14: Phytoremediation

Question 1

Define phytoremediation, phytodegradation, phytovolatilization, phytoextraction, phytoaccumulation, phytostabilization, rhizodegradation, and hyperaccumulators.

Answer 1

Phytoremediation: The use of plants and their associated microbes for environmental cleanup

Phytodegradation: Breakdown of organic pollutants directly by plant enzymatic activities

Phytovolatilization: Volatilization of organic pollutants after uptake by plants

Phytoextraction: Removal of organic pollutants from an environment by plant uptake

Phytoaccumulation: Accumulation of organic pollutants in plant tissue after uptake

Phytostabilization: Stabilization of organic pollutants in soil

Rhizodegradation: Degradation of pollutants in a plants rhizosphere (roots)

Hyperaccumulators: Special category of plants that accumulate inorganic elements 100 times greater than other species.

Question 2

Explain how trees can be used to contain contaminants through hydraulic control.

Answer 2

Trees with large water uptakes can act as natural pumps that transport water and contaminants out of the subsurface. They can create a cone of depression and change local groundwater flows.

Question 3

List advantages and disadvantages of phytoremediation.

Answer 3

Advantage
§ Relative low cost
§ May reduce exposure to pollutants
§ Viewed as a “clean” remediation technique by the public

Disadvantages
§ Plants must be able to survive in contamination zone. Soil properties, toxicity levels, and climate may kill plants.
§ Shallow treatment 50 cm to 3 m range.
§ Slower remediation timeline
§ Management of contaminated plants

Question 4

Describe the types of plants and pollutants best treated by phytoaccumulation.

Answer 4

Hybrid poplar whips work well due to high accumulation rates.

Question 5

Describe the types of plants and pollutants best treated by hydraulic control.

Answer 5

Phreatophytes (mainly poplars and willows) are excellent at hydraulic control due to their large water uptake rates (1,000 gal/day) and deep root structure.

Question 6

Describe the types of plants and pollutants best treated by phytovolatilization.

Answer 6

Poplars are best due to high transpiration rates.

Question 7

Explain how KOW can be used to predict how chemicals will be taken up by plants.List the ranges and typical pollutants

Answer 7

Kow = octanol:water partition coefficient, a measure of hydrophobicity

Pollutants with log Kow values of 0.5 to 3 are candidates for phytoremediation. <0.5 pollutants cannot be uptaken by plants, and > 3 get stuck in plant cells.

Typical pollutants with acceptable Kow values include TCE, herbicides, explosives, petroleum hydrocarbons, MTBE, and PCBs

Question 8

Explain the mechanism in the plant for phytovolatilization and where in the plant it is most effective.

Answer 8

Transpiration is the mechanism in a plant that enables phytovolatilization. The leaves are the most effective part of the plant.

Question 9

Describe the significance of enzymatic transformation in phytovolatilization of chlorinated solvents.

Answer 9

Enzymatic transformation of chlorinated solvents involves the bonding of chlorinated solvents to bigger molecules, reducing the overall toxicity.

Question 10

Define root exudates and explain how they can enhance rhizodegradation.

Answer 10

Root exudates may contain lipophilic compounds that increase pollutant water solubility