What’s in My Water Bottle? A Question of Environmental Estrogens - Case Teaching Notes - Case Study Collection - National Center for Case Study Teaching in Science

Introduction / Background

I developed this case study because I wanted to introduce an environmental aspect into my Developmental Biology course so that my students could see the larger impacts of what they were studying in the course. In addition, I wanted to push my students to become more personally involved in the material and in making educated decisions.

The case focuses on bisphenol A (BPA), a monomer plastic and plasticizer used in the production of polycarbonate plastics and epoxy resins in many consumer products, including water bottles. BPA has been identified as an “environmental hormone,” a general term that refers to chemical substances present in the environment that disrupt the endocrine functions of humans and animals. Environmental hormones may also impede reproductive and other functions. Environmental estrogens have been a concern since Rachel Carson brought to light the problems with using DDT in this country. Since then we have been faced with the challenge of keeping our environment safe for ourselves and its other inhabitants while keeping pests and disease-carrying vectors under control. The manufacture of products we consider essential, such as plastics, introduces estrogenic compounds not only into the environment, but more recent information shows that these products may be introducing such compounds into the people who use the materials.

For this case study, I chose one small set of studies for students to examine, namely, Howdeshell et al., 1999; Howdeshell et al., 2003; and Masuno, 2002. These studies look at the potential for BPA to hydrolyze and leach from products it is used in and the effects of the chemical on living organisms. The research papers contain data presented in the form of tables, figures, and graphs. The case is meant to bring the issue of environmental estrogens to light as well as to give students experience with analyzing data and coming to their own conclusions. I have found that students do not get enough opportunities to analyze and evaluate data. This case allows them to do so in a controlled environment where the instructor is involved and can guide them. I have found that my students are successful at this analysis. Important to their success are the group discussions and the guided nature of the case study, which helps them work through how to analyze data.

The case is an interrupted case, that is, it consists of several sections, or parts, which students receive, and work on, in succession. It was designed to be given during a lab period in an upper-level Developmental Biology course. However, it could be adapted to environmental-oriented courses as well. I have included dialogue between the two main characters to explain some of the more difficult aspects of the data. This is meant to make the case study accessible to introductory level courses. The more advanced the students are, the less guidance they should need and the more robust the conversations should be about the quality of the data.

Objectives

Have students consider what good scientific evidence is.
Give students real data to analyze.
Have students evaluate a scientific argument.
Have students consider their own role as a scientifically literate member of society.

Classroom Management

This case was developed to take about two hours for upper-level students to complete. It would be quite easy to spend almost three hours on it if there is time for that.

Students receive the information in the case in sections, which they discuss in small groups of two to three students, followed by a large group discussion in which groups share the answers they have developed with the entire class.

Part I of the case is designed to get students to consider what they think good evidence is, before they are confronted with some evidence. In each of the remaining parts of the case, students look at and attempt to analyze real data. Some of the tables presented in the case may be challenging for students to read and interpret, a point which instructors can use to discuss with the students how best to present data. Giving this case study before assigning a major lab report can serve as a method of getting students to think about how they should present their own data. More details about what what is covered in the case and how it is taught can be found in the Blocks of Analysis section below.

The final assignment is a short paper that requires students to consider the issues, draw some conclusions, and reflect upon their own role in society as scientists.

In teaching the case, I make available copies of three research papers (see References) for students to refer to in case they want more background information. The case study is designed to work without this additional information, but if students are interested in looking at the analysis in greater detail, it is nice to have the three research papers readily available. Students could be asked to retrieve and read the papers on their own as an additional assignment.

Students may observe that two of the three papers have the same first author. I use this fact to discuss the possibility of bias on the part of those authors, and therefore on the part of “Susan,” the protagonist of the case.

Blocks of Analysis

Bisphenol A

The importance of bisphenols has increased with the growth of the plastics industry. The plastic monomer and plasticizer bisphenol A (BPA) is widely used to manufacture polycarbonate plastic and epoxy-based resins used in many consumer products, including water bottles, baby bottles, and cans. According to ICIS Chemical Business, more than two billion pounds of BPA, a known endocrine disrupter, is used annually in the U.S. (Erickson, 2008). A study conducted by the U.S. Centers for Disease Control and Prevention (CDC) in the United States found traces of BPA in 93 percent of the people tested (Anon., Consumer Reports, 2008). Whether this exposure poses significant risks to human health is a topic of controversy. Representatives of the plastics industry have taken the position that the scientific evidence supports the safety of BPA. A panel of experts from around the world convened by the National Institutes of Health (NIH), however, maintains otherwise. Their review of hundreds of studies over the past decade suggested “a connection between exposure to BPA at levels typical in the U.S. and increased rates of breast and prostate cancer, reproductive system abnormalities, and, for exposure in the womb, problems such as attention deficit hyperactivity disorder, obesity, and diabetes” (Anon., Consumer Reports, 2008).

Scientific Evidence and Data Analysis

Part I of the case begins by setting up the initial problem, including relevance, and then asking students what they think good evidence is. Giving students time to discuss the matter in their small groups allows them to “warm up” their thoughts. Sharing these with the entire class allows the instructor to verify that they have considered all of the issues.

Students should be able to identify the need for controls, for large enough sample sizes, the repeatability of the experiment, and that the experiment is relevant to the question. The instructor may need to inform the students about the widespread use of plastics; my students were not aware of this. Finally, having the students begin to design an experiment pushes the students to become more involved in the experimental design as well as to practice using the scientific method.

In Parts II–IV of the case, students are presented with data in the form of tables and graphs. The way I teach my course, the students have been asked to look at tables and graphs throughout the semester. This case study will be more accessible if students have already been confronted with data in previous experiences. The text of the case study gives them enough information to understand the figures, and the dialogue between Susan and Steve is meant to explain the most confusing aspects of the data, such as what the different controls are and the peculiarities of the data (such as the dashes found in Table 1 and some of the abbreviations used). It can be useful to have copies of the papers available for the students to view if necessary, though this has not been important for most students.

Students often will ask the instructor for clarification, and I periodically bring the whole class together after about five minutes to see what is confusing for students. Then, once I have clarified issues such as the replicates question (in Table 1) or why the sex of the neighboring embryo matters (in Figure 1), I have the students work together again to discuss the data. It is important to discuss with the entire group what the meaning is of each figure after they have had time to truly study and discuss the meaning; this allows the instructor to correct any misunderstandings students have and to push them to be critical of the data. Some students will merely accept what the data say, while others will be highly critical; bringing these issues to light allows all of the students to learn to be critical of the data, but to realize that not every question can be answered perfectly. Students are asked about what other data they would like to see. Students often find they would like to see more replicates of the data and often a better statistical analysis.

Evaluation of Evidence and Scientific Argument

The in-class discussion, both in small groups and as a whole, is important for helping students grapple with the meaning of the data. In the end, they are asked to write their own evaluation of the evidence and argument. As part of that, they are asked if they are convinced by the data. The point here is for each student to come to his or her own conclusion, based solely on how he or she interprets the data, but after having had the benefit of receiving input from others. This simulates how scientists work, and pushes students to become responsible for their own ideas and conclusions.

Students in my class have not been convinced by the evidence; they believe that more studies should be done to look at the effects of BPA (the main compound discussed) and are not convinced that BPA was present in products that they would be using.

Students as Members of Society

The final assignment asks students to consider their role in this issue. This question forces them to take responsibility not only for their own opinion, but for others, since they have more scientific knowledge than the average citizen. They cannot hide behind statements about what “the government” or “scientists” should do. They must say what they, themselves, would do. This is meant to plant the seed that they have a responsibility to be involved in helping others make scientifically literate decisions.

Answer Key

Answers to the questions posed in the case study are provided in a separate answer key to the case. Those answers are password-protected. To access the answers for this case, go to the key. You will be prompted for a username and password. If you have not yet registered with us, you can see whether you are eligible for an account by reviewing our password policy and then apply online or write to answerkey@sciencecases.org.

Editor’s Note

Readers may be interested in a related case study in our collection entitled Baffled by the Baby Bottle (see also the case’s teaching notes on our website). That case uses an article about the safety of polycarbonate baby bottles to develop critical thinking and reasoning skills and acquaint students with the fundamentals of polymer chemistry.

References

Research Papers

Howdeshell, K.L., A.K. Hotchkiss, K.A. Thayer, J.G. Vandenbergh, and F.S. vom Saal. 1999. Environmental toxins: Exposure to bisphenol A advances puberty. Nature 401:763–764.
Howdeshell, K.L., P.H. Peterman, B.M. Judy, J.A. Taylor, C.E. Orazio, R.L. Ruhlen, F.S. vom Saal, and W.V. Welsons. 2003. Bisphenol A is released from used polycarbonate animal cages into water at room temperature. Environmental Health Perspectives 111:1180–1187.
Masuno, H., T. Kidani, K. Sekiya, K. Sakayama, T. Shiosaka, H. Yamamoto, and K. Honda. 2002. Bisphenol A in combination with insulin can accelerate the conversion of 3T3-L1 fibroblasts to adipocytes. Journal of Lipid Research 43:676–684.

Magazine Articles

Anon. 2008. A new focus on plastic ingredient in bottles and cans. Consumer Reports 73(5): 0–11.
Erickson, Britte E. 2008. Bisphenol A under scrutiny. Chemical & Engineering News 86(22): 36–39.

Websites

The following web sites include different points of view on the safety of BPA.

The Green Guide: The Bisphenol-A Debate: A Suspect Chemical in Plastic Bottles and Cans by Catherine Zandonella, M.P.H. Last accessed: June 24, 2008.: http://www.thegreenguide.com/doc/114/bpa; Web page published by the National Geographic Society; points out some of the issues (pro and con) associated with BPA.
Our Stolen Future. Last accessed: June 24, 2008.: http://www.ourstolenfuture.org/index.htm; This website includes a collection of papers about the dangers of BPA.
The Polycarbonate/BPA Global Group’s Bisphenol-A Website. Last accessed: June 24, 2008.: http://www.bisphenol-a.org/

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Acknowledgements: This case was published with support from the National Science Foundation under CCLI Award #0341279. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Date Posted: September 22, 2008.

Originally published at http://www.sciencecases.org/water_bottle/notes.asp

Case Teaching Notesfor “What’s in My Water Bottle? A Question of Environmental Estrogens”