Māris kļaviņŠ, azamat azizov, JĀnis zaļoksnis environment, pollution, development: the case of uzbekistan

 9.2. 
 Contamination of soils with inorganic 
substances
When growing a variety of agricultural crops and harvesting the 
yield, the main plant nutrients – nitrogen, phosphorus, potassium, 
and microelements such as magnesium, iron, boron, etc., which 
plants  require  in  lesser  quantities,  are  removed  from  the  field.  If 
the content of these elements in the soil is not compensated, the soil 
degrades and becomes unsuitable for crop production. Therefore, to 

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9. POLLUTION OF SOIL 
 197
maintain soil fertility and increase crop yields, natural and artificial 
fertilizers in agriculture are extensively used.
Under intensive farming conditions mineral fertilizers (super-
phosphate, potassium chloride, ammonium nitrate and others) are 
widely applied, and the goal is to provide the necessary balanced 
nutrient quantities for the agricultural crops. Due to economical 
reasons, these fertilizers are usually as raw products, therefore 
with each dose of fertilizer the soil could be polluted with certain 
quantities of toxic metals and their compounds. For example, super-
phosphate contains metals such as arsenic, cadmium, chromium, 
lead, vanadium, cobalt and others. These elements, along with 
pesticide residues, accumulate in the soil over a long period of time 
and contaminate it.
Soil pollution also consists of excessive mineral and organic 
nitrogen and phosphorus amounts. Some of them are leached 
from the soil into groundwater, wells and watercourses. However, 
agricultural crops also are subject to the increased intake of nitrates, 
for example, spinach, in which their quantity, depending on the 
availability of nitrogen compounds in the soil, may vary between 1.4 
to 3.5 g/kg. Increased phosphorus and nitrogen discharge into rivers 
and lakes causes eutrophication. Furthermore, high concentra tions of 
nitrates in drinking water and consumable plants can cause disease 
in humans. During industrial processing, including conservation and 
preservation, as well as consuming nitrate-rich vegetable products 
into the human intestinal tract, nitrate ions NO
3
–  
turn into nitrite ions 
NO
2
–
. In the human body they interact with the haemoglobin in red 
blood cells – erythrocytes, which ensure the oxygen transfer in the 
organism. As a result, methaemoglobin is formed, which is incapable 
to bind oxygen and causes serious illness – methemoglobinemia, a 
disorder resulting in the oxygen starvation in the tissues of the body, 
despite the fact that breathing is normal. In addition, it has been 
established that nitrates in human intestinal tract can also turn into 
nitrosamines, which are considered carcinogenic compounds.
A  number  of  heavy  metals  that  accumulate  in  the  soil  as  a 
result of fertilizer over-use are in the form of insoluble compounds, 
which at the given conditions can not be consumed by plants and 
microorganisms and, therefore, they are not biologically dangerous. 
Such a set of sedentary chemical elements are chemical «time 
bombs».  Due  to  some  changes  in  the  external  conditions  (such  as 
human economic activities or climate change, increased soil acidity) 
these compounds change into a soluble form and may pass into 
ecological food chains with all the ensuing dangerous consequences.
It is to be recognized that one of the major factors of soil fertility 
are organic fertilizers, whose misuse can locally cause high levels of 
nitrogen pollution. This situation has been observed in many European 
countries, including the Netherlands, Denmark and Germany.

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198 
ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
A  very  serious  environ mental  problem  today  is  the  use  of 
sewage  sludge  as  field  fertilizer.  Wastewater  treatment  plants  in 
the world every year accumulate thousands of tons of sludge, which 
form huge piles at the treatment plants. Since sewage sludge is rich 
in phosphorus and other plant nutrients, it was recommended to 
address the sludge problem by using it as a fertilizer for growing 
agricultural crops. However, the chemical analysis of sludge shows 
that it also contains a lot of harmful chemicals – organic compounds 
and heavy metals, which enter the sludge during the factory and 
urban waste water treatment process. Thus, the harmful substances 
which a man has tried to get rid of in wastewater treatment process, 
and which are concentrated in one place, are dispersed again over a 
wide area and injected into the soil from where they can be ingested 
by plants or leach into groundwater. Many researchers have warned 
against the dangers of such practice to environ ment.
Industrial pollution is caused by a variety of manufacturing 
processes associated with processing of substances and materials, 
power generation and fuel use in manufacturing processes. The 
most important is the industrial pollution, which is ejected into 
the atmo sphere from the factory chimneys. It consists of gases, 
aerosols and dust particles, which in the air masses are carried 
over long distances, during the precipitation formation processes 
dissolve within the water droplets in the atmo sphere and eventually 
settle or fall on vegetation or soil. The chemical composition of 
industrial pollution is largely dependent on the substances used in 
the production and technological processes. It is as diverse as the 
industrial production, therefore in each particular case the industrial 
pollution interaction with the environ ment is specific. 
A very topical problem in the 20
th
 century was sulfur-containing 
industrial emission impact. Most industrial plants and heat-electric 
generating plants used the coal as fuel, but in its combustion process 
great quantities of sulfur dioxide SO
2
 are released. This gas dissolves 
in precipitation water to form acid rain, therefore much attention 
was  paid  to  research  the  ecological  effects  of  soil  acidification.  It 
has been found that the acid rain most of all affects plants and soil 
microorganisms.
Since the the end of 1980s the production technology improve-
ment, introduction of filter systems and replacement of coal as a pri-
mary fuel with natural gas, sulfur-containing emissions are reduced 
considerably. However, environ mental problems caused by acid rain 
have not become less acute, because due to the rise in car ownership 
and, consequently, the amount of car exhaust, nitrogen oxide emis-
sions in the world have increased significantly, which, dissolving in 
atmo spheric precipitation water enter the soil in the form of ammo-
nium NH
4
+
 and nitrate ions NO
3
–
.
Of all the industrial 
enterprise types, the 
most important in the 
context of environmental 
pollution are considered:
 
Œ chemical complexes;
 
Œ smelting companies;
 
Œ mining companies;
 
Œ building complexes;
 
Œ heat‑electric 
generating plants.

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9. POLLUTION OF SOIL 
 199
Near the mines and smelting plants the soils are profusely 
contaminated with heavy metals. Under severe pollution conditions 
over a wide area around the metal smelting plants the so-called 
industrial deserts develop, where almost no vegetation or animals are 
found. An example of such a desert is the surroundings of the non-
ferrous metal production complex «Severonikel» built in the North of 
Russia. Forest soil pollution with heavy metals has a negative impact 
on soil microorganisms and fauna.
The persistent pollution, which could not be destroyed collapse 
biologically,  is  of  special  significance.  The  term  ‘heavy  metals’ 
commonly denotes the metals, whose relative density is greater 
than 5 g/cm
3
 and thus about 70, or seven-eighths of all the known 
metals are heavy metals. In the environ mental protection, according 
to the use of metals in the economy and the severe danger of their 
compounds, more attention is paid only to certain heavy metals 
and  non-metals,  the  effects  of  which  may  pose  a  threat  to  living 
organisms,  such  as  arsenic  (As),  mercury  (Hg),  cadmium  (Cd), 
selenium  (Se),  copper  (Cu),  zinc  (Zn),  chromium  (Cr),  nickel  (Ni), 
lead (Pb), tin (Sn), antimony (Sb), bismuth (Bi), cobalt (Co).
Heavy metals enter the atmo sphere as a result of a variety 
of pollu tion sources, and with time as a result of the wet and the 
dry deposition they land on the soil. It is estimated that in Europe 
annually 130 g/ha of Ni, 500 g/ha of Zn, 20 g/ha of Pb, 75 g/ha 
of  C,  20  g/ha  of  Cr  and  3.5  g/ha  Cd  land  on  the  soil.  Industrial 
activity, energy production and motor transport impact result in 
the increased concentrations of heavy metals in the upper soil layer 
on a global scale, as the soil has very high metal sorption capacity.