Progress 06/01/18 to 05/31/23
Outputs
Target Audience:Academics; farmer and commodity groups; federal, state and local government, and herbicidal industry and manufacturers, stakeholders on the soil health Changes/Problems:Thisproject completed all tasks and exceeded the expected outcomes originally included in the proposal with an NCE that was applied due toexternal reasons (COVID-19). What opportunities for training and professional development has the project provided?This project supported 2 PhD students (fully funded), 3 MS students (partially funded), and 2 postdoctoral associates (unfunded project contributions). 1. Hui Li: PhD completed in 2019 and now an assistant professor at North Carolina State University. 2. Spencer Moller: PhD completed in 2023;now a postdoctoral fellow at Yale University 3. June Hazewski: MS completed in 2021;now at Delaware Geological Survey 4. Rumana Zahir: MS completed; now a PhD student at the University of Central Florida 5. Meg Musser: MS completed in 2022;now a scientist in a private consulting firm. 6. Dr. Mingjing Sun: Now an associate professor atKean University, NJ. 7. Dr. Abrar Quadery: Continued postdoctoral associate with Adam Wallace in new project 8/9. Sarah Tuoni and Chris Townsend (both undergrads) completed their degrees and are now in a job and starting MS degree in chemistry, respectively. Training and professional experience provided to them are included in the annual reports. Here we highlight the impact of the training provided on them landing successful careers. How have the results been disseminated to communities of interest? Interacted with state government body (DNREC) on glyphosate application that is currently done for controlling invasive species. Significant effort on outreach made through presentations in the stakeholders in the region (commodity groups, poultry, and animal husbandry industries, regional fertilizer suppliers), connecting to collaborations, student and postdoc mentoring, publications, and keynote/invited/volunteered presentations in conferences and meetings Other modes of interactions include: Publications: 18 publications. The list includes 2 edited books, 1 book chapter, 1 review paper, and 10 peer-reviewed publications. Invited and meeting presentations: 6 invited talks and 9 presentations at national and international conferences and meetings. What do you plan to do during the next reporting period to accomplish the goals?In total, the outcomes of the project exceeded the expected outcomes originally included in the proposal.
Impacts
What was accomplished under these goals?
?Completed major research activities of this project (all project years) are: Major highlights of thisproject are 18 publications (2 edited books, 1 book chapter, 1 review paper, and 10 peer-reviewed papers). Other outcomes include 6 invited talks and 9 presentations at national and international conferences and meetings. Science outcomes: i) novel method of extraction and quantitation of glyphosate from soil developed and validated and used for the accurate understanding of the fate of glyphosate (Moller et al., 2023a), ii) RexFit and DFT modeling and calculation of energy barrier provided independent evidence of suppression or formation of specific degradation products, iii) n novel Orbitrap-MS/MS based method on measuring mass fragments of glyphosate and its metabolites were developed and tested, iv) Difference in biotic and abiotic pathways of degradation and ability to track in the environment known from chemical and gene encoding specific (C-P lyase and oxidoreductase enzymes) results (Moller et al., 2023b). Project data provided preliminary results to a successful major research instrumentation award from NIFA (Orbitrap quadrupole MS/MS), one pending (cryoprobe NMR to NSF), and two unsuccessful MRI proposals to DOD. Continued collaborations with researchers outside UD: Ralf Greiner (Max Rubner-institut, Germany); Gulnihan Ozbay (Delaware State University), Philip Larese-Casanova (Northeastern University), Ludmilla Aristilde (Northwestern University), David O'Connell (Trinity College, Ireland), Charles Brierley (East Angelia University, UK). These research collaborations are centered on method development, preparation of labeled compounds, and enzyme purification, and the continued collaboration will contribute to our efforts in tracking herbicides and related organic phosphorus compounds that are present in the environment. All project objectives are fully achieved. It opened up several avenues for further research (foundational and applied) and will be explored in the future.
Publications
- Type:
Other
Status:
Accepted
Year Published:
2023
Citation:
Summary of the project products: 18 peer-reviewed publications (2 edited books, 1 book chapter, 1 review paper, and 10 peer-reviewed publications), two PhD dissertations, 3 MS theses, and 15 presentations in meetings and conferences.
- Type:
Journal Articles
Status:
Published
Year Published:
2022
Citation:
Moller, S., Sakhno, Y., Aristilde, L., Blake, R.E., and Jaisi, D. Evolution of oxygen isotopologues in phosphate and pyrophosphate during enzyme-catalyzed isotopic exchange reactions. ACS Earth and Space Chemistry, 6, 15431551.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2023
Citation:
Moller, S., Wallace, A.F., Zahir, R., Quadery, A., and Jaisi, D. Effect of temperature on the degradation of glyphosate by Mn-oxide: Products and pathways of degradation. Journal of Hazaroud Materials (under review).
- Type:
Journal Articles
Status:
Submitted
Year Published:
2023
Citation:
Moller, S., and Jaisi, D. Oxygen isotope effect during synthesis and degradation of adenosine triphosphate. Environmental Science & Technology (ready to submit).
Moller, S., Bakkur, R., and Jaisi, D. Fate of glyphosate in a costal wetland soil in central Delaware. Science of the Total Environment (ready to submit).
- Type:
Journal Articles
Status:
Submitted
Year Published:
2023
Citation:
Sun, M., Li, H., Moller, S., and Jaisi, D. Advanced analytical methods for detection and source tracking of glyphosate and its environmental fate-A review. Environmental Science and Technology Letters (in preparation).
- Type:
Theses/Dissertations
Status:
Accepted
Year Published:
2023
Citation:
Moller, S.R. (2023). Hydrolysis of glyphosate and other organic phosphorus compounds and associated isotope effects. PhD dissertation, Department of Plant and Soil Sciences, University of Delaware, 152 pp.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Sun, M., Li, H., Moller, S., Wallace, A., and Jaisi, D.P. Glyphosate degradation and bioavailability in soil system. 2022 Goldschmidt, Honolulu, HI (Jul 11-15, 2022).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Bai, Y., Stout, L.M., Li, J., and Jaisi, D.P. Mechanism of polyphosphate formation and degradation in wastewater treatment plants. International conference on sustainable chemical and environmental engineering, Crete, Greece (Aug 31-Sep 4, 2022)
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Jaisi, D.P., Hollenback, A., Stout, L.M., Massudieh, A., and Guan, Y. Advanced analytical methods for linking phosphorus sources and transformation in the soils and waters. 22nd World Congress of Soil Sciences, Glasgow, United Kingdom (Jul 31-Aug 5, 2022).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Tuoni, S., Sakhno, Y., Ghimire, R., and Jaisi, D.P. Extraction and characterization of phosphorus in soils treated with slow-release fertilizer for plant growth. DENIN Symposium, University of Delaware, Newark, DE (Aug 13, 2022).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Townsend, C., Gray, K., and Jaisi, D.P. Seasonal and spatial trends in dissolved organic phosphate from Murderkill River watershed. Undergraduate Research Celebratory Symposium. University of Delaware, Newark, DE (Aug 18, 2022).
|
Progress 06/01/21 to 05/31/22
Outputs
Target Audience:Academics; farmer and commodity groups; federal, state and local government, and herbicidal industry and manufacturers, stakeholders on the soil health Changes/Problems:The impact of COVID-19 still lingered significantly in this project year. While the University of Delaware remained fully opened for research under Phase 4 (with minor restrictions) coordination and access among analytical facilities and delay in the supply chain continue to interrupt research. The sluggishness of the research required one more year of NCE, which was applied and approved. We all plans on hand and are fully certain that the remaining tasks of the project will be completed by May 2023. What opportunities for training and professional development has the project provided?The major opportunities provided to researchers are as follows: Spencer Moller (PhD student, intake Fall 2018) is now well versed in key analytical tools, including IRMS, NMR, and Raman. His work on isotope methods to discriminate glyphosate-derived P is encouraging. Outcomes of this project on a rapid method of detecting and measuring isotopes in phosphate is under review. The outcome of his related research on method development was presented in DENIN symposium. He is collaborating with Dr. Wallace team on model simulation of C-P bond hydrolysis and rate calculations. Rumana Zahir completed the project on DFT calculations and molecular dynamics simulations with the Gaussian and LAMMPS software packages. She completed MS degree has used these methods to fit a reactive potential for glyphosate which now enables us to perform dynamical simulations of glyphosate degradation pathways. Rumana recently gave a talk on her progress at the Spring 2021 meeting of the American Chemical Society. She defended her master's thesis in Summer 2021 and now a PhD student in Physics at the University of Central Florida. Undergraduate students: Sarah Tuoni has made excellent progress on the characterization of soils P cycling impacted by agricultural use and glyphosate application. She presented her work in two presentations at UD: one Undergraduate Research Celebratory Symposium (Fall 2021) and the other at the DENIN Symposium (Spring 2022). Christopher Townsend. Partially funded in research is working on separating of P from water and purifying and processing for isotopes. His work will involve analyzing multi-isotopes (C, N, PO4) to track sources of phosphorus (inorganic and organic- released from hydrolysis, including glyphosate) into soils and waters. Outcome of his work was presented in the Undergraduate Research Celebratory Symposium (Fall 2021) This year, the project has provided the following opportunities to graduate students supported by this project: Training and experience on isotope biogeochemistry; refined processing of samples and isotope measurements using Raman and NMR and DFT and molecular modeling methods; ii) honing skills by working closely and training undergraduate students, to develop their supervisory and interpersonal skills; iii) further develop management skills by working closely on lab/project management; iv) training students on manuscript writing, highlighting key scientific findings; they will be trained on reviewing the manuscript and critical thinking skills; v) students undergoing Ph.D. and MS defense exams and writing research proposals, here they are trained to developing next career search, and vi) improving speaking and poster/presentation skills. Further training included career preparation, interviews, and planning. Rumana Zahir is now a PhD student in Florida State University and Spencer Moller received another prestigious Wharry Fellowship. Following opportunity was provided to undergraduate student: basic training in separation, quantification of phosphorus pools in soils, instrumentation (UV-VIS, HPLC, mass spectrometry) and related measurement of P and other nutritional elements in soil and water and analysis of water chemistry. How have the results been disseminated to communities of interest?Scientific findings are published in peer-reviewed journals and presented (both invited talks and volunteered presentations) in the professional society meetings and invited talks in the department seminar series. Key interactions include: • Two volumes of special issues on phosphorus cycling published. • Two peer-reviewed publications and one under review and other submitted for peer review (see details in the accomplishment section). • Two invited presentations and three volunteered presentations to professional society meeting and departmental seminar series (see details in the accomplishment section). What do you plan to do during the next reporting period to accomplish the goals?The impact of COVID-19 still lingered significantly in this project year. While the University of Delaware remained fully opened for research under Phase 4 (with minor restrictions) coordination and access among analytical facilities and delay in the supply chain continue to interrupt research. The sluggishness of the research required one more year of NCE, which wasapproved. The project is continuing to progress and achieving the stated milestones. After completing a series of investigations in glyphosate degradation in mono- and bi-mineralcomposition, a more realistic to field condition soil and water from fields was chosen to study next. Here experimental research included natural soil for extraction, quantitation, and isotope analyses that are proposed in the second and third research objectives. Spencer Moller, graduate student completed in the project on enzymatic isotope exchange. He is moving forward on details of glyphosate degradation that include the isotope effect of different enzymes and metal catalysis in glyphosate hydrolysis. An effort will be made to analyze field samples- which requires the collection of significant amounts of field waters and processing and is time-consuming- which is planned to be run in summer 2022. These data will provide an assessment of glyphosate degradation under biotic and abiotic pathways and connect to the field. The reactive force field modeling was completed (Rumana Zahir graduated), which provided suitability and preference of C-P and C-N bond dissociation and calculated rate constants. The DFT calculations of metal-glyphosate interactions for the purpose of extending the glyphosate force field under environmentally relevant metals will be a major focus of the upcoming year. We have a good track of disseminating published works. We will continue to disseminate the research findings in publications, presentations at professional society meetings, and communicating with stakeholders at state and regional levels. Both PIs are dedicated to developing a highly-skilled workforce. The successful placement of past postdocs and graduate students attests to the quality of training, which will be continued.
Impacts
What was accomplished under these goals?
Major research activities and findings of the fourth year of the project are: 1. Progress on controlled experiments, field analyses, and method developments The major emphasis of the fourth year of the project was on third and fourth research objectives. Experiments on single and multi-mineral association catalyzed degradation of glyphosate and rate parameters during catalysis were studied. A part of the work is presented in meeting and written into thesis. Our particular focus was on degradation products and recycling of P released from glyphosate. Below include the details of the key findings. i) Revised the method of extraction and separation of glyphosate and its major metabolites in soil and water is still ongoing. One method adapted from past work was partly successful, the results of were published and reported in past progress report (Sun et al., 2019). ii) Advanced methods of characterization of degradation reactions continues. It includes stable isotopes, Orbitrap and HPLC-MS method, and NMR and Raman spectroscopies. iii) Difference in biotic and abiotic pathways of degradation is being investigated. Series of experiments on enzymatic degradation using C-P lyase and Mn-catalyzed degradation is investigated. Based on the results, the abiotic degradation follows the less toxic product pathway. 2. Progress in DFT modeling: The reactive molecular dynamics we have developed has been used to simulate C-P and C-N bond breaking pathways in glyphosate. From these simulations we have obtained free energy landscapes that enable us to ascertain which types of degradation pathways may be dominant under certain conditions. Our results indicate that the preferred mechanism of glyphosate degradation may depend upon the zwitterionic form of glyphosate that is dominant in the environment. In all our simulations, the GLY/MPA reaction pathway was favored over the traditional AMPA pathway. However, when the form of glyphosate contained a fully deprotonated phosphonate group, the sarcosine pathway was significantly favored over both the GLY/MPA and AMPA pathways. When the singly protonated zwitterion was present, our results indicate that the GLY/MPA and AMPA pathways are favored over the sarcosine pathway. This suggests that solution pH may exhibit some control over the preferred degradation pathway, with the GLY/MPA and AMPA pathways preferred below pH ~6 and the sarcosine pathway preferred under more alkaline conditions. To further substantiate these findings, we plan to perform additional higher-level DFT calculations of the reaction pathways. Graduate student Spencer Moller is also performing kinetic experiments that may enable us to obtain the activation energies associated with each reaction pathway, and which can be used to evaluate the accuracy of our modeling efforts. 3. Other activities: • Progress has been made in Orbitrap-based method for isotope measurement for the identification of glyphosate molecule and its byproducts (this will continue in the final NCE year of the project). • A major instrumentation proposal (UD DOE) is submitted (pending). Another instrument proposal to USDA-EGP was submitted (was not funded). Both proposals included preliminary data generated from this award and helped strengthen the quality of proposal. • Continued collaborations with researchers outside UD: Ralf Greiner (Max Rubner-institut, Germany); Gulnihan Ozbay (Delaware State University), Philip Larese-Casanova (Northeastern University), Ludmilla Aristilde (Northwestern University), David O'Connell (Trinity College, Ireland), Charles Brierley (East Angelia University, UK). These research collaborations are centered on method development, preparation of labeled compounds and enzyme purification, and help us connect research on herbicide and related organic phosphorus compounds that are present in the environment. • UD collaborations with Neil Sturchio, Donald Sparks, Wei-Jun Cai, and Andrew Wozniak have aided field access for field sampling (which is often challenging for glyphosate sampling study). • Rumana Zahir, fully funded by this project graduated with MS thesis in summer 2021. • Spencer Moller, funded student in this project, received a prestigious Warry Fellowship (he received DENIN Fellowship before), continues to work on the project. • Two undergrads (Sarah Tuoni and Chris Townsend) are trained in the P-cycling aspect of the project and their works have been presented in the university undergraduate symposium related to field studies (progress will be reported next year). Integration of educational activities to research activities: Two major ways used to integrate educational activities on research done on this project year are: i) Incorporated some of the research findings into the course 'PLSC 405: Environmental Forensics and Society'. It included a field trip to a heavily glyphosate used field in the state and the watershed where the herbicide is drained off and discussed its potential fate. Students took assignments on searching reports and analyzing data on herbicidal usages in agriculture in the state and identifying safer ways to maintain healthy crops and save the environment. ii) Incorporated new methods on isotope analysis using orbitrap for glyphosate and other organic compounds in the existing graduate course (PLSC 645: Biogeochemical Cycling of Nutrients).
Publications
- Type:
Books
Status:
Published
Year Published:
2021
Citation:
Ross, D., Young, E and Jaisi, D. (2021). Challenges and successes in identifying transfer and transformation of phosphorus from soils to open waters and sediments. Special issue in Soil Systems. MDPI.
- Type:
Books
Status:
Published
Year Published:
2021
Citation:
Yan, X., Zhao, X., and Jaisi, D. (2021). Agricultural and Environmental Challenges in Agroecosystem. Special issues in Pedosphere.
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Young, E.O., Ross, D. S., Jaisi, D.P., and Vidon, P.G. (2021). Closing phosphorus transport gaps along the croplandriparianstream continuum in cold climate agroecosystems of the USA: A review. Soil System, 5, 1-5.
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Yan, X., Zhao, X., and Jaisi, D. (2021). Agricultural and Environmental challenges in the agroecosystem. Preface to the Special volume. Pedosphere, 31, 1-2.
- Type:
Book Chapters
Status:
Published
Year Published:
2022
Citation:
Jaisi, D.P., Mingus, K.A., Joshi, S.R., Upreti, K., Sun, M., McGrath, J., and Massudieh, A. (2022). Linking sources, transformation, and loss of phosphorus in the soil-water continuum in a coastal environment. In Multi-scale biogeochemical processes in soil ecosystems: Critical reactions and resilience to climate changes (Yu Yang, Marco Keiluweit, Nicola Senesi, and Baoshan Xing, editors).
- Type:
Journal Articles
Status:
Under Review
Year Published:
2021
Citation:
Moller, S., Sakhno, Y., Aristilde, L., Blake, R.E., and Jaisi, D. Evolution of oxygen isotopologues in phosphate and pyrophosphate during enzyme-catalyzed isotopic exchange reactions. ACS Earth and Space Chemistry (under review).
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2021
Citation:
Zahir, R. (2021). Development of a ReaxFF force field for glyphosate. MS thesis, Department of Geological Sciences, University of Delaware, 71 pp.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Jaisi, D.P. Source, cycling, and impact of phosphorus loading in the Chesapeake Bay. Department of Fishery Sciences, Auburn University, Auburn, AL (Apr 8, 2022) [Invited Departmental Seminar]
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Jaisi, D.P. Tracing the sources of phosphorus in the Love Creek Watershed, Delaware. Center for the Inland Bay (CIB) (Oct 26, 2021) [Invited Talk]
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Aristilde, L., Jaisi, D.P. Elucidation of hierarchical phytase-catalyzed phosphorus recycling from organic mixtures using high-resolution mass spectrometry coupled with molecular docking simulations. ACS Fall Meeting (Aug 22-27, 2021), Atlanta GA [Invited]
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Li, H., Sun, M., Wallace, A., Moller, S., and Jaisi, D.P. Degradation of glyphosate in water, mineral surface, and soil. Goldschmidt (July4-9, 2021), Virtual.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Moller, S., Sakhno, Y., Stout, L., and Jaisi, D.P. Oxygen isotope effect during synthesis and degradation of adenosine trisphosphate (ATP). ACS Fall Meeting (Aug 22-27, 2021), Atlanta GA
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Moller, S.R., Sun, M., Li, H., Wallace, A., and Jaisi, D.P. Pathways of glyphosate degradation and potential bias towards less toxic products. Soil Science Society of America Annual meeting, (Nov 07-10, 2021), Salt Lake City, UT.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Zahir, R., Quadery, A., and Wallace, A.F., Development of a ReaxFF force field for glyphosate. Spring Meeting of the American Chemical Society (April 5-30, 2021), virtual
|
Progress 06/01/20 to 05/31/21
Outputs
Target Audience:Academics; farmer and commodity groups; federal, state and local government, and herbicidal industry and manufacturers, stakeholders on the soil health Changes/Problems:The COVID-19 had a significant impact on project personnel (student and their family). The sluggishness of the research required one year of NCE, which was applied and approved in early 2021. Pending how the post-COVID activities go, we might need to request for a second NCE. What opportunities for training and professional development has the project provided?The major opportunities provided to researchers are as follows: Spencer Moller (PhD student, intake Fall 2018) completed his candidacy exam in Jul 2020 and now well versed in key analytical tools, including IRMS, NMR, and Raman. His work on isotope methods to discriminate glyphosate-derived P is encouraging. Outcomes of this project on rapid method of detecting and measuring isotopes in phosphate is submitted for peer review. The outcome of his related research on method development was presented in DENIN symposium. He is collaborating with Dr. Wallace team on model simulation of C-P and C-N bond hydrolysis. Rumana Zahir(MS student) has been trained to perform DFT calculations and molecular dynamics simulations with the Gaussian and LAMMPS software packages, respectively. She has used these methods to fit a reactive potential for glyphosate which now enables us to perform dynamical simulations of glyphosate degradation pathways. Rumana recently gave a talk on her progress at the Spring 2021 meeting of the American Chemical Society. She is planning on defending her master's thesis in Summer 2021. Margaret Musser(MS student) Partially funded in research (not in stipend) completed the master's degree on source tracking of phosphorus (including glyphosate) in a watershed in Delaware. Her work involved using multi-isotopes (C, N, PO4) to track sources of phosphorus (inorganic and organic- released from hydrolysis, including glyphosate). Outcomes of her work werepresented at Goldschmidt 2020 conference. This year, the project has provided the following opportunities to graduate students supported by this project: Training and experience on isotope biogeochemistry; refined processing of samples and isotope measurements using Raman and NMR and DFT and molecular modeling methods; ii) honing skills by work closely and train undergraduate students, to develop their supervisory and interpersonal skills; iii) further develop management skills by working closely on lab/project management; iv) training students on manuscript writing, highlighting key scientific findings; they will be trained on reviewing the manuscript and critical thinking skills; v) students undergoing Ph.D. and MS candidacy exams and writing research proposals, here they are trained to developing research questions and research hypotheses, and vi) improving speaking and poster/presentation skills. Further training included career preparation, interviews, and planning. Margaret Musser landed a job in a reputed consulting firm and Spencer Moller received a prestigious DENIN Fellowship. While this will evolve over time, both PIs are highly committed and have track records of taking additional approaches as needed to achieve these goals for the students. How have the results been disseminated to communities of interest?Scientific findings are published in peer-reviewed journals and presented in the department seminar series. Key interactions include: Two peer-reviewed publications (paper and book chapter) and one submitted manuscript (see details in the accomplishment section). Two presentations to professional society meetings (see details in the accomplishment section). What do you plan to do during the next reporting period to accomplish the goals?The COVID-19 had a significant impact on project personnel (student and their family). By the Phase 3 opening at the University of Delaware in mid-June, lab members had full access to the laboratory. However, coordination and access needed to analytical facilities in the university and delay in the supply chain caused significant interruption of research. We are in the almost full resumption of research activities since early 2021, which has helped move forward the research plans. The sluggishness of the research required one year of NCE, which was applied and approved in early 2021. Besides the delay mentioned above, the project is at a good pace and in tune to meet stated milestones. It might need a second NCE pending how the progress goes after COVID recovery. After completing a series of investigations in glyphosate degradation in mono- and bi-mineral composition, a more realistic field condition soil and water from fields was chosen to study next. Here experimental research included natural soil for extraction, quantitation, and isotope analyses that are proposed in the second and third research objectives. Spencer Moller completed the first project on enzymatic isotope exchange. This has delved research into the details of glyphosate degradation. He will investigate the isotope effect of different enzymes, substrate, and cofactor-related reaction kinetics and fractionations in glyphosate hydrolysis besides analyzing field samples. These data will provide an assessment of glyphosate degradation under biotic and abiotic pathways and connect to the field. With the fitting of our reactive glyphosate force field nearing completion, we plan to perform simulations of C-P and C-N bond dissociation and to compute rate constants and activation energies for each degradation reaction. We have already begun performing DFT calculations of metal-glyphosate interactions for the purpose of extending the glyphosate force field to include environmentally relevant metals. In the next NCE year, we aim to use DFT and the reactive glyphosate force field to assess the influence of metals on the rates of the C-P and C-N dissociation reactions. Research findings will be disseminated via publication, presentations at professional society meetings, stakeholders at state and regional levels. Both PIs are dedicated to developing a highly skilled workforce. Placement of past postdocs and graduate students attests to the quality of training, which will be continued.
Impacts
What was accomplished under these goals?
Major research activities and findings of the second year of the project included: Progress on experimental and method development The specific focus of the third year of the project included the continuation of work done in the second year, which spread over three research objectives. Experiments on single and multi-mineral association catalyzed degradation and soil incubation where biotic degradation predominates were completed and results published before. Our particular focus was on degradation products and recycling of P released from glyphosate. Below include the details of the key findings. Revised the method of extraction (still ongoing) and separation of glyphosate and its major metabolites in soil and water and been used to extract and quantify glyphosate from environmental samples. While the environmental matrices are unique for each site and pose a unique challenge, new techniques using Orbitrap and HPLC-MS method has higher promise. Advanced methods of characterization of isotope exchange are developed using NMR and Raman methods. We found that the equilibrium fractionation value determined by the spectroscopic methods was within 2-3 permil to that measured by sensitive isotope ratio mass spectrometry methods. Therefore, Raman and NMR methods can be applied for rapid and low-cost monitoring of the oxygen isotope exchange rate between phosphate isotopologue and water. This could serve as an additional proxy for enzyme activity and glyphosate-derived P cycling in the environment. Progress in DFT modeling We have made significant progress towards the development of a new reactive force field for glyphosate. Although several classical non-reactive force fields for glyphosate exist in the literature, these do not enable the study of bond-breaking mechanisms or degradation pathways. Our newly developed ReaxFF force field is a step in this direction. At the time of our last report, we had chosen to refit a reactive model by Bedrov et al., 2012 which was designed for ethylene carbonate. Although we had obtained a good empirical fit of the model to DFT, we found that orthophosphate was unstable during dynamical simulations of C-P bond dissociation. To correct for this, we continued parallel efforts with a ReaxFF force field that was originally developed for glycine (Rahaman et al., 2012). The glycine force field did not have a C-P interaction defined in it. However, the previous fit that we performed with the Bedrov et al. force field enabled us to incorporate the C-P interaction terms that we developed previously into the glycine force field prior to fitting. To fit this new model, we extended our DFT training set to include the DFT energy curves for the C-P distance, C-P-O and N-C-P angles, and the C-P-O-H and N-C-P-O dihedral angles. For dynamic validation, we performed molecular dynamics simulations of the most abundant zwitterionic forms of glyphosate in natural waters. All bond lengths and angles were found to be consistent with experimentally observed values. Moreover, both glyphosate and orthophosphate were found to be stable with this new force field. We have also performed preliminary free energy calculations to obtain the energy barriers associated with C-N and C-P bond dissociation. These preliminary findings predict that the C-P bond dissociation barrier is ~20 kcal/mol (consistent with our previous DFT calculations of the sarcosine pathway) and that the C-N dissociation pathways leading to the formation of AMPA and MPA are 45 and 35 kcal/mol, respectively. Other activities: Initiated a new method for using Orbitrap-based method for isotope measurement for the identification of glyphosate molecule and its byproducts. A major instrumentation proposal (EGP-USDA) submitted. It included preliminary data generated from this award. Collaborations with researchers outside UD: Gulnihan Ozbay (Delaware State University), Philip Larese-Casanova (Northeastern University), Ludmilla Aristilde (Northwestern University), David O'Connell (Trinity College, Ireland), Charles Brierley (East Angelia University) have been instrumental in method development and connecting research on herbicide and other organic phosphorus compounds. UD collaborations with Neil Sturchio, Donald Sparks, Wei-Jun Cai, and Andrew Wozniak have aided field access for field sampling (which is often challanging for glyphosate sampling study) and initiated collaborative research. Margaret Musser, partially supported in research, completed MS thesis and graduated in summer 2020. Spencer Moller, funded student in this project, received a prestigious DENIN Fellowship, a highly competitive university-wide fellowship for PhD students. Two undergrads are trained in the project related to field studies (progress will be reported next year). Integration of educational activities to research activities. Two major ways used to integrate educational activities on research done on this project year are: Incorporated some of the research findings into the course 'PLSC 405: Environmental Forensics and Society'. It included a field trip to heavily glyphosate used fields in the state and the watershed where is drained off and the potential fate discussed. Students took assignments on finding reports and analyzing data herbicidal uses in agriculture in the state and identify safer ways to maintain healthy crops and save the environment. Incorporated new methods on isotope analysis using orbitrap for glyphosate and other organic compounds in the existing graduate course (PLSC 645: Biogeochemical Cycling of Nutrients). A representative abstractfrom a manuscript is included below: Evolution of oxygen isotopologues in phosphate and pyrophosphate during enzyme-catalyzed isotopic exchange reactions. Talanta (submitted). Inorganic pyrophosphatase (PPase) is an enzyme that catalyzes the hydrolysis of the phosphoanhydride bond in pyrophosphate (PPi) to release inorganic phosphate (Pi) and simultaneous exchange of oxygen isotopes between Pi and water. Here we quantified the exchange kinetics of oxygen isotopes between the five Pi isotopologues (P18O4, P18O316O, P18O216O2, P18O16O3, and P16O4) and water using Raman and 31P nuclear magnetic resonance (NMR) during PPase-catalyzed 18O -16O isotope exchange reaction in Pi-water and PPi-water systems. At high PPi concentrations (300 mM), hydrolysis of PPi by PPase was predominant, and only a small fraction of PPi (<<1%) takes part in the reversible hydrolysis-condensation reaction (PPi ↔Pi), leading to the oxygen isotope exchange between Pi and water. We found that the equilibrium fractionation value determined by the spectroscopic methods was within 2-3 permil to that measured by sensitive isotope ratio mass spectrometry methods. Therefore, Raman and NMR methods can be applied for successful monitoring the oxygen exchange rate between Pi isotopologue and water, which could serve as an additional proxy for enzyme activity and P cycling in the environment.
Publications
- Type:
Journal Articles
Status:
Submitted
Year Published:
2021
Citation:
Moller, S., Sakhno, Y., Aristilde, L., Blake, R.E., and Jaisi, D.P (2021). Evolution of oxygen isotopologues in phosphate and pyrophosphate during enzyme-catalyzed isotopic exchange reactions. Talanta (submitted).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Zahir, R., Quadery, A., and Wallace, A.F., Development of a ReaxFF force field for glyphosate. Spring Meeting of the American Chemical Society, April 5-30, 2021.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Musser, M. and Jaisi, D. Phosphorus sources, bioavailability, and cycling in the Murderkill River, Delaware. Goldschmidt 2020 (virtual), Jun 21-26, 2020.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Moller, S., Sakhno, Y., and Jaisi, D. Enzyme-catalyzed exchange of oxygen isotopes in phosphate, glyphosate, and pyrophosphate. DENIN Symposium, March 10, 2021.
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Bai, Y., Stout, L., Unal-Tosun, G., Li, J., and Jaisi, D.P. (2020): Synthesis and degradation of polyphosphate: Isotope effects in enzyme- and bacteria-catalyzed reactions. ACS Earth and Space Chemistry, 12, 23272336
- Type:
Book Chapters
Status:
Accepted
Year Published:
2021
Citation:
Jaisi, D.P., Mingus, K.A., Joshi, S.R., Upreti, K., Sun, M., McGrath, J., and Massudieh, A. (2021). Linking sources, transformation, and loss of phosphorus in the soil-water continuum in a coastal environment. In Multi-scale biogeochemical processes in soil ecosystems: Critical reactions and resilience to climate changes (Yu Yang, Marco Keiluweit, Nicola Senesi, and Baoshan Xing, editors).
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Progress 06/01/19 to 05/31/20
Outputs
Target Audience:Academics; farmer and commodity groups; federal, state and local government, and herbicidal industry and manufacturers, stakeholders on the soil health Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The major opportunities provided to researchers are as follows: Spencer Moller (PhD student, intake Fall 2018) is being trained on isotope methods and forms and fate of glyphosate and its products. The outcome of her first research is presented in the SSSA meeting in Nov 2019. He is working in PhD candidacy exam in Summer 2020 and will focus on the experimental part of the project from late summer. Mingjing Sun (postdoc, unfunded participant) worked on soil incubation with glyphosate to degradation of glyphosate and transformation of phosphorous (P) product in a soil-water system. The LC-MS and ESI-Orbitrap MS results showed that glycine formed during the early stage but was rapidly utilized by soil microorganisms. Dr. Sun is now a tenure-track faculty position at Emporia State University, KY. June Hazewski (M.S. student) worked on the project during the Summer of 2019 to train incoming graduate student Rumana Zahir to perform DFT calculations on glyphosate. Ms. Hazewski previously screened available ReaxFF potentials in the literature for their applicability to glyphosate. Rumana Zahir (M.S. student) began working on the project in the Summer of 2019 and has continued on the project since starting her M.S. program in Fall 2019. Rumana has worked with another student (June Hazewski) who trained Ms. Zahir to perform DFT calculations. Ms. Zahir has also received training from co-PI Wallace and postdoc Abrar Quadery (unfunded project participant) on the performance of molecular dynamics simulations and on the parameterization of ReaxFF force fields. Abrar Quadery (postdoc, unfunded participant) Dr. Quadery's expertise is in the use and refinement of ReaxFF potentials for molecular dynamics simulations. Dr. Quadery's main involvement in the project is in the refitting of a ReaxFF potential for glyphosate alongside Ms. Zahir. This year, the project has provided the following opportunities to graduate students and postdoc associates supported by this project: i) Training and experience on isotope biogeochemistry; refined processing of samples and isotope measurements and DFT and molecular modeling methods; ii) honing skills by work closely and train undergraduate students, to develop their supervisory and interpersonal skills; iii) further develop management skills by working closely on lab/project management; iv) training students on manuscript writing, highlighting key scientific findings; they will be trained on reviewing the manuscript and critical thinking skills; v) students undergoing Ph.D. and MS candidacy exams and writing research proposals, here they are trained to developing research questions and research hypotheses, and vi) improving speaking and poster/presentation skills. Mingjing Sun landed on a tenure track faculty position. While this will evolve over time, both PIs are highly committed and have track records of taking additional approaches as needed to achieve these goals for the students. How have the results been disseminated to communities of interest?Scientific findings are published in peer-reviewed journals and presented in the department seminar series. Key interactions include: Two peer-reviewed publications in Water Research ACS Earth and Space Chemistry (see details in the accomplishment section). One presentation to professional society meeting (see details in the accomplishment section). What do you plan to do during the next reporting period to accomplish the goals?The project is in good pace and meeting stated milestones. After completing a series of investigations in mono- and bi-mineral composition, a more realistic to field condition, soil was chosen. Here experimental research included natural soil for extraction, quantitation and isotope analyses that are proposed in second and third research objectives. Graduate student for experimental research is trained in general biogeochemistry and isotope methods. His first project on enzymatic degradation of organic P compounds is wrapping up and delved into the details of glyphosate degradation. He will investigate the isotope effect of different enzymes, substrate and cofactor related reaction kinetics and fractionations. These data will provide an assessment of glyphosate degradation under biotic and abiotic pathways. In the next reporting period, we aim to complete our fitting of the ReaxFF force field for glyphosate. To do so we will be expanding the size of the fitting training set beyond the current minimal set of configurations to include additional DFT results for glyphosate and its degradation products. Upon completion of the fitting process, we will perform molecular dynamics simulations of various degradation pathways in solution. From these simulations, we will obtain free energy landscapes for competing for glyphosate degradation pathways and be able to estimate the relative rates of passage through each. We will also introduce certain cations into the simulations, which may play a role in the selection of the degradation pathway. These cations will also be used in our tandem experimental efforts to characterize the influence of ions on glyphosate degradation. Research findings will be disseminated via publication, presentations at professional society meetings, stakeholders at state and regional levels. Both PIs are dedicated to developing a highly-skilled workforce. Placement of past postdocs and graduate students attest the quality of training. More training and activities will be planned in the coming years as the project continues.
Impacts
What was accomplished under these goals?
Major research activities and findings of the second year of the project included: The specific focus of the second year of the project included addressing all three research objectives. It included single mineral catalyzed degradation as well as multi-mineral associations and to soil incubation where biotic degradation predominates. We used liquid chromatography-mass spectrometry (LC-MS) and electrospray ionization (ESI) source Q Extractive Orbitrap mass spectrometry (ESI-Orbitrap MS) to identify glyphosate degradation products and combined with sequential extraction and stable isotopes to investigate the degradation of glyphosate and transformation of phosphorous (P) product in a soil-water system. Our particular focus was on degradation product and recycling of P released from glyphosate. Below include the details of the key findings. i) A satisfactory method of extraction and separation of glyphosate and its major metabolites in soil was developed, which could be used to identify the fate of glyphosate in a variety of environments. The absence of degradation in sterilized soil showed the soil microorganisms play an essential role in the degradation of glyphosate. The temporal presence of glycine and AMPA varied as well as their microbial uptake and degradation. AMPA was found to be 3e6 times resistant than glyphosate against degradation, which brings a higher concern to the safety of the environment. ii)The distribution of glyphosate-derived Pi in a soil was investigated. About half of the glyphosate-derived Pi transferred into the readily bioavailable P pool. A slow but steady release of Pi from the degradation of glyphosate could mean that its supply could be slightly more synchronous with plant P demand during plant growth especially because it is applied more than one time during a crop cycle. This means that a higher proportion of glyphosate-derived P, than P from commercial fertilizers which release P all at once, could be taken up by plants. iii)Glyphosate-derived Pi has a distinct isotopic signature and can aid in the identification of its source. The natural environment, however, is complex and could pose additional challenges, most likely due to the low content of glyphosate and inappropriate sampling time could miss detecting significant offset of isotope values. This is because the isotope signature could be erased or overprinted due to the biological cycling of glyphosate-derived P. iv)?18O-labeling in water and application of phosphate oxygen isotope method allowed an explicit understanding of microbial uptake and extent of biological turnover of glyphosate derived- P. The microbial turnover of original P in soil and glyphosate derived P was comparable, but it was found that the microorganisms were more efficient to utilize and recycle glyphosate derived P. The research tool developed could be further used to investigate the extent of microbial activities in soils and other natural environments For more environmentally relevant minerals, the role of Mn-coatings on ferrihydrite mineral to degrade glyphosate varies with Mn:Fe molar ratios. Experiments with ferrihydrite/d-MnO2 composites --relevant to their relative natural abundance--Competition between sorption versus degradation was controlled by the molar ratio of Mn and Fe. For example, at low Mn/Fe ratios (<0.0167), the dominant mechanism of glyphosate removal from the aqueous solution was through sorption by ferrihydrite, although the extent of removal was low. Progress in DFT modeling: To date, theoretical investigations of glyphosate degradation have utilized quantum mechanical methods exclusively, namely, density functional theory calculations (DFT). While these methods promise high accuracy, they are best suited to the treatment of a small number of atoms, and incorporation of hydration effects is challenging. In our current efforts, we are developing a reactive classical force field (ReaxFF) to enable undertaking simulations of glyphosate degradation in more expansive environments, including bulk solvent. An initial survey of the literature showed that existing ReaxFF force fields developed for systems with C-P bonds do not adequately describe the C-P interaction in glyphosate. Wecomparedthe potential energy of glyphosate as a function of the C-P distance computed by DFT with potential energies obtained from the existing ReaxFF models. As Bedrov et al.'s potential model were most similar to our DFT result, we chose to refit this model to the DFT derived potential energy curve for glyphosate. The current state of the refit model is a much better agreement between the ReaxFF and DFT C-P potential energy curves. We have performed some preliminary molecular dynamics simulations of glyphosate in a solution using this potential, but are continuing to refine the model to improve the value of the ReaxFF C-P bond length compared to DFT. One most representative abstracts from the published paper is included below: Degradation of glyphosate and bioavailability of phosphorus derived from glyphosate in a soil-water system. Water Research 2019, 163, 11480. Glyphosate, the most commonly used herbicide in the world, can be degraded into more toxic and persistent products such as aminomethylphosphonic acid (AMPA) or non-toxic products such as sarcosine and glycine. In this study, we used liquid chromatography-mass spectrometry (LC-MS) and electrospray ionization (ESI) source Q Extractive Orbitrap mass spectrometry (ESI-Orbitrap MS) to identify glyphosate degradation products and combined with sequential extraction and stable isotopes to investigate the degradation of glyphosate and transformation of phosphorous (P) product in a soil-water system. The LC-MS and ESI-Orbitrap MS results showed that glycine formed during the early stage but was rapidly utilized by soil microorganisms. AMPA started to accumulate at the late stage and was found to be 3-6 times more resistant than glyphosate against degradation, while no sarcosine was formed. The 18O labeling and phosphate oxygen isotope results allowed a clear distinction of the fraction of inorganic P (Pi) derived from glyphosate, about half of which was then rapidly taken up and recycled by soil microorganisms. Our results provide the first evidence of the preferential utilization of glyphosate-derived Pi by microorganisms in the soil-water system. The rapid cycling of Pi derived from this disregarded source has important implications on nutrient management as well as water quality. ??
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Sun, M., Li, H., and Jaisi, D.P. (2019). Degradation of glyphosate and bioavailability of phosphorus derived from glyphosate in a soil-water system. Water Research, 163, 114840
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Li, H., and Jaisi, D.P. (2019). Competition of sorption and degradation reactions during glyphosate degradation by ferrihydrite/delta manganese oxide composite. ACS Earth and Space Chemistry 3,1362?1370.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Moller, S., Sakhno, Y., and Jaisi, D.P. Enzyme-catalyzed inorganic pyrophosphate hydrolysis reveals position-specific oxygen isotope exchange. Soil Science Society of America Annual Meeting, San Antonio. Nov 10-14, 2019.
|
Progress 06/01/18 to 05/31/19
Outputs
Target Audience:Academics; farmer and commodity groups; federal, state and local government, and herbicidal industry and manufacturers, stakeholders on the soil health Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The major opportunities provided to researchers are as follows: Hui Li (Ph.D. student, degree completed in 2018) undertaking major portion of this research using conventional and advanced characterization methods for glyphosate degradation research. Her research is published in two peer reviewed publications. She is now at UMass Amherst for her postdoctoral research. Spencer Moller (PhD student, intake Fall 2018) is being trained on isotope methods and forms and fate of glyphosate and its products. The outcome of her first research is going to be presented at the SSSA meeting in Nov 2019. He continues to work on this project in next project year. June Hazewski (MS student, intake Fall 2017) worked during the Summer of 2018 to assess the suitability of existing reactive classical molecular dynamics force fields for glyphosate degradation. Her work revealed some deficiencies in these models that a newly recruited student will address (beginning Fall 2019). This year, the project has provided following opportunities to two graduate students supported by this project: i) Training and experience on isotope biogeochemistry; refined processing of samples and isotope measurements; ii) honing skills by work closely and train undergraduate students, to develop their supervisory and interpersonal skills; iii) further develop management skills by working closely on lab/project management; iv) training students on manuscript writing, highlighting key scientific findings; they will be trained on reviewing manuscript and critical thinking skills; v) both students undergoing Ph.D. and MS candidacy exam and writing research proposal, here they will be trained to developing research questions and research hypotheses, and vi) improving speaking and poster/presentation skills. While this will evolve over time, both PIs are highly committed and have track records of taking additional approaches as needed to achieve these goals for the students. How have the results been disseminated to communities of interest?Scientific findings are published in peer reviewed journals and presented in the department seminar series. Key interactions include: Three peer-reviewed publications in Environmental Science & Technology and ACS Earth and Space Chemistry (see details in the accomplishment section). One invited talk at the University of Massachusetts, Amherst (see details in the accomplishment section). What do you plan to do during the next reporting period to accomplish the goals?The project has a good start and next stage of experimental research include natural soil for extraction, quantitation and isotope analyses that are proposed in second and third research objectives. A new graduate student (Rumana Zahir), will join the project in Fall 2019. She has been hired to investigate potential reaction pathways for glyphosate degradation using DFT methods. She will also obtain theoretical isotope fractionations associated with candidate reaction pathways. These data will be used to update a force field model for reactive classical molecular dynamics simulations of glyphosate and its degradation products in water. Ms. Zahir will also investigate the utility of new machine learning tools for predicting glyphosate degradation pathways (e.g., Coley et al., Prediction of Organic Reaction Outcomes Using Machine Learning, ACS Cent. Sci. 2017 35434-443; DOI: 10.1021/acscentsci.7b00064). Research findings will be disseminated via publication, presentations at professional society meetings; stakeholders at state and regional level. Both PIs are dedicated to developing the highly skilled workforce. More training and activities will be planned in coming years as the project continues.
Impacts
What was accomplished under these goals?
Major activities of the first year of the project included: Specific focus of the first year of the project included addressing research objective listed in the Axis 1: biotic and abiotic degradation and isotope discrimination of degradation products. It included single mineral catalyzed degradation as well as multi-mineral associations to a series of ratios relevant to soil environment. Below include the details of the activities Glyphosate degradation along the two major degradation pathways (via AMPA and sarcosine intermediates), and oxygen isotope effect during degradation and the relationship of sources and products were analyzed. On the basis of the product and pathways, mechanisms of bond cleavage during degradation was proposed. Among the product identified, sarcosine is always illusive and remained to be tested whether it is a necessary product. So we performed series of careful studies that aimed to identify and quantify degradation products, with a special focus on sarcosine, glycine, and AMPA, during the degradation of glyphosate by a synthetic birnessite. Series of advanced methods including one? and two-dimensional (1?D and 2-D) nuclear magnetic resonance (NMR) spectroscopy, high-performance liquid chromatography (HPLC) and density function theory (DFT) modeling were applied as major research methods along with colorimetric methods to identify and quantify products. Based on these results, we discuss the relative significance of the degradation pathways, and implication of results for further investigation on glyphosate degradation towards a preferential pathway generating less toxic products in the environment. For more environmentally relevant minerals, we sought to identify the role of Mn-coatings on ferrihydrite mineral to degrade glyphosate. To do so, ferrihydrite/d-MnO2 composites were synthesized at various Mn:Fe molar ratios--relevant to their relative natural abundance. We investigated the structural and morphological characteristics of the ferrihydrite/d-MnO2 composites and to determine the competitive sorption vs. degradation of glyphosate at various Mn:Fe ratios and the main degradation pathways. The major research findings include: Two most representative abstracts from published papers are included below: Degradation of glyphosate by Mn-oxide may bypass sarcosine and form glycine directly after C−N bond cleavage. Environ. Sci. Technol. 2018, 52, 1109−1117; DOI: 10.1021/acs.est. 7b03692) Glyphosate is the active ingredient of the common herbicide Roundup. The increasing presence of glyphosate and its byproducts has raised concerns about its potential impact on the environment and human health. In this research, we investigated abiotic pathways of glyphosate degradation as catalyzed by birnessite under aerobic and neutral pH conditions to determine whether certain pathways have the potential to generate less harmful intermediate products. Nuclear magnetic resonance (NMR) spectroscopy and high-performance liquid chromatography (HPLC) were utilized to identify and quantify reaction products, and density functional theory (DFT) calculations were used to investigate the bond critical point (BCP) properties of the C−N bond in glyphosate and Mn(IV)-complexed glyphosate. We found that sarcosine, the commonly recognized precursor to glycine, was not present at detectable levels in any of our experiments despite the fact that its half-life (∼13.6 h) was greater than our sampling intervals. Abiotic degradation of glyphosate largely followed the glycine pathway rather than the AMPA (aminomethylphosphonic acid) pathway. Preferential cleavage of the phosphonate adjacent C−N bond to form glycine directly was also supported by our BCP analysis, which revealed that this C−N bond was disproportionately affected by the interaction of glyphosate with Mn(IV). Overall, these results provide useful insights into the potential pathways through which glyphosate may degrade via relatively benign intermediates. Competition of sorption and degradation reactions during glyphosate degradation by ferrihydrite/delta manganese oxide composite. ACS Earth and Space Chemistry (accepted) Ever since its introduction into the herbicidal industry in the 1970s, glyphosate has been a very effective weed control herbicide and its application has steadily increased; however at the same time, its toxicity has been increasingly questioned. In the present research, ferrihydrite/d-MnO2 composites were synthesized at different Mn:Fe molar ratios and competition of sorption and degradation of glyphosate on these minerals was analyzed using colorimetric, nuclear magnetic resonance (NMR), and high-performance liquid chromatography (HPLC) methods. Our results showed that the degradation of glyphosate was accomplished exclusively by d-MnO2, while both ferrihydrite and d-MnO2 played important roles in the sorption processes. The difference, however, is that glyphosate sorbed onto d-MnO2 underwent rapid degradation. Competition between sorption vs. degradation was controlled by the molar ratio of Mn and Fe. For example, at low Mn:Fe ratios (<0.0167), the dominant mechanism of glyphosate removal from the aqueous solution was through sorption by ferrihydrite, although the extent of removal was low. When the Mn:Fe ratio was higher than 0.0167, the degradation reaction dominated. The direct C-P bond cleavage to generate glycine was the major degradation pathway and the AMPA (aminomethylphosphonic acid) pathway was minor. Changes in the Mn:Fe ratios incurred no detectable influence on the preference for either of the two degradation pathways. Present results highlighted the additive effects of the two oxides that are commonly present in soils on the degradation and sorption of glyphosate and thus reducing the negative impacts of glyphosate in the environment.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2018
Citation:
Li, H., Wallace, A., Sun, M., Reardon, P., and Jaisi, D.P. (2018). Degradation of glyphosate by Mn?oxide may bypass sarcosine and form glycine directly after C-N bond cleavage. Environmental Science & Technology, 52, 11091117.
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Li, H., and Jaisi, D.P. Competition of sorption and degradation reactions during glyphosate degradation by ferrihydrite/delta manganese oxide composite. ACS Earth and Space Chemistry (accepted).
- Type:
Other
Status:
Other
Year Published:
2019
Citation:
Invited talk: Li, H. and Jaisi, D.P. Degradation of glyphosate by Mn?oxide: Role of catalysts and isotope fingerprinting methods of tracking phosphate derived from glyphosate. Fall seminar series, University of Massachusetts, Amherst, MA, 2018.
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2018
Citation:
Li, H. Degradation of glyphosate by Mn-oxides: Mechanisms,
pathways, and source tracking. PhD dissertation, University of Delaware. 2018
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