What areas might
In wildlife, endocrine disruptors have been clearly shown to cause
abnormalities and impaired reproductive performance in some species,
and to be associated with changes in immunity and behaviour and skeletal
In humans, endocrine disruptors have been suggested as being responsible
for apparent changes seen in human health patterns over recent decades.
These include declining sperm counts in some geographical regions,
increased incidences in numbers of male children born with genital
malformations, and increases in incidences of certain types of cancer
that are known to be sensitive to hormones. More controversially,
links have been suggested with impairment in neural development and
A number of observations of adverse effects have been made in which
endocrine disruptors could play a role, including:
- Declining sperm counts: Some studies in certain western
countries have reported decreases in sperm numbers over the last
50 years. However, other studies in different regions have failed
to detect such changes.
- Congenital malformations in children: In recent years
there has been an increase in the incidence of hypospadias (a
congenital abnormality of the urethra in the penis) and cryptorchidism
(undescended testes) in humans. However, no causal association
with chemical exposure has yet been established.
- Cancer: Increased incidences of hormone-related cancers
of both women (breast & ovary) and males (testes & prostate)
have been observed in the West and in countries adopting Western
lifestyles. Again a causal association with chemicals has not
been shown, and numerous other lifestyle factors are known to
- Retarded sexual development: A few reports have been
published suggesting that adolescents in polluted areas may take
longer to reach puberty. However, the potential mode of action
of any such effect is unknown.
- Retarded neurobehavioural development: Studies in Denmark
and USA have suggested that children born in polluted areas have
some impairment of memory and intelligence.
No clear relationship has been established between adverse health
effects and exposure to endocrine disruptors. More research is needed
on a range of topics in order to understand the potential effects
of endocrine disruption including :
- Large-scale human epidemiology studies relating specific health
effects with exposure to endocrine disruptors
- Basic research into mechanisms of endocrine disruption
- Research into the effects of different types of exposure in the
environment which may lead to unexpected effects e.g. mixtures of
endocrine disruptors, long-term low dose exposure
- Exposure at different ages to see if humans are vulnerable to
endocrine disruptors at any particular stage of life
- Exposure of individuals who may be especially susceptible
Unlike the situation for humans, the evidence for endocrine
disruption occurring in some wildlife species is much more
compelling. This may reflect a greater level of exposure for
some wildlife populations or it may be due to differences
in susceptibility between humans and animals.
Some well established examples of adverse effects in wildlife
- Historically, egg-thinning with resultant poor
reproductive success was noted in some bird species exposed
to high levels of DDT. Disturbed nesting behaviour and
beak and skeletal abnormalities have also been noted in
other species exposed to high levels of environmental
- Imposex (male genitalia in female) in marine
molluscs; known to be due to exposure to antifouling paints
on ships that contain organotin compounds
- Feminisation (development of female gonadal tissue
and production of an egg yolk protein, vitellogenin) in
male fresh water fish in rivers or lakes exposed to treated
sewage effluents, in many parts of Europe ; similar changes
also being noted in estuaries.
- Impaired reproductive development, and abnormalities
of the reproductive system in alligators in a polluted
lake in Florida USA, and in turtles in the Great Lakes,
Other adverse changes in wildlife species that have been
suggested, but not proven, to relate to exposure to pollutants,
- Reproductive impairment or abnormalities in whales, seals
and polar bears.
- Impaired immune function in seals.
- Skeletal deformities in frogs.