Chlorpyrifos is an organophosphate insecticide that has been widely used in agriculture, gardens, and homes since the 1960s. It works by inhibiting acetylcholinesterase, an enzyme essential for nerve function. Decades of research have established it as a developmental neurotoxin capable of impairing brain development in children even at low doses. The EU banned all uses in 2020; the US EPA restricted food uses in 2021 after prolonged legal battles. Despite bans, residues persist in soil, waterways, and imported food.
Where it's found
Residues on conventionally grown fruits and vegetables — particularly apples, citrus, stone fruits, grapes, and strawberries — are the primary dietary source. Garden insecticide sprays for aphids, ants, and caterpillars have historically been a significant home garden source, though now banned in many countries. Indoor use products for termites, cockroaches, and other pests have been phased out in the EU and UK but may persist in older properties. Agricultural drift from nearby fields can contaminate garden soil, water, and indoor dust. Drinking water downstream of agricultural areas may contain chlorpyrifos residues.
Routes of exposure
Dietary ingestion via food residues is the dominant route for children and non-occupationally exposed adults. Inhalation of spray droplets and vapours during or after garden or indoor application is significant. Dermal absorption from treated surfaces, garden soil, and indoor dust is relevant for children who play on the ground and engage in hand-to-mouth behaviour. Farm workers and residents near agricultural operations experience inhalation exposure from drift. Drinking water contamination represents a distinct pathway in agricultural regions.
Health concerns
Chlorpyrifos is a confirmed developmental neurotoxin. Prenatal exposure — even at levels within the range of common dietary and residential exposure — is associated with lower IQ, impaired working memory, delayed language development, reduced attention, and increased rates of autism spectrum disorder and ADHD. MRI studies of children with higher prenatal chlorpyrifos exposure show structural brain differences — enlarged superior temporal gyrus and affected cortical thickness. Acute high-dose exposure causes cholinergic crisis: nausea, seizures, paralysis, and death. Chronic lower exposure is also associated with Parkinson's disease in adults.
Evidence
The developmental neurotoxicity evidence is among the strongest for any pesticide. Multiple large prospective birth cohort studies (Columbia University CCCEH, CHAMACOS, PEACH cohorts) have followed children from prenatal exposure through childhood and adolescence, consistently finding dose-dependent cognitive impairment. Brain imaging data showing structural differences is particularly compelling. EFSA concluded in 2019 that no safe level could be established for developmental neurotoxicity, leading to the EU ban. The EPA's own scientists reached similar conclusions.
Who's most at risk
The developing fetal brain is exquisitely sensitive to chlorpyrifos — prenatal exposure is the greatest documented risk. Infants and young children with hand-to-mouth behaviour are disproportionately exposed via dust and soil. Farm workers and their families living near treated fields experience elevated exposure. People consuming high volumes of conventionally grown fruits and vegetables without washing may have higher dietary intakes.
Regulatory status
RegulationThe EU banned all authorisations for chlorpyrifos and chlorpyrifos-methyl in January 2020 (Reg. EU 2020/17 and 2020/18). The UK retained this ban post-Brexit. The US EPA prohibited all food uses in February 2022 following a Ninth Circuit Court of Appeals ruling. However, chlorpyrifos remains registered for agricultural use in many countries and may be present in imported food. Maximum residue levels (MRLs) for imported food containing chlorpyrifos are set at the limit of detection in the EU.
How to reduce your exposure
Choose organic or low-pesticide produce, particularly for the highest-residue crops: apples, citrus, grapes, strawberries, stone fruit, celery, and spinach. Thoroughly washing and peeling fruit and vegetables reduces (but does not eliminate) residues. In the garden, use physical pest controls — netting, companion planting, physical removal — rather than broad-spectrum insecticides. Do not allow children to play in garden soil that has been previously treated with organophosphate pesticides. Check import origin of produce where possible — some non-EU growing regions use higher pesticide loads.
The nutrition connection
Choosing organic produce for the highest-residue fruits and vegetables is one of the most directly evidenced dietary interventions for reducing pesticide body burden. Studies consistently show that switching to organic produce lowers urinary organophosphate metabolite levels within days. The "dirty dozen" list (published annually by EWG) provides a practical guide for prioritising organic choices. A diet built around varied vegetables, legumes, and whole grains — many of which carry lower pesticide loads than soft fruits — naturally reduces chlorpyrifos exposure while improving overall nutritional quality.