Residue Analysis of Dicamba and its Metabolites in Vegetation and Soil

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1 1 Office of Pesticide Programs (OPP) Biological & Economic Analysis Division Analytical Chemistry Branch Environmental Science Center Fort Meade, Maryland Residue Analysis of Dicamba and its Metabolites in Vegetation and Soil SFIREG Meeting, Arlington, VA April 10, 2017 Thuy Nguyen ( ) Yaorong Qian ( ) EPA-OPP Do Not Cite or Distribute

2 OUTLINE Summary of Dicamba Fate in the Environment Summary of Dicamba Metabolism in Plants ACB Residue Analytical Method Round Robin Study ACB Modified Residue Analytical Method Challenges and Next Steps EPA-OPP Do Not Cite or Distribute 2

3 Fate of Dicamba in Environment Dicamba is a broad spectrum herbicide to control weed Very soluble in water Short half-life in field dissipation studies Dicamba t ½ ~ 4-20 days Metabolites of concern are 5-OH Dicamba and 3,6-dichlorosalicylic acid ( DCSA). DCSA is the major degradate in the environment, and is more persistent than parent Dicamba Relatively volatile with possible post-application vapor-phase off-site transport Spray drift potential EPA-OPP Do Not Cite or Distribute 3

4 Metabolism of Dicamba in Plants Degrades to 5-OH Dicamba and DCSA in non-dicamba-resistant plants Dicamba t ½ ~ 7 28 days Converts quickly to DCSA in genetically modified (GMO) plants that are resistant to dicamba Dicamba t ½ ~ hours to days DCSA t ½ ~ 30 days. DCSA further degrades to DCGA Degradation onto DCSA is more complete in GMO plants than in non-gmo plants EPA-OPP Do Not Cite or Distribute 4

5 Residue Analytical Method for Dicamba and its Metabolites in Vegetation and Soil ACB reviewed several methods from state and federal laboratories for Dicamba and other acidic herbicides and adapted one for the LC-tandem mass spectrometer (LC-MS/MS). % Rec Spike Recovery Limits of Quantitation for target analytes: - Dicamba 30 ng/g - DCSA 3 ng/g - 5-OH Dicamba 75 ng/g v 2,4-D 1.5 ng/g Dicamba DCSA 5-OH dicamba 2,4-D UL LL Instrument: LC-MS/MS Waters Xevo TQ MS (2009) EPA-OPP Do Not Cite or Distribute 5

6 Round Robin Study: Dicamba Residue Analytical Method in Vegetation and Soil Purpose: Determine strength and limitation of the method(s) and the instrumentation used by each participating laboratory. Participating Laboratories: 10 Instruments: 7 LC-MS/MS, 2 LC/HRMS (1 Orbitrap, 1 QTOF), 1 GC/MS TOF Various extraction methods: LOQs ü QuEChERS based (with and without clean up) ü Methylation for GC/MS ü Liquid/Liquid Extraction ü Dicamba: 2.1 ng/g to 40 ng/g ü 5-OH Dicamba: ü DCSA: ü 2,4-D: 4.2 ng/g to 75 ng/g 2.1 ng/g to 12 ng/g 1.5 ng/g to 10 ng/g 6 EPA-OPP Do Not Cite or Distribute

7 Round Robin Study Residue Analytical Method in Vegetation and Soil (continued) Round Robin Study Summary of Results: Dicamba - OK by many labs. But some have high LOQs and low recoveries DCSA OK by most labs (vegetation and soil) 5-OH Dicamba OK by most labs in vegetation. Challenging in soil (recovery at 200 ppb spikes less than 10% for most labs) 2,4-D OK in vegetation. Some low recovery in soil at low level EPA-OPP Do Not Cite or Distribute 7

8 New Residue Analytical Method for Dicamba and its Metabolites in Vegetation and Soil A new method was successfully developed for our new HRMS, with average recovery from low 80% to high 90% and detection limit for Dicamba from 10 ng/g to 1 ng/g Similar to the currently used methods. Sample preparation and extraction are simple and rugged Limits of Quantitation for target analytes: - Dicamba 3 ng/g - DCSA 2 ng/g - 5-OH Dicamba 7.5 ng/g Instrument: LC- HRMS Thermo Q-Exactive (2015) v 2,4-D 1.5 ng/g EPA-OPP Do Not Cite or Distribute 8

9 Challenges and Next Steps Challenges: Short half-life of Dicamba Current method is specific to HRMS High detection limit for Dicamba on LC-MS/MS Low recovery of 5-OH Dicamba in soil Next Steps: ACB is currently exploring the feasibility of the method to be used on LC-MS/MS Additional cleanup may be needed for LC-MS/MS to reduce the matrix interference Look into improving the recovery of 5-OH Dicamba in soil EPA-OPP Do Not Cite or Distribute 9