What is an endocrine disruptor?
The endocrine system is composed of all the glands producing hormones, and receptors of hormones in the body. It plays a very important role in the development of embryos and in reproduction. It also plays a role in the regulation of metabolism in general.
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’ (EDCs).
Why this growing concern about endocrine disruption and its relation to some chemicals?
Negative impacts on reproduction and development have been observed, and there
is good evidence that wildlife populations can be affected. Over the last two
decades, there has been evidence of increases in many endocrine-related
disorders in humans.
The notion that exposure to some chemicals contributes to endocrine disorders
in humans and wildlife is supported by extensive laboratory studies. Exposure
during critical periods of development can cause irreversible and delayed
effects that do not become evident until later in life. Nevertheless, there are
significant difficulties in linking specific chemicals to endocrine disruption,
especially when they do not stay for long periods in the body.
What are the main effects of endocrine disruptors that are considered?
There are four main groups of effects considered:
Impact on human reproductive health.
This is one of the key topics of human
health effects of endocrine
disruptors. There are effects on both male and female, ranging from
incomplete sexual development to fertility problems.
cancers in humans
A number of cancers in humans are influenced by hormones, and in those
cases, endocrine disruptors can have a role
in their development. However, for a number of hormonal cancers there is a lack
of information on the potential role of endocrine disrupters.
Impact on development and
metabolism in humans
Endocrine disruptors can have effects on a
number of hormone systems, including the
thyroid system. They can also have
effects on immune system functions. Some
evidence points to a link between chemical exposure and the ongoing
Impact on wildlife
The main endpoints that are considered when looking at animals have to
do with reproduction and development. Impacts have been observed on many groups
of animals, from invertebrates to mammals.
What makes endocrine disruptive chemicals (EDCs) hard to assess?
Many chemicals are capable of interacting with steroid receptors (“endocrine
activity”), but whether this always leads to adverse effects is often
Endocrine disrupting chemicals can have effects at doses much lower than what
is usually used in toxicological tests, and the current risk assessment methods
might need to be adapted.
It is put into question whether thresholds exists for endocrine disruptors, which is a dose below which
there is no effect. For example, since there is already a certain level of
natural estrogen in the body, it can be
argued that any amount of externally added estrogenic agent could have an
effect, without any threshold.
This introduces considerable uncertainties, with the likelihood of overlooking
harmful effects in humans and wildlife. Until better tests become available,
hazard and risk identification has to rely also on epidemiological
What is the “State of the Science” for various families of chemical substances?
Here is a summary of the main groups of chemicals that are considered for
their endocrine disrupting potential.
- Bisphenol A. Its effects are multifaceted because it can interfere with
estrogen, progesterone, and
thyroid hormones. Exposure
during organ development has been demonstrated to produce irreversible adverse
effects on reproductive organs.
- Phthlates. There is good evidence that they can cause developmental problems in male fetuses by interfering with
testosterone synthesis. Some
benzyl-butyl-phthalate (BBP) and di-ethyl-hexyl-phthalate (DEHP)) also
interact with estrogen receptors. Effects on wildlife remain largely
- Parabens. Epidemiological evidence in humans is very
limited. There is some evidence of an effect on the density of breast
tissue, but no evidence that it may increase breast
- PCBs (polychloro biphenyls). PCB exposure has been
associated with an increased risk of breast cancer and of other
cancers. They also have an
effect on neural development. Effects have also been found in animal models.
- Dioxins (PCDDs and PCDFs). These have some of the
effects of PCBs. They are linked to early menopause, breast cancer and
- Polybrominated biphenylethers (used notably as flame
retardants). Exposure during early development can have important
effects on neural development. There are also a number of potential effects
- Perfluorinated compounds (PFCs). There is evidence
that these chemicals interfere with thyroid
hormone conversion. There also is
an association with increased
cholesterol levels, indicating that
they could create metabolic disorders.
The effects of PFCs on wildlife have yet to be determined.
Various families of pesticides are considered:
- Dicarboxamides. Experimental evidence, but no
direct evidence of exposure-disease associations exists yet for
either humans or wildlife.
- Azole fungicides (including triazoles and
imidazoles). Effects on the
babies of mothers exposed to these pesticides during pregnancy were proven, but
no link to a specific compound.
- Triazines (atrazine and simazine are among
the most widely used herbicides). Wild frogs collected from
contaminated sites showed sexual development problems. Effects in
mammals remain largely undetermined.
- Methylmercury has multiple modes of action
relating to the endocrine
- Lead release
of the thyroid hormone TSH by the pituitary gland.
- Cadmium, a weak link is made by some
of occupational exposure and breast cancer. There is also some
evidence that cadmium may have other effects on male and female
health. Its effects in wildlife are understudied.
- Other chemicals. Multiple new chemicals and groups of
chemicals have come to the fore over the last decade as being of potential
concern. In the case of sunscreen UV filters and of
artificial musks, which are present in many cosmetic
and personal care products, there is not yet direct evidence on humans, but
some evidence do exist for some of them from studies conducted in animals
and in vitro.
What are the main recommendations of the report?
The six recommendations made in this report to the European Commission
- Implement validated and internationally recognised test methods in the
testing and information requirements for regulation,
- Develop further guidance documents for the interpretation of test
- Consider the creation of a separate regulatory class
“Endocrine Disruptor” (ED);
- Develop weight-of-evidence procedures that deal with the available
evidence by weighing the criteria “adversity” and “mode of action” in
parallel, but not by applying these criteria sequentially to exclude
substances from the assessment;
- Abandon “potency” as the only criterion, and consider potency
together with other criteria such as toxicity, specificity, severity and
irreversibility, in a weight-of-evidence approach.
- Create regulatory categories that stimulate the generation of the
necessary data, including test methods that are not validated, beyond the
OECD Conceptual Framework for Endocrine Disrupter Testing.