PHYTOREMEDIATION INTRODUCTION q Phytoremediation is the use

PHYTOREMEDIATION

INTRODUCTION q 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.

OVERVIEW Phytoextraction Metal Phytodegradation Rhizofiltration Rhizodegradation organic Phytostabilisation Phytovolatilisation

PHYTOEXTRACTION Ø Plant roots uptake metal contaminants from the soil and translocate them to their above soil tissues Ø Once the plants have grown and absorbed the metal pollutants they are harvested and disposed off safely Ø This process is repeated several times to reduce contamination to acceptable levels Ø Hyper accumulator plant species are used on many sites due to their tolerance of relatively extreme levels of pollution Contaminants removed: Ø Metal compounds that have been successfully phytoextracted include zinc, copper, and nickel

RHIZOFILTRATION q It is concerned groundwater q 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 q with the remediation of contaminated Chernobyl - sunflowers were grown in radioactively contaminated pools

PHYTOSTABILISATION v Phytostabilization is the use of plants to prevent the migration of contaminants through control of the hydraulic gradient or by reinforcing the soil structure.

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

RHIZODEGRADATION Ø Ø Ø Ø 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

PHYTOVOLATILIZATION q Plants uptake contaminants which are water soluble and release them into the atmosphere as they transpire the water q 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 q Poplar trees volatilize up to 90% of the TCE they absorb Selenium and Mercury - Arabidopsis thaliana L. and tobacco q

PHYTOHYDRAULICS v v 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

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

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