TCE Contamination and Cleanup Curriculum How Much TCE is Allowed by Law in Drinking Water? Author: S. Stewart Editor: Stephanie Nardei Time: 30 min Preparation 15 min Time: Materials: Per student group: Solution of green food coloring in water, 5 mL Small beakers or cups, 6 Pipette to measure 1 mL, 1 Graduated cylinder, 1 Test tube brush Abstract This Explain lesson introduces students to Environmental Protection Agency (EPA) limits on concentrations of contaminants in drinking water. Students perform a serial dilution to produce a 5 ppb solution of food dye, a simulation of the allowed concentration of TCE. Students discover at this low concentration, detection of the contaminant is difficult. This means cleaning up all of a contaminant is not possible since detection methods cannot tell when the contaminant is completely gone. Purpose This Explain lesson has students visualize the EPA limit on concentration of TCE allowed in drinking water by creating an equivalent dye concentration through serial dilution. Objectives Students will be able to: 1. Perform a serial dilution. 2. Calculate concentrations of dilutions. 3. Explain why EPA standards are above 0 ppb (why we can’t get rid of all the toxins). National Science Education Standard: Content I to be added Teacher Background The unit ppb is measured in micrograms solute per liter total solution (solute plus solvent). Parts per billion = ppb = mass in ug of solute volume in L of total solution Example: 8 ppb TCE = 8 ug TCE 1 L solution of TCE Contamination and Cleanup Curriculum water and TCE Prepare initial green dye solution ahead of time by adding green food dye to tap water. Color should be deep green. Use at least five drops dye per 100 mL water. Related and Resource Websites Council on water quality: http://www.councilonwaterquality.org/ ATSDR Toxicological Profile for Trichloroethylene (TCE) http://www.atsdr.cdc.gov/toxprofiles/tp19.html Activity 1. Teacher explains that EPA sets limits for concentrations of contaminants allowed in drinking water. Usually these limits are measured in parts per billion (ppb), because the amounts of contaminants that can affect living things are often very tiny. a. Teacher explains to students that the green dye represents the contaminant TCE. They will be diluting it to the concentration allowed in drinking water by the EPA, in order to visualize 5 ppb, the EPA standard for TCE. 2. Teacher explains how to make a serial dilution. 3. Students start with 5 mL green dye in 95 mL water, and then continue by transferring 1 mL of the first solution into 99 mL water, and so on. See student lab sheet. 4. Students complete student lab sheet. Closure Teacher prompts discussion of questions on lab sheet. Embedded Assessment Assess the student responses on student lab sheet. Homework N/A