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What areas might they affect?

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 deformities.

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 sexual behaviour.

Human studies

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 be important.
  • 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

Wildlife

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 include:

  • 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 chemicals
  • 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, USA.

Other adverse changes in wildlife species that have been suggested, but not proven, to relate to exposure to pollutants, include:

  • Reproductive impairment or abnormalities in whales, seals and polar bears.
  • Impaired immune function in seals.
  • Skeletal deformities in frogs.