» Endocrine Disruptors »
Context - Some chemicals, both natural and man-made, can interfere with the hormonal system. They are called 'endocrine disruptors’. The most controversial issue is whether low level exposures to such chemicals can have adverse effects. Have endocrine disruptors affected wild life and our hormonal system? How much do we know so far?
1. What are Endocrine Disruptors (EDCs)?
The endocrine system is a set of glands and
the hormones they produce, which help guide the
development, growth, reproduction, and behaviour of animals and humans. Some hormones
are also released from parts of the body that are not glands, such as the stomach,
intestines or nerve cells, and act closer to
where they are released.
Some chemicals, both natural and man-made, can interfere with
endocrine glands and their
hormones or where the hormones act - the
target tissues. These chemicals are called
‘endocrine disruptors’ or ‘endocrine disrupting chemicals’
The presence of EDCs in our environment
raises concerns because:
- harmful effects have been observed on reproduction, growth and development
in certain species of wildlife,
- there are increases in some human reproductive disorders and some
cancers which could be related to
disturbance of the endocrine system, and
- adverse effects from some environmental chemicals known to act on the
endocrine system have been observed in laboratory animals.
2. How do EDCs act?
Endocrine disrupting chemicals (EDCs) can act
in a number of ways in different parts of the body, they may:
In many cases, it is not yet clear exactly how
EDCs act, even in some cases where a link has
been shown between EDC
exposure and an adverse effect.
What has been established mainly in the laboratory is:
EDCs during early development (e.g. in the
womb, during childhood) may cause permanent effects,
- exposure to EDCs during adult life may not show any significant or visible
- exposure to EDCs may produce varying effects depending upon the stage of
the life cycle or even the season, and
- unforeseen effects may occur in the target
tissues due to endocrine interactions.
The most controversial issue is whether low level
EDCs can have adverse effects. Some scientists
have found effects at low doses in laboratory
experiments, while others have not been able to corroborate these findings. Some say
that traditional testing methods are not robust enough to pick up low-dose effects.
These are important issues to resolve because of the presence of low levels of EDCs in
3. Do EDCs affect wildlife?
Certain endocrine disrupting chemicals
(EDCs) have affected reproduction in wildlife
populations. While some EDCs disappear
quickly from the natural environment, others persist and these have been the most
studied. Aquatic animals are particularly affected, especially carnivores, because
they are at the top of the ‘food chain’ where high levels of persistent chemicals
build up over time.
Some examples of effects in wildlife include:
- reduction in the population of Baltic
- eggshell thinning in birds of prey,
- decline in the alligator population in a polluted lake,
- reduction in frog populations,
- adverse effects on fish reproduction and development, and
- development of male sex organs in female marine animals such as whelks and
The effects in seals, birds and alligators are most likely due to
EDCs such as
and other pesticides that contain chlorine. The effects on fish appear to be caused by
oestrogens in the water flowing from sewage treatment works into rivers. The effects
on marine whelks and snails are due to the use of TBT –
tributyltin -in anti-fouling paints on boats and
Overall, the current evidence shows that certain effects seen in wildlife can be
attributed to EDCs. Most effects have been
observed in highly contaminated areas. Moreover, in many cases where wildlife has been
affected, it is still not known how the EDC is
working to bring about these effects.
4. Do EDCs affect human health?
At the moment there is no firm evidence that environmental endocrine disrupting
chemicals (EDCs) cause health problems at low
levels of exposure. However, the fact that high
levels of chemicals can impair human health through interferences with the
endocrine system, raises concerns about the
possible harmful effects of mixtures of so called endocrine disrupting chemicals, even
at low background-levels.
It has been suggested that in humans EDCs may
- reductions in male fertility,
- abnormalities in male reproductive organs,
- female reproductive diseases,
- earlier puberty, and
- declines in the numbers of males born.
Some EDCs may affect development of the
nervous system and the immune system.
As yet, there is no substantial evidence to show that
exposure to environmental
cancer, such as breast cancer, uterine cancer,
testicular cancer, prostate cancer or thyroid
However, it is plausible that EDC
exposure could be harmful to humans and could be a
reason for some of the increases in human disorders mentioned above, but more research
is needed to investigate this possibility.
5. What are potential sources of EDC exposure?
Most of the information on exposure to
endocrine disrupting chemicals (EDCs) has focused
on the presence of so-called ‘persistent organic pollutants’ in lakes, rivers and
seas. Exposure of humans can occur via contaminated food or water, combustion sources
– from industrial processes and burning of waste – and chemicals used in consumer
products. Humans are also exposed to natural oestrogens from plants that are found in
foods like soya.
There is some evidence that humans are vulnerable to endocrine disrupting
chemicals (EDCs) at high levels of
exposure. However, effects from exposure to
long-term and low-level EDCs have yet to be proven.
Evidence suggests that wildlife has been harmed by
EDCs, especially aquatic species in highly
Present knowledge of effects on wildlife and humans is insufficient. Further
research is needed to better understand this important issue.