This Herbicide Is Everywhere. But Should It Be?

When it comes to international bullying, the U.S. has never been shy about throwing its weight around. But sometimes the victims resist. That’s the case with plucky Mexico, which is pushing back hard against American demands that it cancel a planned ban on genetically modified corn and the herbicide glyphosate, used by farmers around the world to control weeds. Washington is insisting there is no scientific basis for the bans, and that they violate the U.S.-Canada-Mexico Agreement on trade.

The official U.S. position is that genetically modified organisms and commonly used herbicides, such as glyphosate, have been scientifically demonstrated to be safe for human consumption. But the science is anything but conclusive. Indeed, with regard to glyphosate, there is mounting evidence pointing in the opposite direction. Dozens of new studies over the past few years strongly suggest that the herbicide, even in the relatively low concentrations that farmers are supposed to use, has demonstrably harmful effects on humans, animals, insects (especially bees; more about that below), microbes and the environment in general. While the evidence that glyphosate can cause cancer in humans is controversial and less definitive, the support for so-called non-cancer effects in humans and other organisms is steadily piling up. This research is validating decades of efforts by governments, local communities and activists who have fought hard to limit or ban its use.

The weed-killer glyphosate is the most widely used herbicide in the world. It is manufactured by a number of companies, but is best known by its original trade name, “Roundup.” (Rolled onto the market by Monsanto in 1974, the product is now sold worldwide by Bayer, which purchased Monsanto in 2018.) In the United States alone, the Environmental Protection Agency has estimated that about 280 million pounds are applied to croplands each year. To get a perspective on that number, the combined weight of all the kale, brussels sprouts and eggplants consumed annually in the U.S. is just a bit over 300 million pounds. Of course, when you eat those healthy vegetables, all their good nutrients go straight into your body. Unfortunately, the ubiquitous use of glyphosate since it first came on the market has meant the chemical also makes its way into human bodies: A study last year by the U.S. Centers for Disease Control found that glyphosate showed up in the urine of 80% of adults and children from a representative sample.

Some activists charge that Bayer and other chemical companies have acted as agribusiness drug pushers, getting farmers addicted to glyphosate and then blocking all routes to rehab. This has been accomplished, they argue, by developing and selling seeds genetically engineered to better withstand glyphosate, which targets a metabolic process in plants (including weeds) called the shikimate pathway. Farmers plant the seeds, spray the glyphosate and the crop survives while the weeds die. (That’s the concept, at least; in recent years, weeds have been developing resistance to glyphosate, even though Bayer said that would not happen.)

The strategy has been wildly successful for Bayer and other chemical companies, along with their profits: More than 90% of corn, soybeans and upland cotton are GMOs varieties, according to the U.S. Department of Agriculture.

But in 2015, the conversation about glyphosate took a dramatic turn. That year, the International Agency for Research on Cancer (IARC), a branch of the World Health Organization, concluded from a widespread survey of the peer-reviewed literature that glyphosate was “probably carcinogenic to humans.” That finding had two almost immediate effects: In the United States, attorneys for glyphosate users who had developed non-Hodgkin’s lymphoma, the rare cancer most closely associated with glyphosate use, began filing lawsuits against Bayer (which by then had purchased Monsanto) — and winning them, along with multimillion dollar damages and penalties from juries. More recently, as Bayer has fine-tuned its legal strategy, there have been wins and losses for plaintiffs. And while Bayer has settled many lawsuits, there are still some 30,000 left to be adjudicated.

In parallel with its legal strategy, Bayer has engaged in an intense public relations campaign to defend its very profitable product from any and all accusations that it could cause health or environmental problems.
But a recently released study by the activist group U.S. Right to Know, authored by journalist Stacy Malkan and others, entitled “Merchants of Poison,” accuses Bayer of playing fast and loose with the truth of the science behind glyphosate. Likening Bayer’s campaign to that carried out by tobacco companies in the 1950s and 1960s to deny that smoking caused lung cancer, the authors argue that Bayer employed a scorched earth strategy, going all out to try to destroy the credibility not only of critical scientists and activists but IARC as well (the agency, which has a reputation for calling it as it sees it about what causes cancer and what doesn’t, has long been a target of corporate rage.)

During the tail end of the Trump administration, in 2020, Bayer succeeded in getting the EPA on its side for a short while: After a long review that appeared to ignore the opinions of its own scientists as well as the advice of an external review board, the agency declared that the herbicide was not a carcinogen. But last year, the U.S. Court of Appeals for the 9th Circuit sent the EPA back to the drawing board, agreeing with litigants who argued that the agency had violated its own rules when it gave the herbicide a clean bill of health.

That means the official jury on whether glyphosate is a carcinogen is still out, although recent studies continue to suggest the herbicide could cause cancer under certain circumstances. This past January, for example, researchers in Argentina found that rural communities surrounded by agricultural lands where glyphosate and other herbicides were heavily used suffered higher cancer and death rates.

Research also continues into whether the herbicide can cause other maladies in humans. There are hints, still not definitively confirmed, that glyphosate may be linked to neural disorders such as autism and Parkinson’s disease, kidney disease in agricultural workers, asthma and even irritable bowel syndrome. In a study just released on March 1, a team of California researchers found that children exposed to glyphosate and its primary metabolic breakdown product have a higher incidence of liver inflammation and metabolic syndrome (which increases risk of heart disease, stroke and diabetes) by the time they reach young adulthood.

One of the most worrying risks is the harm that glyphosate might be able to do to the unborn children of pregnant women.

We already know that exposure to glyphosate, as indicated by its presence in urine samples, is ubiquitous in the United States, and not just in farming communities. A number of studies have suggested that glyphosate might be a so-called “endocrine disruptor” — meaning that it could interfere with normal hormone activity, especially during fetal development — although these remain controversial. In one recent study, a team of researchers from several U.S. institutions found evidence that exposure to higher levels of glyphosate might be associated with a greater anogenital distance (the distance between the anus and the genitalia) in female infants. Changes in the anogenital distance can be an important indicator of whether the reproductive system is developing normally.

The research team pointed out that these findings confirmed earlier studies in rats, and “suggest that glyphosate is a sex-specific endocrine disruptor with androgenic effects in humans. Given the increasing glyphosate exposures in the U.S. population, larger studies should evaluate potential developmental effects on endocrine and reproductive systems,” they concluded.

Given these and similar results, the recently published findings of a research team working in Brazil may come as little surprise. A team led by Mateus Dias, a researcher at Princeton University, carried out a meticulous study of birth outcomes in soybean producing areas of the country (soybean farmers use large amounts of glyphosate on their crops, and that use has increased dramatically in recent years.) Previous studies in Brazil and the United States have shown that a very high percentage of pregnant mothers have detectable levels of glyphosate in their urine, and after birth, in their breast milk.

Employing an established database of birth outcomes from 2000 to 2010 in soybean producing areas, the researchers found that increases in glyphosate use were associated with an average 5% increase in the infant mortality rate — and that the increases were largely concentrated in families that lived downstream of glyphosate application rather than upstream. The researchers carefully controlled for a number of factors that could have biased their results, such as differences in land use and water supply (surface water opposed to underground water sources). The results held firm. The team concluded:

Overall, our exercises show that the effect we document is indeed related to the expansion in soybean production following the adoption of genetically modified seeds, that it operated through water bodies, that it was particularly intense during the season of application of glyphosate, and that it was not due to other potential changes brought about in the expansion of soybean production.

As scientists sharpen our understanding of glyphosate’s impact on human health, other researchers have produced evidence that the herbicide is not good for some of our animal friends, most notably the bees.

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The dramatic decline in bee populations — especially honey bees and bumblebees, which have nearly vanished from eight U.S. states — have been noted and studied for many years now. But the possible reasons remain multiple and controversial. One major suspect is the class of neonicotinoid herbicides, which many researchers and environmentalists believe are definitively linked to bee declines. But over the last several years, glyphosate has also come under scrutiny as an enemy of bee survival, and the number of scientific papers finding deleterious effects on the insects has begun to pile up.

This is potentially bad news for both bees and humans, because bees are critical pollinators, without which many agricultural crops (not to mention many flower varieties) would be in deep trouble, along with the people who rely on them.

It’s taken scientists some time to figure out what glyphosate does to bees, because the herbicide does not seem to kill them directly. More often, glyphosate appears to interfere with many of the bee traits that allow bee colonies to thrive, including proper growth and development, strong immune responses, thermoregulation and the ability to navigate effectively to find food and get back to their hives.

Sometimes the harmful effects of glyphosate can be subtle, and thus hard to spot unless researchers are looking for them. One recent study, for example, found that exposure to glyphosate at levels similar to those found in agricultural fields impairs the ability of bumblebees to distinguish colors, which is essential to their ability to find the flowers that have the nectar and pollen they need to survive.

And the research has made it clear that the herbicide is harmful to bees in ways that are not immediately obvious. One of the most important findings, confirmed by multiple studies, is that glyphosate perturbs the bacteria in the guts of honeybees, disrupting their microbiomes along with their immune systems — thus increasing the risk from dangerous rather than friendly microbes. This is perhaps not surprising, because bacteria, but not bees, possess the shikimate pathway that glyphosate acts on to kill weeds and other plants. (Some scientists have postulated that glyphosate’s ability to harm microbe communities is an important contributor to its effects on humans and animals, as well as beneficial plants that become collateral damage when weeds are being sprayed.)

As sensitive as bees may be to glyphosate, Bayer is to bad publicity around scientific findings. The company routinely disputes studies using its own scientists as “explainers.” Indeed, Bayer devotes enormous resources to communicating the message that it is doing its best to help protect bee populations, even as the company continues to insist that the highly toxic neonicotinoids have nothing to do with bee colony decline.

A related body of evidence suggests that glyphosate harms not only bees but other insects as well. Among the potential victims are green lacewings, which eat aphids and have been used in biological pest control. These delicate insects suffer high mortality and impaired development from glyphosate exposure. And recent studies showing that glyphosate can interfere with the formation of the hard cuticle of beetles, apparently by also harming symbiotic bacteria the insect needs to form this hard exoskeleton, has raised further alarms about the herbicide’s effects on insect populations.

As scientists continue to study glyphosate’s effects on humans, insects, animals (including birds) and microbes, it seems there are few organisms that have not been potentially affected as use of the herbicide and its accumulation in the environment have greatly increased. That’s why anti-herbicide activists are so determined to see it banned from agricultural use as well as in local communities, using a combination of activism and lawsuits to achieve those goals. And while Bayer and other agrochemical companies are formidable opponents, it is becoming harder to argue that the activists don’t have science on their side.