Grantee Research Project Results

Final Report: Use of Vegetation to Enhance Bioremediation of Surface Soils Contaminated with Pesticide Wastes

EPA Grant Number: R825549C045
Subproject: this is subproject number 045 , established and managed by the Center Director under grant R825549
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: National Research Program on Design-Based/Model-Assisted Survey Methodology for Aquatic Resources
Center Director: Stevens, Don L.
Title: Use of Vegetation to Enhance Bioremediation of Surface Soils Contaminated with Pesticide Wastes
Investigators: Coats, Joel R. , Anderson, Todd A.
Institution: Iowa State University
EPA Project Officer: Hahn, Intaek
Project Period: May 1, 1995 through April 1, 1997
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management

Objective:

The long-term goal of our research is to determine whether vegetation can have a positive effect on microbial degradation of pesticide wastes in soils as a result of the rhizosphere effect. Under a variety of environmental conditions, vegetation has been shown to enhance microbial degradation rates of organic chemical residues in soils. These findings are important because vegetation may provide a low-cost alternative or supplement to expensive, capital-intensive technologies for soil cleanup.

The primary objective of this project is to determine the role of herbicide-tolerant plants and commodity plants in facilitating microbial degradation of herbicide wastes in soils. This information can then be used in defining the potential role of vegetation, under specific types of chemical contamination (herbicides, insecticides, industrial chemicals) in the bioremediation process. The specific use of vegetation to enhance the microbial degradation of surface and near-surface soils contaminated with pesticide wastes could provide a cost-effective remediation strategy for soils containing low to moderate concentrations of these compounds when engineering approaches to cleanup are not practical. The research could also provide important information for assessing the bioavailability and potential human health implications of pesticide wastes in soils at agrochemical dealership sites.

Summary/Accomplishments (Outputs/Outcomes):

With the increase in pesticide usage since the early l950s has come a rapid growth in the numbers of agrochemical dealerships. Unfortunately, many of these dealerships have, through normal operating procedures, contaminated the soil and water at these sites, creating one of the most ominous issues facing the agrochemical industry. The expense of most of the current technologies for cleanup of contaminated soil and water preclude their use at agrochemical dealership sites. Biological restoration using indigenous microbial populations is potentially an effective remediation strategy for these sites. The use of vegetation to enhance microbial degradation is a viable technique for overcoming some of the limitations inherent with bioremediation.

A screening study for mineralization of metolachlor and atrazine in rhizosphere soils of fifteen plant species was carried out. Rhizosphere soils were collected from the root zone of plants in areas with previous herbicide exposures. Several rhizosphere soils tested positive for 14C-atrazine mineralization (> 8.5% of the applied 14C mineralized) after 50-d incubation, including kochia, lambsquarters, foxtail barley, witchgrass, catnip, and musk thistle. The greatest amount of mineralization occurred in rhizosphere soils of kochia (62 + 4.3%). None of the fifteen rhizosphere samples tested exhibited a positive response for metolachlor mineralization e 8.5%). Rhizosphere soils from corn exhibited the highest mineralization of 14C-metolachlor (Anderson and Coats, 1995).

To determine if high concentrations of herbicide mixtures could inhibit degradation of atrazine in a soil that rapidly mineralized atrazine at 50 mg/g, Bravo rhizosphere soil was treated with 14C-atrazine at 200 mg/g, individually or in combination with metolachlor (200 mg/g) and/or trifluralin (200 mg/g). No toxicity to the atrazine-degrading population was seen in this experiment. Rapid mineralization of atrazine occurred in all soil treatments (Kruger et al., 1997), with 60% to 80% mineralization after 60 days. This is even greater mineralization than that observed in soils treated individually with 14Catrazine at 50 mg/g. Quantification of atrazine degraders in rhizosphere and nonrhizosphere soils (with the use of a 14C-mostprobable-numbers technique) indicated a population existed in this soil (Kruger, 1996). To determine if this degradative capability could be transferred to another agrochemical dealer site (contaminated) soil, soil mixtures were made, and soils were spiked with 14C-atrazine at 50 mg/g. Mixing the soils did not increase the mineralization of atrazine in the less active soil (Kruger et al., 1997).

A screening study for enhanced degradation of atrazine, metolachlor, pendimethalin, and alachlor was conducted using pesticide-contaminated soils from four agrochemical dealer sites (Kruger, 1996). Pesticide-contaminated soils from four agrochemical dealer sites were sampled, analyzed for background contaminant concentrations, treated with individual herbicides (50 mg/g soil concentration), and incubated under controlled conditions. Complete mineralization of uniformly ring-labeled 14C-atrazine, metolachlor, alachlor, and pendimethalin was monitored in soils for 9 weeks. Atrazine mineralization was extensive in four of the soils tested, with mineralization as high as 35% of the applied 14C. In rhizosphere soil from Bravo, a shorter lag time was seen for atrazine mineralization than in the soil from a nonvegetated area. Very low amounts of metolachlor, alachlor, or pendimethalin were mineralized in these soils. Analyses of soils extracts are in progress to determine the quantities of parent compound remaining and degradation products formed during the 9-week incubation.

Complete metabolism studies of atrazine and metolachlor applied as a mixture to pesticide-contaminated soils from agrochemical dealer sites were carried out. Both nonvegetated and rhizosphere soil samples were taken from two agrochemical dealer sites, Alpha and Bravo. Soils were treated with a mixture of either 14C-atrazine and unlabeled metolachlor or 14C-metolachlor and unlabeled atrazine. At the end of 30 d, a significantly greater percentage of applied 14Catrazine was mineralized in soil taken from the rhizosphere of kochia than from nonvegetated soils from Bravo (Perkovich et al., 1996). Atrazine was less persistent in the rhizosphere soil than in nonvegetated soils, with only 2% and 7% extractable from soil, respectively (Arthur et al., 1997; Kruger, 1996). Mineralization of metolachlor was minimal after 30 d (Perkovich et al., 1996). In soils from Alpha, the half-life of atrazine in rhizosphere soil was significantly less than in nonvegetated soils (50 and 193 d, respectively) (Arthur et al., 1997; Kruger, 1996).

A study was conducted to evaluate of the influence of kochia and canola on the degradation of a mixture of aged atrazine and metolachlor in soil from a pesticide-contaminated site (Kruger et al., 1997; Arthur et al., 1997; Kruger, 1996). Soils treated with a mixture of 14C-atrazine and unlabeled metolachlor were incubated for 165 days prior to introducing plants to the soils. Soils were either left unvegetated or transplanted with kochia or canola plants. Soil/plant incubations were carried out in an enclosed chamber that was kept in a temperature-controlled room (24 ?C) with a light:dark cycle of 16:8. Twenty-seven days' after planting, the Brassica plants appeared very stressed, and all Brassica-vegetated samples along with a portion of the Kochia-vegetated and nonvegetated samples were extracted and analyzed at this time point. Kochia plants were thriving, so the study was continued with the remaining set of unvegetated and Kochia-vegetated soils. At 240 days postherbicide treatment, 75 days after planting, the experiment was ended. At the end of each incubation period, entire plants were analyzed for 14C residue in plants by combusting pellets made up of plant tissue and hydrolyzed starch in a Packard Sample Oxidizer (Packard Instruments, Downer's Grove, IL). Soils were extracted and analyzed. Subsamples of extracted soil were combusted to detennine the amount of unextractable 14C-residue in soil. After 27 days post-planting, significantly less atrazine was extractable from soils vegetated with Kochia scoparia compared to soils vegetated with Brassica napus, with 4.3% and 9.8% of the applied 14C-atrazine extractable from these soils, respectively (ANOVA; p < 0.05) (Kruger, 1996). From the nonvegetated soil, 9.3% of the applied 14C-atrazine was extractable, which was not significantly different from either of the vegetated soils. A significantly greater amount of 14C was taken up by Kochia plants (10% of the applied14C) than by the Brassica plants (less than 1%) (ANOVA; p = 0.0001). Significantly less atrazine was extractable from Kochia-vegetated soils than from nonvegetated soils 75 days post planting (240 days post-herbicide treatment) (ANOVA; p < 0.01). From the Kochia-vegetated soil 5.3% of the applied atrazine was extractable from soil, while 8.3% was extractable for the nonvegetated soil. There were no significant differences in quantities of degradates formed or nonextractable residues between the two treatments. Combustion of plants revealed that 6.5% of the applied 14C was taken up by the Kochia.

Quantification of specific herbicide degraders in pesticide-contaminated soils from agrochemical dealer sites was carried out by using a 14C-most-probable-number technique (Arthur et al., 1997; Kruger, 1996). Low numbers of atrazine degraders were seen in soils from Alpha site; significantly more degraders were quantified in kochia rhizosphere soil compared to nonrhizosphere soil, with a mean of 1,126 and 17 organisms g-1, respectively). For metolachlor degraders, 281 and 70 organisms g-1 were quantified in rhizosphere and nonvegetated soils, respectively. Considerably greater quantities of atrazine degraders were seen in Bravo soils with 17,412 and 1,107 organisms g-1, respectively. Significantly more degraders were seen in the nonvegetated soil than rhizosphere soil from this site, which is the opposite of what would be expected since the rhizosphere normally has orders of magnitude more degraders than surrounding nonvegetated soils. It may be that increased numbers of predators, such as protozoa, may have existed in the rhizosphere soil (T. B. Moorman, personal communication), which may have resulted in lower numbers of microorganisms g-1 in this quantification procedure.

A study was conducted to determine if high concentrations of herbicide mixtures could inhibit degradation of atrazine in a soil that rapidly mineralized atrazine at 50 mg/g (Kruger et al., 1997). Soil from the Bravo rhizosphere was treated with 14C-atrazine at 200 mg/g, individually or in combination with metolachlor (200 mg/g) and/or trifluralin (200 mg/g). The soil moisture was adjusted to 60% saturation, and soils were incubated as described earlier. No toxicity to the atrazine-degrading population was seen in this experiment. Rapid mineralization of atrazine occurred in all soil treatments, with 60% to 80% mineralization after 60 days. This is an even greater mineralization rate than that observed in soils treated individually with 14C-atrazine at 50 mg/g.

A study was conducted to determine if a soil's ability to degrade atrazine could be transferred to a soil that could not mineralize atrazine by mixing the two soil types in an attempt to "inoculate" the slow atrazine-degrading soil (Kruger et al., 1997). The two soils used for this study were from Bravo and Echo. Four combinations of soil mixtures were used for this study: (1) 100% Bravo, (2) 90% Echo: 10% Bravo, (3) 80% Echo: 20% Bravo, (4) 100% Echo. The treating solution consisted of analytical grade and uniformly ring-labeled 14C-atrazine in acetone. Soil combinations were mixed thoroughly, and 20 g of each combination (two replications) were treated in 250-ml incubation jars to obtain a soil concentration of atrazine at 50 mg/g. The methods of soil moisture adjustment, 14CO2 trapping, and incubation were identical to the previous studies described above. Thirty-six percent of the applied 14C-atrazine was mineralized in the 100% Bravo soil. The 100% Echo soil did not mineralize any atrazine. The soil combination made up of 80% Echo and 20% Bravo had significantly greater mineralization than did the 100% Echo soil or the combination of 90% Echo and 10% Bravo soil. On a percentage mineralized per gram soil basis, the addition of Bravo soil to the Echo soil did not enhance mineralization of atrazine in the Echo soil. It is possible that characteristics of the Echo soil did not provide an optimal environment for survival of the degraders. Echo soil had a much lower pH (4.3) compared to the Bravo soil (pH = 7.5). The Echo soil was also a very saline soil, with an electrical conductivity value of 8.9 mmho cm-1. Fertilizer spills at this site may have contributed to the high salt content in this soil.

A study has been conducted to evaluate degradation of herbicides applied in pesticide mixtures to determine if interactions alter degradation of individual herbicides (Anhalt et al., 1997). Bravo soil was treated with atrazine at a concentration of 50 mg/g per herbicide. Treatments that included atrazine in this study were: (1) atrazine; (2) atrazine and metolachlor; (3) atrazine and pendimethalin; and (4) atrazine, metolachlor, and pendimethalin. Atrazine degradation applied in mixtures with metolachlor and pendimethalin showed no significant differences among the treatments (Kruger et al., 1997). Atrazine was very degradable in this soil with 6 and 2% of the applied compound remaining after 21 and 160 days, respectively. The half-life of atrazine, based on extractable atrazine, was calculated at 45 d.
A field microplot study is in progress to investigate the influence of single species and mixed species of natural prairie grasses on degradation of aged herbicides in soil. Additionally, the survivability of soil inoculations of known herbicide degraders in vegetated and nonvegetated contaminated soils is being assessed by plate counts and 14C-most-probable-number techniques in a collaborative project with Dr. Tom Moorman, USDA-ARS, National Soil Tilth Laboratory, Ames, IA. This microplot study was initiated in September at Iowa State University. Soil from an agrochemical dealer site was spiked with atrazine (100 mg/g), trifluralin (25 mg/g) and metolachlor (25 mg/g) by treating soils in a cement mixer. Concentrations of herbicides were determined in the soil before and after treatment by sequential extraction of subsamples of soils with ethyl acetate. Soil extracts were analyzed by gas chromatography. Soils were allowed to age in tubs in the field plot prior to introducing plants and inoculum to the soils. On day 34 post-treatment, plants and microbial inoculum were introduced to the plots. Six treatments (with four replications) included: (1) planting with big blue stem (2) planting with a mixture of yellow indiangrass, big bluestem, and switchgrass (3) no vegetation (4) big bluestem inoculated with known atrazine and metolachlor degraders (5) inoculated grass mixture (6) no vegetation, but inoculation with the two known degraders. The prairie grasses were sprouted in potting soil. The plants were inoculated with known atrazine and metolachlor degraders in the greenhouse 24 hours before transplanting them to the field plots. Inoculation of unvegetated plots was achieved by pipetting a solution containing the degraders to the soil. On day 53, soil and grass/root samples were taken from each plot. Soils are in the process of being extracted and analyzed. A time series of subsampling will take place over the growing season, with analyses of soil extracts by gas chromatography. Big blue stem, individually and/or in combination with yellow indian grass and switch grass, had a positive effect on the degradation of atrazine, metolachlor, and trifluralin contaminants. Enhanced degradation of metolachlor was noted in soils vegetated and inoculated with metolachlor degraders compared to uninoculated and unvegetated soils. Concentrations of atrazine in the same field microplot study decreased from 100 mg/g to approximate 10 mg/g, with no differences seen among inoculated and uninoculated treatments.

Technology Transfer:
--Discussions of practical implementation of phytoremediation were conducted with the following people:

Tom Dishno, T.E.D. Environmental, 4553 Mulford Rd., Monroe Center, IL 61052

Bob Drustrup, Environmental Engineer, Iowa Department of Natural Resources, Des Moines IA 50319

Louis Licht, Ecolotree, Iowa City, IA 52240

--Presentations of the research and technical publications with the Air & Waste Management Association Kruger, E.L., Anderson, T.A., and J.R. Coats. 1996. Proceedings from the 89th annual meeting, Air & Waste Management Association, paper no. 96-RP141.03.

--Technical publication with ASTM
Anderson, T.A., E.L. Kruger, and J.R. Coats. 1995. In B.S. Schepart, ed. Bioremediation of Pollutants in Soil and Water. ASTM. Philadelphia, PA, pp. 149-157.

--Report for the Iowa Groundwater Quarterly: Fate of atrazine and metabolites in soil. Iowa Groundwater Quarterly 6:28.
-- Symposia Organized
Kruger, E.L., T.A. Anderson, and J.R. Coats. 1996. Phytoremediation of Soil and Water
Contaminants. American Chemical Society, 212th national meeting, Orlando, FL, August 25-30.

Journal Articles on this Report : 6 Displayed | Download in RIS Format

Publications Views

Other subproject views:	All 39 publications	12 publications in selected types	All 6 journal articles
Other center views:	All 904 publications	230 publications in selected types	All 182 journal articles

Publications

Type	Citation	Sub Project	Document Sources
Journal Article	Anderson TA, Coats JR. Screening rhizosphere soil samples for the ability to mineralize elevated concentrations of atrazine and metolachlor. Journal of Environmental Science and Health Part B - Pesticides Food Contaminants and Agricultural Wastes 1995;B30(4):473-484.	R825549C045 (Final)	not available
Journal Article	Anhalt, J.C., E.L. Kruger, A.L. Chouhy, T.A. Anderson, and J.R. Coats. 1996. Effects of aging herbicide mixtures on soil respiration and plant survival in soils from a pesticide-contaminated site. Society of Environmental Toxicology and Chemistry, Joint meeting of Ozark-Prairie, South Central, and Rocky Mountain Regions, Stillwater, OK, May 16-18.	R825549C045 (Final)	not available
Journal Article	Anhalt JC, Arthur E, Anderson TA, Coats JR. Degradation of atrazine, metolachlor, and pendimethalin in pesticide-contaminated soils: Effects of aged residues on soil respiration and plant survival. Journal of Environmental Science and Healther Part B - Pesticides Food Contaminants and Argicultural Wastes 2000;35(4):417-438.	R825549C045 (Final)	not available
Journal Article	Arthur EL, Moorman TB, Zhau SM, Coats JR. Evaluation of microbial inoculation and regulation to enhance the dissipation of atrazine and metachlor in soil. Environmental Toxicology and Chemistry 2005;24(10):2428-2434.	R825549C045 (Final)	not available
Journal Article	Arthur, E.L., J.C. Anhalt, S. Zhao, B. Nelson, D. Sorensen, and J. R. Coats. 1997. Phytoremediation of pesticide mixtures with native prairie grasses. Society of Environmental Toxicology and Chemistry, Ozark-Prairie Chapter, Columbia, MO May 15-17.	R825549C045 (Final)	not available
Journal Article	Perkovich BS, Anderson TA, Kruger EL, Coats JR. Enhanced mineralization of C-14-atrazine in Kochia scoparia rhizospheric soil from a pesticide-contaminated site. Pesticide Science 1996;46(4):391-396.	R825549C045 (Final)	not available

Supplemental Keywords:

vegetation, bioremediation, pesticides, agrochemicals, rhizosphere., Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Waste, Water, Toxics, Fate & Transport, pesticides, Environmental Chemistry, Contaminated Sediments, Geochemistry, Bioremediation, Ecology and Ecosystems, adsorption, migration, contaminant transport, bioremediation of soils, biotechnology, contaminated sediment, microbial degradation, phytoremediation, biodegradation, fate and transport, chemical kinetics, agrochemicals, contaminants in soil, contaminated soils

Relevant Websites:

http://www.engg.ksu.edu/HSRC Exit

Progress and Final Reports:

Original Abstract

1995

Main Center Abstract and Reports:

R825549    National Research Program on Design-Based/Model-Assisted Survey Methodology for Aquatic Resources

Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825549C006 Fate of Trichloroethylene (TCE) in Plant/Soil Systems
R825549C007 Experimental Study of Stabilization/Solidification of Hazardous Wastes
R825549C008 Modeling Dissolved Oxygen, Nitrate and Pesticide Contamination in the Subsurface Environment
R825549C009 Vadose Zone Decontamination by Air Venting
R825549C010 Thermochemical Treatment of Hazardous Wastes
R825549C011 Development, Characterization and Evaluation of Adsorbent Regeneration Processes for Treament of Hazardous Waste
R825549C012 Computer Method to Estimate Safe Level Water Quality Concentrations for Organic Chemicals
R825549C013 Removal of Nitrogenous Pesticides from Rural Well-Water Supplies by Enzymatic Ozonation Process
R825549C014 The Characterization and Treatment of Hazardous Materials from Metal/Mineral Processing Wastes
R825549C015 Adsorption of Hazardous Substances onto Soil Constituents
R825549C016 Reclamation of Metal and Mining Contaminated Superfund Sites using Sewage Sludge/Fly Ash Amendment
R825549C017 Metal Recovery and Reuse Using an Integrated Vermiculite Ion Exchange - Acid Recovery System
R825549C018 Removal of Heavy Metals from Hazardous Wastes by Protein Complexation for their Ultimate Recovery and Reuse
R825549C019 Development of In-situ Biodegradation Technology
R825549C020 Migration and Biodegradation of Pentachlorophenol in Soil Environment
R825549C021 Deep-Rooted Poplar Trees as an Innovative Treatment Technology for Pesticide and Toxic Organics Removal from Soil and Groundwater
R825549C022 In-situ Soil and Aquifer Decontaminaiton using Hydrogen Peroxide and Fenton's Reagent
R825549C023 Simulation of Three-Dimensional Transport of Hazardous Chemicals in Heterogeneous Soil Cores Using X-ray Computed Tomography
R825549C024 The Response of Natural Groundwater Bacteria to Groundwater Contamination by Gasoline in a Karst Region
R825549C025 An Electrochemical Method for Acid Mine Drainage Remediation and Metals Recovery
R825549C026 Sulfide Size and Morphology Identificaiton for Remediation of Acid Producing Mine Wastes
R825549C027 Heavy Metals Removal from Dilute Aqueous Solutions using Biopolymers
R825549C028 Neutron Activation Analysis for Heavy Metal Contaminants in the Environment
R825549C029 Reducing Heavy Metal Availability to Perennial Grasses and Row-Crops Grown on Contaminated Soils and Mine Spoils
R825549C030 Alachlor and Atrazine Losses from Runoff and Erosion in the Blue River Basin
R825549C031 Biodetoxification of Mixed Solid and Hazardous Wastes by Staged Anaerobic Fermentation Conducted at Separate Redox and pH Environments
R825549C032 Time Dependent Movement of Dioxin and Related Compounds in Soil
R825549C033 Impact of Soil Microflora on Revegetation Efforts in Southeast Kansas
R825549C034 Modeling the use of Plants in Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances
R825549C035 Development of Electrochemical Processes for Improved Treatment of Lead Wastes
R825549C036 Innovative Treatment and Bank Stabilization of Metals-Contaminated Soils and Tailings along Whitewood Creek, South Dakota
R825549C037 Formation and Transformation of Pesticide Degradation Products Under Various Electron Acceptor Conditions
R825549C038 The Effect of Redox Conditions on Transformations of Carbon Tetrachloride
R825549C039 Remediation of Soil Contaminated with an Organic Phase
R825549C040 Intelligent Process Design and Control for the Minimization of Waste Production and Treatment of Hazardous Waste
R825549C041 Heavy Metals Removal from Contaminated Water Solutions
R825549C042 Metals Soil Pollution and Vegetative Remediation
R825549C043 Fate and Transport of Munitions Residues in Contaminated Soil
R825549C044 The Role of Metallic Iron in the Biotransformation of Chlorinated Xenobiotics
R825549C045 Use of Vegetation to Enhance Bioremediation of Surface Soils Contaminated with Pesticide Wastes
R825549C046 Fate and Transport of Heavy Metals and Radionuclides in Soil: The Impacts of Vegetation
R825549C047 Vegetative Interceptor Zones for Containment of Heavy Metal Pollutants
R825549C048 Acid-Producing Metalliferous Waste Reclamation by Material Reprocessing and Vegetative Stabilization
R825549C049 Laboratory and Field Evaluation of Upward Mobilization and Photodegradation of Polychlorinated Dibenzo-P-Dioxins and Furans in Soil
R825549C050 Evaluation of Biosparging Performance and Process Fundamentals for Site Remediation
R825549C051 Field Scale Bioremediation: Relationship of Parent Compound Disappearance to Humification, Mineralization, Leaching, Volatilization of Transformaiton Intermediates
R825549C052 Chelating Extraction of Heavy Metals from Contaminated Soils
R825549C053 Application of Anaerobic and Multiple-Electron-Acceptor Bioremediation to Chlorinated Aliphatic Subsurface Contamination
R825549C054 Application of PGNAA Remote Sensing Methods to Real-Time, Non-Intrusive Determination of Contaminant Profiles in Soils
R825549C055 Design and Development of an Innovative Industrial Scale Process to Economically Treat Waste Zinc Residues
R825549C056 Remediation of Soils Contaminated with Wood-Treatment Chemicals (PCP and Creosote)
R825549C057 Effects of Surfactants on the Bioavailability and Biodegradation of Contaminants in Soils
R825549C058 Contaminant Binding to the Humin Fraction of Soil Organic Matter
R825549C059 Identifying Ground-Water Threats from Improperly Abandoned Boreholes
R825549C060 Uptake of BTEX Compounds by Hybrid Poplar Trees in Hazardous Waste Remediation
R825549C061 Biofilm Barriers for Waste Containment
R825549C062 Plant Assisted Remediation of Soil and Groundwater Contaminated by Hazardous Organic Substances: Experimental and Modeling Studies
R825549C063 Extension of Laboratory Validated Treatment and Remediation Technologies to Field Problems in Aquifer Soil and Water Contamination by Organic Waste Chemicals