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
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 • Plants are hydroponically grown in clean water rather than soil, until a large root system has 1 developed • Water supply is substituted for a polluted 2 water supply to acclimatize the plant • They are planted in the polluted area where the roots uptake the polluted water and the 3 contaminants along with it • As the roots become saturated they are Chernobyl - sunflowers 4 harvested and disposed of safely were grown in radioactively contaminated pools
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
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.
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
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 plants 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
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
LEVEL OF POLLUTANT Analytical methods Sampling Parameter Media Acceptable Field sampling quality assurance Test Avoiding contamination of Methods samples Petroleum Water & Gas Equipment cleaning Hydrocarbo soil chromatogra Sample labels ns phyRecent trend Volatiles Water & Infra-red Immunoassay testing and other (including soil based technology may be used to provide BTEX) methods on site screening. This work shall only be carried out Semi- water EPA by properly trained personnel volatiles Standards (including PAH)
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.
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
The genes originated in gram-negative bacteriaMer BOrganomercurial LyaseMethyl Mercury Ionic MercuryMerAMercuric ReductaseIonic Mercury Elemental Form
Arabidopsis plants were transformed with either MerA or MerB coupled with aconstitutive promoterThe MerA plants were more tolerant to ionic mercury, volatilised elementalmercury, and were unaffected in their tolerance of methylmercuryThe MerB Plants were significantly more tolerant to methylmercury and otherorganomercurials and could also convert methylmercury to ionic mercury whichis approximately 100 times less toxic to plantsMerA MerB double transgenics were produced in an F2 generation. These plantsnot only showed a greater resistance to organic mercury when compared to theMerA, MerB, and wildtype plants but also capable of volatilizing mercury whensupplied with methylmercury.The same MerA/MerB inserts have been used in other plant species includingtobacco(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.
Risk AssessmentPotential for the gene to recombine with other genes possiblyleading to the hyperaccumulation of non-contaminantcompoundsReporter/marker genes may also escape into the environmentThe GM plants may revert to a wild type genotype
Advantages of phytoremediationIt is more economically viable using the same tools andsupplies as agricultureIt is less disruptive to the environmentDisposal sites are not neededAesthetically pleasing than traditional methodsAvoids excavation and transport of polluted media thusreducing the risk of spreading the contaminationIt has the potential to treat sites polluted with morethan 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