Phytoremediation Lab

Phytoremediation Lesson Plan

for AP Environmental Science

By Sara Dorsey and Krista Larsen

The series of lessons on this page are in part based on a lab, Phytoremediation in Education: Textile dye teaching experiments. The original lab is designed for use in undergraduate environmental science labs and was adapted for use in middle school classrooms. The series of lessons presented here describe the teaching required prior to the lab, the incorporation of experimental design practice for students which makes the lab more appropriate for AP Environmental Science students, and the writing of a formal lab report by students.

This series of lessons and hands-on laboratory activities is designed for use in an AP Environmental Science high school class taught to 12th grade students. By the end of this lesson and experiment series, students will understand how phytoremediation works, under which circumstances it is useful, and how to conduct an experiment to explore phytoremediation. This experiment will take place in the second semester of the course, after significant scaffolding and practice in experimental design have already been provided. Students will work in groups to support differences in ability and understanding of the material and skills required.

The outcomes of this work are :

1. to design an effective experiment to demonstrate phytoremediation,
2. to complete and present a poster describing a specific mode of phytoremediation,
3. to read and incorporate aspects of published scientific work on phytoremediation and genetic modification into their own investigation, and
4. to complete a formal lab report containing an introduction, methods, results, and discussion section.

To know whether students have successfully completed this lab, students will complete structured peer-review of one-another’s work throughout the series. Work will also be assessed by the teacher.

Scientific Background:

Phytoremediation is a cost-effective and efficient method to remove environmental toxins from soils and wetlands. Different species of plants use different mechanisms for removal of toxins including taking up the toxin, using enzymes to digest the toxin, and using microbes within the root system to break down toxins. Plants can successfully remediate heavy metals, organic toxins, gasoline, textile dyes, and many other hazardous wastes. Some work is being done to genetically alter plants with phytoremediation capabilities to perform at higher efficiencies leading to increased environmental benefit.

Instructional objectives for students:

• Students will be able to explain the uses and limitations of phytoremediation
• Students will be able to discuss the various mechanisms of phytoremediation
• Students will be able to design an experiment using limited variables (either dye concentration or type of dye) and sufficient sample sizes to explore the uses and limitations of phytoremediation
• Students will be able to construct an argument using evidence from their experiments identifying the mechanism of phytoremediation and its limitations
• Students will be able to describe how genetic modification can be used to increase the phytoremediation capability of specific plants
• Students will be able to justify whether benefits of genetic modification of plants to increase phytoremediation outweigh the drawbacks.

Brief description of lesson

Prior to beginning this series of lessons, the teacher or students must start seedings. Sunflower seeds take 7-10 days to germinate and plants should be allowed to reach approximately 3 inches tall in potting soil. Once they reach that height, they can be moved into tubes containing Hoagland’s Solution (a hydroponic growing medium). To move the seedlings, carefully extract them from the soil including as much of the root matter as possible. Rinse soil from the roots in water and place the roots of the seedlings into the Hoagland’s Solution. Allow the plant to grow in Hoagland’s Solution for another week to ensure they will be ready to take up dyes during student experiments.

While our students will be designing labs on their own, they will be given some basic parameters for how to conduct this lab.

Students will enter these lessons with a basic understanding of toxicology, chemical spills, and hazardous wastes. The goals of Day 1 are for students to understand the concept of phytoremediation and to design their own phytoremediation experiments. The goals Day 2 are for students to explore the mechanisms of phytoremediation in greater depth, to have their experimental designs reviewed by peers, and to begin implementing their experiments. The goals of Day 3 are for students to measure their results and begin working on their written lab reports. The goals for Day 4 are for students to learn about genetic modification of plants to increase phytoremediation and to outline a risk/benefit analysis of GM of plants to increase phytoremediation.

Timing:

Day 1

• 10 minutes: Teacher will elicit prior knowledge. Facilitate student discussion of methods for addressing toxins in the environment. Students will pair-share and then discuss as a class known methods for addressing toxins in the environment. Generate a list on the whiteboard.
• 35 minutes: Teacher will lecture on current methods for addressing toxins in the environment including phytoremediation. Facilitate reading the abstract of the paper “Phytoextraction of Heavy Metals: A Promising Tool for Clean-Up of Polluted Environment?”. Student will: take notes, read abstract, participate in discussion, and ask questions.
• 10 minutes: Teacher will explain homework assignment on mechanisms of phytoremediation. Students will get started on homework.

Day 2

• 15 minutes: Teacher will facilitate productive group work and answer student questions. Students will share research on different mechanisms of phytoremediation from homework assignments. Take notes on each mechanism using graphic organizer provided.
• 10 minutes: Teacher will present problem for students to address and materials available for experimental design. Students will ask questions. Break into 6 groups.
• 30 minutes: Teacher will facilitate beginning student group discussions of experimental designs. Answer student questions. Students will work in groups to design an experiment using experimental design rubric. Write methods section of full lab report.

Day 3

• 20 minutes: Teacher will present experimental design checklist to students for use in peer review process. Facilitate productive group work and answer student questions. Students will peer review experimental designs from other groups using experimental design peer feedback form. Edit own experimental design and methods section of lab report after peer feedback.
• 20 minutes: Teacher will pass out materials and supervise student handling of dyes. Students will work in groups to implement experiment.
• 15 minutes: Teacher will review reading from previous night. Present lab report expectations to students. Students will receive lab report grading rubric

Day 4

• 55 minutes: Teacher will facilitate data collection from group experiments. Before students begin, demonstrate use of colorimeter to test dye removal. Demonstrate use of scalpel on experimental plants to create microscope slides. Supervise student use of tools and be available to answer questions. Students will work in groups to measure and record results using colorimeter and microscopes. Begin work on data compilation and analysis.

Day 5

• 25 minutes: Teacher will introduce genetic modification of plants to increase their phytoremediation capabilities. Facilitate group investigation of Table 2 and the Conclusion section of the scientific paper “Phytoextraction of Heavy Metals: A Promising Tool for Clean-Up of Polluted Environment?”. Students will read and participate in discussion.
• 30 minutes: Teacher will assist students in beginning their risk/benefit analysis for their discussion. Students will complete discussion notes to assist in writing risk/benefit analysis for discussion section of lab report.

Homework:

• Day 1: Students will be assigned a mechanism of phytoremediation to research (rhizofiltration, phytotransformation, phytoextraction, phytostabilization, rhizodegradation, or phytovolatization). Students will create a small poster presentation that includes a brief explanation of their assigned phytoremediation mechanism and 1-2 examples of how their mechanism has been used in the field.
• Day 2: Students will read the introduction section of the paper “Phytoextraction of Heavy Metals: A Promising Tool for Clean-Up of Polluted Environment?”.
• Day 3: Students will work on writing their introduction section of their full lab report.
• Day 4: Students will work on their results and analysis sections of their full lab report.
• Day 5: Students will write the discussion section of their full lab report.

Student assessment (Knowledge, skills, and understanding)

Students will be assessed on their learning based on their peer reviewed experimental design and their written lab reports. Prior to the implementation of their experiments, students will peer review one another’s designs using a checklist of important concepts in experimental design. Students will demonstrate their understanding of the uses, limitations, and mechanisms of phytoremediation in the introduction section of their lab reports. Their evidence-based arguments will be assessed via the results and discussion sections of their lab reports.

Adjustments for special needs students:

Students will be working in groups to design and implement their experiments. The requirements for their final written lab reports lab reports may be modified for students based on their specific learning requirements.

Methods and results sections may be written as a group. All other sections written will be completed independently.

Materials, equipment and supplies*:

• Potting soil (30L)
• Pots (72)
• Grow lights (4 shelves)
• Sunflower Seeds Helianthus annuuss (100)
• Hoaglands solution (5 L)
• Test Tubes (72)
• Paper support circles (72)
• Dyes (Bismark Brown, Methyl Red, Methyl Blue, Methyl Green, Alizarin Yellow, Crystal Violet)
• Microscopes (6)
• Scalpels (6)
• Vernier Colorimeter and LabQuest Data Interface (6)
• Cuvettes (30)

*All quantities are approximate, numbers listed here are for one class based on a class size of 20-25 students working in 6 groups

Safety concerns:

Because some dyes are toxic, students will be required to use gloves and safety goggles when handling dyes and treated plants. The teacher will demonstrate appropriate use of scalpels for creating microscope slides and will be present to supervise student use of all tools and dyes.

References and Resources

Phytoremediation in Education: Textile dye teaching experiments, Jwan H. Ibbini, Lawrence C. Davis, and Larry E. Erickson, International Journal of Phytoremediation, 11:451–462, 2009

• The lab investigation described in this lesson plan was adapted from this article for use in a high school setting. This article also contains a robust introduction that describes the process and mechanics of phytoremediation.

Phytoextraction of Heavy Metals: A Promising Tool for Clean-Up of Polluted Environment?, Jachym Suman, Ondrej Uhlik, Jitka Viktorova, and Tomas Macek, Front Plant Sci. 2018; 9: 1476.

• This is the article that students will read and refer to in their own laboratory write-up. This article is a meta-analysis of research about genetic modification of plants to increase phytoremediation of heavy metals. Table 1 presents the advantages and disadvantages of GM for phytoremediation. Table 2 lists studies prior to 2018 involving GM of plants. It lists the gene name, source of the gene, species the gene was inserted into, heavy metal studied, and effect of the GM.

Phytoremediation, Andreas D. Peuke and Heinz Rennenberg, EMBO Rep. 2005 Jun; 6(6): 497–501.

• This article contains a detailed description of many of the specific mechanisms of phytoremediation. It also outlines the usefulness of phytoremediation for large-scale repair of degraded soils.

Phytoremediation Database

• This website provides a searchable listing of plants that can be used for phytoremediation. When possible, the toxin that the plant can take up and the phytoremediation method that the plant uses is also listed in the database.

Phytoremediation of textile dyes and effluents: Current scenario and future prospects, Rahul V. Khandare, Sanjay P. Govindwar, Biotechnology Advances Volume 33, Issue 8, December 2015, Pages 1697-1714

• This article describes specific plant species and enzymes used in phytoremediation of textile dyes. The article also describes the successful creation of a constructed wetland including plants to conduct phytoremediation of textile dyes.