Honors & Awards
Earth Science Postdoctoral Fellowship, National Science Foundation (08/01/2020)
Doctor of Philosophy, University of New Mexico (2020)
Master of Science, University of New Mexico (2015)
Bachelor of Science, University of New Mexico (2012)
Ph.D., University of New Mexico, Civil and Environmental Engineering (2020)
Scott Fendorf, Postdoctoral Faculty Sponsor
Mobilization of As, Fe, and Mn from Contaminated Sediment in Aerobic and Anaerobic Conditions: Chemical or Microbiological Triggers?
ACS earth & space chemistry
2022; 6 (7): 1644-1654
We integrated aqueous chemistry, spectroscopy, and microbiology techniques to identify chemical and microbial processes affecting the release of arsenic (As), iron (Fe), and manganese (Mn) from contaminated sediments exposed to aerobic and anaerobic conditions. The sediments were collected from Cheyenne River Sioux Tribal lands in South Dakota, which has dealt with mining legacy for several decades. The range of concentrations of total As measured from contaminated sediments was 96 to 259 mg kg-1, which co-occurs with Fe (21 000-22 005 mg kg-1) and Mn (682-703 mg kg-1). The transition from aerobic to anaerobic redox conditions yielded the highest microbial diversity, and the release of the highest concentrations of As, Fe, and Mn in batch experiments reacted with an exogenous electron donor (glucose). The reduction of As was confirmed by XANES analyses when transitioning from aerobic to anaerobic conditions. In contrast, the releases of As, Fe and Mn after a reaction with phosphate was at least 1 order of magnitude lower compared with experiments amended with glucose. Our results indicate that mine waste sediments amended with an exogenous electron donor trigger microbial reductive dissolution caused by anaerobic respiration. These dissolution processes can affect metal mobilization in systems transitioning from aerobic to anaerobic conditions in redox gradients. Our results are relevant for natural systems, for surface and groundwater exchange, or other systems in which metal cycling is influenced by chemical and biological processes.
View details for DOI 10.1021/acsearthspacechem.1c00370
View details for PubMedID 36238447
View details for PubMedCentralID PMC9555341
- Mobilization of As, Fe, and Mn from Contaminated Sediment in Aerobic and Anaerobic Conditions: Chemical or Microbiological Triggers? ACS EARTH AND SPACE CHEMISTRY 2022
Arsenic Accumulation in Hydroponically Grown Schizachyrium scoparium (Little Bluestem) Amended with Root-Colonizing Endophytes.
ACS earth & space chemistry
2021; 5 (6): 1278-1287
We integrated microscopy, spectroscopy, culturing and molecular biology, and aqueous chemistry techniques to evaluate arsenic (As) accumulation in hydroponically grown Schizachyrium scoparium inoculated with endophytic fungi. Schizachyrium scoparium grows in historically contaminated sediment in the Cheyenne River Watershed and was used for laboratory experiments with As(V) ranging from 0 to 2.5 mg L-1 at circumneutral pH. Arsenic accumulation in regional plants has been a community concern for several decades, yet mechanisms affecting As accumulation in plants associated with endophytic fungi remain poorly understood. Colonization of roots by endophytic fungi supported better external and vascular cellular structure, increased biomass production, increased root lengths and increased P uptake, compared to noninoculated plants (p value <0.05). After exposure to As(V), an 80% decrease of As was detected in solution and accumulated mainly in the roots (0.82-13.44 mg kg-1) of noninoculated plants. Endophytic fungi mediated intracellular uptake into root cells and translocation of As. Electron microprobe X-ray mapping analyses detected Ca-P and Mg-P minerals with As on the root surface of exposed plants, suggesting that these minerals could lead to As adsorption on the root surface through surface complexation or coprecipitation. Our findings provide new insights regarding biological and physical-chemical processes affecting As accumulation in plants for risk assessment applications and bioremediation strategies.
View details for DOI 10.1021/acsearthspacechem.0c00302
View details for PubMedID 34308092
View details for PubMedCentralID PMC8302048
- Arsenic Accumulation in Hydroponically Grown Schizachyrium scoparium (Little Bluestem) Amended with Root-Colonizing Endophytes ACS EARTH AND SPACE CHEMISTRY 2021; 5 (6): 1278-1287
Emerging investigator series: entrapment of uranium-phosphorus nanocrystals inside root cells of Tamarix plants from a mine waste site.
Environmental science. Processes & impacts
We investigated the mechanisms of uranium (U) uptake by Tamarix (salt cedars) growing along the Rio Paguate, which flows throughout the Jackpile mine near Pueblo de Laguna, New Mexico. Tamarix were selected for this study due to the detection of U in the roots and shoots of field collected plants (0.6-58.9 mg kg-1), presenting an average bioconcentration factor greater than 1. Synchrotron-based micro X-ray fluorescence analyses of plant roots collected from the field indicate that the accumulation of U occurs in the cortex of the root. The mechanisms for U accumulation in the roots of Tamarix were further investigated in controlled-laboratory experiments where living roots of field plants were macerated for 24 h or 2 weeks in a solution containing 100 μM U. The U concentration in the solution decreased 36-59% after 24 h, and 49-65% in two weeks. Microscopic and spectroscopic analyses detected U precipitation in the root cell walls near the xylems of the roots, confirming the initial results from the field samples. High-resolution TEM was used to study the U fate inside the root cells, and needle-like U-P nanocrystals, with diameter <7 nm, were found entrapped inside vacuoles in cells. EXAFS shell-by-shell fitting suggest that U is associated with carbon functional groups. The preferable binding of U to the root cell walls may explain the U retention in the roots of Tamarix, followed by U-P crystal precipitation, and pinocytotic active transport and cellular entrapment. This process resulted in a limited translocation of U to the shoots in Tamarix plants. This study contributes to better understanding of the physicochemical mechanisms affecting the U uptake and accumulation by plants growing near contaminated sites.
View details for DOI 10.1039/d0em00306a
View details for PubMedID 33325952
Effect of bicarbonate and phosphate on arsenic release from mining-impacted sediments in the Cheyenne River watershed, South Dakota, USA
ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS
2019; 21 (3): 456–68
The mobilization of arsenic (As) from riverbank sediments affected by the gold mining legacy in north-central South Dakota was examined using aqueous speciation chemistry, spectroscopy, and diffraction analyses. Gold mining resulted in the discharge of approximately 109 metric tons of mine waste into Whitewood Creek (WW) near the Homestake Mine and Cheyenne River at Deal Ranch (DR), 241 km downstream. The highest concentrations of acid-extractable As measured from solid samples was 2020 mg kg-1 at WW and 385 mg kg-1 at DR. Similar sediment mineralogy between WW and DR was identified using XRD, with the predominance of alumino-silicate and iron-bearing minerals. Alkalinity measured in surface water at both sites ranged from 1000 to 2450 mg L-1 as CaCO3 (10-20 mM HCO3- at pH 7). Batch laboratory experiments were conducted under oxidizing conditions to evaluate the effects of NaHCO3 (0.2 mM and 20 mM) and NaH2PO3 (0.1 and 10 mM) on the mobilization of As. These ions are relevant for the site due to the alkaline nature of the river and nutrient mobilization from the ranch. The range of As(v) release with the NaHCO3 treatment was 17-240 μg L-1. However, the highest release (6234 μg L-1) occurred with 10 mM NaH2PO3, suggesting that As release is favored by competitive ion displacement with PO43- compared to HCO3-. Although higher total As was detected in WW solids, the As(v) present in DR solids was labile when reacted with NaHCO3 and NaH2PO3, which is a relevant finding for communities living close to the river bank. The results from this study aid in a better understanding of As mobility in surface water sites affected by the mining legacy.
View details for DOI 10.1039/c8em00461g
View details for Web of Science ID 000461883400005
View details for PubMedID 30714588
View details for PubMedCentralID PMC6474758
Effect of Calcium on the Bioavailability of Dissolved Uranium(VI) in Plant Roots under Circumneutral pH
ENVIRONMENTAL SCIENCE & TECHNOLOGY
2018; 52 (22): 13089–98
We integrated field measurements, hydroponic experiments, microscopy, and spectroscopy to investigate the effect of Ca(II) on dissolved U(VI) uptake by plants in 1 mM HCO3- solutions at circumneutral pH. The accumulation of U in plants (3.1-21.3 mg kg-1) from the stream bank of the Rio Paguate, Jackpile Mine, New Mexico served as a motivation for this study. Brassica juncea was the model plant used for the laboratory experiments conducted over a range of U (30-700 μg L-1) and Ca (0-240 mg L-1) concentrations. The initial U uptake followed pseudo-second-order kinetics. The initial U uptake rate ( V0) ranged from 4.4 to 62 μg g-1 h-1 in experiments with no added Ca and from 0.73 to 2.07 μg g-1 h-1 in experiments with 12 mg L-1 Ca. No measurable U uptake over time was detected for experiments with 240 mg L-1 Ca. Ternary Ca-U-CO3 complexes may affect the decrease in U bioavailability observed in this study. Elemental X-ray mapping using scanning transmission electron microscopy-energy-dispersive spectrometry detected U-P-bearing precipitates within root cell walls in water free of Ca. These results suggest that root interactions with Ca and carbonate in solution affect the bioavailability of U in plants. This study contributes relevant information to applications related to U transport and remediation of contaminated sites.
View details for DOI 10.1021/acs.est.8b02724
View details for Web of Science ID 000451245700016
View details for PubMedID 30412391
View details for PubMedCentralID PMC6341987
Uranium mobility and accumulation along the Rio Paguate, Jackpile Mine in Laguna Pueblo, NM
ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS
2017; 19 (4): 605–21
The mobility and accumulation of uranium (U) along the Rio Paguate, adjacent to the Jackpile Mine, in Laguna Pueblo, New Mexico was investigated using aqueous chemistry, electron microprobe, X-ray diffraction and spectroscopy analyses. Given that it is not common to identify elevated concentrations of U in surface water sources, the Rio Paguate is a unique site that concerns the Laguna Pueblo community. This study aims to better understand the solid chemistry of abandoned mine waste sediments from the Jackpile Mine and identify key hydrogeological and geochemical processes that affect the fate of U along the Rio Paguate. Solid analyses using X-ray fluorescence determined that sediments located in the Jackpile Mine contain ranges of 320 to 9200 mg kg-1 U. The presence of coffinite, a U(iv)-bearing mineral, was identified by X-ray diffraction analyses in abandoned mine waste solids exposed to several decades of weathering and oxidation. The dissolution of these U-bearing minerals from abandoned mine wastes could contribute to U mobility during rain events. The U concentration in surface waters sampled closest to mine wastes are highest during the southwestern monsoon season. Samples collected from September 2014 to August 2016 showed higher U concentrations in surface water adjacent to the Jackpile Mine (35.3 to 772 μg L-1) compared with those at a wetland 4.5 kilometers downstream of the mine (5.77 to 110 μg L-1). Sediments co-located in the stream bed and bank along the reach between the mine and wetland had low U concentrations (range 1-5 mg kg-1) compared to concentrations in wetland sediments with higher organic matter (14-15%) and U concentrations (2-21 mg kg-1). Approximately 10% of the total U in wetland sediments was amenable to complexation with 1 mM sodium bicarbonate in batch experiments; a decrease of U concentration in solution was observed over time in these experiments likely due to re-association with sediments in the reactor. The findings from this study provide new insights about how hydrologic events may affect the reactivity of U present in mine waste solids exposed to surface oxidizing conditions, and the influence of organic-rich sediments on U accumulation in the Rio Paguate.
View details for DOI 10.1039/c6em00612d
View details for Web of Science ID 000399908400014
View details for PubMedID 28352908