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The
Rise & Reckoning of Roundup |
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Author: Bruce Lanphear, MD, MPH NOTE: This article was originally published on March 24, 2026 by Plagues, Pollution & Poverty on Substack. Glyphosate was once hailed as the safest herbicide ever invented. For nearly half a century it helped reshape modern agriculture, spreading across farms, parks, gardens, and roadsides around the world. Today it sits at the center of one of the most contentious scientific and legal debates of our time. The controversy is no longer confined to scientific journals. It has moved into courtrooms and may soon reach the U.S. Supreme Court in Monsanto v. Durnell. At stake is not simply the fate of one lawsuit over Roundup, the herbicide that made glyphosate famous. The case raises a deeper question about how societies regulate chemicals: who bears responsibility for warning the public about risk—the government, the manufacturer, or the courts? For decades, pesticide regulation in the United States has rested on a delicate balance: federal oversight, state authority, and the ability of injured people to seek justice in court. The Roundup litigation now tests that balance. To understand why the stakes are so high, it helps to revisit how glyphosate—Roundup’s active ingredient—came to be regarded as one of the safest pesticides ever developed. The Promise of a “Safe” Herbicide When Monsanto introduced glyphosate in the 1970s, it seemed almost too good to be true. Unlike many earlier herbicides, glyphosate targeted an enzyme in the shikimate pathway, a metabolic route plants use to produce the aromatic amino acids phenylalanine, tyrosine, and tryptophan. Animals do not possess this pathway; we obtain those amino acids from food. Because of this biological difference, the herbicide was long assumed to pose little risk to humans. The implication seemed reassuring. If the herbicide disrupted a biological pathway humans lacked, how could it harm us? Early toxicology studies reinforced that confidence. Compared with many herbicides of the era, glyphosate appeared relatively benign. Paraquat could cause severe poisoning. Atrazine raised environmental concerns. Older herbicides such as 2,4-D came with their own controversies. Glyphosate degraded more quickly in soil and water and seemed to pose fewer immediate hazards. Regulators approved it. Farmers adopted it. Homeowners bought it by the bottle. Over time, Roundup became one of the most widely used herbicides in history. The Herbicide that Conquered Agriculture Glyphosate’s rise accelerated dramatically in the 1990s with the introduction of Roundup Ready crops, genetically engineered plants designed to tolerate the herbicide. Farmers could spray entire fields, killing weeds while leaving soybeans, corn, or cotton unharmed. Weed control became simpler, cheaper, and more predictable. Monsanto also promoted glyphosate as safe enough to use without protective gear, reinforcing the idea that it was not only effective but essentially harmless. What began as a useful tool soon became a cornerstone of modern agriculture. Since its introduction in 1974, more than 8.6 billion kilograms of glyphosate have been applied worldwide—making it the most heavily used herbicide in history. By the early 2000s glyphosate was everywhere—on farms, in gardens, along roadsides, in parks, and on school grounds. Remarkably, nearly three-quarters of that total has been sprayed in just the past two decades. For years the story seemed straightforward: a modern pesticide, carefully tested and widely considered safe. But science rarely leaves simple stories intact. The Studies that Shaped Glyphosate’s Reputation Early regulatory decisions about glyphosate relied largely on industry-sponsored animal studies. They were later reinforced by influential reviews—including one later retracted after it was revealed to have been ghostwritten by Monsanto employees—blurring the line between independent science and corporate influence. Some studies showed little evidence of harm. Others raised questions. In one mouse study from the early 1980s, animals exposed to glyphosate developed a dose-related increase in kidney tumors. EPA scientists initially interpreted the findings seriously enough to classify glyphosate briefly as a possible human carcinogen. The classification did not last. Monsanto argued that the tumors reflected statistical artifacts or unrelated pathology. After additional review, EPA reclassified glyphosate as not classifiable as to human carcinogenicity, and later as not likely to be carcinogenic to humans. One detail would later prove crucial. The studies regulators relied on tested technical-grade glyphosate, the purified active ingredient. They did not generally examine the commercial formulations people actually used. At the time, that distinction seemed minor. Later, it would become central. Molecule versus Mixture Farmers and landscapers do not spray pure glyphosate. They spray Roundup, a mixture containing surfactants designed to drive glyphosate through plant tissue. Those same surfactants can also enhance absorption through human skin. Regulators were evaluating the molecule. Workers were exposed to the mixture. The difference may sound technical, but it reflects a recurring problem in environmental health. Regulatory systems often test chemicals in isolation under controlled conditions. Real-world exposure is messier. People encounter mixtures of chemicals through multiple pathways—on their skin, in the air they breathe, and in the environments where they work and live. The gap between controlled testing and real-world exposure can create what might be called an acceptable daily illusion. Risk assessments identify doses that appear safe for an individual. Yet when exposures are repeated across millions of people, the cumulative consequences may become much harder to ignore. A Growing Controversy Beginning in the early 2000s, researchers started reporting associations between heavy exposure to glyphosate-based herbicides and certain cancers, particularly non-Hodgkin lymphoma among agricultural workers. The debate intensified in 2015 when the International Agency for Research on Cancer, part of the World Health Organization, classified glyphosate as a probable human carcinogen. Regulators in the United States and Europe reached a different conclusion. After reviewing many of the same studies, agencies such as the U.S. Environmental Protection Agency maintained that glyphosate was not likely to be carcinogenic to humans under typical exposure scenarios. Two groups of experts examined much of the same evidence and reached very different conclusions. When “Low Risk” meets Widespread Exposure Much of the debate about glyphosate has focused on heavily exposed applicators—farmers, landscapers, and groundskeepers who mix and spray the herbicide repeatedly. But another question has begun to emerge: what happens when a chemical considered relatively low in toxicity is used so widely that millions—or even billions—of people are exposed? Researchers at the Ramazzini Institute in Italy recently conducted long-term experiments exposing rats to glyphosate-based herbicides at doses intended to reflect real-world exposures—including levels regulators consider safe. The animals developed increased rates of leukemia, often appearing earlier in life, along with other signs of toxicity. The findings suggest that chronic, low-dose exposures—especially those beginning before birth—may produce harms that traditional toxicology studies, focused on short-term or high-dose effects, are poorly designed to detect. The bottom line is hard to ignore: exposures long assumed to be safe may be reshaping cancer risk in ways our standard methods were never built to detect—and that regulators have not pushed hard enough to uncover. A Population Problem This leads to a broader point. A pesticide does not have to be highly toxic to cause widespread harm. Even a small increase in risk, spread across millions of people, can produce a large burden of disease. Glyphosate is now the most widely used herbicide in history. It is sprayed on farms, in parks, along roadsides, and in home gardens across much of the world. Residues are routinely detected in food, water, and human urine samples. In that context, scale becomes part of the risk equation. The epidemiologist Geoffrey Rose described this phenomenon decades ago. A risk factor that increases disease only slightly for each individual can still produce many cases when nearly everyone is exposed. Glyphosate may—or may not—prove to be such a case. But the possibility helps explain why the debate over its safety has become so intense. From Journals to Courtrooms The scientific debate moved from journals to courtrooms in 2018, when a California jury awarded $289 million to a school groundskeeper who developed non-Hodgkin lymphoma after years of using Roundup. Several similar verdicts followed. In court, juries heard testimony about scientific studies, internal company documents, and allegations that Monsanto influenced scientific publications and regulatory discussions. Monsanto—now owned by Bayer—has consistently maintained that glyphosate is safe when used as directed. The company points to decades of regulatory reviews supporting that conclusion. But the lawsuits exposed tensions between regulatory assessments and emerging scientific concerns. The Legal Question At the center of Monsanto v. Durnell lies a deceptively simple claim. In legal terms, the company argues that federal pesticide law preempts state failure-to-warn claims. Plaintiffs counter that federal law establishes minimum standards but does not eliminate the role of courts in holding companies accountable. Yet there is an irony in this argument. By claiming that EPA approval should shield manufacturers from liability, companies are asking courts to assume something regulators themselves have never claimed: that EPA already knows enough to anticipate every meaningful risk. In reality, pesticide approvals rely on a small set of studies, mostly industry-funded, typically testing the active ingredient alone under conditions that don’t reflect real-world use. The influence of industry in shaping that evidence base—and in minimizing potential hazards—can’t be ignored. If courts accept the idea that EPA approval makes a label legally definitive, the next question becomes unavoidable: does the agency actually have the evidence needed to justify that authority? The answer could push regulation in the opposite direction the industry intends—forcing EPA, and perhaps Congress, to require more extensive testing of pesticides before they reach the market. For companies like Bayer, the strategic calculation is straightforward. Litigation risk is large, immediate, and unpredictable. A jury verdict can produce billions of dollars in damages and trigger thousands of new lawsuits almost overnight. Regulatory change, by contrast, tends to move slowly. Under laws like the Federal Insecticide, Fungicide, and Rodenticide Act, tightening regulations usually takes years of scientific review, public comment, and political negotiation. Even when new evidence raises concerns, regulators often revise labels or exposure limits rather than banning a product outright. From a corporate perspective, the greater threat is not future regulation but the uncertainty of the courtroom. Limiting lawsuits therefore becomes the more urgent priority. The Reckoning The glyphosate debate points to something larger than one herbicide. Many of the great public-health gains of the twentieth century came from reducing widespread exposures—cleaner water, improved sanitation, less lead, and cleaner air. These measures lowered risk across entire populations. Today health discussions often emphasize individual behavior. But chemicals like glyphosate remind us that many risks arise not from personal choices but from the environments societies collectively create. Farmers do not design the agricultural systems that determine which herbicides dominate their fields. Landscapers do not write pesticide regulations. Consumers rarely know which chemicals move quietly through the supply chains that produce their food. These are shared exposures—and shared decisions. Glyphosate began as a symbol of agricultural progress. Half a century later, it has become something else: a case study in how societies struggle to balance innovation, uncertainty, and the duty to protect public health. ■
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