ABSTRACT
Polychlorobiphenyls (PCBs) are synthetic semivolatile
chlorinated aromatic hydrocarbons, which are chemi-
cally very stable and have similar physical properties,
ranging from oily to waxy solids. The PCB family
includes 209 congeners divided into 10 congener
classes, and named according to the IUPAC number-
ing from PCB1 (monochlorobiphenyl) to PCB209
(decachlorobiphenyl) (Table 1). PCBs were synthe-
sized more than 100 years ago, and commercialized
under various trade names, e.g., Aroclor, Clophen,
Kanechlor, and Fenclor from around 1930. Table 2
shows the typical percentage composition of a few
commercial PCB mixtures. Due to their very low
flammability, chemical stability, high boiling point,
and insulating properties, commercial PCB mixtures
have been massively used in many industrial applica-
tions, especially in capacitors, transformers, and other
electrical equipment. (1-3). It has been estimated that
about 1.2 106 tons were produced on a world level between 1930 and 1974. Of this, about one-third has
been released into the environment, more than 50% is
still in use or deposited in landfills, and only a very low
percentage has been destroyed or incinerated (3). PCB
mixtures such as Aroclor 1260 are also currently being
released to the environment both from landfills con-
taining PCB waste materials and products, and from
open areas due to illegal disposal of PCB-containing
materials. The half-life of PCBs ranges from a few days
to about 10 years for mono-to penta-chlorobiphenyls,
and it can be as high as 20 years for higher substituted
congeners (1). This has led to the widespread occur-
rence of PCBs in the terrestrial ecosystem (1,4), even in
remote areas (5). Recently, new epidemiological, toxi-
cological, and mechanistic data have been reported,
in particular with respect to neurodevelopment, repro-
ductive and endocrine effects, which seems to indicate
that the toxic properties of PCBs have been under-
estimated. Consequently, there is considerable public,
Table 1 Chemical Structure, Congener Classes, Number of
Isomers, and IUPAC Numbering of PCBs
Congener class Number of isomers (IUPAC nos.)
Monochloro 3 PCB1-PCB3
Dichloro 12 PCB4-PCB15
Trichloro 24 PCB16-PCB39
Tetrachloro 42 PCB40-PCB81
Pentachloro 46 PCB82-PCB127
Hexachloro 42 PCB128-PCB169
Heptachloro 24 PCB170-PCB193
Octachloro 12 PCB194-PCB205
Nonachloro 3 PCB206-PCB208
Decachloro 1 PCB209
Total 209
scientific, and regulatory concern over the negative effects on human health and on the environment of long-term exposure to PCBs. In the past two decades the European Commission has introduced specific legislations aimed at reducing human exposure, but more incisive actions are needed since it has been shown that the dietary exposure to PCBs exceeds the tolerable weekly intake (TWI) for most of the European population.
