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U.S. EPA’s chlorpyrifos decision spurs pushback

Top-selling organophosphate insecticide is at the heart of U.S. political, legal fight

by Britt E. Erickson
September 11, 2017 | A version of this story appeared in Volume 95, Issue 36

A farmworker harvesting corn.
Credit: Bob Nichols/USDA
Farmworkers, pregnant women, and children have the highest risk of exposure to chlorpyrifos.

On a summer evening in 2012, Bonnie Wirtz and her family hurried inside and shut all the windows in their rural Minnesota house when they heard the roar of a plane spraying pesticides on a neighboring farm.

Moments later, the plane flew over their house. “It sounded so close we thought it was going to crash,” Wirtz says. Within seconds, their house began to fill with a white mist coming in around the air-conditioning unit.

“I stumbled out coughing and I was having trouble breathing,” Wirtz recalls. Her husband rushed her and their eight-month-old son to the emergency room.

Tests revealed that she had been exposed to chlorpyrifos, a neurotoxic insecticide that the U.S. Environmental Protection Agency proposed twice to ban on food under the Obama Administration. The agency has since decided to allow its use to continue for at least five years.

In 2013, Wirtz collected air samples using a technique called drift catching to estimate the levels of chlorpyrifos that she and her family were likely exposed to. “When the results came in, we were devastated,” she says. The estimated exposure levels were four times as high as the EPA-recommended safe limit for a one-year-old child.

Chlorpyrifos has been associated with developmental delays and other health problems in children. “Up until this point, our son had met all of his developmental milestones,” Wirtz says. By the age of two and a half, his speech had regressed. He has since been diagnosed with a developmental disorder, which Wirtz is convinced is related to his exposure to the insecticide.

Wirtz spoke about her experiences at a rally outside the U.S. Capitol building in late July to garner support for legislation that would ban the use of chlorpyrifos on food crops in the U.S. She joined dozens of environmental activists, farmworkers, physicians, and parents in opposition to EPA’s 2017 decision to allow chlorpyrifos to stay on the market while the agency reviews its safety over the next five years.

In 2015 and 2016 under the Obama Administration, in response to a 2007 petition from environmental groups, EPA proposed to ban chlorpyrifos from use on food crops. The agency concluded at the time that combined exposure to the insecticide from food and drinking water exceeds safe levels, particularly for children.

But under the Trump Administration, EPA reversed its decision. In March, just weeks after EPA Administrator Scott Pruitt took the helm of the agency, he denied the 2007 petition to ban chlorpyrifos. EPA now claims that the science related to the neurodevelopmental risks of chlorpyrifos in children is uncertain. The agency plans to complete its health assessment of the insecticide by Oct. 1, 2022.

EPA says that its decision to hold off on banning chlorpyrifos was influenced by concerns the U.S. Department of Agriculture raised last year. In an Aug. 21 statement, EPA says, “We continue to examine the science surrounding chlorpyrifos, while taking into account USDA’s scientific concerns with methodology used by the previous administration.”

EPA shifts to epidemiology data

USDA, several farm groups, state agriculture officials, and external experts who advise EPA on pesticide issues criticized EPA’s 2016 chlorpyrifos human health risk assessment for relying too heavily on one human epidemiological study. That study by researchers at Columbia University found an association between chlorpyrifos levels in umbilical cord blood and neurodevelopmental effects in children during their first three years of life (Pediatrics 2006, DOI: 10.1542/peds.2006-0338).

The Columbia researchers measured chlorpyrifos levels in umbilical cord blood plasma collected from 254 women in New York City at the time they gave birth. The births occurred from 1998 to 2002.

The study found that children who were highly exposed to chlorpyrifos in the womb were more likely to experience cognitive and motor development delays, attention problems, and attention deficit hyperactivity disorder by age three.

EPA’s 2016 human health risk assessment is controversial because, for the first time, the agency used neurodevelopmental effects, rather than inhibition of the enzyme acetylcholinesterase in the nervous system, as the critical toxic effect. In the past, EPA has used acetylcholinesterase inhibition in laboratory animals to predict the level of chlorpyrifos at which toxic effects occur in humans.

Acetylcholinesterase is an important enzyme that breaks down the neurotransmitter acetylcholine into choline and acetic acid. When the enzyme is inactivated, acetylcholine accumulates in motor neuron synapses, causing overstimulation of muscles, glands, and the central nervous system.

The agency in 2016 chose to move beyond the acute neurotoxic effects of chlorpyrifos. “EPA believes that evidence from epidemiology studies indicates effects may occur at lower exposures than indicated by” animal studies, the agency stated at the time.

EPA has been struggling for years to assess the neurodevelopmental risks of chlorpyrifos to children and fetuses. The agency’s pesticide Scientific Advisory Panel, a group of outside experts, held multiple meetings beginning in 2008 to help EPA get a handle on incorporating human epidemiology data into pesticide risk assessments.

In 2015, EPA reviewed many epidemiology studies associating exposure to chlorpyrifos and neurodevelopmental effects in children, including a few that were conducted outside the U.S. But in 2016, the agency concluded that three U.S. studies have the most robust data sets available.

Those three studies are the Columbia study, another study conducted in New York City by researchers at Mount Sinai School of Medicine (Am. J. Epidemiol. 2007, DOI: 10.1093/aje/kwm029), and work by researchers at the University of California, Berkeley, that focused on pregnant women in a farmworker community in Salinas Valley in California (Basic Clin. Pharmacol. Toxicol. 2008, DOI: 10.1111/j.1742-7843.2007.00171.x).

Each of the three studies showed an association between prenatal exposure to chlorpyrifos and neurodevelopmental effects in young children. But ultimately, EPA relied solely on data from the Columbia study to derive the level at which no neurodevelopmental effects are expected to occur in humans.

EPA justified its decision by stating in 2016 that the Columbia study was the only one of the three to estimate exposure by measuring chlorpyrifos directly in umbilical cord blood. The California study measured a metabolite of chlorpyrifos, 3,5,6-trichloro-2-pyridinol (TCP), in maternal urine and dialkyl phosphate (DAP) metabolites in maternal and child urine. The Mount Sinai study tested for DAP metabolites in maternal urine to estimate chlorpyrifos exposure.

Many organophosphates break down into DAP metabolites, so monitoring such metabolites provides a nonspecific measure of organophosphate exposure. TCP is a metabolite specific to chlorpyrifos exposure.

EPA received pushback from pesticide manufacturers, farm groups, and USDA about its decision to shift from using acetyl­cholinesterase inhibition to epidemiological evidence from the Columbia study to estimate the level of chlorpyrifos associated with harmful effects in humans.

Such a switch by EPA “is momentous and cannot be understated,” Sheryl Kunickis, director of USDA’s Office of Pest Management Policy, told EPA during an advisory panel meeting last year. “This is a major shift in pesticide regulation, and there are major potential impacts—the cost to our food supply, to our economy, to taxpayers, and to low-income Americans,” she said. The way EPA regulates chlorpyrifos “will reach far beyond this one active ingredient,” Kunickis said. EPA’s decision will affect how other organophosphate insecticides, as well as many other broad classes of pesticides, are regulated, she argued.

“The loss of chlorpyrifos use would have significant economic impact on the production of many crops in the U.S. and by its major trading partners,” says Dow AgroSciences, which is the primary manufacturer of chlorpyrifos in the U.S. “Products containing chlorpyrifos protect more than 50 food crops from damage and destruction due to a variety of insect pests,” the company claims. Chlorpyrifos is critical for controlling pests on citrus fruits, corn, cotton, soybeans, sugar beets, and wheat, Dow says.

Chlorpyrifos is the most-used organophosphate insecticide in the U.S. Approximately 3 million to 5 million kg of chlorpyrifos was applied in the U.S. in 2014 on corn, soybeans, orchards, grapes, cotton, alfalfa, wheat, vegetables, and other crops, according to USDA estimates.

Demand for organophosphates falls

The use of organophosphate insecticides, including chlorpyrifos, has been on the decline in the U.S. since 1996, when then-President Bill Clinton signed the Food Quality Protection Act. The law directs EPA to consider all sources of exposure, including food, water, residential use, and other nonoccupational uses, in deriving food tolerances—or acceptable residue levels—for pesticides. It also requires the agency to consider susceptible populations, particularly children. Under this law, EPA chose organophosphate insecticides as the first class to undergo reassessment.

Since the 1996 pesticide law was enacted, the use of organophosphate insecticides has fallen dramatically, from 32 million kg, or 71% of all insecticides used in the U.S., in 2000 to about 9 million kg, or 33% of all insecticides used in the U.S., in 2012.

The use of chlorpyrifos in the U.S. has also dropped significantly since 2000, when EPA and pesticide manufacturers agreed to eliminate nearly all residential uses of the pesticide because of concerns about harmful health effects in children. Before then, chlorpyrifos was widely used to control roaches, termites, and other pests in apartment buildings and homes. Also in 2000, EPA canceled the use of chlorpyrifos on tomatoes and restricted its use on apples and grapes.

Now, Dow AgroSciences is seeking alternative chemicals that could replace chlorpyrifos and other organophosphate insecticides. But the company is finding it difficult to find a substitute that acts as extensively as chlorpyrifos. “The broad-spectrum nature of the insecticidal efficacy of chlorpyrifos—when used as part of an integrated pest management program—makes it tough to replace with any one alternate,” Dow says. “New products tend to have narrower spectrums of control that provide only partial replacement.”

While demand for chlorpyrifos in the U.S. is declining because of stringent regulations, in other parts of the world, particularly Asia-Pacific and South America, demand is growing. China is the leading manufacturer of chlorpyrifos, according to Grand View Research, a U.S.-based market research firm.

“The sustained importance of chlorpyrifos for global insect pest management is due to its outstanding efficacy and favorable environmental and human health characteristics,” Dow says.

Environmental advocates, farmworkers, pediatricians, and some Democratic state attorneys general and members of Congress disagree with the latter part of Dow’s statement.

The United Farm Workers of America, the largest farmworkers’ union in the U.S., points to a recent case of acute poisoning attributed to chlorpyrifos in dozens of farmworkers in a cabbage field south of Bakersfield, Calif. The May 5 incident occurred about an hour after the workers entered the field. Several of them experienced tingling lips, vomiting, and fainting. At least five received medical attention, according to the United Farm Workers. Local authorities have confirmed that chlorpyrifos was one of the pesticides involved.

“The pesticides drifted a half-mile from where they were applied, in violation of California law,” the union says.

Groups rally for a ban

In June, EPA received several letters urging the agency to reconsider its decision to put off banning chlorpyrifos. One was from seven state attorneys general, led by New York’s Eric T. Schneiderman.

The attorneys general argue that EPA’s March decision not to ban chlorpyrifos conflicts with agency scientists’ recommendations and violates the Federal Food, Drug & Cosmetic Act. That law requires the U.S. Food & Drug Administration to show that the allowable level of chlorpyrifos on fruits and vegetables is safe.

EPA also received a letter in June from the American Academy of Pediatrics and the Environmental Working Group, an advocacy organization. “EPA’s decision to allow the continued use of chlorpyrifos contradicts the agency’s own science and puts developing fetuses, infants, children, and pregnant women at risk,” the groups wrote.

Meanwhile, environmental groups led by Earthjustice are appealing EPA’s denial of their 2007 petition for a ban. They claim the agency made “no new safety findings” and no “final determination as to whether chlorpyrifos food tolerances must be revoked.”


The groups, along with the state attorneys general, filed a formal request with EPA in April asking the agency to reconsider the proposed chlorpyrifos ban. EPA has yet to respond.

At the rally outside the U.S. Capitol building in late July, Sen. Tom Udall (D-N.M.) held a briefing to build support for his legislation (S. 1624) to ban chlorpyrifos on food crops. “If parents, farmers, and farmworkers can’t trust the Administration to do the right thing, then Congress must step in,” he said. “The science hasn’t changed since EPA proposed to ban chlorpyrifos in 2015 and 2016; only the politics have,” Udall stressed.

“Dow Chemical, the manufacturer of chlorpyrifos, gave the President $1 million for his inauguration. Its CEO attended the signing ceremony when the President issued an executive order requiring agencies to roll back unnecessary regulations. The CEO even got the signing pen,” Udall said. Dow’s CEO, Andrew Liveris, met with EPA Administrator Pruitt just weeks before he decided not to ban chlorpyrifos—one of Dow’s biggest moneymakers, Udall noted.

Udall was joined at the briefing by Rep. Nydia M. Velázquez (D-N.Y.), who introduced a measure (H.R. 3380) in the U.S. House of Representatives to ban chlorpyrifos.

Megan Horton, an assistant professor of environmental medicine and public health at Icahn School of Medicine at Mount Sinai, spoke at the rally about follow-up work to the Columbia study involving magnetic resonance imaging of the brains of children exposed to chlorpyrifos.

The researchers examined the brains of the children between the ages of five and 11. “We compared kids who had prenatal exposure to chlorpyrifos to kids who had no exposure to chlorpyrifos,” Horton explained. “We saw marked changes in the brains of the kids who were exposed to chlorpyrifos, particularly in regions of the brain that support things like language development, reward processing, inhibition, and working memory,” she said. “These are very low levels of exposure from residential use or ingestion from pesticide residues on food.”

Horton was accompanied by Philip J. Landrigan, a pediatrician and epidemiologist on the faculty of Mount Sinai. “The bottom line here is we have abundant scientific evidence that chlorpyrifos causes brain damage to children in the womb,” Landrigan said. “We have three epidemiologic studies, a great deal of animal research in rats, and we have an MRI study, all coming up with convergent findings.” Landrigan urged EPA to ban chlorpyrifos immediately.

California poised to act

Meanwhile, California is moving to increase restrictions on the use of chlorpyrifos within the state. California ranks number one in terms of chlorpyrifos usage in U.S. states. About 592,000 kg of chlorpyrifos was used in California in 2014.

In an updated draft risk assessment released on Aug. 18, scientists with the California Department of Pesticide Regulation (DPR) conclude that chlorpyrifos may pose a health risk as a toxic air pollutant. DPR is accepting public comments on its assessment and plans to hold a public workshop to discuss it in Sacramento on Sept. 15. The assessment will then go through a peer review process. DPR hopes to complete the process by the end of 2018.

California’s Office of Environmental Health Hazard Assessment is also considering listing chlorpyrifos as a developmental toxicant under a law known as Proposition 65. If the state follows through with that listing, businesses will have to warn consumers when they know exposures are above minimum levels.

“While chlorpyrifos has been protecting crops for more than 50 years, new information in the scientific community leads us to believe the level of risk it poses is greater than previously known,” said California EPA Secretary Matthew Rodriquez. “We need to better understand the science to ensure our actions protect public health.”

In the meantime, farmworker groups, environmentalists, and parents continue to push EPA to follow through with its earlier proposal to ban chlorpyrifos on food crops.

“Every spring season, children around the U.S. are facing low-dose exposure to this dangerous chemical,” says Wirtz, the Minnesota mother who was sickened, along with her infant son, by chlorpyrifos. “It is in the air they breathe, the water they drink, and the food they eat,” she adds. “By leaving this chemical on the market, we are gambling with the lives of children. It is stealing their futures from them and increasing the amount of health care dollars they will need for treatment,” she continues. “It is breaking the hearts of parents who realize that their children will likely always struggle.”


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