Endocrine
Disruptors
What is the endocrine system?
The endocrine system is
comprised of a number of glands in the body that do not have ducts and other
similar structures. The endocrine system include the ovaries; the testes; the
thyroid, parathyroid, adrenal, and pituitary glands; the pineal body; the
pancreas; as well as cells releasing hormones found in the gastrointestinal tract,
kidney, heart and placenta. What distinguishes endocrine glands from other
glands is that endocrine glands secrete certain chemicals called hormones and
other glands produce other chemicals or fluids; for example, lacrimal glands
secrete tears, salivary glands produce saliva, and sweat glands produce sweat.
Hormones (so-called
"chemical messengers") produced by endocrine glands enter the
capillaries (and lymph vessels) of the blood circulatory system. They travel
through the bloodstream to specific "receptors" in target organs or
systems where they can trigger their biological effects.
The endocrine system is
important because it coordinates and regulates many essential body functions
such as:
·
Growth and maturation.
·
Behaviour.
·
Reproduction and embryo development.
·
Production, use and storage of energy.
·
Balance and maintenance of water and salt (electrolytes) in the
body.
·
Reaction to stimuli (e.g., fright, excitement).
What are some examples of hormones?
Some examples of
hormones secreted by the endocrine system are:
·
ACTH (adrenocorticotrophic hormone) - produced by the pituitary
gland to influence the release of corticosteroid hormones from the adrenal
glands.
·
ADH (anti-diuretic hormone, vasopressin) - produced by the
pituitary gland to stimulate water reabsorption by the kidney tubules.
·
Adrenaline (epinephrine) and noradrenaline (norepinephrine) - two
hormones formed in the adrenal gland that help the body to react (e.g., flight
or fight, body defense mechanisms) under stressful conditions (they can
increase the heart rate, blood pressure, blood sugar levels, blood clotting
rate).
·
Estrogen - a female sex hormone produced by the ovaries.
·
Testosterone - a male sex hormone produced by the testes, ovaries,
and adrenal glands.
·
Insulin - secreted by the pancreas and regulates the storage and
use of carbohydrates in the body.
·
Thyroid hormone - produced in the thyroid and influences the
function of virtually every cell in the body (growth, development and
metabolism).
Why should we be concerned about the endocrine system?
Concerns have been
raised over the possible roles of chemicals since many of the complex
activities of the human body are controlled by the endocrine system. In
addition, endocrine systems are present in most animals such as other mammals,
non-mammalian vertebrates (e.g., birds, fish, amphibians, and reptiles) and
invertebrates (e.g., insects, spiders, snails, crabs, lobsters, etc.).
The endocrine system
controls many functions of the body, both immediate reactions and life-long
functions. The hormones stabilize or balance functions in the normal body. In
turn, the levels of hormones produced in the body are influenced by stimuli the
body receives and are regulated by complex biological feedback systems. Any
disruption to this balance can cause changes in the reproduction, development,
growth, or behaviour that can affect that animal or human or their offspring or
children.
Certain substances, both
naturally-occurring and man-made, can affect the endocrine system. Some
chemicals in plants (phytoestrogens) have estrogen-like effects. Certain drugs
and environmental pollutants can either mimic or block actions of some
hormones. When there is interference with the normal communication between the
"messenger" hormone and the cell receptors, the chemical message is
misinterpreted and an abnormal response is generated in the body.
Understanding the role
of the endocrine system (and the hormones that they produce) in the normal
functioning of the body gives us some indication of the types of problems that
might occur when proper endocrine function is disrupted. Many of these organs
influence each other's activities, producing very complex interactions and
making the effect of the disruptors exceedingly difficult to identify or
predict.
How can the normal communication of the endocrine system be
disrupted?
Substances can disrupt
the normal function of endocrine systems in three different ways:
1. They can mimic a natural
hormone and lock onto a receptor within the cell. The disruptor may give a
signal stronger than the natural hormone, or a signal that occurs at the
"wrong" time.
2. They can bind to a
receptor within a cell and thus prevent the correct hormone from binding. The
normal signal then fails to occur and the body fails to respond properly.
3. The disruptors can
interfere or block the way natural hormones and receptors are made or
controlled. This interference or blockage may occur only if relatively large
doses of the substance are present.
If the endocrine
disruptor stimulates or inhibits the endocrine system, then increased or
decreased amounts of hormone may be produced. In some cases, even very small
amounts of a disruptor may have a detectable effect. In addition, small amounts
of different endocrine disruptor chemicals may have a cumulative effect.
In some cases the by-products of the chemicals may have greater harmful
effect than the parent chemical.
What kinds of substances can be endocrine disruptors?
The number of substances
believed to act as endocrine disruptors is wide and varied, including both
natural and synthetic materials. Concern arises because potential endocrine
disruptors may be present in the environment at very low levels but still may
be able to cause effects.
Many plants and animals
produce substances that can have endocrine effects. Some of the substances are
toxic but certain effects have proven beneficial in some circumstances. For
example, some "endocrine disruptors" have been used to control
fertility (birth control pills), to treat cancer (corticosteroids), and to
treat psychiatric disorders and other medical conditions. Natural substances,
such as sex hormones or phytoestrogens (plant chemicals having estrogen-like
effects), can become concentrated in industrial, agricultural and municipal
wastes. Exposure to these wastes may produce reactions in humans, wildlife,
fish or birds.
Endocrine disruptors are
found also in synthetic chemicals used as industrial solvents, lubricants, and
their byproducts. These include polychlorinated biphenyls (PCBs),
polybrominated biphenyls (PBBs), and dixons. Other examples of endocrine
disruptors include bisphenol A (BPA) from plastics,
dichlorodiphenyltrichloroethane (DDT) from pesticides, vinclozolin from fungizides,
and diethylstilbestrol (DES) from pharmaceutical agents. Certain metals such as
cadmium, mercury, arsenic, lead, manganese, and zinc also disrupt endocrine
systems.
Many consumer products
like cosmetics, personal care products and cleaners, (especially the fragranced
products), contain complex mixtures of chemicals that have endocrine disruption
properties.
Where are endocrine disruptors often found and what are some
examples?
Synthetic chemicals
suspected as endocrine disruptors may reach humans and animals in a variety of
ways. Some, such as pesticides, are released intentionally. Others are
by-products of industrial processes and waste disposal - these include dioxins
and PCBs - or are discharged from industrial or municipal treatment systems (See
Table below)
Sources, category (type)
and examples of substances that have been reported as potential endocrine
disruptors include:
Sources
|
Category
|
Substances
|
Incineration, landfill
|
Polychlorinated
Compounds (from industrial production or by-products of mostly banned
substances)
|
Polychlorinated
dioxins, polychlorinated biphenyls
|
Agricultural runoff /
Atmospheric transport
|
Organochlorine
Pesticides (found in insecticides, many now phased out)
|
DDT, dieldrin, lindane
|
Agricultural runoff
|
Pesticides currently
in use
|
Atrazine, trifluralin,
permethrin
|
Harbours
|
Organotins (found in
antifoulants used to paint the fulls of ships)
|
Tributyltin
|
Industrial and
municipal effluents
|
Alkylphenols
(Surfactants - certain kinds of detergents used for removing oil - and their
metabolites)
|
Nonylphenol
|
Industrial effluent
|
Phthalates (found in
placticizers)
|
Dibutyl phthalate,
butylbenzyl phthalate
|
Municipal effluent
Agricultural
runoff
|
Natural Hormones
(Produced naturally by animals); synthetic steroids (found in contraceptives)
|
Estradiol, estrone,
and testosterone; ethynyl estradiol
|
Pulp mill effluents
|
Phytoestrogens (found
in plant material)
|
Isoflavones, lignans,
coumestans
|
Consumer products
|
Cosmetics, personal
care products, cleaners
|
Parabens, phthalates,
glycol ethers, fragrances, cyclosiloxanes
|
(Source: Endocrine
Disruptors Update, 2000, Environment Canada, and Endocrine Disruptors and
Asthma-Associated Chemicals in Consumer Products. R.E. Dodson, M. Nishioka,
L.J. Standley, et all. (2012). « Environment Health Perspective ». Vol. 120,
No. 7, pages 935-943)
What are some possible health effects from exposure to endocrine
disruptors?
The most prominent and
well documented health concerns from exposure to endocrine disruptors are
reproductive and developmental effects. Some of the disorders that have been
seen in animal studies include oligospermia (low sperm count), testicular
cancer, and prostate hyperplasia in adult males; vaginal adenocarcinoma,
disorders of ovulation, breast cancer, and uterine fibroids in adult females.
Disruption to thyroid functions, obesity, bone metabolism and diabetes are also
linked to exposure endocrine disruptors.
Outcomes from
occupational exposure of endocrine disruptors have been documented in limited
studies. The table below summarizes some of these studies:
Endocrine Disruptors
|
Occupation
|
Effect
|
Reference
|
Pthalate
|
Exposure of mothers
during pregnancy; occupation not specified
|
Hypospadias
(urogenital congenital anomalies affecting baby boys)
|
1, 5
|
Alkylphenolic
compounds
Phthalates PCB Dioxins |
Motor vehicle
mechanics Paper makers Painters Forestry and logging workers Furniture manufacture workers |
Male breast cancer
|
2
|
BPA
|
Male factory workers
|
Male sexual
dysfunction
|
3
|
Phthalates
|
Plastic workers
|
6-fold increased risk
of testicular cancer
2 times increased risk of breast cancer among the women working in plastic and rubber industry |
4, 6
|
1. Endocrine Disruptors in
the Workplace, Hair Spray, Folate Supplementation, and Risk of Hypospadias:
Case-Control Study. G. Ormond et al. Environmental Health Perspectives. Vol.
117, no. 2 (February 2009)
2. Occupation and
occupational exposure to endocrine disrupting chemicals in male breast cancer:
a case-control study in Europe. S. Villeneuve et al. Occupational And
Environmental Medicine. Vol. 67 (2010), p. 837-844
3. Occupational exposure to
bisphenol-A (BPA) and the risk of self-reported male sexual dysfunction. D. Li
et al. Human Reproduction. Vol. 25, no. 2 (February 2010), p. 51-27
4. The effects of metals as
endocrine disruptors. I. Iavicoli et al. Journal of Toxicological Environmental
Health. Vol. 12, no. 3 (March 2009), p. 206-23
5. Effect of endocrine
disruptor pesticides: A Review. W. Mnif et al. International Journal of
Environmental Research and Public Health. Vol. 8, no. 6 (June 2011), p. 2265-2303
6. Breast cancer risk in
relation to occupations with exposure to carcinogens and endocrine disruptors:
a Canadian case-control study. J.T. Brophy et al. Environmental Health. Vol.
11:87 (November 2012
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