Citation:

Strynar, M J., J. Dec, A. Benesi, A. D. Jones, R. A. FRY, AND J. BOLLAG. USING ¹⁹F-NMR SPECTROSCOPY TO DETERMINE TRIFLURALIN BINDING TO SOIL. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. American Chemical Society, Washington, DC, 38(24):6645-6655, (2004).

Impact/Purpose:

The objective of this task is to develop state-of-the-art methods for measuring xenobiotic compounds, to include the isolation of the analyte from the appropriate matrix (extraction), preconcentration (typically sorbent-based), and analysis via GC/MS and/or LC/MS. Once established, these methods will be applied in small scale pilot studies or demonstration projects. Particular emphasis will be placed on methods which are readily transferable to other laboratories, including those within the Human Exposure and Atmospheric Sciences Division (HEASD), the National Exposure Research Laboratory (NERL), other EPA Laboratories, Program Offices, Regions, and academic institutions.

Specific objectives of this task include the following:

1) Development of GC/MS and LC/MS methods for the measurement of key xenobiotic compounds and their metabolites (to include the pyrethroid pesticides, perfluorinated organic compounds, and the BFRs) in relevant environmental and biological matrices.

2) Development of efficient low cost methods for the extraction and clean up of these compounds collected from relevant matrices.

3) Determination of xenobiotic compound and metabolite concentrations in samples derived from laboratory and field monitoring studies to help assess exposures and evaluate associated risks.

Description:

Trifluralin is a widely used herbicide for the control of broad leaf weeds in a variety of crops. Its binding to soil may result in significant losses in herbicidal activity and a delayed pollution problem. To investigate the nature of soil-bound trifluralin residues, ¹⁴C-labeled herbicide was incubated for 7 weeks with four soils under anoxic conditions. As determined by radiocounting, trifluralin binding ranged between 10 and 53% of the initial ¹⁴C depending on the soil tested. ¹⁹F NMR analyses of the methanol extracts and different fractions of the extracted soil suggested that bound residue formation largely involved reduced metabolites of the herbicide. A 2,6-diamino product of trifluralin reduction with zero-valent iron (Fe-TR), and the standard of a 1,2-diamino trifluralin derivative (TR6) formed covalent bonds with fulvic acid (FA), as indicated by the ¹⁹F NMR spectra taken periodically over a 3-week contact time. At short contact times, TR6 and Fe-TR formed weak physical bonds with FA, as the respective spin-spin relaxation times (T1) decreased from 1300-1831 msec for TR6 or Fe-TR analyzed in the absence of FA to 150-410 msec for TR6/FA or Fe-TR/FA mixtures. In general, the results indicated that trifluralin immobilization involved a variety of mechanisms (covalent binding, adsorption, sequestration), and with time it became increasingly stable.

Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.

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