Using Thlaspi plants to clean zinc-contaminated soil
The materials required for the science fair project:
- 400 Thlaspi seeds
- 1 shallow container (~10cm height)
- Soil with 600ppm zinc (enough to fill the shallow container)
- 5 small containers
1. For this science fair project, the independent variable is the number of cycles for planting the Thlaspi plant in the soil. The dependent variable is the parts per million (ppm) of zinc in the soil. This is determined by sending the soil samples to an independent laboratory for testing. The constants (control variables) are the amount of the soil, the surface area of the container, the number of plants and the growth cycle of the plants.
2. Label the 5 small containers as “Initial”, “1st cycle”, “2nd cycle”, “3rd cycle” and “4th cycle”. Pour a small amount of soil into the container labeled “Initial”.
3. Fill the shallow container with soil.
4. Count and spread exactly 100 Thlaspi seeds over the surface of the soil. Allow the seeds to grow and mature over the next 30 days.
5. After 30 days, remove the Thlaspi plants from the soil. Scoop out a sample of soil from the shallow container and transfer it to the container marked “1st cycle”.
6. Repeat steps 4 and 5 another 3 times using the same soil. Do not add any fresh soil to the container. Keep the soil samples taken on the 60th, 90th and 120th days in the containers marked “2nd cycle”, “3rd cycle” and “4th cycle” respectively.
7. At the end of the 4th cycle, send all 5 soil samples to an independent test laboratory to check for the zinc content in the soil. Record the results in a table, as shown below.