Phytoremediation Lab: Basic Procedure

In the lesson sequence, we describe allowing students to design their own experiments. To help aid students in how to do this lab, we will provide the following basic parameters on how this lab works.

Step 1: Grow sunflowers. It takes between 10-14 days to germinate and produce seedlings that are tall enough for this experiment. We used "Renee's Garden" brand seeds from a hardware store and experienced a 2/3 successful germination rate. Whatever seeds you use, be sure to plant more than enough to supply your experimental needs.

Step 2: Once sunflowers have reached 2-3 inches tall, VERY CAREFULLY remove them from their pots and rinse as much soil as possible from their roots with squirt bottles and swishing them in a dish of water. You can see that the sunflowers grow roots quickly. A 2-3 inch seedling can easily grow roots out the bottom of a 4 inch pot. Don't let the seedlings grow too tall in the pots.

Step 3: Place seedlings in 25 x 100 mm test tubes in a rack. If needed, support them with paper rings.

Step 4: Fill the test tubes with a hydroponic growing solution and allow seedlings to grow for another week (this allows damaged roots to recover). We used a general hydroponic growing medium called "MaxiGro" and followed the package guidelines for mixing the solution.

Step 5: Following "Phytoremediation in Education: Textile Dye Teaching Experiments", we selected dyes that we had on hand that we knew would likely be taken up by the sunflowers: Methyl Green, Bisthmuth Brown, Methylene Blue, Phenol Red, Crystal Violet, and Methyl Orange. We used a Vernier Colorimeter to standardize our dye concentrations. All dyes shown are at the highest concentration we will be using.

• Our students will be designing which variable they are interested in- either dye concentration or dye type.

Step 6: After recording a starting absorbance of the dye, transfer the sunflower seedlings into the solution.

Step 7: 24 hours after the seedlings were transferred, the absorbance of the dye was measured again.

Step 8: Students will collect data and will find a % change in absorbance.

Step 9: Prepare wet mount slides of thin slices of seedling stems. Under high power with a compound microscope, see if any dye is visible within the sunflower cells.