Grass Phytoremediation: Explosives Uptake and Fate in Decomposing Plant Tissue
R. Guy Riefler, Ohio University, Athens, OH

Assessing Plant Derived Organic Matter in PAH Phytoremediation
Samuel T. Gregory, NC State University, Raleigh, NC

Elucidating Enzymes Involved in the Degradation of Trichloroethylene in Plants
Sarah Strycharz, University of South Carolina, Columbia, SC

Increased Polycyclic Aromatic Hydrocarbon (PAH) Contamination and Plant Type Determine Plant/microbe Interaction in the Rhizosphere
Cairn Ely, University of Connecticut, Storrs, CT  

Exploitation of Endophytic Bacteria to Improve Phytoremediation of Organic Contaminates
Daniel van der Lelie, Brookhaven National Laboratory (BNL), Upton, NY

Phytoremediation of Arsenic in the Spring Valley Area of Washington, DC

Michael J. Blaylock, Edenspace Systems Corporation, 15100 Enterprise Court, Suite 100, Chantilly, VA, 20151, Tel: 703-961-8700, Fax 703-961-8939, Email: blaylock@edenspace.com
Mark P. Elless, Edenspace Systems Corporation, 15100 Enterprise Court, Suite 100, Chantilly, VA, 20151 Tel. 703-961-8700, Fax 703-961-8939, Email: elless@edenspace.com
Cindy L. Teeter, USACE ERDC Vicksburg, 3909 Halls Ferry Road, Vicksburg, MS 39183, Tel: 601-634-4260, Email: Cindy.L.Teeter@erdc.usace.army.mil

The residential area of Spring Valley encompasses approximately six hundred sixty-one (661) acres in the northwest section of Washington, D.C. During World War I, at the American University Experiment Station (AUES), the Department of Defense produced the arsenic-based chemical warfare agents, Lewisite and Adamsite. Chemists and engineers tested these agents in the areas surrounding the AUES, which is now known as the Spring Valley residential neighborhood. Investigative soil sampling indicated the presence of arsenic at levels above background and risk-based concentrations (RBCs).  In 2001, the Corps of Engineers initiated a removal action to address these areas of concern.  The main remediation technology to be applied at residences with elevated arsenic is excavation followed by backfilling with clean soil. This technology can be environmentally disruptive and expensive. Phytoremediation is being considered as an alternative, in elevated grids of Spring Valley, to minimize destruction of existing trees and reduce restoration costs in these reseidential areas. In 2004, a field verification study was conducted to evaluate the potential of phytoremediation to address the elevated arsenic soil concentrations. The field verification study consisted of two residential areas and one public access area encompassing 14 study sites. Three species of ferns, Pteris vittata, P. cretica and P. multifida, were planted and grown from May to November. The 2004 activities were successful in reducing arsenic concentrations in the surface soils below target levels in 12 of the 14 study areas. Based on these results, the field activities were expanded in 2005 to include additional sites. The results of the 2005 field demonstration will be presented.

Grass Phytoremediation: Explosives Uptake and Fate in Decomposing Plant Tissue

R. Guy Riefler, Department of Civil Engineering, Ohio University, Athens, OH  45701, Tel: 740-593-1471, Fax:  740-593-0625, Email: riefler@ohio.edu
Victor Medina, U.S. Army Corps of Engineers, Engineer Research & Development Center, Vicksburg, Mississippi 39180, Email: Victor.F.Medina@erdc.usace.army.mil

The commonly used explosives and propellants, trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and nitroglycerine (NG), are often found in soil and groundwater from military firing ranges.  Because of the need for continued training with live ammunition, cleanup of these contaminants may prove expensive.  One alternative being considered to manage sites exposed to these contaminants is the use of grasses in phytoremedation.  In this study, the uptake of TNT, 2,4-DNT, RDX, and NG in hydroponic studies using three common grasses, yellow nutsedge, yellow foxtail, and common rush, was investigated.  Rapid removal from solution by all grasses was observed, with some accumulation of contaminants in the grass tissues.  Higher concentrations were observed in killed roots, demonstrating the presence of plant based enzymes actively transforming the uptaken contaminants.  Grass with TNT and RDX present in their tissues from previous hydroponic experiments were buried in clean soil to determine the ultimate fate of the contaminants.  In twelve days, 97% of the initial TNT and RDX were removed in soil/grass extracts while spiked controls retained high levels of the contaminants.  Several of the grass/soil mixtures were soaked in acidic water overnight with shaking to determine the level of leaching possible from the contaminated tissues.  Initially, only 18% of RDX could be leached from the plant tissues and after seven days of decomposition that decreased to 7%.  No TNT was leached from any of the plant tissues.  TNT and RDX were both leached in significant amounts from spiked controls.  These studies indicate that TNT, 2,4-DNT, RDX, and NG can be rapidly taken up by several common grasses; that contaminants in plant tissues appear to be removed as the tissues decompose, and that leaching of TNT and RDX is significantly reduced after uptake into grasses and even further as those grasses decompose.

Assessing Plant Derived Organic Matter in PAH Phytoremediation  

Samuel T Gregory, NC State University Dept of Environmental and Molecular Toxicology, 2800 Faucett Dr. Raleigh, NC, 27514, Tel: 919-513-3972, Fax: 919-515-7559, Email: stgregor@unity.ncsu.edu
Jeramy Bell, NC State University Dept of Forestry, 2800 Faucett Dr. Raleigh, NC, 27514, Tel: 919-542-7518, Fax: 919-515-7559, Email: jeramy_bell@yahoo.com
Elizabeth Nichols Ph.D. NC State University Dept of Forestry, 2800 Faucett Dr. Raleigh, NC, 27514, Tel: 919-513-4832, Fax: 919-515-7559, Email: Elizabeth_Nichols@ncsu.edu

Elevated levels of petrogenic PAHs are often found at historical sites of petroleum refinement and use.  Knowledge about the impact of plant derived organic matter (PdOM) at such sites is necessary to fully evaluate risk reduction and remediation efficacy by phytoremediation.  The purpose of this research is to identify and separate the mechanisms by which PdOM impacts the fate and bioavailability of weathered PAHs.  Samples have been collected across successional gradients along a freshwater canal and saltwater marsh where historically high levels of PAHs remain.  Sediment samples of both a freshwater and saltwater marsh impacted by creosote contamination are also under investigation.     

Alkylated and non-alkylated PAH concentrations (GC/MS SIM) allow the use of chemical fingerprinting techniques to detect contaminant weathering and degradation.  Isotopic signatures (δ¹³C, D¹⁴C) of sediment fractions represent another approach to probe the impact of PdOM on PAH bioavailability.  Density separations of whole sediment can separate labile carbon pools (light fractions) from more recalcitrant older carbon pools (heavy fractions), with PdOM more likely to appear in lighter density fractions, as evidenced by radiocarbon dating, (D¹⁴C-AMS).  Contaminant profiles from bulk sediment, humic fractions, and density fractions all contribute information about the fate of PAHs in soils and sediments with PdOM. 

Humic fractions, size fractions, and density fractions of whole sediment have been analyzed for both alkylated and non-alkylated PAH concentrations and isotopic signatures.  Fractions from vegetated sites show different PAH distribution profiles than non-vegetated fractions.  Preliminary data show that petrogenic and pyrogenic PAH source contamination cycles at different rates among sediment density fractions. Both vegetated and non-vegetated sediments have greater mass amounts of PAHs in lighter density fractions where labile organic carbon is present.  Because lighter density fractions may represent more bioavailable carbon pools, these results are important to evaluate PAH bioavailability, degradation, and potential risk to organisms in plant-impacted sediments.

Elucidating Enzymes Involved in the Degradation of Trichloroethylene in Plants

Sarah Strycharz, University of South Carolina, Arnold School of Public Health, Dept. of Environmental Health Sciences, 800 Sumter St., Columbia, SC, 29169, Tel: 803-777-6410, Fax: 803-777-6410, Email: sarahstry@yahoo.com, strychar@mailbox.sc.edu, strycharz@srel.edu
Lee Newman, University of South Carolina, Arnold School of Public Health, Dept. of Environmental Health Sciences, 800 Sumter St., Columbia, SC, 29169, Tel: 803-777-4795, Fax: 803-777-6410, Email: newman2@gwm.sc.edu, newman@srel.edu

As the use of phytoremediation for cleanup of halogenated hydrocarbons becomes increasingly widespread, it is imperative to determine the route of metabolism of such chemicals in plants to increase effectiveness and efficiency of degradation.  In humans and other organisms, cytochrome P450s are involved in degradation of the common groundwater contaminant trichloroethylene (TCE). Enzymes that have the potential to be involved in TCE degradation in plants include cytochrome P450s, peroxidases, dehalogenases, laccases, and reductases. We have shown that the model plant species, Arabidopsis thaliana, is capable of TCE degradation using a sterile technique to expose seedlings to TCE. We are furthering our results by comparing TCE metabolite production in WT Arabidopsis to plants that have been modified for certain genetic traits. Analysis of genes whose protein products have sequence similarity to the substrate-binding domain of CYP2E1 may provide insight into whether these genes play a role in plant mediated TCE degradation. We have obtained T-DNA seed lines for 5 probable P450s from Arabidopsis that contain sequence homology in 5 conserved residues from the substrate-binding site of human cytochrome P450 2E1 (CYP2E1). These genes are also being over-expressed in Arabidopsis and tobacco. CYP2E1 is involved in the rate-limiting step in TCE degradation in mammals. In addition, we are continuing our screening of a tobacco cDNA library using ion chromatography.

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