||What Does Endocrine Disruption Mean?
Our understanding of how endocrine disrupting chemicals (EDCs) interfere with hormones and other chemical signalers is growing rapidly. Once thought to primarily interfere with hormone receptors, we now know the culprits impact a wide range of signaling processes. They can interfere with hormone binding, transport, and production; gene expression; and a host of other cell regulatory mechanisms. These disruptions may affect the endocrine, immune and neural systems and may lead to developmental, reproductive, metabolic, brain, and behavior problems.
There is no doubt that the physical world, and a good portion of its human and animal life, is exposed to and contaminated with EDCs. Some are natural plant compounds called phytochemicals. Others are synthetic versions mostly released during human activities.
Still, no simple conclusions about effects can be drawn. Even though exposure is widespread, we still don’t know the full extent of health risks and problems associated with EDCs.
Clearly, wildlife studies, laboratory experiments, and human experiences do provide evidence of health effects and intergenerational impacts from exposure to high concentrations of these ubiquitous substances. Male feminization, lower fertility, and other reproductive and developmental problems occur in a host of invertebrate species and wild fish, amphibians, reptiles, birds, and mammals.
Human impacts could be likely for certain individuals or populations in specific regions of the world. Attention has focused on health problems arising when EDCs interfere with estrogens, androgens, and other sex hormones and the thyroid hormones. These powerful messengers are key for proper functioning of the reproductive, immune, and central nervous systems. Health effects associated with EDCs include reproductive problems, such as reduced fertility, male and female reproductive tract abnormalities, and skewed male/female sex ratios; early puberty; brain and behavior problems; impaired immune functions; and various cancers.
Probably the most convincing evidence for human impacts comes from diethylstilbestrol (DES). DES, a strong synthetic estrogen banned since the 1970s, was given to pregnant women to prevent miscarriages. Years later, the grown daughters and sons of women who took the drug were having more reproductive problems and higher cancer rates than those not exposed to DES in the womb. Mice studies confirmed that DES caused the reproductive problems and certain cancers (including the rare rete-testicular cancer in males). More recent animal studies find granddaughters and sons may also be affected (CDC 2005).
Less clear, though, are impacts from daily, low level exposures to chemical mixtures.
Whether long-term exposure to low levels of EDCs causes health problems in adult wildlife and humans is still a question. Developing fetuses and embryos, whose growth and development is highly controlled by endocrine signals, may be the most vulnerable to and have the most lasting effects.
Many consensus statements issued and endorsed by scientists and scientific organizations echo this. The Wingspread statements, the Weybridge Report, and the Prague Declaration on Endocrine Disruption are examples.
This heightened awareness - due to observed wildlife effects, increases in certain human endocrine diseases, and endocrine disruption seen in laboratory experiments - has raised global concern about EDCs. In response, governments (mainly European Union, the US, and Japan), international organizations, scientists, advocacy groups, policy makers, and individuals are backing efforts to understand, regulate, and educate about the contaminants.
But, many, including scientists, still disagree about the extent of detrimental health impacts of EDCs. What, if anything, should be done to reduce use and exposure? The debate continues, and opinions, it seems, fall into one of three camps:
Cause and effect data are elusive with issues like EDCs because they involve complex biological systems, unclear exposure facts, and diverse health responses. In these cases, we use scientific, political, and public debate to weigh the evidence and decide how to deal with the potential effects.
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All in all, EDCs are still largely an enigma. Unraveling the mysteries of how they interact with and influence endocrine, immune, neural and other systems in humans and wildlife requires more time, money, and research. In the long run, these efforts will pinpoint how EDCs interfere with signaling systems so we can fully understand their ultimate impact on reproduction, development, and health of individuals and populations.
Because of the likely health, social, and economic risks, some governments are taking action by gathering information, funding research initiatives, developing chemical screening and testing programs, and enacting new policies. US, Japan, and Europe are creating testing programs. The European Commission’s proposed Registration, Evaluation, and Authorisation of Chemicals (REACH) is a comprehensive, precautionary-based approach to regulate chemicals. Several states and countries are banning or restricting use of convicted EDCs such as brominated flame retardants (PBDEs), plasticizers (phthalates), and pesticides. New ways to treat sewage and drinking water to lower or remove hormone-like substances are being developed.
Right now, there is still much to learn. For instance, there is a great need to better understand the basic gene expression, cell signal pathways, and chemical messengers that guide and regulate almost every bodily response. From there, it’s important to decipher EDCs unique modes of actions, quantify potency and dose, and clarify effects so we can identify vulnerable life stages and species. More data on human and wildlife exposure, including bioaccumulation, is also needed.
A broader approach can show if and how EDCs affect lesser studied processes and systems. These include nonsteroid hormones, enzymes, fat production and storage, immune responses, adrenal function, genetic controls such as methylation, and behavior and population effects (Guillette In Press; Tabb and Blumberg 2005).
Many questions remain unanswered and await further investigation. Some of these, as outlined in consensus statements, workshop reports, and other sources, include:
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Colborn, T, Dumanoski D, and Myers JP. 1996. Our Stolen Future. New York: Penguin Books.
Controversial Issues Overview. Endocrine Estrogen Letter.
Scientific Committee on Problems of the Environment/International Union of Pure and Applied Chemistry (SCOPE/IUPAC). 2003. Implications of Endocrine Active Substances for Humans and Wildlife. Pure and Applied Chemistry 75(11/12):1617-2615.