Monitoring and Modeling Glyphosate Transport in the Belize River Watershed

Glyphosate, an effective herbicide used worldwide as a weed control, can be transported from application areas to unintended locations. In this study, we use high performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA) kits, and liquid chromatography with tandem mass spectrometry (LC-MS/MS) to quantify concentrations of glyphosate, and the Soil Water Assessment Tool (SWAT) to model transport of glyphosate in the Belize River Watershed. Water samples were collected from two rural communities with rudimentary drinking water systems. Quantification analyses showed that glyphosate was not present in the water samples. The model confirms that glyphosate is not expected to be present in the sampling locations. However, the model did reveal that glyphosate transport to the Belize River may be occurring and identified three subbasins most likely to be at risk due to having the highest percentages of days exceeding the EU standard for glyphosate of 0.1 μg/L. One of these subbasins, located just downstream of the sampling locations, was the most significant contributor of soluble glyphosate to the river (p-values <0.0). Soluble glyphosate concentrations in this subbasin inflow and outflow exceeded the EU standard by 12.53% and 11.65% of the time, respectively. Additionally, concentrations of glyphosate sorbed to sediment were significantly greater than soluble glyphosate in surface runoff (p-values <0.0). 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 and measurement of sustainable development progress when monitoring data is unavailable.