PhD 1st Semester
Department of Botany
Dr Aziz Ullah
Department of Botany
Introduction of Phytoremediation
2. Various phytoremediation processes
3. Role of genetics
6. Advantages and limitations
The use of plants which lessen the
environmental problem without the need to dig
up the contaminant material and dispose of it
phyto = plant
remedium = restoring balance
Phytoremediation may be applied
wherever the soil or stagnant water
environment has become polluted or
Examples where phytoremediation
has been used successfully include
the restoration of abandoned metalmine workings, reducing the impact
of contaminants in soils, water, or air.
How does Phytoremediation work?
First process is Phytodegradation, which is when a plant
takes in TCE(Trichloroethylene) and degrades it into CO2
and chlorine before released into the atmosphere.
Another process is phytovolatilization which is when some
chemicals are taken in through the xylem and converted
into a gas through the stomata of the plant.
When plants go through these processes they leave
chemicals in stem for easy collection.
Various phytoremediation processes
A range of processes mediated by plants or algae are
useful in treating environmental problems:
Plant roots uptake metal
from the soil and translocate them to their
above soil tissues
Once the plants have grown and absorbed
the metal pollutants they are harvested
and disposed off safely
This process is repeated several times to
reduce contamination to acceptable levels
Hyper accumulator plant species are used
on many sites due to their tolerance of
relatively extreme levels of pollution
Avena sp. , Brassica sp.
Metal compounds that have been
successfully phytoextracted include zinc,
copper, and nickel
Vegetation holds contaminated soils in place
Root system and low growing vegetation
prevent mechanical transportation of pollutants
from wind and erosion.
Trees transpire large quantities of water
(more than 15 gal/day) so pumping action
prevents contaminants from migration into the
water table (leaching).
chemical modification of environmental substances as a
result of plant metabolism resulting in their inactivation,
degradation (phytodegradation), or immobilization
Trichloroethylene (TCE), a widespread ground
water contaminant, transformed to less toxic
metabolites by using hybrid poplar tree.
Air Force facility in Texas using cottonwoods to
treat a large ground water cloud of TCE.
EPA research lab using parrot feather (a
common aquatic weed) for TNT treatment.
Phytostimulation is the process where root released
compounds enhance microbial activity in
Rhizosphere = soil + root + microbes
Enhanced rhizosphere biodegradation
Plant assisted bioremediation
Sugars, alcohols, and organic acids act as carbohydrate
sources for the soil microflora and enhance microbial
growth and activity.
Act as chemotactic signals for certain microbes.
The roots also loosen the soil and transport water to the
rhizosphere thus enhancing microbial activity
Digest organic pollutants such as fuels and solvents,
producing harmless products
Plants uptake contaminants which are water soluble and
release them into the atmosphere as they transpire the
The contaminant may become modified along the way,
as the water travels along the plant's vascular system
from the roots to the leaves, whereby the contaminants
evaporate into the air surrounding the plant
Poplar trees volatilize up to 90% of the TCE they absorb
filtering water through a mass of roots to
remove toxic substances or excess
The contaminants are either adsorbed onto the
root surface or are absorbed by the plant roots
1995, Sunflowers were used in a pond near
Plants used for
Chernobyl -sunflowers were grown in
radioactively contaminated pools
Role of genetics
Genetic engineering is a powerful method for
enhancing natural Phytoremediation
capabilities, or for introducing new capabilities
Example, genes encoding a
nitroreductase from a bacterium were inserted
into tobacco and showed faster removal of TNT
and enhanced resistance to the toxic effects of
A plant that absorbs toxins, such as heavy
metals, to a greater concentration than that in
the soil in which it is growing
A number of interactions may be affected by
mutualism (including mycorrhizae)
Plants are able to translocate and accumulate
particular types of contaminants:
plants can be used as biosensors of subsurface
Phytoscreening may lead to more optimized site
investigations and reduce contaminated site
Cost effective when compared to other more
“natural” method, more aesthetically pleasing.
minimal land disturbance.
reduces potential for transport of
contaminants by wind, reduces soil erosion
hyper-accumulators of contaminants mean a
much smaller volume of toxic waste.
multiple contaminants can be removed with the
Slow rate and difficult to achieve acceptable
levels of decontamination.
Possibility of contaminated plants entering
the food chain.
Possible spread of contaminant through
Trees and plants require care.
Contaminant might kill the tree.
Degradation product could be worse than
Only surface soil (root zone) can be treated
Cleanup takes several years
Although much remains to be studied,
Phytoremediation will clearly play some role in the
stabilization and remediation of many contaminated
The main factor driving the implementation of
Phytoremediation projects are low costs with significant
improvements in site aesthetics and the potential for