The modeling of chlorpyrifos toxicity to human health is a classic example of how characterization of pesticide exposures can impact the policy of regulatory agencies. Until 2016, the American Environmental Protection Agency (EPA) relied on the inhibition of acetylcholinesterase (the biological effect most sensitive to the action of chlorpyrifos) to establish that the health risk to exposures of agricultural products with “tolerable” levels of chlorpyrifos was relatively low. By 2016, unreported findings from industry-funded studies, and new epidemiological studies between 2003 and 2014, showed that children exposed during pregnancy, documented by measurements of chlorpyrifos in umbilical blood, suffered major developmental and neurological disorders. In 2017-2020, analogous neurological disorders were reproduced in rats at doses lower than those that inhibited acetylcholinesterase. These studies in rats had no uncertainty about prenatal exposure levels. In August 2021, the EPA finally banned all uses of chlorpyrifos in the United States, while the European Union had already done so in January 2020. This shows that pesticide regulation policy can vary greatly depending on what scientific studies are used to assess health risks. In Colombia, the list of pesticides registered by ICA as of September 2021 includes 28 chlorpyrifos-based products for agricultural use, not counting those for livestock use. As long as there are no stricter environmental and public health laws in Colombia, chlorpyrifos will continue to be imported and commercialized from countries that have already banned them.