Chemistry Reference
In-Depth Information
Fig. 2 Molecular structure of HCB
HCB
HCH
PCBs
energy production
waste
agriculture
industrial processes
road transport
commercial,residencial
Fig. 3 European Union emissions of HCB, HCHs and PCBs (adapted from [
7
])
global emission of 23,000 kg per year has been estimated with a range between
12,000 and 92,000 kg per year [
21
].
This compound is poorly soluble in water and evaporates rapidly after release
into the atmosphere. Due to its relatively high vapour pressure, it is usually found in
the gas phase, not in the aerosol fraction. Today, its production is banned. However,
it is present in many products as an impurity and can be released unintentionally.
HCB has shown to be toxic for men, when in Turkish Kurdistan, between 1955 and
1959, it caused an outbreak of
porphyria cutanea tarda
after intake of contaminated
food. A relationship between thyroid cancer increase and chronic exposure to HCB
has been identified [
22
].
2.1.3 Polychlorobiphenyls
PCBs are industrial compounds used as industrial, dielectric and heat transfer fluids,
organic solvents, flame retardants, plasticizers, sealant and surface coatings. They
may also be released to the atmosphere by waste incineration (Fig.
3
). The world-
wide production of this compound has been 1.3 million tonnes, of which 97% in the
northern hemisphere [
23
]. The amount of chlorine atoms in the biphenyl mixtures is
related to the duration and temperature of the chlorination process. The commercial
mixtures were distributed under names such as Aroclor (Monsanto, USA) or
Clophen (Bayer, EU). The chlorine atoms can substitute the
para
,
meta
and/or
ortho
positions of the biphenyls. There are 209 possible congeners. PCBs can be
divided into nine isomeric groups and one decachlorobiphenyl, all with an empiri-
cal formula of C
12
H
10
-
n
Cln (
n
ΒΌ
1-10) (Fig.
4
).
