Over the past two decades the use of glyphosate on core crops has increased dramatically. The introduction of the genetically modified crops in the late 1990s was a boon to the industry. Roundup Ready crops, including corn, soy, canola, sugar beets, alfalfa, cotton, and tobacco, are genetically modified by the insertion of a microbial gene that produces a version of the enzyme EPSP (5-enolpyruvylshikimate-3-phosphate) synthase that is resistant to glyphosate’s effects. This is the enzyme in the shikimate pathway that glyphosate disrupts.
As you may know, many non-GMO crops are also commonly exposed to glyphosate. These crops are commonly sprayed right before harvest, with glyphosate acting as a ripener or a drying agent. Particularly in northern regions such as Canada where the growing season is short, the goal is to force the crop to ripen before frost sets in.
This practice is also increasing in part because farmers have learned that synchronizing plants to go to seed at the same time improves yield. Crops commonly treated right before harvest include wheat, oats, barley, sugar cane, sunflower seeds, and legumes such as chickpeas, lentils, and soybeans.
Like the United States and Canada, Argentina has seen a rapid rise in glyphosate use over the past two decades, along with the widespread adoption of genetically modified glyphosate-resistant soy crops, mainly for export. Introduced in the 1980s, glyphosate use quadrupled in Argentina between 1996 and 2012. Some of the highest glyphosate residues have been accumulating year by year in the Pampas region, a center for soy production.
Monsanto contends that glyphosate disappears quickly from the environment after it is applied. The company claims that glyphosate is largely metabolized by soil bacteria within a couple of weeks. Scientific research paints a different picture. Of five herbicides used in Finnish sugar beet fields, glyphosate was found to be the second most persistent, still present well into the spring following a fall application.
Scientists have also found that, in places where glyphosate is heavily used, the total amount of glyphosate used over time correlates more strongly with the amount of glyphosate detected in the soil than the amount of glyphosate used in the most recent applications. This was found to be true in the Pampas region of Argentina where Roundup Ready soybeans are grown. Practically speaking, this means that the amount of glyphosate a farmer applies each year likely exceeds the degradation rate. With every five applications, there is an estimated increase of one milligram of glyphosate per kilogram of soil.
How quickly does glyphosate actually degrade in natural soils? Slowly. In one experiment, radiolabeled glyphosate was added to undisturbed sand and clay. Scientists then analyzed samples, taken weekly for more than two years. They found that after 748 days, 59 percent of the glyphosate was still present.
No one denies that there is an environmental crisis unfolding today. Different species from multiple phyla, from fungi to insects to amphibians to birds, are experiencing rapid and alarming population declines.
Of course, not all environmental destruction can be attributed to glyphosate. But it is a major factor in biodiversity loss, including the dramatic collapse of monarch butterflies and honeybees, and declining overall health in plants, animals, other living organisms, and entire ecosystems.
Toxic Legacy: How the Weedkiller Glyphosate Is Destroying Our Health and the Environment by Stephanie Seneff (Chelsea Green Publishing, July 2021) is available for pre order now.