Encyclopedia of Environmental Science and Engineering, Volume I and II

845

PCBs AND ASSOCIATED AROMATICS

INTRODUCTION

Polychlorinated biphenyls (PCBs) are a family of chemical

compounds which do not exist in nature but which are man-

made. Commercial mixtures are clear, pale yellow liquids

manufactured by the replacement of hydrogen atoms on the

biphenyl molecule by chlorine. The reaction is controlled

according to the percentage replacement of hydrogen and

results in a product which contain chlorobiphenyls with one

or, more usually, several chlorine atoms attached to each

molecule.

The family of polychlorinated biphenyls can contain

from 1 to 10 chlorine atoms arranged within the molecule

in 209 different ways. The different molecular combina-

tions are called congeners. The congeners which comprise

the series of compounds with the same number of chlorine

atoms are known as an homologous series.

The congeners are named according to the homologous

series to which they belong. For example, a PCB containing

3 chlorine atoms would be called a trichlorobiphenyl, or one

with 5 chlorine atoms a pentachlorobiphenyl. The homolo-

gous series of PCBs and the number of isomers contained in

each are listed in Table 1.

The synthesis of biphenyl and its subsequent reaction

with chlorine to yield polychlorinated biphenyls is shown

in Figure 1.

PCBs have been manufactured by various companies

throughout the world and are often referred to by the manu-

facturer’s trade name. Table 2 lists the main producers.

The perceptions of risk associated with ownership and

operation of PCB containing equipment is related to the risk

of fires, spills, cleanup or noncompliance with regulations.

The following time line focuses on the development of PCB

risk perceptions as new knowledge grew from the time that

PCBs were first used in industrial applications.

1881

PCBs were first described in the chemical literature in 1881

by Schmidt and Schultz.

1929–1931

PCBs were developed by the Federal Phosphorus Company

and Swann Research Co. The latter business was bought by

Monsanto in the Early 1930’s.

The available data on the toxicity of PCBs were first

summarised in an article published in 1931 (Smyth, 1931).

1933

The first reported episode of PCB-related toxicity occurred

in 1933, at the Swann Chemical Co. Twenty three of 24 men

working on the manufacture of PCB almost simultaneously

developed skin eruptions that were diagnosed as ‘chloracne’.

Some of the men also complained of lassitude. The investi-

gators report on the episode concluded that the toxic agent

was an unidentified impurity, which had probably appeared

TABLE 1

Chlorobiphenyl Empirical Formula # of Isomers Weight% Cl

mono C 12 H 9 Cl 3 18.8

di C 12 H 8 Cl 2 12 31.8

tri C 12 H 7 Cl 3 24 41.3

tetra C 12 H 6 Cl 4 42 48.6

penta C 12 H 5 Cl 5 46 54.3

hexa C 12 H 4 Cl 6 42 58.9

hepta C 12 H 3 Cl 7 24 62.8

octa C 12 H 2 Cl 8 12 66.0

nona C 12 HCl 9 3 68.7

deca C 12 Cl 10 1 71.2

Adapted from Reference 1: Hutzinger et al.

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