Acute Toxicity: LD50 by the Numbers
From IPM for Teachers Curriculum:IPM Tactic
Time : / 1 class periodPreparation Time :
Materials : /
- Brine Shrimp (available from most pet stores or can be cultivated from dry eggs)
- Handouts
- Petri Dishes
- Plastic Pipets
- Bathroom Cleaners (4 with one being environmentally friendly)
- Waste Container
Abstract
Students observe brine shrimp as they are affected by household cleaners. Students develop an observation scale, collect and analyze data.
Objectives
Students will be able to
- make observations about a living organism
- recognize that household products impact their environment
- Compare the relative toxicity of chemicals by observing the relationship of dose to response on shrimp.
National Science Education Standards
Content Area C- The Interdependence of Organisms
Human beings live within the worlds ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening global stability, and if not addressed, ecosystems will be irreversibly affected.
Teacher Background
Many people are not aware of the potential harmful effects of household chemicals and pesticides. Toxicity is the ability of a chemical to cause injury or death. This activity allows students to quantitatively measure the toxic effects of common household chemicals and/or pesticides on brine shrimp (sea monkeys). Students will dose a group of brine shrimp with specific amounts of test chemicals and notice how the chemicals affect their ability to swim. At some point, enough chemical will be added so that some of the shrimp are killed. LD50 is the term for "lethal dose at which 50% of the animals die". This measurement is used by the Environmental Protection Agency to measure the acute toxicity pesticides, that is, how much in a single dose will cause injury or death. A small number for the LD50 means a small amount of the chemical is acutely toxic. In this experiment, students will be able to compare the relative toxicity of chemicals chosen by observing the relationship of dose to effect on the shrimp.
Resource URLs
Teacher:
Read background material on chemical use and acute toxicity
Activity
1. Ask students "Have you ever cleaned your bathroom?" then lead them in a discussion about what they use to clean and what the bathroom smells like right after using the cleaners. Have the students talk about how being around the cleaners for too long makes them feel.
2. Group students into groups of 4 or 5 and show students some common bathroom cleaners, (pick one environmentally friendly cleaner to be part of the group) and tell them that they will be testing these cleaners' toxicity on brine shrimp.
3. In each group have students place ten brine shrimp in each of 5 Petri dishes using a pipet to transfer the shrimp.
4. Have students make observations about how the shrimp are moving in the Petri dish. Come up with some common terminology that describes the movement.
5. Have students place a few drops or sprays of each cleaner in 4 of the petri dishes, use a different cleaner for each dish. Do not add any cleaner to the 5th dish.
6. During the exercise, have groups write and draw how the chemicals affect how the shrimp swim.
7. Based up on the previous experience, students, as a group, design a more vigorous test of their cleaners.
8.Remind students of the LD50 definition. Can they incorporate it into their experiment? Does their experiment include controls? Have they identified the variables in this experiment? Students write up protocols and carry out the experiment.
9. Students collect data and analyze it. They should include in their write-up how the shrimp are affected and which cleaner they would pick for their home.
Hold a class discussion as to what this has taught the students about the use of chemicals in their home.
Assessment
Students can be evaluated on their inclusion of controls and analysis of data.