To help students understand how environmental “surprises” and scientific uncertainty related to endocrine disruptors influence perceptions of benefits and costs, and thus the decisions that people make.
This lessons addresses current environmental issues in a broad context of present scientific understanding, human drivers and effects through time, and linkages to societal concerns such as human health and economic well-being.
This lesson focuses on endocrine disruptors: chemicals that mimic the body's own internal hormone communication system. Students are introduced to the endocrine system, they study what we know and do not know about chemicals that disrupt this system, and they consider the kinds of choices that individuals and societies have with regard to endocrine disruptors. Finally, they are asked to consider how what they know and don't know influence the decisions that they and others might make.
We live in a world where human population, technology, and lifestyle are driving environmental change of a scope and scale unprecedented in human history. This lesson introduces environmental surprises, scientific uncertainty, and social decision making in the context of the environmental change represented by endocrine disruptors.
Anthropogenic (human-created) chemicals that persist in the environment are pervasive in the modern world. These chemicals, most of which are invisible, tasteless, and odorless, result from ubiquitous features of our culture. Some possible endocrine disruptors include:
- Dioxins – toxic byproducts of paper manufacturing and incineration
- Chemicals in pesticides and chemicals that result from the breakdown of banned pesticides such as DDT
- PCBs – chemicals used in electrical equipment that are found in river and lake sediments in industrial areas
- Chemicals found in the epoxy lining of "tin" cans
- Plastics used for storing food (e.g., bisphenol-A in polycarbonate plastic)
- Dental sealants sometimes used on the teeth of children
- Chemicals in detergents (e.g., nonylphenol)
- Fungicides used on fruit, such as Vinclozolin
Many of these chemicals have produced benefits for society and created wealth for those who develop, sell, and use them. These kinds of benefits are, for the most part, well documented and obvious. The risks that these chemicals pose for humans and wildlife are much more poorly understood, and there are massive unknowns. These unknowns, and the distance in space and time between where the chemical is put to beneficial use and where the chemical ends up in the environment, have led to some unhappy environmental "surprises."
This lesson was developed by Dr. Penny Firth, a scientist, and Mr. Doug Widener, of The Chicago Academy of Sciences and its Peggy Notebaert Nature Museum, as part of a set of interdisciplinary Science NetLinks lessons aimed at improved understanding of environmental phenomena and events. Some of the lessons integrate topics that cross biological, ecological, and physical concepts. Others involve elements of economics, history, anthropology, and art. Each lesson is framed by plain-language background information for the teacher and includes a selection of instructional tips and activities in the boxes.
Note: You can contact Dr. Firth at firstname.lastname@example.org and Dr. Widener at email@example.com.
The lesson will take approximately two periods, depending on how many of the exercises are selected.
Every now and then, nasty little environmental surprises catch us humans unawares. Sometimes the surprises are not of our doing—volcanoes, earthquakes, and hailstorms for example. Increasingly, however, human actions are responsible for environmental surprises.
Students should begin by reading the examples of environmental surprises in the box below. In each case, the surprise was due to a lack of understanding of biological, chemical, or physical patterns and processes. Discuss these examples with your class using these questions as a guide:
- What did these three environmental surprises have in common? (All were negative; all were caused by inadequate understanding of natural phenomena.)
- How would you contrast these environmental surprises? (In the first example, the understanding came too late; in the second and third, people were able to respond.)
- What could be done to minimize the chances of future environmental surprises?
|Surprise Example 1: When the Passenger Pigeon went extinct at the beginning of the 20th century, people were surprised. This was once the most abundant land bird on the planet, numbering in the billions! Habitat loss, forest fragmentation, hunting, and disturbance of nesting all took a toll. But the surprise was in the biology of the bird. People did not understand that very large flocks were required for successful foraging and reproduction. If they had, the story might have ended differently. Passenger Pigeons provides more information for students who wish to pursue this surprise further.|
|Surprise Example 2: When the Bald Eagle and other birds of prey began to have trouble reproducing in the 1960s and 1970s, people were surprised. Scientists discovered that their eggshells were extremely thin, and were breaking before the baby birds were mature enough to hatch. Research determined that the pesticide DDT was accumulating at the top of the food chain (i.e., in the eagles) and causing the thin shells. People did not understand that chemicals can persist in the environment and cause harm to wildlife. Once they did understand, they faced an important decision. Was the benefit of mosquito and other pest control outweighed by the cost to our national bird and other raptors?|
|Surprise Example 3: When a hole was discovered in earth's vital ozone shield over Antarctica in the late 1980s, people were surprised. Scientists learned that chemical reactions involving chlorofluorocarbons (CFCs) in the atmosphere were causing the loss of ozone, and thus increased dangerous ultraviolet (UV) radiation reaching the planet. CFCs were then widely used in a variety of appliances including refrigerators and air conditioners. People did not understand that even minuscule amounts of certain chemicals can influence planetary-scale physical phenomena. Once they did understand, they faced an important decision. Was the benefit of inexpensive and effective refrigeration outweighed by the cost to humans and ecosystems of increased UV radiation?|
Now the class should go on to consider another environmental surprise that is the focus of this lesson. Not too long ago, people were surprised to learn that certain synthetic (human-made) chemicals mimic the natural chemicals that mammals and other animals use as internal messenger systems, i.e., hormones. They were further surprised—even alarmed—to discover that some of these chemicals persist in the environment for fairly long time periods. Scientists discovered that these chemicals could disrupt the normal signal process and they began to refer to them as endocrine disruptors. There is much that people still do not understand about endocrine disruptors.
Hormone Signals and Their Disruptors
The endocrine system is a very reliable internal signaling system for the body. Hormones are the chemical signals that move through the bloodstream from where they are produced to cells that have specialized external receptor molecules. When the hormone locks into the receptor that is specific to it, the signal is delivered. The signal might be for the cell to divide, or to produce a certain protein, or to start or stop some other process.
|A Distributed Study
Working in small teams, have your class do a quick, distributed study of the endocrine system. One way might be to assign a part of the endocrine system to each team and ask them to report out to the class what hormone(s) are produced and what kinds of signals are delivered inside the body. Possibilities include: hypothalamus, pineal, pituitary, parathyroid, thyroid, thymus, adrenal, ovaries, and prostate.
As your class will demonstrate, hormones are used by the body in lots of different ways, including reproduction, growth, and immune function. They perform at vanishingly small concentrations: parts per billion or even parts per trillion. Chemicals that are effective at such low concentrations are worth watching if they get into the environment.
Unfortunately, certain artificial chemicals can enter the bloodstream and mimic hormones, sending bad signals or blocking normal signals. Because hormones are part of the endocrine system, these artificial chemicals are known as endocrine disruptors.
Researching the Theory of Endocrine Disrupting Chemicals
Divide the class into teams. Each team will investigate specific aspects of the endocrine disruption theory and present its findings to the class. Begin with a brainstorming session to develop a small number of topics for research. Here are some possibilities:
- Links between animal health and endocrine disrupting chemicals
- Links between human health and endocrine disrupting chemicals
- Effects of endocrine disrupting chemicals on adults, juveniles, and the unborn
- The case against the endocrine disruption theory
- How widespread endocrine disrupting chemicals are in the environment
- How long endocrine disrupting chemicals persist in the environment
- The applicability of animal evidence to humans for endocrine disrupting chemicals
|Researching the Known and the Unknown
Divide students into teams of about five persons. Using the Endocrine Disruptors student esheet, each team will use the resources listed to conduct research on one of the research topics identified. If there are more teams than topics, assign more than one team to a topic or further subdivide topics.
The teams should focus their research on finishing these three statements:
Once students have finished their research, have them list their main points (the finished statements) on a poster board or on the chalkboard. Have a representative of each team present the team's findings to the class. Students should try to present their findings with as little jargon as possible. They should strive to communicate as clearly and concisely as possible.
Considering Consensus: What about Uncertainty?
Certainty is an obvious concept. It is "what we know." Uncertainty is the unknown, the "what we don't know." But wait! The "what we don't know" can actually be subdivided. Now pay close attention: There is "what we know we don't know” and "what we don't know we don't know."
When scientists and engineers talk about reducing uncertainty, they often are referring to "what we know we don't know." For the endocrine disruptor theory, that is where this lesson has concentrated. There may be more surprises out there, however. In fact, history would suggest that there probably are more surprises. The "what we don't know we don't know" category could be very large. For the general public, one could argue that it is essentially the only category! This cannot help but influence societal decision making.
After you have explained this to the class, take them through this exercise:
|Where Are We Uncertain?
Given each teams' findings and their critical analysis of them, ask teams to support one of these statements. If a team cannot reach consensus, have individuals select which statement they support, and give their rationale for selecting that statement.
Now, engage the class in a group discussion of the three consensus statements above. List the pros and cons students give in support or opposition to each statement. Ask students if any of their opinions changed based on what others found or said. If so, why? Take a poll to see if students feel that any of the statements can be supported completely. Is there a level of uncertainty inherent in each statement? If so, how might this influence perceptions of benefits and costs, and thus the decisions that people make? Do students think that perceptions of benefits and costs will be the same for individuals as for private industry or the government? Why or why not?
At a societal level, the benefits and risks associated with choices include consequences that are long term as well as short term, and indirect as well as direct. For students to understand the complexities of social decisions, they need to understand some of the difficulties of predicting consequences of decisions, and the importance of considering the costs and benefits associated with alternative courses of action.
In deciding among alternatives, a major question is who will receive the benefits, and who will bear the costs. In general, the more remote the consequences of a personal or social decision, the harder it usually is to take these consequences into account in considering alternatives. It is particularly hard if the person or group is not "at the table" when the alternatives are being discussed. For example, how might the decision process proceed if most of the benefits go to the present generation in the United States, and most of the costs are borne by future generations, or people from other lands? Students should be reminded that the decisions of one generation both provide and limit the range of the possibilities open to the next generation.
Ask the teams to discuss these concepts and how their understanding of the endocrine disruption theory relates to individual and social decision making about chemicals. Assign each team one of the following documents to read:
- The Wingspread Consensus Statement: a summary of several scientists' opinions on what we know and what we need to know in relation to the endocrine disruption theory.
- Emcom: Science: an industry perspective on what is known and unknown for the endocrine disruption theory.
When they have read it, the team should develop a one-page position paper that responds to the document. Have the team members present their paper to the class. The paper and presentation can be used to assess students' understanding of the content, their ability to synthesize and critically analyze resources, and use these resources to support their opinion on the endocrine disruption theory.
Endocrine disruptors are active at vanishingly small concentrations: parts per billion or parts per trillion. Students should look up and/or calculate how many gallons (or liters) of water there are in the Atlantic Ocean (or the Pacific Ocean, Lake Superior, or a similarly huge body of water). Then have them calculate what volume would be a part per billion and a part per trillion.
- How much of a chemical (gallons, liters) would be required to be present in the Atlantic Ocean at one part per billion?
- How much would be required to be present in one part per trillion?
- How much water is in your local water tower? What volume of a chemical would be required to be present in one part per trillion in the water supply?