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Reduction of Mesotrione in Aquifers and Surface Waters

Reduction of Mesotrione in Aquifers and Surface Waters. Amber Grandprey Chem 4101 10 Dec 2010. Background on Mesotrione. Mesotrione is part of the triketone class of pesticides. Approximately 150,000 lbs of mesotrione has been sold over the past six years in Minnesota alone.

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Reduction of Mesotrione in Aquifers and Surface Waters

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  1. Reduction of Mesotrione in Aquifers and Surface Waters Amber Grandprey Chem 4101 10 Dec 2010

  2. Background on Mesotrione • Mesotrione is part of the triketone class of pesticides. • Approximately 150,000 lbs of mesotrione has been sold over the past six years in Minnesota alone. • Because of its widespread use, mesotrione finds its way into aquifers and surface waters, which can have effects on families as well as industrial and commercial practices which require groundwater. • The reaction is mediated by iron mineral surfaces found naturally in aquifers and surface waters. • The reduction of a similar compound, trifluralin, has been studied by a professor here at the University of Minnesota, Bill Arnold.

  3. Degradation of Mesotrione • Mesotrione is known to degrade into two compounds: MNBA and AMBA. • The kinetics and effects on the sediment of the environment as an effect of this degradation are still unknown.

  4. Hypothesis Hypothesis • The degradation of mesotrione causes changes in the sediment mineralogy of aquifers and surface water. These changes are in response to continual exposure to oxidized contaminants in the water system, which allows for the development of pseudo-steady state reactivity. Significance of Solving Problem • Quantifying the pseudo-steady state reactivity will open the door to determining the potential for long-term attenuation of mesotrione in the environment.

  5. Experimental Setup • Single injection batch reactions will be used to simulate natural conditions in aquifers and surface waters • A buffer solution of pH 7.5 will be used with all batch reactions • MOPS (3-(N-morpholino)propanesulfonic acid) or MES (2-(N-morpholino)ethanesulfonic acid) buffers are the most appropriate for the experiments • After addition of a reducing compound (mainly Fe(II)) and goethite or goethite sand to the buffer solution, the reactor will be set on a rotator at approx. 50 rpm to equilibrate for at least 12 hours • Mesotrione can then be spiked into the reactor and samples taken at specific time intervals. These samples can then be analyzed via HPLC-UV/Vis for degradation.

  6. Sample Preparation • All reactions will be run in 124 mL serum bottles. • Each serum bottle will contain the following (assuming reaction is run to test Fe(II) kinetics): • 5 mg goethite or 600 mg of goethite • 0.124 mL 1.1 M FeCl2 • Fill serum bottle to the top with de-oxygenated pH 7.5 MOPS or MES buffer, cap with a crimp cap, and set to equilibrate. • After equilibration, remove crimp cap, spike in enough mesotrione to bring concentration to 5 μM (0.2 mg), cover with aluminum foil, and begin sampling. • Samples must be filtered with 0.2 μm nylon filter and added to 0.5 μL hydroxylamine hydrochloride before HPLC analysis to prevent the oxidation of Fe(II)

  7. Instrumentation • Degradation Kinetics Technique: HPLC-UV/Vis Absorption • Detection Wavelengths: 200 nm for mesotrione, 562 nm for Fe(II) • Changes in Sediment Mineralogy: Transmission Electron Microscopy

  8. HPLC-UV/Vis • HP 1090 photodiode array detector • Column: Reverse phase stainless steel, 250 x 4.6 mm, C18, 5 μM particles (ex. Inertsil ODS-3V) • Mobile Phase: 40% MeOH, 60% water acidifed to pH 3 using phosphoric acid • Flow rate: 1 mL/min • LOD: 0.5 μg/L • Linear range: 104 • Adequate sensitivity • Good reproducibility

  9. Transmission Electron Microscopy (TEM) • Works on same basic principles as a light microscope • Shoots electrons through a thin sample onto an electromagnetic lense, which magnifies and focuses the image onto an imaging device • High resolution capability allows observation of objects to the order of a few angstrom • Suitable instrument for this type of analysis is an HRTEM equipped with a charge-couple device camera • Specific model to use: FEI Techni T12

  10. Figures of Merit

  11. Conclusions • By determining the degradation kinetics of mesotrione and quantifying changes in mineralogy of the sediment due to this degradation, the possibility of long-term attenuation of mesotrione can be assessed. • The kinetics can be determined using HPLC-UV/Vis techniques and the changes in mineralogy can be quantified using TEM.

  12. References • Minnesota Department of Agriculture, http://www.mda.state.mn.us/chemicals/pesticides/useandsales.aspx, Accessed: Sept. 21, 2010. • Ter Halle,A.; Richard, C. Environ. Sci. Technol.2006,40, 3842-3847 • Chun, C. L.; Penn, R. Lee.; Arnold, W. A. Environ. Sci. Technol.2006,40, 3299-3304 • Klupinski, T. P. Environ. Sci. Technol.2003,37, 1311-1318 • Nobel Foundation: The Transmission Electron Microscope. http://nobelprize.org/educational/physics/microscopes/tem/index.html (Accessed Dec 7, 2010).

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