Source: PENNSYLVANIA STATE UNIVERSITY submitted to
CHEMICAL AND BIOGEOCHEMICAL PROCESSES INVOLVED IN TRACE AND TOXIC ELEMENT CYCLING IN SOILS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0198903
Grant No.
(N/A)
Project No.
PEN04004
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Jan 1, 2004
Project End Date
Dec 31, 2008
Grant Year
(N/A)
Project Director
Martinez, C. E.
Recipient Organization
PENNSYLVANIA STATE UNIVERSITY
208 MUELLER LABORATORY
UNIVERSITY PARK,PA 16802
Performing Department
CROP & SOIL SCIENCES
Non Technical Summary
Soils are biogeochemical systems under continual modification by biological and chemical processes. The proposed investigation focuses on the biogeochemical cycling of trace elements in conjunction with their solid- and solution- phase chemical speciation in both complex environmental systems as well as model systems in the laboratory.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1010110200050%
1020110200050%
Goals / Objectives
The proposed work involves investigations of trace and toxic elements (Ni, Zn, Cu, Pb, Cd) solubility, solid-phase speciation, and spatial distribution in soils and model systems. Soils and soil constituents can concentrate trace and toxic elements by biogeochemical processes, and the solubility, mobility and bioavailability of these elements can increase after long-term reaction in soils due to the oxidation of organic matter and mineral transformations. In addition, this research will help us understand the impact of microbes on biogeochemical processes in soils. The specific aims of this work include: 1. To assess the importance of sulfur in trace and toxic element retention and cycling in soils and in other systems of environmental relevance, 2. To determine the solution- and solid- phase speciation of trace and toxic elements in soils and model systems, 3. To determine the elemental associations and distribution in soil particles, 4. To assess the spatial distribution and identity of microbes, elements, and minerals in soil particles.
Project Methods
The proposed research includes field as well as laboratory investigations. Field-collected soils from several locations will be sampled as a function of spatial, temporal, and vertical variability. Elemental concentrations and soil organic matter content will be determined. Elemental solubility will be measured by ICP and labile concentrations of some metals using DPASV. Discrimination between total soluble and labile concentrations of metals provides information on the formation and stability of soluble metal-organic complexes. Total soluble S and sulfate will be analyzed in solution by ICP and ion chromatography methods, respectively. To further characterize the solution phase, dissolved organic carbon measurements will be undertaken. In this way, the results from metal and S solution speciation will be interpreted in view of changes in solution chemistry. The use of spectroscopic techniques will result in molecular level information of the chemical forms and distribution of metals in complex soil systems. X-ray absorption spectroscopy (XAS) techniques are essential in the solid-phase speciation of trace and toxic elements, providing direct evidence on their binding environment and on the oxidation states of S. The EXAFS and XANES spectra will be collected at the National Synchrotron Light Source, Brookhaven National Laboratory. Novel techniques such as synchrotron-based microprobe- x-ray fluorescence (u-XRF), x-ray diffraction (u-XRD), and x-ray absorption (u-XAS) and scanning electron microscopy (SEM) coupled to energy or wavelength dispersive x-ray analysis (E/W-DS) will be used in characterizing organic-matter rich soils. Synchrotron-based microprobe radiation offers high spatial resolution and sensitivity so that elements that occur at low concentrations can be studied. Microprobe techniques will expose the micro-heterogeneity of soil particles. Specifically, u-XRD in the identification of minerals at micro-locations within soil particles (mineralogy at the u-scale), u-XRF for the elemental composition, distribution and associations, and u-XAS to determine the chemical bonding environment (elemental speciation) at micro-sites. By coupling synchrotron-based u-XRF, u-XRD, and u-XAS to CLSM imaging of fluorescently stained or labeled FISH probes, we will be able to assess the spatial distribution (co-location) and identity of microbes, elements, and minerals in the same soil particle. I hypothesize that specific bacterial densities will be spatially correlated with metal concentrations and specific minerals in the same soil samples. Confocal laser scanning microscopy images will be captured over an appropriate depth across an area delimited by specific coordinates at the most appropriate level of magnification. Following CLSM analysis, u-XRF, u-XRD, and u-XAS spectroscopic data will be collected to provide spatially correlated data.

Progress 01/01/04 to 12/31/08

Outputs
OUTPUTS: Seven scientific papers were published in highly ranked peer reviewed journals and sixteen presentations were delivered at local, national, and international conferences. Three graduate students (2 Ph.D. and 1 M.S.), two post-doctoral associates, and two undergraduate students were trained as a result of this project; of these, five are young female scientists. With the present situation that women and ethnic minorities are seriously underrepresented in high-level science positions in academia, this project has provided opportunity for the advancement of women into academic research positions. Students and post-docs involved in this project have learned skills in analyzing for low trace levels of heavy metals in soil and water and to determine metal species in solid phases using state-of-the-art methods like inductively coupled plasma (ICP) spectrometry, electrochemical methods (voltammetry and ion selective electrodes), synchrotron-based spectroscopy, microscopy, and isotopic analysis. Perhaps more importantly, they have learned to communicate with each other and to synthesize a variety of data and ideas that result from interdisciplinary projects. The project encompassed three sub-projects. In the first sub-project, vertical redox stratification in metalliferous (Zn and Cd at highly elevated levels) peatlands was found where topmost peats were typically acidic and oxidizing and deeper peats were typically circumneutral and reducing. As illustrated in this study, changes in redox conditions affect bacterial community composition and downward mobility and speciation of toxic elements, which has implications for water contamination and the design of metal remediation strategies. The second sub-project demonstrated the importance of organic soil constituents (both solid and solution phase organics) in controlling the distribution, solubility, and chemical forms (speciation) of copper in soil environments. Studies of trace element associations with Fe-and Mn-oxides in soil nodules, however, showed that P, As and Cr were mainly present in Fe-oxides, while Co was mainly associated with Mn-oxide phases. Lastly, the third sub-project showed a synthetic layer silicate mineral (highly charged swelling mica) was effective in reducing free and extractable Cu levels and in reducing the bioavailability of copper to perennial ryegrass in copper-contaminated soils in central Chile. This mica warrants further testing of its ability to assist re-vegetation and reduce Cu bioavailability in acidic Cu-contaminated surface soils. PARTICIPANTS: Carmen Enid Martinez, Associate Professor and Principal Investigator. Nadia V. Martinez-Villegas, Ph.D. (completed: 2008), Department of Crop and Soil Sciences, The Pennsylvania State University; Jason W. Stuckey, M.S. (completed: 2007), Department of Crop and Soil Sciences, The Pennsylvania State University; Soh-joung Yoon, Post-doctoral Associate (completed: 2007), Department of Crop and Soil Sciences, The Pennsylvania State University; Carolina Yanez, Ph.D. (completed: 2006), Department of Crop and Soil Sciences, The Pennsylvania State University; Alexander Neaman, Post-doctoral Associate (completed: 2006), Department of Crop and Soil Sciences, The Pennsylvania State University; Krystal Hamlett, summer fellow, undergraduate student from Lincoln University; and Magaly Resto-Roldan, summer fellow, undergraduate student from The University of Puerto Rico, Rio Piedras campus. TARGET AUDIENCES: The primary target audience is the scientific community. The research projects are an exemplary study of complex biogeochemical systems in soils and models systems. They show how an understanding of both biological and chemical aspects is necessary to understanding bioavailability and cycling of Cd, Zn and S in an ecosystem. They contribute to the scientific disciplines of soil chemistry, soil science, microbial ecology, geochemistry, environmental engineering, and geology. Furthermore, the development of remediation technologies could potentially be exploited with this increased understanding of the control of Cd and Zn solubility in peatland soils and of Cu in Cu-contaminated soils. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The behavior of trace metals under conditions of fluctuating redox potential is not a subject well understood or described in teaching materials such as textbooks of soil science or environmental chemistry. The results of this research will fill in some obvious gaps in knowledge, and allow future efforts, such as the modeling of Cd and Zn mobility in wetland ecosystems, to be based on a more sound understanding of the fundamental processes. For example, Martinez has already incorporated the knowledge gained thru this work into the redox chemistry module of her Soil Chemistry class and homework assignments have been developed. Cadmium (Cd) contamination is a major problem in regions of the world where paddy rice is a staple food crop. Because these soils are anaerobic for much of the growing season, it can be expected that metal sulfides control Cd phytoavailability. However, a better understanding of how the management of these soils water status and redox potential affects Cd bioavailability could lead to food crops with lower Cd and less likelihood of disease. Smelting is a principal anthropogenic source of trace metal emissions into the atmosphere, along with energy production, manufacturing processes, and waste incineration. More than 65 percent of anthropogenic atmospheric emissions of copper (Cu) come from smelting Cu ore, thus causing contamination of nearby soils. A means to restrict Cu mobility and uptake by plants is to remove it from the aqueous phase by applying an adsorptive material, such as the mica tested in this project. The findings of this basic research work provided sound ideas that can be used to promote the remediation of metal contaminated soils using biomineralization and/or in situ stabilization technologies. Stakeholders can use the results of this research to make decisions about environmental pollution control and soil and water quality issues. In this case, stakeholders are regulatory agencies such as the EPA and USDA. The activities conducted under this project can be categorized as Basic Research and combine research and education. This project is international in nature as knowledge of the basic biogeochemical reactions of metals in soils has implications to all soils. The research conducted under this project was performed by graduate and undergraduate students, and post-docs enrolled at Penn State University. The students obtained a university degree that integrates education (formal classes) and research activities. This project advanced our knowledge and understanding of the chemical and biogeochemical processes controlling trace and toxic element cycling (partitioning, redistribution, solubility) in complex soil environments. This will enhance our predictive capability of metal association and distribution in soils while providing critical information for the long-term management of soils and for establishing safe heavy metal loadings.

Publications

  • Martinez, C.E. and N. Martinez-Villegas. 2008. Copper-alumina-organic matter mixed systems: alumina transformation and copper speciation as revealed by EPR spectroscopy. Environmental Science & Technology. 42: 4422-4427.
  • Martinez-Villegas, N. and C.E. Martinez. 2008. Solid- and solution- phase organics dictate copper distribution and speciation in multi-component systems containing ferrihydrite, organic matter, and montmorillonite. Environmental Science & Technology. 42:2833-2838.
  • Stuckey, J. W., A. Neaman, R. Ravella, S. Komarneni, C.E. Martinez. 2008. Highly charged swelling mica reduces Cu bioavailability in Cu-contaminated soils. Environmental Pollution. 157: 12-1.
  • Stuckey, J.W., A. Neaman, R. Ravella, S. Komarneni, and C.E. Martinez. 2008. Highly charged swelling mica reduces free and extractable Cu levels in Cu-contaminated soils. Environmental Science & Technology. (In Press).
  • Martinez-Villegas, N., L.M. Flores-Velez, K. Turrubiartes-Higuera, and C.E. Martinez. 2006. Speciation of Pb and Zn in soils contaminated by tailings: An environmental risk study. 18th World Congress of Soil Science. Philadelphia, PA USA. CD-ROM.
  • Martinez-Villegas, N. and C.E. Martinez. 2006. Understanding elemental interactions between heavy metals and soils. 12th Annual Graduate and Undergraduate Research Exhibition, The Pennsylvania State University, University Park, PA. CD-ROM.
  • Martinez-Villegas, N. and C.E. Martinez. 2006. Alumina transformation in binary alumina-organic matter systems and its effects on copper solubility and speciation. 9th Annual Environmental Chemistry Student Symposium, The Pennsylvania State University, University Park, PA. CD-ROM.
  • Neaman, A., C.E. Martinez, F. Trolard, and G. Bourrie. 2008. Trace element associations with Fe- and Mn-oxides in soil nodules: comparison of selective dissolution with electron probe microanalysis. Applied Geochemistry. 23:778-782.
  • Martinez-Villegas, N. and C.E. Martinez. 2007. Influence of DOC on Cd, Cr, Cu, and Ni retention by solid-and solution-phases. Soil Science Society of America Meetings. New Orleans, LA. CD-ROM.
  • Stuckey, J., A. Neaman, R. Ravella, S. Komarneni, and C.E. Martinez. 2007. Highly-charged swelling mica reduces exchangeable Cu in Cu-contaminated soils. Soil Science Society of America Meetings. New Orleans, LA. CD-ROM.
  • Resto, M., N. Martinez-Villegas, and C.E. Martinez. 2007. Distribution of copper on model soil constituents. Division of Chemical Education - Undergraduate Research. American Chemical Society (ACS). Chicago, IL. CD-ROM.
  • Martinez-Villegas, N. and C.E. Martinez. 2006. Partition of Cu among model soil constituents. 18th World Congress of Soil Science, Philadelphia, PA USA. CD-ROM.
  • Hamlett K., C. Yanez, C.E. Martinez, and M.A. Bruns. 2004. Dissimilatory Sulfite Reductase (Dsr) Gene Detection in Soils Containing Varied Metal Concentrations. American Society of Microbiology. New Orleans, LA. CD-ROM.


Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: Spatial relationships in peat cores showed elemental distributions, S redox speciation and detection of dsrAB genes varied with depth. The highest concentrations of Zn, Cd and S occurred at intermediate depths. Concentrations of redox sensitive elements, S and Mn, but not Fe, seemed to respond to variations in water content and indicated vertical redox stratification in peat cores where topmost peats were typically acidic and oxidizing and deeper peats were typically circumneutral and reducing. Even then, S-XANES analyses showed that surface peats contained >50% of the total S in reduced forms. While bacterial RISA profiles of the peats were diverse, dsrAB gene detection followed redox stratification chemistry closely. For the most part, dsrAB genes were detected in deeper peats, where S accumulation was evident, while they were not detected in topmost peat layers where oxic conditions prevailed. As illustrated in this study, changes in redox conditions affect bacterial community composition and downward mobility of toxic elements, which has implications for water contamination and the design of metal remediation strategies. Linear combination fit analyses of XANES spectra suggest Zn binds to nitrogen- and sulfur- containing functional groups of soil organic matter in addition to binding to the more abundant oxygen- containing functional groups. The XANES spectra were best fitted by the Zn-arginine reference compound and therefore seem to indicate Zn bonding to nitrogen. Thus, these results provide compelling evidence of the formation of strong Zn-organic bonds in the organic-rich surface soils that were studied. These are significant results that may explain, in part, why organic soils can withstand higher concentrations of metals than mineral soils and why metal partition coefficients (Kd) are generally higher in organic soils. In deep peats, synchrotron-based XRD clearly indicated the presence of poorly crystalline ZnS as the main mineral specie. We observed framboidal aggregates of ultra-fine mineral particles composed mostly of Zn and S, but sometimes contained small amounts of Cd. The ZnS framboids were attached to organic debris and often embedded within the organic matrix. Based on Zn K-edge extended X-ray absorption fine structure (EXAFS) analyses of the peat samples, we found ~50% of the total zinc was bonded to sulfur thus indicating that ZnS accounted for ~50% of the zinc accumulated in deep soils. The other fraction of zinc is complexed with organic matter functional groups. We have also identified microbial populations--specifically sulfate reducing bacteria--that might be responsible for the formation of ZnS in deep peats. Corroboration of the biogenic nature of ZnS found in deep peats came from S isotopic analysis. The isotopic composition of sulfur species in the peat indicated that ZnS had been subjected to more biological reduction than other sulfur species. Detection of dsrAB functional genes and the results of sulfur isotope analyses are consistent with ZnS formation by bacterial sulfate reduction in the peats. PARTICIPANTS: Soh-joung Yoon, Post-doctoral Associate, Department of Crop and Soil Sciences, The Pennsylvania State University; Carolina Yanez, Ph.D. (completed), Department of Crop and Soil Sciences, The Pennsylvania State University; Nadia V. Martinez-Villegas, Ph.D. candidate, Department of Crop and Soil Sciences, The Pennsylvania State University; Krystal Hamlett, summer fellow, undergraduate student from Lincoln University. TARGET AUDIENCES: The project is an exemplary study of a complex biogeochemical system, with linked chemical and microbial processes. It shows how an understanding of both biological and chemical aspects is necessary to understanding bioavailability and cycling of Cd, Zn and S in an ecosystem. It contributes to the scientific disciplines of soil chemistry, soil science, microbial ecology, geochemistry, and geology. Furthermore, the development of remediation technologies could potentially be exploited with this increased understanding of the control of Cd and Zn solubility in peatland soils.

Impacts
This study demonstrates the intricate link between soil chemistry and soil microbial community dynamics over both spatial and temporal scales and may potentially lead the way for developing more effective microbial or plant-based remediation strategies for Zn and Cd contaminated sites. The ability of ZnS to immobilize other heavy metals, particularly Cd, may prove to be useful in contaminated wetlands or paddy rice soils, for example, as Zn added to such anaerobic soils may well result in the formation of Zn sulfides which would lower Cd bioavailability. Isolates of metal-resistant bacteria capable of reducing oxidized forms of sulfur could also be used as a remediation strategy for sites contaminated with Zn and Cd. The demonstration of these promising management technologies for reducing Cd in plants and food crops has not yet been attempted. The scientific findings of this project have been presented at other universities and great interest in the topic has been generated. The scientific findings of this work have been incorporated into the classes taught by the PIs of this project. Four female scientists (two graduate students, a post-doc, and an undergraduate student) have contributed to this project. They have learned skills in analyzing for low trace levels of heavy metals in soil and water and to determine metal species in solid phases using state-of-the-art methods like inductively coupled plasma (ICP) spectrometry, synchrotron-based spectroscopy, microscopy, and isotopic analysis. Perhaps more importantly, they have learned to communicate with each other and to synthesize a variety of data and ideas that result from an interdisciplinary project.

Publications

  • Martinez, C.E., C. Yanez, S. Yoon, and M. A. Bruns. 2007. Biogeochemistry of metalliferous peats: Sulfur speciation and depth distributions of dsrAB genes and Cd, Fe, Mn, S, and Zn in soil cores. Environmental Science & Technology. 41:5323-5329.
  • Martinez, C.E., S. Yoon, C. Yanez, N. Martinez-Villegaz, and M. A. Bruns. 2007. Biogeochemistry of metalliferous peat cores: Distribution of Zn, S, Mn, Fe and dsrAB genes and sulfur and zinc speciation.Paper presented at the Goldschmidt Conference, Cologne, Germany. Geochimica et Cosmochimica Acta, Volume 71, Issue 15, Supplement 1, Page A627.
  • McBride, M. B., K.A. Barrett, and C.E. Martinez. 2007. Oxidative dissolution rates of Cd and Zn in synthetic Zn-Cd sulfide solid solutions and high-Zn organic soils. Paper presented at the 9th ICOBTE Meeting, Beijing, China. Conference Proceedings. p.425.


Progress 01/01/06 to 12/31/06

Outputs
In this project we tested the hypothesis that microbial populations involved in sulfur cycling determine the solid-phase speciation and distribution of Zn and Cd in metal- and organic matter- rich soil environments. Surface soils and vertical soil profiles were collected within an agricultural field of drained peat during wet and dry seasons along a lateral transect with the center of the field having high enough levels of Zn (phytotoxic concentrations) to prevent plant growth. We observe distinct chemical and microbiological characteristics as a function of depth (surface vs deep soils) in the peat soils investigated. Total concentrations of Zn, Cd and S were generally much higher in the seasonally water-saturated subsoils than at the surface. Sulfur-XANES analyses reveal that sulfide/thiol groups (reduced forms of S) and sulfonate groups (oxidized forms of S) are the two dominant S species. Using micrometer-scale synchrotron-based techniques to study the elemental distribution and chemical forms of Zn in surface soils we find that Zn, S, and Ca are consistently co-located within soil particles. Furthermore, linear combination fit (LCF) analyses of Zn-XANES spectra reveal that in surface soils Zn binds to nitrogen and sulfur containing functional groups of soil organic matter in addition to binding to the more abundant oxygen containing functional groups. These are significant results that provide evidence of highly covalent Zn-organic bonds in the organic-rich surface soils studied and may explain in part why organic soils can withstand higher concentrations of metals than mineral soils. Extended x-ray absorption fine structure (EXAFS) spectroscopy also reveals sulfur and oxygen/nitrogen coordination around Zn and Cd in surface soils with second neighbors (the carbon atom) arising from organic matter. Results from our microbiological work coincide with the spectroscopic data. The characterization of bacterial communities involved in sulfate reduction provides several lines of evidence to suggest that sulfur cycling in these metalliferous surface soils is driven by Gram-positive bacteria related to Desulfotomaculum sp. and Clostridium sp. and some members of the delta subgroup of Proteobacteria. The typical sulfate reducing bacteria (SRBs) do not seem to be present in surface soils; Zn/Cd sulfide species are not present either. We have also identified bacterial populations--sulfate reducing bacteria (SRBs)--that are presumed responsible for the formation of ZnS phases in deep organic soils. Specifically, we identified sulfate-reducing prokaryotes in soil profiles by analysis of dsrAB genes (key enzyme in sulfate respiration) in soils deeper than 45 cm. Furthermore, the sequences of dsrAB genes present in soil samples from both dry and wet seasons have not been previously described in the literature. Thus, our results suggest that novel sulfate reducing prokaryotes are present in the peat soils and that they might be specialized colonists in these metalliferous soil environments.

Impacts
This project will advance our knowledge and understanding of chemical and biogeochemical processes controlling trace and toxic element cycling in complex soil environments. Emphasis is given to coupled-biogeochemical cycles of metals (Zn and Cd) and sulfur and its effect on metal speciation and microbial activity. These processes are important in organic matter rich environments (i.e., organic soils, wetlands, sewage sludge, sewage sludge amended soils, sediments) and can contribute to their detoxification. Understanding basic processes will enhance our predictive capability of metal association and distribution in soils while providing critical information for the long-term management of soils. Stakeholders can use the results of this research to make decisions about environmental pollution control and soil and water quality issues.

Publications

  • Martinez, C.E., Bazilevskaya, K.A., and Lanzirotti, A. 2006. Zinc coordination to multiple ligand atoms in organic-rich surface soils. Environmental Science & Technology, 40, 5688-5695.
  • Yanez, C., Bruns, M.A., and Martinez, C.E. 2006. Temporal and spatial variability of sulfate-reducing bacteria populations in metalliferous sulfur-rich organic soils. 18th World Congress of Soil Science, Philadelphia, PA USA. CD-ROM.
  • Yanez C., Bruns M.A., and Martinez C.E. 2006. Sulfate-reducing prokaryotes in sulfur-rich peats: Influence of depth and moisture content (Bacterias sulfato- reductoras en turbas ricas en azufre: influencias de la profundidad y del contenido de humedad). XVIII Congreso Latinoamericano de Microbiologia ALAM 2006. Pucon, Chile. CD-ROM.


Progress 01/01/05 to 12/31/05

Outputs
We study peat deposits with elevated concentrations of S, Cd, and Zn. Our efforts for this year were focused on (1) studying the temporal and spatial variability of sulfate-reducing bacteria populations and (2) analyzing our Zn and Cd extended X-ray absorption fine structure (EXAFS) spectroscopy data collected at the National Synchrotron Light Source (Brookhaven National Laboratories). We studied the variability in bacterial microbial community, enzymes involved in sulfate respiration, rate of sulfate reduction, and sulfur redox species as a function of soil depth and moisture content in intact soil cores collected during dry and wet seasons. The soil cores were collected along a gradient (visual inspection) starting in an area where there was no plant (onion) growth and moving eastwards for about 10 meters (second core), and for about 15 additional meters (third core). A total of three soil columns were pulled from the soil each season and brought to the laboratory where they were kept at 4oC. The undisturbed soil columns were then cut open and sectioned (5 cm intervals) for analyses. DNA was extracted from the sub-samples and ribosomal intergenic spacer analysis (RISA) was used to study bacterial communities. The dissimilatory sulfite reductase gene (dsrAB), a key enzyme in sulfate respiration (reduction of sulfite to sulfide), was amplified by PCR to asses the presence of sulfate reducers. The activity of sulfate reducers was determined by a sulfate reduction test. Bacterial communities differed along the profile and between seasons. The dsrAB genes were detected in sub-samples deeper than 45 cm. The rate of sulfate reduction was correlated to the presence of dsrAB genes. Furthermore, S-XANES analyses show that 40-60 % of the total sulfur in these soils exists in reduced forms (e.g., sulfides and/or thiol groups) while 20-30 % exists in more oxidized forms such as sulfonate (R-S-O3) but not sulfate (R-O-S-O3). We observe Zn-S coordination in the deep soil only, where zinc and sulfur concentrations are very high. Using synchrotron-based X-ray diffraction (XRD), we identified zinc sulfide mineral crystallites in the deep soil. Scanning electron microscopy shows that the crystallites are agglomerates, approx. 500 nano-meters in diameter, and are composed of smaller, 5nm in diameter ZnS nanoparticles. Synchrotron studies revealed another rather exciting and novel result; that is, the presence of cadmium as a coprecipitate within the larger ZnS structure. This has not been observed in a natural system and not in an organic-matter rich soil where cadmium bonding to organic matter is presumed. In summary, our results suggest that bacteria that specialize in sulfate reduction show distribution and activity patterns that may be relevant to understanding biogeochemical processes occurring in these metal- and sulfur- rich organic soils, and that in fact, the formation of metal coprecipitates such as Zn1-xCdxS, may be the end result of such activity.

Impacts
This project will advance our knowledge and understanding of chemical and biogeochemical processes controlling trace and toxic element cycling in complex soil environments. Emphasis is given to coupled-biogeochemical cycles of metals (Zn and Cd) and sulfur and its effect on metal speciation and microbial activity. These processes are important in organic matter rich environments (i.e., organic soils, wetlands, sewage sludge, sewage sludge amended soils, sediments) and can contribute to their detoxification. Understanding basic processes will enhance our predictive capability of metal association and distribution in soils while providing critical information for the long-term management of soils. Stakeholders can use the results of this research to make decisions about environmental pollution control and soil and water quality issues.

Publications

  • McBride, M.B., Barrett, K.A., and Martinez, C.E. 2005. Zinc and cadmium behavior in peats developed on metalliferous Silurian dolomite. Canadian Soil Science/Geological Science meeting, Halifax, Canada. CD-ROM.
  • Yoon, S-J., Martinez, C.E. 2005. Zinc Speciation in Partially Barren Organic Soils. American Chemical Society (ACS) meetings, San Diego, CA. CD-ROM.


Progress 01/01/04 to 12/31/04

Outputs
We study the formation and dissolution of zinc and cadmium sulfides in natural metalliferous soils in relation to microbial populations involved in S cycling. The soils are peat deposits that overlie a mineral bed of Lockport Dolomite in Western New York State. These peat deposits concentrate Cd and Zn by biogeochemical processes, and the solubility, mobility and bioavailability of these metals can increase when such deposits are drained, initiating oxidation of organic matter and sulfides under aerobic conditions and leading to phytotoxicity. Surface soils and vertical profiles were sampled during wet and dry seasons. We employed culture and non-culture based approaches to investigate the presence of sulfur reducing bacteria (SRB) in the surface soils collected during the dry season. We enumerated SRB using a modified Barr's medium for sulfate reducers and the most-probable number technique and carried out enrichments for different groups of SRB: Desulfobulbus, Desulfobacter, and Desulfovibrio (delta-proteobacteria) and Desulfotomaculum (Gram positive). Although a key step in sulfate respiration is mediated by the dissimilatory sulfite reductase (dsr), no PCR products were obtained from any soil or enrichment using dsr-specific primers. Bacterial community profiles, obtained from these enrichments with universal bacterial primers for ribosomal RNA genes, yielded no sequences belonging to known SRB in delta-Proteobacteria. The arsA gene that codifies for an enzyme that performs reduction of sulfite to sulfide was identified in a sulfur-reducing archaea. We designed degenerated primers for the asrA gene and tested for its presence in the soils and SRB enrichments. The asrA gene was identified in some of the SRB enrichments (using acetate and lactate as electron donor) that selected for Clostridium sp. isolates. Thus far, our results suggest that bacteria belonging to phylum Firmicutes have an important role in the sulfur cycling in these soils. These microorganisms may use a sulfur metabolism pathway different than the one described for the known SRB. We are also probing the zinc chemical (bonding) environment in soil columns collected during wet and dry seasons using Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. Zinc has a relatively strong affinity for reduced sulfur and we also quantify reduced sulfur in the organic soils using S K-edge X-ray absorption near edge structure (XANES) spectroscopy. We find that a large percentage of the total S is present in the most reduced oxidation state (such as thiol and sulfide) in all soils, at all depths, and in soils collected during both dry and wet seasons. We, however, observe Zn-S coordination in the deep soil only, where zinc and sulfur concentrations are conspicuously higher than those in the surface soil. Using synchrotron-based X-ray diffraction (XRD), we also determine whether zinc sulfide mineral crystallites, which are potentially biogenic, exist in the deep soil.

Impacts
This project will advance our knowledge and understanding of the chemical and biogeochemical processes controlling trace and toxic element cycling (partitioning, redistribution, solubility) in complex soil environments. Emphasis is given to sulfur cycling and its effect on metal speciation and microbial activity. These processes are important in organic matter rich environments (such as wetlands) and can contribute to their detoxification. Understanding these basic processes will enhance our predictive capability of metal association and distribution in soils while providing critical information for the long-term management of soils. Stakeholders can use the results of this research to make decisions about environmental pollution control and soil and water quality issues.

Publications

  • Yanez, C., Bruns, M.A., and Martinez, C.E. 2004. Enzymes Involved in Sulfur Cycling in Natural Metalliferous Organic-Rich Soils. In International Society for Microbial Ecology (ISME) Meetings Abstracts, August 2004, Cancun, Mexico. Page 41.
  • Yanez, C., Bruns, M.A., and Martinez, C.E. 2004. Sulfate-Reducing Bacteria in Naturally Metalliferous Soils. In American Society of Microbiology (ASM) Annual Meetings Abstracts, May 2004, New Orleans, LA. CD-ROM.
  • Martinez, C.E. and Lanzirotti, A. 2003. Probing the Chemical Environment and Elemental Distributions in Natural Metalliferous Organic Soils Using Microbeam (m) XRD, XRF, and XAS. In Soil Science Society of America (SSSA) Annual Meetings Abstracts, November 2003, Denver, CO. CD-ROM.
  • Yanez, C., Bruns, M.A., and Martinez, C.E. 2003. Molecular Analyses of Sulfur Bacteria in Metalliferous Organic Soils. In Soil Science Society of America (SSSA) Annual Meetings Abstracts, November 2003, Denver, CO. CD-ROM.