Supplemental information from: Antecedent and Post-Application Rain Events Trigger Glyphosate Transport from Runoff-Prone Soils
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(Authors and Abstract from a related journal paper of similar title: Brian K. Richards, Steven Pacenka, Michael T. Meyer, Julie E. Dietze, Anna L. Schatz, Karin Teuffer, Ludmilla Aristilde, Tammo S. Steenhuis - all were with Cornell University during 2017 except Meyer and Dietze with US Geological Survey, Organic Geochemistry Research Laboratory, Lawrence, Kansas) Recent environmental surveys report widespread detections of the herbicide glyphosate [N-(phosphonomethyl)glycine] in surface waters, despite its strong immobilization and rapid biodegradation in soils. We carried out four sampling campaigns (during 2015 to 2017) following controlled spray applications on an experimental perennial grass field site with wetness-prone marginal soils. We monitored dissolved glyphosate concentrations in the outflow (runoff and shallow drainage) using liquid chromatography-mass spectrometry and enzyme-linked immunosorbent assays. Rainfall-triggered outflow events occurred between 3 and 13 days following spray application. Outflow concentrations varied widely from 0.01 µg L-1 up to 90 µg L-1, peaking during the first significant outflow event in each campaign and diminishing as flows subsided. Subsequent outflow peaks caused concentrations to again rise but to a lesser extent. Cumulative mass efflux in outflow ranged among campaigns from 0.06 to 1.0 percent of applied glyphosate. Cumulative glyphosate losses in outflow were not associated with total rainfall during the post-spray sampling period but rather with soil hydrologic conditions at the time of spraying as reflected by the 7-day cumulative pre-spray rainfall, with wetter antecedent conditions favoring greater cumulative mobilization. Avoiding spraying under such conditions may mitigate potential glyphosate mobilization.
Deeper, non peer-reviewed explanations of water sampling and analytical methodology for glyphosate beyond detail in journal papers and their directly accompanying Supplemental Information.
This work was supported in part by New York State Department of Environmental Conservation contract number C008211 and Cornell University's David R. Atkinson Center for a Sustainable Future Academic Venture Fund Grant number 2015-AVF-Richards, using field site development and operation funded by USDA-NIFA Sustainable Bioenergy grant number 2011-67009-20083. Funding for any analysis conducted by the by the Organic Geochemistry Research Laboratory was provided by the U.S. Geological Survey Toxic Substances Hydrology Program. The use of manufacturer and trade names is for identification purposes only and does not imply endorsement by the U.S. Government.
glyphosate; runoff; agriculture; pesticides
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