What are endocrine disruptors?
"An endocrine disruptor is an exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or (sub)populations" 'Community strategy for endocrine disruptors'
Mechanisms of disruption
Some chemicals can act on the endocrine system to disturb the homeostatic mechanisms of the body or to initiate processes at abnormal times in the life cycle. The chemicals can exert their effects through a number of different mechanisms:
Up to now, because of a series of observations in both humans and wildlife the spotlight has focused on disruption to those hormones that play a major part in the control of reproduction and development. The main area of concern has been the steroid hormones produced by the gonads which, in conjunction with some other hormones (particularly those produced by the pituitary), control processes such as reproduction and sexual behaviour, fetal differentiation and development, and maturation. They also influence the immune system and general metabolism. The main sex steroids are:
Oestrogens: a group of chemicals of similar structure mainly responsible for female sexual development and reproduction. They are produced mainly by the ovaries but also by the adrenal glands and adipose (fat) tissue. The principal human oestrogen is 17beta-oestradiol.
Androgens: chemicals responsible for the development and maintenance of the male sexual characteristics. They are structurally similar to oestrogens ; indeed, oestrogens are produced in the body from androgenic precursors. Testosterone, produced mainly by the testes, is the principal human androgen.
More recently, research has indicated that some chemicals may disrupt thyroid function, with concerns focusing particularly on the role of the thyroid in the developmental process.
There is some evidence that known endocrine disruptors may affect the immune system and may also have some neurotoxicity although the mechanisms by which these effects may occur have not been elucidated.
What do we know about endocrine disruptors ?
The main evidence suggesting that exposure to environmental chemicals can lead to disruption of endocrine function comes from changes seen in a number of wildlife species. Effects suggested as being related to endocrine disruption have been reported in molluscs, crustacea, fish, reptiles, birds and mammals in various parts of the world.
There is also some limited evidence in humans that adverse endocrine-mediated effects have followed either intentional or accidental exposure to high levels of particular chemicals. The clearest example of an endocrine disruptor in humans is diethylstilbestrol (DES), a synthetic oestrogen prescribed in the 1950s and 1960s to five million pregnant women for the prevention of spontaneous abortion. It was found that some of the children who had been exposed in the uterus had developmental abnormalities, and that some of the girls developed an unusual form of vaginal cancer when they reached puberty. As a consequence, DES was banned in the 1970s. In addition, a number of adverse changes have been suggested to have occurred in a population living near a chemical plant in Seveso, Italy as a result of the accidental release of the chemical dioxin, a suspected endocrine disruptor.
Chemicals with hormonal activity, i.e. potential endocrine disruptors, include :
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