A Simple Qualitative Test for Surfactants in Glyphosate-Based Herbicides

Overview

In 2016, 286 million pounds of glyphosate were used on crops in the United States. Glyphosate is the active ingredient in glyphosate-based herbicides (GBHs), such as Round-up®️ and Rodeo®️. Only 2% of the commercial final product applied to crops is glyphosate, with the other 98% composed of “undisclosed “or “other” ingredients. To allow the glyphosate to get past the cuticle of plants, many GBHs contain surfactants formulated in these undisclosed ingredients. A surfactant can be defined as a substance which reduces the surface tension of a liquid. Surfactants disrupt cell membranes and are known to be toxic to aquatic organisms. Considering the broad use of GBHs, this presents a potential ecological threat. This investigation devised a simple method to determine whether there was surfactant present in the GBHs Round-up and Rodeo. The presence of surfactant in herbicides and controls was tested using a qualitative loss of surface tension. For each test, six milliliters of pure reverse osmosis water were placed on a standard microscope slide cleaned with isopropyl alcohol. This was tested to be the maximum amount of water that could be held on a slide when 5μL of pure water as a negative control was added to the slide. If the surface tension broke after the addition of 5μL of a test herbicide, it was recorded to contain a surfactant. Triton X-100 was used as a positive control and pure reverse osmosis water was the negative control. The Triton X-100 was diluted to concentrations of 100, 10, 5, 2.5, 1.25, 0.625, 0.3125, 0.15625% and the Round-up and Rodeo were diluted to concentrations of 100, 50, 25, 12.5, 6.25, 3.125, 1.5625%. It was found that the surface tension did not break at any levels of concentration tested of Rodeo while the surface tension broke for high levels of concentration (100, 50, 25%) of Round-up. All trials of the Triton X-100 broke the surface tension at a concentration of 0.625% and above, and some trials of the Triton X-100 broke the surface tension at concentrations of 0.3125 and 0.15625%. All trials of the negative control did not break the surface tension. These results suggest that there is little to no surfactant in the herbicide Rodeo but there is some surfactant in the herbicide Round-up. We hope this method can be used to quickly determine whether any of the many GBHs contain surfactants. These results also suggest that the high amounts of GBHs being applied to crops may present an ecological threat to water supplies.

Competition history

• AJAS 2020 Category not listed

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