15.4 General chemical structure of a Polychlorinated Biphenyl. 

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