Phytoextraction and forms

2. Phytoextraction is a type of
phytoremediation
PHYTOREMEDIATION
Phytoremediation is an
emerging technology that uses
plants to clean up pollutants (metals
and organics) from the environment.

3.  PHYTOEXTRACTION
Within this field of phytoremediation, the
utilization of plants to transport and
concentrate metals from the soil into the
harvestable parts of roots and above-ground
shoots is usually called phytoextraction.

4.  Phytoextraction is the use of plant to take up
metal contaminants from soil through the
absorption by plant roots.
 The metal absorbed are stored or
accumulated in the aerial portions of the
plants (Stems & Leaves).
 Plants intended for this application are
called hyper accumulators.

5.  These species of plants have high tolerance
to heavy metals and are capable of absorbing
larger amount of metal in comparison to
other plants.
 Today, researchers are developing genetically
engineered hyper accumulators that have a
higher metal accumulation and tolerance
capacity.

6.  After the plants are allowed to absorb the
contaminants for some time, they are
harvested to either be disposed by
incineration or be composted to recycle
metals.
 Although plants that were incinerated will be
disposed off in a hazardous waste landfill,

7.  volume of ash will be less than 10% of the
volume that would be created if the
contaminated soil itself were dug up for
treatment.
 The plants take up the contaminant through
the system of roots and store them in the
roots or transport them up into the stems
and leaves.

8.  The plants will carry on absorbing
contaminants until it is being harvested
 After the harvest, the soil will contain a
lower concentration of contaminant
 As such, this growth and harvest cycle is
usually repeated for a number of times to
achieve a considerable clean up

9.  After the process, the remediated soil can
be put into other beneficial uses
 FORMS OF PHYTOEXTRACTION
 There are two forms of phytoextraction:

10.  Natural hyper-accumulation
In this form a plants take up the contaminants
in soil unassisted. In many cases natural
hyperaccumulators are metallophytes plants that
can tolerate and incorporate high levels of toxic
metals.

11.  Induced (assisted) hyper-accumulation,
In this a conditioning fluid containing
a chelator or another agent is added to soil
to increase metal solubility or mobilization
so that the plants can absorb them more
easily.

12.  fast growth rates
 high biomass production
 deep roots
 tolerance to metal uptake
 metal specificity
 a high rate of metal transport from roots to
shoots
 accumulation in shoots

13.  The metal needs to be dissolved in something
the plant roots can absorb
 The plant roots need to absorb the heavy metal
 The plant needs to chelate the metal in order to
both protect itself and make the metal more
mobile

14.  The plant moves the chelated metal to a
place to safely store it
 Finally, the plant must adapt to any damages
the metals cause during transportation and
storage

15.  Metals need to be dissolved as an ion in solution
to be mobile in an organism
 Once the metal is mobile, it can be directly
transported over the root cell wall by a specific
metal transporter
 The plant roots mediate this process by
secreting agents that capture the metal in
the rhizosphere and then transport the metal
over the cell wall.

16.  Some examples are:
phytosiderophores, organic acids,
or carboxylates
 If the metal is chelated at this point, then
the plant does not need to chelate it later
and the chelater serves as a case to conceal
the metal from the rest of the plant
 This is a way that a hyper-accumulator can
protect itself from the toxic effects of
poisonous metals

17.  The first thing that happens when a metal is
absorbed is it binds to the root cell wall
 The metal is then transported into the root
 Some plants then store the metal through
chelation or sequestration

18.  Many specific transition metal ligands
contributing to metal detoxification and
transport are up-regulated in plants when
metals are available in the rhizosphere
 At this point the metal can be alone or already
sequestered by a chelating agent or other
compound
 In order to get to the xylem the metal then
needs to pass through the root symplasm

19.  The root-to-shoot transport of heavy metals is
strongly regulated by gene expression
 The genes that code for metal transport systems
in plants have been identified
 These transporters are known as heavy metal
transporting ATPases (HMAs)

20.  One of the well-documented HMAs is HMA4,
localized at xylem parenchyma plasma
membranes
 HMA4 is upregulated when plants are exposed
to high levels of Cd and Zn
 This may be to speed up the root-to-shoot
process limiting the amount of time the metal is
exposed to the plant systems before it is stored

22. There are three factors
 Soil depth
 Bioavailibilty of metals
 Biomass production and physiological
adoptability

23.  The roots of plants play an important role
in phytoextraction. As phytoextraction is
limited to the zone influenced by the roots
of plants, the depth and size of the root
determines the depth of phytoextraction
(Keller et al. 2003).
 If contamination is at substantially greater
depths (e.g., 6 to 10 feet), deep-rooted
poplar trees can be used, however, there is
concern about leaf litter and associated toxic
residues.

24. Metals present in a soil can be divided into a
number of fractions including;
 the soluble metal in the soil solution,
 metal-precipitates,
 metal sorbed to clays,
 hydrous oxides and organic matter,
 and metals within the matrix of soil minerals

25.  Fraction of the metal which plants can absorb is
known as the available or bioavailable fraction
 Metals within the soil solution are the only soil
fraction directly available for plant uptake
(Fageria et al., 1991; Marschner, 1995;
Whitehead, 2000)
 Many factors affect the bioavailability of metals
in soil, the most important being the total metal
concentration, pH, the presence of organic
matter, redox conditions, and the presence of
clays and hydrous oxides.

26. Phytoextraction can also be affected by
 limited biomass production
 physiological adaptability to varying climatic
conditions
 adaptability to current agronomic techniques

27.  Arsenic using the sunflower or the chinese
brake fern a hyperacumalator.Chinese brake
fern stores arsenic in its leaves

28.  Cadium using willow.As willow has some
specific characteristics like high transport
capacity of high metals from roots to shoots
huge amount of biomass production can use
also for production of bio energy in the
biomass energy power plant.

29.  Zinc using Alpine pennycress a
hyperacumulator of this metal at level that
would be highly toxic for plants.

30.  Lead,using indian mustard,radweed,hemp
which sequencer lead in its biomass.

31. A problem in the use of
phytoaccumulator:
Not having enough biomass and growth rate to
be applied in large scale practices.
Solution:
 Transfer of genetic traits from hyper
accumulator into plants that has high biomass
and growth rate. Plants with high biomass:
 High growth Rate
 High take up of metals.

32.  Poplar and willow do not accumulate metals
to high concentration.
 Still effective remediators because of their
deep root system and biomass.
 Excellent candidate to be genetically
engineered to have traits of hyper-
accumulators.

33.  Metals accumulated poses significant risk to
consumers of plants.
 So plants capable of producing substances
that deter or discourage herbivores from
feeding them can be transformed to have
improved metal tolerance and capabilities.
 With such a system in place, it will help
prevent the transfer of metals to food chain.

34.  Transfer of gene extracted from bacteria or
animals into plants systems can improve the
potential of remediation.
 Some bacteria have the genetic
characteristic to detoxify toxic elements.
 Today, the transfer of such genes into plants
had already produced promising results.

35.  No plants have been shown to be able
tolerate some elements such as mercury or
lead.
 Can be changed by transferring genes from
bacteria that has the ability to detoxify these
metals (mercury & lead) into plants.

36.  So can be used to clean up these metals
which were once seemed to be impossible.
 With the transfer of the expressing gene,
plants can be genetically altered

37. The use of transgenic plants:
Addresses the problem of mix
contamination (happening in a polluted site)
Methods which involve introducing
several genes at once into plants:
Help in the removal of complex and mixed
pollutants.

38.  Recover heavy metals from soils
 Greenhouse-based hydroponic systems
1: High contaminant root uptake
2: Poor translocation to the shoots
for removal of heavy metals and
radionuclides from water.
These plants also are referred to as
‘Hyperaccumulators’

39.  Phytoextraction is able to trap metal and radionuclide
contaminants that are in mobile chemical forms. These
forms are the most threatening to human and
environmental health.
 Compared with other remediation technologies, such
as excavation, materials handling is limited (similar to
that in normal agricultural processes), and costs are
typically lower. Usually the technology leaves the soil
fertile and able to support subsequent vegetation.
 Up to 95% of TCE present in water could be
removed by simply planting trees and letting
them grow. (Gordon, 1996 )

40.  This technology is longer than other technologies:
several crops are usually required to remove all
the contaminants to the desired levels.
 Mercury removal is considered experimental and
has shown promise using genetically modified
plants that vaporize mercury.
 One of the main drawbacks of chelator-induced
phytoextraction is that most synthetic chelators,
such as EDTA, form chemically and
microbiologically stable complexes with heavy
metals that pose a threat of groundwater
contamination.

41.  Most of the plants that are considered good
candidates for use with this technology do not
grow well under submerged (wetland) conditions.
Phytoextraction has not been applied to wetlands.
 Extensive treatability studies are needed before
this technology can be considered for
implementation in wetlands.
 Portions of the river may have to be re-routed for
the duration of the treatment.

42.  Plants that are good phytoextraction candidates
are not native to the area.
 Plants used for phytoextraction will have to be
harvested over multiple growing seasons.
 If soil additives are used, additional precautions
must be taken to avoid leaching of the mobilized
contaminants outside the area where roots can
take them up.

43.  Accumulation of contaminants in the
aboveground part of the plants may pose a risk to
animals eating these plants and fences may be
needed to deter grazing animals.
 Phytoextraction will not directly remove organic
contaminants (PCBs, DDD) from soils and
sediments. However, microbial activity associated
with plant roots may accelerate the degradation
of these contaminants to non-toxic forms.

44.  Phytoextraction appears a very promising technology
for the removal of metal pollutants from the
environment and may be, at present, approaching
comercialization.
 Metals such as nickel, zinc, and copper are the best
candidates for removal by phytoextraction because
the majority of the approximately 400 known plants
that absorb unusually large amounts of metals have a
high affinity for accumulating these metals.
 The heavy metals that plants extract are toxic to the
plants as well.