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

This article examines the history of risk assessments of the organophosphate pesticide chlorpyrifos at the US Environmental Protection Agency (EPA), especially after a ban on household uses in 2000. Federal funding enabled more noncorporate and place-based scientific investigations of this pesticide's harms, including child-cohort epidemiology of populations impacted through environmental injustices. This article argues, first, that their findings challenged the thin knowledge base, mostly from corporate-sponsored toxicology, that originally justified chlorpyrifos's continued use. Second, for decades, outside a court-induced interval in 2015-2016, EPA's risk assessments favored "de-placed" toxicological modes and standards of knowledge-forged in the controlled environment of experimental laboratories-while marginalizing science gathered from the actual places and people EPA is supposed to protect. Third, agency officials stuck with a quantifiable, laboratory- and modeling-centered calculus for assessing health risks in part because a united front of corporate and corporate-consultant scientists harped on the uncertainties of newer findings. The article concludes that the agency needs to rethink its risk assessment practices and dependence, as well as more effectively account for financial conflicts of interest in evaluations of policy-relevant science. (Am J Public Health. Published online ahead of print May 1, 2025:e1-e11. https://doi.org/10.2105/AJPH.2025.308073).