Salmon, Pacific Northwest Tribes, and the Discovery of 6PPD in Organic Chemistry

This page is authored by Jennie Mayer and Sonya Doucette, Bellevue College, Chemistry Program

Author Profile
Initial Publication Date: June 17, 2024

Summary

The activity begins with a case study about the importance of salmon to Pacific Northwest tribes (USA) and how they are affected by water pollution. Students learn how high resolution mass spectrometry, fractionation techniques, nuclear magnetic resonance, and some radical chemistry are used to understand the oxidation of tire materials to 6PPD quinone, which is a chemical that kills salmon. Students also learn how affected communities are addressing the challenges they face and how governments, industry, and the scientific community are responding, as well as ways that individuals can support strategies that address the 6PPD issue.

Share your modifications and improvements to this activity through the Community Contribution Tool »

Learning Goals

1. Explain how high resolution mass spectrometry, fractionation techniques, and NMR are applied to a real-world problem.

2. Propose a step-by-step radical mechanism for how the rubber in tires is oxidized, explaining why 6PPD is used as a tire preservative.

3. Define petrochemicals and how they are harmful to human health and marginalized communities.

4. Explain why automobile tires are a climate justice issue for local communities and Pacific Northwest tribes.

5. Describe how local communities affected by 6PPD are addressing the challenges they face and how governments, industry, and the scientific community are responding.

6. Identify ways that individuals can support strategies that address the 6PPD issue.

Context for Use

The activity is composed of a class discussion, class activity, and two assignments completed outside class, which are all threaded throughout the second quarter (term) of organic chemistry. This course is 10 weeks long and is part of a three-quarter year-long organic chemistry series at a two-year college with a class size of 24 to 48 students (laboratory sessions have only 24 students in each). The total time for the activity is four to six hours, with about 1 to 1.5 hours of time in the classroom (during two different class sessions) and 3 to 4.5 hours of work by students outside the classroom (for two different assignments). Prior to encountering this activity, students should know (step-by-step) how electron-pushing mechanisms work for radical reactions and how to analyze proton Nuclear Magnetic Resonance (NMR) spectra. I implement this activity after students have studied fractionation (i.e., chromatography), in order to strengthen their understanding of these topics, and while they are learning other aspects of radical chemistry and NMR. Students need access to an internet connection to watch the online videos. I also use a mix of printed handouts and the Canvas online Learning Management System (LMS) to distribute assignments and collect student work, but any LMS will work and is not necessary at all, as instructors can instead print out all handouts and assignments for distribution to students during class. The activity can also be adapted for a similar but larger organic chemistry course at a four-year college or university, with certain parts of the assignment completed during smaller breakout or laboratory sessions, as well as for the organic chemistry portion of a high school chemistry course.

Description and Teaching Materials

Instructor Preparation: Check links to all online videos and articles; prepare PowerPoint presentation and student worksheet for the radical oxidation activity; upload the 6PPD assignments (Steps 3 and 4) to your LMS and set up a submission link for student work (or print out the assignments for distribution to students during class time if you do not use an LMS).

Step 1: Stormwater, Salmon People, and Climate Justice (45 minutes). During the first week of class, I show students two videos during class time that introduce students to a case study of how salmon are affected by pollution and convey the importance of salmon to Pacific Northwest (PNW) tribes. Before starting the videos, I ask students to write down (as they are watching!) their thoughts and reactions to the videos, as well as what they already know and what they want to know about how organic chemicals in the water affect salmon and PNW tribes. The purpose of the questions is for me to get a feel for students' prior (current) knowledge of organic chemistry, their misconceptions, and what aspects of organic chemistry they are most interested in learning. Students share their responses to these questions after they watch the videos, which allows me to make connections for them to the organic chemistry that they will learn this quarter, based on how they respond to the questions. The first video, Solving Stormwater, is six minutes and introduces stormwater and how salmon are harmed by it. (There is no mention of 6PPD in the video. That will come later in Step 2.) The second video is a 24-minute-long documentary called Salmon People: A Native Fishing Family's Fight to Preserve a Way of Life, which shows why salmon are important to tribes and how they are being affected by the loss of salmon. Although the video does mention climate change, there is not a specific mention of water pollution or 6PPD.

Introduction to Salmon & Toxic Chemicals.pptx (PowerPoint 2007 (.pptx) 44kB May20 24)

Step 2: Radical Oxidation of Tires Activity (45 to 60 minutes): During the first month of the term, students learn about radical oxidation. I use an activity during class time, focused on oxidation of tires, to help them learn this organic chemistry content as well as continue to learn about the stormwater, salmon, and PNW tribes case study. To start the activity, students watch a three-minute-long video called Worn tires contribute to chemical that kills Coho salmon, which describes how chemists in Washington state recently (in 2020) discovered a previously unknown chemical present in stormwater that is responsible for the detrimental effects on the salmon described in the Solving Stormwater video that they watched earlier in the quarter. After the video, I ask students to work in small groups of two or three students to provide electron pushing arrows for each step of the radical oxidation of tire rubber (hydrocarbon rubber chain). To end the activity, students learn that sixty percent of the rubber in tires is made from petrochemicals. They learn what petrochemicals are, what they are used for, and how petrochemical processing facilities harm the communities that live near them. I provide students with a definition of climate injustice, which includes fossil fuel extraction and processing activities as well as atmospheric climate impacts, and ask them to explain why automobile tires are a climate justice issue for local communities and Pacific Northwest tribes.

Radical Oxidation of Tires.docx (Microsoft Word 2007 (.docx) 218kB Jun17 24)

Step 3: Discovery and Chemistry of 6-PPD (1.5 to 2 hours): Later on in the term, when students are learning about Nuclear Magnetic Resonance (NMR), they complete an assignment outside class. Students watch a 50-minute video, A Ubiquitous Tire-Derived Chemical Killing Coho Salmon (49 minutes), and complete an accompanying assignment. The video provides more detail about the analytical chemistry behind the discovery of 6PPD. The video highlights the use of high resolution mass spectrometry, fractionation techniques (i.e., chromatography), NMR for compound identification (which they just learned in the class this term); some radical chemistry is involved for understanding how 6PPD gets oxidized to 6PPD quinone, which is the chemical actually causing the neurological disorder in salmon. For Part 1 of the assignment, I ask students to explain what stormwater runoff is, the chemicals that are in it, and how the runoff affects salmon. I also ask students to describe the hypothesis or goals of the scientists' work and their findings.

For Part 2 of the assignment, I ask students about the analytical techniques that we used to first discover 6PDD. Students have not learned about mass spectrometry in my course, so they hear about it for the first time in the video and how it was used to identify 6PPD. They also learn how fractionation was used, which may be new terminology for many students, but is similar in concept to chromatography, which we do cover in the course, as well as how NMR was used to identify the 6PPD molecule. After the analytical techniques, students apply radical chemistry, which is not in the video but that they have learned previously in the course, to show the reaction mechanism for the oxidation of 6PPD by photodegradation to produce 6PPD quinone, the chemical that is actually harmful to salmon. Overall, the video illustrates how the scientific method is used, starting with observations made by the scientists, followed by a hypothesis and the design of an experiment to test it.

Stormwater Salmon & 6PPD.docx (Microsoft Word 2007 (.docx) 59kB Jun17 24)

Step 4: Addressing the 6PPD Issue (1 to 2 hours): At the end of the term, students complete this part of the activity outside class time and the amount of time required can depend on the length of their conversation with family and friends (Questions 2 and 3 in the "Addressing the 6PPD Issue.docx" Word file). In this part of the activity, students learn more about how local communities affected by 6PPD are addressing the issue, as well as about the response of the government, the tire industry, and the scientific community. They listen to a 14-minute-long NPR news story, EPA sides with tribes on petition to regulate toxic tire chemical that kills salmon, from November 2023 to learn about these things. (NPR is the National Public Radio channel in the United States.) After listening to this news story, students answer a series of questions about actions taken by the West Coast tribes and the Pacific Coast Federation of Fishermen to address the 6PPD issue, as well as the response of the U.S. Tire Manufacturers Association. Students then read about how researchers are discovering alternatives to 6PPD in tire manufacturing. I give them an example of how the Berkeley Center for Green Chemistry published a report (2021) that describes four strategies for Alternatives for 6PPD in tire manufacturing and ask them to read about the alternatives they are working on. I also ask them to read about actions that the Washington state legislature has taken by passing SB 5931 to promote safer tire products sold in Washington: Salomon bill to protect salmon from toxic chemicals passes House, Senate. After exploring these additional resources, students discuss what they learned in the NPR news story, and the additional Berkeley and Washington state resources, with a family member or friend. They also discuss what they think would be the most effective strategies for addressing the 6PPD and what individuals can do to support these strategies.

Addressing the 6PPD Issue.docx (Microsoft Word 2007 (.docx) 17kB Jun17 24)

Teaching Notes and Tips

Students find this topic very engaging, especially in the midst of an organic chemistry course that covers very technical, often abstract, and rigorous organic chemistry content. Engaging in this activity also allows time for students to gain a deeper understanding of topics that I do not have time to cover in-depth in the course, such as chromatography, mass spectrometry, and applications of laboratory analytical techniques and instrumentation.

I have students complete two parts of the activity outside of class (Steps 3 and 4), but doing Step 2 in class is very beneficial to student learning, especially for the reaction mechanism part where students have questions. The Salmon People documentary is also engaging and it is nice to show this (Step 1) during class time to allow a space for meaningful discussion about the organic chemistry involved in the case study and how Pacific Northwest tribes are connected to salmon.


Assessment

1. Explain how high resolution mass spectrometry, fractionation techniques, and NMR are applied to a real-world problem.

I assess this learning goal during Step 3, using Questions 5, 6, and 8 in Part 2 of the "Stormwater Salmon & 6PPD.docx" Word file. Students complete this assignment on their own outside class time for a grade and I collect it from them using Canvas (my LMS).

2. Propose a step-by-step radical mechanism for how the rubber in tires is oxidized, explaining why 6PPD is used as a tire preservative.

I assess this learning goal during Step 2, using Question 2 of the "Radical Oxidation of Tires Activity.docx" Word file. Students complete this worksheet during class time, working in small groups of two or three students, so I initially conduct a formative assessment of this learning goal by walking around the classroom while they work, interacting with groups and answering questions. At the end of this class session, students turn in the worksheet to me for a grade.

3. Define petrochemicals and how they are harmful to human health and marginalized communities.

I assess this learning goal during Step 2, using Question 3(a) of the "Radical Oxidation of Tires Activity.docx" Word file. Students complete this worksheet during class time, working in small groups of two or three students, so I provide formative assessment during class time. When grading the worksheet after class time, I give credit for any answers that cite a statistic or data point from the article I ask them to read for this question.

4. Explain why automobile tires are a climate justice issue for local communities and Pacific Northwest tribes.

I assess this learning goal during Step 2, using Question 3(b) of the "Radical Oxidation of Tires Activity.docx" Word file. Students complete this worksheet during class time, working in small groups of two or three students, so I provide formative assessment during class time. When grading the worksheet after class time, I give credit for any answers that apply the definition of climate justice (either given for the question or another valid definition of climate justice) to local communities and Pacific Northwest tribes.

5. Describe how local communities affected by 6PPD are addressing the challenges they face and how governments, industry, and the scientific community are responding.

I assess this learning goal during Step 4, using Question 1 of the "Addressing the 6PPD.docx" Word file. Students complete this assignment on their own outside class time for a grade and I collect it from them using Canvas (my LMS). I give credit for any answers that cite specific information from the NPR news story that I ask them to listen to for this question.

6. Identify ways that individuals can support strategies that address the 6PPD issue.

I assess this learning goal during Step 4, using Questions 3(b) and 3(c) of the "Addressing the 6PPD.docx" Word file. Students complete this assignment on their own outside class time for a grade and I collect it from them using Canvas (my LMS). I give credit for any answers that cite any of the strategies they learned about during this case study.

References and Resources