THE BACKYARD of our Berkeley home is crisscrossed with gravel-lined paths. Not long after we moved in two years ago, I sought advice on how to keep rainy-season weeds from swallowing them whole. One gardener recommended a handheld Japanese blade called a scraper, but using it was like painting the Golden Gate Bridge: by the time I finished it was time to start over again. A second gardener suggested something called a hula hoe; slightly better than the scraper, but still. A third came by, looked at the yard, and said there was only one solution: Roundup. A quick spray, he said, and all the weeds would be gone.

I had used the weed killer before, a few years earlier, on a stubborn stand of poison ivy one of our dogs kept rooting through in the yard of our previous home, in Atlanta. It was magic. Yanking out the ivy by the roots didn’t do the trick; Roundup did.

But I bought that first bottle with reservations. As someone who studies the history of health and the environment, and the infamous and long-banned pesticide DDT in particular, I was familiar with Roundup’s backstory. The weed killer — active ingredient glyphosate — was introduced in the 1970s, and its use skyrocketed after agricultural giant Monsanto began rolling out “Roundup Ready” soybeans and other crops in the 1990s. The crops were genetically modified to contain plant-bacterial DNA that made them resistant to death by Roundup. Spray a row of Roundup Ready corn, and the surrounding weeds perish while the corn stands tall and green. Today, more than 90 percent of US soy and 80 percent of US corn is genetically modified to stand up to Roundup. And US farmers apply more than 100 million pounds of glyphosate to soy and more than 60 million pounds to corn each year.

My Roundup use, I told myself at the time, would be imperceptible in comparison. I’d spray an ounce or so and be done with it.

But the ivy came back, and during the years we lived in Atlanta, I reached for the Roundup bottle again and again.

So as I stood on the weed-eaten paths of our California yard last spring, I couldn’t make the same decision. But it wasn’t just because I knew the weeds, like the ivy, would keep coming back. It was because the moral costs of Roundup seemed to have compounded in the interim. In 2015, the World Health Organization had declared glyphosate a “probable” cause of human cancer. In 2016, my new home state of California notified the public that it planned to add glyphosate to the Prop 65 list of chemicals known to cause cancer. In 2017, it did. And so our gravel disappeared under a blanket of green.

Then this past fall, Island Press, based in Washington, DC, and known for its books on big environmental problems, published Whitewash, an exposé on Roundup by longtime Reuters agricultural reporter Carey Gillam. Erin Brockovich promised it read “like a mystery novel” as it revealed “Monsanto’s secretive strategies.” I quickly reached for a copy, eager for a good read on the chemical’s unstoppable rise and a journalistically objective assessment of the full range of its health and environmental risks. The book, I’m sorry to report, isn’t quite a mystery novel. But it has stayed with me. By the time I finished it, I was more secure than ever in my decision not to spray Roundup, and I went to greater lengths than usual to bring home organic and pesticide-free foods for my family. But the book also raised more questions for me than it answered. And it made me aware of a troubling set of ironies embedded in the regulatory system charged with upholding health and environmental standards while securing economic interests.

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Over the course of two decades as a Kansas-based reporter for Reuters, Gillam, once a devoted consumer fan of Roundup herself, heard two stories about the chemical.

In the first story, Roundup was, as one farmer put it, a “godsend.” Glyphosate’s properties made it possible for farmers to put acres overrun by weeds back into production. In planted fields, its targeted and thorough weed control increased crop yields, by preventing weeds from sapping crops’ water and nutrients. Better weed control meant bigger yields, and, theoretically, bigger profits. Glyphosate also obviated the need to till fields to control weeds, thereby helping to reduce erosion. By reducing erosion, it also helped decrease chemical runoff from fields into nearby waterways. It did all this while being supposedly safer than table salt. If you could use some help visualizing these claims, watch Monsanto’s slick video, “Glyphosate: Give it a Minute.”

In time, however, Gillam began to hear a second, darker story. Farmers brought her to their fields to show her gargantuan “superweeds” cropping up in defiance of glyphosate. One weed grows an inch a day, reaching a height of 12 feet if left unchecked. Another grows up to three inches a day, producing a stem so tough it can damage farm equipment. By 2016, superweeds had “infested” more than 70 million farm acres in the United States, a more than doubling of the amount affected in 2010. The situation is reportedly most dire in the Southeast, where more than 90 percent of cotton and soybean farms are infested, and farmers have had no choice but to return to hand weeding. “We’re running out of tools,” one farmer told her.

Gillam learned, too, of the country’s dramatic loss of the iconic North American monarch butterfly, whose numbers, according to one study, have declined so precipitously since the turn of the millennium that it may be extinct within 20 years. Monarchs prefer to lay their eggs on milkweed, and their caterpillars like to eat it, but glyphosate sees milkweed the same as any other weed. In Iowa alone, nearly all of the state’s milkweed — 98.7 percent — disappeared in roughly the first decade of our millennium, thanks to widespread adoption of glyphosate.

The most troubling thing Gillam heard, given its prominence in the book, is a story all too familiar to those who know the long and troubled history of pesticides: the story of sick and dying farmers. In fact, this is how Whitewash begins: with the story of Jack and Terri McCall, who once grew avocado, lemon, and orange trees on their central California farm. Jack used just one chemical on the farm, Roundup, but he used lots of it. In late 2015, Jack succumbed to non-Hodgkin’s lymphoma, a deadly cancer whose numbers have “spiked” in recent decades, according to Gillam, especially in North America. The lymphoma is now the seventh-most common cancer in the United States, and Terri, now Jack’s widow, has turned the farm into a bed-and-breakfast instead.

The science linking glyphosate to non-Hodgkin’s lymphoma, it’s important to note, is far from conclusive. By the early 1990s, a handful of studies had found higher levels of non-Hodgkin’s lymphoma among US farmers in the United States. A subsequent National Cancer Institute–led study that pooled data on farmers in Iowa, Kansas, Nebraska, and Minnesota found that the risk of the lymphoma seemed to increase with exposure to nine different agricultural chemicals, glyphosate among them. Meanwhile, the Agricultural Health Study, a massive, ongoing, government-funded study that follows tens of thousands of farmers in Iowa and North Carolina, has found no link to date between glyphosate and the lymphoma. (Though the most recent investigation of the data did find a link between glyphosate and another cancer, acute myeloid leukemia.)

This whole line of research on farmers built on lab studies in which glyphosate damaged chromosomes and DNA and caused tumors in rats and other animals. In fact, it was exactly the latter type of study that had led the EPA to originally classify glyphosate as a carcinogen back in 1985.

According to Gillam, however, the agency reversed that decision following six years of pressure from Monsanto, and glyphosate has been considered “safe” ever since.

Then, in 2015, the World Health Organization convened 17 experts from 11 countries at its International Agency for Research on Cancer (IARC) in Lyon, France, to review the data on glyphosate and four other pesticides. The agency operates as an independent international coordinator for global cancer research. It also regularly reviews the evidence on suspected carcinogens and publishes reports that rank their carcinogenicity on a five-point scale, from “probably not” carcinogenic to “carcinogenic.” Its glyphosate assessment, which revisited the 1985 data that originally concerned the EPA, ranked glyphosate at level four, just shy of definitely carcinogenic. There was only “limited evidence” that it caused non-Hodgkin’s lymphoma in people, the group concluded, but there was “convincing evidence” it caused cancer in lab animals, and it caused clear damage to human genetic material in the lab.

The IARC’s report dealt glyphosate a hard blow. Outraged consumers in Europe (which has long been less tolerant of GMOs than Americans have been) called for a Union-wide ban. Some European countries went ahead and enacted their own, limited bans; others restricted glyphosate’s sale. And California, of course, announced its intention to list the herb-killer on its Prop 65 list. Monsanto, in response, filed suit against the state. It subpoenaed the emails of the IARC review panel’s chair. It devised a plan to discredit IARC scientists and their research.

Today, the IARC’s own website says that since the 2015 announcement, it “has been the target of an unprecedented number of orchestrated actions by stakeholders seeking to undermine its credibility.”

As she watched these events unfold, Gillam knew exactly what was going on. When her own reporting on glyphosate had turned critical, she writes, she was cajoled, intimidated, and bullied. One Monsanto ally, she said, called her “hideous” and “disgusting” on social media. The story of glyphosate as godsend had prevailed for too long, she believed. She had at hand evidence of the details behind the darker story, and then some: documents obtained through Freedom of Information Act requests to federal agencies, court records and tax filings, reporting trips to places (Hawaii, parts of Argentina) where glyphosate use outpaced that in the mainland United States, and interviews with silenced scientists. It all pointed to the underlying machinations behind the superweeds, disappearing butterflies, and cancer cases: a long-standing and troublingly “cozy” relationship between Monsanto and the EPA.

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When the EPA declared glyphosate a carcinogen back in 1985, it did so only after the weed killer had been on the market for more than a decade. A team of agency scientists reviewed a collection of studies in which glyphosate appeared to cause thyroid tumors in female rats, testicular tumors in male rats, and a rare form of kidney tumor in mice. It was the latter finding that led the EPA to declare glyphosate a “possible” cause of cancer.

In documents that Gillam’s reporting turned up, a Monsanto manager responded to the EPA’s news by arranging for the kidney tumor slides to be reexamined by an academic pathologist — one who would “persuade the agency that the observed tumors are not related to glyphosate.” And that’s exactly what the pathologist did, by finding a tumor no one else had noticed among the control mice, thereby calling into question any conclusive scientific meaning that might be attached to the tumors in the mice given glyphosate.

The EPA’s own scientists couldn’t find any tumors in the control mice. Monsanto nonetheless argued that the chemical’s profile needed to be reevaluated by the agency. When the agency asked Monsanto to repeat the study (it was, in fact, Monsanto’s study to begin with), the company declined.

Monsanto’s influence, in this version of events, got glyphosate downgraded from a Group C carcinogen in 1985 — something “possibly” carcinogenic to humans — to a Group D carcinogen in 1986: “not classifiable as to human carcinogenicity.” When EPA reviewed the data on glyphosate again, in 1991, it downgraded the weed killer to Group E: “evidence of noncarcinogenicity in humans.”

Not all of the scientists on the panel agreed with the conclusion, Gillam notes; one wouldn’t even sign it. In the end, the panel added a caveat: their classification of the chemical should not be interpreted to mean that glyphosate would not cause cancer under any circumstances.

When the IARC made its 2015 announcement, by contrast, the EPA didn’t have to capitulate to Monsanto’s wishes gradually; instead, it anticipated them. The agency, Gillam reports, gave the company advance notice of the IARC’s decision before it was announced. After the IARC’s announcement, the EPA conducted yet another review of its own, finding glyphosate once again “not likely” to cause cancer in people. The IARC’s conclusion was based on studies published in peer-reviewed journals; the EPA’s was based on a collection of studies that included unpublished work submitted by Monsanto. Ditto for the EPA’s assessment of glyphosate’s potential to disrupt human hormones, which it also undertook after the IARC review. Glyphosate was not a so-called endocrine disruptor, EPA declared, but it did not disclose that it drew the conclusion based on 32 studies, 27 of which were “conducted by or funded by Monsanto or its industry allies,” according to Gillam.

There’s more, she notes. When Monsanto asked the agency to raise glyphosate “tolerances,” the amounts of chemical residue allowed on crops after harvest, the EPA complied. The EPA now considers it “safe” for people to ingest 1.75 milligrams of glyphosate per kilogram of their body weight on a daily basis — an amount nearly six times what the European Union considers safe.

Whitewash details the factors making this possible: the EPA has employed scientists who acted in the direct interest of industry, has selectively ignored certain scientific findings, and has repeatedly heeded industry requests to remove certain scientists, those not so friendly to industry, from its scientific review panels. In fact, when the agency convened a panel to reevaluate glyphosate after the IARC announcement, it excluded a scientist of its very own who had been considered expert enough to take part in the IARC review.

Gillam’s findings are backed up by now-decade-old survey results from the Union of Concerned Scientists: 889 EPA scientists responded that they had experienced “inappropriate interference” in their work; almost 400 said they had witnessed EPA officials misrepresenting scientific findings; and 284 said they had seen data used selectively to “justify a specific regulatory outcome.”

Add to that a bureaucratic backlog of a frightening scale: a 2013 Government Accountability Office investigation found that more than 11,000 of the 16,000 pesticides registered by the EPA for use in the United States were only “conditionally” approved for market, on the agreement that companies would submit the full suite of required data within a few years. Because the EPA failed to keep track or keep up, some of those 11,000-plus pesticides have been conditionally registered for 20 years or more.

The EPA isn’t the only agency catering to industry interests over those of public and environmental health, though. Since the 1960s the FDA has conducted an ongoing study of roughly 800 contaminants and nutrients in the American diet, but it didn’t test for glyphosate until 2016 — and then only because a GAO report chastised the agency for not yet doing so. The USDA tests food products for residues of more than 400 agricultural chemicals, but it doesn’t test for glyphosate, even though it’s the top agrochemical and it’s sprayed directly on crops.

And Monsanto did more than just pressure the EPA. Gillam documents fraud in laboratories Monsanto used for its safety testing: one lab falsified data on pesticide residues, the other swapped healthy animals for dead ones in its studies, without noting the fatalities. She digs up evidence that Monsanto employees ghostwrote research manuscripts and had independent scientists outside the company sign their names to them. She names the seemingly independent academics who champion and promote the company’s products and their underlying technologies at the company’s behest, and with company support, via international talks, blogs, policy briefs, social media campaigns, and more.

At least one such academic ally, a University of Nebraska food science professor, used his influence to orchestrate a defense against a widely reported rat study showing that alarmingly low levels of Roundup — far lower than that allowed in US drinking water — in their diet caused increased death rates, tumors, and liver and kidney damage. Not long after the study was published in a peer-reviewed journal, the professor was named an editor of the journal, and a year after that, the study was retracted. (It was subsequently republished elsewhere.)

As sustainable food advocate Anna Lappé once put it, “Sure, PR is an old game, but Big Ag is giving the age-old techniques of shaping public opinion a new, sneakier spin.”

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Whitewash may not be a mystery novel, but it is a well-documented compendium of wrongs, fraud, conflicts of interest, undue influence, and troubling forms of plain old public relations. Some of its revelations are hardly surprising, like the fact that Monsanto uses no end of dubious but permissible practices to protect its profits. Some of its revelations are downright infuriating: scientists replacing sick or dead lab animals with healthy ones, federal regulators increasing the amounts of agrochemicals permitted in our diets at industry’s request, the dance between regulators and industry representatives that determines whose scientific findings count when evaluating which chemicals to approve for market, and whose don’t.

The most vexing revelation, however, is somewhat hidden between the lines of Gillam’s pages. I already knew that traces of DDT persist in my body; now I also know that glyphosate is in me, too. It’s there because the chemical is so widely used in agriculture that we all encounter it somewhere, never mind corn and soy. It’s in tap water, wine, and beer; cereal and honey; flour and eggs; baby formula and breast milk. And it hasn’t just been used on farms: it’s been sprayed for decades in city parks, school playgrounds, golf courses, and zoos. When the European Union’s Green Party invited members of parliament to take a urine test for glyphosate in the wake of the IARC announcement, the herbicide was found in every last sample submitted. Glyphosate defenders said this was nothing to worry about, as it indicated the chemical was being excreted as expected.

That may be true, but I have no way of knowing exactly what the glyphosate in my body means for my health — let alone the health of the gardeners and farmers who use it every day.

As Gillam reminds her readers again and again, published, peer-reviewed studies conducted by independent scientists suggest that glyphosate may cause non-Hodgkin’s lymphoma, not to mention other forms of cancer, endocrine disruption, birth defects, and Parkinson’s disease. Industry studies, by contrast, show it to be safe. The public isn’t allowed to see industry studies, however, because they’re considered trade secrets. Regulators can, but whether they do is an open question, thanks to industry influence and bureaucratic inefficiency.

Even if all of the industry’s safety testing was made public, however, it likely still wouldn’t tell us what we need to know. When the FDA approves new drugs, it does so on the basis of clinical trials that show the drugs to be effective and safe in people. But as Linda Birnbaum, director of the National Institute of Environmental Health Sciences and National Toxicology Program, wrote in a 2013 editorial, environmental chemicals such as pesticides “are not required to be tested for side effects and potential hazards prior to their commercial use.” The scientific assumption has long been that if the chemicals seem safe in animal tests, they’ll be safe in people — especially given that people eat mere “residues,” tiny, nearly infinitesimal amounts.

But environmental health advocates say there are two key problems with this approach. First, animal tests don’t always predict what will happen in people. And second, as Birnbaum notes, just because a dose is small no longer means it’s safe, because some chemicals can cause more harm at small doses than large ones, depending on a person’s age or stage of life. As she put it, “the classical dichotomy of toxic versus non-toxic no longer holds.”

And there are still other challenges to revealing the possible health effects of environmental chemicals. Long-term health consequences, like cancer, are notoriously difficult to study because such illnesses can take decades to develop. When they do develop, causality is hard to pinpoint because we are exposed to so many chemicals over the course of a lifetime, and because we have so little knowledge about how all of the chemicals we encounter interact with each other once they’re inside our bodies.

In the face of such challenges, scientists conduct studies that look like the Agricultural Health Study: observe as many farmers as much and as long as possible, with a close eye on their chemical exposures. By design, these “observational studies” have long excelled at determining correlation, not causation. When a carcinogen is exceptionally potent — like cigarettes, sun exposure, arsenic, or asbestos — the correlation is generally accepted as causal. More recently, scientists have developed more sophisticated methods for determining causality in less blunt scenarios. But observational studies still excel at generating, as science writer Gary Taubes once put it, “what researchers call hypothesis-generating evidence — what a defense attorney would call circumstantial evidence.”

So how to fully elucidate the health risks posed by chemicals like glyphosate? Back in the early 1950s, a federal toxicologist determined to settle the question of DDT’s safety took an unusual step by carrying out a randomized, controlled study, the study type now generally considered the gold-standard for testing new drugs. He randomly selected some people to consume either DDT or a placebo every day for a year, and then examined them to see what happened to their health. His conclusion: DDT was absolutely safe (over such a short period, at least). Such studies, even if scientists wanted to carry them out on glyphosate, are now impossible, for a number of reasons. One reason: Because glyphosate is so ubiquitous it wouldn’t be possible to find people who had never been exposed to it. Another: Because no research oversight board would approve a study that assigned people to be exposed to a strongly suspected carcinogen with no curative value.

Of course, that’s exactly what our regulatory system has done, by approving glyphosate for market on the basis of secret science, and permitting its use for decades at levels that, by now, have led to a little bit of the weed killer in all of us.

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When DDT was first released in the 1940s, the public was told it was a revolutionary discovery; decades later, farmers heard the same thing about glyphosate. DDT was initially marketed as the safest pesticide ever brought to market; later, so was glyphosate. In its time, DDT quickly became the most ubiquitous agricultural chemical in the country, sprayed not only on farms but on yards and parks and fairgrounds, and it made its way into every element of the American diet and into every American body — again, just like glyphosate.

Glyphosate has now been on the market for almost a quarter of a century. DDT was banned after less than 30 years on the market, thanks in part (so the story goes) to Rachel Carson’s Silent Spring, which detailed the pesticide’s harms to wildlife and humans. Gillam writes that she wishes we still heeded the lessons of Silent Spring. I’m just not sure those lessons apply.

Surely, there’s good ecological evidence for a ban on glyphosate, just as there were ample ecological reasons for abandoning DDT. But superweeds and disappearing monarchs may not be enough. When the then-new EPA held hearings on DDT’s risks and benefits in 1971, scientists presented hundreds of studies linking DDT to environmental harm — and three very preliminary studies linking it to cancer in humans. When the head of the EPA banned DDT in 1972, he cited cancer risk prominently in his decision. (And DDT defenders dismissed the cancer claim as a red herring.)

But there are two critical differences between DDT’s life story and glyphosate’s.

By the time DDT became the object of federal hearings, it was a failing technology. Flies had evolved to withstand the pesticide by the late 1940s, and mosquitoes honed their resistance to the pesticide in the 1950s and ’60s. Evolution has given us superweeds in response to glyphosate — not surprisingly, since the gene for glyphosate resistance was found in organisms in a waste pond outside a Roundup plant in Luling, Louisiana. But for now, Roundup Ready crops and Roundup are still, on the whole, working as advertised more often than not.

Moreover, DDT was not just failing from early on, it was also not terribly profitable. DDT manufacturers (and Monsanto was among the first) had been complaining since the 1950s that it was hard to make money on the non-proprietary pesticide, which was produced by so many companies that its price was persistently low. And as historian Frederick Rowe Davis has argued in his book Banned, DDT was included in thousands of products made by so many companies that no single company had a strong interest in keeping it in play. In other words, it was an easy target for a ban.

In the course of her research, one of Gillam’s sources tells her that in time we may come to realize that glyphosate is in fact more toxic than DDT. That may be true. But the harder truth to accept may be that the bar for proving its toxicity has been set so irretrievably out of reach. Perhaps the best we can do is more fully acknowledge the tilted balance our regulatory system is designed to strike between proof of safety and profitability.

In the eulogy for Jack McCall, his son Paul invoked DDT’s legacy to call for a ban on glyphosate. “They got rid of DDT,” he said. “They need to get rid of this, too.” Until it fully fails, consumers revolt, or we innovate our way around it, I just don’t see that happening any time soon, no matter the evidence of harm to ourselves or to our environment.

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Elena Conis is a writer and historian of medicine, public health, and the environment. She currently teaches at the Berkeley Graduate School of Journalism. She has also taught history at Emory University as a Mellon Fellow in Health and Humanities.