Environmental groups have been trying since 2007 to force the federal government to ban the common insecticide chlorpyrifos, which extensive research has shown can harm the developing brains of fetuses and children who eat food from plants treated with the compound. In the last few years of the Obama administration, the Environmental Protection Agency had moved toward prohibition. But in March 2017, the EPA’s new director tabled discussions of any ban, shocking environmental and patient advocacy groups, but relieving farmers who depend on chlorpyrifos to protect their crops. The Natural Resources Defense Council, among others, have petitioned a federal court to force a ban.
Much of the EPA’s own research outlines chlorpyrifos’s adverse health effects. In 2016 the EPA reported “sufficient evidence” that low levels affect brain development and concluded that some American 1- to 2-year-old children are receiving up to 140 times what are considered safe levels in their food. The EPA has also reported elevated levels in water supplies and established that the compound adversely affects 1,778 out of 1,835 studied species of wild animals.
Chlorpyrifos, a type of insecticide known as an “organophosphate,” was first marketed in 1965 and was banned for most residential uses in 2000. Today, it is widely used on corn, soybeans, fruit and nut trees, Brussels sprouts, cranberries, broccoli and cauliflower, among many other foods. It is also used on golf courses, to protect utility poles and fence posts, and to kill mosquitoes, cockroaches and ants.
Dow Chemical markets chlorpyrifos under the name Lorsban and argues that the science is inconclusive.
Farmers are alarmed at attempts to ban the insecticide. It is a “critical tool,” a farmer in Oregon wrote on a federal website that collected comments in late 2016 as the Obama administration was weighing a ban. “Taking an important product like chlorpyrifos off the market would leave Oregon farmers, like me, more vulnerable to pests,” the grower wrote, adding that critics of chlorpyrifos often misstate how it is used.
The available science on chlorpyrifos can be difficult to find, buried in anodyne EPA reports. Here we have assembled research to help journalists writing about the chlorpyrifos debate.
Scientific research
The EPA’s 2016 summary of health effects in humans draws largely on 10 studies in some of the top academic journals, including three cohort studies lead by Virginia A. Rauh at Columbia University and published between 2006 and 2015. Rauh and her colleagues compared high- and low-exposure children at age 3 and found increased odds of mental development delays, psychomotor delays, attention disorders and attention deficit hyperactivity disorder in the high-exposure group. In a follow-up study with the same children at age 11, the authors found the high-exposure children more likely to have developed mild to moderate tremors. In 2011, the same researchers reported a negative correlation between chlorpyrifos exposure and both IQ and working memory.
Here are the other studies that led to the EPA’s conclusions — including one that observes a possible link between chlorpyrifos and autism in babies born to mothers who work in fields treated with the insecticide:
- “Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides.” Pediatrics, 2010.
Organophosphates like chlorpyrifos may contribute to ADHD. - “Urinary 3,5,6-tichloro-2-pyridinol (TCPY) in Pregnant Women from Mexico City: Distribution, Temporal Variability, and Relationship with Child Attention and Hyperactivity.” International Journal of Hygiene and Environmental Health, 2014.
Fetal exposure to chlorpyrifos may contribute to ADHD in childhood. - “Prenatal Exposure to Organophosphate Pesticides and Reciprocal Social Behavior in Childhood.” Environment International, 2014.
A study of African Americans in New York City found prenatal exposure to compounds in the same family as chlorpyrifos may impair social functioning, especially in boys. - “Organophosphate Pesticide Exposure and Neurodevelopment in Young Shanghai Children.” Environmental Science and Technology, 2012.
Children may be more vulnerable to pesticides like chlorpyrifos because they lack the enzymes to deactivate them. This study from Shanghai did not find a relationship between such pesticides and impaired mental development, though the authors urge caution interpreting the results and call for a longitudinal study. - “Urinary Metabolites of Organophosphate and Pyrethroid Pesticides and Behavioral Problems in Canadian Children.” Environmental Health Perspectives, 2013.
Found no link between organophosphates and children’s behavior, though it did find evidence that some compounds used to replace organophosphates may be linked to behavioral problems in children. - “Impact of Prenatal Chlorpyrifos Exposure on Neurodevelopment in the First 3 Years of Life Among Inner-City Children.” Pediatrics, 2006.
Children exposed to high levels of chlorpyrifos in utero and in early childhood scored significantly worse on motor- and mental-development tests at age 3 than children with low exposure. - “Seven-Year Neurodevelopmental Scores and Prenatal Exposure to Chlorpyrifos, a Common Agricultural Pesticide.” Environmental Health Perspectives, 2011.
Exposure to chlorpyrifos in utero and infancy is associated with lower cognitive performance at age 7 in inner-city, minority children. - “Neurodevelopmental Disorders and Prenatal Residential Proximity to Agricultural Pesticides.” Environmental Health Perspectives, 2014.
The use of chlorpyrifos near a pregnant woman’s home may increase the risk her baby develops an autism spectrum disorder.
Other research:
This 2017 paper in Environment International found prenatal chlorpyrifos exposure linked to reduced motor function in infants at nine-months. Girls, the study found, were more susceptible than boys.
A 2012 paper in the Proceedings of the National Academy of Sciences describes an association between exposure to chlorpyrifos in the womb and changes in the shape of the developing brain.
This 2006 paper in Environmental Health Perspectives monitored pesticides in children’s urine and found a “dramatic and immediate” decline when the children were fed organic foods.
Other resources:
Some EPA pages dating before January 20, 2017, have been deleted. To see a searchable version of the site as it was on January 19, 2017, click here.
California has studied the use of chlorpyrifos and considered tighter regulations. The state also has a comprehensive database of pesticide use, including an annual report on how many pounds of each chemical were distributed over how many acres.
The U.S. Department of Agriculture also has resources on pesticide usage nationwide.
If you are looking for exactly which species of fish or plant or arachnoid is impacted by chlorpyrifos, check out this EPA biological evaluation.
In its Toxic Substance Portal, the Centers for Disease Control and Prevention (CDC) describes, in plain language, how humans can come into contact with chlorpyrifos, how it enters and leaves the body and what kind of test can demonstrate human exposure.
Dow Chemical has a website defending chlorpyrifos.
Expert Commentary