The human body is immensely
complex, and our knowledge and awareness of its complexity continues to grow.
One of the most disquieting
discoveries in recent years concerns the possible roles of environmental chemicals
on endocrine systems. Endocrine systems are present not only in humans but in
"higher" animals such as birds, fish, and mammals. Endocrine systems
coordinate and regulate many important body functions such as growth and maturation,
behaviour, reproduction and embryo development. They do this by making and releasing
hormones which act as "chemical messengers." Certain tissues in the
body have very specific receptors for the hormones. By interacting with these
receptors, the hormones trigger responses.
Several organs within the human
body make up the endocrine system. These organs include the ovary, testes, thyroid
and adrenal glands, pancreas, pituitary, as well as the placenta, liver, kidneys
and cells of the gastrointestinal tract. Understanding the role of these organs
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. Moreover,
many of these organs influence each others activities, producing very
complex interactions and making the effect of disruptors exceedingly difficult
to identify or predict.
Among the hormones ("chemical
messengers") operating within the endocrine system are estrogen (a female
sex hormone produced by the ovaries); thyroid hormone (influencing the function
of virtually every cell in the body); and ACTH (produced by the pituitary gland
to influence the release of adrenalin from the adrenal gland).
Endocrine systems can be affected
by certain substances outside of the body, both naturally-occurring and artificial.
By interfering with the normal communication between the messenger and the cell
receptors, the chemical message is misinterpreted, generating abnormal response(s)
in the body.
Substances can disrupt the
normal function of endocrine systems in three different ways.
One, 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 at the wrong time. In some cases
even very small amounts of a disruptor may have a detectable effect.
Two, they can bind to a receptor
within a cell, and prevent the correct hormone from binding. The normal signal
then fails to occur and the body fails to respond properly.
Three, disruptors can interfere
with 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.
Wide and varied distribution
of suspected substances
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, unrecognized but possibly able to cause effects
at low concentrations.
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 and to treat cancer,
psychiatric disorders and other medical conditions. Natural substances, such
as sex hormones or phytoestrogens, can become concentrated in industrial, agricultural
and municipal wastes. Exposure to these wastes may produce reactions in humans,
wildlife, fish or birds.
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 1)
SOURCE: ENVIRONMENT CANADA
"Endocrine Disrupting Substances in the Environment", 1999
Canada is considered a world
leader in studying the distribution and effects of endocrine disruptors on humans
and wildlife. While much research has been focused on persistent substances,
such as PCBs and DDT, a shift has been made towards substances not so
highly persistent but widespread in the environment. These include materials
found in industrial and municipal effluents, agricultural runoff, natural estrogens
in plants, and specific chemicals such as alkylphenols, tributyltin and pesticide
A reliable source for
chemical data and regulatory information
ChemAdvisor is a database of
over 100,000 chemicals, which includes current regulatory and advisory data
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Potential endocrine disruptor
substances identified by organizations such as the U.S. Environmental Protection
Agency and Japans Environment Agency are identified in the The Chemical
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