Dependence of Metal Ion Bioavailability on Biogenic Ligands and Soil Humic Substances

EPA Grant Number: R825960
Title: Dependence of Metal Ion Bioavailability on Biogenic Ligands and Soil Humic Substances
Investigators: Higashi, Richard M. , Lane, Andrew N. , Fan, Teresa W-M.
Institution: University of California - Davis
EPA Project Officer: Lasat, Mitch
Project Period: January 1, 1998 through December 31, 2001
Project Amount: $345,816
RFA: EPA/DOE/NSF/ONR - Joint Program On Bioremediation (1997) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management


Organic matter, can strongly affect metal ion binding to soil and sediment. In fact, production of a major form of organic matter - low-molecular weight organic ligands - is the principal mechanism by which plants and microbes acquire metal ions, so that the chemistry of biogenic organic matter is the key to understanding mechanisms of bioavailability for bioremediation purposes.

Thus, the complex interaction between metal ions, biogenic ligands, and humic substances must be understood in order to engineer the proper organisms and conditions for bioremediation of metal ion contamination. We propose to investigate this critically lacking area of knowledge through the following objectives:

    i. Determine the sorption behavior of metal ions on isolated humic substances in the presence of biogenic and synthetic ligands;
    ii. Conduct a subset of experiments from (i) as longer-term ageing experiments;
    iii. Investigate the properties of isolated humic substances that are involved in (i) and (ii);
    iv. Assess the relationship of (i) and (ii) to metal ion bioavailability to vascular plants, including evaluation of soils from a Federal demonstration site (McClellan AFB);
    v. Use the findings from (i) thru (iv) to identify key rhizospheric processes that regulate metal bioavailability, additionally incorporating findings from a complementary project on the biochemistry of metal ion ligands in plants/mycorrhizal systems.


Cadmium, aluminum, and iron metal ion binding to biogenic ligands (ranging from simple organic acids to complex siderophores such as desferrioxamine), ligand binding to isolated humic substances, and the interaction of all three components will be studied using chemical structure and kinetics approaches. The analytical backbone of the project will be techniques from organic chemistry, macromolecular dynamics, and humic structure probes, including multinuclear-multidimensional NMR spectroscopy, fluorescence spectrophotometry, FTIR microspectroscopy, and pyrolysis GCMS.

The investigation will additionally include whole soil experiments utilizing spiked soils as well as soils from a DOD/DOE/EPA National Environmental Technology Test Site, McClellan AFB. Actual metal ion bioavailability will be assessed throughout the study by measuring accumulation in vascular plants: Lemna sp. (duckweed) for aqueous phase experiments and Triticum sp.(wheat) for whole soil assessments.

Expected Results:

This study is designed to probe fundamental mechanisms of metal ion/ligand/humic interactions that are currently unknown. This is vital to soil bioremediation since the production of organic ligands is a principal mechanism by which plants and microbes acquire metal ions. Furthermore, biogenic ligands and metal ions will alter the structure and properties of soil humic substance, opening a means by which soils and sediments may be altered chemically by organisms or amendments to obtain desired long-term characteristics. For example, a bioremediation goal may be to alter soil characteristics such that plant/microbe systems will readily accumulate contaminant metal ions, yet reduce leaching to groundwater. Another goal may be to achieve long-term "entombment" of metal ions to stablize a site against both leaching and food-chain accumulation. However, these are possible only if we have a thorough understanding of metal ion/ligand/humic chemistry, and how ligands and metal alter the structure-activity of humic substances.

Publications and Presentations:

Publications have been submitted on this project: View all 28 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 4 journal articles for this project

Supplemental Keywords:

soil, sediments, adsorption, chemical transport, heavy metals,bioremediation, environmental chemistry, Scientific Discipline, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Contaminated Sediments, Remediation, Environmental Chemistry, State, Fate & Transport, Bioremediation, West Coast, fate, fate and transport, sorption, biogenic ligands, humic substances, NMR spectroscopy, pyrolysis GCMS, rhizospheric, contaminated sediment, soils, adsorption, chemical transport, vascular plants, metal ion bioavailability, FTIR microspectroscopy, wheat, California, phytoremediation, sediments, soil humic substances, biogenic organic matter, heavy metals, metal compounds, metals, fluoroescence spectrophotometry, duckweed

Progress and Final Reports:

  • 1998
  • 1999 Progress Report
  • 2000 Progress Report
  • Final Report