Monday, March 23, 2009

Phytoremediation as an alternative method in Reclamation Strategies

Phytoremediation is the use of plants to clean up toxic levels of heavy metals, organic contaminants or pesticides by the absorption within the plant body and either converting the compound or storing it in the plant material, or immobilizing the contaminant within the soil area. Phytoremediation processes include 1) Phytostabilization, 2) Phytodecontamination 3) Rhizosphere Degredation 4) Phytoaccumulation and 5) Phytoextraction. These processes can safely clean contaminated water, wetlands, soil and air pollutants. As shown above, plants can be used as a natural way to clean up polluted waterways, and can even safetly clean up effluent from sewage contamination.

In all of the processes, except for phytostabilization, plants actively take up the contaminant and process it in a variety of ways which depend on the nature of the contaminant and the plant species itself. Sunflowers have been used to remove arsenic compounds and brassicas to remove lead compounds. Each species has its own growth rate and bioaccumulation rate which are important factors for deciding how to remove contaminants. Seasonal removal of plant material thereby removes the contaminants from the area to be safely disposed or stored in an alternate location. This method requires several seasons for the complete removal, and in fact complete removal of the contaminant may not be possible.

Phytoremediation can even occur inside the home. Air pollution that occurs inside newly built homes, known as off-gassing of new products can affect the health of the residents. NASA had conducted a study in the 80's showing that plants are effective at removing formaldehyde and benzene and other off-gasses from the environment just by growing popular houseplants.

Phytoremediation is not the whole story of course; important microorganisms such as Bacteria and Archaea are invaluable for providing in-house cleaning for a fraction of the work plants require. Already used in all tailings ponds (in the Tar-Sands of Northern Alberta), multiple fermentation Bacterias and methanogenic Archaeas provide the cheap & easy way of converting organic contaminants into methane and carbon dioxide. Of course this takes years as well, but they do not need seasonal removal of organic material like plants do. However, when plants and bacteria/archaea work in concert with each other, it is the fastest method of reclamation and probably safer than most other methods.

Gratao, P.L, et al. (2005). Phytoremediation: green technology for the clean up of toxic metals in the environment. Braz. J. Plant Physiol. 17(1) 53-64.

Meagher, R.B. (2000). Phytoremediation of toxic elemental and organic pollutants. Current Opinion in Plant Biology. 3: 153-162

Meers, E., Hopgood, M., Lesage, E., Verv.aeke, P., Tack, F. M. G. and Verloo, M. G. (2004). Enhanced Phytoextraction: In Search of EDTA Alternatives',International Journal of Phytoremediation. 6(2): 95 — 109.

Van Aken, B. (2008). Transgenic plants for phytoremediation: helping nature to clean up environmental pollution. Trends in Biotechnology. 26(5) 225-227.

Wolverton, B.C., Johnson, A., and Bounds, K. (1989). Interior Landscape Plants for Indoor Air Pollution Abatement Final Report. National Aeronautics and Space Administration. Stennis Space Center, MS.

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