Progress 10/01/13 to 09/30/18
Outputs
Target Audience:Undegraduate students, graduate students, and faculty in the fields of soil science, environmental science, earth science and biogeochemistry Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided research and professional development opportunities for one postdoctoral scholar, Joyabrata Mal, as well as research and training opportunities for two undergraduate students at UC Berkeley. The undergraduate students, Shea Nolan and Aaron McDowell-Sánchez have been trained in microbiology methods, including working in sterile conditions, preparing culture media, maintaining pure cultures, and studying bacterial growth curve during a one semester internship. How have the results been disseminated to communities of interest?The results have been presented by at two international conferences and two invited seminars. Pallud, C. and Charlet, L. Selenium fate in soils and sediments: spectroscopy, kinetics and reactive transport. Soil Science Seminar, ETH, Zürich. Dec 4, 2017. Pallud, C. Spatial patterns and modelling of iron, selenium and arsenic cycling in soil aggregates. Séminaire Géochimie, ISTerre, Université Grenoble Alpes. May 15, 2018. Mal, J., Yee, N., Schilling, K., Geoff, J., Dhillon, K. and Pallud, C. Abiotic and biotic oxidation of chemically synthesized Se(0) nanoparticles. Goldschmidt Conference, Boston. Aug. 12-17, 2018. Wasserman, N., Schilling, K., Johnson, M. and Pallud, C. Selenium isotopic fractionation during the oxidation of clausthalite. AGU Fall Meeting, Washington. Dec. 10-14, 2018. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
We tested the abiotic oxidation of Se(0) by three oxidants i.e. MnO2 , KMnO4 and FeCl3 and their efficiency under oxic and acidic conditions at 25 °C. Dissolved Se concentration increased over the duration of all experiments. After 21 days, 2.3, 6.4 and 3.2 % of the initial Se(0) was oxidized to selenite, in the presence of MnO2 , KMnO4 and FeCl3 , respectively. The increase in dissolved Se concentration could either be attributed to oxidation and/or solubilization of Se(0). Our results showed the ability of strain JG-17 to dissolve elemental selenium, with 0.05 % of initial Se(0) (~ 0.01 mM) being oxidized to selenite after 3 days at pH 7 and 25 °C. The results indicated that strain JG-17 releases sulfur-containing extracellular compounds including sulfite, thiosulfate and sulfide during Se(0) oxidation which might be responsible for Se(0) dissolution. We also tested the abiotic oxidation of Se(IV) by the same three oxidants under oxic and acidic conditions at 25 °C. After 21 days, 27.6, 25.8 and 37.9 % of the initial Se(IV) (100 µM) was removed due to adsorption and/or oxidation to selenite (Se(VI)), in the presence of MnO2 , KMnO4 and FeCl3 , respectively. Total dissolved Se was also measured to confirm the oxidation of Se(IV) to Se(VI). The results showed that 7.6, 9.5 and 10. 6% of the initial Se(IV) was oxidized to Se(VI) in the presence of MnO2 , KMnO4 and FeCl3 , respectively after 21 days. Concentrations of Mn2+ (aq) and Fe (total Fe and Fe(II)) in experimental solution during abiotic oxidation of Se(IV) by MnO2 , KMnO4 and FeCl3 , respectively were also monitored. Mn2+ (aq) concentrations increased with time in presence of MnO2 , it decreased gradually in presence of KMnO4 . Similarly, Fe(III) concentration decreased over time with increase of Fe(II) concentration in aqueous phase. We also investigated the solubilization of Se(0) in the presence of various inorganic sulfur compounds under anoxic conditions at 25°C. We showed that dissolved Se concentration increase over time in presence of sulfite, thiosulfate and sulfide indicating that sulfur compounds influence the Se(0) solubilization. Results also showed that the dissolution of Se(0) increased linearly with increasing concentrations of sulfite, thiosulfate and sulfide between 0.5 to 2.0 µM. Total dissolved Se was 0.26, 0.31 and 0.37 µM in presence of 0.5, 1.0 and 2.0 µM of sulfite, respectively, while it was 0.14, 0.18 and 0.23 µM in presence of thiosulfate, respectively. In presence of sulfide, total dissolved Se was 0.42, 0.52 and 0.57 µM, respectively.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2018
Citation:
Geoff, J., Terr, L., Mal, J., Pallud, C. and Yee, N. 2018. Role of extracellular reactive sulfur metabolites on microbial Se(0)
dissolution. Geobiology. doi: 10.1111/gbi.12328.
- Type:
Journal Articles
Status:
Published
Year Published:
2018
Citation:
Schilling, K., VillaRomero, J.F. and Pallud, C. 2018. Selenate reduction rates and kinetics across depth in littoral
sediments of the Salton Sea, California. Biogeochemistry. 140: 285-298
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Progress 10/01/16 to 09/30/17
Outputs
Target Audience:Target audiences for my work on selenium cycling in water and sediments include USFWS, USDA, Cal-EPA as well as faculty and students and in the fields of soil science, environmental science, earth science and biogeochemistry. Changes/Problems:As reported last year, due to changes in outside funding, the focus of our project has slightly changed, and some of our objectives have been changed accordingly. Two components of the project have been dropped, namely the microbial diversity and the ecosystem partitioning model. Additionally, instead of focusing the project on selenium reduction, the scope has been extended to looking at a more complete picture of the selenium cycle, by including selenium oxidation, a widely understudied process. Our project also extended from one study site to three. Our new project objectives are the following: 1. To investigate the environmental factors controlling the rates of selenium biogeochemical reactions (sorption, reduction, oxidation) in selenium-contaminated ecosystems; 2. To investigate the kinetics of selenium biogeochemical reactions in sediments; 3. To determine the magnitude of selenium isotopic fractionation caused by abiotic and biotic oxidation of Se(-II), Se(0) and Se(IV), 4. To investigate selenium oxidation and selenium isotopic fractionation in natural soil/sediment matrices. What opportunities for training and professional development has the project provided?This project has provided research and professional development opportunities for one postdoctoral scholar, as well as research and training opportunities for 2 undergraduate students at UC Berkeley. Through this project, the postdoctoral scholar, Joyabrata Mal was trained in laboratory work, data analysis and paper preparation, he mentored two students, and he grew as an interdisciplinary scientist due to the collaborative nature of this research. The project also provided training opportunities for two undergraduate students, Shea Nolan and Aaron McDowell-Sánchez. They has been trained in various laboratory methods, including basic microbiology methods (working in sterile conditions, preparing culture media, maintaining pure cultures...) and chemistry methods (preparing culture media, analyzing selenium concentration in liquid samples...) How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?The major efforts during the next reporting period will be: To use the bacterial isolates JG-17 and CW-20 to determine rates and kinetics of microbial Se(0) oxidation and the associated magnitude of the Se isotope fractionation for microbial Se(0) oxidation; To conclude the abiotic Se oxidation work using Fe(III), MnO2 and KMnO4 under different environmental condition (pH, oxygen etc) and to determine the associated Se isotopic fractionation; To study the abiotic and biotic oxidation of biogenic Se(0) and its isotopic fractionation; To investigate and confirm the effect of sulfite on Se(0) oxidation and/or solubilization and Se isotopic fractionation under different pH.
Impacts
What was accomplished under these goals?
Major Activities Biotic oxidation of Se(0) We tested the ability of bacteria isolates from three Se-rich study sites (Punjab, India, Salton Sea, USA and Swansea Valley, United Kingdom) to oxidize Se(0). Bacteria were isolated and characterized by co-PI Nathan Yee (Rutgers University). We tested the ability of approximately 50 new bacterial isolates (Swansea Valley) to oxidize chemically synthesized red Se(0) in bench-top experiments. We selected one isolate from Punjab, designated strain JG-17, and one isolate from Swansea Valley , designated strain CW-20, for detailed studies. Further experiments were conducted with JG17 and CW20 in order to obtain growth curves in rich and minimal media and to determined rates of biotic oxidation of Se(0). Abiotic oxidation of Se(0) To study the possibility of abiotic oxidation of Se(0), we conducted a series of batch experiments at pH 4 in presence of three different oxidants i.e. MnO2, Fe(III), KMnO4, under open vessel and anaerobic conditions. Samples were collected at regular time intervals. Concentrations of soluble Se were determined using ICP-OES. Samples will be sent to our co-PI Thomas M. Johnson at University of Illinois, Urbana-Champaign, to perform the Se isotope measurements using MC-ICP-MS for further analysis; We also investigated the effect of sulfite on Se(0) oxidation and/or solubilization. Significant Results Ability of bacterial isolates to oxidize Se(0) One isolate from Swansea Valley, designated strain CW-20, was shown to be able to solubilize Se(0). It was identified as a Bacillus sp.; When grown in minimal medium at pH 7, both isolates JG-17 and CW-20 were able to solubilize/oxidize Se(0) rather quickly, with a faster solubilisation rate for JG-17. After 6 days of incubation, 23.07 and 9.57 µg/L dissolved Se was found in the medium in presence of JG17 and CW20, respectively. Abiotic oxidation of Se(0) by Fe(III), MnO2 and KMnO4 Abiotic oxidation of Se(0) experiments with three different oxidants was conducted at pH 4 under aerobic and anaerobic condition in batch experiments for periods of 5-18 days. Dissolved Se concentration increased over the duration of all experiments. The increase in dissolved Se concentration could either be attributed to oxidation and/or solubilization of Se(0). Although several reports of similar experiments of abiotic oxidation of sulfur/sulfide has already been reported (Herszage et al., 2003; Mazumdar et al., 2008), further experiments will be conducted to confirm the abiotic oxidation of Se(0) and its isotopic fractionation. Interestingly, oxidation of Se(0) was much faster and stronger in presence of MnO2 and KMnO4 than Fe(III) under open vessel condition. Under anaerobic condition, although the Se(0) oxidation by MnO2 was much slower till 5 days of experiment, KMnO4 shows strong oxidation of Se(0). We are currently running more experiments to investigate the effect of pH and oxygen on abiotic oxidation of Se(0) and samples will be sent to co-PI Thomas M. Johnson at University of Illinois for measuring Se isotopic fractionation. Se(0) solubilization by sulfite Preliminary results showed that dissolved Se concentration increase over time in presence of sulfite, indicating that sulfite influence the Se(0) oxidation and/or solubilization. We are currently running more experiments to confirm the reason behind it whether the increase of soluble Se is due to oxidation or solubilization or both.
Publications
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Progress 10/01/15 to 09/30/16
Outputs
Target Audience:Undegraduate students, graduate students, and faculty in the fields of soil science, environmental science, earth science and biogeochemistry. Changes/Problems:Due to changes in outside funding, the focus of our project has slightly changed, and some of our objectives have been changed accordingly. Two components of the project have been dropped, namely the microbial diversity and the ecosystem partitioning model. Additionally, instead of focusing the project on selenium reduction, the scope has been extended to looking at a more complete picture of the selenium cycle, by including selenium oxidation, a widely understudied process. Our project also extended from one study site to three. Our new project objectives are the following: 1. To investigate the environmental factors controlling the rates of selenium biogeochemical reactions (sorption, reduction, oxidation) in selenium-contaminated ecosystems; 2. To investigate the kinetics of selenium biogeochemical reactions in sediments; 3. To determine the magnitude of selenium isotopic fractionation caused by abiotic and biotic oxidation of Se(-II), Se(0) and Se(IV), 4. To investigate selenium oxidation and selenium isotopic fractionation in natural soil/sediment matrices. What opportunities for training and professional development has the project provided?This project has provided research and professional development opportunities for one postdoctoral scholar, as well as research and training opportunities for 3 students at UC Berkeley. Through this project, the postdoctoral scholar, Kathrin Schilling mentored three students, she developed good self-management skills, including the ability to prioritize work appropriately and deliver results according to schedule, and she grew as an interdisciplinary scientist due to the collaborative nature of this research. The project also provided training opportunities for a graduate student, Tuesday Simmons, and two undergraduate students, Shea Nolan and Rachel Quock. They has been trained in geomicrobiology methods including working in sterile conditions, preparing culture media, maintaining pure cultures (undergraduates), as well as working with pure bacterial cultures, testing for the ability of bacterial strains to oxidize selenium, synthesizing Se(0) and characterizing it using atomic force microscopy and scanning electron microscopy. How have the results been disseminated to communities of interest?The results have been presented by the postdoctoral scholar Kathrin Schilling as an oral presentation in the session "Progress in calibrating isotope fractionation factors: Laboratory experiments and field observations" at the 2016 Goldschmidt Conference: Schilling, K., Johnson, T.M. and Pallud, C. Selenium isotopic tracer of abiotic oxidation by Mn-oxides. Goldschmidt Conference, Yokohama. June 26-July 1, 2016. What do you plan to do during the next reporting period to accomplish the goals?The major efforts during the next reporting period will be: 1. To conclude abiotic selenium oxidation work using manganese-oxides; 2. To determine the selenium isotopic fractionation caused by other potential abiotic selenium oxidation reactions, 3. To use our bacterial isolates to determine the magnitude the selenium isotope fractionation for microbial Se(0) oxidation and elucidate the mechanism of microbial Se(0) oxidation.
Impacts
What was accomplished under these goals?
During the reporting period, we addressed the following research objective: "To determine the magnitude of selenium isotopic fractionation caused by abiotic and biotic oxidation of Se(-II), Se(0) and Se(IV)". Since this objective is new, the work done so far was mainly preliminary, but provided the basis for the work that will be performed in the next reporting year. 1) We isolated bacteria from two soils contaminated with selenium (Punjab, India and Salton Sea, USA) and tested their ability to oxidize Se(0). None of the isolates from the Salton Sea sediments, a hypersaline environment where selenium originates from irrigated agriculture, were able to oxidize red Se(0) or black Se(0). There was no noticeable oxidation of black Se(0) by any of the bacterial isolates from the Punjab site over a duration of three months. However, one of the Punjab isolate, a Bacillus megaterium, was able to reduce red Se(0), and will be the focus of our future work. Four other isolates were characterized as Bacillus megaterium, but were not able to oxidize red Se(0). 2) We determined the magnitude of Se isotopic fractionation caused by abiotic oxidation of Se(IV) to Se(VI) by manganese (Mn) oxides. For that purpose, we conducted a series of batch experiments (i) at different pHs, (ii) with MnO2 from different synthesis techniques, and (iii) with varying amount of MnO2. Concentrations of Se(IV) and total Se were determined using HG-ICP-MS and Se isotope measurements were made using MC-ICP-MS. For all Se(IV) oxidation experiments with Mn-oxides, we observed a constant decrease in Se(IV) concentrations over the duration of the experiments, with up to 35-40% of Se(IV) removed after 300-400 hours. This Se(IV) removal over time could be attributed to oxidation, but we still need to confirm this, although adsorption as the main Se(IV) removal process is unlikely. Our Se isotopic fractionation analyses showed that oxidation of Se(IV) by MnO2 fractionates selenium isotopes, with the Se(VI) product enriched in the lighter isotopes and that subtle differences in experimental conditions affect the magnitude of the fractionation.
Publications
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Progress 10/01/14 to 09/30/15
Outputs
Target Audience:Undegraduate students, graduate students, and faculty in the fields of soil science, environmental science, earth science and biogeochemistry Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The project has trained one graduate student, JF VillaRomero, and one postdoctoral scientist, K. Schilling, during the reported period. How have the results been disseminated to communities of interest?The results have been presented by PI Pallud at two international conferences and seminars: Invited presentations: Pallud, C. and Kausch, M. Effects of coupled biogeochemical and transport processes on soil aggregate-scale selenium speciation. American Geophysical Union (AGU) Fall Meeting, San Francisco. Dec. 15-19, 2014. Pallud, C., Kausch, M., Schilling, K. and Villa-Romero, J.F. A multi-scale study of agricultural selenium contamination in California. Environmental Science, Policy and Management (ESPM) Department Colloquium, UC Berkeley. Oct. 2, 2014. What do you plan to do during the next reporting period to accomplish the goals?We propose to conduct laboratory experiments to determine the selenium oxidation rates through biotic and abiotic pathways and the concomitant Se isotopic fractionation.
Impacts
What was accomplished under these goals?
We investigated the kinetics of selenate reduction in littoral sediment from the North and South shores of the Salton Sea (CA). We used flow-through reactor (FTR) experiments containing intact sediment slices to investigate the centimeter-scale vertical distribution of apparent maximum selenate reduction rate, Rmax and selenate half-saturation concentration, Km and to identify the sediment characteristics that control selenium retention in Salton Sea littoral sediments. We also investigated selenate and selenite sorption, as well as performed selenium sequental extraction on the same sediment samples. Our data demonstrate that in situ selenate reduction is limited by the low availability of selenate and that sediment chemical and physical characteristics leads to spatial heterogeneity in selenium retention in Salton Sea littoral sediments. We completed a set of preliminary experiments investigating selenium isotopic fractionation for abiotic selenite oxidation by a Mn-oxide (birnessite) and observed a 1.0‰ fractionation for this oxidation reaction, much smaller than the range most commonly seen for selenium reduction. This suggests that selenium oxidation may have a relatively small effect and that selenium isotope data in environmental settings can be interpreted largely in terms of reduction effects. However, this is highly speculative at present, as we have only a few experiments and other oxidation mechanisms, such as microbial ones, could be radically different.
Publications
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Progress 10/01/13 to 09/30/14
Outputs
Target Audience: The target audience is other scientists Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? The project has trained one graduate student, JF VillaRomero, and one postdoctoral scientist, K. Schilling, during the reported period. How have the results been disseminated to communities of interest? The results have been presented at international conferences and seminars: Invited presentations: Pallud, C. and Kausch, M. Effect of aggregate-scale heterogeneity on selenium immobilization in soil. Ecological Society of America (ESA) Annual Meeting, Sacramento. Aug. 10-15, 2014. Pallud, C. Spatial heterogeneity of biogeochemical processes controlling iron and selenium cycling in soils. IPGP, Université Paris Diderot. July 9, 2014. Contributed presentations: Villa-Romero, J.F., Schilling, K. and Pallud, C. Surficial littoral sediments of hypersaline lake, the Salton Sea, a sink for selenium mobilized from the Colorado River delta. Goldschmidt Conference, Sacramento. June 8-13, 2014. Schilling, K., Basu, A., Johnson, T.M., Sanford, R., Pallud, C. and Mason, P.R.D. Se isotopic fractionation during microbial reduction of selenoxyanions: Tracing different biogenic Se transformation pathways? EnvironMetal Isotope (EMI) Conference, Ascona. Aug. 18-23, 2013. What do you plan to do during the next reporting period to accomplish the goals? - To investigate the kinetics of selenium biogeochemical reactions in sediments and how they are affected by changes in key environmental factors (salinity, oxygenation and temperature); - To determine how variations in key environmental factors (salinity, oxygenation) impact sediment phylogenic and functional diversity; - To develop a mechanistic ecosystem partitioning model for predicting selenium fate in contaminated aquatic environments by linking dynamic biogeochemical transformations of selenium, reactive transport in sediments, and exchange between sediment and water column with trophic transfer through the food web.
Impacts
What was accomplished under these goals?
We analyzed the history and current developments in science, policy, and management of irrigation-induced Se contamination in California. We evaluated the effects of improvements in the design of local attenuation methods (drainage reuse and evaporation ponds) in conjunction with the development of programs for selenium load reductions at the regional scale. We concluded that by combining the proven management tools with a novel policy approach, it may be possible to avoid future events of irrigation-induced contamination. We investigated Se isotope fractionation during enzymatic selenium reduction by five phylogenetically and physiologically different microbial strains. We showed that microbial Se(VI) reduction can induce much greater fractionation under donor-poor conditions. For all microbial species tested, Se fractionation was not affected by selenium concentration and the cell-specific reduction rates of Se(VI) and/or Se(IV) varied depending on the Se-species and the microbial strains. The variability in selenium isotopic fractionation factors reflected differences in reduction mechanisms and the Se-species reduced. Discussions were included in the graduate seminar Soil Pollution and Remediation taught in Fall 2014 by PI.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Kausch, M. and C. Pallud. 2013. Science, policy, and management of irrigation-induced selenium contamination in California. J. Environ. Qual. 42: 1605-1614.
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