ENVIRONMENTAL CHEMISTRY 



PCBs are organic compounds commerciany produced by chlorination of a 

 biphenyl (BP) with anhydrous chlorine in the presence of iron filings or 

 ferric chloride as the catalyst. The purified product is a complex mixture of 

 chlorobi phenyls containing 18 to 79% chlorine; the precise composition depends 

 on the conditions under which chlorination occurred (EPA 1980). Ten possible 

 degrees of chlorination of the biphenyl molecule give rise to ten PCB congener 

 groups: mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, and 

 decachlorobiphenyl (Figure 1). Within any congener group, a number of 

 positional isomers (discrete chemical compounds) are possible, depending on 

 the number of chlorines in the molecule. For example, the tetrachloro- and 

 pentachlorobiphenyl congener groups are composed of 30 and 46 possible 

 isomers, respectively. Not all 209 possible isomers are likely to be formed 

 during the manufacturing process. In general, the most common ones are those 

 that have either an equal number of chlorine atoms on both rings, or a 

 difference of only one chlorine atom between rings (MAS 1979). Although 

 chlorine substitution is favored at the ortho and para positions (Figure 1), 

 the commercial products are complex mixtures of isomers and congeners with no 

 apparent positional preference for halogen substitution (Safe 1984). 



Recent advances in the identification and quantification of PCB isomers 

 through mathematical and computer-assisted techniques (Dunn et al. 1984; 

 Schwartz et al . 1984) will prove useful in data interpretation of metabolic 

 fate studies. Unfortunately, the results of PCB analyses vary widely among 

 cooperating laboratories. An interlaboratory comparison of spiked and 

 unspiked samples of herring oil by 23 participating European and North 

 American laboratories showed that calculated spike recoveries ranged from 23 

 to 136% (Musial and Uthe 1983). This was attributed to serious deficiencies 

 in most steps in the analytical procedures. It seems that until these 

 deficiencies are corrected, PCB analyses will have credibility from only a few 

 selected laboratories. 



Toxic materials as impurities in PCBs include polychlorinated dibenzo- 

 furans (PCDF) in some domestic and foreign mixtures at levels of 0.8 to 33 

 mg/kg. The concentrations of PCDFs in Great Lakes fish were related to the 

 concentrations of PCBs (Stalling et al . 1983). Sometimes, PCBs used in 

 electrical capacitors and transformers are converted under the action of heat 

 or electrical arcing to form PCDFs including 2,3,7,8-tetrachlorobenzofuran 

 and 2,3,4,7,8-pentachlorobenzofuran. Kanechlor 400 (Table 1), for example, 

 with an initial PCDF content of 20 mg/kg, yielded fluid with a PCDF content of 



