Encyclopedia of Environmental Science and Engineering, Volume I and II

866 PCBs AND ASSOCIATED AROMATICS

TABLE 11

The International Union of Pure and Applied Chemistry

numbering system for PCB congeners

No. Structure

Monochlorobiphenyls

1 2

2 3

3 4

Dichlorobiphenyls

4 2,2


5 2,3

6 2,3


7 2,4

8 2,4


9 2,5

10 2,6

11 3,3


12 3,4

13 3,4


14 3,5

15 4,4


Trichlorobiphenyls

16 2,2
,3

17 2,2
,4

18 2,2
,5

19 2,2
,6

20 2,3,3


21 2,3,4

22 2,3,4


23 2,3,5

24 2,3,6

25 2,3
,4

26 2,3
,5

27 2,3
,6

28 2,4,4


29 2,4,5

30 2,4,6

31 2,4
,5

32 2,4
,6

33 2 
,3,4

34 2 
,3,5

35 3,3
,4

36 3,3
,5

37 3,4,4


38 3,4,5


39 3,4
,5

Tetrachlorobiphenyls

40 2,2
,3,3


41 2,2
,3,4


42 2,2
,3,4


(continued)

atoms per molecule, also increased, relative to Aroclor 1242.

The product is more biodegradable and less toxic than Aroclor

1242. Aroclor 1242 was the principal capacitor impregnant
      in the U.S. prior to about 1971 when it was replaced by
      Aroclor 1016.
      Table 10 shows the percentage distribution of isomers
      amongst different homologous series.
      Table 11 shows the IUPAC numbering and substitution
      pattern for PCB congeners.
      The numbering system for PCB congeners is important
      because it allows isomers to be referred to easily and with-
      out ambiguity. In particular, instances in which particular
      congeners are recognized, such as in chromatographic anal-
      yses of commercial PCB products, and in considerations of
      toxic isomers, the IUPAC numbering system is extremely
      valuable.
      Receptor-mediated responses are characterized by
      the stereoselective interaction of ligands with receptors.
      Structure-activity relationships for PCBs have been exten-
      sively investigated and are thought of as the basis for the role
      of the Ah receptor in initiating the toxic effects observed

TABLE 9

A variety of Aroclors were used throughout industry

Application Types of Aroclor Used

Transformers 1242, 1254, 1260

Capacitors 1016, 1221, 1242, 1254

Vacuum pumps 1248, 1254

Hydraulic fluids 1232, 1242, 1248, 1254, 1260

Heat exchangers 1242

Waxes 1242, 1254, 1268

Dust-control agents 1254, 1260

Inks, lubricants, cutting oils 1254

Carbonless copy paper 1242

TABLE 10

The number of chlorine atoms in the series tends to increase as the

amount of chlorine in the PCB increases

% of Homologous Series in Aroclors

Chlorobiphenyl 1242 1248 1254 1260

C 12 H 9 Cl 3———

C 12 H 8 Cl 2 13 2——

C 12 H 7 Cl 3 28 18 — —

C 12 H 6 Cl 4 30 40 11

C 12 H 5 Cl 5 22 36 49 12

C 12 H 4 Cl 6 4 4 34 38

C 12 H 3 Cl 7 —— 641

C 12 H 2 Cl 8 ——— 8

C 12 HCl 9 ——— 1

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