Lead in paint and gasoline is safe and poses no health risk.

By 1924, the Ethyl Corporation, a joint venture between Standard Oil and General Motors, was already moving leaded gasoline into American service stations. The additive, tetraethyl lead, had been developed by Thomas Midgley Jr. at the request of General Motors, which wanted a cheap way to prevent engine knock without switching to ethanol as an alternative. At the ceremony announcing commercial production, Midgley poured tetraethyl lead over his hands and held a vial of vapor to his face for sixty seconds, asserting there was no problem whatsoever. Workers at the production facility in Bayway, New Jersey, had already begun dying from acute lead poisoning. Inside the plant, employees called it the looney gas building.

The evidence that lead was dangerous was not new in 1924. Classical physicians had described lead colic in craftsmen working with lead pipes and paint. In the 1890s, Australian researchers had connected childhood lead poisoning to lead-based paint on verandas and railings. Alice Hamilton, the pioneering occupational physician at Harvard, had documented lead toxicity extensively in industrial workers in the first decades of the twentieth century. The toxicology was not controversial. What was contested was whether the low-level, chronic exposure that came from leaded gasoline and painted household surfaces constituted a health risk at all.

The industry's answer was no. Robert Kehoe, a toxicologist at the University of Cincinnati who received substantial funding from the Ethyl Corporation and the Lead Industries Association, articulated the position that was taught in medical schools and repeated in public health guidance for decades: the body had natural mechanisms for excreting lead, the levels found in Americans were essentially natural, and no harm had been demonstrated from typical exposures. The Kehoe paradigm, as historians of science would later call it, inverted the normal requirements of scientific proof, insisting that harm be demonstrated before restrictions were imposed, rather than that safety be established before a neurotoxic substance was introduced into the air, water, and soil of every American city.

It was Clair Patterson, a geochemist at Caltech who had been trying to measure the age of the Earth using lead isotopes, who first systematically documented the discrepancy between the amount of lead in modern humans and the amount in pre-industrial populations. His 1965 paper in Archives of Environmental Health argued that Americans were being subjected to chronic lead insult at levels far exceeding anything natural, and that the entire framework of industry-sponsored reassurance was not science but industry-funded advocacy. The lead industry responded by attempting to defund his research and have him removed from government advisory committees, a campaign that was largely successful for nearly a decade.

The clinical evidence came from Herbert Needleman, a pediatrician at Harvard, who spent years designing a study that could measure the effects of lead at levels too low to produce obvious poisoning symptoms. His 1979 paper in the New England Journal of Medicine analyzed the lead content in shed baby teeth from 2,146 Boston-area schoolchildren, dividing them into low-lead and high-lead groups and measuring their cognitive and behavioral development. Children with higher lead levels scored significantly lower on IQ tests and exhibited more classroom behavior problems on every measure the study employed. The association was dose-dependent and held after controlling for 39 potential confounding variables.

The Clean Air Act of 1970 began the process of phasing out leaded gasoline, and lead paint was banned from residential use in 1978. The phaseout of leaded gasoline was not completed until 1996. The lead already deposited in the soil of American cities and in the deteriorating paint of older housing continues to expose children today. The generation that grew up during the peak of the leaded-gasoline era, roughly 1940 through the early 1970s, experienced blood lead levels that would, by current medical standards, be considered evidence of poisoning.