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What is Phytoremediation? - Definition & Techniques

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

Scientists have come up with different ways to help keep our environment clean. We are going to discuss phytoremediation and the techniques used in this process in this lesson.

Phytoremediation

What do you do when your carpet is dirty? You vacuum. What do you do when you spill something on your kitchen floor? You mop it. What do you do when water and soil are dirty? Not as easy of a question to answer.

Well, scientists have come up with an answer to that question. The answer is phytoremediation. This is a process of using green plants or trees, such as poplar trees, to clean water and soil by removing, stabilizing, destroying, or transferring contaminants. The contaminants that are cleaned up using phytoremediation are things like metals, such as zinc and iron, and organic contaminants that remain after living organisms die, such as polycyclic aromatic hydrocarbons.

Techniques

To learn more about how phytoremediation works, we are going to follow along as an environmentalist named Rick explains these techniques to budding scientists that are interested in this field.

Rhizofiltration

Rick: The first phytoremediation technique we are going to discuss is one that we use to clean groundwater. Rhizofiltration is the process of using plant roots to take up and store contaminants from surface water or groundwater. This process is either carried out by plants raised in a greenhouse or ones grown in contaminated surface water.

Andy: Groundwater is usually located further down in the soil than plant roots grow. So, how does the groundwater get to the plant roots?

Rick: That's a great question Andy! We pump the groundwater to the surface, mix it with a soil mixture, and then irrigate the plants. Once the roots of the plants are completely saturated with the contaminants, then we pull the roots up and dispose of them as biohazardous waste or burn them.

Phytodegradation

Rick: The next technique I want to discuss is phytodegradation, which is the process of plants taking up the contaminants from water, storing them for a period of time, and then breaking them down within their tissues. This works great because the plants do all the work and we don't have much to do for this technique to work.

Ashley: So what type of contaminants are cleaned by phytodegradation? Also, how do the plants break down the contaminants?

Rick: Phytodegradation is good for breaking down organic contaminants. This includes chemicals that make up carbohydrates and proteins. The plants that we use for this process have enzymes that break down some of the chemicals. The other chemicals are broken down through metabolism, which is the chemical reactions that break apart or build up organic molecules.

Rhizosphere Biodegradation

Rick: This next technique that we use is one that I think is really cool. It uses both plants and microorganisms. Microorganisms, for those of you who don't know, are the very tiny living organisms such as bacteria, fungi, and parasitic worms. Rhizosphere biodegradation, also called phytostimulation, is the technique where the plants release certain substances through their roots into the soil or groundwater. The substances released increase the microorganisms' ability to break down and destroy contaminants at a faster rate.

Kevin: I would assume that this process works mostly with bacteria and fungi. Is that correct?

Rick: Yes, that is correct Kevin. Both bacteria and fungi form symbiotic relationships with plants. These are relationships where both organisms benefit. The plants are able to get rid of substances they don't need and the bacteria or fungi get that same substance since they do need it. It is a win-win!

Phytoextraction

Rick: Our next phytoremediation technique that we use is somewhat similar to rhizofiltration. Phytoextraction is also sometimes referred to as phytoaccumulation. In this technique, the plants absorb the contaminants as they absorb water from the soil. The contaminants are then stored in the plant's leaves, roots, and shoots. The contaminants do not get broken down in this technique.

Andy: Then what happens to the contaminants? Do they just stay in the plant forever?

Rick: What happens next really depends on what we were trying to clean up. We normally utilize this technique to clean metals out of the soil. We either pull the plants and melt them down to extract the metals and send the metals off for recycling or dispose of the plants as biohazardous waste.

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