2002 Progress Report: Phytoremediation in Wetlands and CDFs

EPA Grant Number: R828773C003
Subproject: this is subproject number 003 , established and managed by the Center Director under grant R828773
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (2001) - South and Southwest HSRC
Center Director: Reible, Danny D.
Title: Phytoremediation in Wetlands and CDFs
Investigators: Pardue, J. , Theegela, C. , Moe, William
Current Investigators: Pardue, J. , Moe, William
Institution: Louisiana State University - Baton Rouge , Southern University - New Orleans
Current Institution: Louisiana State University - Baton Rouge
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2001 through September 30, 2006 (Extended to September 30, 2007)
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management


The primary objective of this research project is the development of a scientific basis for a plant-based remedial approach for subaqueous and wetland sediments contaminated with chlorinated organic compounds. A specific objective of this research project is to identify the types of sediments where a plant-based remedial approach would be applicable. It is hypothesized that vegetating sediments will yield the best results in sediments where highly reducing conditions are not yet present due to insufficient organic carbon content or other barriers to achieving low-redox potential. Our previous research on plant uptake of desorption-resistant contaminants has demonstrated the importance of root sorption as an uptake mechanism. Understanding the fate of chlorinated organics on or near the root itself is an important goal of the study.

Progress Summary:

Hydrophobic chlorinated organics are common sediment contaminants that pose a threat to sensitive receptors. These compounds are often recalcitrant in sediments and bioaccumulate through the food chain. By contrast, rapid contaminant attenuation for certain chlorinated organics is observed in vegetated sediments (i.e., wetlands). In these sediments, enhanced biological processes (aerobic and anaerobic biodegradation and plant uptake) have been observed in the root zone that drives rapid natural recovery. Previous research has indicated that herbaceous wetland vegetation stimulates degradation of chlorinated organics, primarily through rhizospheric reductive dechlorination biodegradation processes. The primary hypothesis of this research project is that vegetating sediments contaminated with chlorinated compounds, root matter, and exudates will serve as a source of hydrogen for halorespiring organisms that can biodegrade the target compounds. Plant uptake and aerobic biodegradation of lower chlorinated daughter products also may be important mechanisms for certain contaminants.

We are conducting two groups of studies in this year of the project. The first group of studies is the completion of an extensive set of experiments on reductive dechlorination of chlorinated ethenes and ethanes in vegetated wetland peat beds. This research examined factors controlling the reductive dechlorination of chlorinated ethenes and ethanes in the rhizosphere. We conducted these studies in upflow-core mesocosms and in serum-bottle microcosms. We used natural wetland peats from a freshwater marsh and a constructed wetland mixture in the experiments. We measured chlorinated ethenes and ethanes using gas chromatography-mass spectrometry (GC-MS). We measured H2 using GC with a reduction gas detector. We identified specific components of the microbial consortia using polymerase chain reaction PCR-based detection using primers for Dehalococcoides sp. and certain methanogens. In microcosm studies, we used measured reactant and product concentrations to determine actual potential in situ energy yields, which in turn were used to predict the potential for a given hydrogen oxidizing process occurring in the sediment.

The second group of studies are experiments designed to establish the effects of vegetating sediments contaminated with more hydrophobic-chlorinated organics. We chose 1,2,3,4-tetrachlorobenzene (1,2,3,4-TeCB) as a test contaminant because of its chlorination pattern and because it has been shown to be the most hydrophobic chlorobenzene that is directly dechlorinated by halorespiring organisms. We conducted initial mechanistic studies in serum bottle and core mesocosms using two bayou sediments (Bayou Duplantier and Baton Rouge Bayou adjacent to the Petro Processor, Inc. [PPI], site) and two highly organic peat soils for contrast. We conducted serum bottle studies under anaerobic conditions to establish dechlorination kinetics, the effects of the methanogenic inhibitor, 2-bromoethanesulfonate (BES), and the effects of root material on dechlorination. Core studies also were conducted with herbaceous wetland vegetation with known differences in detrital pathways (Phragmites and Typha). Chlorinated benzenes were measured using GC-MS. We measured H2 using GC with a reduction gas detector. We also identified changes in the microbial consortia using denaturing gradient gel electrophoresis (DGGE).

We completed experiments on the reductive dechlorination of chlorinated ethenes and ethanes in the first year. Because of the rapid rate of treatment in the peat beds, these studies provide a guide to the type of conditions that would be targets for establishing in subaqueous sediments held in a confined disposal facility, for example. Major findings of the completed wetland peat studies germane to this research project are the following:

· High rates of complete reductive dechlorination of chlorinated ethenes and ethanes were established in the rhizosphere of wetland cores. These rates have been maintained for 2 years without supplemental sources of nutrients or carbon.

· Energetics calculations for reductive dechlorination of chlorinated ethenes and ethanes were useful in predicting which terminal electron accepting processes would occur temporally and under which conditions.

· Hydrogen thresholds and the effects of sulfate and sulfite also have been examined in detail, leading to a better understanding of the interaction of various terminal electron-accepting processes in the rhizosphere.

We have begun studies in subaqueous sediments to establish the types of sediments where a plant-based approach would yield results. Laboratory microcosm studies conducted in the initial year of the study have established the kinetics of 1,2,3,4-TeCB dechlorination in sediments with a range of organic matter content. In addition, the studies have identified the role of H2 as an electron donor, the expected daughter products of dechlorination, and the relative role of methanogens in dechlorination. Results indicate that the ability to dechlorinate tetrachlorobenzene is widespread in sediments. 1,2- and 1,3-Dichlorobenzene readily forms, and subsequently, these are dechlorinated at slower rates to chlorobenzene and benzene. Rapid decreases in H2 as dechlorination commences suggest that H2 is the electron donor. BES, an inhibitor of methanogenesis, decreased rates in some cases, and patterns of dechlorination did not completely inhibit the process.

We also performed a large factorial core-study experiment to examine dechlorination and microbial interactions in a more realistic setting. We spiked sediment from the PPI site with 1,2,3,4-TeCB and Typha latifolia, and we grew Phragmites communis in the cores. We sacrificed cores over time and established the temporal and spatial location of 1,2,3,4-TeCB, lower chlorinated degradation products, H2, and methane. Although we detected some differences in observed dechlorination patterns and rates, dechlorination occurred rapidly throughout the core. Microbial community structure analysis of these core samples is ongoing. We conducted additional microcosm studies with root material from P. communis (common reed) and T. latifolia (cattail). These plants differ in their observed detrital pathways. In sediments amended with fresh Phragmites roots, dechlorination rates increased in direct proportion to the amount of root matter added. Ambient H2 and methane also increased. As observed in previous studies, the low molecular weight organic acid, propionate, accumulated as the primary intermediate. DGGE indicated changes in the microbial community after the addition of roots. We conducted a more extensive study utilizing a wider range of inhibitors of various anaerobic metabolic processes in anaerobic media without sediments or chlorobenzenes to better understand anaerobic metabolism of root matter from these two types of plants. These results indicated that the Phragmites roots stimulated an order of magnitude higher above the rate of methane production than Typha roots.

Future Activities:

Work during the first year of this research project has identified factors in vegetated peat sediments that are desirable for creation in subaqueous sediments. Experiments in serum bottles and core mesocosms in several types of subaqueous sediments demonstrated that the reductive dechlorination of the tetrachlorobenzene readily occurred. Root material stimulated the dechlorination process; however, we will proceed with sediments that are not easily reduced to better demonstrate the stimulatory effect of planting. In addition, we will conduct experiments using the techniques developed in previous projects for establishing known amounts of chlorobenzene in the labile and desorption-resistant fraction, which are expected to be more representative of "aged" field sediments.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other subproject views: All 7 publications 3 publications in selected types All 3 journal articles
Other center views: All 279 publications 92 publications in selected types All 63 journal articles
Type Citation Sub Project Document Sources
Journal Article Kassenga GR, Pardue JH, Blair S, Ferraro T. Treatment of chlorinated volatile organic compounds in upflow wetland mesocosms. Ecological Engineering 2003;19(5):305-323. R828773C003 (2002)
not available

Supplemental Keywords:

marshes, natural attenuation, wetlands, bioavailability, biochemistry, biodegradation, bioremediation of soils, chlorinated organics, contaminants in soil, contaminated sediment, contaminated soil, degradation, microbial degradation, natural recovery, phytoremediation, wetland sediments, marshes, natural attenuation, wetlands., RFA, Scientific Discipline, Waste, Water, Contaminated Sediments, Microbiology, Analytical Chemistry, Environmental Microbiology, Hazardous Waste, Bioremediation, Ecology and Ecosystems, Molecular Biology/Genetics, Hazardous, degradation, Hexachlorobenzene, microbial degradation, wetland vegetation, bioavailability, biodegradation, contaminated sediment, contaminated soil, contaminants in soil, bioremediation of soils, natural recovery, wetland sediments, biochemistry, chlorinated organics, phytoremediation

Relevant Websites:

http://www.hsrc.org/hsrc/html/ssw/ Exit

Progress and Final Reports:

Original Abstract
  • 2003 Progress Report
  • 2004 Progress Report
  • 2005
  • 2006
  • Final

  • Main Center Abstract and Reports:

    R828773    HSRC (2001) - South and Southwest HSRC

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R828773C001 Bioturbation and Bioavailability of Residual, Desorption-Resistant Contaminants
    R828773C002 In-Situ Containment and Treatment of Contaminated Sediments: Engineering Cap Integrity and Reactivity
    R828773C003 Phytoremediation in Wetlands and CDFs
    R828773C004 Contaminant Release During Removal and Resuspension
    R828773C005 HSRC Technology Transfer, Training, and Outreach