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

particular importance is the effect of toxic substances on the nucleic 
acids, since it is based on the mutagenic and carcinogenic effects of 
substances. Among the known carcinogens which affect the nucleic 
acids are such substances as polycyclic hydrocarbons, polycyclic 
amines, aminoazobenzene, nitrosamines, aliphatic alkylating agents.
Accumulation of substances in living organisms can take place 
directly  from  air,  soil  or  water,  however,  a  significant  proportion 
(depend ing on the nature of the substance and the place of the 
respective living organism in the food chain) can be taken with food. 
When substance is released into the environ ment, it is subjected to 
the impact of various factors, that leads to a possibility of quick and 
sign ifi cant decrease of the substance’s content. However, there are 
many substances, whose stability against biological degradation is 
high. Among such substances one must mention DDT, all chlori na ted 
organic compounds, metals, and toxic microelements, orga no metallic 
compounds, radioactive elements.
For example, many sea birds that prey on fish are very effective 
bioconcentrators of toxic substances (Figure 6.4). Today, these bird 
species therefore are gravely exposed to pollution. Physiologically, 
it may take the form of bird sterilization and bird eggshell thinning.
For example, the ability of algae Fucus or Laminaria to  bio con-
centrate iodine from sea water allows them to be used for industrial 
extraction of iodine. Bioconcentration is the process by which the 
organism absorbs the substances necessary for its existence (trace 
elements, vitamins, fatty acids) from the environ ment. 
Bioconcentration factor can also be expressed as the ratio 
between the speed of intake of a substance and its elimination speed 
from the body. In other words, the speed of metabolism or the speed 
of specific metabolic processes may greatly influence the character 
of substances’ accumulation. At the same time the bioconcentration 
phenomenon is typical for substances that are not hydrophobic, in 
case if particular systems of organism are capable to assimilate the 
respective element in increased quantities. Particular research has 
The sustained high 
resistance of toxic sub‑
stances to the influence 
of various environmental 
factors can be explained 
with their bioconcentra‑
tion. Its measure is the 
bioconcentration factor 
(BCF). BCF is the ratio 
between the concen‑
tration of a substance 
in the organism and in 
the environment (water, 
soil). Bioconcentration 
ability of a substance is 
considered to be low, if 
BCF < 500, to be average 
high, if BCF ≈ 500‑1000, 
but high if BCF > 1000.
BCF = C
organism
/C
environment

---

6. Action of toxic substances in the environment – basic concepts of ecotoxicology 
 103
been devoted to the bioconcentration of organochlorine compounds. 
At the first trophic level a role of bioconcentrator may be assigned to 
phytoplankton and plants, especially if they are either rich in lipids 
(nuts, especially peanuts) or carotenoids, terpenes. Of particular 
importance is the ability of phytoplankton to concentrate, for 
example,  organochlorine  compounds.  Accordingly,  in  the  higher 
trophic  levels  the  bioconcentration  effect  is  determined  not  only 
by the consideration that the food base consists of the primary 
producers, but also by the fact that, once the living organism 
becomes more complex, the organs appear, in which toxicants can 
be deposited easier. Of aquatic animals, the molluscs should be 
mentioned  first  of  all.  It  should  be  noted  that  the  fish  may  ingest 
quite large quantities of toxic substances through the skin directly 
from the water.
An  important  factor  that  determines  the  degree  of  bio-
concentration is the length of the food chain, which in case of 
aquatic living organisms is, on average, longer than for those living 
on the land. The DDT transfer and bioconcentration takes place 
similarly. Pesticides’ bio-concentration in the terrestrial food chains 
is less pronounced.
All  these  facts  prove  that  pollutants’  dissipation  process,  as  a 
result of which they enter the environ ment, can be considered as 
rather conditional. Since pollutants can concentrate at higher stages 
of the food chain, which also include the man, it is possible to create 
an  inverted  «pyramid  of  bioconcentration»,  by  analogy  with  the 
«trophic pyramid».