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51

Determination of soybean rust fungicides in surface-water samples by solid-phase extraction GC/MS

Presenter: M. W. Sandstrom

All authors and affiliations: M. W. SANDSTROM (1), K. M. Fehlberg (1), and W. A. Battaglin (2). (1) U.S. Geological Survey, National Water Quality Laboratory, Denver, CO; and (2) U.S. Geological Survey, Colorado Water Science Center, Denver, CO

The fungicides chlorothalonil, pyraclostrobin, and azoxystrobin were registered in the United States in 2004 for the treatment of soybean rust, and other fungicides (propiconazole, tebuconazole, and myclobutanil) were given special exemption for use in certain states. Some of these fungicides are highly toxic to fish and aquatic invertebrates. Monitoring of fungicide concentrations is required to understand if increasing fungicide use to control soybean rust will result in increasing stream concentrations. We have developed a method to measure six fungicides (chlorothalonil, azoxystrobin, pyraclostrobin, propiconazole, tebuconazole, and myclobutanil) at nanogram-per-liter (ng/liter) concentrations in filtered surface-water samples. Compounds are isolated from a 1-liter water sample onto a 0.5-g octadecyl bonded silica solid-phase extraction column and eluted with 2 ml of ethyl acetate. After solvent evaporation and exchange to toluene, the extract is analyzed by gas chromatography, with selected-ion monitoring mass spectrometry. The method was applied in 2005 to 53 samples from 26 USGS surface-water sites in areas of soybean use. Chlorothalonil was not detected; azoxystrobin, myclobutanil, propiconazole, pyraclostrobin, and tebuconazole were detected infrequently at low concentrations (10600 ng/liter) in streams in areas where soybean rust had not yet been identified, so their use was probably related to the control of other pathogens. These samples can be used as a baseline of fungicides in streams as soybean rust spreads. Field matrix spikes indicated that azoxystrobin and pyraclostrobin have matrix-enhanced recovery of up to 300 and 500% in some samples, suggesting method improvements are needed for quantitative determination of these compounds.

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