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PHYTOREMEDIATION: USING PLANTS TO CLEAN UP CONTAMINATED SOIL, GROUNDWATER, AND WASTEWATER
Citation:
Ellington, J J. AND N L. Wolfe. PHYTOREMEDIATION: USING PLANTS TO CLEAN UP CONTAMINATED SOIL, GROUNDWATER, AND WASTEWATER. Presented at First Baltic Symposium on Environmental Chemistry, Tartu, Estonia, September 26-29, 2001.
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
Phytoremediation is an emerging cleanup technology for contaminated soils, groundwater, and wastewater that is both low-tech and low-cost. The cleanup technology is defined as the use of green plants to remove, contain, or render harmless such environmental contaminants as heavy metals, trace elements, organic compounds, and radioactive compounds in soil or water. Phytoremediation takes advantage of the unique and selective uptake capabilities of plant root systems together with the translocation, bioaccumulation, and contaminant storage/degradation abilities of the entire plant. Research in our laboratory indicates that plants can transform many organic contaminants in sediments, soils and natural waters to more environmentally acceptable products. Furthermore, plant enzyme systems have been shown to be stable in sediments and soils for long periods of time and still maintain their activity. The diagram illustrates the mechanisms for pollutant uptake by plants.
Using the knowledge that some plants have a high enzymatic activity for breaking down chemical toxins in soils and surface waters will bring about hazardous waste technology that is both economical and environmentally friendly to clean up waste sites. The objectives of our research are to determine which plants contain the most effective enzyme systems for transforming chemicals to safer products and to develop and incorporate plant/enzyme mediated transformation algorithms into multimedia models. We want to quantitatively describe these processes through air, water and soil systems using molecular descriptors of the organic compounds and physical/chemical descriptors of the system to model plant mediated pollutant fate.
Our approach has been to first identify the plants native to the site under consideration for phytoremediation. Native plants are harvested homogenized in the laboratory and the whole plant homogenate is fortified with the chemical(s) of interest. The fortified homogenate is monitored to determine extent of degradation of the chemicals. If degradation is observed, the stems, shoots, tubers, and roots are also assayed. Plants that are identified as degrading species are then evaluated in controlled greenhouse and field experiments. A second approach is to use axenically cultured plants to eliminate the possibility that microorganisms associated with the plant are responsible for the degradation. To date several plants (aquatic and terrestrial) have been identified as containing the enzyme that reacts to degrade 1,3,5-trinitrotoluene (TNT), a munition that contaminates many military sites. Another study has shown that many aquatic and land plants can degrade chlorine compounds. Still other plants including parrot feather Mariophyllum aquaticum), duckweed (Spirodela oligorrhiza), and elodea (Elodea canadensis) have been shown to uptake and degrade organophosphate compounds such as pesticides to innocuous products.
Results from a recent study based on using native cattails for remediation of a perchloroethylene plume will be discussed.