Threat by chemical substances: Legislation, production, use and waste - Environmental Deterioration and Contamination: Problems and their Management - page 62

hormones carry and thus affect the normal functions of tissues and organs. The molec-
ular basis of the behavior of these exogenous molecules is the similarity to endogenous
hormones in molecular conformity, and therefore their ability to bind to and occupy
the receptor site of hormones but without fulfilling the role of hormones. Another
mechanism is developing false response in the regulation of metabolic pathways.
Exogenous hormone disruptors may:

- Inhibit the interaction between endogenous hormones and receptors : ED may
modify the binding of a hormone with its receptor, thereby affecting normal cellular
functions involving the hormone;
- Function as false hormones : ED similar to a hormone in structure may interact
directly with the hormone receptor, thereby causing unnecessary and abnormal
cellular functions;
- Alter the development of receptors and their functions : ED may activate or
suppress the development of a cell receptor and alter the normal hormonal
activities;
- Interact with hormones and alter the message issued by the hormone, thereby
altering cellular functions;
- Cause abnormalities or deficiencies due to the impairment of hormone production;
- Bind to hormone receptors and result in alteration in the transcription of messenger
RNA, followed by altered protein synthesis;
- Cause alteration in hormone synthesis , metabolism and transport as well as
effects mediated through changes in the hypothalamic-pituitary-gonadal axis,
which regulates, for example, steroid metabolism, thereby may cause hormone
abnormalities or deficiencies;
- Unnecessarily activate immune system , nervous system or any other hormone-
mediated function of the body;
- Have a secondary effect on development , reproduction, cancer development, the
immune system and the nervous system.

- Influences gene expression: even low level exposure may have an effect on gene

regulation, switching them in and out, which is the key in the course of fetal
development.

Summing up, an ED interferes with the synthesis, secretion, transport, binding, action,
or elimination of natural hormones in the body responsible for the maintenance of
homeostasis, reproduction, development and/or behavior.
Timms et al. report that two estrogenic chemicals in widespread use - the birth
control hormone, ethinylestradiol and the plastic molecule, bisphenol A - cause adverse
effects on the development of the prostate in fetal mice, at levels beneath common
exposures experienced by the American public. Their findings may provide important
insights into factors responsible for increases in prostate disease, including prostate
cancer. There are several evidences of adverse effects on wildlife. Some examples are
provided by IPCS (2002) and are given here:

- Exposure to chlorinated organic compounds (PCBs, dichlorodiphenyldichloro-

ethane or DDE) has adversely affected Baltic seals' reproductive and immune
systems, causing large population declines;