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

 6.3.6.  Teratogenic substances
Teratogenic substances affect the reproductive function of living 
organisms. These chemicals cause foetal (embryonic) defects. This 
phenomenon occurs both in humans and in animals and plants. 
From Greek, the words ‘terat-, teras’ mean ‘monster, monstrosity’.
Hereditary pathology studies have shown that it occurs in 
2-3% of newborn children. 25% of the pathologies are genetically 
inherited, including mutagenic pathologies, 50-10% are caused by 
teratogenic  effects,  while  the  remaining  60-65%  have  unknown 
causes – most likely, it is a joint effect of both genetic and environ-
mental factors. There are about 25 known chemicals that have 
teratogenic effects on humans and up to 800 – on animals. Many of 
the latter can also be potential human teratogens.
There are several risk periods in the development process of an 
embryo. For a human embryo such a period is the 18
th
 to the 55
th
 day 
of pregnancy, when the organs are developing (Figure 6.12). During 
this period, the embryo is especially sensitive to chemical factors. 
Contact with teratogens can reduce the size and number of cells, 
Malignant tumours can 
be caused by
 
Œ any substances or 
factors that cause DNA 
damage: chemicals 
(carcinogens), ionising 
radiation;
 
Œ substances, organisms 
or factors that stimulate 
cell division. For 
example, hormones 
that stimulate cell 
division, viruses (the 
papilloma virus, 
which is a risk factor 
for cervical cancer, 
hepatitis B and C 
viruses, which can 
facilitate cancer 
development in the 
liver, herpes viruses).

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ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
which can lead to the retardation of vital organs or foetal growth in 
general. In the 1960s, the sleeping pill thalidomide was the cause of 
incompletely formed limbs in neonates (e.g., a shorter arm or no arm 
at all). Mothers had been using this drug during the first months of 
pregnancy.
10
20
30
40
50
60
70
80
90
280
Ce
ll proliteratio
n
Ce
ll differen
ta
tion
Ce
ll migratio
n
Continued growth
Functional Maturation
Histogenesis
Organogenesis
Degree
 of 
Sensitivit
y
Fe
rtiliz
atio
n
Implantation
Birth
Foetal Period
Embryonic Period
The effects of teratogens were also observed from large doses 
of vitamin D and the use of drugs for treating certain malignant 
tumours. Tests on animals have shown that even relatively common 
environ mental pollutants, such as carbon monoxide CO (from car 
exhaust  and  smoking),  have  teratogenic  effects.  Carbon  monoxide 
can  diffuse  through  the  placenta  and  increase  the  concentration 
of carboxymethyl-haemoglobin in the embryo’s blood. Cadmium, 
lead and mercury are also teratogenic. The chemical mechanism of 
teratogenicity has not been fully researched yet. The most important 
groups of substances that have teratogenic effects are summarised in 
Table 6.4. Compounds of various classes can be teratogenic, but their 
common property is the capacity to diffuse through the placenta.
There is a close relationship between the sub stances with 
carcinogenic  and  mutagenic  effects,  whereas  teratogens  cannot  be 
likened to any of these groups.