Phytoremediation uses plants to remove, transfer, stabilize, or destroy contaminants in soil, sediment, surface water and groundwater. It involves processes such as phytoextraction, rhizofiltration, phytostabilization, phytodegradation, rhizodegradation, phytovolatilization, and phytohydraulics. Genetic engineering can be used to enhance plants' natural abilities to remediate contamination. While phytoremediation is more environmentally friendly than traditional methods, it typically takes longer and plant growth conditions must be suitable for the contaminants present.

1. PHYTOREMEDIATION

2. Introduction
 Phytoremediation is the use of living green plants for
in situ risk reduction and/or removal of contaminants
from contaminated soil, water, sediments, and air.

3. OVERVIEW

4. Phytoextraction
 Plant roots uptake metal contaminants
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.
Contaminants removed:
 Metal compounds that have been
successfully phytoextracted include zinc,
copper, and nickel

5. Rhizofiltration
 It is concerned with the remediation of contaminated groundwater
 The contaminants are either adsorbed onto the root surface or are
absorbed by the plant roots
 Plants used for rhizofiltration are acclimated to the pollutant
1
• Plants are hydroponically grown in clean water
rather than soil, until a large root system has
developed
2
• Water supply is substituted for a polluted
water supply to acclimatize the plant
3
• They are planted in the polluted area where
the roots uptake the polluted water and the
contaminants along with it
4
• As the roots become saturated they are
harvested and disposed of safely
Chernobyl - sunflowers
were grown in radioactively
contaminated pools

6. Phytostabilisation
 To immobilize soil and water contaminants from
migration
 Mechanisms
Phytochemical complexation in the root zone –
precipitation
Transport protein inhibition on the root membrane (B)
Vacuolar storage in the root cells (C)
Pb, Cu, Zn – Agrostis tenuis

7. Phytodegradation
 It is the degradation or breakdown
of organic contaminants by internal
and external metabolic processes
driven by the plant
 Mechanisms:
(A) Plant enzymatic activity
oxygenases- hydrocarbons
nitroreductases- explosives
(B) Photosynthetic oxidation
 Used in breakdown of ammunition
wastes, chlorinated solvents such
as TCE (Trichloroethane),
degradation of organic herbicides.

8. Contd..
External Process Internal Process

9. Rhizodegradation
 It is the breakdown of organic contaminants in the soil by soil dwelling
microbes which is enhanced by the rhizosphere‘s presence
 Rhizosphere = soil + root + microbes
 Symbiotic relation
 Also called:
Enhanced rhizosphere biodegradation
Phytostimulation
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

11. Phytovolatilization
 Plants uptake contaminants which are
water soluble and release them into the
atmosphere as they transpire the water
 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
or volatilize into the air surrounding the
plant
 Poplar trees volatilize up to 90% of the
TCE they absorb
 Selenium and Mercury - Arabidopsis
thaliana L. and tobacco

12. Phytohydraulics
 The use of plants to control the migration of
subsurface water through the rapid uptake of
large volumes of water by the plants
 Plants - acting as natural hydraulic pumps
 A dense root network established near the
water table can transpire up to 300 gallons of
water per day
 This fact has been utilized to decrease the
migration of contaminants from surface water
into the groundwater (below the water table)
and drinking water supplies

13. LEVEL OF POLLUTANT
 Sampling
 Field sampling quality assurance
 Avoiding contamination of
samples
 Equipment cleaning
 Sample labels
Recent trend
 Immunoassay testing and other
technology may be used to provide
on site screening.
 This work shall only be carried out
by properly trained personnel
Parameter Media Acceptable
Test
Methods
Petroleum
Hydrocarbo
ns
Water &
soil
Gas
chromatogra
phy
Volatiles
(including
BTEX)
Water &
soil
Infra-red
based
methods
Semi-
volatiles
(including
PAH)
water EPA
Standards
Analytical methods

14. Measurement of aquatic biodegradation rates by determining
heterotrophic uptake of radiolabeled pollutants.
F K Pfaender and G W Bartholomew
• The heterotrophic uptake technique was modified to provide a rapid
and simple technique for estimating the rates of biodegradation of
organic pollutants under environmental conditions.
• The methodology is based on an evaluation of uptake into cells and
subsequent respiration of radiolabeled organic substrates in short-
term experiments.
• The resulting data can be used to calculate either turnover times or,
if multiple concentrations of substrate are used, kinetic parameters.
• The procedure was applied to assess the biodegradation rates of m-
cresol, chlorobenzene, nitrilotriacetic acid, and 1,2,4-
trichlorobenzene in fresh, brackish, and marine water samples from
the coastal areas of North Carolina.
• Saturation kinetics for uptake were obtained with each of the
compounds tested.
• Rates of metabolism were shown to be dependent on sample
location and time of year.

15. Phytoremediation & Biotechnology
 Maximizing potential for phytoremediation
 GM approaches can be used to over express the enzymes involved in
the existing plant metabolic pathways or to introduce new pathways
into plants.
 Richard Meagher and colleagues introduced a new pathway
into Arabidopsis to detoxify methylmercury, a common form of
environmental pollutant to elemental mercury which can be volatilised
by the plant

16. Mer B
Organomercurial Lyase
Methyl Mercury Ionic Mercury
MerA
Mercuric Reductase
Ionic Mercury Elemental Form
The genes originated in gram-negative bacteria

17. Arabidopsis plants were transformed with either MerA or MerB coupled with a
constitutive promoter
The MerA plants were more tolerant to ionic mercury, volatilised elemental
mercury, and were unaffected in their tolerance of methylmercury
The MerB Plants were significantly more tolerant to methylmercury and other
organomercurials and could also convert methylmercury to ionic mercury which
is approximately 100 times less toxic to plants
MerA MerB double transgenics were produced in an F2 generation. These plants
not only showed a greater resistance to organic mercury when compared to the
MerA, MerB, and wildtype plants but also capable of volatilizing mercury when
supplied with methylmercury.
The same MerA/MerB inserts have been used in other plant species including
tobacco(Nicotiana tabacum), yellow poplar(Liriodendron tulipifera)
Wetland species (bulrush and cat-tail) and water tolerant trees (willow and poplar)
have also been targetted for transformation.

18. Risk Assessment
Potential for the gene to recombine with other genes possibly
leading to the hyperaccumulation of non-contaminant
compounds
Reporter/marker genes may also escape into the environment
The GM plants may revert to a wild type genotype

19. Advantages of phytoremediation
It is more economically viable using the same tools and
supplies as agriculture
It is less disruptive to the environment
Disposal sites are not needed
Aesthetically pleasing than traditional methods
Avoids excavation and transport of polluted media thus
reducing the risk of spreading the contamination
It has the potential to treat sites polluted with more
than one type of pollutant

20. Disadvantages of phytoremediation
Growing conditions required by the plant (i.e., Climate,
geology, altitude, temperature)
Tolerance of the plant to the pollutant
Contaminants collected in senescing tissues may be released
back into the environment in autumn
Contaminants may be collected in woody tissues used as fuel
Time taken to remediate sites far exceeds that of other
technologies
Contaminant solubility may be increased leading to greater
environmental damage and the possibility of leaching