Final Report: Fate and Transport of Heavy Metals and Radionuclides in Soil: The Impacts of Vegetation

EPA Grant Number: R825549C046
Subproject: this is subproject number 046 , 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: HSRC (1989) - Great Plains/Rocky Mountain HSRC
Center Director: Erickson, Larry E.
Title: Fate and Transport of Heavy Metals and Radionuclides in Soil: The Impacts of Vegetation
Investigators: Schwab, Arthur Paul , Banks, M. Katherine , Erickson, Larry E. , Pierzynski, G. M. , Schnoor, J. L. , Tracy, J. C.
Institution: Kansas State University , Purdue University - Main Campus , University of Iowa
EPA Project Officer: Hahn, Intaek
Project Period: August 16, 1993 through May 18, 1998
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (1989) RFA Text |  Recipients Lists
Research Category: Fate and Transport , Land and Waste Management


The overall objective of this research was to determine whether establishment of vegetation in heavy metal- and radionuclide-contaminated soil will significantly affect retention of metals in soils and to develop mathematical models to predict the movement of metals in vegetated versus unvegetated soil.

Summary/Accomplishments (Outputs/Outcomes):

Vegetation is often the primary method of reclamation in mining areas to stabilize waste with respect to wind and water erosion and to minimize downward translocation of contaminants. Plants may reduce the possibility of metal leaching through decreased water infiltration, adsorption of metals to root surfaces, plant uptake of metals, and stimulated microbial immobilization in the rhizosphere. However, plants may also increase metal leaching through reactions with rhizosphere organic acids exuded by roots, produced by microbial activity, or generated by decomposition of soil organic matter. Field and laboratory determinations are needed to quantify the effects of vegetation on the leaching of metals. Models that attempt to predict the fate of heavy metals in soils have focused primarily on the geochemical aspects of the problem and have not considered the effect of a plant's geochemistry. The difficulty associated with using models to stimulate the fate of a heavy metal in the root-soil environment is properly accounting for all interactions among water movement, contaminant transport, and uptake of water and metals by plant roots and geochemistry.

Impact of vegetation and revegetation schemes on the mobility of metals (lead, cadmium, zinc, barium, etc.) was investigated on contaminated soil and/or mine waste from zinc and lead mining regions of southeast Kansas, lead mines of Montana, and a paint-producing industry in southern Kansas. A series of experiments was employed to pursue the following objectives: a sequential extraction procedure for determination of various fractions and mineral associations of the metals; batch (laboratory-scale equilibrations) and column experiments to directly assess impact of organic acids on heavy metal mobility; large soil columns to determine effects of vegetation overlying soil depth on mobility of metals and metal uptake by plants; sorption/desorption and determination of potential or existing solid phases of the metals to quantify the soil chemical aspects of metal retention; and integration of geochemical and solute transport modeling to predict and analyze the fate of metals as influenced by the presence of vegetation.

Mobility of Metals in Large Columns Soil and mine tailings were collected from the mining area of southeast Kansas and packed into large columns (60 cm x 7.5 cm i.d.) to simulate reclamation practices in the field. The layers within the columns were 30 cm subsoil at the bottom, 30 cm mine tailings, and an overlying layer of 30 or 60 cm topsoil. Columns also were constructed with no topsoil or no subsoil. Leaching of lead, zinc, and cadmium were strongly influenced by the presence of vegetation and the absence of subsoil, but the depth of topsoil had only a small impact. Leaching of zinc and cadmium was by far the greatest in vegetated columns with no subsoil and was the least in unvegetated columns with no topsoil and 30 cm subsoil. The presence of a subsoil in vegetated columns reduced leaching by as much as a factor of ten compared the columns with subsoil; apparently, the subsoil was a highly effective sink for the Zn and Cd. Leaching of Pb was positively correlated with the volume of leachate. Thus, plants the reduced leachate reduced Pb mobility.

From these experiments, we hypothesized that plant roots somehow are able to mobilize Cd and Zn (perhaps through alteration of rhizosphere chemistry), but the subsoil keeps the metals from leaching to great depths.

The Effects of Organic Acids on Metal Translocation Several organic acids, particularly citric and succinic, are produced by plant roots and rhizosphere microorganisms and have the capability to solubilize metals. To determine if these acids could be responsible for the trends observed in the column experiments (reported above), we conducted a series of batch adsorption and small column experiments that measured the mobility of Pb and Zn in soil in the presence and absence of these organic acids. For both Pb and Zn, adsorption increased with increasing citric acid concentration. This trend held for concentrations up to 3.0 mM citrate for both of the soils examined; in one soil, citric acid concentrations greater than 3.0 mM resulted in decreased adsorption. This result was tested further in small soil columns in which an influent solution containing various concentrations of citrate and either Pb or Zn was leached continuously through the columns for a period of several weeks. In small columns (containing <200 g soil) with restricted microbial activity and citrate concentrations of 5 mM or higher, metal breakthrough occurred after approximately 2 pore volumes. In large columns (2500 g soil) with normal microbial activity and citrate concentrations <10 mM, neither metal nor citrate were detected in significant concentrations in the effluent solution, probably because the citrate was degraded rapidly by the soil microorganisms, seriously limiting the mobility of the metals.

The results of these column experiments suggest that, although citrate is quite capable of solubilizing both Zn and Pb, rapid microbial degradation of this compound prevents metal movement. The organic acid seemed to act as a stimulant for the microorganisms and enhanced microbial fixing of the metals. Metal Mobility as Affected by Organic Amendments Establishing vegetation in highly contaminated soils is often difficult because of poor soil fertility, low microbial activities, and inadequate physical structure. Many of these problems can be overcome by adding organic amendments such as composted yard waste, manure, or sewage sludge ("biosolids"). These organic materials have the capacity to fix metals through cation exchange and surface complexation, but they also can mobilize the metals because of the presence of soluble chelating agents. The impact of organic amendments on the mobility of Cr, Cd, Pb, and Zn was examined in two column experiments in which metal-contaminated soil was mixed with different kinds of organic amendments and subjected to leaching.

In a chromium contaminated soil, columns were constructed to contain the following treatments in a factorial design: composted cattle manure (10% or none), Cr(VI) (476 or 119 mg Cr/kg soil), and vegetation (tall fescue or none). After 90 days of leaching, the greatest amount of Cr in the effluents was found in the columns with the higher amount of Cr(VI) contamination. The vegetation treatment was found to have no impact. However, adding composted manure reduced Cr leaching by 50% as a direct result of the reduction of Cr(VI) to less mobile Cr(III).

In a soil contaminated with Pb, Cd, and Zn, the source of organic amendment was found to be important. Composted manures were found to have no impact on metal mobility, but a material that had been only slightly weathered was found to significantly increase metal concentrations in leachates from the columns. We hypothesize that the composting process degrades most of the lower molecular weight organic acids that could solubilize metals. In the non-composted material, soluble organics continued to mobilize the metals; this effect should diminish with time as the manure weathers in the soil.

Results from this project have been published in peer-reviewed journals. Results have been presented to consultants, regulators, and other researchers in seven different presentations at various technical conferences in 1995, 1996, 1997, and 1998. In addition to the presentations listed below, the following were part of our technology transfer efforts:

  • January, 1998. Participated in a workshop at Kansas State University concerning the use of plants in the remediation of soils contaminated with heavy metals.
  • May, 1996. Participated in a workshop concerning the management of soils contaminated with heavy metals in Denver, Colorado at the U.S. EPA regional office.
  • April, 1996. Meeting in southeast Kansas with representatives for U.S. EPA, U.S. Bureau of Mines, U.S. Corps of Engineers, and Kansas Department of Health and Environment to help assess and discuss future plans for the reclamation of the mine tailing in Cherokee County.
  • January, 1996. Participated in a workshop at Kansas State University concerning the use of plants in the remediation of soils contaminated with heavy metals.

    Journal Articles on this Report : 5 Displayed | Download in RIS Format

    Other subproject views: All 27 publications 6 publications in selected types All 5 journal articles
    Other center views: All 904 publications 230 publications in selected types All 182 journal articles
    Type Citation Sub Project Document Sources
    Journal Article Abdelsaheb I, Schwab AP, Banks MK, Hetrick BA. Chemical characterization of heavy-metal contaminated soil in southeast Kansas. Water Air and Soil Pollution 1994;78(1-2):73-82. R825549C033 (Final)
    R825549C046 (Final)
    not available
    Journal Article Burckhard SR, Schwab AP, Banks MK. The effects of organic acids on the leaching of heavy metals from mine tailings. Journal of Hazardous Materials 1996;41:135-145. R825549C046 (Final)
    not available
    Journal Article He YH, Schwab AP, Banks MK. Influence of citrate on adsorption of zinc in soils. Journal of Environmental Science and Technology 2004;130(10):1180-1187. R825549C046 (Final)
    not available
    Journal Article Nedunuri KV, Erickson LE, Govindaraju RS. Modeling the role of active biomass on the and transport of a heavy metal in the presence of root exudates. Journal of Hazardous Substance Researcj 1998;1(9):1-25. R825549C046 (Final)
    not available
    Journal Article Zhu D, Schwab AP, Banks MK. Heavy metal leaching from mine tailings as affected by plants. Journal of Environmental Quality 1999;28(6):1727-1732. R825549C046 (Final)
    not available

    Supplemental Keywords:

    vegetation, heavy metals, radionuclides, soil, fate and transport, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Contaminated Sediments, Environmental Chemistry, Geochemistry, Remediation, Fate & Transport, Analytical Chemistry, Ecology and Ecosystems, fate and transport, contaminant transport, radionuclides, acid mine drainage, contaminated sediment, kinetics, hazardous waste, contaminated soil, vegetation, mining waste, heavy metal contamination, phytoremediation, heavy metals

    Relevant Websites: Exit

    Progress and Final Reports:

    Original Abstract
  • 1994
  • 1995
  • 1996
  • 1997

  • Main Center Abstract and Reports:

    R825549    HSRC (1989) - Great Plains/Rocky Mountain HSRC

    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