Phytostabilization refers to establishing a plant cover on the surface of the contaminated soils, which reduces their exposure to wind, water, and direct contact with humans or animals. Phytostabilization reduces the mobility, and therefore the risk, of inorganic contaminants without necessarily removing them from the site.
2. OUTLINE
Introduction
Role Of Plants In Phytostabilization
Phytostabilisation
Role of Soil Amendments in Phytostabilization
Phytostabilization In Mine Tailings
Advantages
Disadvantages
Bioavailability In Phytostabilization
Processes Involved In Phytostabilization
Enhancement Of Phytostabilization
Environmental Factors
Conclusion
Reference
3. INTRODUCTION
Phytostabilization refers to establishing a plant
cover on the surface of the contaminated soils,
which reduces their exposure to wind, water,
and direct contact with humans or animals.
Phytostabilization reduces the mobility, and
therefore the risk, of inorganic contaminants
without necessarily removing them from the site.
4. Role of Plants in Phytostabilization
• Protect the contaminated soil from wind and water erosion
• Reduce water percolation through the soil to prevent leaching of
the contaminants
• Alter the chemical form of the contaminants by changing the soil
environments (e.g. pH, redox potential) around plant roots
• Accumulate and precipitate heavy metals in the roots or adsorb
metals to the roots
• Micro-organisms living in the rhizophere of plants may have an
important role in these processes
6. Role of Soil Amendments in Phytostabilization
Convert the soluble and exchangeable metals
to more geochemically stable solid phases
resulting in a reduced biological availability of
heavy metals
reduction of trace element transfer to surface-
and groundwater
Use of soil amendments to lower metal uptake
in crops
7. Phytostabilization In Mine Tailings
Mine tailings, or mill tailings, are the
materials remaining after extraction and
beneficiation of ores. they are characterized
by elevated concentrations of metals such as
arsenic, cadmium, copper, manganese, lead,
and zinc
Furthermore, tailings contain no organic
matter or macronutrients, and usually exhibit
acidic pH
8. Phytostabilization In Mine Tailings Contd
Autotrophic iron and sulfur-oxidizing bacteria
dominate the microbial community in mine
tailings and are associated with plant death in
acidic tailings (Schippers et al. 2000).
Today, surface containment of tailings within
embankments remains a commonly used
approach. In 1995 it was estimated that on an
annual basis over 700 million kg of metals in
mine tailings were disposed on land (Warhurst
2000).
9. Phytostabilization In Mine Tailings Contd
Phytostabilization creates a vegetative cap
for the long-term stabilization and
containment of the tailings. The plant canopy
serves to reduce eolian dispersion whereas
plant roots prevent water erosion, immobilize
metals by adsorption or accumulation, and
provide a rhizosphere wherein metals
precipitate and stabilize.
11. Advantages
It may combine treatment with ecosystem restoration. The
technology usually enhances the soil fertility.
Stabilization reduces mobility. This may be a risk, of organic
contaminants without removing them from their location.
Material handling is limited compared to other remedial
technologies, such as excavation. Therefore costs will be typically
lower.
inorganic contaminants such as heavy metal(loid)s in the soil are
immobilized, thereby minimizing their transport in water or dust
12. Disadvantages
If soil additives are used, they may need to be periodically reapplied.
This is to maintain the effectiveness of the immobilization.
The site must be monitored perpetually to make sure the stabilization
conditions continue because the contaminants are left in place.
Toxic effects may prevent plants from growing until extensive
amendment application reduce their bioavailability to plants. This will
occur if the contamination concentration elevate.
Phytostabilization is useful at sites with shallow contamination and
where contamination is relatively low.
Metals that are readily translocated to leaves in plants may limit the
applicability of phytostabilization due to potential affects to the food
chain.
13. Bioavailability In Phytostabilization
Bioavailability of contaminants in soil Is the fraction of the total
metal(loid) in the interstitial pore water (i.e., soil solution) and soil
particles that is available to the receptor organism (Naidu et al.
(2008a)
Bioavailability can also be defined as the potential for living
organisms to take up metal(loid)s through ingestion or from the
abiotic environment (i.e., external) to the extent that the metal(loid)s
may become involved in the metabolism of the organism (NRC,
2003).
More specifically, it refers to the biologically available fraction (or
pool) that can be taken up by an organism and can react with its
metabolic machinery, or it refers to the fraction of the total
concentration that can interact with a biological target (Vangronsveld
and Cunningham, 1998).
14. Processes Involved In Phytostabilization
uptake and sequestration of contaminants in the root system;
alteration of soil factors that influence the speciation and immobilization
of contaminants (pH, organic matter, redox levels);
root exudates that regulate the precipitation and immobilization of the
contaminants;
establishment of vegetation barrier that reduces the likelihood of
physical contact with the soil by animals and humans;
mechanical stabilization of the site to minimize erosion by wind and
water;
15. Enhancement Of Phytostabilization
Phytostabilization can be enhanced by
increasing plant growth using both organic and
inorganic amendments. Fertilizer application
increases plant growth thereby enhancing
phytostabilization
Therefore, organic amendments such as bio-
solids and manures and biological inoculants
such as plant growth-promoting bacteria
(PGPB) are used to enhance plant growth.
16. Environmental Factors
Rainfall controls the leaching of contaminants and
erosion of soil and sediments.
Temperature affects both the plant growth and soil
surface characteristics such as cracking and crust
formation.
While cracking increases the leaching of
contaminants, loose, dry, and bare soil is susceptible
to wind erosion by dispersion.
17. CONCLUSION
Phytostabilization is primarily aimed at containing the
mobility of contaminants through their immobilization
within the root zone of plants and “holding” soil and
sediments, thereby preventing off-site contamination
through their migration via wind and water erosion
and leaching, and soil dispersion.
This technique is readily suited to monitor natural
attenuation of contaminated sites which is employed
within the context of a carefully controlled site-specific
clean up strategy
18. REFERENCE
Adriano, D. C., Wenzel, W. W., Vangronsveld, J., and Bolan, N. S.
(2004). Role of assisted natural remediation in environmental
cleanup.Geoderma122,121–142.
Bolan, N. S., Adriano, D. C., and Naidu, R. (2003a). Role of
phosphorus in (im)mobilization and bioavailability of heavy metals
in the soil-plant system. Rev. Environ. Contam. Toxicol.177,1– 44.
Bolan, N. S., Adriano, D. C., Mani, S., and Khan, A. R. (2003d).
Adsorption, complexation and phytoavailability of copper as
influenced by organic manure. Environ. Toxicol. Chem. 22,450–
456.
