Grantee Research Project Results

Physiochemical and Microbial Controls on the Speciation and Release of Arsenic into Ground and Surface Waters

EPA Grant Number: R826189
Title: Physiochemical and Microbial Controls on the Speciation and Release of Arsenic into Ground and Surface Waters
Investigators: Hamers, Robert J. , Banfield, Jillian F.
Institution: University of Wisconsin - Madison
EPA Project Officer: Aja, Hayley
Project Period: January 1, 1998 through December 31, 2000 (Extended to April 14, 2002)
Project Amount: $312,496
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Air , Safer Chemicals , Land and Waste Management

Description:

The central goal of this research is to understand, at a molecular level, the physiochemical and biological factors affecting the release of As into the environment by weathering of primary arsenic-bearing sulfide minerals. The research focuses on understanding how surface chemical composition and surface microstructure affect the rate of release and oxidation state of arsenic in the aqueous phase. Specific goals include: (1) identification of surface phases that form on As-bearing minerals, identification of the chemical processes that form these phases, and quantitative understanding of how these surface phases alter rate of release and oxidation state of As; (2) identification of the potential importance of microstructural defects in controlling As release rates, (3) determination of whether microbial processes that affect As release rate and/or oxidation state occur indirectly through control of the bulk solution phase, or whether they involve direct attachment of microbes to As-bearing mineral surfaces, and (4) quantitative understanding of the role of pyrite and other minerals in catalyzing oxidation of As3+ to As5+.

Approach:

The approach involves an integration of microscopic structural and chemical probes of mineral surfaces together with measurements of solution chemistry and includes both laboratory and field components. Samples of rocks, water, and microorganisms have been collected from As-contaminated sites in California and the Fox River Valley of Wisconsin and enrichment cultures of microorganisms for biotic experiments have been established. X-ray photoelectron spectroscopy and Raman spectroscopy will be utilized to identify the elements and oxidation states present at the surfaces of As-bearing minerals, and Raman spectroscopy will be utilized in situ to identify specific surface species (arsenates, sulfides, etc.) on minerals in direct contact with aqueous phases. Quantitative measurement of rate of release and oxidation state of As using ion chromatography and atomic absorption spectroscopies will be performed on the solution phases, and correlated with the surface chemical composition date to develop atomistic models for understanding As release rate. Scanning tunneling and high-resolution transmission electron microscopies will provide information on atomic to nanometer length scales; these will be linked to optical microscopy to identify the effects of structural spatial inhomogeneity (defects, steps, etc.) and chemical composition (phase separation, surface phases, etc.) on the surface reactions. To understanding the role of microbial processes, enrichment cultures will be used to isolate arsenic-resistant microbes from the field sites. Quantiative experiments will be performed with these microbes to assess their efficacy in modifying rate of release and oxidation state of As in solution. As time permits, 16s-RDNA sequencing will be used to identify As-resistant microbes, and biological probes will be developed to permit identify these microbes in mixed environmental samples.

Expected Results:

The product of this research will be a fundamental understanding of the structural, chemical, and biological factors that control the rate of release and speciation of arsenic in the environment. The research will provide information needed to assess the contributions of aqueous alteration of As-bearing sulfides to ground water contamination and the role of chemical and biological factors in determining the speciation of As and thus, the risk to human health.

Publications and Presentations:

Publications have been submitted on this project: View all 40 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 11 journal articles for this project

Supplemental Keywords:

water, watersheds, groundwater, land, acid deposition, adsorption, absorption, leachate, human health, bioavailability, heavy metals, organics, ecosystem, aquatic, remediation, bioremediation, decision making, environmental chemistry, geology, analytical, measurement methods, Midwest, California (CA), Wisconsin (WI), mining., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Geographic Area, Water, Waste, Toxics, POLLUTANTS/TOXICS, pesticides, State, Ecosystem Protection, Chemistry, Ecology, Watersheds, Environmental Chemistry, Ecosystem/Assessment/Indicators, Groundwater remediation, Microbiology, Arsenic, Ecological Effects - Environmental Exposure & Risk, Bioavailability, Bioremediation, Drinking Water, Water & Watershed, Water Pollutants, California (CA), arsenic transformation, chemical probes, heavy metals, physicochemical controls, arsenic release, health effects, mining impacted watershed, kinetic studies, weathering, physiochemical controls, microbial, microbial controls, ecosystem, speciation and release of arsenic, microbial risk assessment, pyrite, groundwater, fate and transport, biodegradation, ecological exposure, arsenic oxidation reduction, aquatic restoration, chemical transport, Wisconsin (WI), electron microscope, human health effects, rate of release, weathering of minerals, spectroscopic studies, aquatic ecosystems, arsenic exposure, surface water, chemical releases

Progress and Final Reports:

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.