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Fact Sheet
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National Strategy

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Endocrine Disrupting Substances
in the Environment

	Endocrine Systems
	Endocrine Disruption
	What Type of Substances Disrupt Endocrine Systems?
	Effects of Endocrine Disruptors
	Research on Endocrine Disruptors
	Environment Canada: Leader in Addressing the Endocrine Disruptor Issue

Endocrine systems are complex mechanisms, coordinating and regulating internal communication among cells. Endocrine systems release hormones that act as chemical messengers. The messengers interact with receptors in cells to trigger responses and prompt normal biological functions such as growth, embryonic development and reproduction.

Scientists know that endocrine systems can be adversely affected by a wide variety of substances. A substance can interfere with the normal communication between the messenger and the receptor in the cell, so that the chemical message is not interpreted properly. Even very subtle effects on the endocrine system can result in changes in growth, development, reproduction or behaviour that can affect the organism itself, or the next generation. The specific mechanisms by which substances disrupt the endocrine systems are very complex, and not yet completely understood.

Substances can interact with endocrine systems and cause a disruption to normal functions in several ways.

• They can act like a natural hormone and bind to a receptor. This causes a similar response by the cell, known as an agonist response.
• They can bind to a receptor and prevent a normal response, known as an antagonistic response.
• A substance can interfere with the way natural hormones and receptors are synthesized or controlled.

Public attention has been drawn to substances that mimic or block the feminizing effects of natural female sex hormones: for example, estrogens such as 17ß-estradiol. This is only part of the story, however. Substances can also affect male sex hormones or other endocrine systems that influence growth, development and behavior.

Given the complexity of endocrine systems, it is not surprising that the range of substances thought to cause endocrine disruption is wide and varied, and includes both natural and manufactured (synthetic) chemicals.

Industrial, agricultural and municipal wastes can expose organisms in the environment to unusually high concentrations of natural substances such as sex hormones, or phytoestrogens. Manufactured chemicals may be released intentionally - pesticides, for example; as by-products of industrial processes and waste disposal - dioxins or PCBs; or as discharges from industrial or municipal treatment systems - alkylphenols. The wide variety of sources and substances presents an enormous challenge to environmental managers in industry and government.

Canadian scientists are among the world’s leaders in studying reproduction and developmental effects on wildlife populations. Their research, particularly in the Great Lakes, has been vital in bringing international attention to the issue.

Recently, scientists have seen a variety of endocrine-related effects in fish and wildlife in many parts of the world, including Canada. Fortunately, in many of these cases, action has been taken to reduce exposure, and at least some wildlife populations have recovered.

Until recently, much of the research has focused on persistent, bioaccumulating, toxic substances (PBTs). These are substances still widely distributed in the environment and found in birds, fish and mammals, even though their manufacture and use have been reduced or banned completely. For instance, many persistent, bioaccumulating toxic substances (such as dioxins, PCBs and organochlorine pesticides) are a concern in ecosystems across the country.

Scientists have now focused attention on a number of substances not so highly persistent, but still widespread in the environment. Even at relatively low levels, these can affect growth, reproduction and development of organisms in Canadian ecosystems. They include substances in industrial and municipal effluents and in agricultural runoff, natural estrogens in plants (phytoestrogens), and specific chemicals such as alkylphenols and tributyltin and those found in some pesticides.

Environment Canada scientists continue to study effects on reproduction and development as an important means to assess endocrine-disrupting substances. They are also gaining a better understanding of other types of biological impacts. To help in this work, scientists are re-examining and adapting many of the tools and approaches used in the past so that they can detect subtle, but critical impacts on the endocrine systems of wild populations of fish and wildlife.

Endocrine disrupting substances (EDS) are a complex problem that requires a co-ordinated response from government agencies, universities, industry and the public. Environment Canada has made EDS a research priority to produce the knowledge necessary for informed policy and regulatory decisions.

In partnership with Health Canada, Environment Canada manages the Toxic Substances Research Initiative, which includes support for research on EDS. In addition, Environment Canada has included research on EDS in each of the major Regional Ecosystem Initiatives, and has established a national multidisciplinary research program in collaboration with other government agencies, universities and industry.

To address this emerging global issue, Environment Canada is working with international organizations such as the Organization for Economic Cooperation and Development (OECD), United Nations Environment Programme (UNEP) and others.

Research on this question will produce sound scientific assessments of the potential impacts of EDS on the Canadian environment. Such assessments are essential for the development and implementation of effective regulations and controls.

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