Current Research

The Aqueous Geochemistry and Mineralogy Group studies geochemical processes controlling mineral transformations and the fate of trace elements, nutrients, and contaminants in terrestrial and planetary aquatic systems.  Our work focuses on topics of relevance to environmental biogeochemistry, planetary geochemistry, and geobiology.  A summary of our current research projects is listed below.

ENVIRONMENTAL BIOGEOCHEMISTRY RESEARCH

Structural and Interfacial Geochemistry of Rare Earth and Platinum Group Elements
Funded by the Department of Energy
Collaborators: Prof. Daniel Giammar (Wash. U.), Dr. Eugene Ilton (PNNL), Dr. Eric Bylaska (PNNL)

Critical elements are essential to key technologies that underlie energy storage and generation, transportation, communications, and computing. The availability of the rare earth elements (REEs) and the platinum group elements (PGEs) are of particular concern because of the lack of adequate U.S. domestic production and, especially for PGEs, their overall low abundance in Earth’s crust. REEs and PGEs in deposits formed by rock weathering represent new potential resources for future exploitation. However, the fundamental geochemical processes that dictate the migration and enrichment of REEs and PGEs during weathering are poorly constrained. The mechanisms controlling how REEs and PGEs bind to the surfaces of mineral, become trapped inside the structures of minerals, and are mobilized from mineral surfaces and structures in weathering environments represent major areas of uncertainty. The foundational scientific knowledge required to accurately predict the formation and occurrence of deposits of REEs and PGEs formed via weathering is currently inadequate. This project seeks to elucidate the roles of mineral surfaces and structures in controlling the migration and enrichment of REEs and PGEs in weathering environments. Through coordinated laboratory experiments, synchrotron-based X-ray techniques, and advanced computational studies, this project will obtain fundamental new insight into the basic chemical processes controlling the formation of rare earth and platinum group element deposits near Earth’s surface.

Evaluating Trace Metal Limitations on Methane Fluxes in Terrestrial Ecosystems
Funded by the Department of Energy
Current Participants: Jinshu Yan, Elaine Flynn
Collaborators: Prof. Daniel Giammar (Wash. U.), Dr. Scott Brooks (ORNL), Dr. Ken Kemner (ANL), Dr. Dan Kaplan (SRNL)

Freshwater aquatic systems are critical locations of diverse anaerobic biogeochemical processes, including denitrification, methanogenesis, and mercury methylation. The activity of the microbial community in these environments degrade excess nutrients, generate the greenhouse gases methane and nitrous oxide, and alter contaminant bioavailability. While the controls on the biogeochemistry of subsurface regions of aquatic systems has been studied from many perspectives, the role of low availability of bioessential trace metals has been under-examined to date. The project seeks to establish whether natural aquatic systems display trace metal-limitations on biogeochemical processes, specifically methanogenesis, nitrous oxide reduction during denitrification, and mercury methylation.

Dynamic Recrystallization and Trace Element Redistribution at Mineral Surfaces
Funded by the National Science Foundation
Current Participants: Greg Ledingham
Collaborators: Prof. Daniel Giammar (Wash. U.)

Components in water have been demonstrated to cause the recrystallization of iron and manganese oxide minerals, affecting the fate of micronutrients and contaminants associated with these phases. This project explores whether lead and uranium oxide phases also undergo such recrystallization in drinking water system and contaminated subsurface sediments, respectively. In addition, we are developing isotope exchange methods to probe trace element fate during iron oxide recrystallization and the mobility of adsorbed heavy metals.

Impact of Intracellular Nanoparticle Exposure on Metal Homeostasis in Aquatic Organisms
Funded by the National Science Foundation
Current Participants: Elaine Flynn, Jeff Catalano
Collaborators: Prof. Matteo Minghetti (Oklahoma State U.)

Aquatic organisms, including fish, are widely exposed today to metal nanoparticles released via anthropogenic activities. Uptake in the intestines of these organisms causes intracellular exposure to nanoparticles in epithelial cells. The mechanisms of toxicity that occur, especially the impacts on metal homeostasis by the cells, is currently unknown. Using a novel Rainbow Trout cell line, this collaborative project seeks to understand the intracellular chemical transformations of silver and titanium oxide nanoparticles and the resulting impact of the abundance and distribution of essential metals.

Heavy Metal Hazard and Soil Quality in Peace Park, St. Louis
Funded by Washington University
Current Participants: Elaine Flynn
Partners: Green City Coalition, St. Louis Development Corporation, The Nature Conservancy, Missouri Department of Conservation

Unoccupied land in the College Hill neighborhood of St. Louis is being repurposed to create a new place for the community to gather for events, entertainment, and recreation. The planned Peace Park seeks to health, well-being, and overall landscape of this community. We are working to assess soil heavy metal hazards that may exist in the vacant urban land that is the home for Peace Park and also assessing aspects of soil health to aid in implementing the park design and maintenance.

PLANETARY GEOCHEMISTRY RESEARCH

Oxyhalogen Species as Oxidants of Iron and Manganse of Mars
Funded by the National Aeronautics and Space Administration
Current Participants: Kaushik Mitra

Oxyhalogen species have been widely detected on Mars, and laboratory studies of their formation processes indicate a diversity of these compounds are expected. While the potential impact of these species on organic matter preservation on Mars has been considered, little work has investigated their role as chemical oxidants. The high solubility of oxyhalogen salts may enable their percolation into the subsurface as oxidizing brines, overprinting the original redox record on early Mars. This project investigates how chlorate and bromate oxidize dissolved and solid-phase forms of iron and manganese and the mineral phases that result.

Iron Oxide Diagenesis on Mars: Seeking Environmental Constraints on Coarse-Grained Hematite Formation
Funded by Washington University
Current Participants: Abigail Knight

Fe-Mg smectite clay minerals have a widespread occurrence in the Noachian-aged crust of Mars.  These are often interpreted to contain iron in the ferric state yet conditions during this time period were likely anoxic.  In addition, these clays likely formed in the subsurface, possibly through hydrothermal alteration.  This suggests that the ferric clays observed today may be oxidation products of ferrous clays that formed during the Noachian.  We are investigating Fe(II)-bearing smectite formation during alteration of mafic rock of various compositions and the mineralogical products of subsequent oxidation.  We are also investigating how trace elements repartition during clay formation and oxidation to determine if trace element profiles can serve as proxies for clay formation pathways.

Extracting Trace Element Concentrations from Mars Exploration Rover APXS Data: Implications for Alteration Processes and Crustal Composition
Funded by the National Aeronautics and Space Administration
Current Participants: Abigail Knight
Collaborators: Dr. Scott VanBommell (Wash. U.)

Alpha Particle X-ray Spectrometer (APXS) instruments on the Mars Exploration Rovers (MER) Opportunity and Spirit amassed a large collection of data from two distinct landing sites. Existing analysis of these data have provided the abundance of Cr, Mn, Ni, Zn, and Br, but a wide array of trace elements have not be quantified to date. Principal investigator Scott VanBommel has recently developed new data processing methods for the Mars Science Laboratory mission to quantify a diverse array of additional trace elements, and under his leadership this project seeks to port this capability to the large archive of APXS data from the MER missions. This project will develop Ga and Ge abundances as well as Ga/Al and Ge/Si ratios as indicators of petrogenesis, hydrothermal alteration, and acidic leaching on Mars. We will also utilize a collection of redox-active and redox-inactive trace elements to provide new insight in aqueous alteration processes at the MER landing site.

GEOBIOLOGY RESEARCH

Fe(II) Smectite Clay Minerals as Electron Donors on the Early Earth and Other Planetary Bodies
Funded by the National Aeronautics and Space Administration
Current Participants: Robert Kupper
Collaborators: Prof. Clara Chan (U. Delaware)

Trioctahedral Fe(II) smectite clay minerals are a dominant product of anoxic basalt alteration on the modern Earth and should have been the largest oceanic Fe(II) pool before the great oxidation event. These minerals are likely widely abundant on other bodies throughout the Solar System, including on the surface of early Mars. However, it is unclear whether microorganisms can utilize Fe(II) in these minerals as an energy source and, if so, whether this produces distinct biosignatures. This project thus investigates microbial oxidation of Fe(II) smectites in comparison to the rates and products of abiotic oxidation of these widespread clay minerals.

Reconciling Prebiotic Paradigms: Mapping Planetary Reality onto Experimental Strategies
Funded by the National Aeronautics and Space Administration
Current Participants: Emily Millman
Collaborators: Prof. Karyn Rogers (RPI) plus 14 other scientists at multiple institutions
Project Website: http://earthfirstorigins.rare.rpi.edu/

The large collaborative project consists of one of the major teams involved in NASA's Prebiotic Chemistry and Early Earth Environments Consortium supported by the NASA Astrobiology Program. The overarching goal is to develop a new understanding of conditions on the early Earth and the prebiotic chemistry that occurred with rocks, minerals, and fluids actually present during this period. The Washington University team is specifically focused on phyllosilicates that formed on the early Earth from mafic and ultramafic crystal alteration and how key prebiotic compounds bound to and were selectively concentrated by these phases.