Serial Dilution and Chemical Toxicity Lab Objective: To allow students to demonstrate an understanding of a serial dilution while assessing the relative toxicity of a chemical. Time: This lab will take between 1 hour and 1½ hours. Materials: 6 large test tubes Test tube rack 60 live brine shrimp per lab group Liquid “toxic” substance to be tested Salt water (1 teaspoon salt to 100 mls water) 10-ml graduated cylinder Procedure: 1. Chose a “toxic” substance you would like to test. Your goal is to determine what percentage of the substance will kill 50% of the brine shrimp. Label the test tubes 1 through 6. 2. Add 10 mls of the substance you are testing to test tube #1. 3. The next step is to set up a serial dilution. Add 9 mls of salt to each of the other 5 test tubes. 4. Remove 1 ml of the substance from test tube #1 and add it to test tube #2. Cover the opening of the test tube and invert it 3 times. 5. Remove 1 ml of the substance from test tube #2 and add it to test tube #3. Cover the opening of the test tube and invert it 3 times. 6. Remove 1 ml of the substance from test tube #3 and add it to test tube #4. Cover the opening of the test tube and invert it 3 times. 7. Continue until you have done the serial dilution for 5 of the 6 test tubes. Do not add liquid from test tube #5 to test tube #6. Instead, remove 1 ml of the substance from test tube #5 and dispose of it. Test tube #6 is your control. 8. Now add 10 brine shrimp to each of the 6 test tubes. 9. After 10 minutes, count the number of live shrimp in each tube and record it in the data table that follows. 10. Graph your results. Data Table: Concentration of toxic substance Number of shrimp still alive 100% 10% 1% 0.1% 0.01% Control (0%) Graph: Analysis: 1. What does the term LD50 mean? Explain. 2. What was the LD50 of your substance? 3. Can the information you obtained be applied to humans? Why or why not? 4. Do you have any concerns during this lab about doing testing on animals? Why or why not?