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Banned by Obama, Revived by Trump, Banned Again by Biden: the Pesticide Chlorpyrifos

Health Letter, April 2022

By Michael T. Abrams, M.P.H., Ph.D.

Image: David Moreno Hernandez/Shutterstock.com

After a more than 30-year battle that began when the Natural Resources Defense Council (NRDC) in 1989 issued a report about the health risks of pesticides in children’s food, the U.S. Environmental Protection Agency (EPA), as of Feb. 28, 2022, officially banned the widely used insecticide chlorpyrifos (pronunciation: klôrˈpirəˌfäs) in the U.S. as a method to keep insects from damaging the nation’s crops. The chemical is still widely deployed as an agricultural pesticide in other countries, and it continues to be used as an insecticide in U.S. homes (for example, in enclosed roach traps) and in nonfood settings such as golf courses and decorative-plant nurseries.

Labor and environmental groups estimate that this ban on food-crop use will eliminate more than 90% of the chlorpyrifos currently deployed in the U.S.

Chlorpyrifos is a chlorinated organophosphate that has long been one of the most commonly used chemical insecticides in the world. It was first marketed in 1965 by Dow Chemical as a presumed safer replacement for the banned insecticide DDT (dichlorodiphenyltrichloroethane) — eventually becoming one of several such “regrettable substitutions.” U.S. farms have sprayed about five to eight million pounds of chlorpyrifos on their crops every year, accounting for 16% of all global agricultural use. By pounds of active ingredient, as of 2019, chlorpyrifos was the most widely used conventional insecticide and the U.S. EPA-registered uses included numerous food crops (for example, fruit and nut trees, many types of fruits and vegetables, and grains), golf course turf, greenhouses, and treatment of wood products like telephone poles and fence posts.

Unfortunately, chlorpyrifos, like many pesticides, is toxic to plants and animals, including humans. Organophosphates, which compose about 36% of the global pesticide market, are estimated to cause 3 million human poisonings and over 200,000 deaths globally each year. The negative consequences of exposure to organophosphates range in severity and duration, and they include depression, skin irritation, hormonal disturbances, immunologic abnormalities, rapid muscle shrinkage and nervous system effects. Chronic chlorpyrifos exposure is characterized by light-headedness, tachycardia (abnormally rapid heart rate), paresthesia (tingling) and an increased risk of various cancers, whereas acute exposure can cause seizures, coma and death.

In humans and other mammals, chlorpyrifos’ toxicity is mainly due to its ability to cause accumulation of the neurotransmitter (chemical messenger) acetylcholine in the nervous system.

Chlorpyrifos has been connected to developmental problems in young children exposed early in life as well as those exposed in utero. A 2022 study published in the journal PloS One of 110 apparently healthy pregnant women living in Isfahan Province in central Iran found that 70% of those women had detectable levels of chlorpyrifos metabolites in their urine, and 20% had levels high enough to pose a chronic health threat.

Non-occupational human exposure to chlorpyrifos is believed to occur most commonly through ingestion of contaminated food. Occupational exposure occurs from contact with the skin and absorption through the lungs (via inhalation), often in agricultural workers who apply chlorpyrifos or harvest crops sprayed with the insecticide.

Advocates for banning chlorpyrifos use in agriculture for years argued that the health risks from food-supply contamination with the insecticide were unacceptable — particularly to infants in utero — whereas proponents of maintaining such use highlighted the benefits, including higher crop yields. The calculus regarding this tradeoff has shifted back and forth between the Obama, Trump and Biden administrations. During Trump’s presidency, controversial EPA Administrator Scott Pruitt withdrew a 2015 proposed regulation to ban chlorpyrifos that was initiated by the Obama administration in response to a 2007 citizen petition filed by the Natural Resources Defense Council and Pesticide Action Network North America (PANNA). Thanks to an April 2021 ruling by the Ninth Circuit Court of Appeals, the Obama administration’s proposed ban is now being implemented.

In 2000, the EPA prompted makers and users of chlorpyrifos to voluntarily eliminate, phase out or modify certain uses of the insecticide. For example, chlorpyrifos-containing insecticide sprays for indoor use and other household products were eliminated. Encouraged in part by these events, the NRDC and PANNA in 2007 petitioned the EPA to ban the use of chlorpyrifos on all food.

In response to the NRDC/PANNA petition, the EPA under the Obama administration in 2015 issued a proposed rule that would have effectively banned the use of chlorpyrifos on food. In 2016, in support of this proposed regulatory action, EPA scientists issued an important memorandum that assess the health risks of chlorpyrifos exposure. Key among the results cited were those from the Columbia Center for Children’s Environmental Health (CCCEH) study, which described the association between umbilical cord blood levels of chlorpyrifos and neurodevelopment delays in the children at age 3 years.

The 2016 EPA memorandum acknowledged uncertainties regarding “if and how” chlorpyrifos is toxic to humans but concluded that there was substantial epidemiological evidence in support of a causal link between chlorpyrifos exposure and neurodevelopmental problems. That memorandum cited CCCEH studies demonstrating that 3-year-olds with relatively high levels of chlorpyrifos in umbilical cord blood at birth had a twofold greater risk of mental delay, a fivefold greater risk of psychomotor delay, an 11-fold greater risk of attentional disorders and a fivefold greater risk of pervasive developmental disorders (for example, autistic spectrum disorders). Moreover, a follow-up CCCEH study observed that at 11 years of age, those exposed to chlorpyrifos during their prenatal period also were more likely to have tremors, reduced IQ and lower performance on working memory tests.

However, in 2017 EPA Administrator Pruitt shockingly disregarded the findings and recommendations of EPA scientists by denying NRDC/PANNA’s 2007 petition — a denial order that Trump’s EPA would formally finalize in July 2019.

In response to lawsuits filed by NRDC, PANNA and multiple other advocacy groups, the Ninth District Court of Appeals in April 2021 ruled that the EPA had to either declare with evidence that chlorpyrifos was safe or allow the Obama administration’s proposed ban on the agricultural use of the insecticide to proceed.

As ordered by the court, on Aug. 18, 2021, the EPA issued a final rule banning chlorpyrifos in food due “in part to the potential for neurodevelopmental effects in children.” That action now stands as the official response to the NRDC/PANNA petition that the Trump EPA tried to deny in the face of considerable evidence of chlorpyrifos’ toxicity to children, presumably because Pruitt favored commercial interests over human safety and other environmental concerns — including known toxic effects of chlorpyrifos on a wide variety of fresh and salt-water organisms.

The NRDC recently noted that soon after Trump took office in 2017, Administrator Pruitt took a meeting with the Dow Chemical CEO, whose company contributed $1 million to Trump’s inaugural activities, and then proceeded to reverse the EPA’s plan to ban chlorpyrifos in food. In addition to enforcing this new ban on chlorpyrifos, the current EPA further plans to continue review of chlorpyrifos to consider if nonfood uses of the insecticide should be restricted beyond current limits.

Though this action by Biden’s EPA is notable, it was decades in the making and nearly scuttled by the Trump administration. Moreover, over 150 organophosphorous pesticides besides chlorpyrifos remain on the market, and the industry-sponsored trials that regulators use to evaluate pesticide safety can be compromised by conflicts of interest and the quest for profits. Accordingly, vigilance and action (like the 2022 chlorpyrifos ban) must be tenaciously pursued by lawmakers, regulators, scientists and other public leaders if our food supply is to be safe for eating, and safely cultivated.