PHYTOSTABILISATION

By

Elegbeleye Oladipo Ayodamope

Cyprus International University

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

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.

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

Phytostabilisation

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

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

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 (Warhurst2000).

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.

ORGANIC AMENDMENTS REDUCE METAL TOXICITY IN

MINE TAILINGS

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

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.

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 (Vangronsveldand Cunningham, 1998).

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;

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.

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.

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

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.

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