Grantee Research Project Results
1999 Progress Report: Physiochemical and Microbial Controls on the Speciation and Release of Arsenic into Ground and Surface Waters
EPA Grant Number: R826189Title: 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 Period Covered by this Report: January 1, 1998 through December 31, 1999
Project Amount: $312,496
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Safer Chemicals
Objective:
The objective of this work is to understand, at a fundamental level, inorganic and biologically mediated reactions that liberate arsenic from primary sulfides (arsenopyrite and As-pyrite) and control the fate of As in solution and secondary phases. The research has both field and laboratory components.Progress Summary:
Field work is being conducted at Iron Mountain in northern California. This is a massive sulfide ore body that produces large volumes of acidic mine drainage with high As concentrations (50 ppm As). Three trips to Iron Mountain were conducted in 1999. Precharacterized, sterilized arsenopyrite samples of known weight and surface characteristics were left at the site in different locations. A subset of these has been retrieved for characterization; others remain at the site for longer term experiments.Pyrite-Catalyzed Oxidation of As(III) to As(V). We are studying the kinetics of pyrite-catalyzed oxidation of As(III) to As(V) to gain insight into the mechanism for this reaction. Barrett and co-workers have shown that this catalysis occurs.1 Our goal is to quantitatively determine the rate constants that control the oxidation of As(III). We have significantly improved our ability to study this process by setting up an HPLC-hydride generation-flame AA apparatus for the measurement of arsenic (III) and (V) in our samples.
Arsenic Release and Surface Modification of Arsenopyrite. As the most abundant arsenic-containing mineral, arsenopyrite (FeAsS) is a potential source of toxic levels of arsenic in the environment. Like pyrite (FeS2), the most well-studied of the sulfide minerals, arsenopyrite oxidatively dissolves when exposed to air and water and can contribute to the problem of acid mine drainage (AMD). One of the fundamental questions regarding the oxidative dissolution of arsenopyrite is the stoichiometry of the reaction in the presence of ferric ion, Fe(III), under acidic conditions. Two examples include:
1. FeAsS + 13Fe3+ + 8H2O
14Fe2+ + SO42-
+ 13H+ + H3AsO4(aq) 2
2. FeAsS + 5Fe3+ As3+
+ 6Fe2+ + S0 3
These equations represent two extremes that have very different implications for the fate of sulfur released from arsenopyrite. Previous studies in our laboratory found that Thiobacillus caldus, a S-oxidizing bacterium isolated from the Richmond Mine at Iron Mountain, CA, effectively removed most of the elemental sulfur from the arsenopyrite surface but did not increase the rate of dissolution.4 These findings suggest that although elemental sulfur forms at the arsenopyrite surface during the oxidative dissolution of the mineral, either the sulfur layer remains permeable to reactants and products, or the sulfur is not distributed uniformly across the mineral surface. A rough calibration of the Raman intensity from elemental sulfur revealed that the layer would be hundreds of angstroms thick if distributed uniformly.5 Precise quantification of the sulfur layer by Raman spectroscopy is difficult. Efforts in our laboratory have focused on better quantification of the sulfur layer. Our new method is being used to quantify elemental sulfur under a variety of reaction conditions to develop a more complete description of the reaction stoichiometry during the oxidative dissolution of arsenopyrite. Quantification of the elemental sulfur from arsenopyrite that was reacted in an air-purged sulfuric acid solution at pH 1.5 and 42 °C for several weeks indicates that elemental sulfur comprises a sustantial fraction of the total reacted sulfur.6 These measurements, to the best of our knowledge, constitute the first direct quantification and that elemental sulfur is a major product in the oxidation of arsenopyrite under acidic conditions.
Biological Controls on the Geochemistry of Arsenic. Our work has been focused on two important arsenic-rich environments to investigate microbial contributions to arsenic geochemical cycles. The work has involved both laboratory and field components, with microbes and in situ experiments conducted at two field sites: the Richmond Ore body at Iron Mountain, near Redding, CA, and the Hanna Ranch geothermal basin, adjacent to Mt. Lassen National Park. The solutions at this site are boiling (approximately 95 °C), and contain total metal concentrations and approximately 15 ppm arsenic.
Arsenic Resistance. We isolated a new archaea from Iron Mountain. This extremely pH-tolerant archaea is very abundant at the site (it grows down to pH 0). We noted that the organism, referred to as Ferroplamsa acidarmanus, can grow on arsenopyrite (FeAsS) and thus, began to investigate its As tolerance and As tolerance mechanism (as this can involve redox and other reactions that directly impact As speciation). We are characterizing the organism Ferroplamsa acidarmanus and its ability to interact with arsenic species and have evaluated its tolerance to a wide range of arsenite or arsenate concentrations. Cell densities were measured in addition to levels of As(III) and As(V). Doubling times and maximum cell densities were characterized, and the ability of this organism to affect arsenic speciation has been evaluated. A genetic and biochemical study of the arsenic tolerance mechanism of this organism has begun.
Experimental Studies: Microbial Leaching of Pyrite and Arsenopyrite. Leaching patterns on pyrite, marcasite, and arsenopyrite were investigated using optical and scanning electron microscopy. Pitting patterns on pyrite surfaces reacted with the iron-oxidizing bacteria Thiobacillus ferrooxidans (at 25 °C) and an iron-oxidizing archaeal isolate (at 37 °C) were compared with (abiotically) Fe3+ reacted samples to determine the microbial role in pit formation. Observations suggest that pit formation on pyrite is inherent to this mineral, and that cells may not be directly involved. However, fer1 cells were found within numerous shallow (< 0.5 µm deep), cell-shaped (round rather that elliptical, conforming to the shape of fer1 cells) pits on arsenopyrite. Results of this study suggest that sulfide mineral dissolution may be dominated by surface reactions with Fe3+ rather than reactions at the cell-mineral interface. To understand the ecological role of sulfur-oxidizing organisms in the generation of AMD, growth and attachment of a Thiobacillus caldus on the sulfide minerals pyrite, marcasite, and arsenopyrite was studied. Growth curves were estimated based on total cells in suspension and attached to the mineral surfaces. More cells were attached to surfaces than were detected in suspension. Preferential colonization of surfaces relative to solution and oriented cell attachment on these sulfide surfaces suggest that T. caldus may chemotactically select the optimal site for growth.
Rates of Microbial Sulfide Dissolution and the Microbial Contribution to Acid Mine Drainage Generation. Dissolution and surface morphology evolution of pyrite, marcasite, and arsenopyrite have been monitored during 22 days of reaction with mixed enrichment cultures, an iron oxidizing isolate (Ferriplasma acidarmanus), a sulfur oxidizing isolate (Thiobacillus caldus), and abiotic controls. Results show that dissolution in the presence of T. caldus caused a reduction of iron released to solution by approximately 18 percent in marcasite, and 30 percent in arsenopyrite relative to controls. The microbial contribution to dissolution rates of pyrite, marcasite, and arsenopyrite in enrichment cultures of iron- and sulfur-oxidizing organisms was approximately 1.5, six times greater than in cultures of F. acidarmanus. Cell-normalized dissolution rates in experiments containing iron-oxidizing microorganisms, calculated based on the average number of iron oxidizing cells present, were determined.
References:
1. Barrett J, Ewart DK, Hughes MN, Poole RK. FEMS Microbiology Reviews 1993;11:57-62.
2. Rimstidt JD, Chermak JA, Gagen PM. Rates of reaction of galena, sphalerite, chalcopyrite, and arsenopyrite with Fe(III) in acidic solutions. In: Alpers CN, Blowes DW, eds. Environmental Geochemistry of Sulfide Oxidation, American Chemical Society, 1994, pp. 2-13.
3. Ruitenberg R, Hansford GS, Reuter MA, Breed AW. The ferric leaching kinetics of arseno-pyrite. Hydrometallurgy 1999;52(1):37-53.
4. McGuire MM, Edwards KJ, Banfield JF, Hamers RJ. Geochimica et Cosmochimica Acta (in review).
5. McGuire MM, Banfield JF, Hamers RJ (in preparation).
6. McGuire MM, Banfield JF, Hamers RJ (in preparation).
Future Activities:
We are continuing to explore both the microbiological and chemical factors controlling arsenic release and speciation. No significant changes from the original plan are anticipated.Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 40 publications | 12 publications in selected types | All 11 journal articles |
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Edwards KJ, Goebel BM, Rodgers TM, Schrenk MO, Gihring TM, Cardona MM, McGuire MM, Hamers RJ, Pace NR, Banfield JF. Geomicrobiology of pyrite (FeS2) dissolution: case study at Iron Mountain, California. Geomicrobiology Journal 1999;16(2):155-179. |
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Edwards KJ, Bond PL, Banfield JF. Characteristics of attachment and growth of Thiobacillus caldus on sulfide minerals: a chemotactic response to sulphur minerals? Environmental Microbiology 2000;2(3):324-332. |
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Edwards KJ, Bond PL, Druschel GK, McGuire MM, Hamers RJ, Banfield JF. Geochemical and biological aspects of sulfide mineral dissolution: lessons from Iron Mountain, California. Chemical Geology 2000;169(3-4):383-397. |
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Edwards KJ, Hu B, Hamers RJ, Banfield JF. A new look at microbial leaching patterns on sulfide minerals. FEMS Microbiology Ecology 2001;34(3):197-206. |
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Supplemental Keywords:
environmental chemistry, geology, analytical, measurement methods, heavy metals, acid deposition, ecological effects, groundwater, bioremediation, remediation., RFA, Scientific Discipline, Toxics, Water, Waste, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Water & Watershed, Bioavailability, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Environmental Chemistry, Arsenic, State, Chemistry, pesticides, Ecological Effects - Environmental Exposure & Risk, Microbiology, Bioremediation, Water Pollutants, Groundwater remediation, Drinking Water, Watersheds, chemical probes, electron microscope, fate and transport, ecological exposure, health effects, microbial risk assessment, arsenic transformation, human health effects, physicochemical controls, weathering of minerals, spectroscopic studies, aquatic restoration, biodegradation, physiochemical controls, surface water, chemical transport, kinetic studies, rate of release, arsenic release, pyrite, chemical releases, contaminant release, weathering, aquatic ecosystems, ecosystem, speciation and release of arsenic, Wisconsin (WI), arsenic exposure, microbial controls, California (CA), groundwater, heavy metals, microbial, mining impacted watershedProgress and Final Reports:
Original AbstractThe 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.