8. WATER POLLUTION
179
example, the pesticide dieldrin concentration factor in such surface
film increases up to 10 000 times. In addition, such a surface layer can
accumulate heavy metals, particularly mercury compounds.
After entry of oil and its products into the environ ment, further
transformation processes take place. First of all,
the volatile oil
fractions (benzene, xylene, octane, lower paraffins and cyclo-
paraffins) evaporate.
Further transformations take place through a variety of micro-
organisms. Since the oil composition is very complex, its bio destruc-
tion takes place under the influence of several groups of organisms,
each of which has its own specifics. Primary degradation processes
result in a new group of compounds, which themselves may not
be less toxic than the
original oil products, and their further
transformations are implemented by different organisms. Of the oil
products the first to be degraded are paraffins, and subsequently
cycloparaffins
. The polyaromatic hydrocarbons are most stable.
The total oil oxidation rate depends on the ambient temperature
and oxygen content in the water, and this last factor can be used
as the indicator of the intensity of contamination destruction
processes.
It
is estimated that, in order to oxidize 4 liters of crude oil, as
much oxygen is consumed, as is contained in 1 500 000 litres of sea
water saturated with oxygen. It is contained by a 30 cm thick layer
of sea water in the area of 500 m
2
. As a result of the degradation
process and the mechanical action of waves the homogeneous oil
film is gradually being destroyed, initially through formation of the
oil droplet emulsion in the water, from which, through
evaporation
and adhesion, greasy oil clumps are formed, which then are often
washed ashore.
Through the natural oil degradation processes the water
environ ment decontamination of the oil pollution is accomplished.
In the past, water pollution with oil was eliminated either by
adding a variety
of surfactants to the water, which helped to destroy
the film on the surface, or carbonized sand, which contributed to
the sedimentation of the surface film. However, this approach had a
disadvantage – it did not fundamentally eradicate the environ mental
pollution, but simply transferred it to another location or time
postponed?. In addition, the toxic effects of many surfactants were
even greater than those of oil products.
Given the urgency of the matter, recently many techniques
have been developed to prevent the environ ment pollution by oil
products, among which the preference should be given to the use of
selectively operating micro-organisms.
Today, the question arises regarding
the contamination of water
environ ment with synthetic detergents.
Synthetic detergents
contain a variety of sub‑
stances that may pollute
the aquatic environment:
bleaches / whitening
agents (various
oxidizing agents) such
as sodium perborate;
enzymes such as lipase;
corrosion
inhibitors
such as sodium silicate;
fragrances;
inert substances
(fillers) such as sodium
sulphate;
stabilizers, such as
magnesium silicate.
However, from an
environmental
point of
view, the most important
are two components of
synthetic detergents:
1. surfactants;
2. water softeners.
180
ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
Surfactants are a group of water-soluble organic substances,
which concentrate on surfaces and reduce the surface tension of
water. The main constituting elements which determine the impact
of a substance on the surface tension of the aqueous solution is an
asymmetric molecular structure: surfactant
molecules consist of
two parts – a water-repellent grouping – a hydrophobic part and
a – hydrophilic (water attracting) part. In soaps the hydrophobic
group has a relatively long linear hydrocarbon residue, and the
hydrophilic group is the carboxyl group.
There are the following groups of surface active agents (SAA):
1. Anionactive SAA. The molecules of these surface-active
substances are composed of hydrocarbon residue (hydrophobic
Do'stlaringiz bilan baham: 
