Author: Amira Aker

Editors: Brittany Dixon, Kevin Boehnke

Tinkering with an organism’s genes is the subject of one of the most controversial debates today – and rightfully so. The resulting organisms are commonly referred to as genetically modified organisms (GMOs), and figuring out how to use GMOs in a safe and sustainable manner is hotly debated. This issue isn’t simply a matter of technology, but one of safety, ecology, economics and even morality. Yet, there has been a notable absence of discussion around the broad-based herbicide glyphosate in mainstream media; namely, that over 80% of GMOs on the market today are modified to tolerate glyphosate. This effective herbicide kills pesky weeds without affecting farmers’ GMO crops, saving time and, potentially, money. However, given the vast opportunities that GMO science opens to us, is dedicating so many resources to this single GMO product the right way to go?

Is glyphosate safe for humans?

Due to increasing global production of GMOs and the coupling of GMOs and glyphosate, glyphosate usage increased from 4% of the overall herbicide usage in the United States in 1996 to over 50% in 2014. GMO glyphosate-tolerant plants do not metabolize the herbicide, leaving more residue on the plant. This means people are exposed to more glyphosate now than ever before. There’s also concern over the way farmers apply herbicides to GMOs versus traditional crops. Anti-GMO groups argue that because glyphosate won’t kill GMO crops, farmers apply more, leading to higher levels of herbicides on our plants – and potentially in our bodies. However, there isn’t a scientific consensus about this. While one study reported an increase in overall US herbicide usage since the introduction of GMOs (driven mostly by glyphosate), another reported a decrease. Pro-GMO groups argue that even if the use of glyphosate increased, overall herbicide toxicity decreased since glyphosate is safer than other herbicides.

But this doesn’t necessarily mean that glyphosate is without risk. Glyphosate kills plants by inhibiting a specific enzyme which stops protein production. This same mechanism could cause endocrine disruption in animals and humans by inhibiting liver enzymes responsible for synthesizing estrogen. A comprehensive review recently cast doubt on glyphosate’s supposed low toxicity, reporting evidence of liver, brain, and reproductive effects in both animal and human studies. The World Health Organization also recently classified glyphosate as a potential carcinogen. Furthermore, while the majority of the studies included in the review were based on glyphosate exposure alone, other studies showed that the adjuvants added to glyphosate formulations (like those in Roundup) make the mixture more toxic than glyphosate alone. This evidence supports the idea that farmers and agricultural workers are especially vulnerable to the effects of glyphosate—due to increased exposure as they apply the herbicide and harvest crops—but the risks associated with glyphosate are low for the average consumer.

Effects on agricultural production

Amira-crop sprayer
Self-propelled row-crop sprayer applying pesticide to growing corn.

On top of their increased exposure to glyphosate, farmers also feel the economic effects of glyphosate overuse. The increasing dependence on glyphosate has led to weed resistance because the constant use of a single herbicide allows rare, resistant plants to reproduce and dominate the weed population. In turn, farmers apply more to control the weeds, perpetuating a cycle of resistance and heavy herbicide application, which has led to a five-fold increase in herbicide spending over the past several years. Further, resistance to glyphosate can occur through several mechanisms in weeds, making the issue complex to decipher and “fix”. For example, some plants make several copies of the gene glyphosate targets to potentially save one of the copies, while others rely on a microorganism in the soil to cleave glyphosate into a less toxic form. One of the most common and most concerning weeds is waterhemp. Despite farmers’ best efforts, in some states, more than 70% of the waterhemp population is glyphosate-resistant. No new herbicides have been introduced to the market in over 30 years, leading to more chances of weed resistance. Overreliance on glyphosate makes this tool less effective, and farmers have turned to other weed management practices that could be detrimental to the environment, such as extensive tillage, which leads to crop growth disruption through soil erosion.   

Don’t throw the baby out with the bathwater

Despite the questionable amount of resources dedicated to herbicide-resistant GMOs, GMOs in general have great potential for use. Take, for example, the papaya, one of GMO technology’s greatest triumphs. Twenty years ago, ringspot virus was destroying papaya crops in Hawaii, despite farmers trying various methods to combat virus-carrying insects. Genetically modifying papayas to include a gene from the virus saved the crop. There also has been a push to modify crops to withstand climate change, and Scientific American recently published a story about biotechnologists modifying rice to withstand growing in saltwater. Other successes, however, have been exaggerated.  Close to two decades ago, scientists engineered rice to contain beta-carotene, a precursor to vitamin A that could help prevent half a million children going blind every year. This new rice strain was called Golden Rice and has since been touted as the GMO humanitarian miracle. Time magazine featured Golden Rice on its cover in the year 2000, and some even claimed that it could save the lives of millions of children. However, Golden Rice, which doesn’t grow as well as other rice varieties, is not yet available to consumers. Golden Rice could still help with severe vitamin A deficiency in parts of the developing world, but its slow adoption reminds us of the importance of understanding current imperfections of GMO technology.

While antiviral papaya and salt-resistant rice showcase the immense potential of GMOs, the fact remains that almost 100% of GMOs are engineered to withstand herbicides (mostly glyphosate) or to be resistant to insects. Ninety-nine per cent of GMOs are one of four crops: corn, soy, cotton and canola, which are used mainly for animal feed and ingredients for processed foods. As such, claims of feeding the world made by pro-GMO groups are often dismissive of the realities of GMO companies’ priorities (i.e., profit). In this landscape, it becomes easy for consumers to distrust GMO companies and technologies, especially given the general lack of science literacy of U.S. citizens today. Thus, the coupling of GMOs and herbicides (especially glyphosate) extends beyond the typical science conversations to ethical and moral debates.  (These ideas are explored further in two great blog posts found here and here.)

There is so much potential in GMOs, and it’s a shame that companies have focused so much of their effort towards limited biotechnological products. The evidence for limited long-term efficacy and potential safety issues indicate that we should de-couple the GMO-herbicide link, and redirect our resources to work towards the grander opportunities GMOs have to offer.

About the author

Amira picAmira is a PhD student in Environmental Health at the University of Michigan. Her research looks at how chemicals in our products can affect the health of the mother and fetus during pregnancy. When not staring at her data, she’s either making or talking about food.

Read more from Amira here.

Image Credit:

Crop sprayer: By Pl77 – Own work, CC BY-SA 3.0,

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