Six Things You Should Know about the Pesticide Chlorpyrifos


Last week was a bad one for farmers. Two legal decisions were released that promise to undermine access to valuable agrochemicals that farmers need to produce a safe and affordable food supply. Both of these decisions came about thanks to a series of lies, misinformation, and junk science peddled by environmental activists and trial lawyers.

This is the first of two posts on these cases, and in it I address the agricultural pesticide chlorpyrifos, and the next post will address glyphosate, which is a herbicide used as the active ingredient in the product known as “Roundup.” 

Last Friday, the Ninth Circuit Court of Appeals ordered the U.S. Environmental Protection Agency (EPA) to ban chlorpyrifos because of an activist petition filed back in 2007. The Trump EPA denied this petition in March 2017 based on solid scientific grounds, but the court has now ordered the agency to ban the chemical within 60 days. The Trump EPA attempted to fight this latest legal battle based on procedural grounds, rather than debate the merits of their position. They should have stuck with the merits; they certainly can justify their decision based on the science. EPA may (and should) appeal the decision and maybe even take it to the Supreme Court.

The issue has been in dispute for more than a decade, so if you want all the details, see my paper on the topic. But let’s quickly set the record straight on some key points.

EPA did not reverse itself or go against its “own science.” The court opinion states (see page 11): “EPA’s own internal studies continued to document serious safety risks associated with chlorpyrifos use, particularly for children.” This is a claim that activists and peddled to the media, but it’s false.

The agency doesn’t have any of its “own science” on which to base this decision. The agency has been reviewing the full body of scientific research conducted outside the agency, which is part of a scheduled scientific review. Before 2015, the agency appeared to be moving toward a determination that chlorpyrifos uses were safe based on the complete body of science. But near the end of the Obama administration, agency officials reversed course and proposed a ban, eventually releasing a risk assessment claiming that its review of the science indicates that the risks are unacceptable.

Yet this proposed ban was not based on actual EPA research; it was based on a single, privately-produced study for which data remains unavailable to the public—even the EPA staff have never been able access to the underlying data. If anything, this situation underscores the need for greater transparency of regulatory science rather than the need for EPA to blindly regulate away useful products.

There is no body of science showing chlorpyrifos is dangerous; all the Obama EPA had was a single junk science study. EPA’s proposal to ban chlorpyrifos was based entirely on a single study conducted by Columbia University’s Center for Children’s Environmental Health, which is a university-housed anti-pesticide advocacy group (see my paper for details about this group). This study maintained that children whose mothers had higher exposures to chlorpyrifos from home pest control uses during 1997-2000 were more likely to experience developmental delays or neurological problems such as autism than other children. According to the study, the children’s’ exposures were based on trace levels found in the mothers’ umbilical cords when the babies were born.

Members of EPA’s Science Advisory Panel (SAP) were highly critical of this study at a meeting in March 2016. Among other things, they pointed out that EPA reliance on this single study was “premature and possibly inappropriate.” In addition, panel members criticized the study design and methodologies, voicing concerns that a “large fraction” of the data was basically fabricated because exposure was too low to measure. At least one SAP member questioned the biological plausibility of health effects given the fact that human exposures were so minute, in the “low parts per trillion.” Most importantly, they also noted that the blood cord data was not a good measure of exposure to the babies, which made the study flawed and conclusions questionable. So rather than use the study’s flawed data, the EPA revised risk assessment explains, agency staff developed new data based on agency estimates on how much exposure the women in these homes might have had from such chemical use.

That is, EPA staff basically made data up to fit the predetermined conclusions of the Center for Children’s Environmental Health study. That’s pretty outrageous and certainly not how scientific research should be performed. In fact, this approach fits the definition of junk science.

The Trump EPA’s refusal to ban chlorpyrifos was a return to a scientific approach, not a repudiation of science. Obviously, the Trump EPA has solid reasons for rejecting the activist petition because the only science supporting it was garbage. It’s important to remember that the agency is continuing its scheduled safety review, which will be more thorough review of the full body of science. 

Farmers need products like chlorpyrifos to produce an affordable food supply. While the risks alleged about chlorpyrifos safety are speculative, its crop protection benefits are well understood. Chlorpyrifos is one among a shrinking number of products available for farmers to fight serious pests that otherwise destroy many crops. Public comments filed in response to the November 2016 EPA chlorpyrifos risk assessment include numerous statements from farmers and university agricultural experts that reveal the extensive value of this chemical in crop protection.

Consider the orange industry. The national orange crop has already shrunk in recent years because of a bacterial disease transmitted by an insect known as the Asian citrus psyllid, and chlorpyrifos is one of few pesticides available to help control this disease. The citrus industry’s challenge is just the tip of the iceberg, as multiple comments to EPA related to its risk assessment reveal serious impacts for a wide range of crops if the chemical is banned. Commenters also addressed adverse impacts for alfalfa, almonds, corn, peanuts, cotton, soybeans, wheat, cranberries, and other products.

Despite much alarmist media coverage, chlorpyrifos exposure isn’t akin to that of sarin gas and its use to grow fruits and veggies is not going to give your kids or anyone else’s children brain damage. Such absurd claims can be found in “reputable” sources including The New York Times and the Washington Post, but you should laugh rather than cry when you read them. Farmers have safely used chlorpyrifos for decades without any measurable adverse public health impacts. And sure, it’s technically a neurotoxin like sarin gas—but only for bugs.

Chlorpyrifos is an organophosphate pesticide, which means it works by inhibiting the effectiveness of an enzyme called cholinesterase, which is necessary for the proper functioning of the nervous system. In very low, dilute doses, the impact of chlorpyrifos on insects’ nervous systems is enough to kill them. In humans, exposure must be far higher and concentrated levels for a period of time before significant health effects can occur. Federal pesticide regulation keeps human exposures low enough to avoid health effects on people, while still high enough to kill crop-destroying insects. In fact, most foods have no detectible residues of synthetic pesticides and anything remaining can be washed off. To put the issue in further perspective, if we banned chlorpyrifos on these grounds we would have to ban many healthy foods too. Similar neurotoxins naturally form in many fruits and vegetables, such as potatoes, tomatoes, eggplants, peppers, blueberries, apples, cherries, and more. Remember it’s the dose that makes the poison. You can read more about that here.

Finally, home uses of chlorpyrifos were not banned in 2000 for safety reasons. In 2000, the EPA canceled most home uses of chlorpyrifos, while allowing its use in agriculture to continue. Activists maintain these cancelations amount to bans based on safety concerns. In reality, it was the companies that make chlorpyrifos that chose to discontinue registrations for in-home uses because heavy regulations make those uses unprofitable—not because there were any significant risks.

So that’s today’s scoop on chlorpyrifos. Again, see more details in my paper.