History of Risk Assessments of the Organophosphate Pesticide Chlorpyrifos at the US Environmental Protection Agency, 1980‒2024.

This article analyzes the history of risk assessments of the organophosphate pesticide chlorpyrifos by the US Environmental Protection Agency (EPA), focusing on the period after the 2000 ban on its household uses. It highlights how federally funded, place-based epidemiological studies—particularly involving children in farmworker and environmental justice communities—challenged the EPA's earlier reliance on corporate-sponsored, laboratory-based toxicology that prioritized acetylcholinesterase (AChE) inhibition as the sole toxicity mechanism. Despite growing scientific evidence of chlorpyrifos's neurodevelopmental harms, EPA risk assessments largely marginalized these findings for two decades, influenced in part by coordinated skepticism from corporate-aligned experts and regulatory mandates balancing economic and health interests. The article concludes that EPA's epistemological preference for "de-placed" laboratory data over "place-based" epidemiology has hindered protective regulatory action, underscoring the need for reforms that better integrate diverse scientific evidence and address conflicts of interest in pesticide risk evaluation.