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

Figure 6.9. 
Hormone-
producing glands in the 
human body

---

6. Action of toxic substances in the environment – basic concepts of ecotoxicology 
 111
Usually, the intensity of natural reproductive hormone action 
is significantly higher than that of environ mental estrogen (except 
for diethylstilbestrol and contraceptives). It has been proved that 
many  structurally  different  substances  have  the  capacity  to  affect 
the endocrine system. Environ mental estrogens typically have both 
synergistic and antagonistic effects.
Natural hormones are unstable and disintegrate within a period 
ranging from a few minutes up to several hours after the formation. 
Unlike naturally occurring substances, environ mental estrogens are 
persistent and may even accumulate in living tissue.
The main difference between the hormones produced in human 
or animal organisms and the substances that degrade the endocrine 
system is their origin and possible ways of assimilation. Considering 
the extensive use of various exoestrogens, their high concentrations 
in the environ ment have been proven (Table 6.3). The high environ-
mental concentration of substances that degrade the endocrine system 
is also attributable to their high persistence as a result of metabolic 
transformations and chemical and biological degradation processes. 
Many substances that degrade the endocrine system are quite volatile; 
therefore, they may be disseminated with air masses although 
usually they are spread by water. Examples of such substances are the 
pesticide DDT, a substance that is widely used in the production of 
polymers – bisphenol A, a synthetic estrogen diethylstilbestrol as well 
as a variety of substances of a natural origin (Table 6.3).