ABSTRACT
Polychlorinated biphenyls (PCBs) are a family of compounds produced commercially by directly chlorinating biphenyl. The 209 possible PCB compounds are referred to as "congeners." PCB congeners with the same number of chlorine atoms are known as "homologs" or "isomers" of each other. The compounds now collectively referred to as PCBs are actually several dozen individual congeners clustered around some average degree of chlorination. Chemical structures of phenyl and biphenyl groups are shown in Figure l. Congeners may be grouped in terms of the number of chlorine atoms attached to the biphenyl molecule. For instance, one chlorine would produce a monochlorobiphenyl, two a dichlorobiphenyl, ten a decachlorobiphenyl. Polychlorinated biphenyl is the term used to cover all of the various congeners. The symbols 0, m, and p define the positions of chlorine substituents (ortho-, meta-, or para-) that characterize varying chemical and physical properties and influence the biodegradation process [1). The chemical structures of sclective PCBs are shown in Figure 2. Table 1 lists the molecular weight, chlorine number, and percent of chlorine for each homolog.
