Phytoremediation uses plants to remove pollutants from soil and water. Plants can uptake and concentrate metals and organic compounds in their roots and biomass (phytoextraction), transform contaminants into less toxic forms (phytotransformation), or stabilize pollutants through root sorption and prevention of mobility (phytostabilization). The mechanisms depend on the contaminant type and soil properties. Phytoremediation can be an effective, low-cost in situ technique for cleaning contaminated sites.

2. Phytoremediation
• Use of vegetation to contain,
sequester, remove, modify or degrade
pollutants from soil and water
• Pollutants: metals or organic
compounds
• Metals either taken up or adsorbed on
roots
• Organic compounds degraded or
detoxified
– before uptake by the plants
– by agents released to the rhizosphere

3. • Terrestrial, aquatic and wetland
plants and algae can be used for the
phytoremediation process under
specific cases and conditions of
hydrocarbon contamination
(Nedunuri et al. 2000, Radwan et al.
2000, Siciliano et al. 2000).

4. Mechanism
• The mechanisms and efficiency of
phytoremediation depend on the type of
contaminant, bioavailability and soil properties
(Cunningham and Ow, 1996).
• There are several ways by which plants clean up
or remediate contaminated sites.
• The uptake of contaminants in plants occurs
primarily through the root system, in which the
principal mechanisms for preventing toxicity
are found.
• The root system provides an enormous surface
area that absorbs and accumulates water and
nutrients essential for growth along with other
non-essential contaminants (Raskin and Ensley,
2000).

5. • Phytoextraction or phytoaccumulation
– Plants used to accumulate contaminants in the roots and
aboveground biomass
– Can be a relatively low cost option for a large area
– Results in biomass that must be properly disposed of or
reused
• Phytotransformation or phytodegradation
– Uptake of contaminants and transformation to more stable,
less toxic, or less mobile forms
– Eg. metal chromium can be reduced from hexavalent to
less mobile (and non-carcinogenic) trivalent chromium
• Phytostabilization
– Mobility and migration of contaminants are reduced through
sorption onto or into the plant
• Rhizodegradation
– Breakdown of contaminants through activity of the
rhizosphere
• Rhizofiltration
– Water remediation technique
– Used to reduce contamination in natural wetlands and
estuary areas.

6. Phytoextraction
 Uptake of chemical by the plant.
 Works well on metals such as lead, cadmium,
copper, nickel etc.
Detroit lead contaminated site was removed with
Sunflower and Indian Mustard.
- recently researchers at the University of
Florida have determined that a species of
fern, native to the south east, stores high
concentrations of arsenic in its fronds and
stems more than 200 times the
concentration in the soil.

7. Phytotransformation/Phytodegradation
 pollutant is taken up by the plant and
transformed in plant tissue (to be
effective
must be transformed to a less toxic form).
 Trichloroethylene (TCE), a prevalent
ground water contaminant, transformed
to less toxic
metabolites by using hybrid poplar tree.

8. Phytostabilization
 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.

9. Rhizofiltration
 Use the extensive root system of plants
as a filter.
 1995, Sunflowers were used in a pond
near Chernobyl
• approx. 1 week they had
hyperaccumulated several thousand times
the concentration ofcesium and strontium.
• hyperaccumulation can contain 100 times
or more of contaminant than normal plant.

10. Phytovolatilization
• This involves the use of plants to take up contaminants
from the soil, transforming them into volatile forms and
transpiring them into the atmosphere (USEPA, 2000).
• also involves contaminants being taken up into the body
of the plant, but then the contaminant, a volatile form
thereof, or a volatile degradation product is transpired
with water vapor from leaves (EPA, 2000).
• may also entail the diffusion of contaminants from the
stems or other plant parts that the contaminant travels
through before reaching the leaves (Raskin and Ensley
2000).

11. Hydraulic Control
• This is the control of the water table and the soil field capacity by
plant canopies.
• Phytoremediation projects employing hydraulic control generally use
phreatophytic trees and plants that have the ability to transpire large
volumes of water and thereby affect the existing water balance at
the site.
• The increased transpiration reduces infiltration of precipitation
(thereby reducing leaching of contaminants from the vadose zone) or
increases transpiration of groundwater, thus reducing contaminant
migration from the site in groundwater plumes.

13. waste
water

14. Conclusion
• To remove pollutants from soil, sediment and/or water and
air, plants can break down, or degrade organic pollutants or
contain and stabilize inorganic contaminants by acting as
filters or traps.
• The success of phytoremediation at a given site cannot
always be attributed to just one of these mechanisms
because a combination of mechanisms may be at work.
• Phytoremediation is a low cost, solar energy driven and
natural cleanup technique, which are most useful at sites
with shallow, low levels of contamination.
• They are useful for treating a wide variety of
environmental contaminantsand are effective with or in
some cases, in place of mechanical cleanup methods

15. • Phytoremediation harnesses natural processes to assist in the clean-
up of pollutants in the environment.
• The mechanisms by which plants promote the removal of pollutants
are varied, including uptake and concentration, transformation of
pollutants, stabilization, and rhizosphere degradation, in which plants
promote the growth of bacteria underground in the root zone that in
turn break down pollutants.
• Phytoremediation is amenable to a variety of organic and inorganic
compounds and may be applied either in situ or ex situ.
• In situ applications decrease soil disturbance and the possibility of
contaminant from spreading via air and water, reduce the amount of
waste to be land filled (up to 95%) and are low-cost compared with
other treatment methods.
• In addition to this, it is easy to implement and maintain, does not
require the use of expensive equipment or highly specialized
personnel and is environmentally friendly and aesthetically pleasing
to the public.