Chemistry Reference
In-Depth Information
used to describe the actual status of the atmospheric contamination in the
European continent by these compounds and to anticipate future perspectives
(Sects.
5
and
6
).
2 Objectives
1. To describe the atmospheric background levels of POPs over Europe
2. To identify the processes that are responsible for the atmospheric transport and
fate of POP in the European atmosphere
3. To describe the state of the art of POP contamination at the European scale
4. To describe the future trends of POP contamination in the European atmosphere
2.1 Organohalogen Compounds
OC are man-made chemical substances that encompass a wide range of compounds
with different structures and applications. They are known for their high chemical
stability, which stems from their large proportion of halogen substituents, either
chlorine, bromine or others. Some of them were synthesised for use as pesticides
and others for industrial applications.
The OC pesticides were initially produced to protect crops and human beings
against plague organisms. They are generally incorporated into the environment as
consequence of their use in agriculture. Nevertheless, they can also enter into the
environment due to bad storage practices.
2.1.1 Hexachlorocyclohexanes
These compounds were originally used as mixtures of different isomers (Fig.
1
).
These mixtures contained five isomers,
-HCH was
the one having insecticide properties. The half-life in biological tissue and other
environmental compartments of this isomer is relatively short in comparison to
other OCs.
a
-,
b
-,
g
-,
d
-,
e
-HCH, of which
g
-HCH and its metabolites have relatively high water solubility, so they
can be rather easily washed out from the atmosphere by rain [
13
].
The first production of this group of compounds started in 1943. The production of
lindane (
g
-HCH) in developed countries has been estimated to be 720,000 tonnes. The
global production of technical-grade HCHs over the period between 1948 and 1997
has been estimated to be 10 million tonnes. Today, the production and use of HCHs
have been strongly reduced due to the international restriction. The principal emission
sources of this group of compounds are shown in Fig.
3
. Their physical-chemical
properties are summarised in Table
1
.
g
