CAS: Understanding Glyphosate's Reactions at Mineral and Organic-Coated Mineral Surfaces: Sorption-Desorption Dynamics

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The Environmental Chemical Sciences Program of the NSF Division of Chemistry funds Professor Carmen Enid Martínez at Cornell University to study the dynamics of glyphosate reaction with mineral and organic-coated mineral surfaces present in soils. Glyphosate is the world’s most heavily applied herbicide used to kill broadleaf plants and grasses. As a result, environmental contamination with glyphosate occurs frequently and widely in U.S. soils, sediments, surface and groundwater. Glyphosate’s interaction with soil greatly influences glyphosate’s environmental behavior including toxicity, mobility, and bioavailability. The goal of this project is to learn how and how fast glyphosate is retained and released upon interaction with soil components. Given the widespread use of glyphosate, it is essential to understand the conditions for its accumulation. Of interest is also whether its reactions with soil components create a reservoir with slow-release capability, which is a route to surface and groundwater contamination. This project provides research opportunities and training for graduate students. The project integrates an outreach component with the Sciencenter (Ithaca, NY), and outreach activities with NYS 4-H and Cornell Cooperative Extension. Graduate students participate in all outreach activities which supports their development and professional training.This project provides comprehensive information on molecular-scale processes of glyphosate at mineral and organic-coated mineral surfaces. The overarching question is: Does glyphosate accumulate in soils, and is its accumulation a reversible process? Research activities are designed to test the hypothesis that mineral and organic-coated mineral surfaces differ in their ability to retain (sorb) and release (desorb) glyphosate, and that glyphosate sorption at mineral surfaces outcompetes sorption of dissolved organic matter. Mechanisms of interaction and kinetics of glyphosate sorption-desorption are investigated using minerals that represent a variety of surface structures, and organic-coated minerals where the organic-coating differ in structural characteristics, functionality and aromaticity. Molecular-scale sorption-desorption behavior and kinetics of these processes are probed utilizing surface sensitive approaches coupled to simultaneous analyses of outflow solutions from these experiments. Process-based parameters are obtained that help explain glyphosate sorption-desorption behavior (binding constants, sorption maximum) and their rate constants. The simultaneous monitoring of surface reactions and solution chemistry facilitates a more comprehensive understanding of molecular-scale processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.