Environmental Issues: Health
An Overview and Resource List
The Endocrine System
The endocrine system controls maturation, development, growth, and regulation within the body. It consists of glands (such as the pituitary, the pancreas, the adrenals, and the testes) and hormones, which are natural chemical messengers. The endocrine glands secrete carefully measured amounts of these messenger chemicals into the bloodstream. They travel to different parts of the body and bind to specific receptors in order to control and adjust many life functions. For example, estrogen is a hormone secreted primarily by the ovaries. It controls the menstrual cycle, fertility, and maintenance of a healthy pregnancy, among other critical activities in adults. In the fetus, estrogen is essential for normal development of both males and females.
There is increasing evidence that some synthetic chemicals in our environment may interfere with our bodies' complex and carefully regulated hormonal messenger system. Chemicals can disrupt the endocrine system in several ways. They can mimic or block chemicals naturally found in the body, alter hormonal levels, and thus, affect functions that these hormones control. Less direct interferences involve alteration of the body's ability to produce hormones, interference with the ways hormones travel through the body, and changes in numbers of receptors.
In adults hormones mainly regulate ongoing physiologic processes. As a result, adult bodies can sometimes compensate or recover from temporary hormonal modulation. Hormonal effects in the fetus are much more profound because they affect gene expression that governs development of organs as well as lifelong hormonal "set points", such as receptor numbers and hormonal production. In the case of endocrine disruptors and other developmental toxicants, the timing of exposure may be more important than the dose.
Suspected endocrine disrupting chemicals are found in insecticides, herbicides, fumigants, and fungicides that are used in agriculture as well as in the home. Other endocrine disruptors are found in industrial chemicals such as detergents, resins, plasticizers, and monomers in many plastics. Exposure to these chemicals occurs through direct contact in the workplace or at home, or through ingestion of contaminated water, food, or air. Studies have found that some of these chemicals do leach out of plastics, such as the PVC plastics used to make IV bags. When these plastics, or other materials, are burned (as well as in their production) many unwanted byproducts that are endocrine disruptors or suspected endocrine disruptors are released into the air or water.
Most endocrine disrupting chemicals are fat-soluble. This means that they do not get rapidly flushed out of the body, but rather are stored in fat. These chemicals bioaccumulate up the food chain. (An individual higher up on a food chain must consume many individuals of a lower level in order to obtain sufficient energy. In doing this, an organism not only acquires the energy it needs to live, but it also ingests and accumulates the sum of the chemicals stored in its food.) This means that very low levels of a chemical in the air, water, or soil result in higher levels in plant life, still higher levels in herbivores, and even higher levels in carnivores. An individual will accumulate more of these chemicals throughout his/her lifetime. The major routes of removing these chemicals involve transfer from mother to child, through the placenta and in breast milk.
Examples in Wildlife
In 1992 researchers at Lake Apopka in Florida connected a declining alligator population with a depressed reproduction rate. Many of the male alligators had tiny penises that prevented successful reproduction. These developmental problems were connected to a large organochlorine pesticide spill several years earlier; although the water tested clean, the alligators and their eggs had detectable levels of endocrine disrupting pesticides.
Fish in the Great Lakes, which are heavily contaminated with polychlorinated biphenyls (PCBs) and other organochlorines, have been exhibiting numerous reproductive function problems and swelling of the thyroid gland. Fish-eating birds, such as eagles, terns, and gulls are also showing similar health effects, as are mink, a mammal that also eats fish from the Great Lakes. These findings are consistent with lab studies that indicate that PCBs interfere with thyroid function and with sex hormones.
Experiments in lab animals indicate that while high doses of PCBs can be toxic, lower doses can cause hypo- or hyper-activity, impaired performance on tests of learning, balance, reaction time, and impaired hearing. The doses of exposure that result in behavioral abnormalities, sex hormone abnormalities, and enzyme abnormalities are close to the current exposure levels in humans. We are concerned about endocrine disruption because this is a means by which subtle effects from human actions can have species- and population-extinction outcomes. Small, but critical, changes in the chemical makeup of an environment are enough to trigger outcomes that could lead to population decline and loss of biodiversity.
The Human Tragedy of DES
One of the situations that most clearly indicates the extent to which synthetic chemicals can harmfully affect humans involves the drug diethylstilbestrol (DES), a synthetic estrogen, that was prescribed to many women in an effort to prevent miscarriages in the 1950s and 1960s. Not only did DES not prevent miscarriages, but it also had many harmful effects on the children of many of these women. In 1971 physicians reported that numerous teenage girls were developing very unusual cancers of the vagina. An investigation of these girls' environmental exposures eventually traced the problem back to maternal use of DES. The effects of DES in the offspring of these women were not only cancers, they also include birth defects of the uterus and ovaries, and immune suppression. From the DES event, we have learned that:
- The placenta is not an impenetrable barrier, as was once thought. We must be careful about exposures during pregnancy.
- Exposure to the mother can have unexpected effects in the offspring, even decades later. The individual directly exposed may not be the one who experiences an outcome; we must be aware of transgenerational effects.
- Exposure to hormonally active chemicals may result in a range of adverse health effects (cancer, reproductive abnormalities, etc.)
- People are more likely to notice an increase in a very unusual disease (such as vaginal cancer in young women) and trace it to an environmental cause, than they are with common diseases.
Implications of the Endocrine Disruptor Problem
Endocrine disruption raises some important issues and implications. It demands that we question our chemical testing practices. Many chemicals do not undergo the required tests for toxicity before they are put on the market and used regularly. In their Chemical Hazard Data Availability Study, EPA's Office of Pollution Prevention and Toxics states that "of the 3,000 chemicals that the US imports or produces at more than 1 million lbs/yr, a new EPA analysis finds that 43% of these high production volume chemicals have no testing data on basic toxicity and only seven percent have a full set of basic test data. This lack of test data compromises the public's right to know about the chemicals that are found in their environment, their homes, their workplace, and the products that they buy. Industry must do more to ensure that basic information is available on every high-production chemical they manufacture." [http://www.epa.gov/opptintr/chemtest/hazchem.htm] The tests that are required do not evaluate endocrine disrupting effects, so even tested chemicals can have unidentified hazardous health effects. It is important to remember that the phrase "not proven to cause harm or adverse health effects" in no way means that a substance has been proven to be harmless or conducive to regular health functioning.
Because the environment is a global entity, not divisible by political boundaries, these issues are concerns for everyone. Dioxin from a paper mill in the US can accumulate within livestock that is exported to another country; water vapor carrying DDT (now banned in the US) from Mexico can be rained down in Minnesota. Individuals living near the North Pole, where DDT has never been used, have surprisingly high levels of it in their body fat. The laws that ban the production and use of specific chemicals in the United States do little to regulate against exposure via imported products from countries that allow the use of these chemicals.
The consumer is often uninformed about the substances to which he/she is exposed. Individuals have a right to know which chemicals have been used in the production of products that they purchase. One of the requirements of the 1996 Food Quality Protection Act (FQPA) is the distribution of brochures in grocery stores that explain the health effects of pesticides, offer suggestions for risk avoidance, and identify foods with tolerable pesticide residues. Right-to-know laws enable consumers to learn more about specific potential exposures. Although individuals can limit some exposures by changing their personal habits, there is often no choice regarding exposure when chemical agents are in water or air. California's Proposition 65 creates a tool whereby citizens and citizen groups can help to make industries more responsible about their chemical use and potential exposures. Under Prop 65, the Governor of California must create a list of known carcinogens and reproductive toxicants. Farmers and businesses that have more than 10 workers and that operate as producers and/or users of these chemicals must warn people before possible exposure to these substances and are prohibited from discharging them into state drinking water.
We all have a right to be free of chemical trespass. Children are born with toxic chemicals already in their bodies. Workers around the world are exposed to chemicals thought to be carcinogens and endocrine disruptors without their knowledge. Pesticides are used in neighborhoods in which the residents are not informed nor given a choice about the use. Exposure to such substances is the equivalent of an uncontrolled experiment using subjects who have not given informed consent
Responsible action with regard to public health operates using the model of the Precautionary Principle. That is, instead of waiting for proof that chemicals are hazardous, we ought to minimize or eliminate exposures until we are certain that they do not have deleterious health effects. Erring on the side of caution will help to ensure a healthful and responsible chemical industry. As it is, the burden of proof tends to fall on the public and the government to prove that a chemical causes harm before any action to reduce exposures can be taken. Because we do not perform direct studies on human subjects, it is extremely difficult to produce "proof" of human harm. Until we shift the burden of proof from organizations and communities (responsible for proving harm) to industries (responsible for proving harmless), unnecessary exposures to unsafe chemical substances will continue to prevail.
Endocrine disruption is a complex issue and certainly needs to be studied more extensively. NRDC's program of action and involvement with endocrine disruption includes:
Testing: We need to know which chemicals may be endocrine disruptors, and which are probably not. Thus far, discoveries of endocrine effects have mostly occurred by accident in the laboratory or in highly polluted areas. We need a systematic testing system. NRDC recently participated in a federal advisory committee -- the U.S. Environmental Protection Agency's Endocrine Disruptor Screening and Testing Advisory Committee -- to design a program to prioritize the over 86,000 chemicals in current use and screen them for effects on estrogen, androgen, and thyroid hormone. The advisory committee's final report was released in September 1998. Now NRDC is working to ensure that the recommendations of the committee are fully and rapidly implemented.
Right to Know: People have a right to know which chemicals may be endocrine disruptors and how they might be exposed. Some known and suspected endocrine disruptors are not yet reportable on the federal Toxics Release Inventory. Many others are not listed as reproductive or developmental toxicants under California's Proposition 65. We are working to get endocrine disruptors listed under these important right to know laws so their emissions to air, water, and land can be tracked and reported, and so that if consumers may be exposed they will first be warned.
Detecting Exposures: The National Center for Environmental Health at the Centers for Disease Control and Prevention has developed analytic techniques which allow measurements of human exposures to many known and suspected endocrine disrupting chemicals. Currently these measurements, which are usually done on blood samples, are expensive and not available except for specific research projects. NRDC is working to increase funding for this testing so that in the future, people may be able to go to their doctor to find out their exposure levels to some of these chemicals. In addition, better measurements of exposure mean better research studies. Exposure measurements also allow us to set goals for exposure reduction and then make sure those goals are met.
Decreasing Exposures: Some known endocrine disruptors are still legally used in the United States. For example, a pesticide called vinclozolin is legally used on beans and other food crops even though it is known to block the normal function of male hormones such as testosterone. NRDC is challenging the continued use of this pesticide and of other known endocrine disrupting chemicals. In addition, we are working hard to address sources of dioxin such as incinerators and diesel engines.
Education: Many members of the public are not aware of this important issue. More disturbingly, many health care workers and physicians are also unfamiliar with the scientific and health issues related to endocrine disruption. Gina Solomon, a physician at NRDC is working to educate the medical community and the general public about this issue. She has given grand rounds and conferences at hospitals, has spoken at major scientific conferences, and frequently addresses various audiences to spread the word about endocrine disruptors.