Polychlorinated Biphenyls and Polybrominated Biphenyls - Organic Pollutants: An Ecotoxicological Perspective - page 133

6 Polychlorinated

Biphenyls and
Polybrominated
Biphenyls

6.1 Background
The polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) are
industrial chemicals that do not occur naturally in the environment. The properties,
uses, and toxicology of the PCBs are described in detail in Safe (1984), Robertson
and Hansen (2001), and Environmental Health Criteria 140. PBBs are described in
Safe (1984) and Environmental Health Criteria 152.
PCBs were first produced commercially around 1930. The commercial products
are complex mixtures of congeners, generated by the chlorination of biphenyl. Most
of them are very stable viscous liquids, of low electrical conductivity and low vapor
pressure. Their principal commercial applications have been

1. As dielectrics in transformers and large capacitors

2. In heat transfer and hydraulic systems

3. In the formulation of lubricating and cutting oils

4. As plasticizers in paints, and as ink solvents in carbonless copy paper

With such a diversity of uses, they entered the natural environment by many differ-
ent routes before they were subject to bans and restrictions. The level of chlorina-
tion determines the composition and properties and, ultimately, the commercial use
of PCB mixtures. Depending on reaction conditions, levels of chlorination ranging
from 21 to 68% (percentage by weight) have been achieved. The commercial prod-
ucts are known by names such as Aroclor, Clophen, and Kanechlor, usually super-
seded by a code number that indicates the quality of the product. Thus, in one series
of products, Aroclor 1242 and Aroclor 1260 contain about 42% chlorine and about
60% chlorine respectively. The first two numbers of the code indicate that the prod-
uct is derived from biphenyl, and the second two indicate the approximate level of
chlorination. Since the discovery of pollution problems in the 1960s, the production
of PCBs has greatly declined, and there are few remaining uses at the time of writ-
ing. Further details of the regulation of PCBs internationally are given in Robertson
and Hansen (2001).

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