4.4 Phytoremediation
Untreated waste water from domestic, agricultural, breeding, and industrial activities introduces hazardous heavy metals and pollutants into water sources and soil. Phytoremediation provides an eco-friendly biological alternative to clean up these contaminated environments using specific plants capable of absorbing, degrading, or extracting pollutants.
Learning Objectives
- Define the term phytoremediation and state the origin of the word.
- Explain the role and daily-life applications of phytoremediation in treating polluted soil and water.
- Identify examples of phytoremediation plants and the specific pollutants they absorb.
- Describe the experimental setups used to investigate the effectiveness of phytoremediation plants in controlling water and soil pollution.
Phytoremediation Plants and Their Target Contaminants
Each phytoremediation plant species is suited to a specific habitat and removes particular pollutants from soil or water.
Sunflower (Helianthus annuus)
Hyperaccumulator used to remediate soil polluted by the 1986 Chernobyl nuclear plant explosion. Eliminates heavy metals and radioactive substances.
Water Hyacinth (Eichhornia crassipes)
Long roots accumulate heavy metals such as copper and lead from water, and absorb nutrients like ammonia.
Water Lettuce (Pistia stratiotes)
Fast-growing aquatic plant suitable for treating waste water in waste plants. Accumulates heavy metals and absorbs nutrients.
Water Spinach
Ground water spinach absorbs mercury from soil; river water spinach absorbs cadmium from water. Also absorbs ammonia in soil.
Short Explanation
Term Analysis and Definition
The word phytoremediation combines phyton, meaning plant, and remediate, meaning repair. Phytoremediation is one of the treatment methods that uses plants for the purpose of degradation, extraction, or elimination of polluting substances from soil and water.
Why is phytoremediation important?
It serves as an alternative method in waste water management by eliminating heavy metals and trapping harmful nutrients and microorganisms.
How does it work?
Living plants absorb, degrade, extract, or immobilise environmental pollutants such as toxic heavy metals, excess nutrients, and radioactive isotopes.
Experiment 4.4: Controlling Water Pollution
Problem statement: Are phytoremediation plants effective in controlling water pollution?
Aim: To study the effectiveness of phytoremediation plants in controlling water pollution.
Hypothesis: The roots of common water hyacinth can absorb ammonia found in lake water.
Variables:
- Manipulated: presence of water hyacinths
- Responding: reading of ammonia at the end of the experiment
- Constant: volume of lake water
Procedure overview:
- Dirt and mud are washed and removed from the water hyacinths.
- Containers A and B are filled with 5 litres of lake water and 50 ml of 10% ammonium chloride solution.
- Initial ammonia readings are recorded with an ammonia test kit.
- Six water hyacinths are placed into container A; container B is left without plants.
- Both containers are kept at room temperature for seven days before final ammonia readings are recorded.
Problem statement: Are phytoremediation plants effective in controlling soil pollution?
Aim: To study the effectiveness of phytoremediation plants in controlling soil contamination.
Hypothesis: The roots of water spinach can absorb nutrients such as ammonia in soil.
Variables:
- Manipulated: presence of water spinach
- Responding: reading of ammonia in the soil at the end of the experiment
- Constant: mass of black soil
Procedure overview:
- Black soil is dried in an oven.
- Containers A and B each receive 2.5 kg of dried black soil mixed evenly with 2.5 kg of food waste.
- Ammonia content is tested at the beginning using potassium chloride extraction, filtration, dilution with distilled water, and an ammonia test kit.
- 20 water spinach stalks are planted in container A, while container B acts as a control without plants.
- Equal amounts of water are supplied daily for two weeks before recording final ammonia readings.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is meant by phytoremediation?
Which radioactive substances can be eliminated from contaminated soil by sunflowers?
What heavy metal can be absorbed from soil by the roots of ground water spinach, and which heavy metal is absorbed from water by river water spinach?
Common Mistakes
- Confusing the specific heavy metals absorbed by different plants, for example stating that sunflowers absorb cadmium instead of caesium, strontium, zinc, chromium, copper, lead, and nickel.
- Forgetting that excessive proliferation (blooming) of phytoremediation plants such as water hyacinths can lead to water deoxygenation and harm aquatic life.
- Omitting the control container (container B without plants) when describing experiments testing the phytoremediation of water or soil.
Concept Misunderstandings
Phytoremediation adds chemical reagents to break down contaminants.
Phytoremediation is a biological process relying on the natural absorption, extraction, and accumulation abilities of living plants.
All plants can absorb radioactive substances equally.
Only certain plants, known as hyperaccumulators like sunflowers, have the specialised capacity to accumulate radioactive substances and high levels of toxic metals.
Summary
- Phytoremediation means using plants (phyton = plant, remediate = repair) to degrade, extract, or eliminate contaminants from soil and water.
- Sunflowers are hyperaccumulators used to remediate soil contaminated with heavy metals (Zn, Cr, Cu, Pb, Ni) and radioactive materials (caesium and strontium) after nuclear disasters like Chernobyl.
- Eichhornia crassipes (water hyacinth) and Pistia stratiotes (water lettuce) clean waste water by taking up nutrients (ammonia) and heavy metals (such as copper and lead).
- Water spinach absorbs mercury from the ground, cadmium from water, and nutrients like ammonia from soil.
Short Activity
Objective: identify phytoremediation plants, their pollutants, and the meaning of key terms.
A. Objective Quiz
Which plant was used to remediate soil polluted by radioactive caesium and strontium following the Chernobyl nuclear disaster?
What is a negative ecological effect if water hyacinths bloom excessively in a water body?
B. Fill in the Blanks
In the term phytoremediation, the word phyton means plant and remediate means .
The roots of ground water spinach can absorb from contaminated soil.
C. Matching / Drag and Drop
Match each plant used in phytoremediation with its specific pollutant or role described in the textbook. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Plant to Its Target Pollutant / Role
Write the correct plant next to each description.
| Target Pollutant / Role | Phytoremediation Plant |
|---|---|
| 1. Absorbs radioactive caesium and strontium from soil | |
| 2. Accumulates copper, lead, and ammonia from water | |
| 3. Fast-growing aquatic plant used to treat waste water in waste plants | |
| 4. Absorbs cadmium from water |
Answer choices: Sunflower • Eichhornia crassipes • Pistia stratiotes • River water spinach
