2002 Progress Report: Redox Transformations, Complexation and Soil/Sediment Interactions of Inorganic Forms of As and Se in Aquatic Environments: Effects of Natural Organic Matter

EPA Grant Number: R829515C001
Subproject: this is subproject number 001 , established and managed by the Center Director under grant R829515
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC - Rocky Mountain Regional Hazardous Substance Research Center for Remediation of Mine Waste Sites
Center Director: Shackelford, Charles D.
Title: Redox Transformations, Complexation and Soil/Sediment Interactions of Inorganic Forms of As and Se in Aquatic Environments: Effects of Natural Organic Matter
Investigators: Macalady, Donald L. , Westall, John C. , Ahmann, Dianne , Garbarino, John
Institution: Colorado State University , United States Geological Survey , Oregon State University
Current Institution: Colorado State University , Oregon State University , United States Geological Survey
EPA Project Officer: Lasat, Mitch
Project Period: November 1, 2001 through October 31, 2003
Project Period Covered by this Report: November 1, 2001 through October 31, 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

Objective:

The objectives of this research project are to:

• Characterize water samples and their associated natural organic matter (NOM) from sites within and beyond U.S. Environmental Protection Agency (EPA) Region 8 for pH, alkalinity, conductivity, metals content, anion character and quantity, total organic and inorganic carbon, elemental composition, acidity, aromatic content, Fourier Transform Infrared Spectroscopy (FTIR) spectrum, and average molecular weight of the NOM.

• Determine the ability of each NOM sample to form aqueous complexes with As and Se.

• Determine the ability of each NOM sample to compete with As and Se for sorption onto hematite and gibbsite, and to estimate the extent to which each NOM sample accelerates redox transformations of As and Se.

• Quantify the abilities of selected NOM samples to accelerate redox transformations as a function of sample history and presence or absence of microorganisms and external electron donors and acceptors.

• Codify observed relationships among NOM characteristics, aqueous geochemistry, influences on complexation, sorption, and redox reactions of As and Se in an attempt to correlate measurable NOM properties with the magnitudes of the observed effects using techniques such as ANOVA and principle component analysis.

• Investigate the influences of selected samples of NOM on As and Se bioavailability and toxicity in regards to known influences of NOM samples on As and Se complexation, adsorption, and redox behavior.

• Formulate a conceptual model describing the interactions between NOM, As, and Se that are pertinent for remediation design.

• Test this model with experiments from field sites for which predictions of As and/or Se behavior can be formulated and tested based on the site properties and the conceptual model.

Progress Summary:

Because funding was not available at the Colorado School of Mines (CSM) until late January 2002, progress during 2002 represents approximately 9 months of effort. During this time, we have established the influence of NOM on the adsorption of As species on hydrous iron oxides, and we have detailed variations in these effects among five different NOM samples. NOM facilitates the partial release of adsorbed As species, and prevents the total adsorption of As species from solution in cases where both NOM and As are cosolutes. The redox chemistry associated with these adsorption events is not understood at this point, and we are working on the reproducibility and fundamental characterization of the apparent nonequilibrium processes that govern the redox speciation of As in the presence of NOM and iron oxide solids.

In addition, we have worked with aluminum oxyhydroxide suspensions to remove the complications associated with iron redox chemistry. However, the presence of very small colloidal material in aqueous systems containing Al oxides has provided analytical challenges to isolating the role of adsorption, formation of NOM-Al-As complexes, redox processes mediated by NOM and/or bacteria, and chromatographic separation of various As and As-Al(OH)x species. These difficulties have revealed the care that is required to eliminate microbial processes from consideration, and will cause a revisitation of initial conclusions about the role of NOM in As redox speciation in iron oxyhydroxide suspensions.

We have focused on investigations designed to elucidate the nature of As-NOM-Fe interactions at iron oxyhydroxide surfaces. This understanding is crucial for the application of this research to the design and operation of remediation systems and general problems of As mobility in aqueous systems. We are attempting to determine the extent to which such interactions are dependent on the precise nature of the oxide surface and the origin and functional composition of the NOM samples.

Finally, we are developing the analytical capability to extend this work to selenium. We have developed and tested a reliable technique for the separation and quantification of Se(IV) and Se(VI) in aqueous systems and we are working on the capability to reliably detect and quantify aqueous complexes of Se with NOM and colloidal Fe and/or Al oxyhydroxides.

We have not started the toxicity studies projected in the original proposal for month 9 of this research project. A better understanding of the nature of NOM/As/Fe aqueous systems is required before this phase of the research is started.

Future Activities:

In the next 6 months, the laboratory characterizations of As redox chemistry and adsorption to mineral surfaces should be completed. Following this, we will begin field testing of the understandings generated in the laboratory at selected As contaminated sites in the region. For Se, a similar, if not slightly retarded, timetable is anticipated, with field sites in Utah and Colorado. Laboratory experiments with field samples will be a critical part of these studies.

We also will initiate laboratory toxicity measurements in a few months, along with investigations of the role of NOM and mineral surfaces on microbially mediated redox transformations of As and Se. This will precede the development of a comprehensive model of the role of NOM in As and Se geochemistry. Finally, we will evaluate the application of these understandings and this model to the design and operation of existing and future mine-waste remediation efforts.

Supplemental Keywords:

groundwater, sediments, environmental chemistry, mining, geochemistry, toxicology, remediation, metal mobility, subsurface, microbiology, selenium, acid mine drainage, acid mine runoff, aquatic ecosystems, arsenic, contaminant transport, contaminated marine sediment, contaminated waste sites, field monitoring, groundwater, heavy metals, mining-impacted watershed, mining wastes, natural organic matter, NOM, redox, remediation technologies, risk assessment, runoff, sediment transport, stream ecosystems, suspended sediment., RFA, Scientific Discipline, Industry Sectors, Waste, Water, Contaminated Sediments, Remediation, Mining - NAIC 21, Hazardous Waste, Ecological Risk Assessment, Ecology and Ecosystems, Geology, Hazardous, Environmental Engineering, risk assessment, contaminant transport, contaminated waste sites, contaminated marine sediment, suspended sediment, acid mine drainage, runoff, sediment transport, stream ecosystems, remediation technologies, natural organic matter, field monitoring, mining, Selenium, treatment, aquatic ecosystems, arsenic, groundwater, heavy metals, mining impacted watershed, mining wastes, acid mine runoff

Relevant Websites:

http://www.engr.colostate.edu/hsrc/ Exit

Progress and Final Reports:

Original Abstract
  • Final

  • Main Center Abstract and Reports:

    R829515    HSRC - Rocky Mountain Regional Hazardous Substance Research Center for Remediation of Mine Waste Sites

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R829515C001 Redox Transformations, Complexation and Soil/Sediment Interactions of Inorganic Forms of As and Se in Aquatic Environments: Effects of Natural Organic Matter
    R829515C002 Fate and Transport of Metals and Sediment in Surface Water
    R829515C003 Metal Removal Capabilities of Passive Bioreactor Systems: Effects of Organic Matter and Microbial Population Dynamics
    R829515C004 Evaluating Recovery of Stream Ecosystems from Mining Pollution: Integrating Biochemical, Population, Community and Ecosystem Indicators
    R829515C005 Rocky Mountain Regional Hazardous Substance Research Center Training and Technology Transfer Program
    R829515C006 Technical Outreach Services for Communities and Technical Assistance to Brownfields
    R829515C007 Evaluation of Hydrologic Models for Alternative Covers at Mine Waste Sites
    R829515C008 Microbial Reduction of Uranium in Mine Leachate by Fermentative and Iron-Reducing Bacteria
    R829515C009 Development and Characterization of Microbial Inocula for High-Performance Passive Treatment of Acid Mine Drainage
    R829515C010 Reactive Transport Modeling of Metal Removal From Anaerobic Biozones
    R829515C011 Assessment of Electrokinetic Injection of Amendments for Remediation of Acid Mine Drainage
    R829515C012 Metal Toxicity Thresholds for Important Reclamation Plant Species of the Rocky Mountains
    R829515C013 An Improved Method for Establishing Water Quality Criteria for Mining Impacted Streams