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

Table 6.1. 
Dioxin toxicity for various living organisms
Test organisms
LD
 50
 (µg / kg body weight)
Guinea pig
0.6
Rat (female)
22
Rat (male)
45
Rabbit
115
Dog
30-300
Man (calculated)
>100
Hamster
1160
The effects of a substance can vary within quite a broad range in 
one substance test group (population) – some individuals may have 
a high resistance against the effects of the substance, whereas this 
resistance may be low in other individuals.
The understanding of the effects of substances is based on the 
study of the reactions of living organisms in response to changing 
doses or concentrations of the substances studied. At the same time, 
the toxicity of a substance is considered to be one of its properties 
Figure 6.7. 
Reactions 
in living organisms 
depending on the 
quantity of the 
substance taken in: 
a) the substance is 
necessary for the 
functioning of the body; 
b) the substance is not 
necessary for the body
Figure 6.8. 
2,3,7,8-TCDD 
(dioxin) – One of the 
most toxic substances 
known to be formed as a 
by-product of a number 
of organic synthesis 
processes, burning of 
organic materials.

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ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
determined by its molecular structure (a property similar to the 
substance’s molecular weight, volatility or the capacity to adsorb on 
solid surfaces). Consequently, the study of correlations between the 
toxicity of the substance and its composition can also be used for 
toxicity assessment.
The toxic effects are caused by the presence of a substance in 
the body. It can be taken in at one time, or its effects may add up. 
In the latter case, it may be necessary to assess the doses that can 
be taken in over a longer period of time. The simplest criterion of 
toxicity evaluation is mortality (lethality) although this indicator 
provides little information about the processes that determine the 
toxic effects.
One of the most widely used methods for toxicity assessment 
consists of the determination of the lethal dose of a toxic substance. 
Lethal dose (LD) is the amount of a substance that causes the 
organism’s death.
The  dose  that  causes  death  in  a  fixed  part  (usually  50%)  of 
an animal testing group following the contact with the analysed 
substance over a given period (usually 24, 48 or 96 hours) is denoted 
as LD
50
. Lethal dose is expressed in milligrams per kilogram of 
live weight (mg/kg). For toxic substances, LD
50
 is usually less than 
15 mg/kg (Table 6.2). The LD
50
 value may vary depending on the 
duration of the action and the nature of the population.