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Author: Bruce Lanphear, MD, MPH NOTE: This article was originally published on May 12, 2026 by Plagues, Pollution & Poverty on Substack. We’ve gotten very good at reading the aftermath of disease. The harder—and more important—task is learning to read its origins.
What we’ve lacked is a way to see further upstream—to identify the exposures that quietly set disease in motion years or decades earlier. That’s where epigenetic fingerprints may matter most. Not merely as markers of disease, but as clues to what caused it—and how we might finally prevent it. Pesticides are a recognized—and growing—risk factor for cancer. That should no longer be controversial. What remains controversial is something more basic: our failure to protect people from them. Not because the evidence is absent. But because we still struggle to answer a deceptively simple question: Which chemical caused this cancer? The Story We Tell Ourselves When someone is diagnosed with cancer, we reach for familiar explanations. Genetics. Lifestyle. Bad luck. These explanations are familiar and comforting, but they are also incomplete. Genes matter, but they rarely act alone. “Bad luck” is a placeholder for what we have failed to measure. And lifestyle—diet, smoking, exercise—has become a convenient catch-all that obscures the role of carcinogens and other toxic chemicals embedded in the environments we’ve created. Meanwhile, cancer rates are changing in ways that are hard to explain by genes alone. Early-onset cancers—colon and breast—are rising in younger adults. These are not diseases driven by slow genetic drift. They are signals. Among the suspects, pesticides stand out. Their use has expanded dramatically over the past half century. They are now woven into modern agriculture and dispersed through food, water, soil, and air. Many are biologically active by design—engineered to disrupt cellular processes in plants, insects, or fungi. It should not surprise us that some may also disrupt human biology. Yet pesticides often remain strangely invisible in conversations about cancer. Suspected, debated, endlessly litigated—but rarely pinned down. The Missing Fingerprint The problem is not just whether pesticides cause cancer. The problem is whether we can convincingly link a specific chemical to a particular disease in a particular person. For smoking, we have fingerprints: tar in the lungs, characteristic DNA mutations, unmistakable dose-response relationships. The evidence became overwhelming because the trail was visible. For most pesticides, the trail has been far murkier. We rely on animal studies at high doses, occupational studies with imperfect exposure histories, ecological analyses, or self-reported pesticide use collected years after exposure occurred. Each provides a fragment of the story. None provides the kind of definitive signature that changes public understanding—or legal accountability. That gap between exposure and attribution has enormous consequences. It allows doubt to persist. It slows regulation. It shifts the burden of proof onto the public. And it gives manufacturers room to argue that causation remains uncertain. If you cannot measure exposure precisely, responsibility becomes endlessly contestable. A New Way to Read the Past A recent Nature Medicine study offers a way forward—and it is as elegant as it is disruptive. Instead of trying to measure pesticide exposure directly, the researchers asked a more provocative question: What if the exposure is already recorded in the tumor itself? They turned to epigenetics—the chemical marks on DNA that regulate gene expression. Unlike mutations, which alter the DNA sequence itself, epigenetic marks can shift in response to environmental exposures. And importantly, they can persist. In effect, they are a biological memory or fingerprint. Using data from multiple cancer cohorts, the researchers constructed what they call methylation risk scores—patterns of DNA methylation associated with specific exposures, including several pesticides. These scores act as epigenetic fingerprints. They didn’t measure the pesticide in blood or urine. They inferred past exposure from the imprint left behind in tumor tissue. That’s the conceptual leap. From Signal to Evidence The study focused on early-onset colorectal cancer, one of the most alarming emerging cancer trends worldwide. After constructing these epigenetic fingerprints, the researchers compared tumors from younger and older patients. What they found was striking. A consistent signal linked early-onset colorectal cancer with exposure to the herbicide picloram. But the researchers did not stop there. They replicated the findings across multiple independent cohorts. Then they zoomed outward to population-level data, examining county-level pesticide use across the United States over two decades. Counties with higher picloram use showed higher rates of early-onset colorectal cancer. Three independent lines of evidence—epigenetic, clinical, and population-level—all pointing in the same direction. This is what environmental health research has often lacked. Not merely associations. Not merely plausibility. But a coherent chain linking exposure to disease. Why this Matters This approach changes the terms of the debate. Epigenetic fingerprints offer something new: a way to reconstruct exposure after the fact—a biologic record of what the body has encountered. They move us from vague suspicion toward something far more concrete: evidence that an exposure likely occurred and left a measurable imprint. In utero and early childhood pesticide exposure is consistently associated with DNA damage, chromosomal abnormalities, altered gene expression. These molecular signatures may eventually serve as biologic “fingerprints” of exposure, allowing scientists to reconstruct environmental exposures with far greater precision than traditional epidemiology has allowed. They will never be perfect. No biomarker is. But they shift the burden of proof. Instead of demanding absolute certainty before acting, we can begin to ask a more reasonable question: does the evidence—from biology, toxicology, and epidemiology—point consistently in the same direction? That is how science advances. The Broader Pattern If this were just about one herbicide, it would be interesting. But it’s not. The same study found signals for other pesticides—glyphosate, atrazine, and more. The details will evolve. Some findings will strengthen; others may fall away. But the pattern is clear: We are beginning to see the outlines of how environmental exposures become biologically embedded. And once you see that, it becomes harder to maintain the fiction that cancer is primarily a matter of genes or chance. The Legal Endgame At the same time that science is inching toward clearer attribution, the legal landscape is moving in the opposite direction. The ongoing Supreme Court case involving glyphosate is, in many ways, a last-ditch effort to avoid liability by redefining the rules of evidence. The argument is familiar: if federal regulators have approved a product, can manufacturers still be held accountable under state law for failing to warn about its risks? Strip away the legal language, and the underlying strategy is straightforward: emphasize uncertainty, challenge causation, and shift the burden of proof. It is a strategy that has been used before—by tobacco, by asbestos, by lead. And it depends on one thing above all: the absence of clear, individual-level evidence linking exposure to harm. That is exactly the gap studies like this begin to close. What We Choose to See We are at an inflection point. On one side is a familiar narrative: cancer as an inevitable consequence of aging, genetics, and chance. A problem to be managed, treated, endured. On the other is a more uncomfortable reality: cancer as, in part, a consequence of the environments we have created—and can change. The difference between these narratives is not just scientific. It is political, economic, and moral. If cancer is due to genes or bad luck, there is little to be done beyond better treatments If it is, in part, environmentally driven, then prevention becomes possible—and responsibility becomes unavoidable. The Next Step This study gives us a new tool—a way to read the biological record of exposure. Now the question is whether we will use it. Will we expand biomonitoring and epigenetic surveillance? Will we integrate these measures into public health? Will we act on early signals, or wait for certainty that never quite arrives? We have seen this story before. With lead, we waited decades to act, long after the evidence was clear. With tobacco, we debated while millions died. With air pollution, we underestimated until the burden became impossible to ignore. Pesticides may follow the same path. Or they may not. Because for the first time, we are beginning to see their fingerprints in cancer. And once you can see the cause, it becomes much harder to look away. ■ |
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