OREGON STATE UNIVERSITY

Herbicides in Needle Branch Streamwater

Louch, J., G. Allen, G. Ice, T. Garland, V. C. Hale, and J. McDonnell
Apr-18-2013

Glyphosate, aminomethylphosphonic acid (AMPA), imazapyr, sulfometuron methyl, and metsulfuron methyl were measured in Needle Branch streamwater during and after application of herbicide(s). All herbicides were applied by helicopter in a single tank mix. Samples were collected at three sites: NBH (at the fish/no-fish interface in the middle of the harvest unit), NBU (at the bottom of the harvest unit), and NBL (well downstream). AMPA, imazapyr, sulfometuron methyl and metsulfuron methyl were not detected in any sample at 15 ng/L, 0.6 μg/L, 0.5 μg/L and 1 μg/L, respectively. However, a clear pulse of dissolved glyphosate manifested at NBH during the application (baseflow conditions).  Subsequent baseflow samples collected three days after treatment (DAT) showed ≈25 ng/L dissolved glyphosate at all three sites. Samples collected during the first storm event (8 DAT) showed a clear pulse of dissolved glyphosate at NBU, but not at NBH or NBL. The maximum concentration observed during this pulse at NBU was 115 ng/L, and the pulse persisted for about six hours. During the next storm event (10 DAT) a clear pulse of dissolved glyphosate manifested at NBH, but not at NBU or NBL. The maximum co centration observed was 42 ng/L, and this pulse persisted for about ten hours. Results from all subsequent storm events showed dissolved glyphosate at <20 ng/L in all samples. A limited number of analyses on suspended sediment (SS) showed that SS held de minimis masses of glyphosate and AMPA.

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