20.109 F(10) Rhizofiltration

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Authors: Team Grape, 20.109 F(10)

Water purification is a growing concern worldwide with issues spanning environmental, economic, and fiscal sectors. Of specific concern is the contamination of groundwater with heavy metals as a side effect of societal and industrial pollution. While moderate quantities of certain metals are acceptable for consumption, larger quantities can lead to acute poisoning. Especially in countries where water sources are scarce or and purification techniques primitive, new methods are necessary serious health crises.

Considering alternatives, rhizofiltration is a a cost-effective and ecologically conscious means of water purification. The technique is a form of phytoremediation which uses plant roots to remove target species from water. Through absorption and eventual sequestering of specified contaminants in the leaves or roots, toxic solutes can be easily and efficiently removed from water making it suitable for consumption. Specific removal of heavy metals such as Cu2+, Cd2+, Cr6+, Ni2+, Pb2+, and Zn2+ have already been demonstrated in current research.[1]

This technique has the potential to span the gamut of water purification needs. Large, established facilities can reduce costs by moving to this natural water purification technique as an alternative to current methods while small populations devoid of such resources can apply rhizofiltration on a local, manageable scale. In the case of small populations, no new infrastructure is necessary as plant purification can be applied directly to groundwater sources.

The current state of the art in water purification involves significant investments in terms of financial strains and infrastructure. Before any treatment occurs, water must be moved from its native location often requiring an initial investment in miles of pipeline. Once at the factory, a myriad of techniques ranging from flocculation, sedimentation, filtration, and disinfection are applied before reaching a final product with each step requiring additional technology and manpower to operate. While the complete process is effective, the resources needed to carry out this process are too great for certain populations. For example, populations in third world countries lack the fiscal acuity to invest in the infrastructure required for such extensive purification.

Current estimates for the construction of a fully operation filtration system range into the hundreds of millions of dollars depending on the volume of water to be purified and the level of purification needed; this is a stark contrast to the tens of dollars per thousands of gallons of water purified via rhizofiltration. This cost effective advantage is the result of the ease with which this plant-based filtration system can be implemented: no heavy industry is required to build this system allowing it to be used effectively anywhere, the system is self sustaining as long as sufficient nutrients and sunlight are available, and the system can be easily removed and disposed of.[2]

The application and returns on this technique show clear potential. While current research indicates that several plant species have shown the ability to absorb and sequester heavy metals to achieve water detoxification, little attention has been given to improving the natural filtration efficiencies of plants using recombinant DNA technology. Through analysis of the molecular mechanism of rhizofiltration, we will attempt to optimize the affinity and capacity for sequestration of heavy metals in a model plant species.

Specifically, we aim to analyze the mechanism by which certain plants, shown to demonstrate the ability to remove high levels of heavy metals from water, are able to sequester these materials in plant biomass. Once the mechanism underlying the ability of our target plant species to chelate heavy metals from water has been characterized, we will focus on enhancing its rate of sequestration and increasing the threshold for heavy metal toxicity. Further we will attempt to restrict the deposition of heavy metal ions, absorbed by the roots, to the stalk and leaves; by concentrating toxins in the dry mass of the plant. This will facilitate easier disposal of spent biomass by excluding water weight. Through this approach, we hope to engineer a genetically modified plant species capable of the selective absorption and targeted deposition of particular heavy metal ions. Ideally this end product will serve as a cost-effective and environmentally friendly water purification system that can be applied in regions that do not have sufficient infrastructure or resources to support more traditional means of water purification.

Experiments to Consider:

The following suggested experiments are to be performed on P.vittata as suggested by Wang et.al (2002).[3]

* Use virus to introduce PO3 transport gene under the control of a constitutive promote to upregultate levels of the phophate transporter. Can be used to investigate idea that arsenate interacts with this ion transporter as a mean of entering the cell.

               Need plant specific virus

* If the phosphate transporter is found to preferentially allow arsenate to enter the cell compare sequences of phosphate transporter from P.vittata to other, non-hyperaccumulator, plants in same genus to determine regions that may confer the hyperaccumulator phenotype.

Works Cited

[1] Dushenkov, Viatcheslav, Harry Motto, Ilya Raskin, and P.b.a. Nanda Kumar. "Rhizofiltration: the Use of Plants to Remove Heavy Metals From Aqueous Streams." Environmental Science Technology 30 (1995): 1239-1245.

[2] Examining the Cost of Building and Operating a Water Purification System to Provide a New Source of Water for an Arid Region. Fountain Valley California: GRW System. PDF. <http://www.gwrsystem.com/images/stories/pdfs/White-Paper-Cost-of-GWRS.pdf>.

[3] Wang J, Zhao F, Meharg A, Raab A, Feldmann J, McGrath S. Mechanisms of Arsenic Hyperaccumulation in Pteris vittata. Uptake Kinetics, Interactions with Phosphate, and Arsenic Speciation.

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