Author ORCID Identifier

https://orcid.org/0000-0002-5683-2215

Year of Publication

2020

Degree Name

Master of Science in Civil Engineering (MSCE)

Document Type

Master's Thesis

College

Engineering

Department

Civil Engineering

First Advisor

Dr. Shakira Hobbs

Abstract

Glyphosate is the most widely used herbicide worldwide and is often transported from application areas to surface water when solubilized in runoff or sorbed to eroded sediment. There is evidence that suggests both glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) may pose a risk to human health, as well as cause adverse effects in the environment. However, consistent monitoring data is still limited, especially in developing countries. Belize is a developing nation with agriculture being a major sector of its economy and is heavily reliant on glyphosate. The widespread use of glyphosate in Belize may be resulting in glyphosate transport to drinking water resources. Samples were collected from two rural communities that rely on the Belize River for their drinking water systems, Bullet Tree and Spanish Lookout, at points upstream of the abstraction site, at the abstraction site, and at the site of drinking water distribution. Samples were analyzed using HPLC, ELISA kits, and LC-MS/MS. From these analyses, it was concluded that glyphosate was not present in any water samples at a detectable concentration. The Soil and Water Assessment Tool (SWAT) was used to develop a model of the Belize River Watershed. The model was calibrated and validated for observed flow rates using the SWAT Calibration and Uncertainty Program (SWAT-CUP), which revealed acceptable model performance for simulating flow. Model results indicate that glyphosate transport to the Belize River is occurring, with contributions from glyphosate sorbed to eroded sediment being significantly greater than soluble glyphosate in surface runoff (p-values <0.0). Average simulated concentrations of soluble glyphosate in both wet and dry seasons are below the European Union (EU) standard of 0.1 ppb across the watershed. However, subbasins 2, 3, and 28 were identified as higher risk areas, due to having the highest percentages of days exceeding the EU standard. Subbasin 28, located just downstream of the Spanish Lookout drinking water system, was the most significant contributor of soluble glyphosate to the river, as compared to soluble glyphosate concentrations in subbasins 2 (p-values <0.0) and 3 (p-values <0.0). Soluble glyphosate concentrations in subbasin 28 inflow and outflow exceeded the EU standard 12.53% and 11.65% of the time, respectively. This work demonstrates a framework for applying SWAT for pesticide transport modeling in developing countries, and has the potential to be a powerful and accessible tool for watershed management when monitoring data is unavailable.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.359

Share

COinS