The Hidden Risks of Pesticides


  • Exposure to low doses of atrazine leads to changes in the gut microbiota of wasps, increasing their resistance to pesticides
  • Researchers exposed wasps to atrazine at concentrations of 300 parts per billion, an amount meant to simulate the exposure level that would occur among pollinators visiting a field that was recently sprayed
  • Changes in gut microbiota occurred, Changes in gut microbiota occurred, including not only the herbicide atrazine but also glyphosate — a chemical to which the wasps had not been exposed
  • The microbial changes in the wasps’ guts persisted across successive generations, meaning that the wasps’ offspring were affected even though they weren’t exposed to atrazine
  • Host-microbiome interaction is not part of standard biorisk assessments for pesticides

Chemical pesticides have become a mainstay of modern agriculture, despite red flags that they’re slowly destroying ecosystems. (Technically, pesticides are designed to kill insects, while herbicides are used to kill weeds or substances like bacteria or fungi, but when discussing them, the U.S. EPA lumps them all together as “pesticides.”1)

Part of what makes assessing the health and environmental risks of pesticides so difficult is that many of the risks remain unknown, and those that are known can be difficult to quantify, no matter what they’re called.

So, researchers like Robert Brucker, who heads up a lab in the Microbial Sciences Initiative at the Rowland Institute of Harvard, are invaluable. Brucker and colleagues are looking into the hidden risks of pesticides — silent, insidious changes that are occurring before our eyes yet often under the radar, such that standardized risk assessments do not consider them, but should.

In research published in Cell Host & Microbe, the researchers looked into the effects of atrazine, an herbicide that’s banned in the European Union but widely used in the U.S., on Nasonia vitripennis, a wasp. According to the study, “atrazine is the second-most-sold pesticide globally.”2

The study revealed that exposure to low doses of atrazine leads to changes in the gut microbiota of the wasps, increasing their resistance to pesticides. What’s more, the changes were transferred to subsequent generations. “The big surprise,” Brucker said in a news release, “was that one exposure, even at a nontoxic level, was enough to cause a heritable change in the microbial community.”3

Atrazine Changes Gut Microbes, Increases Pesticide Resistance

Pesticides are an example of one of the greatest exposure risks to xenobiotics — chemical compounds found in a living organism that are not normally produced or consumed by the organism in question. When consumed, xenobiotics are either absorbed directly by the gut or metabolized by gut microbiota.

It’s often said that atrazine is a “safe” pesticide because animals lack the ability to metabolize it, but it’s known that bacteria in soil and water can metabolize the chemical.4

“We chose atrazine because it’s widely used for corn crops, and is considered to be safe to most animals: Up to 3 [parts per billion, or ppb] is allowable in drinking water,” Brucker stated. “One of the first things we did was evaluate whether it was even toxic to our wasps — we had no reason to think it would be [at lower doses].”5

For the study, researchers exposed wasps to atrazine at concentrations of 300 ppb, an amount meant to simulate the exposure level that would occur among pollinators visiting a field that was recently sprayed. Changes in gut microbiota occurred, which increased the insects’ tolerance to pesticides, including not only atrazine but also glyphosate — a chemical to which the wasps had not been exposed.

The microbial changes in the wasps’ guts persisted across successive generations, meaning that the wasps’ offspring were affected even though they weren’t exposed to atrazine.

“Pesticide resistance is something that agriculture scientists are continually looking to avoid, so this finding is important,” Brucker continued. “When the wasps were only exposed to only 30 ppb of atrazine, the effect over 36 generations was increased resistance.”6

Wild Honeybees Also Affected by Atrazine

The researchers then screened wild honeybees from Brucker’s Ohio family farm, which live in an area with cornfields that had been sprayed with atrazine. Bacterial genes capable of degrading atrazine and, probably, other xenobiotics were found — genes that were “nearly identical” to genes found in the laboratory wasps.7 Writing in Cell Host & Microbe, the researchers concluded:8

“The rare gut bacteria Serratia marcescens and Pseudomonas protegens contributed to atrazine metabolism. Both of these bacteria contain genes that are linked to atrazine degradation and were sufficient to confer resistance in experimental wasp populations.

Thus, pesticide exposure causes functional, inherited changes in the microbiome that should be considered when assessing xenobiotic exposure and as potential countermeasures to toxicity.”

Notably, despite increasing attention to the extensive role the gut microbiome plays in health, host-microbiome interaction is not part of standard biorisk assessments for pesticides, though Brucker believes it should be. He stated in a Harvard news release:

“Everyone feels strongly about protecting our pollinator species, so we may need to be mindful of our uses of xenobiotics in crop management.

We need to understand multigenerational exposure better, and make host–microbiome interaction part of biorisk assessment in the future, especially in light of increasing xenobiotic exposure to humans, plants, animals, fungi, and bacteria across the globe.”9

Moving toward regenerative agriculture is the answer to reducing the toxic reliance on pesticides that is harming the environment and pollinators along with it. However, in the meantime Brucker and colleagues are even looking to develop probiotics for wasps that could help to stem some of the risks caused by multiple exposures to pesticides.

Atrazine Linked to Reproductive Problems

If you’re wondering why atrazine has been banned in the European Union, it’s because it’s already been linked to a wealth of health and environmental problems, including that it may be chemically castrating male frogs, essentially turning them into female frogs — a finding made by Tyrone Hayes, Ph.D., an integrative biologist at the University of California, Berkeley.

Hayes’ research hypothesized that atrazine turned on an enzyme (aromatase) that caused testosterone to be converted into estrogen. If you’re a male, this means that you won’t make sperm, but you will make estrogen, even though you shouldn’t.

According to Hayes and colleagues in research published in Nature in 2002,10 exposure to water-borne atrazine contamination led to “gonadal abnormalities such as retarded development and hermaphroditism” in 10% to 92% of male wild leopard frogs. Hayes published another study in 2010 in Proceedings of the National Academy of Sciences (PNAS), which similarly found:11

“Atrazine-exposed males suffered from depressed testosterone, decreased breeding gland size, demasculinized/feminized laryngeal development, suppressed mating behavior, reduced spermatogenesis, and decreased fertility.”

Atrazine is known to be a widespread water contaminant as well, including in drinking water. In the U.S., atrazine has been detected in 78% of drinking water,12 and as noted by the authors of the featured study, “Previous studies have shown atrazine has multiple impacts on a host animal, including changes in stress response gene expression, protein production, male mating ability, egg production, mating choice, mitochondrial dysfunction, insulin resistance, and overall survival.”

Further, by inducing aromatase,13 which causes overproduction of estrogen, atrazine is also suspected of contributing to breast cancer14 and is a potent endocrine disrupter.

More Evidence Glyphosate Causes Cancers

Atrazine is only one pesticide that’s causing potentially devastating effects. In March 2015, the International Agency for Research on Cancer (IARC), which is the research arm of the World Health Organization (WHO), determined glyphosate to be a “probable carcinogen” (Class 2A).

Since then, Monsanto (which was acquired by Bayer in June 2018), has been inundated by lawsuits from people claiming their cancer was caused by Roundup, which contains glyphosate as its active ingredient.

In the U.S., approximately 42,700 U.S. lawsuits from individuals alleging that glyphosate caused them to develop cancer have already been filed.15 Bayer is in settlement talks to resolve the litigation but continues to deny that the chemical causes cancer.

Ken Feinber, a court-appointed mediator, stated in January 2020 that Roundup cancer claimants could surpass 75,000.16 In the first three cases to go to trial, Bayer has been ordered to pay billions of dollars to the plaintiffs, although the awards were later slashed to the tens of millions range.

Research published in Frontiers in Genetics also supports glyphosate’s cancer link, finding that exposure in low concentrations (in parts per trillion) may induce cancer in cells when combined with microRNA-182-5p (miR182-5p).17

MicroRNA-182-5p is a gene regulatory molecule found in everyone, and overexpression of the molecule has been linked to cancer. Michael Antoniou of King’s College London, who peer reviewed the study, stated, “These observations highlight for the first time a possible biomarker of glyphosate activity at the level of gene expression that could be linked with breast cancer formation.”18

Glyphosate Review Finds ’37 Significant Tumor Findings’

Likewise, a February 2020 study published in Environmental Health conducted a comprehensive analysis on animal carcinogenicity data for glyphosate, revealing 37 significant tumor findings. The researchers wrote:19

“The strongest evidence shows that glyphosate causes hemangiosarcomas, kidney tumors and malignant lymphomas in male CD-1 mice [a type of mice often used in cancer research], hemangiomas and malignant lymphomas in female CD-1 mice, hemangiomas in female Swiss albino mice, kidney adenomas, liver adenomas, skin keratoacanthomas and skin basal cell tumors in male Sprague-Dawley rats, adrenal cortical carcinomas in female Sprague-Dawley rats and hepatocellular adenomas and skin keratocanthomas in male Wistar rats.”

Further, according to research by Stephanie Seneff, a senior research scientist at the Massachusetts Institute of Technology, glyphosate inhibits cytochrome P450 (CYP) enzymes that catalyze the oxidation of organic substances.20 One of the functions of CYP enzymes is to detoxify xenobiotics.

By limiting the ability of these enzymes to detoxify foreign chemical compounds, glyphosate enhances the damaging effects of those chemicals and environmental toxins you may be exposed to. If you’re interested, the Health Research Institute (HRI) in Iowa developed the glyphosate urine test kit, which will allow you to determine your own exposure to this toxic herbicide.

They’re also in the process of doing hair testing for glyphosate, which is a better test for long-term exposure. If it turns out that you have measurable levels of glyphosate in your body, Seneff shared some tips for detoxing glyphosate here.

Atrazine Could Be Dropped Without Harming Economy

It’s often assumed that the reason harmful chemicals like atrazine are tolerated is because they contribute to significant gains for crop yields and the economy.

In the case of atrazine, however, cost-benefit studies suggest atrazine may boost corn yields by as much as 6%, while others have found a 3% to 4% increase and others have found only a 1% increase in yields. Yet, when Italy and Germany banned atrazine in 1991, no decrease in corn yields or harvested area occurred.

And, as noted by the late Frank Ackerman, an economist who formerly worked at Tufts University, “Even if atrazine leads to 6% more corn production, it is not certain that this would justify its continued use; a 1%, or perhaps zero, change does not warrant large-scale exposure of humans and the environment to this potentially hazardous chemical.”21

Unfortunately, the U.S. continues to lag behind other nations in banning harmful pesticides like atrazine and glyphosate, at the expense of human health and the environment. According to Nathan Donley, of the Environmental Health Program at the Center for Biological Diversity:22

“Many pesticides still widely used in the USA, at the level of tens to hundreds of millions of pounds annually, have been banned or are being phased out in the EU, China and Brazil. Of the pesticides banned in at least two of these nations, many have been implicated in acute pesticide poisonings in the USA and some are further restricted by individual states.

The United States Environmental Protection Agency (US EPA) has all but abandoned its use of non-voluntary cancellations in recent years, making pesticide cancellation in the USA largely an exercise that requires consent by the regulated industry.”

You can help protect the welfare of humans, animals, insects and the environment alike every time you shop organic, biodynamic and grass fed, as you are “voting” for less pesticides and herbicides with every organic and pastured food and consumer product you buy.

In addition, take steps to make your own backyard healthier for everyone by eliminating the use of pesticides and other chemicals and planting a diverse variety of native flowers and other plants.

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