effects of endocrine disrupters
Impaired reproduction and development causally linked
to endocrine-disrupting chemicals are well documented
in a number of species and have caused local or regional
population changes. These include:
||Masculinisation (imposex) in female
marine snails by tributyltin (TBT), a biocide
used in anti-fouling paints. The dogwhelk is particularly
sensitive and imposex has resulted in decline
or extinction of local populations worldwide,
including in coastal areas all over Europe and
in the open North Sea.
||DDE-induced egg-shell thinning in birds
is probably the best example of reproductive impairment
causing severe population declines in a number
of raptor species in Europe and North America.
Developmental exposure to the DDT complex has
been firmly linked to the induction of ovotestis
in male Western gulls.
||EDCs have adversely affected a variety of fish
species. In the vicinity of certain sources (e.g.
effluents of water-treatment plants) and in the
most contaminated areas this exposure is causally
linked with effects on reproductive organs, which
could have implications for fish populations.
Turtles can also be affected in the same way.
||In mammals, the best evidence comes from the
field studies on Baltic grey and ringed seals
and from the semi-field studies on Wadden Sea
harbour seals, where both reproduction and immune
functions have been impaired by PCBs in the food
chain. Other mammals affected include the polar
bear, mink, rabbit, and guinea pig.
||Distorted sex-organ development and function
in alligators has been connected
with a major pesticide spill into a lake in Florida,
USA. The oestrogenic/antiandrogenic effects observed
in this reptile have been causally linked in experimental
studies with alligator eggs to the DDT complex.
For terrestrial (land-living) wildlife, including
aquatic mammals, exposure is primarily expected to
be of dietary origin. The situation is different for
aquatic wildlife where direct uptake of dissolved
chemicals from the water is a significant route to
Effects on humans
For humans, possible pathways of exposure to endocrine
disrupters include direct exposure via the workplace
or via consumer products such as food, certain plastics,
paints, detergents and cosmetics, as well as indirect
exposure via the environment (air, water, soil). In
general, the vulnerability of a given species will
depend on the intrinsic properties of the chemical,
on the magnitude, duration, frequency and means of
exposure and on the way in which a given species can
absorb, distribute, transform and eliminate substances.
It will also depend on the sensitivity of specific
organs at different stages of development.
|Estrogen receptor: From H.M.
Berman, J. Westbrook, Z. Feng, G. Gilliland, T.N.
Bhat, H. Weissig, I.N. Shindyalov, P.E. Bourne:
Protein Data Bank. Nucleic Acids Research,
28 pp. 235-242 (2000)
The endocrine-disrupter hypothesis was originally
formulated for xenoestrogens, i.e. chemicals, which
affect the estrogen-signalling pathway. The greatest
attention to endocrine disruption has focused on estrogenic
effects, but a clear cause-effect relationship has
not yet been established. However, it is now becoming
generally accepted that compounds of various types
can interact with different components in several
cell-regulatory systems, including the steroid and
thyroid hormone receptor families. Aside from the
drug DES (synthetic oestrogen), environmental oestrogens
have never been proved to cause human health problems,
so we can only speculate on possible human health
effects documented from animal studies.
EDCs which act via receptors of the steroid receptor
super-family can have effects on many organs of the
body. Steroid receptors for oestrogens, androgens,
adrenocorticoid and thyroid hormones are found in
practically all cells of the body. The functions of
the brain, the cardiovascular, the skeletal and the
urogenital systems are regulated by these hormones
and can therefore be affected by EDCs. An EDC with
a defined action in one organ (e.g. oestrogenic activity)
can exert similar or no oestrogenic or even antagonistic
effects in other organs.
Potential human health effects
caused by EDCs:
- For women:
Breast and reproductive organ tissue cancers, fibrocystic
disease of the breast, polycystic ovarian syndrome,
endometriosis, uterine fibroids and pelvic inflammatory
diseases. Declining sex ratio (fewer women)
- For men:
Poor semen quality (low sperm counts, low ejaculate
volume, high number of abnormal sperm, low number
of motile sperm), testicular cancer, malformed reproductive
tissue (undescended testes, small penis size), prostate
disease and other recognised abnormalities of male
Other potential effects: impaired behavioural/mental,
immune and thyroid function in developing children;
osteoporosis, precocious puberty.