Grantee Research Project Results
1999 Progress Report: Rates of Arsenic Oxidation-Reduction Reactions in Contaminated Soils: Effects on Arsenic Fate and Mobility
EPA Grant Number: R825403Title: Rates of Arsenic Oxidation-Reduction Reactions in Contaminated Soils: Effects on Arsenic Fate and Mobility
Investigators: Inskeep, William P. , Jones, C. A. , Macur, R. E. , Langner, H. W.
Institution: Montana State University
EPA Project Officer: Chung, Serena
Project Period: December 15, 1996 through December 14, 1999
Project Period Covered by this Report: December 15, 1998 through December 14, 1999
Project Amount: $329,735
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Objective:
Arsenic (As) is an important priority pollutant found in soils contaminated by arsenical pesticides, natural geothermal sources, and mine tailings. The chemical and biological processes that control the fate and mobility of As in contaminated soils and mine tailings are complex, primarily due to transformations of numerous As species, which occur under temporally variable oxidation-reduction conditions. The objectives of this project are to: (1) determine rates and underlying mechanisms of the reduction of sorbed arsenate in model systems, contaminated soils and mine tailings; (2) evaluate the importance of As-sulfide formation under conditions typical of As-contaminated soils, and mine tailings; and (3) evaluate the role of reduction of sorbed arsenate on the mobility and transport of As in contaminated soils, mine tailings, and aquifers. It is our goal that results obtained from this study will improve the link between fundamental kinetic processes controlling As speciation and watershed-scale processes such as mobility, transport, and bioavailability.During the final year of this project, we have finished four major initiatives designed to understand chemical and microbial interactions that control rates of arsenate reduction in soils and sediments. Specifically, we have: (1) characterized As reduction rates catalyzed by a fermenting microorganism isolated from an As-contaminated soil, (2) studied the reduction of arsenate in the presence and absence of iron (Fe) oxides using different microbial populations, (3) evaluated the role of arsenate reduction on solubilization of arsenic in contaminated mine tailings under aerobic conditions, and (4) evaluated the reduction of arsenate and subsequent precipitation of As sulfides under constructed wetland environments. This report will summarize experimental progress during Year 3 of a 3-year project. A detailed analysis of the entire project accomplishments will be documented in the Final Report.
Progress Summary:
Reduction of Arsenate Under Fermentative Conditions. During this reporting period, our work on As reduction kinetics catalyzed by a fermenting microorganism was submitted and accepted in the Soil Microbiology division of Soil Science Society of America Journal. The manuscript is due in print in early 2000. The primary finding was that As reduction kinetics are very rapid under fermentative conditions where As(V) is presumably not serving as a primary electron acceptor for respiration. The fact that As(V) is reduced by this particular isolate suggests that not all reduction processes are driven by dissimilatory reduction.Reduction of Arsenate in the Presence of Iron Oxides. During the last year, we completed a draft of an additional manuscript describing As reduction kinetics of a Clostridium sp. in the presence and absence of ferrihydrite. This manuscript was submitted to Environmental Science and Technology (December 1999), and is still out for review. The primary finding was that in the absence of reductive dissolution of Fe oxide phases, desorption of As(V) is a rate-limiting step for reduction and accumulation of As(III) in the aqueous phase.
Reduction of Arsenate Under Column Conditions Using Arsenic Contaminated Mine Soils. In the last annual report, we described experiments designed to evaluate the solubilization of As from contaminated mine tailings under aerobic conditions. These experiments showed that biotic activity after liming caused significant increases in the amount of effluent As(III). The fact that As(III) was the dominant As species under predominantly aerobic column conditions prompted us to investigate in more detail the nature of microbial communities responsible for As reduction. During the last year, our work under this initiative has focused exclusively on molecular analysis of microbial communities present in these soils and microbial isolates obtained from these columns.
We have analyzed microbial communities (using denaturing gradient gel electrophoresis [DGGE] of 16 S rDNA fragments) present in As-contaminated soil columns and have isolated several organisms from these columns that reduce As(V) to As(III) under well aerated conditions. Microbial community analyses of soil column environments demonstrated changes in microbial populations after liming. One of the bacterial isolates obtained from the limed soil treatment was found to be closely related to Sphingomonas yanoikuyae; this band matches one of the bands observed in soil treatments after liming. The ability of the S. yanoikuyae-like isolate to reduce As(V) to As(III) was confirmed under aerobic batch-reactor conditions. Consequently, our results show that As(V) reduction may be fairly common in contaminated soils or sediments at redox values that have previously been considered too high to favor As(III). We believe that the mechanism of As reduction in such cases involves detoxification via reductases as has been noted in the literature with several enteric microorganisms. Future work in subsequent grant submissions will focus on the diversity of microorganisms important in As(V)-As(III) cycling in natural soil water systems.
Reduction of Arsenate in Constructed Wetlands. In the last progress report, we described experiments designed to evaluate the fate of As(V) in reduced wetland environments. We have now finished all experimental work on this initiative and a draft of this manuscript currently is under author review. Specifically, our work during 1999 focused on identification of As2S3 solid phases and subsequent mineral solubility calculations to confirm equilibrium with the aqueous phase. This manuscript will be submitted to Environmental Science and Technology in early 2000. The primary findings suggest that wetland environments conducive to sulfate reduction will result in accumulation of phases; however, these amorphous precipitates are susceptible to rapid oxidation and re-release of As(V).
Future Activities:
The project period ended December 14, 1999.Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 12 publications | 7 publications in selected types | All 7 journal articles |
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Jones CA, Inskeep WP, Bauder JW, Keith KE. Arsenic solubility and attenuation in soils of the Madison River Basin, Montana: impacts of long-term irrigation. Journal of Environmental Quality 1999;28(4):1314-1320. |
R825403 (1999) R825403 (Final) |
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Jones CA, Langner HW, Anderson K, McDermott TR, Inskeep WP. Rates of microbially mediated arsenate reduction and solubilization. Soil Science Society of America Journal 2000;64(2):600-608. |
R825403 (1999) R825403 (Final) |
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Langner HW, Inskeep WP. Microbial reduction of arsenate in the presence of ferrihydrite. Environmental Science & Technology 2000;34(15):3131-3136. |
R825403 (1998) R825403 (1999) R825403 (Final) |
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Macur RE, Wheeler JT, McDermott TR, Inskeep WP. Microbial populations associated with the reduction and enhanced mobilization of arsenic in mine tailings. Environmental Science & Technology 2001;35(18):3676-3682. |
R825403 (1999) R825403 (Final) R827457E03 (Final) |
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Supplemental Keywords:
soil, water, leachate, ecological effects, bioavailability, metabolism, effluent, arsenic, aquatic, remediation, environmental chemistry, microbiology, ecology, analytical, molecular analyses, northwest, Montana, MT, EPA Region 8., RFA, Scientific Discipline, Toxics, INTERNATIONAL COOPERATION, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Bioavailability, National Recommended Water Quality, Water & Watershed, Contaminated Sediments, Environmental Chemistry, Geochemistry, Arsenic, State, Fate & Transport, Hazardous Waste, Ecological Risk Assessment, Water Pollutants, Hazardous, fate and transport, hazardous waste treatment, aquatic, contaminated mines, fate, sediment treatment, contaminant transport, redox metabolism, contaminated sediment, mine tailings, sediment transport, transport contaminants, arsenic sulfide, arsenic oxidation, contaminated soil, chemical contaminants, toxicity, mining, watershed influences, aquatic ecosystems, environmental stressors, environmental toxicant, harmful environmental agents, aquifers, redox cycle, aresenic oxidation reduction, arsenic mobility, water quality, Montana , hazardous waste sites, arsenic exposure, exposure assessment, arsenic oxidation reduction, groundwater, 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.