Some of the most compelling evidence linking a widely used pesticide to developmental problems in children stems from what scientists call a “natural” experiment.
Though in this case, there was nothing natural about it.
Chlorpyrifos (pronounced klor-PYE-ruh-fahs) had been used to control bugs in homes and fields for decades when researchers at Columbia University began studying the effects of pollutants on pregnant mothers from low-income neighborhoods. Two years into their study, the pesticide was removed from store shelves and banned from home use, because animal research had found it caused brain damage in baby rats.
Pesticide levels dropped in the cord blood of many newborns joining the study. Scientists soon discovered that those with comparatively higher levels weighed less at birth and at ages 2 and 3, and were more likely to experience persistent developmental delays, including hyperactivity and cognitive, motor and attention problems. By age 7, they had lower IQ scores.
The Columbia study did not prove definitively that the pesticide had caused the children’s developmental problems, but it did find a dose-response effect: The higher a child’s exposure to the chemical, the stronger the negative effects.
That study was one of many. Decades of research into the effects of chlorpyrifos strongly suggests that exposure at even low levels may threaten children. A few years ago, scientists at the Environmental Protection Agency concluded that it should be banned altogether.
Yet chlorpyrifos is still widely used in agriculture and routinely sprayed on crops like apples, oranges, strawberries and broccoli. Whether it remains available may become an early test of the Trump administration’s determination to pare back environmental regulations frowned on by the industry and to retreat from food-safety laws, possibly provoking another clash with the courts.
In March, the new chief of the E.P.A., Scott Pruitt, denied a 10-year-old petition brought by environmental groups seeking a complete ban on chlorpyrifos. In a statement accompanying his decision, Mr. Pruitt said there “continue to be considerable areas of uncertainty” about the neurodevelopmental effects of early life exposure to the pesticide.
Even though a court last year denied the agency’s request for more time to review the scientific evidence, Mr. Pruitt said the agency would postpone a final determination on the pesticide until 2022. The agency was “returning to using sound science in decision-making — rather than predetermined results,” he added.
Agency officials have declined repeated requests for information detailing the scientific rationale for Mr. Pruitt’s decision.
Lawyers representing Dow and other pesticide manufacturers have also been pressing federal agencies to ignore E.P.A. studies that have found chlorpyrifos and other pesticides are harmful to endangered plants and animals.
A statement issued by Dow Chemical, which manufactures the pesticide, said: “No pest control product has been more thoroughly evaluated, with more than 4,000 studies and reports examining chlorpyrifos in terms of health, safety and environment.”
A Baffling Order
Mr. Pruitt’s decision has confounded environmentalists and research scientists convinced that the pesticide is harmful.
Farm workers and their families are routinely exposed to chlorpyrifos, which leaches into ground water and persists in residues on fruits and vegetables, even after washing and peeling, they say.
Mr. Pruitt’s order contradicted the E.P.A.’s own exhaustive scientific analyses, which had been reviewed by industry experts and modified in response to their concerns.
In 2015, an agency report concluded that infants and children in some parts of the country were being exposed to unsafe amounts of the chemical in drinking water, and to a dangerous byproduct. Agency researchers could not determine any level of exposure that was safe.