7. AIR POLLUTION
145
medicine, and the production of substances that are used in
everyday life. Already two examples of this group of substances –
pesticide DDT and polymer polyvinyl chloride compound shows
broad spectrum of features and usability characteristic to
organohalogens. However, to talk about the effects of exposure to
these substances, one
must discuss the structure, areas of use and
the main characteristics, as well as the main sources of environ-
mental pollution with halogenated organic compounds. First of all,
halogenated organic compounds can be divided into organofluoride
organic, chloro-organic and organobromide compounds.
Despite the extensive production, organofluorine compound
application range is narrower than
that of the chloro-organic
substances, which is mainly due to their high cost. The most popular
of the organofluorines is dichlofluormethane (Freon). The methane
derivatives are: Freon 11 (CFCl
3
, b.t. 23.8 °C); Freon 12 (CF
2
Cl
2
, b.t.
–29.8 °C); Freon 13 (CFCl
3
, b.t. –81.4 °C) and ethane derivatives
Forane 114 (CF
2
ClCF
2
Cl, b.t. 3.6 °C) and Forane 113 (CFCl
2
CF
2
Cl, b.t.
47.6 °C).
Such a wide scope of use of these substances is determined by
many unique features of freons, among which the first to be noted
is the high chemical stability of these substances (they do not break
down in the aquatic environ ment,
or when exposed to acids, bases
and oxidizers). Freons are also characterized by low acute toxicity:
inhalation of freons F11, 12, 22 and other freon vapour (0.5% vol.)
for 90 days, 6 hours a day does not result in any symptoms of toxic
effects. The maximum permissible concentration in the air for most
of the freons is about 1000 mg/m
3
, but for liquid freons F11 and
F113LD
50
it is above 15 g/kg.
Furthermore, the other characteristics important from the prac-
tical point of view determine the extensive production of freon
today. Taking into account the specificity of freon use, most of this
volume is dispersed into the atmo sphere, where
the freon decom-
position is slow. At the same time, in the stratosphere under the
influence of UV radiation, freon molecules decompose, releasing
the halogen radicals, which may subsequently act as catalysts
for ozone decomposition reaction. Given the harmful effects of
organo halogens, degrading the ozone layer (primarily freons), the
production and consumption amount in the European Union Member
States (Figure 7.22) as well as in other countries has significantly
decreased in the last decades.
Chlorine derivatives C
1
and C
2
belong to low molecular weight
organochlorine. Typically, this group of
substances includes methane
chlorine derivatives (carbon tetrachloride CCl
4
, chloroform CHCl
3
,
methylene chloride CH
2
Cl
2
, methyl chloride CH
3
Cl), chlorine
derivatives of ethane or ethylene. These substances form a separate
These gaseous or easily
liquefiable substances are
mainly used, as follows:
1. as propellants in
aerosols (freons are
chemically inert,
non‑combustible,
practically non‑toxic);
2. as
heat carriers in
cooling devices;
3. as foaming agents in
the manufacture of
porous polymers;
4. in microelectronics;
5. in chemical industry.
146
ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
group, taking into account the production of substantial size, and
the similar toxicological spectrum. Halogenated hydrocarbons are
obtained both by the direct
chlorination of hydrocarbons, and by
chlorination in the presence of atmo spheric oxygen as an oxidizing
agent. Typical lower chlorinated hydrocarbons are liquid substances
(with the exception of methyl and vinyl chloride, which are gases,
and hexachloroethane, which is solid). Annual production of vinyl
chloride (CH
2
=CHCl) amounts to 10 million tons. 1,2-dichloroethane
is also produced in significant quantities (13 million tons per year)
as well as carbon tetrachloride (1 million tons per year). Large
amounts of trichalomethanes (THMs) are formed as a result of
water chlorination. These substances may be also formed as a result
of various natural processes. It is assumed
that burning fossil fuels
and biomass release 5 × 10
6
tons of methyl chloride per year into
environ ment, but up to 40 000 tons of methyl chloride are formed in
the ocean and sea algae life processes.
0
300
400
250
200
150
100
50
350
450
Thousand Ozone Depleting Potential Tonnes (ODP Tonnes)*
* Tonnes multiplied by the ozone depleting potential of the considered gas.
CFCs
United
States
China
Russia
European Community (25)
1990
1995
2000
2005
2008
Lower halogenated hydrocarbons are widely used as solvents
in the manufacture of polymers (vinyl chloride). The large amounts
and mode of use result in release of significant volumes of these
substances into the environ ment, and it can affect human health
in the living and working environ ment. Lower molecular mass
chlorinated
hydrocarbons, when inhaled, act as anaesthetic
substances, which can easily lead to poisoning, especially affecting
the liver. In some chlorinated hydrocarbons the carcinogenic effects
have been proven.
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