Environmental Engineering Reference
In-Depth Information
cannot speak of a conventional exposure. The specific mechanisms underlying the dis-
ruption by chemicals of the endocrine systems are quite complex and certainly not for all
chemicals elucidated. Substances can in many ways disrupt normal functions:
• They can act as natural hormones and bind to a receptor. This provokes a response
from the cell, similar to that following a stimulus of a natural hormone (agonist
response).
• They can bind to a receptor and prevent a normal response (antagonistic response).
• The substance may bind to the hormone receptor without initiating a response
and thus the operation of the natural hormone is blocked. This is called an anties-
trogenic or antiandrogenic activity.
• The endocrine-disrupting substance affects hormone production. The substance
has an inhibitory or enhancing effect on the hormone production.
• The endocrine-disrupting substance affects the degradation of hormones. Examples
of such pesticides are DDT, DDE, lindane, endosulfan, kepone, or triazine.
• EDCs can accelerate the degradation of endogenous hormones. The accelerated
degradation of hormones can cause a serious disruption of hormonal balance. The
synthetic estrogen DES, for example, stimulates the cytochrome P450 leading to an
enhanced degradation of hormones.
• EDCs can affect aromatase function. Many fungicides inhibit aromatase activity.
• The substance may cause changes in the feedback mechanism.
• Chemicals may provoke changes in the enzymes involved in the biosynthesis and
metabolism of circulating hormones.
• Structural changes may occur in the endocrine glands.
The impact of endocrine disruptors on homeostasis depends on several factors:
• Exposure during the adult period may be offset by normal homeostatic mecha-
nisms. Ultimately, there is no observable effect.
• Exposure during the period of programming of homeostasis can result in a per-
manent change of reaction or sensitivity to signals.
• Exposure to EDCs at different stages of life, or during different seasons, results in
different effects.
• An interaction exists between the various endocrine glands, so it is unpredictable
in which gland the effects will occur (not necessarily in the expected system).
A lot of caution is needed to extrapolate in vitro results in vivo situations.
Xenoestrogens are chemicals that mimic the effects of natural estrogens. They are a part
of the very heterogeneous group of endocrine disruptors. Xenoestrogens are exogenous
estrogens with hormonal side effects. They can work synergistically to enhance the effect
of estrogen, which can lead to an estrogen dominance. Examples are atrazine, dieldrin,
DDT, endosulfan, lindane, and methoxychlor.
The cytochrome P450 enzyme system (CYP, P450, or CYP450) is a collection of enzymes
some of which are important in the degradation of various xenobiotics, such as medica-
tions, toxins, and endocrine disruptors.
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