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.