Classroom Activities
Lesson 1 - Introduction to Pesticide Residue on Common Foods
The "hook" into this unit will be the question I posed at the beginning of the narrative about pesticide residues on apples, bananas, green beans, and bread. I will lead the class through the calculation for the "worst-case" chlorpyrifos residue on an apple. Following that example, I will give a more formal lesson on converting units by Dimensional Analysis. Students will then calculate their own weights in oz, kg, g, mg, and heights in cm, m, km and yd. If time permits, I will have them estimate and then calculate how many seconds they have been alive (it's always interesting to see their reactions to their misperceptions!). Next, to reinforce the concepts of pesticide residues and converting units, I will have the students work in groups to estimate the "worst-case" pesticide levels on a variety of foods that I supply. (Note: If it were not the first day of a new semester, I would ask students to bring in fruits and/or vegetables themselves.) I will either display or hand out printed copies of data from Appendix J of the USDA Pesticide Data Program, which gives a list of commodities and the pesticide residues (in ppm) that have been found on them. Each group will be assigned a different food commodity. They will determine the mass of the food supplied, and each student in the group will calculate the residue from a different pesticide in milligrams and also in ounces using the maximum level reported. To extend this lesson, I would have students go to the EPA website to find tolerances for the different pesticides they just used in their calculations, and do the calculation that I demonstrated for daily maximum allowable residue levels based on body weight, and compare the results.
To conclude this first lesson, I will give a brief history of pesticides, especially the use of DDT during WWII, so students can consider the benefits versus the risks of pesticide use. I found an article in a 1971 issue of American Heritage Magazine for this purpose. (Refer to the Teacher Resources section at the end of this unit.)
Lesson 2 - Routes of Pesticide Exposure
The "Warm-up" Activity for this lesson will be an extended Reading Activity. I selected an excerpt from John Wargo's book, Our Children's Toxic Legacy. As a pre-reading activity, I will ask the class to list all of the pesticides they can think of, and compile the list on the board. Next, I will ask them how they come in contact with each of these pesticides, and write their responses on the board, as well. Finally, before they read the excerpt, I will ask them to (silently) consider their own definition of the word pesticide and whether or not it changes as they read. I prepared a graphic organizer to accompany the reading with some headings already filled in and spaces for students to fill in as they read. The graphic organizer is in Appendix D. After students finish the reading, I will review the information they filled in and elaborate as needed. I want to be sure that they recognize that the word pesticide covers a broad span of products from herbicides to insecticides to disinfectants. Finally, before moving on to "Math," I will ask students to write two or three sentences on the back of the graphic organizer about what they learned from the reading, and if there are any changes they plan to make at home or at school because of what they read.
The Math for this lesson will cover all three pesticide exposure routes. I showed the oral/ingestion route in Lesson 1, so my examples for this lesson will only illustrate inhalation and dermal routes of exposure. I will use the pet collar example given in the narrative above. The problem set I developed is in Appendix E. Problems cover the topics of drinking water, aerosol bug killer, turf weed killer, and food residues. Questions ask for concentration, maximum mass of pesticide allowed, or mass of pesticide detected. All problems require students to consider the units associated with the data provided and figure out how to answer the question, in terms of the units specified. Hopefully they will see how Dimensional Analysis helps them in the process.
Lesson 3 - Interpreting Tables and Graphs
I have another Reading Activity as a Warm-up for this lesson. It's a local newspaper article about families using natural cleaning products in their homes. My introductory questions would be about what products students use to clean their homes, and whether anyone uses common household products like vinegar or baking soda. This article is simpler than the previous one, so I will just ask students to split their paper into three columns. The three headings are "Green Cleaning Examples," "Pros," and "Cons" and students will fill in the columns as they read. Again, I will ask students to write a sentence or two on the back about what they learned and any changes they might make because of what they read.
I selected pieces from governmental documents for students to get a glimpse of the type of reports that are generated by the EPA, and to practice interpreting graphs and tables. The first table, in Appendix F, compares residue levels for three foods, both fresh and dried. I ask students to compare the residue levels and make some generalizations.
Appendix G has a table of Relative Potency Factors for a list of chemicals for all three exposure routes, where applicable. All factors are ratios relative to the chemical Methamidophos, but I want my students to figure that out for themselves; the factor for Methamidophos equals one for each exposure route because the numerator and denominator are the same value (it's being compared to itself). Questions based on the table are also available in the Appendix. The third piece, in Appendix H, is a written explanation plus two graphs that show data for three exposure routes for pest strips and flea collars. Again, I wrote some questions to go with the reading and graphs to check for understanding.
There is certainly a lot more that can be done to teach students about pesticides in their environment, but my goal here is to use the topic as a means to get my students thinking about math at the start of the semester. To conclude this brief unit with an assessment, I will ask the students to keep a food diary for several days. Then, I will provide a table of Chlorpyrifos residue values for them to estimate their total ingestion during that period, and scale it up to estimate the amount they would ingest in a year.
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