Endocrine disruptor
Endocrine disruptors are exogenous substances that act like hormones in the endocrine system and disrupt the physiologic function of endogenous hormones. Studies have linked endocrine disruptors to adverse biological effects in animals, giving rise to concerns that low-level exposure might cause similar effects in human beings.[1]
Background
Since the publication of Rachel Carson’s Silent Spring (Carson, 1962), there has been increasing awareness that chemicals in the environment can exert profound and deleterious effects on wildlife populations and that human health is inextricably linked to the health of the environment. The last two decades, in particular, have witnessed a growing scientific concern, public debate, and media attention over the possible deleterious effects in humans and wildlife that may result from exposure to chemicals that have the potential to interfere with the endocrine system.
Endocrine disrupting compounds encompass a variety of chemical classes, including natural and synthetic hormones, plant constituents, pesticides, compounds used in the plastics industry and in consumer products, and other industrial by-products and pollutants. They are often pervasive and widely dispersed in the environment. Some are persistent, can be transported long distances across national boundaries, and have been found in virtually all regions of the world. Others are rapidly degraded in the environment or human body or may be present for only short periods of time but at critical periods of development.
One example of the devastating consequences of the exposure of developing animals, including humans, to endocrine disruptors is the case of the potent drug diethylstilbestrol (DES), a synthetic estrogen. Prior to its ban in the early 1970's, doctors mistakenly prescribed DES to as many as five million pregnant women to block spontaneous abortion and promote fetal growth. It was discovered after the children went through puberty that DES affected the development of the reproductive system and caused vaginal cancer.
The endocrine system
Endocrine systems are found in most varieties of animal life. The endocrine system is made up of glands, which secrete hormones, and receptors which detect and react to the hormones.
Hormones are released by glands and travel throughout the body, acting as chemical messengers. Hormones interface with cells that contain matching receptors in or on their surfaces. The hormone binds with the receptor, much like a key would fit into a lock.
Endocrine disruptors
Disruption of the endocrine system can occur in various ways. Some chemicals mimic endogenous hormones, perhaps at inappropriate times. Other endocrine disruptors block the effects of a hormone from certain receptors by blocking the receptors on a cell. Still others directly stimulate or inhibit the endocrine system and cause overproduction or underproduction of hormones. Medical interventions may manipulate the endocrine system for the betterment of a patient, and unwanted effects of such therapy can be interpreted as due to endocrine disruption, but the term usually refers to disruption by environmental contaminants. Substances in question are also known as Endocrine Disrupting Chemicals (EDCs) or Hormone Disrupting Chemicals (HDCs), and belong to the group of xenobiotics, foreign chemicals that affect a biological system.
Some of the most well-known examples of EDCs are 17-alpha ethinylestradiol (the contraceptive pill), Dioxins, PCBs, PAHs, furans, phenols and several pesticides (most prominent DDT and its derivatives). Substances with estrogenic side effects include the xenoestrogens. There is a long list of substances which may disrupt the endocrine system but have not yet been scientifically proven to do so.
In recent years, some scientists have proposed that chemicals might inadvertently be disrupting the endocrine system of humans and wildlife. A variety of chemicals have been found to disrupt the endocrine systems of animals in laboratory studies, including naturally occurring substances, and there is strong evidence that chemical exposure has been associated with adverse developmental and reproductive effects on fish and wildlife in particular locations. The relationship of human diseases of the endocrine system and exposure to environmental contaminants, however, is unproven. (Kavlock et al., 1996, EPA, 1997).
In addition to disruption of reproductive endocrinology, modulation of adrenal, thyroid and growth hormone function have also been described for various compounds in both humans and some animals, although the significance of these effects is unclear.
Legal approach
The Congress of the United States has improved the evaluation and regulation process of drugs and other chemicals. The Food Quality Protection Act of 1996 and the Safe Drinking Water Act of 1996 simultaneously provided the first legislative direction requiring the EPA to address endocrine disruption through establishment of a program for screening and testing of chemical substances.
In 1998 the EPA began the endocrine disruptor screening and testing program by establishment of a framework for priority setting, screening and testing more than 85,000 chemicals in commerce. As of this writing ((2006)) the EPA is continuing to validate test methods for this program and has issued a notice of intent to begin the initial priority setting process. [citation needed] The basic concept behind the program is that prioritization will be based on existing information about chemical uses, production volume, structure-activity and toxicity. Screening is done by use of in vitro test systems (by examining, for instance, if an agent interacts with the estrogen receptor or the androgen receptor) and via the use of in animal models, such as development of tadpoles and uterine growth in prepubertal rodents. Full scale testing will examine effects not only in mammals (rats) but also in a number of other species (frogs, fish, birds and invertebrates).
The multitude of possible endocrine disruptors are technically regulated in the United States by many laws, including: the Toxic Substances Control Act, the Federal Insecticide, Fungicide, and Rodenticide Act, the Food, Drug and Cosmetic Act, the Clean Water, the Safe Drinking Water Act, and the Clean Air Act.
See also
External links
- List of suspected or possible endocrine disruptors
- Global assessment of the state-of-the-science of endocrine disruptors published in 2002 by the World Health Organisation (WHO).
- Scientific Facts on Endocrine Disruptors, a peer-reviewed summary of the above WHO assessment, by GreenFacts.
- The NSF sponsored Environmental Signaling Network's website
- The EU strategy on EDCs
- The US EPA (strategy) on EDCs
- Synopses of new scientific findings about endocrine disruption
- Journalist's report on endocrine disruptors (OnEarth Magazine, Winter 2006)
- PBS Frontline Interview of Dr. Theo Colborn by Doug Hamilton, 1998.
- Hormonal Chaos: The Scientific and Social Origins of the Environmental Endocrine Hypothesis by Sheldon Krimsky
- "Sex-change chemicals in Potomac", BBC News, last updated 18 January 2007.
References
- ^ "Executive Summary" (PDF). Global assessment of the state-of-the-science of endocrine disruptors. International Programme on Chemical Safety, World Health Organization. 2002. Retrieved 2007-02-28.
An endocrine disruptor is an exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or (sub)populations.
Colborn, Theo; Dianne Dumanoski; and John Peterson Myers. Our stolen future : are we threatening our fertility, intelligence, and survival? : a scientific detective story. New York : Dutton, 1996. 306 p. ISBN 0452274141