Chlorpyrifos

Chlorpyrifos was developed by Dow Chemical in 1965, derived from nerve agent chemistry developed during World War II [1]. Organophosphate pesticides work by blocking acetylcholinesterase — the enzyme that breaks down nerve signal molecules — which is exactly how nerve agents like sarin work, just at lower potency. Chlorpyrifos became one of the most widely used pesticides in the US, applied to millions of acres of fruits, vegetables, and grain crops. It was also used in homes (Dursban brand) until 2001, when a consent agreement with the EPA ended residential uses after evidence of children's exposure [2]. The battle over food use has been protracted: EPA scientists in 2016 recommended banning all food uses based on evidence of harm to children's brains. Political pressure during the Trump administration reversed that recommendation in 2017. A federal court ordered the ban reinstated; it was finalized in 2021. Some state uses and international uses continue [3].

Dietary exposure from residues on conventional produce is the primary pathway for children and adults not living near agricultural fields [1]. Strawberries, apples, citrus fruits, grapes, and bell peppers consistently show among the highest chlorpyrifos residue rates in USDA Pesticide Data Program surveys. Washing reduces but does not eliminate residues because chlorpyrifos penetrates plant surfaces [2]. Children in agricultural communities — particularly in California's Central Valley, Pacific Northwest, and Florida citrus regions — face exposure through air (drift from nearby applications), dust, and water as well as food. Agricultural worker children carry body burdens 10–20 times higher than non-agricultural community children. Drinking water in agricultural areas where chlorpyrifos is used can have detectable residues after rain events [3].

Chlorpyrifos disrupts brain development at doses far below those that cause acute pesticide poisoning — this was the key insight that drove the proposed food ban [1]. Prenatal exposure studies from the Columbia Center for Children's Environmental Health, led by Dr. Virginia Rauh, showed that children whose mothers had higher chlorpyrifos exposure during pregnancy had smaller brain volumes in multiple regions, lower IQ scores at age 7, and increased rates of ADHD and autism-like behaviors [2]. The mechanism goes beyond acetylcholinesterase inhibition: chlorpyrifos also disrupts the developing brain through axon guidance proteins and neural cell growth pathways at exposures too low to cause cholinesterase symptoms. These brain effects are irreversible once development is disrupted [3].

Fetuses and young children are the most vulnerable — the developing brain is uniquely sensitive to chlorpyrifos's non-cholinesterase developmental effects [1]. Pregnant women living in agricultural communities near chlorpyrifos-sprayed fields face the highest combined air and dietary exposure during the critical developmental windows. Agricultural workers and farmworkers' children who live near treated fields face regular inhalation and dermal exposure [2]. Conventional produce consumers — especially those who regularly eat strawberries, apples, and citrus without organic alternatives — have measurable chlorpyrifos metabolites in their urine.

Choose organic versions of strawberries, apples, grapes, bell peppers, spinach, and citrus — the EWG Dirty Dozen list identifies produce with consistently highest pesticide residues including chlorpyrifos [1]. Wash conventional produce thoroughly under running water (scrubbing helps with firm produce), though this does not eliminate all residues. If you live in an agricultural community, keep windows closed and run air conditioning during and after nearby spray applications — check CalPIP (California Pesticide Information Portal) or your state's equivalent for spray records in your area [2]. Pregnant women should prioritize organic produce for high-residue crops during the first trimester when brain development is most sensitive. For agricultural workers: follow re-entry interval requirements, change clothes and shower before contact with children after fieldwork, and request blood cholinesterase monitoring from your occupational health provider [3].