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Environmental Processes
Antecedent and Post-Application Rain Events Trigger Glyphosate Transport from Runoff-Prone Soils Brian K. Richards, Steven Pacenka, Michael T. Meyer, Julie E. Dietze, Anna L. Schatz, Karin Teuffer, Ludmilla Aristilde, and Tammo S. Steenhuis Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.8b00085 • Publication Date (Web): 23 Apr 2018 Downloaded from http://pubs.acs.org on April 24, 2018
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Environmental Science & Technology Letters
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Journal: Environmental Science and Technology Letters
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Antecedent and Post-Application Rain Events Trigger Glyphosate Transport from Runoff-Prone Soils
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Brian K. Richards*1, Steven Pacenka1, Michael T. Meyer2, Julie E. Dietze2, Anna L.
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Schatz1, Karin Teuffer1, Ludmilla Aristilde1, Tammo S. Steenhuis1
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Life Sciences, Cornell University, Ithaca, NY 14853, USA
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Department of Biological and Environmental Engineering, College of Agriculture and
Kansas Water Science Center Organic Geochemistry Laboratory, U.S. Geological
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Survey, Lawrence, KS 66049 USA
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*Corresponding author. Phone: (607) 255-2463. Fax: (607) 255-4449. E-mail:
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[email protected] 13 14 15
ABSTRACT Recent environmental surveys report widespread detections of the herbicide
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glyphosate [N-(phosphonomethyl)glycine] in surface waters, despite its strong
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immobilization and rapid biodegradation in soils. We carried out four high-
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frequency sampling campaigns (during 2015 to 2017) following controlled spray
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applications on an experimental perennial grass field site with wetness-prone
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marginal soils. We monitored dissolved glyphosate concentrations in the outflow
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(runoff and shallow drainage) using liquid chromatography-mass spectrometry
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and enzyme-linked immunosorbent assays. Rainfall-triggered outflow events
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occurred between 3 and 13 days following spray application. Outflow
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concentrations varied widely from being nondetectable up to 90 µg L-1, peaking [1] ACS Paragon Plus Environment
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during the first significant outflow event in each campaign and diminishing as
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flows subsided. Subsequent outflow peaks caused concentrations to again rise
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but to a lesser extent. Cumulative mass efflux in outflow across the different
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campaigns ranged from 0.06 to 1.0 percent of applied glyphosate. Cumulative
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glyphosate losses in outflow were not associated with total rainfall during the
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post-spray sampling period, but rather with soil hydrologic conditions at the time
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of spraying as reflected by the 7-day cumulative pre-spray rainfall, with wetter
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antecedent conditions favoring greater cumulative mobilization. Avoiding
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spraying under such conditions may mitigate potential glyphosate mobilization.
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INTRODUCTION Glyphosate [N-(phosphonomethyl)glycine] has become the most heavily-used
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herbicide active ingredient in the United States (U.S.) and the world1 due to
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widespread adoption of glyphosate-tolerant crop varieties2, with 2017 global use
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estimated to be 1.35 Tg 3. Surveys from 2015-2016 report that glyphosate-
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tolerant varieties occupied 81 to 97 percent of planted areas of corn, cotton and
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soybeans in the 19 U.S. states that produced the most of each crop4. It was long
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held that little post-spray mobility potential exists for glyphosate, given strong
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binding to clay minerals and metal oxides in soil5, 6, 7 as well as rapid microbial
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decomposition of glyphosate and its degradation product, AMPA (aminomethyl-
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phosphonic acid)8. Reviews through the prior decade5,9 suggested that
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mobilization occurs only in limited cases10 such as via preferential transport
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under heavy rainfall5. However, recent environmental surveys have shown that
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glyphosate and AMPA are now commonly detected in diverse hydrologic
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settings11-16 including urban watersheds17. Accompanying these detections are
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increasing concerns over adverse impacts at these ambient concentrations18,19.
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Battaglin et al.11 summarized nine U.S. studies representing over 3,700
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samples spanning 2001 to 2010. Water in agricultural ditches and drains had the
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greatest frequency of glyphosate detection (71% of samples) and median
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concentration (0.2 µg L-1), whereas streams had relatively lower detection rates
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(53%) and median concentration (0.03 µg L-1). Groundwater had the lowest
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detection frequency (6%) and median concentration (
